P-51B Mustang: North American’s Bastard Stepchild that Saved the Eighth Air Force

[Bruno Anthony]

That said, he did contribute to bringing Energy Manueverability into the conversation.

Absolutely and his work with GD on the F-16.

Once we get into the Cult of Boyd, I tend to check out.

 

[HoHun]

Hi Bill,

For Penetration and Withdrawal, the climb was normally 28-30000 feet to have altitude advantage over any encountered LW fighters attacking the bombers.

I've had a look at Freeman's "The Mighty Eight - War Manual", and he details a typical mission profile as follows:

• Engine Start
• Taxying and Marshalling - 8 min
• Take-off whole group - 12 to 15 min
• Forming up - Single orbit of the base (P-38 and P-47 switch to drop tanks now, P-51 only after bringing down fuselage tank to 30 gallons)
• Climb out on course to rendezvous point - for P-51: 700 fpm @ 240 to 270 mph IAS
• Escorting bombers
  • 2 groups at bomber altitude, 1 group 4000 ft above
  • orbiting/weaving as necessary (throttling back was possible when no enemy aircraft were in the vicinity)
  • Typical escort distance - 150 to 200 miles from rendezvous to turning back
• Flight back - at high altitude until let-down over the channel

By assigning a power setting to each phase of the flight, one would have the basis for a quantified comparison of escort ranges in the European Theatre. The altitude for the cruise to the rendezvous point is missing, but I suppose we could use 18000 ft.

For the maximum return distance, I'd use the following estimation method:

• Internal fuel minus
  • For Starting, warm-up, take-off and forming up:
    • 15 min at maximum continuous (in the case of the P-51, internal fuel is reduced to a constant 30 gallons instead)
  • For escorting the bombers:
    • Fuel for 40 min maximum continuous.
    • Fuel for 15 min military power
    • Fuel for 5 min war emergency power
  • Reserve:
    • Fuel for 15 min maximum continuous

The values are a bit arbitrary, but Freeman states that bomber air speeds were 130 to 150 mph IAS while carrying bombs, and 160 to 180 mph IAS without bombs. So 60 min for 200 miles is more or less in the middle of the ballpark. The reserve and take-off allowance are loosely based on examples from the F-51H Standard Aircraft Characteristics Sheets.

Unfortunately, I don't seem to have a complete manual for the P-38 which includes the Flight Operation Instruction Chart (which show range depending on fuel reserve), so I can't include the type in the comparison, and it's a bit hairy to find and select perfectly comparable numbers for the P-47 and P-51, but using the P-51D Pilot Training Manual and the "Pilot Flight Operation Instructions for Army Models P-47D-25, -26, -27, -28, -30, and -35 Aiplanes und British Model Thunderbolt" with the 305 gallon tank size of the earlier Thunderbolts, I get the following return distances (at Maximum Air Range settings):

The fuel available (excluding reserve) for escorting and return:

• P-51D (184 gal internal): 184 gallons <- Stand-in for P-51B/C without fuselage tank
• P-51D (269 gal internal): 214 gallons
• P-47D (305 gal internal): 260 gallons
• P-47D (370 gal internal): 315 gallons

The fuel available for return (excluding reserve):

• P-51D (184 gal internal): 70 gallons @ 5.5 mpg
• P-51D (269 gal internal): 100 gallons @ 5.5 mpg
• P-47D (305 gal internal): 36 gallons @ 2.5 mpg (P-47D manual) or @ 4 mpg (P-47B/C/D/G manual)
• P-47D (370 gal internal): 101 gallons @ 2.5 mpg (P-47D manual) or @ 4 mpg (P-47B/C/D/G manual)

Well, the USAAF threw a spanner in the works there by providing two vastly different miles-per-gallons values for the P-47 in two different manuals! Glad I noticed that just before posting ... I can't resolve this right now, but of course it results even more uncertainty in return ranges than we'd have anyway:

• P-51D (184 gal internal): 385 statue miles
• P-51D (269 gal internal): 550 statue miles
• P-47D (305 gal internal): 90 statue miles OR 144 statue miles
• P-47D (370 gal internal): 253 statue miles OR 405 statue miles

These values sort of represent the maximum combat radius for the desired mission profile in a fairly realistic, apples-to-apples comparison for the European Theatre.

I have simply assumed that the range on the specified amount of internal fuel that's consumed prior to switching to drop tanks, plus the fuel that's consumed from the drop tanks, are enough to get the fighters to the rendezvous points. As long as that's given, and as long as we specify that the drop tank is not to be carried while escorting the bombers, the size of the drop tanks doesn't actually play a role for the combat radius.

(Not to say the aircraft can't range farther and return safely if they don't encounter enemy resistance that is hard enough to require them to use the power setting outlined above, or if they are allowed to start the return flight before the hour is up - for example, because they are relieved earlier, which could be a planned aspect of a particular mission. Accordingly, you could change the mission profile to increase the combat radius, but that would obviously reduce the mission effectiveness.)

Since I'm talking about actual mileages, for once I'd like to point out that your mileage migth vary ;-)

Hi Henning - good observations. I will never be talked into using iPhone again as the meeting tool as I had zero access to my laptop folders.

You might not have noticed it as you were losing connection occasionally, but the moderator did a fairly good job of showing your material while you were reconnecting. It might have been a bit out of sequence, but it probably wasn't as bad as it must have looked to you.

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



I've had a look at Freeman's "The Mighty Eight - War Manual", and he details a typical mission profile as follows:

• Engine Start
• Taxying and Marshalling - 8 min
• Take-off whole group - 12 to 15 min
• Forming up - Single orbit of the base (P-38 and P-47 switch to drop tanks now, P-51 only after bringing down fuselage tank to 30 gallons)

SOP forLR escort was to burn to 65gal. AAF recommendation was to burn to 45-50gal

• Climb out on course to rendezvous point - for P-51: 700 fpm @ 240 to 270 mph IAS
• Escorting bombers
  • 2 groups at bomber altitude, 1 group 4000 ft above
  • orbiting/weaving as necessary (throttling back was possible when no enemy aircraft were in the vicinity)
  • Typical escort distance - 150 to 200 miles from rendezvous to turning back
• Flight back - at high altitude until let-down over the channel

By assigning a power setting to each phase of the flight, one would have the basis for a quantified comparison of escort ranges in the European Theatre. The altitude for the cruise to the rendezvous point is missing, but I suppose we could use 18000 ft.

Based on NA 8449 P-51D Performance Report, climb to altitude was made at 160-180mph (SL through 12K- low blower), 180-210 plus at Max Continuous power (12K through 20K -high blower). Time to 25K =20min. Distance covered 66mi. Cruise at 60% power ~ 322mph. Cruise at 2200RPM/32"MP and 2x75gal tanks ~ 285mph.

The straight line calcs for Combat Radius, 415gal (incl 30min reserve) was 802mi w/15min MilPwr/5min WEP. Also stipulated dropping 75gal tanks 625mi out. Sourcs Fig 4., page 7.

That said, in no universe was that CR actually attained with 20min combat and 30min reserve.

For the maximum return distance, I'd use the following estimation method:

• Internal fuel minus
  • For Starting, warm-up, take-off and forming up:
    • 15 min at maximum continuous (in the case of the P-51, internal fuel is reduced to a constant 30 gallons instead)
  • For escorting the bombers:
    • Fuel for 40 min maximum continuous.
    • Fuel for 15 min military power
    • Fuel for 5 min war emergency power
  • Reserve:
    • Fuel for 15 min maximum continuous

The values are a bit arbitrary, but Freeman states that bomber air speeds were 130 to 150 mph IAS while carrying bombs, and 160 to 180 mph IAS without bombs. So 60 min for 200 miles is more or less in the middle of the ballpark. The reserve and take-off allowance are loosely based on examples from the F-51H Standard Aircraft Characteristics Sheets.

Unfortunately, I don't seem to have a complete manual for the P-38 which includes the Flight Operation Instruction Chart (which show range depending on fuel reserve), so I can't include the type in the comparison, and it's a bit hairy to find and select perfectly comparable numbers for the P-47 and P-51, but using the P-51D Pilot Training Manual and the "Pilot Flight Operation Instructions for Army Models P-47D-25, -26, -27, -28, -30, and -35 Aiplanes und British Model Thunderbolt" with the 305 gallon tank size of the earlier Thunderbolts, I get the following return distances (at Maximum Air Range settings):

The fuel available (excluding reserve) for escorting and return:

• P-51D (184 gal internal): 184 gallons <- Stand-in for P-51B/C without fuselage tank
• P-51D (269 gal internal): 214 gallons
• P-47D (305 gal internal): 260 gallons
• P-47D (370 gal internal): 315 gallons

The fuel available for return (excluding reserve):

• P-51D (184 gal internal): 70 gallons @ 5.5 mpg
• P-51D (269 gal internal): 100 gallons @ 5.5 mpg
• P-47D (305 gal internal): 36 gallons @ 2.5 mpg (P-47D manual) or @ 4 mpg (P-47B/C/D/G manual)
• P-47D (370 gal internal): 101 gallons @ 2.5 mpg (P-47D manual) or @ 4 mpg (P-47B/C/D/G manual)

Well, the USAAF threw a spanner in the works there by providing two vastly different miles-per-gallons values for the P-47 in two different manuals! Glad I noticed that just before posting ... I can't resolve this right now, but of course it results even more uncertainty in return ranges than we'd have anyway:

• P-51D (184 gal internal): 385 statue miles
• P-51D (269 gal internal): 550 statue miles
• P-47D (305 gal internal): 90 statue miles OR 144 statue miles
• P-47D (370 gal internal): 253 statue miles OR 405 statue miles

These values sort of represent the maximum combat radius for the desired mission profile in a fairly realistic, apples-to-apples comparison for the European Theatre.

I have simply assumed that the range on the specified amount of internal fuel that's consumed prior to switching to drop tanks, plus the fuel that's consumed from the drop tanks, are enough to get the fighters to the rendezvous points. As long as that's given, and as long as we specify that the drop tank is not to be carried while escorting the bombers, the size of the drop tanks doesn't actually play a role for the combat radius.

The drop tanks were retained until engaged - and the drag of the pylons are considerable. The P-51B and P-38J and P-47D pylon drag was of order of 10mph at max power.The P-51D pylon ~ 6mph. Less for cruise speed but still more than 'true clean' as most often cited in flight testing.

That said, I know that when carrying steel tanks, the pilots were encouraged to keep them if not engaged. Conversely the Bowater-lloyd composite tanks were always dropped when empty.

Also, the 85gal tank was rarely drained below 50gal on a long range escort. Anecdotally my father's 355th loaded 85gal and only burned some after arriving at R/V south of Stettin for FRANTIC VII. His logbook had 7hr 50min for that leg. SOP for 355th was to load 65gal on most missions, but switch to wing tanks first after take off and forming up to begin climb.

(Not to say the aircraft can't range farther and return safely if they don't encounter enemy resistance that is hard enough to require them to use the power setting outlined above, or if they are allowed to start the return flight before the hour is up - for example, because they are relieved earlier, which could be a planned aspect of a particular mission. Accordingly, you could change the mission profile to increase the combat radius, but that would obviously reduce the mission effectiveness.)

In complete agreement. The Fighter Mission (Sweep) range was considerably farther then escort range.

Since I'm talking about actual mileages, for once I'd like to point out that your mileage migth vary ;-)

As usual your calcs are sound, but the base assumptions on actual cruise settings and escort durations seem at variance with SOP, at least based on actual recollections of many that I grew up around. More common cruise power for P-51B/D was in range of 32-36"MP (lead vs wing) for 220+IAS at 25K - which ties nicely to the below test reports.

200mi for one hour of escort seems fine based on a typical historical target escort durations for a P-51 or P-47 in Ess/Racetrack pattern. The diffeences were largely the R/V and Break Escort locations on the continent.

That said, I applied Brequet equation methodolgy in which diminishing gross weight and decreasing angle of attack (and decreasing induced drag) and constantly reducing power required for constant altitude and airspeed - resulted in about 5% more range than NAA calcs.

You might not have noticed it as you were losing connection occasionally, but the moderator did a fairly good job of showing your material while you were reconnecting. It might have been a bit out of sequence, but it probably wasn't as bad as it must have looked to you.

Regards,

Henning (HoHun)

Thank you for that.
Roger Freeman published generally excellent data and information. What Freeman did not focus on was the effect of external tanks and racks on drag - which affected cruise speed at economical settings.

The drag of twin 75gal tanks and pylons on P-51B was considerably less than P-47D with 108 or 150gal tanks and pylons.

Anecdotally, the B-17 inbound cruise speed was 150mph IAS at 25K due to lower performance of some aircraft/engines at cruise settings - outbound 180IAS.

For close escort, more typically the high squadron was 'essing' 3-5000 feet higher, while the other squadrons were more closely at bomber altitudes in a 'racetrack pattern.

Eglin and Wright Field did quite a bit of range testing but I have yet to find flight testing of P-47D. That said, I am quite sure that 4mpg for dirty drop tank config was impossible - closer to 2.5mpg.

Attached is one set of P-51D tables at different altitudes and configurations. The drag of the 75gal tank was about the same as a 500# bomb for reference on fuel consumption.

P 51D Performance Test

and drag curves

http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_Drag_Curves.jpg

and fuel consumption

http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_AppendixB.pdf

 

[bercr]

Just correcting a misprint: Breguet equation (with a g, not Brequet)

 

[HoHun]

Hi Bill,

Thanks a lot for the detailed answer!

As usual your calcs are sound, but the base assumptions on actual cruise settings and escort durations seem at variance with SOP, at least based on actual recollections of many that I grew up around. More common cruise power for P-51B/D was in range of 32-36"MP (lead vs wing) for 220+IAS at 25K - which ties nicely to the below test reports.

Admittedly, Freeman provided some useful starting points, but he didn't give the full mission details, so I had to make some assumptions.

My question would be, which power settings were used on the escort leg as long as no Luftwaffe fighters were sighted? The same 32 to 36" Hg?

The range table from Mike's site for the 25000 ft, 2250 rpm data point aligns nicely with the corresponding Flight Operation Instruction Chart:

Also, the 85gal tank was rarely drained below 50gal on a long range escort. Anecdotally my father's 355th loaded 85gal and only burned some after arriving at R/V south of Stettin for FRANTIC VII. His logbook had 7hr 50min for that leg. SOP for 355th was to load 65gal on most missions, but switch to wing tanks first after take off and forming up to begin climb.

If I schedule 15 min at maximum continuous for start/take-off/form-up, that uses up 24.3 gallons, leaving us with 60.7 gallons in the fuselage tank if it was used first. As that seems both realistic and eliminate a P-51 specific assumption, I'll go with that for now.

For "escort cruise" power (as I'll call it for ease of reference), I'm going to use 25000 ft, 2250 rpm @ 73 gph for 370 mph for the P-51D, and 25000 ft, 2290 rpm @ 146 gph for 324 mph for the P-47D.

Using the same 15 min at maximum continuous for start/take-off/form-up assumption for both aircraft, the reduced "escort cruise" consumption results in return distances:

P-51D (184 gal internal): 350 miles @ 5.625 mpg
P-51D (269 gal internal): 825 miles @ 5.625 mpg
P-47D-25* (305 gal internal): 255 miles @ 3.0 mpg
P-47D-25 (370 gal internal): 455 miles @ 3.0 mpg

(I stayed with the P-47D-25 for now since the Flight Operation Instruction Chart for the P-47B/C/D/G has the 5 mpg cruise data that needs further investigations. Of course, that's not a 1943 type, but I'm trying to reduce complexity right now.)

So that means that a P-47D-25 due to its larger fuel tank could have flown this particular mission profile and returned from Schweinfurt (which is about 425 statue miles from Wattisham, which unlike the wartime fields in the same area can be found on skyvector.com), but the same aircraft with the 305 gallon tank of the earlier versions couldn't have.

Ironically, the P-51D with the fuselage tank would have easily been able fly this mission profile and return from Schweinfurt easily, but without its fuselage tank, it couldn't have done so either.

Again, I've ignored the question of whether the aircraft could have gotten there on drop tanks only, and I've stayed with the assumption that the drop tanks were dropped at the beginning of the actual escort part of the mission. I'll leave that for later posts

Now we can turn this around and see what kind of mission the P-47D-25 with only 305 gallons internal could have flown to Schweinfurt, by reducing the "escort cruise" time: 5 min WEP, 10 min MIL, 17.2 min "escort cruise".

Accordingly, the bombers wouldn't have been escorted by fighters for 60 min, as desired by the mission profile and possible with the mid-to-late-1944 variants of both fighters, but only for 32 min. With regard to mission planning, that would mean that you'd have to schedule twice the number of fighters for the same escort coverage - which perhaps shows in a slightly different way why more range made a better escort fighter.

That said, I applied Brequet equation methodolgy in which diminishing gross weight and decreasing angle of attack (and decreasing induced drag) and constantly reducing power required for constant altitude and airspeed - resulted in about 5% more range than NAA calcs.

Makes perfect sense, but weren't the fighter pilots trained to fly matching power settings? Of course, the Flight Operation Instruction Chart does not show the effect from a speed increase due to the weight reduction either. Sort of odd, since the format of the table would allow to take Breguet into account.

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

Again, I've ignored the question of whether the aircraft could have gotten there on drop tanks only, and I've stayed with the assumption that the drop tanks were dropped at the beginning of the actual escort part of the mission. I'll leave that for later posts

To follow up on this, I added calculations for the cruise out on drop tanks as well as for the escort part and the return flight.

Since the manuals don't give all of the figures required (such as distance covered in climb), and not all versions of the manuals have all of the data (such as the 200 gallon drop tank data only being provided by an older version of the P-47 manual), it's not really rock solid, but I suppose it's not too far off. I wouldn't rule out an occasional mistake on my part when transferring parameters from the manuals into my spreadsheet, but I don't think I would have been dramatically off without noticing.

Anyway, here are the results:

<Edit: Since I made a mistake by subtracting the allowance for engine start, warm-up, take-off, form-up *twice*, and didn't notice that the USAAF hid even more fuel for warm-up and take-off in the climb data , I've edited the results somewhat so future readers don't get unecessarily confused by this error.>

[*]P-47D (370 gallon internal, 200 gallon drop tank):

• Engine start, warm-up, take-off, form-up: 55 gallons (internal) @ 220 GPH
• Climb to 25000 ft: 118 gallons (external), covering ca. 50 miles
• Cruise on drop tanks until empty: 148.8 miles @ 1.81 MPG
• Cruise to rendezvous (408.6 miles out): 92.8 gallons (internal) @ 2.27 MPG
• Escort flight for 6.5 min.(5 min MIL, 1.5 min escort cruise @ 143 GPH)
  • The bombers are assumed to cover the 16.4 miles remaining to the target while thus escorted.
• Return flight: 425 miles @ 3.03 MPG
• Reserves due to HoHun's accounting errors: 85 gallons = 257 miles
  

[*]P-51D without fuselage tank (184 gallon internal, 2 * 75 gallon drop tank):

• Engine start, warm-up, take-off, form-up: 24.3 gallons (internal) @ 97 GPH
• Climb to 25000 ft: 44 gallons (external), covering ca. 61.1 miles
• Cruise on drop tanks to rendezvous (321.3 miles out): 260.2 miles @ 3.92 MPG
  • Tanks are assumed to be dropped at rendezvous, still containing 53.1 gallons total.
• Escort flight for 41.5 min.(5 min MIL, 36.5 min escort cruise @ 73 GPH)
  • The bombers are assumed to cover the 103.7 miles remaining to the target while thus escorted.
• Return flight: 425 miles @ 5.63 MPG
• Reserves due to HoHun's accounting errors: 39.3 gallons = 221 miles

[/LIST]

I'm not sure if that proves anything, but at the very least, it illustrates why long range makes an escort fighter more effective.

Regards,

Henning (HoHun)

 

[drgondog]

Hi Henning - I won't nit pick your calcs, all very good and match your assumptions.

Anecdotally the mission profile would only include METO for a short time and depending on the mission would not even climb at Max Continous. From Steeple Morden, the longer distance from coast compared to Halesworth granted more leeway to climb to altitude over N.Sea.

Anecdotally again from all my sources growing up, a long range mission with R/V near target (such as Munich with R/V s. Augsberg) the cruise with 75gal tanks would have been in 32-36"MP and 2200-2400 RPM from crossing coastline all the way at 25K_ with the top cover assignment climbing to 3-5K above assigned box altitude for escort position at ~220IAS. Cruise w/75gal tank was in range of 295mh TAS and ~260TAS w/108gal tanks at 25K

I believe that all operating manual data were delivered via contractor, tested by AAF and then the FAREP charts were published , accompanied by 'average' start up, taxi, take off and climb fuel consumption.

I published the tables fr P-38, P-47 and P-51 on pg 318 of Bastard Stepchild. Dean's America's One Hundred Thousand publiched the bar chart and I converted the table/bar chart data to map of ETO centered n Duxford (pg 317)

FWIIW the data for a.) SE through take off and climb (no account for formation assembly), b.) Reserve 30min, and c.) combat were:
Clean
P-38J 300int 86 50 111
P-38J 410int 98 50 111
P-47C/D 305int 101 40 89
P-51B 180int 46 26 58
P-51B 265int 51 26 58

As a practical yardstick I dove into 8th AF VCB June 1945 to extract a month by month longest recorded combat encounter for which a victory was claimed.

Showing that calc versus reality were often at odds

The January 11 MOH mission by 354FG P-51B wo 85 gal was Halberstadt, about 406mi from Boxted. The first time the 56thFG fought there was May 1944 w/2x150gal ext, 305int

Jan 11 saw the 354FG provided target escort at Bodeaux - 496mi from Boxted. 180gal int plus 2x75gal drop tanks.

The attached spreadsheet compares actual distances from Halesworth and Boxted for longest 56FG victory credits to the 8th AF Tactical Development map on pg97. It is 'optimistic' compared to the later FAREP charts and ranges.

 

[HoHun]

Hi again,

Hi Henning - I won't nit pick your calcs, all very good and match your assumptions.

Very embarrassing to admit it , but I just noticed that there must be a mistake in the calculations as the parts don't sum up to the correct total.

Stay tuned while I hunt for bugs in my spreadsheet!

Regards,

Henning (HoHun)

 

[drgondog]

Hi again,



Very embarrassing to admit it , but I just noticed that there must be a mistake in the calculations as the parts don't sum up to the correct total.

Stay tuned while I hunt for bugs in my spreadsheet!

Regards,

Henning (HoHun)

I hate to fess up, but I think I may have made an error or tw on spreadsheets...

 

[HoHun]

Hi again,

Stay tuned while I hunt for bugs in my spreadsheet!

After tidying everything up a bit, it turns out I had subtracted the allowance for engine start, warm-up, take-off and form-up *twice*, which did of course affect combat persistence negatively! :-D

After correcting this mistake, even the early P-47D could have made an escort mission to Schweinfurt ... here's the comparison:

- P-47D (early, 305 gal internal + 200 gal drop tank): 5 min MIL, 10.8 min "escort cruise"
- P-47D-25 (370 gal internal + 200 gal drop tank): 5 min MIL, 44.5 min "escort cruise"
- P-51D (184 gal internal + 2 * 75 gal drop tank): 5 min MIL, 56.5 min "escort cruise" <- stand-in for P-51B/C without fuselage tank
- P-51D (269 gal internal + 2 * 75 gal drop tank): 5 min MIL, 126.3 min "escort cruise"

(The "no fuselage tank" P-51D drops 63.2 gal unused fuel at the rendezvous, the standard P-51D drops 98.7 gal. The difference is due to the version with the larger internal fuel volume being able to escort the bombers for longer, thus having the rendezvous earlier in the mission.)

I did not allow for any reserve in the mission profile other than the additional range gained from throttling back during the let-down on the way home.

So, while the early P-47D with a 200 gal drop tank could give bombers roughly a quarter of an hour of escort time over Schweinfurt, that's probably close to the best-case scenario for this configuration, and so I'm not sure the USAAF planners would really have scheduled that kind of mission profile.

I haven't yet checked Bill's latest post for useful information I could use to make my mission profile more realistic since I was distracted by that bug in my calculations ... maybe that will cast yet a different light on the comparison!

Regards,

Henning (HoHun)

 

[HoHun]

Hi Bill,

Anecdotally the mission profile would only include METO for a short time and depending on the mission would not even climb at Max Continous. From Steeple Morden, the longer distance from coast compared to Halesworth granted more leeway to climb to altitude over N.Sea.

Sounds like good practice to stretch the range. The manual only provides limited climb data ... climb speed reducing from 175 mph IAS at sea level to 145 mph IAS at 25000 ft, and climb rate from 1450 fpm to 1100 rpm (at 11000 lbs weight).

Oops, the values contain another 15 gallon warm-up and take-off allowance! That had escaped me ... and it's 30 gallons allowance for the P-47D. Well, I'll just consider my previous calculations to have a 15 to 20 min reserve - I think I saw in the combat radius calculations for the post-war Standard Aircraft Characteristics that a bit more would be more realistic, but it's a step in the right direction.

Anecdotally again from all my sources growing up, a long range mission with R/V near target (such as Munich with R/V s. Augsberg) the cruise with 75gal tanks would have been in 32-36"MP and 2200-2400 RPM from crossing coastline all the way at 25K_ with the top cover assignment climbing to 3-5K above assigned box altitude for escort position at ~220IAS. Cruise w/75gal tank was in range of 295mh TAS and ~260TAS w/108gal tanks at 25K

I'm using the 25000 ft value from the manual, which gives 2100 rpm @ full throttle for 60 GPH at 295 mph TAS, which is a bit slower with less spower. The next column in the table is a bit on the faster side ... probably when flying in formations, they used the faster column but had the leader throttle back just slightly so the wingmen had a bit of throttle to play with?

FWIIW the data for a.) SE through take off and climb (no account for formation assembly), b.) Reserve 30min, and c.) combat were:
Clean
P-38J 300int 86 50 111
P-38J 410int 98 50 111
P-47C/D 305int 101 40 89
P-51B 180int 46 26 58
P-51B 265int 51 26 58

Thanks, that's a useful data set for cross-checking! Looks like a decent fit, considering that the climb altitude is not given and it's not clear to me whether the climb was with drop tanks.

The use of a 30 min reserve confirms my impression that my accidental 15 - 20 min reserve would not have been enough for the USAAF!

The attached spreadsheet compares actual distances from Halesworth and Boxted for longest 56FG victory credits to the 8th AF Tactical Development map on pg97. It is 'optimistic' compared to the later FAREP charts and ranges.

Hehe, that's really good use of data! I've graphed the information, which nicely highlights the systematic bias towards consistently shorter ranges, despite a few kills "outside" the range limits:



Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

After correcting this mistake, even the early P-47D could have made an escort mission to Schweinfurt ... here's the comparison:

Eliminating the redundant allowance "hidden" in the manuals' climb figures and inserting the reserve fuel allocations provided by the USAAF range data quoted by "P-51B Mustang: North American’s Bastard Stepchild", the comparison now looks as follows - for the Schweinfurt escort mission, escorting the bombers to the target at 425 miles out from the fighter airfield:

Type	Internal Fuel [US Gal]	Drop Tank [US Gal]	WEP [min]	MIL [min]	Escort Cruise [min]
P-47D (early)	305	200	0	1	6.4
P-47D-25	370	200	5	5	19.7
P-51D	184	2 * 75	5	5	20.3
P-51D	269	2 * 75	5	15	64.5

(As before, the "no fuselage tank" P-51D drops 63.2 gal unused fuel at the rendezvous, the standard P-51D drops 98.7 gal. The P-47D has to drop the fuel tanks before the rendezvous and use some internal fuel to get there.)

As a useful benchmark, the USAAF according to the table from Bill's book calculated a combat radius of 275 miles for the P-47C/D-15, which according to my calculations would be good for the following mission profile:

Type	Internal Fuel [US Gal]	Drop Tank [US Gal]	WEP [min]	MIL [min]	Escort Cruise [min]
P-47D (early)	305	108	5	5	29.4

That's based on the climb time for the 200 US gallon tank, and being about 600 pounds light might save a couple of gallons and thus give a little more escort time than I account for, but it illustrates nicely what the USAAF at the time considered the requirement for an effective escort mission.

Based on that, one could conclude that the P-47D (early) with a 200 gallon drop tank would not have been effective over Schweinfurt, the P-47D-25 with the same tank as well as the P-51 with no fuselage tank and two 75 gallon drop tanks would have been borderline effective, and the P-51 with fuselage tank would have been very effective.

Regarding the P-47D-25 and the P-51 without fuselage tank, the latter could have become a markdely more effective if it were allowed to carry the drop tanks into the escort part of the mission, as was done historically, so the apparent equivalence is a bit of an artifact of using a standardized mission profile.

Regards,

Henning (HoHun)

 

[drgondog]

Hi again,



After tidying everything up a bit, it turns out I had subtracted the allowance for engine start, warm-up, take-off and form-up *twice*, which did of course affect combat persistence negatively! :-D

After correcting this mistake, even the early P-47D could have made an escort mission to Schweinfurt ... here's the comparison:

- P-47D (early, 305 gal internal + 200 gal drop tank): 5 min MIL, 10.8 min "escort cruise"
- P-47D-25 (370 gal internal + 200 gal drop tank): 5 min MIL, 44.5 min "escort cruise"
- P-51D (184 gal internal + 2 * 75 gal drop tank): 5 min MIL, 56.5 min "escort cruise" <- stand-in for P-51B/C without fuselage tank
- P-51D (269 gal internal + 2 * 75 gal drop tank): 5 min MIL, 126.3 min "escort cruise"

(The "no fuselage tank" P-51D drops 63.2 gal unused fuel at the rendezvous, the standard P-51D drops 98.7 gal. The difference is due to the version with the larger internal fuel volume being able to escort the bombers for longer, thus having the rendezvous earlier in the mission.)

I did not allow for any reserve in the mission profile other than the additional range gained from throttling back during the let-down on the way home.

So, while the early P-47D with a 200 gal drop tank could give bombers roughly a quarter of an hour of escort time over Schweinfurt, that's probably close to the best-case scenario for this configuration, and so I'm not sure the USAAF planners would really have scheduled that kind of mission profile.

The issues with the Republic tank were multifold. Dangerous to eject, leaked badly, tricky stability and unpressurized. The latter forced either cruise at 50+mph below 'clean' at altitudes below 20-22K until fuel used up, THEN Climb to bomber escort altitudes at Max Continous up to 30K for R/V - or carry only enough to climb to 22K (near continent), punch tank and climb on internal fuel.

In either case the Actual combat radius was the German border. The Brisbane 200gal tanks was steel and could be pressurized but rarely did 348th or 35FG climb above 20,000 feet, and rarely were they actually escorting bombers. Kearby's MOH misssion over Wewak was staged at Lae (from Port Moresby) leaving the range to Wewak 325 mi (using distance.com). Fast cruise, drop tanks overWewak, 20 min fight and return to Lae with ~ 50gal. Source Race of Aces, John Brunning.

Note - as you have already explained, there is more Radius available for a Fighter Mission (Kearby) than an Escort Mission. The Fighter Mission cited above was 3/4 distance to Schweinfurt, with a much better 200gal tank and zero essing required.

FWIIW - the spreadsheet I compliled based onvictory credit locations does not differentiate between a Fighter Sweep or bomber escort mission of the 56th FG, but the standard language in a Frag Order was 'to the limit of endurance'. Interpreted, the squadron CO was looking at fuel gauges - not the terrain below looking for landmarks for radius reference.

Based on my research, location citations and cited mission duration, there was no 56th FG mission flown (pre Bubble top, pre D-Day) beyond Celle, Hagenow and Halberstadt - all close to Schwinfurt range, but undefined mission profile until I dive deeply into day by day Mission Summaries stating Ramrod or Fighter Sweep.

I haven't yet checked Bill's latest post for useful information I could use to make my mission profile more realistic since I was distracted by that bug in my calculations ... maybe that will cast yet a different light on the comparison!

Regards,

Henning (HoHun)

Anecdotally again, the metal drop tanks were frequently retained even past drainage until combat imminent. The paper tanks were jettisoned every time, but retained until combat encounter or empty.

In my father's encounter report for June 20 over Rugen Is., he engaged with a stuck 75gal tank and shot down 2 109s in a turning fight... the extra tank released sometime in the fight.

Fo the last Shuttle Mission, most if not all of the 355th FG retained the 110gal steel tanks, even during the brief fight with 109s over Warsaw. His log time was 7hr 50min. R/V was south of Stettin so fast cruise with no essing until the leg to Warsaw.

I still frequenty talk to Bill Lyons, the last 355th pilot -- reaching 100th B'Day on June 20th. Remarkably sharp and very explicit about normal SOP from Start Engine to shutting down after return.

 

[drgondog]

Attached is the table extracted from FAREP data. These data are the source of the bar charts inDean's AOHT, pg 599

 

[HoHun]

Hi Bill,

The issues with the Republic tank were multifold. Dangerous to eject, leaked badly, tricky stability and unpressurized. The latter forced either cruise at 50+mph below 'clean' at altitudes below 20-22K until fuel used up, THEN Climb to bomber escort altitudes at Max Continous up to 30K for R/V - or carry only enough to climb to 22K (near continent), punch tank and climb on internal fuel.

Absolutely. I probably should have stated more clearly that I consider the ranges I calculated for the P-47D with the 200 gallon tank as a "what if" scenario, playing along with the suggestion that they could have been used operationally just fine if they had been provided to the units in the European Theatre in time.

FWIIW - the spreadsheet I compliled based onvictory credit locations does not differentiate between a Fighter Sweep or bomber escort mission of the 56th FG, but the standard language in a Frag Order was 'to the limit of endurance'. Interpreted, the squadron CO was looking at fuel gauges - not the terrain below looking for landmarks for radius reference.

This totally makes sense as there so many unknowns in the way fuel is consumed in the course of an actual mission, especially if you're operating entire formations instead of individual aircraft, where each pilot can carefully optimze his own consumption.

In my father's encounter report for June 20 over Rugen Is., he engaged with a stuck 75gal tank and shot down 2 109s in a turning fight... the extra tank released sometime in the fight.

Quite the feat! Do you know whether it was common for tanks to stick? I'm familiar with the problem from Korean War reports, but I'm not sure I ever heard of this in a WW2 context.

I still frequenty talk to Bill Lyons, the last 355th pilot -- reaching 100th B'Day on June 20th. Remarkably sharp and very explicit about normal SOP from Start Engine to shutting down after return.

I'm thrilled to hear that he's still well at this amazing age, and keen on aviation too!

Eliminating the redundant allowance "hidden" in the manuals' climb figures and inserting the reserve fuel allocations provided by the USAAF range data quoted by "P-51B Mustang: North American’s Bastard Stepchild", the comparison now looks as follows - for the Schweinfurt escort mission, escorting the bombers to the target at 425 miles out from the fighter airfield:

To eliminate as much subjective guesswork as possible from my range calculations, I've tabulated the data from the manuals' Take-off, Climb and Landing Charts and approximated the distances covered in climb from that. I also found a mistake in the P-47 cruise-with-200-gallon tank calculation - that one particular source table stated IAS, not TAS like all the others.

I am sort of set up to re-calculate the combat range and persistence data now, but somehow, the P-47D-25 (and later) source data is really odd in one point.

Here are the two pages of the P-47D-25 Flight Operation Instruction Chart. The yellow marking shows the 25000 ft "column IV" cruise, which for some reason is not to be used in the clean condition, though it's filled in for the condition "with drop tanks".
For my calculations, I'd have to use column III data for cruise at 25000 ft instead, which is for a higher speed, but reduced mileage. (Admittedly, the P-51D cruises even faster, but it's economic while doing so.)

Do you happen to have any suggestion what the background of this apparent anomaly might be? I'd like to avoid any unintentional bias against the P-47D resulting from this inexplicably missing data point ...

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



Absolutely. I probably should have stated more clearly that I consider the ranges I calculated for the P-47D with the 200 gallon tank as a "what if" scenario, playing along with the suggestion that they could have been used operationally just fine if they had been provided to the units in the European Theatre in time.

The wild card on either the Bullfrog Republic 200gal or the Ford/Brisbane tank is the cruise speed reduction imposed by the drag of the tank.

This totally makes sense as there so many unknowns in the way fuel is consumed in the course of an actual mission, especially if you're operating entire formations instead of individual aircraft, where each pilot can carefully optimze his own consumption.



Quite the feat! Do you know whether it was common for tanks to stick? I'm familiar with the problem from Korean War reports, but I'm not sure I ever heard of this in a WW2 context.

Not uncommon, but low statistically.

I'm thrilled to hear that he's still well at this amazing age, and keen on aviation too!



To eliminate as much subjective guesswork as possible from my range calculations, I've tabulated the data from the manuals' Take-off, Climb and Landing Charts and approximated the distances covered in climb from that. I also found a mistake in the P-47 cruise-with-200-gallon tank calculation - that one particular source table stated IAS, not TAS like all the others.

I am sort of set up to re-calculate the combat range and persistence data now, but somehow, the P-47D-25 (and later) source data is really odd in one point.

Here are the two pages of the P-47D-25 Flight Operation Instruction Chart. The yellow marking shows the 25000 ft "column IV" cruise, which for some reason is not to be used in the clean condition, though it's filled in for the condition "with drop tanks".
For my calculations, I'd have to use column III data for cruise at 25000 ft instead, which is for a higher speed, but reduced mileage. (Admittedly, the P-51D cruises even faster, but it's economic while doing so.)

Do you happen to have any suggestion what the background of this apparent anomaly might be? I'd like to avoid any unintentional bias against the P-47D resulting from this inexplicably missing data point ...

Regards,

Henning (HoHun)

Your assumptions are the best that can be drawn from the manual tabular data. Simple answer is No - I do not understand the reason for omitting the reference altitudes above 20,000 feet in Column V.

Here are some thoughts.

All of the values for both clean and 2x165gal drop tanks are straight line calcs - with none of the variables associated with bomber escort. Roughly an hour of close escort for both Withdrawal and Penetration escort so the Mpg is dramatically reduced for same cruise speed in tables as progress along the bomber track is tethered to bomber speeds. For 25K and B-17, that would be 150IAS SOP or 205mph + for TAS

The term 'clean' implies truly clean, as in wing pylons removed - to obtain best possible linear range. If operational planning is contemplated for bomber escort, say in return cruise mode after leaving bmber escort - or combat- this is an important question. The drag of the pylons is significant.

Allegedly the flat 150gal flat tank had more drag than the Lockheed 165/150. The Lockheed tank was not used frequently by P-47s as the P-38FGs had more priority in ETO. Pacific and CBI are different questions.

By comparison the airspeed loss for 2x110gal tanks on P-51D was cited as 46mph @25K for optimal cruise settings. (see spitfireperformance.net July 1945 P-51D range discussions). I certainly would expect more for 2x165gal/P-47 Pylon combo - both in Parasite drag and Induced drag for increased fuel loads. In your P-47D-25 tables the reduction in airspeed between 'Clean' and for 2x165gal tanks is nearly 80mph TAS for approximately same MP/RPM in column V.

That said, I have never seen any detail drag data for P-47, so speculation on my part.

One last question: in the upper LH corner for engines stats the Military Power consumption value of 280gph exceeds WEP of 255gph - have I gone brain dead?

 

[HoHun]

Hi Bill,

One last question: in the upper LH corner for engines stats the Military Power consumption value of 280gph exceeds WEP of 255gph - have I gone brain dead?

You're fine! At War Emergency Power, the engine is running with water injection, which does indeed decrease gasoline consumption. Overall liquid consumption is slightly increased, but the water (or water-alcohol mixture) consumption is not listed in the table. Not to confuse the reader, most likely! :-D

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



You're fine! At War Emergency Power, the engine is running with water injection, which does indeed decrease gasoline consumption. Overall liquid consumption is slightly increased, but the water (or water-alcohol mixture) consumption is not listed in the table. Not to confuse the reader, most likely! :-D

Regards,

Henning (HoHun)

Face Palm...lol.

 

[HoHun]

Hi Bill,

All of the values for both clean and 2x165gal drop tanks are straight line calcs - with none of the variables associated with bomber escort. Roughly an hour of close escort for both Withdrawal and Penetration escort so the Mpg is dramatically reduced for same cruise speed in tables as progress along the bomber track is tethered to bomber speeds. For 25K and B-17, that would be 150IAS SOP or 205mph + for TAS

I have in fact included the time spent with the bomber stream at a lower rate of progress towards the target, as you suggest. Specifically, my mission profile involves picking up the bombers at the point that allows them to be escorted to the target with the combined duration of WEP, MIL and "escort cruise" power, with the escorts cruising back all the way from the target.

(The bombers would then have to picked up by a different escort group, for which the calculation goes differently since they don't necessarily drop fuel with the drop tanks at the rendezvous point, as it's part of my mission profile. I know that's not strictly historic there, but it seems to be in line with the way the post-war Standard Aircraft Characteristics mission profiles calculate combat radius.)

The term 'clean' implies truly clean, as in wing pylons removed - to obtain best possible linear range. If operational planning is contemplated for bomber escort, say in return cruise mode after leaving bmber escort - or combat- this is an important question. The drag of the pylons is significant.

I've ignored the additional losses for now to stay aligned as far as possible with the USAAF manuals. "Clean" so far is more of my shorthand for what the manuals list as "no external load items" - which in the context of a set of Flight Operation Instruction Charts in my opinion might include the drag of the pylons. In the P-51D manual, there's actually no "no external load items" table, but a "wing racks" table ... I take this as a sign that the captions were clarified in that manual, but I guess that the P-47D-25 manual also accounted for the extra drag.

The data I have on the 200 gallon tank is from a PDF that can be found here: https://ww2aircraft.net/forum/threads/p-47-versus-fw-190.54300/page-4?post=1576473#post-1576473

That is a bit of a can of worms, as the R-2800-21 in that chart can be run at 2200 rpm, 32" Hg at 25000 ft for a fuel consumption of 105 GPH, but the R-2800 from the P-47D-25 manual when run at 2200 rpm, 33" Hg at 25000 ft is supposed to consume 125 GPH. Maybe the data in the earlier table was preliminary and marked "red" - hard to tell in a black-and-white copy! But my suspicion is that the increase of fuel consumption by ca. 20% is in fact a bit of a reserve for real-world flying, with aircraft operating in formations.

Note that the title of these tables is "Flight Operation *Instruction* Chart" ... I would read that as a chart that is telling you how much fuel you should have to perform operations consistently, i. e. without that wingmen at the tail end of the formation running out of fuel on the way home since they are by necessity doing a lot of inefficient throttle jockeying.

With regard to the missing data in the 25000 ft "clean" field, I've had a closer look at the numbers for the lower altitudes, and it seems that efficiency drops with increasing altitude, at increasing rate. I'd suspect that to keep the engine cool, it has either to be run inefficiently rich, or the cowl flaps have to be opened so far that they cause excessive drag, and you're not able to maintain the 2.68 MPG mileage that is the basis for the range-over-fuel part of that column. Maybe in the configuration with the tanks still attached, at the lower air speed the absolute drag of the open cowl flaps isn't as high so that it's still a valid cruise condition there. At least, that's the best explanation I've been able to come up with so far

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



I have in fact included the time spent with the bomber stream at a lower rate of progress towards the target, as you suggest. Specifically, my mission profile involves picking up the bombers at the point that allows them to be escorted to the target with the combined duration of WEP, MIL and "escort cruise" power, with the escorts cruising back all the way from the target.

(The bombers would then have to picked up by a different escort group, for which the calculation goes differently since they don't necessarily drop fuel with the drop tanks at the rendezvous point, as it's part of my mission profile. I know that's not strictly historic there, but it seems to be in line with the way the post-war Standard Aircraft Characteristics mission profiles calculate combat radius.)



I've ignored the additional losses for now to stay aligned as far as possible with the USAAF manuals. "Clean" so far is more of my shorthand for what the manuals list as "no external load items" - which in the context of a set of Flight Operation Instruction Charts in my opinion might include the drag of the pylons. In the P-51D manual, there's actually no "no external load items" table, but a "wing racks" table ... I take this as a sign that the captions were clarified in that manual, but I guess that the P-47D-25 manual also accounted for the extra drag.

The data I have on the 200 gallon tank is from a PDF that can be found here: https://ww2aircraft.net/forum/threads/p-47-versus-fw-190.54300/page-4?post=1576473#post-1576473

I would drawyour attention to the note that some 'early versions' have no provision for a belly tank (Upper LH side)- which opens up the question 'which belly tank - the Ford/Brisbane? because the Republic Ferry tank would not operate above the 20000 foot row. Nor, IMO would the Bullfrog tank enable economical cruise settings to achieve 205mph IAS at 20K.
https://ww2aircraft.net/forum/threads/p-47-versus-fw-190.54300/page-4?post=1576473#post-1576473

That is a bit of a can of worms, as the R-2800-21 in that chart can be run at 2200 rpm, 32" Hg at 25000 ft for a fuel consumption of 105 GPH, but the R-2800 from the P-47D-25 manual when run at 2200 rpm, 33" Hg at 25000 ft is supposed to consume 125 GPH. Maybe the data in the earlier table was preliminary and marked "red" - hard to tell in a black-and-white copy! But my suspicion is that the increase of fuel consumption by ca. 20% is in fact a bit of a reserve for real-world flying, with aircraft operating in formations.

I agree your assumption (and question) FWIIW

Note that the title of these tables is "Flight Operation *Instruction* Chart" ... I would read that as a chart that is telling you how much fuel you should have to perform operations consistently, i. e. without that wingmen at the tail end of the formation running out of fuel on the way home since they are by necessity doing a lot of inefficient throttle jockeying.

With regard to the missing data in the 25000 ft "clean" field, I've had a closer look at the numbers for the lower altitudes, and it seems that efficiency drops with increasing altitude, at increasing rate. I'd suspect that to keep the engine cool, it has either to be run inefficiently rich, or the cowl flaps have to be opened so far that they cause excessive drag, and you're not able to maintain the 2.68 MPG mileage that is the basis for the range-over-fuel part of that column. Maybe in the configuration with the tanks still attached, at the lower air speed the absolute drag of the open cowl flaps isn't as high so that it's still a valid cruise condition there. At least, that's the best explanation I've been able to come up with so far

Regards,

Henning (HoHun)

Agree again.

 

[HoHun]

Hi Bill,

I would drawyour attention to the note that some 'early versions' have no provision for a belly tank (Upper LH side)- which opens up the question 'which belly tank - the Ford/Brisbane? because the Republic Ferry tank would not operate above the 20000 foot row. Nor, IMO would the Bullfrog tank enable economical cruise settings to achieve 205mph IAS at 20K.
https://ww2aircraft.net/forum/threads/p-47-versus-fw-190.54300/page-4?post=1576473#post-1576473

Good question. The data sheet is dated 11-20-42 on p. 30 and p. 32 (but "1-20-42" on p. 31, which is odd) ... does that give us a clue? I haven't looked at the timeline of the Brisbane tank.

It would probably be helpful to understand who had the authority to issue the document, T.O. No. 01-65BC-1. If that was an entity in the US, I wouldn't expect it to be dealing with the Brisbane tank specificually, as it probably would have taken some time to get one to the US for testing and administrative processing, if we call issueing the T.O. such.

There's a hint on the process the T.O. was involved for: The editor's note instructs "AAF inspectors at modification centers" to cross out those table parts not using the units the aircraft's instruments are calibrated for, which implies a copy of the T.O. accompanied each individual aircraft, suggesting a US origin of the T.O.

Attached a graph I made from the T.O. range data. It's remarkably jerky, but I've corrected one obvious typo and used both the rounded statue mile and nautical mile values to smooth things a little.

I believe this tells us a bit about the extra drag of the tank, though of course the data points were achieved at different power settings for each configuration.

However, there seems to be a bit of a self-contradiction in the concept of the table, which on one hand assume constant MPG in each column, but on the other hand also assumes a constant power setting regardless of flight weight in each column. The data in the table shows the exact opposite effect from what one should expect, with the heavier airplane getting the better mileage at the same power setting.

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



Good question. The data sheet is dated 11-20-42 on p. 30 and p. 32 (but "1-20-42" on p. 31, which is odd) ... does that give us a clue? I haven't looked at the timeline of the Brisbane tank.

It would probably be helpful to understand who had the authority to issue the document, T.O. No. 01-65BC-1. If that was an entity in the US, I wouldn't expect it to be dealing with the Brisbane tank specificually, as it probably would have taken some time to get one to the US for testing and administrative processing, if we call issueing the T.O. such.

There's a hint on the process the T.O. was involved for: The editor's note instructs "AAF inspectors at modification centers" to cross out those table parts not using the units the aircraft's instruments are calibrated for, which implies a copy of the T.O. accompanied each individual aircraft, suggesting a US origin of the T.O.

Attached a graph I made from the T.O. range data. It's remarkably jerky, but I've corrected one obvious typo and used both the rounded statue mile and nautical mile values to smooth things a little.

I believe this tells us a bit about the extra drag of the tank, though of course the data points were achieved at different power settings for each configuration.

However, there seems to be a bit of a self-contradiction in the concept of the table, which on one hand assume constant MPG in each column, but on the other hand also assumes a constant power setting regardless of flight weight in each column. The data in the table shows the exact opposite effect from what one should expect, with the heavier airplane getting the better mileage at the same power setting.

Regards,

Henning (HoHun)

Hi Henning - i'm the last guy to question one of your well thought out works of art.

That said my first reaction is that the following general aerodynamics rules apply:

For a given altitude and constant Manifold Pressure, the initial full tank state is, a.) highest initial gross weight for the cruise calc, b.) at highest angle of attack, combined with GW, which defines the highest CL, in the example of level flight, c.) by reference that initial state which represents the highest Induced Drag, and d.) the lowest dynamic pressure applied to the airframe/tank system.

1. While maintaining control of altitude, the aircraft must either reduce power as weight is consumed, or maintain power/increase speed, but constantly change trim to more nose down - reducing Lift Coefficient. In the latter condition, parasite drag increases as a function of time and fuel fraction consumption.
2.) the pressure drag of external stores is basically RN independent. Over the course of constant altitude, slightly increasing airspeed with decreased angle of attack, the pressure drag will increase slowly on the tank due to the increased airspeed, as well as combination form drag/parasite drag of the airframe increases.

As neither the CDp as f(RN), or CDp1 of the associated drop tanks is available to us, I'm having a problem on multiple levels making sense of the P-47C/early D tables. They seem unreliable to generate much confidence in spite of your knowledge and skills. Simply stated, the Breguet equations are unavailable due to lack of Cd values.

How do we rationalize CL/CDmax for max range or CL^3/2/CD for max endurance?

How do we believe 'Greg's' assertion that 2x150gal wing tanks at cruise experience a 10-20mi drag penalty when comparable cruise settings for P-51D in extensive flight testing result in 47mph reduction over clean w/racks at 25K?

 

[HoHun]

Hi Bill,

Hi Henning - i'm the last guy to question one of your well thought out works of art.

No worries, questioning is always welcome ... "All models are wrong but some models are useful", and any input to make them more useful is great!

However, the graph I posted is just a visualization of the T.O.'s Flight Operation Instruction Chart, so there's really not much original thought involved.

That said my first reaction is that the following general aerodynamics rules apply:

Fully agreed! I think it's by design that each page of the T.O.'s Flight Operation Instruction Chart can't actually account for Breguet's range equation. Probably the USAAF also subscribes to the "wrong but useful" approach :-/

How do we believe 'Greg's' assertion that 2x150gal wing tanks at cruise experience a 10-20mi drag penalty when comparable cruise settings for P-51D in extensive flight testing result in 47mph reduction over clean w/racks at 25K?

From the data I graphed from the Flight Operation Instruction Chart, the average mileage with the 200 gallon drop tank is 2.55 statue miles/US gallon, and 2.81 statue miles/US gallon for the "none/empty 200 gallon drop tank" case.

Of course, having "none" (which is ambiguous in itself as it might be either "clean" or "clean with racks") and "empty 200 gallon drop tank attached" lumped together in one Flight Operation Instruction Chart is a bit suspicious. However, that's partially why I graphed the data ... as there's a big jump between the two conditions, I would say it's not likely that the data is really for the 200 gallon drop tank still attached.

I'm not sure at the moment what Greg used as a source for his calculations, but I've got a copy of AN-01-65BC-01A here, with two Flight Operation Instruction Charts for external load items "none" and "2 - 165 U. S. Gallon Wing Tanks", both dated 4-1-44, which covers the bubbletop Thunderbolts, but probably are still useful for cross-checking wing tank drag.

These show for 20000 ft in column IV:

- No tanks: 2130 rpm, 31.8" Hg, Auto Lean, 113 GPH, 302 mph TAS
- Two tanks: 2100 rpm, 31.5" Hg, Auto Lean, 101 GPH, 221 mph TAS

That looks like a fairly massive difference. OK, the two-tank configuration uses slightly less power, but that's an 81 mph speed drop from a 11% power reduction, if we assume power is proportional to fuel flow (for closely adjacent operating points).

Weight probably shouldn't have all that much influence on these values, as the "no tanks" Flight Operation Instruction Chart is valid for 14200 to 12000 lbs (13100 lbs median), and the "two tanks" chart is valid for 16200 to 12000 lbs (14100 lbs median).

So we can contrast the two sets of Flight Operation Instruction Charts:

• T.O. No. 01-65BC-1 (for razorback P-47's):
  • No tanks: 2.81 MPG
  • 200 GAL tank: 2.55 MPG
• AN-01-65BC-01A (for bubbletop P-47's)
  • No tanks: 2.68 MPG
  • 2 x 165 GAL tanks: 2.20 MPG

(In AN-01-65BC-01A, the MPG values are actually listed explicitely in column IV, so I didn't need to calculate them from the data points as for T.O. No. 01-65BC-1.)

For the sake of completeness, here the 20000 ft column IV comparison for the T.O. No. 01-65BC-1 data:

- No tank: 2150 rpm, 30" Hg, 95 GPH, 210 mph IAS (~288 mph TAS)
- 200 gallon tank: 2250 rpm, 32" Hg, 105 GPH, 205 mph IAS (~281 mph TAS)

These speeds are quite close, so the 200 gallon tank (of unresolved type) appears to create substantially less drag than the two 165 gallon tanks, at least in the contemporary opinion of the editor of the Flight Operation Instruction Chart

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

How do we believe 'Greg's' assertion that 2x150gal wing tanks at cruise experience a 10-20mi drag penalty when comparable cruise settings for P-51D in extensive flight testing result in 47mph reduction over clean w/racks at 25K?

I've just found this bit in his video:

View: https://www.youtube.com/watch?v=B8DEUO9mqKk&t=1469s


He probably specifies which document the snippets are from, but I haven't found that yet.

For later reference:

• (Greg's razorback document), 20000 ft column "MAX CONT":
  • No tanks: 2550 rpm, Auto Rich, 235 mph IAS, 42" Hg, 210 GPH, 330 mph TAS
  • Two 150 gallon tanks: 2550 rpm, 225 mph IAS, Auto Rich, 37" Hg, 190 GPH, 320 mph TAS

So not only is the speed loss a mere 10 mph, it is also achieved at a reduced power setting.

Correct me if I get this wrong, but assuming power to be proportional to fuel flow, and speed proportional to the cube root of power, the speed difference would be explained by the power difference alone, and drop tank drag would have to be zero.

That makes me suspect that the Flight Operation Instruction Chart version Greg is using is a bit like the "none/empty 200 gallon drop tank" chart you've linked above, which doesn't seem to account for drop tank drag though the chart title would suggest it should.

Oh, this is what I found on Greg's sources:

View: https://youtu.be/I7aGC6Sp8zQ?t=1204


Presumably:

• RAF Pilot’s Notes for the Thunderbolt I (P-47D), AP 2381A-PN dated June 1944 with approx. 28 pages. (https://www.flight-manuals-online.com/product/republic-p-47-thunderbolt/ )

And:

View: https://youtu.be/I7aGC6Sp8zQ?t=1253


That's interesting because it's the T.O. No. 01-65BC-1, pages of which you linked above, and because the title page shown by Greg indicates that there were several dated revisions, his being the January 20, 1943 one.

(The flight manual site shows that they have the 20-11-43 revision of the same document.)

Regards,

Henning (HoHun)

 

[TomcatViP]

Don´t forget that there is the addition of the drag of the tanks and the result of the addition of the airplane drag that have to carry those tanks.
An heavier a/c would see its total drag increase less than for a lighter one.

Then there is the airfoils difference with flatter upper surface increasing the moment shift.,

We know that a fully tanked 51 is pitch itchy. Hence, with an extra load under the wings, the AoA would need more trim than with a more stable platform. More trim equal more drag.

Etc... Etc...

verification. (if possible) P-51D Vs H.

 

[HoHun]

Hi Bill,

Hi Henning - i'm the last guy to question one of your well thought out works of art.

I just found this freshly uploaded A-36 manual, which shows how engineers at North American approached the issue ... example page attached:

North American A-36A-1-NA Pilot’s Operating Instructions

A copy of the North American A-36A-1-NA Pilot’s Operating Instructions. (TO 01-60HB-1).Dated July 10 1943. Download here or here or her...

aviationarchives.blogspot.com

It seems my half-baked home-brew diagram at least went in the same general direction, as they graphed the various parameters over (reducing) weight. They used fuel flow instead of mileage, but as their diagrams assume constant air speed, that makes no big difference.

(Following this diagram doesn't result in the greatest possible range, for the reasons you already pointed out, but I presume flying at constant speed makes navigation easier.)

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



No worries, questioning is always welcome ... "All models are wrong but some models are useful", and any input to make them more useful is great!

Thumbs UP!

However, the graph I posted is just a visualization of the T.O.'s Flight Operation Instruction Chart, so there's really not much original thought involved.\

I'm pretty certain that Range calcs were not well grounded at Wright Field re: Drop Tanks in early 1943

Fully agreed! I think it's by design that each page of the T.O.'s Flight Operation Instruction Chart can't actually account for Breguet's range equation. Probably the USAAF also subscribes to the "wrong but useful" approach :-/

Equally agreed

From the data I graphed from the Flight Operation Instruction Chart, the average mileage with the 200 gallon drop tank is 2.55 statue miles/US gallon, and 2.81 statue miles/US gallon for the "none/empty 200 gallon drop tank" case.

Here is what I find most interesting and you point it out in the next paragraph

Of course, having "none" (which is ambiguous in itself as it might be either "clean" or "clean with racks") and "empty 200 gallon drop tank attached" lumped together in one Flight Operation Instruction Chart is a bit suspicious. However, that's partially why I graphed the data ... as there's a big jump between the two conditions, I would say it's not likely that the data is really for the 200 gallon drop tank still attached.

Agreed again, but even then the table values remain suspicious as the TAS varies little from SL to 15000 feet for the 200gal tank vs clean. And the P-47C was perhaps the cleanest as no B-7 rack, and no wing racks. The infamous quote by Gabreski "looks like a bullfrog in mid croak" very well describes the 200gal Republic tank. When empty the parasite/pressure drag remained the same. Only induced drag decreased as airspeed increased.

I'm not sure at the moment what Greg used as a source for his calculations, but I've got a copy of AN-01-65BC-01A here, with two Flight Operation Instruction Charts for external load items "none" and "2 - 165 U. S. Gallon Wing Tanks", both dated 4-1-44, which covers the bubbletop Thunderbolts, but probably are still useful for cross-checking wing tank drag.

Agreed. I would doubt much difference in drag exists between D-23 Razorback and D-25 Bubble top for 2x165 plus pylons.

These show for 20000 ft in column IV:

- No tanks: 2130 rpm, 31.8" Hg, Auto Lean, 113 GPH, 302 mph TAS
- Two tanks: 2100 rpm, 31.5" Hg, Auto Lean, 101 GPH, 221 mph TAS

That looks like a fairly massive difference. OK, the two-tank configuration uses slightly less power, but that's an 81 mph speed drop from a 11% power reduction, if we assume power is proportional to fuel flow (for closely adjacent operating points).

Weight probably shouldn't have all that much influence on these values, as the "no tanks" Flight Operation Instruction Chart is valid for 14200 to 12000 lbs (13100 lbs median), and the "two tanks" chart is valid for 16200 to 12000 lbs (14100 lbs median).

Should be cautious in assuming based on medians. The difference between full load out - clean, and 2 pylon 2x165gal is nearly 2200 pounds for external fuel/fuel tank alone. GW at TO for full internal load without tanks is ~ 14411 for D-23 Razorback and is 14811 for the D-25 Bubble top. The lesser range in operating manual charts is to account for taking off without full internal load of fuel, say for a cross country trip well within range limits. So, clean but full load out is ~ 12200 for razorback and 12600 for bubble top. To be rational, worst case range wise is take off and climb using internal auxiliary, then switch to external tanks for cruise. That is worst case for high(er) induced drag in the flight profile. The FAREP Range assumptions are 89gal from SE to 25000 feet. So the cruise journey begins about 534 pounds less than at Start Engine, or 13900 for D-23 and 14300 for D-25

So we can contrast the two sets of Flight Operation Instruction Charts:

• T.O. No. 01-65BC-1 (for razorback P-47's):
  • No tanks: 2.81 MPG
  • 200 GAL tank: 2.55 MPG
• AN-01-65BC-01A (for bubbletop P-47's)
  • No tanks: 2.68 MPG The Difference in MPG from P-47C might be accounted for by 65extra gal and pylons
  • 2 x 165 GAL tanks: 2.20 MPG

(In AN-01-65BC-01A, the MPG values are actually listed explicitely in column IV, so I didn't need to calculate them from the data points as for T.O. No. 01-65BC-1.)

That is order of magnitude that I expected but the first thing I would want clarified is the existence of wing racks vs clean. Otherwise doubt that D-25 was that much draggier than C-2 through D-23 without wing racks.

For the sake of completeness, here the 20000 ft column IV comparison for the T.O. No. 01-65BC-1 data:

- No tank: 2150 rpm, 30" Hg, 95 GPH, 210 mph IAS (~288 mph TAS)

(288mi/hr)/(95g/hr) = 3.03mi/g; to achieve 2.81mi/g, the TAS = 266mi/h -------------> something wrong in chart?

- 200 gallon tank: 2250 rpm, 32" Hg, 105 GPH, 205 mph IAS (~281 mph TAS)

281/105 = 2.67m/g... I seriously doubt that for the 205gal Ferry Tank (only 200gal tank available for P47C). That said I have no real Republic drag data to compare.

These speeds are quite close, so the 200 gallon tank (of unresolved type) appears to create substantially less drag than the two 165 gallon tanks, at least in the contemporary opinion of the editor of the Flight Operation Instruction Chart

Republic only made the 205gal composite 'bullfrog' ferry tank until the 150 and 215gal flat steel types delivered late 1943 and late 1944 respectively. Greg is focused on Brisbane 200gal tank made in Australia.

Regards,

Henning (HoHun)

Good stuff Henning. FWIIW I believe AN-01-65BC-01A for bubble top is much closer to actual experience.

 

[HoHun]

Hi Bill,

Agreed again, but even then the table values remain suspicious as the TAS varies little from SL to 15000 feet for the 200gal tank vs clean.

TAS is an arbitrarily selected value, chosen by the table editor to suit the desired mileage. The P-47 Flight Operation Instruction Charts don't state it explicitely, but on a Mustang chart, I found a caption stating that the pilot should establish the stated airspeeds by varying power. (Not quite sure where I saw that, should have taken notes!)

AN-01-65BC-01A states it a little less explicitely on the Flight Operation Instruction Charts, "Manifold pressure (M. P.), gallons per hour (G. P. H.) and true airspeed (T. A. S.) are approximate values for reference. For efficiency maintain indicated airspeed (I. A. S.) hourly. Adjust RPM slightly if necessary to avoid exceeding manifold pressure more than 3 in Hg."

However, your basic observation still holds true if one includes the power setting values, as the slight reduction in selected speed with tanks carried goes along with a slight reduction in power. I tried to quantify this for the 20000 ft case by applying some rules of thumb, and the power reduction alone was sufficient to explain the speed difference. So where Greg used this comparison to argue that the 150 gallon drop tanks had little drag, I would use this to argue that the table doesn't take drop tank drag into account, at all.

That is order of magnitude that I expected but the first thing I would want clarified is the existence of wing racks vs clean. Otherwise doubt that D-25 was that much draggier than C-2 through D-23 without wing racks.

I believe the USAAF was deliberately vague in that regard: AN-01-65BC-01A on p. 47 also states, "a. Two charts are provided; sheet 1 applies only until belly tank fuel is exhausted and sheet 2 gives operating instructions for all other loading conditions. The difference in primarily due to the weight of the belly tank fuel."

"For all other loading conditions" ... they weren't really trying to be accurate.

(288mi/hr)/(95g/hr) = 3.03mi/g; to achieve 2.81mi/g, the TAS = 266mi/h -------------> something wrong in chart?

Nothing wrong, the difference is due to Greg using the Maximum Continuous column and I was consistently using column IV of the Flight Operation Instruction Chart without always pointing this out properly. The TAS is not given in that particular table though, so I assumed IAS = CAS and converted to TAS myself (neglecting the compressibility correction). Since, I have found an air-speed correction table in AN 01-65BC-1, Revision Nov-20-1943, p. 29, which indicates that 205 mph IAS = 211.7 mph CAS, so my result was a little off.

Republic only made the 205gal composite 'bullfrog' ferry tank until the 150 and 215gal flat steel types delivered late 1943 and late 1944 respectively. Greg is focused on Brisbane 200gal tank made in Australia.

Great, that seems to narrow down our T.O. No. 01-65BC-1 "200 gallon tank" to the 'bullfrog' ferry tank then! Was that one droppable at all?

FWIIW I believe AN-01-65BC-01A for bubble top is much closer to actual experience.

Agreed, and I do actually believe that this is typical for war time documents. The USAAF really were quite good when it came to the administrative side of things, I'd say.

Two general observations on range, from reading the manuals:

- T.O. No. 01-65BC-1 states on p. 29, "WARNING FOR THE TROPICS - Hot gas at take-off may reduce range as much as 10 percent. Make allowance!"
- The P-51D manual states in the notes to the Flight Operation Instruction Charts: "Range values are for an average airplane flying alone (no wind)." I presume that this comment was also valid for the P-47 charts, even if it was not explicitely stated on these, since the USAAF seem to have been very consistent in their documentation.

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



TAS is an arbitrarily selected value, chosen by the table editor to suit the desired mileage. The P-47 Flight Operation Instruction Charts don't state it explicitely, but on a Mustang chart, I found a caption stating that the pilot should establish the stated airspeeds by varying power. (Not quite sure where I saw that, should have taken notes!)

AN-01-65BC-01A states it a little less explicitely on the Flight Operation Instruction Charts, "Manifold pressure (M. P.), gallons per hour (G. P. H.) and true airspeed (T. A. S.) are approximate values for reference. For efficiency maintain indicated airspeed (I. A. S.) hourly. Adjust RPM slightly if necessary to avoid exceeding manifold pressure more than 3 in Hg."

However, your basic observation still holds true if one includes the power setting values, as the slight reduction in selected speed with tanks carried goes along with a slight reduction in power. I tried to quantify this for the 20000 ft case by applying some rules of thumb, and the power reduction alone was sufficient to explain the speed difference. So where Greg used this comparison to argue that the 150 gallon drop tanks had little drag, I would use this to argue that the table doesn't take drop tank drag into account, at all.



I believe the USAAF was deliberately vague in that regard: AN-01-65BC-01A on p. 47 also states, "a. Two charts are provided; sheet 1 applies only until belly tank fuel is exhausted and sheet 2 gives operating instructions for all other loading conditions. The difference in primarily due to the weight of the belly tank fuel."

"For all other loading conditions" ... they weren't really trying to be accurate.



Nothing wrong, the difference is due to Greg using the Maximum Continuous column and I was consistently using column IV of the Flight Operation Instruction Chart without always pointing this out properly. The TAS is not given in that particular table though, so I assumed IAS = CAS and converted to TAS myself (neglecting the compressibility correction). Since, I have found an air-speed correction table in AN 01-65BC-1, Revision Nov-20-1943, p. 29, which indicates that 205 mph IAS = 211.7 mph CAS, so my result was a little off.

I really agree with your points, but to be candid the P-47C tables seem so flawed as to be essentially worthless with respect to the 200gal tank airspeed values/

Great, that seems to narrow down our T.O. No. 01-65BC-1 "200 gallon tank" to the 'bullfrog' ferry tank then! Was that one droppable at all?

They were 'droppable, as stated in the pilot manual. That said, they were dangerous to drop in flight with nasty habit of hitting empennage after ejection. Cass Hough LtC VIII Air Tech Services crafted a plywood 'prow' to influence dropping downward. The tank was designed for four point mount on P-47C skid mount and would not fit on B-7 belly rack which was retro fitted in C and D-2, D-4 for the succession of 75gal, 100, 108, 150gal tanks delivered from June (75), then 108 Oct/Nov, 150gal flat tank Dec/Jan 1944. Image below

Agreed, and I do actually believe that this is typical for war time documents. The USAAF really were quite good when it came to the administrative side of things, I'd say.

Two general observations on range, from reading the manuals:

- T.O. No. 01-65BC-1 states on p. 29, "WARNING FOR THE TROPICS - Hot gas at take-off may reduce range as much as 10 percent. Make allowance!"

That's where the volatility of AvGas really is concerning, and also an issue allegedly affecting efficiency of drop tank pressurization from exhaust side of vacuum pump.

- The P-51D manual states in the notes to the Flight Operation Instruction Charts: "Range values are for an average airplane flying alone (no wind)." I presume that this comment was also valid for the P-47 charts, even if it was not explicitely stated on these, since the USAAF seem to have been very consistent in their documentation.

Regards,

Henning (HoHun)

More than just 'no wind' - does not take into account all factors for combat ops such as taxi and elephant walk fuel consumption prior to take off of a 48plane FG, nor the orbit time as each element forms into flights and squadrons.

Also IAS to TAS as you know, is dramatically different with ascending altitude. 150 IAS was nominal cruise speed for B-17 combat formations, tending to be slower because of worn out engines for the few - but at 25K that translated to ~ 210mph TAS over the ground absent winds aloft. That is why I am really confused by 207mph TAS in the 2x165 tank table at 25K. That would be B-17 speed.

 

[HoHun]

Hi Bill,

I really agree with your points, but to be candid the P-47C tables seem so flawed as to be essentially worthless with respect to the 200gal tank airspeed values/

You might be right ...

They were 'droppable, as stated in the pilot manual. That said, they were dangerous to drop in flight with nasty habit of hitting empennage after ejection.

Thanks for the clarification! I was getting a bit confused with all those tanks.

More than just 'no wind' - does not take into account all factors for combat ops such as taxi and elephant walk fuel consumption prior to take off of a 48plane FG, nor the orbit time as each element forms into flights and squadrons.

These other operational consumption figures are supposed to be input in form of the "fuel not available for cruising" figure mentionied in the Flight Operation Instruction Chart, but wind (and throttle-jockeying to stay in formation) would require modification of the table output, which might be the reason the manual specifically mentions it.

150 IAS was nominal cruise speed for B-17 combat formations, tending to be slower because of worn out engines for the few - but at 25K that translated to ~ 210mph TAS over the ground absent winds aloft. That is why I am really confused by 207mph TAS in the 2x165 tank table at 25K. That would be B-17 speed.

That's the column V speed, maximum air range. I suspect these figures are technically accurate (more or less), but operationally irrelevant. Quoting T. O. 01-65BC-1: "NOTE: Ranges listed in column on extreme right should not be attempted with these airplanes above 13,500 ft altitude." If you don't get everything just right, you're probably worse off flying a little too slow than you'd be flying a little too fast for greatest air range, for example by using the values in column IV.

With regard to the European Theatre, do you know whether the fighters, when actually escorting the bombers, used slow cruising settings, or did they increase their speeds in order to be able to react more rapidly (and aggressively) to German attacks? That would be interesting for the range calculations ... basically, which column would they use for escorting? I'm assuming the tanks were already dropped upon rendezvous with the bombers, even if that wasn't always done historically.

Regards,

Henning (HoHun)

 

[drgondog]

Hi Bill,



You might be right ...



Thanks for the clarification! I was getting a bit confused with all those tanks.



These other operational consumption figures are supposed to be input in form of the "fuel not available for cruising" figure mentionied in the Flight Operation Instruction Chart, but wind (and throttle-jockeying to stay in formation) would require modification of the table output, which might be the reason the manual specifically mentions it.

Actually, those fuel reserve allocations encompass single aircraft straight line ferry. significantly more required for Group level combat excursions. Additional considerations to be further calculated/estimated would be close escort in which the fighter block essing or racetrack with the bombers are cruising at higher speeds but only traveling along the ground as fast as the escorted bombers.

Further, they are useful but not definitive to calculate combat radius, for which dropping tanks, fighting for 20min on MP and WEP, then return on economical cruise (~ 300mph TAS) well under Max Continuous power.

That's the column V speed, maximum air range. I suspect these figures are technically accurate (more or less), but operationally irrelevant. Quoting T. O. 01-65BC-1: "NOTE: Ranges listed in column on extreme right should not be attempted with these airplanes above 13,500 ft altitude." If you don't get everything just right, you're probably worse off flying a little too slow than you'd be flying a little too fast for greatest air range, for example by using the values in column IV.

The 200gal Republic tank was not recognized to be capable of high altitude pressurization - which is why the long range ceiling is 15000 feet. 8th AF stretched it to 20,000 feet and dropped before completing climb to 30K for frequent cruise altitude to R/V

With regard to the European Theatre, do you know whether the fighters, when actually escorting the bombers, used slow cruising settings, or did they increase their speeds in order to be able to react more rapidly (and aggressively) to German attacks? That would be interesting for the range calculations ... basically, which column would they use for escorting? I'm assuming the tanks were already dropped upon rendezvous with the bombers, even if that wasn't always done historically.

Regards,

Henning (HoHun)

No to 'slow' like SWP courses over jungle or ocean where no Japanese flak or fighter bases were astride the course. Flying slow over Netherlands or Germany was excellent way to become KIA or POW. P-51 escort in Q1-Q3/1944 was frequently either Target escort leg after taking hand off from P-47 Penetration - or Fighter Mission in which the group was out just looking for trouble. SOP for my father was for 75gal tanks, cruise @ ~ 230mph IAS at 25K, arrive at R/V, keep feeding from externals until dry or engaged. If no combat, would frequently keep steel tanks unless really long mission like to Posnan or Prague and he needed less drag on return leg. Cruise w/108gal was closer to 210mph IAS

 

[HoHun]

Hi Bill,

Actually, those fuel reserve allocations encompass single aircraft straight line ferry. significantly more required for Group level combat excursions. Additional considerations to be further calculated/estimated would be close escort in which the fighter block essing or racetrack with the bombers are cruising at higher speeds but only traveling along the ground as fast as the escorted bombers.

Understood, I only meant that this can all be treated as input data for the Flight Operation Instruction Chart, unlike wind influence or reduced efficiency during formation flight. The latter effects can only be accounted for in different ways. OK, now that I am thinking about it, wind can be figured in if you use predicted air miles rather than geographic distances in your planning. Increased fuel burn due to throttle jockeying would have to be accounted for by modifying the table output, though.

Further, they are useful but not definitive to calculate combat radius, for which dropping tanks, fighting for 20min on MP and WEP, then return on economical cruise (~ 300mph TAS) well under Max Continuous power.

That's indeed a bit complicated, but it can be done. Of course, it depends on accurately portraying the real-world mission profile, and the results of course can't be more accurate than the Flight Operation Instruction Charts's numbers themselves.

No to 'slow' like SWP courses over jungle or ocean where no Japanese flak or fighter bases were astride the course. Flying slow over Netherlands or Germany was excellent way to become KIA or POW.

Thanks, that's what I was thinking, too! I was a bit disappointed by Greg's video on Pacific Theatre missions as he didn't provide full mission profiles, and mostly only stated altitude over the target.

SOP for my father was for 75gal tanks, cruise @ ~ 230mph IAS at 25K, arrive at R/V, keep feeding from externals until dry or engaged. If no combat, would frequently keep steel tanks unless really long mission like to Posnan or Prague and he needed less drag on return leg. Cruise w/108gal was closer to 210mph IAS

Excellent! That would be about column IV in the 2 x 75 gallons tanks Flight Operation Instruction Chart of the P-51D manual, which states 2300 rpm, Full Throttle, 75 GPH, 340 MPH at 25000 ft. The 2 x 110 gallons tanks chart states 2350 rpm for 79 GPH, but the same speed.

I presume if returning without drop tank, a similar speed would be flown? So far, I've been assuming a return flight using column V, Maximum Air Range, but after our last couple of posts here, but as we discussed above that these speeds probably weren't operationally suitable for formation flying, I'd now tend to switch the return leg over to column IV, too.

Here's what the table looks like at the moment ... I admit that I didn't originally expect it to become so convoluted.

Spoiler: Large and boring table with preliminary data

​	​	​	AN 01-65BC-1 Nov 44​	​	​	​	​
​	P-38J-5​	P-38J-15​	P-47D​	P-47D-25f​	P-51D (no fuselage tank)​	P-51D​	F-82E​
Fuel Tank Data​	​	​	​	​	​	​	​
Gross Internal Fuel​	306.0​	416.0​	305.0​	370.0​	184.0​	269.0​	575.0​
Drop Tank Fuel​	330.0​	330.0​	108.0​	200.0​	150.0​	150.0​	330.0​
Take-off Weight LBS​	18740.0​	19400.0​	​	​	10290.0​	10800.0​	23000.0​
​	​	​	​	​	​	​	​
Climb Time from Take-off, Climb and Landing Chart​	​	​	​	​	​	​	​
For Weight​	17400.0​	19400.0​	15000.0​	16000.0​	10000.0​	11000.0​	22000.0​
Minutes to 5000 ft​	2.0​	2.0​	3.0​	2.5​	2.8​	3.4​	​
Minutes to 10000 ft​	4.0​	4.0​	6.0​	5.1​	5.6​	6.8​	7.0​
Minutes to 15000 ft​	6.0​	7.0​	10.0​	8.0​	8.5​	10.5​	10.5​
Minutes to 20000 ft​	​	​	14.0​	10.9​	11.5​	14.0​	14.0​
Minutes to 25000 ft​	10.0​	11.0​	19.0​	14.0​	15.0​	18.5​	19.0​
Minutes to 35000 ft​	15.0​	20.0​	​	​	​	​	25.0​
​	​	​	​	​	​	​	​
mph IAS To 5000 ft​	180​	180​	165​	165​	175​	175​	180​
mph IAS To 10000 ft​	178​	178​	165​	165​	175​	175​	​
mph IAS To 15000 ft​	175​	175​	155​	160​	170​	170​	180​
mph IAS To 20000 ft​	​	​	155​	155​	165​	165​	180​
mph IAS To 25000 ft​	170​	170​	155​	150​	165​	165​	180​
mph IAS To 35000 ft​	165​	165​	​	​	​	​	175​
​	​	​	​	​	​	​	​
mph TAS at sea level​	180​	180​	165​	165​	175​	175​	180​
mph TAS To 5000 ft​	193.9​	193.9​	177.8​	177.8​	188.5​	188.5​	​
mph TAS To 10000 ft​	207.1​	207.1​	192.0​	192.0​	203.6​	203.6​	0.0​
mph TAS To 15000 ft​	220.6​	220.6​	195.4​	201.7​	214.3​	214.3​	226.9​
mph TAS to 20000 ft​	​	​	212.3​	212.3​	226.0​	226.0​	246.6​
mph TAS To 25000 ft​	254.0​	254.0​	231.5​	224.1​	246.5​	246.5​	268.9​
mph TAS To 35000 ft​	296.4​	296.4​	​	​	​	​	​
​	​	​	​	​	​	​	​
Range in Climb​	​	​	​	​	​	​	​
Miles to 5000 ft​	6.2​	6.2​	8.6​	7.1​	8.5​	10.3​	​
Miles to 10000 ft​	12.9​	12.9​	17.8​	15.3​	17.6​	21.4​	10.5​
Miles to 15000 ft​	20.0​	23.6​	30.7​	24.6​	27.7​	34.3​	17.1​
Miles to 20000 ft​	​	​	44.3​	34.8​	38.7​	47.1​	30.9​
Miles to 25000 ft​	35.9​	39.4​	62.8​	46.1​	52.5​	64.9​	52.4​
Miles to 35000 ft​	58.8​	80.7​	​	​	​	​	​
​	​	​	​	​	​	​	​
Range calculated from Take-off/Climb Chart​	​	​	​	​	​	​	​
Range covered in Climb to 25000 ft​	35.9​	39.4​	62.8​	46.1​	52.5​	64.9​	52.4​
​	​	​	​	​	​	​	​
Absolute Consumption GAL​	​	​	​	​	​	​	​
Nominal Fuel for Climb to 25000 ft​	103.0​	103.0​	110.0​	118.0​	40.0​	44.0​	160.0​
Redundant Allowance for Warm-up and Take-off​	40.0​	40.0​	30.0​	30.0​	15.0​	15.0​	30.0​
30 min Reserve​	50.0​	50.0​	40.0​	40.0​	26.0​	26.0​	50.0​
​	​	​	​	​	​	​	​
Consumption GPH from SEFC table​	​	​	​	​	​	​	​
WEP​	360.0​	360.0​	275.0​	255.0​	215.0​	215.0​	450.0​
MIL​	334.0​	334.0​	275.0​	280.0​	187.0​	187.0​	440.0​
Max Cont for Take-off etc.​	226.0​	226.0​	210.0​	220.0​	97.0​	97.0​	280.0​
​	​	​	​	​	​	​	​
Consumption GPH from Flight Operation Instruction Chart​	​	​	​	​	​	​	​
Cruise out with Drop Tanks at 25000 ft​	89.0​	89.0​	105.0​	105.0​	60.0​	60.0​	120.0​
Cruise out clean at 25000 ft​	71.0​	71.0​	143.0​	143.0​	60.0​	60.0​	125.0​
Escort Cruise at 25000 ft​	71.0​	71.0​	143.0​	143.0​	73.0​	73.0​	125.0​
Max Range Cruise at 20000 ft​	66.0​	66.0​	95.0​	95.0​	56.0​	56.0​	115.0​
​	​	​	​	​	​	​	​
Speeds MPH TAS from Flight Operation Instruction Chart​	​	​	​	​	​	​	​
Cruise out with Drop Tanks at 25000 ft​	260.0​	260.0​	283.8​	283.8​	295.0​	295.0​	290.0​
Cruise out clean at 25000 ft​	267.0​	267.0​	324.0​	324.0​	335.0​	335.0​	330.0​
Max Range Cruise at 20000 ft​	248.0​	248.0​	288.0​	288.0​	315.0​	315.0​	305.0​
​	​	​	​	​	​	​	​
Mission Parameters – Escort Conditions​	​	​	​	​	​	​	​
Range to Target​	398.9​	812.3​	288.2​	481.8​	358.6​	822.9​	764.5​
Bomber Speed IAS at 25000 ft​	150.0​	150.0​	150.0​	150.0​	150.0​	150.0​	150.0​
​	​	​	​	​	​	​	​
Mission Parameters – Duration min​	​	​	​	​	​	​	​
WEP​	5.0​	5.0​	5.0​	5.0​	5.0​	5.0​	5.0​
MIL​	5.0​	5.0​	5.0​	5.0​	5.0​	5.0​	5.0​
Escort Cruise at 25000 ft​	30.0​	30.0​	30.0​	30.0​	30.0​	30.0​	30.0​
Max Cont for Take-off etc.​	15.0​	15.0​	15.0​	15.0​	15.0​	15.0​	15.0​
​	​	​	​	​	​	​	​
Mileage MPG​	​	​	​	​	​	​	​
MPG on Cruise out with Drop Tanks at 25000 ft​	2.921​	2.921​	2.703​	2.703​	4.917​	4.917​	2.417​
MPG on cruise out clean at 25000 ft​	3.761​	3.761​	2.266​	2.266​	5.583​	5.583​	2.640​
MPG on return​	3.758​	3.758​	3.032​	3.032​	5.625​	5.625​	2.652​
​	​	​	​	​	​	​	​
Mission Parameters – Consumption Gallons​	​	​	​	​	​	​	​
Max Cont for Take-off etc.​	56.5​	56.5​	52.5​	55.0​	24.3​	24.3​	70.0​
WEP​	30.0​	30.0​	22.9​	21.3​	17.9​	17.9​	37.5​
MIL​	27.8​	27.8​	22.9​	23.3​	15.6​	15.6​	36.7​
Escort Cruise at 25000 ft​	35.5​	35.5​	71.5​	71.5​	36.5​	36.5​	62.5​
Sum of WEP MIL Escort Cruise etc.​	93.3​	93.3​	117.3​	116.1​	70.0​	70.0​	136.7​
​	​	​	​	​	​	​	​
Trip to Rendezuvous​	​	​	​	​	​	​	​
Consumed Fuel for Climb to 25000 ft​	63.0​	63.0​	80.0​	88.0​	25.0​	29.0​	130.0​
Available Drop Tank Fuel for Cruise Out​	267.0​	267.0​	28.0​	112.0​	125.0​	121.0​	200.0​
Available Cruise-Out Distance on Drop Tanks​	780.0​	780.0​	75.7​	302.8​	614.6​	594.9​	483.3​
Available Cruise-Out Range on Drop Tanks​	815.9​	819.4​	138.5​	348.8​	667.1​	659.8​	535.7​
Bomber Speed TAS​	224.1​	224.1​	224.1​	224.1​	224.1​	224.1​	224.1​
Range to Rendezvous​	249.5​	662.9​	138.8​	332.4​	209.2​	673.5​	615.1​
Remaining Distance to Rendezvous on Internal Fuel​	0.0​	0.0​	0.3​	0.0​	0.0​	13.7​	79.4​
Gallons required for Cruise on Internal Fuel​	0.0​	0.0​	0.1​	0.0​	0.0​	2.5​	30.1​
Gallons dropped at Rendezvous​	193.9​	53.6​	0.0​	6.1​	93.1​	0.0​	0.0​
​	​	​	​	​	​	​	​
Return Trip​	​	​	​	​	​	​	​
Available Internal Fuel​	249.5​	359.5​	252.4​	315.0​	159.8​	242.3​	474.9​
Remaining Internal Fuel after Escorting, excluding Reserve​	106.2​	216.2​	95.0​	158.9​	63.8​	146.3​	288.3​
Return Distance​	398.9​	812.3​	288.2​	481.8​	358.6​	822.9​	764.5​
Return Time at Max Range Cruise​	96.5​	196.5​	60.0​	100.4​	68.3​	156.7​	308.9​
Return Speed at Range Cruise​	248.0​	248.0​	288.0​	288.0​	315.0​	315.0​	148.5​
Delta to target​	0​	0​	0​	0​	0​	0​	0​
​	​	​	​	​	​	​	​
Consumption Overview​	​	​	​	​	​	​	​
Total Fuel nominal​	636​	746​	413​	570​	334​	419​	905​
Max Cont for engine start, warm-up, take-off, form-up​	56.5​	56.5​	52.5​	55.0​	24.3​	24.3​	70.0​
Fuel used in climb​	63.0​	63.0​	80.0​	88.0​	25.0​	29.0​	130.0​
Fuel used for cruise with drop tanks​	73.1​	213.4​	28.0​	105.9​	31.9​	121.0​	200.0​
Fuel dropped at rendezvous​	193.9​	53.6​	0.0​	6.1​	93.1​	0.0​	0.0​
Internal fuel used for cruise​	0.0​	0.0​	0.1​	0.0​	0.0​	2.5​	30.1​
Escort fuel for WEP​	30.0​	30.0​	22.9​	21.3​	17.9​	17.9​	37.5​
Escort fuel for MIL​	27.8​	27.8​	22.9​	23.3​	15.6​	15.6​	36.7​
Escort fuel for “escort cruise”​	35.5​	35.5​	71.5​	71.5​	36.5​	36.5​	62.5​
Fuel used for return flight​	106.2​	216.2​	95.0​	158.9​	63.8​	146.3​	288.3​
Total Fuel Consumption​	586.0​	696.0​	373.0​	530.0​	308.0​	393.0​	855.0​
Delta to nominal​	50​	50​	40​	40​	26​	26​	50​

I hope to upload the table complete with formulae soon, but after I recently suggested that, for security reasons, only XLSX tables should be allowed for upload, the forum somehow won't accept my OpenOffice ODS table now! :-D

Regards,

Henning (HoHun)

 

[drgondog]

Greg is very articulate and also adept at changing the subject when confronted by a fact that doesn't fit his narrative.

I've had quite a few email exchanges w/Greg pre- and post debate.

Here are his hard positions:
Brisbane equipped 200gal tanks wopld have enabled P-47s in ETO to escort the 8th AF anywhere the VIII BC attacked in 1943. He used Schweinfurt (425Mi) as his key battleground, ignoring Regensburg 100mi further away.

That the Republic 200gal composite Tank would have been just as useful, despite lack of pressurization capability limiting max ceiling to 20,000 feet - and despites contrary and documented comments from Gabreski and Zemke and 4th FG mission reports.

That straight line calcs he illustrates by example are adequate to narrate an escort mission, when for the escort leg, the ground speed of the P-47 escort must be the same as the bombers escorted.

That SOP for escort missions flown by 348FG were analogous to 8th AF, namely climb to 25-30K, R/V with bombers, escort to the target - as well as citing Lindbergh methodology as important for range extension. When I pointed out the contrast between low altitude and low cruise speed approach over water in SWP en route to target area where R/V was to be made near target - was suicidal and unproductive over continental Europe, he dismisses. I sent several 8th and 49FG P-38 escort mission profiles for B-24 strikes to Wewak and Rabaul in which the inbound course exceeded 12000 feet only at Owen Stanley - and arrived at staggered altitudes of 18000 to 22000 (high cover) or same profile for B-25/A-20/B-26 missions but high cover at 12,000 feet. I asked Greg to provide 348Fg mission summaries but he replied that he doubted they exist. 5th AF was just as anal as 8th and 9th and 15th AF per mission summaries. What I was trying to prove to Greg is that even with 2x108 or 2x165 tanks in mid 1944, that ETO ESCORT missions resulting in combat were 3 1/2. to 3 3/4 hr long from TO time to return time when combat ensued - and the longest radius from Halesworth was 403/408 mi (short of Schweinfurt) to Halberstadt and Hagenow in April & May, with 305gal razorbacks. Both were Fighter Sweeps, not close escort.

I spent a lot of time digging into 56FG victory credits to illustrate the point of maximum actual combat radius for either the Fighter Mission or Escort Mission. (Attached) communication issues prevented presenting and explaining.

FYI the 'blue column' in the comparative range spreadsheet are for 8th AF Fighter Mission, longer than Escort capability/

He dismisses the fact that either imbedded booster pumps in drop tank, or slaving the tank to be pressurized to exhaust output of vacuum pump, he rejects that based on his airline experiences (imbedded booster pumps in internal fuel tanks), seemingly not understanding that drop tanks must be fed compressed air > 5 psi to PUSH the fuel out. Greg is a smart guy and I do not get his stubbornness on this issue. Even when I pulled P-51D and P-47D-25 & Subsequent discussion of Dorp tank fuel system from Pilot's manual and showed him examples of drop tanks with both pressurization and fuel supply lines.

 

[drgondog]

Henning - please PM me at your convenience, I have something for you.

 

[HoHun]

Hi Bill,

I've had quite a few email exchanges w/Greg pre- and post debate.

Here are his hard positions:

Thanks a lot for the summary!

I spent a lot of time digging into 56FG victory credits to illustrate the point of maximum actual combat radius for either the Fighter Mission or Escort Mission. (Attached) communication issues prevented presenting and explaining.

That's pretty good stuff. I once imported the "Tony Woods" Luftwaffe claims list into a database and tried to figure out the geo coordinates for each and every claim from the information contained in that list. The problem is, not all of them have a grid coordinate (not to mention that there were different grid systems), and while it should technically be possible to automatically generate approximate geo coordinates from descriptions like "20 km SW of Abbeville", I abandoned that project halfway through because it consumed so much time. It would make the perfect counterpart to your analysis though, as obviously the Luftwaffe could only shoot down P-47's where the USAAF could fly their P-47's

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

That's pretty good stuff. I once imported the "Tony Woods" Luftwaffe claims list into a database and tried to figure out the geo coordinates for each and every claim from the information contained in that list. The problem is, not all of them have a grid coordinate (not to mention that there were different grid systems), and while it should technically be possible to automatically generate approximate geo coordinates from descriptions like "20 km SW of Abbeville" [...]

I gave it another try today, and with the cloud geolocation services available today, I managed to get another couple of thousand coordinates filled in. It should have been more, but somehow the service I chose fails even for some very unambiguous place names. It doesn't help that the list is full of typos, not to mention random Umlauts to flood the enemy radar screen with meaningless blips.

However, here's a preview of what might be possible if I whack the moleys even more furiously for even longer:



It's just a teaser, incomplete and inaccurate. But I haven't ever seen a map like this before, so maybe it's interesting anyway.

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

It's just a teaser, incomplete and inaccurate.

Of course, as soon as it's posted, one immediately spots suspicious data ... what's that one 1943 P-47 doing down there near Innsbruck?

No idea actually, here's the corresponding record:

ID	Date	Rank	Fname	Lname	Unit	JG	Claimed	Location	Time	Claim	St_Claim	RLM	Prim_Source	Conf	Sec_Source	Notes
5749​	30.07.1943​	Ltn.	Eugen	Wintergerst	9.	JG 1	P-47	IH in See: 5500m	10.42	22	-	yes	C.2027/I	Anerk: Nr.i.O.

"IH in See" is the location text, which my algorithm cut down to "See", for which the online service for some unfathomable reason provided the coordinates N47.083 E010.47.

Quite annoying ... not sure how to quality control stuff like that.

Regards,

Henning (HoHun)