A WW2 fighter design for rugged areas

[paralay]

The number of shells fired in one second, 1 - Hurricane 2C

 

[riggerrob]

Hi Rob,



I wouldn't disagree with the conclusion, but the Me 109's landing gear issues in reality were quite minor, and if you dig for statistics of take-off/landing accidents, or the relation of enemy-inflicted vs. total losses, there is actually no difference to the Fw 190 with its supposedly far superior landing gear. There was a stretch in 1940 in which landing gear damage was a strain on the maintenance and repair organisation, but that concerned the Me 109E that didn't have a tailwheel lock, which was subsequently introduced.

I hasten to add that the bad reputation of the Me 109 is not a post-war thing ... I've actually found German WW2 files that heavily criticize how the separation of flight training schools in basic and advanced training leads to the flight instructors in the basic schools, who did not get to fly the Me 109 and did not train their students on the type, fed stories of how quickly the Me 109 would crash if mishandled to their pupils. These stories lead to a heavy bias of these pupils against the Me 109, and occasional ill-advised panic reactions instead of the smooth and steady inputs one needed to operate a Me 109 safely.

Compare this to the American style of building pilot confidence along with competence, immortalized by variations of, "If you can handle the T-6, flying the P-51 will be a breeze".

Regards,

Henning (HoHun)

Please also consider the time-frame and the amount of gasoline available to train new pilots.
Remember that Me.109 was invented during the 1930s when Luftwaffe student pilots already had plenty of “stick time” from flying Hitler Youth gliders. Then there was also plenty of gasoline available to build flying hours and skills. Some Luftwaffe pilots learned valuable lessons during the Spanish Civil War and shared those lessons-learned with student pilots. Me.109 pilots benefitted from more experience and more experience equates to a lower accident rate on sensitive airplanes.
Fast forward to mid-war and many senior pilots had died in battle, hence fewer lessons-learned passed on to student pilots.
Secondly, restricted supplies of gasoline meany fewer hours flown in training. Insert a scared junior pilot into a faster airplane and accident rates increase.

 

[riggerrob]

So, instead of the Spitfire's elliptical wing, you have the same leading edge and a straight trailing edge?

The idea seems like it could have been invented in the 1940s. And I can see it being done trying to simplify production, not for aerodynamics.

Simplified elliptical wings were invented during the 1930s. The biggest problem was building leading edges precisely enough to maintain smooth airflow. Laminar flow only became practical with precisely-built sheet aluminum leading edges introduced during the 1930s. Precision required the massive hydraulic presses invented by the automotive industry. The slightest imperfection (e.g. rivet head) could grip airflow to increase drag and reduce lift. One of the reasons that it took an extra year to establish a Spitfire shadow-factory at Castle Browich was the need to build large hydraulic presses to precisely from complex-curved leading edge skins.

After Aichi, Heinkel and Supermarine struggled to build perfectly elliptical wings, Reggiane and deSeversky/Republic simplified the process by building straight leading edges and only curving trailing edges. They were able to build leading edges precisely enough to maintain smooth airflow well aft of the leading edges. It is easier to build complex curves on fabric-covered trailing edges (see amateur-built Piel Emeraude and Stolp Starduster). By the time airflow reached ailerons, the boundary layer was already thick enough that minor imperfections (e.g. fabric flexing) were less important.

OTOH Introducing Schumann Wings during WW2 would still require precisely forming complex curved leading edges while simplifying trailing edge construction. They only needed complex curves on wing-tips. Perhaps Regianne and deSeversky invented the best compromise by slightly sweeping their leading edges and pushing all the complex curves to trailing edges.

 

[riggerrob]

But G.55/59 or Macchi 205 also seem like valid bases. …. probably a bit lower aspect ratio wing to emphasise roll rate ….

Another way to improve roll rate is reducing wing area out at the wing tips. You can keep span and wing area the same, just redistribute the area farther inboard. Try to picture a Yakovlev with broad wing root ribs and short ribs in the wing tips.
A disadvantage of more sharply tapered wings is earlier stall beginning at the wing tips. This can cause nasty snap rolls when you fly too slowly.
Back during WW2, the most common solution was to ash-out (aka. twisting) wings to produce shallower angles of incidence in outboard ribs.
A second solution was installing slots or slats to maintain smooth airflow over ailerons Part way into stalls.
The modern method is the drooped and extended outboard leading edges invented by NASA during the 1970s. Drooped leading edges reduce angle-of-attack and the larger radius delays stalls (see the various after-market STOL kits developed by Robertson, Sportsman and Wren).
A secondary function is that the dogs-tooth (aka. step) produces a vortex that acts as a stall fence preventing turbulent wing root airflow from destabilizing airflow over ailerons.

A third method was developed by Red Air Force squadrons flying Lend-Lease P-39 Airacobras. By removing wing-mounted guns, they reduced inertia and improved instantaneous roll rates.

View attachment 716586

 

[Nicknick]

Simplified elliptical wings were invented during the 1930s. The biggest problem was building leading edges precisely enough to maintain smooth airflow. Laminar flow only became practical with precisely-built sheet aluminum leading edges introduced during the 1930s. Precision required the massive hydraulic presses invented by the automotive industry. The slightest imperfection (e.g. rivet head) could grip airflow to increase drag and reduce lift. One of the reasons that it took an extra year to establish a Spitfire shadow-factory at Castle Browich was the need to build large hydraulic presses to precisely from complex-curved leading edge skins.

After Aichi, Heinkel and Supermarine struggled to build perfectly elliptical wings, Reggiane and deSeversky/Republic simplified the process by building straight leading edges and only curving trailing edges. They were able to build leading edges precisely enough to maintain smooth airflow well aft of the leading edges. It is easier to build complex curves on fabric-covered trailing edges (see amateur-built Piel Emeraude and Stolp Starduster). By the time airflow reached ailerons, the boundary layer was already thick enough that minor imperfections (e.g. fabric flexing) were less important.

OTOH Introducing Schumann Wings during WW2 would still require precisely forming complex curved leading edges while simplifying trailing edge construction. They only needed complex curves on wing-tips. Perhaps Regianne and deSeversky invented the best compromise by slightly sweeping their leading edges and pushing all the complex curves to trailing edges.

As I understand it, the eliptical wing fits best to the (by mostly) desired elliptical lift distribution and also helps from a mecanical standpoint since the cross section fits quite well to the bending moment. Keeping the flow laminar depends more on the wing profile and not so much on the projected shape of the wing.

Somewhere here, I read that the Spitfires didn't really have an elliptical lift distribution despite the elliptical wing.

 

[drgondog]

Hi Bill,



You might be right, but all I was looking at was gross drag, with no real way to attribute it to any particular aspect of the airframe. The cooling system as a major change between airframes would be the "usual suspect", but as I haven't even looked at the issue systematically, I'm not actually in a position to even hypothesize.

The eternal question is that of reliable Hp values from the flight tests, next is validity (or lack of) ram air effect on FTH. Fortunately Induced Drag at the top speeds is low so that errors (lack of data) in oswald efficiency is not impactful for 'rule of thumb'. I noticed that in 100% of the NAA Flight Performance calcs for the P-51B and subsequent that e = 1 and that the profile drag of the cooling system at high speed is assumed = zero below 35K and = Deta CDp =0.0064 for climb.

Would you expect the V-1650-1 or some other Merlin-20-series engine to perform better up to 6 km than a Merlin 61, provided the only difference in the airframe we install it in is the intercooler?

Based on the power curves I have seen, yes - but it is a good question depending on boost limit comparisons. To throw another wild card into the qustion is the Allison -81 at 17500 feet with 1125HP. As a second thought, the Allisons were frequently run (by RAF) at 60+"MP vs US 52" MP. IIRC the cooling requirements for the Merlin 20 were higher than the Allison 1710-81 but I'll have to check the R-R package sent to NAA in later 1941. I suspect that the Coolant matrix would be larger for the Merlin,

The Spitfire Vc with Merlin 45 seems to be a faster aircraft than the Spitfire IX at low altitudes at equivalent power levels, that's what got me thinking ... a Merlin 20 should extend that superiority a bit toward higher altitudes, and the weight savings from omitting an intercooler would certainly help us to meet Pasoleati's other performance requirements (aside from speed).

If discussing P-51A/P-51-NA then recall that Fighter mission standard loadout weight was 100-105 gallons - an immediate cut of nearly 500 punds from take off gross weight and still greater range than other airframes discussed. That would/should get the ROC and time to 20K numbers in-line. If P-51-NA, 2x 20mm and ammo reduction rips off another 350 pounds - driving GW below 8,000 pounds. The P-51A without wing racks was ~10mph faster at 18K

Ah, thanks for the warning! Sounds like just the thing that could have thrown me into serious confusion! I'm certainly looking forward to your next book, not only for the corrections. I hope Osprey improved their information security, that's unfortunately becoming ever more important these days.

I have an erata doc if you want it.

Regards,

Henning (HoHun)

 

[tomo pauk]

I have an erata doc if you want it.

It would've been neat if you make that available.

 

[riggerrob]

… elliptical wing … also helps from a mecanical standpoint since the cross section fits quite well to the bending moment.

IOW. Concentrating the longest chord near wing roots maximizes lift near the roots to minimize bending moments on wing spars. Then taper wing tips rapidly to minimize the size of wing tip vortices.
While Heinkel and Aichi built truly-elliptical wings, Supermarine built modified elliptical planforms. Spitfires got straight main spars to simplify spar construction. Since the Spitfires’ main spar was at the deepest part of the wing (25 percent chord) they needed different taper ratios on the leading (shallow) and trailing edges (steep).
One critic suggested that Spitfire got elliptical wings to accommodate guns in a deeper part of the wing, just outboard of the prop arc. To that, I suggest that long 20mm cannons were an after-thought.

 

[Scott Kenny]

One critic suggested that Spitfire got elliptical wings to accommodate guns in a deeper part of the wing, just outboard of the prop arc. To that, I suggest that long 20mm cannons were an after-thought.

Vickers/Maxim gun receivers are deeper than Browning receivers, so that may still be true.

 

[HoHun]

Hi Bill,

The eternal question is that of reliable Hp values from the flight tests

I don't think it would be possible to catch any subtle differences - many aircraft for which multiple tests are available show considerable variation between aircraft. Analysis of flight test results can provide quite a good framework for understanding the major performance drivers though. I don't know if you're into WW1 aircraft too, but last year Anders Jonsson published a book titled "WW1 Aircraft Performance", which illustrates that quite nicely and might actually provide some new insights into the combat realities of the era. Of course, in comparison to the WW1 era, the test data we have on WW2 aircraft fortunately is both more plentiful and much more detailed!

NEW BOOK: WW1 Aircraft Performance Design, Aerodynamics And Flight Performance

NEW BOOK: WW1 Aircraft Performance Design, Aerodynamics And Flight Performance Books and Magazines

www.theaerodrome.com

Based on the power curves I have seen, yes - but it is a good question depending on boost limit comparisons. To throw another wild card into the qustion is the Allison -81 at 17500 feet with 1125HP. As a second thought, the Allisons were frequently run (by RAF) at 60+"MP vs US 52" MP. IIRC the cooling requirements for the Merlin 20 were higher than the Allison 1710-81 but I'll have to check the R-R package sent to NAA in later 1941. I suspect that the Coolant matrix would be larger for the Merlin

For the V-1710-81 on 1/1/1943, it seems this is the relevant engine chart (dated December 18, 1942) ... 3000 rpm @ 57" Hg WEP, for 1480 HP @ 10000 ft (with ram): http://www.wwiiaircraftperformance.org/P-40/P-40N_V-1710-81_specific_engine_flight_chart.jpg

A bit surprising to the 52" Hg take-off power with a time limit of 5 min, but the 57" Hg only labeled with "emergency only".

This later chart has the 57" Hg war emergency power setting with 5 min duration too, but gives the full throttle height at "sea level", confusingly. At also revises the full throttle height in military power downwards by 3500 ft (with ram): http://www.wwiiaircraftperformance.org/P-40/P-40M_V-1710-81_specific_engine_flight_chart.jpg

As an additional data point, an Australian test report for a P-40N, observed a full throttle height at 3000 rpm/57" Hg of 9200 ft in high-speed flight and of 6800 ft in the climb. That's closer to the earlier chart than to the more pessimistic later one, so I'd stay with the earlier one for once.

Then there's this February 23, 1943 calibration chart for the V-1710-81: http://www.wwiiaircraftperformance.org/P-40/P-40N_V-1710-81_Engine_Flight_Calibration_Curves.jpg

It shows a take-off power of 3000 rpm/52" Hg up to 10000 ft, but looking at the chart, I strongly suspect that the 10000 ft limit for take-off power was just a conventional limit set by the USAAF. Eyeballing it, I'd say the engine might actually have sustained the 52" Hg up to 13000 ft.

MIL power critical altitude is 15500 ft, so I assume this is consistent with the December 18, 1942 power chart above, but for a no-ram effect situation. (WEP is not shown on the chart, unfortunately.)

For the V-1650-1 on 1/1/1943, it seems this is the relevant engine chart (dated December 18, 1942) ... 3000 rpm @ 51" Hg WEP, for 1300 HP @ 4600 ft and 12000 ft respectively (both with ram): http://www.wwiiaircraftperformance.org/P-40/P-40F_V-1650-1_specific_engine_flight_chart.jpg

Odd rating, normally you don't get the same power from the same settings at both critical altitudes! Also a bit odd that no time for WEP is given, and time for MIL is limited to 5 min.

To further complicate matters, Pasoleati in the range requirements specified 15 min flight at war emergency rating ... I presume that implies that these 15 min war emergency rating have to be available in a single burst, so we might not be able to use the WEP settings of the US engines at all. Another wrench in the works!

On the V-1710-81 charts, MIL is shown as usable for 15 min, so I think we're limited to MIL then. On the V-1650-1 chart, even MIL is limited to 5 minutes, so I have no idea which power level to use as WEP-in-the-sense-of-the-requiremnts here. The next lower setting on the chart is maximum continuous, which is a much lower power rating.

If discussing P-51A/P-51-NA then recall that Fighter mission standard loadout weight was 100-105 gallons - an immediate cut of nearly 500 punds from take off gross weight and still greater range than other airframes discussed. That would/should get the ROC and time to 20K numbers in-line. If P-51-NA, 2x 20mm and ammo reduction rips off another 350 pounds - driving GW below 8,000 pounds. The P-51A without wing racks was ~10mph faster at 18K

Our fuel requirement (from https://www.secretprojects.co.uk/th...ign-for-rugged-areas.42705/page-3#post-645390):

"Range 1000 km on internal fuel with warm up, take-off and climb to 6000 m at maximum allowed power, 15 minutes at WER, remaining at maximum air range conditions + 30 minute reserve at maximum endurance conditions."

I presume that implies a 500 km combat radius. Let's say - all of this very roughly just to get the order of magnitude right - 10 US Gals for warm-up/take-off, 20 US Gals for climb, 1 hour at maximum cruise for another for another 65 US Gals, 40 US Gals for 15 min WEP, and another 1 hour at maximum cruise for the way back, 65 US Gals again. Then 30 min of reserve for another 30 US Gals. (Roughly based on V-1650-1, V-1710-81 might save a bit fuel on the way back/in reserve, but need a bit more for WEP).

That a total of 230 US Gals, or 870 L. Not sure if Pasoleati will consider drop tanks acceptable. We might end up with the Fisher P-75 yet! ;-)

I have an erata doc if you want it.

Thanks, that would be great! Is it available on ww2aircraft.net somewhere? I only found an announcement thread over there, not sure if there's another more recent one.

Regards,

Henning (HoHun)

 

[HoHun]

Hi again,

For the V-1650-1 on 1/1/1943, it seems this is the relevant engine chart (dated December 18, 1942) ... 3000 rpm @ 51" Hg WEP, for 1300 HP @ 4600 ft and 12000 ft respectively (both with ram): http://www.wwiiaircraftperformance.org/P-40/P-40F_V-1650-1_specific_engine_flight_chart.jpg

Odd rating, normally you don't get the same power from the same settings at both critical altitudes! Also a bit odd that no time for WEP is given, and time for MIL is limited to 5 min.

Here's an interesting document on the use of higher power settings of the British Merlin 20 series engines: http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-21nov42.jpg

I had always wondered why the ratings were +14 lbs/sqin in low supercharger gear, but +16 lbs/sqin in high gear ... seems that it actually an artifact of the way the boost pressure was limited: Not by the normal operation of the governor, but by (I gather) some kind of less sophisticated bypass (or override).

Apparently, this required modification Merlin/458 to be applied to the engine, as evident from the preceding document: http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-18nov42.jpg

It would be interesting to know whether (or when) the V-1650-1 also received this modification. The equivalent boost levels as they would be stated USAAF style would be 58.43"Hg resp. 62.5" Hg. As they are cleared for 5 minutes, that fills in another gap.

One remaining oddity is that the climb rating allows only the use of 2850 rpm/+12 lbs/sqin (confirmed by the Hurricane II Pilot's Notes, with amendmends up to September 1943), with another document on wwiiaircraftperformance.org pointing out that the use of 3000 rpm in a climb is a "definite overload for the engine", and to be reported to the engineer officer: http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-11dec40.jpg

According to the limitations in the Pilot's Notes for the Lancaster, the boost pressure associated with the climb rating was +9 lbs/sqin also for the Merlin 22, 24, 28 and 38. (The Merlin 24 was special otherwise in being good for 3000 rpm/+18 lbs/sqin for combat and take-off).

The climb rating could be used for a full hour, and it uses 48.25" Hg just like the V-1650-1's MIL rating. That gives us 1220 HP @ 9750 ft and 1130 HP @ 17000 ft, both under static conditions.

That beats the V-1710-81's 1125 HP @ 15000 ft, especially as the V-1710-81 is only cleared for 15 min for this power level.

Sea level climb power of the Merlin 20 series is 1120 HP @ 0 ft, compared to the V-1710-81's 1030 HP.

Maximum take-off power of the Merlin 20 series at 3000 rpm/+12 lbs/sqin is 1280 HP, compared to the V-1710-81's 1200 HP at 3000 rpm/52" Hg.

Looks to me as if we should go for the Merlin 20 series.

Regards,

Henning (HoHun)

 

[tomo pauk]

For the V-1650-1 on 1/1/1943, it seems this is the relevant engine chart (dated December 18, 1942) ... 3000 rpm @ 51" Hg WEP, for 1300 HP @ 4600 ft and 12000 ft respectively (both with ram): http://www.wwiiaircraftperformance.org/P-40/P-40F_V-1650-1_specific_engine_flight_chart.jpg

Odd rating, normally you don't get the same power from the same settings at both critical altitudes! Also a bit odd that no time for WEP is given, and time for MIL is limited to 5 min.

The 1300 HP value for the low gear is probably a typo.

To further complicate matters, Pasoleati in the range requirements specified 15 min flight at war emergency rating ... I presume that implies that these 15 min war emergency rating have to be available in a single burst, so we might not be able to use the WEP settings of the US engines at all. Another wrench in the works!

I guess that OP can demand anything he want, but reality might object.

Looks to me as if we should go for the Merlin 20 series.

An excellent fit to the P-51, provided we are allowed to use 100/130 grade fuel.

 

[HoHun]

Hi Tomo,

An excellent fit to the P-51, provided we are allowed to use 100/130 grade fuel.

I think the best engine for the P-51 in this time frame would really be the DB 605A Not only does it run on low-octane fuel as required, it has just the right full throttle height and outperforms the Merlin XX all the way, even at its de-rated 2600 rpm/1.30 ata setting. I don't think we will ever be able to convince Pasoleati to put it his list though :-D

Another engine to check is the Merlin 45. I've just discovered that my memory of the boost increase to +16 lbs/sqin was off by a year, it was actually done in late summer or early fall of 1942.

If we get good fuel for this, that might be the inline engine that gives us the best chances of meeting the take-off and turn rate requirements. At high altitude, it falls a bit short behind the Merlin 20 series, though.

Here's an overview of Spitfire performance graphs, based on the data on wwiiaircraftperformance.org. Somehow, I didn't add the aircraft registrations to the legend when I prepared that back in 2012 ... poor planning on my part!

View attachment 717046

The Merlin 45 at 3000 rpm/+9 lbs/sqin tends to give a full throttle height of about 6000 m as required, which makes it an attractive engine for us. If we are restricted to 2850 rpm/+9 lbs/sqin, maybe the Merlin 46 is a better option. I'm not sure when it arrived.

As this is sort of alternate history, I figure we might even get Rolls-Royce to make us a two-speed Merlin 46 ... the Merlin 45 was basically a Merlin 20 without the two-speed gearbox, if I understand it correctly.

Regards,

Henning (HoHun)

 

[Scott Kenny]

Our fuel requirement (from https://www.secretprojects.co.uk/th...ign-for-rugged-areas.42705/page-3#post-645390):

"Range 1000 km on internal fuel with warm up, take-off and climb to 6000 m at maximum allowed power, 15 minutes at WER, remaining at maximum air range conditions + 30 minute reserve at maximum endurance conditions."

I presume that implies a 500 km combat radius. Let's say - all of this very roughly just to get the order of magnitude right - 10 US Gals for warm-up/take-off, 20 US Gals for climb, 1 hour at maximum cruise for another for another 65 US Gals, 40 US Gals for 15 min WEP, and another 1 hour at maximum cruise for the way back, 65 US Gals again. Then 30 min of reserve for another 30 US Gals. (Roughly based on V-1650-1, V-1710-81 might save a bit fuel on the way back/in reserve, but need a bit more for WEP).

That a total of 230 US Gals, or 870 L. Not sure if Pasoleati will consider drop tanks acceptable. We might end up with the Fisher P-75 yet! ;-)

That may be a bit high, I was under the impression that Mustangs cruised at ~55gph and were at 65gph for higher power settings.

 

[tomo pauk]

I think the best engine for the P-51 in this time frame would really be the DB 605A Not only does it run on low-octane fuel as required, it has just the right full throttle height and outperforms the Merlin XX all the way, even at its de-rated 2600 rpm/1.30 ata setting. I don't think we will ever be able to convince Pasoleati to put it his list though :-D

Yes, if the 87 oct fuel is the best what we have, the 605A is the best bet.
(Merlin 20 series should still beat it at low altitudes, however - but again, this will require teh 100/130 grade to cater for the high levels of boost required)

Another engine to check is the Merlin 45. I've just discovered that my memory of the boost increase to +16 lbs/sqin was off by a year, it was actually done in late summer or early fall of 1942.

If we get good fuel for this, that might be the inline engine that gives us the best chances of meeting the take-off and turn rate requirements. At high altitude, it falls a bit short behind the Merlin 20 series, though.

Altitude power of the M.45 and XX was probably within the manufacturer's tolerances, ie. nothing to write home about. The 45 is a bit lighter, though, and has lower power for take off.
Please be wary of the early data sheets that stipulate for the XX the power of 1175 HP at 20500 ft, these are some 2000 ft above what was really the case.

Here's an overview of Spitfire performance graphs, based on the data on wwiiaircraftperformance.org. Somehow, I didn't add the aircraft registrations to the legend when I prepared that back in 2012 ... poor planning on my part!

Ahem

The Merlin 45 at 3000 rpm/+9 lbs/sqin tends to give a full throttle height of about 6000 m as required, which makes it an attractive engine for us. If we are restricted to 2850 rpm/+9 lbs/sqin, maybe the Merlin 46 is a better option. I'm not sure when it arrived.

As this is sort of alternate history, I figure we might even get Rolls-Royce to make us a two-speed Merlin 46 ... the Merlin 45 was basically a Merlin 20 without the two-speed gearbox, if I understand it correctly.

Merlin 46 arrived some time in late 1941/early 1942. Yes, with a 2-speed gearbox, it would not have the low-altitude weaknesses.
For the purposes of this thread, we'd probably want a Merlin 45 (instead of the 46) + a good pressure injection carb + proper exhausts (again, the 130 grade fuel is a kicker).

 

[HoHun]

Hi Tomo,

Ahem

Oops ... here it is! :-D



Regards,

Henning (HoHun)

 

[HoHun]

Hi Tomo,

(Merlin 20 series should still beat it at low altitudes, however - but again, this will require teh 100/130 grade to cater for the high levels of boost required)

I was referring to the take-off power of the Merlin 20 series engines as specified in the various pilots notes (Maximum take-off power of the Merlin 20 series at 3000 rpm/+12 lbs/sqin is 1280 HP). The DB 605A at 2600 rpm/1.30 ata yields 1310 HP, and that's its 30 min setting. This increases to 1410 HP @ 2100 m, then drops off to 1250 @ 5700 m.

Comparing this to the Merlin 20 series 60 min setting (because we don't have a directly equivalent 30 min setting), we have the Merlin with 1220 HP @ 3000 m and 1130 HP @ 5200 m.

If we take the Merlin 20 series engine to 3000 rpm and +14/+16 lbs/sqin (or even to +18 lbs/sqin), it can compete or even exceed that, but that's a 5 min limit then, so in the context of Pasoleati's requirements, which ask for a 15 min war emergency rating, I chose the climb rating for the comparison. In another context, I'd have used the higher settings just as you suggested!

Please be wary of the early data sheets that stipulate for the XX the power of 1175 HP at 20500 ft, these are some 2000 ft above what was really the case.

Good point, I've seen that one too ... always thought it assumed ram air. The one I've been using is this one, which fortunately is marked clearly as being for static conditions: http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-curve-c1.jpg

Merlin 46 arrived some time in late 1941/early 1942. Yes, with a 2-speed gearbox, it would not have the low-altitude weaknesses.
For the purposes of this thread, we'd probably want a Merlin 45 (instead of the 46) + a good pressure injection carb + proper exhausts (again, the 130 grade fuel is a kicker).

I can't seem to find the supercharger drive gear ratios for the Merlin 20. The Merlin 46 has a 10.85" impeller driven at a 9.089 gear ratio. The Merlin 45 has a 10.25" impeller driven at the same gear ratio, and I understand that the Merlin 20 series impeller is the same as the Merlin 45's, but what are the drive gear ratios?

Regards,

Henning (HoHun)

 

[kaiserd]

If the whole idea is for a fighter to operate from rugged (presumably more remote?) areas than isn’t the idea to have the most rugged and reliable engine that needs less support, servicing/ maintenance and careful looking after than a standard engine in standard service fighter (or at the very least isn’t pushing limits/ the envelope re: manifold pressure and other technical aspects that would actively work against these aspects)?

Doesn’t that almost guarantee that the logical choice is an air-cooled radial, almost certainly a R-2800 or Centaurus depending on timing/ year to enter service if maximising performance is also critical?

 

[HoHun]

Hi,

Doesn’t that almost guarantee that the logical choice is an air-cooled radial, almost certainly a R-2800 or Centaurus depending on timing/ year to enter service if maximising performance is also critical?

The list of engines we have available is limited and doesn't include either the R-2800 or the Centaurus:

Powerplant: Options are the Merlin, Hercules , R-2600, V-1710 and Mitsubishi Kasei. If a liquid-cooled engine is selected, radiator(s) must be arranged so that one punctured coolant radiator does not result in complete loss of cooling. Thus an arrangement with radiators of each wing leading edge are preferred. Water-injection may be used to meet performance requirements with either 87 octane fuel. Fuel system must be compatible with gasoline/alcohol blends.

I agree that a radial engine might be a good choice, but the Kasei in 1943 has a lot of reliability problems, and the Hercules in that timefrime doesn't provide the kind of power advantage over the inline engines, as far as I can tell. (More Hercules data would be appreciated, I don't have all that much about this engine.)

I haven't looked at the R-2600 yet ... hm, it seems the R-2600-23 (company designation GR-2600-A5B) version used in the A-20C would be available in time.

This would offer:

Take-off/MIL (2500 rpm/45" Hg, 5 min): 1600 HP
Climb: 1350 HP @ 1800 m (2300 rpm/36.7" Hg) and 1275 HP @ 3600 m (2300 rpm/41.4" Hg)

(This is a rating according to typical US conventions which often list a constant power up to critical altitude, with a variable boost pressure, in contrast to most other nations' ratings and probably to late-war US ratings too, which typically are given for constant boost pressures instead.)

Remaining power at 5200 m: 1030 HP (2300 rpm/33.5" Hg) ... which is less than the Merlin 20 series' 1130 HP at this altitude (chosen because it's the latter engine's full throttle height).

So this engine would give us a marked improvement in take-off, but top speed at 6000 m would definitely suffer, both because of the greater drag of the radial engine and because of a loss of 100 HP compared to the Merlin 20 series.

For the record: The R-2600-23 could be fitted with individual exhaust stacks so that exhaust thrust could be well exploited, which is a good feature for this engine. (Of course, the same applies to the Merlin 20 series.)

Regards,

Henning (HoHun)

 

[HoHun]

Hi everyone,

Water-injection may be used to meet performance requirements with either 87 octane fuel.

Looking at this statement again, I'm not sure if my earlier interpretation that 87 octane fuel was a must for all engines was correct. What's your take on this?

Regards,

Henning (HoHun)

 

[tomo pauk]

I was referring to the take-off power of the Merlin 20 series engines as specified in the various pilots notes (Maximum take-off power of the Merlin 20 series at 3000 rpm/+12 lbs/sqin is 1280 HP). The DB 605A at 2600 rpm/1.30 ata yields 1310 HP, and that's its 30 min setting. This increases to 1410 HP @ 2100 m, then drops off to 1250 @ 5700 m.

Comparing this to the Merlin 20 series 60 min setting (because we don't have a directly equivalent 30 min setting), we have the Merlin with 1220 HP @ 3000 m and 1130 HP @ 5200 m.

If we take the Merlin 20 series engine to 3000 rpm and +14/+16 lbs/sqin (or even to +18 lbs/sqin), it can compete or even exceed that, but that's a 5 min limit then, so in the context of Pasoleati's requirements, which ask for a 15 min war emergency rating, I chose the climb rating for the comparison. In another context, I'd have used the higher settings just as you suggested!

Same as before - a 15 min WER power was as rare as hen's teeth, especially in early 1943. If WER is allowed, no questions asked, there is a host of engines that can do WER for 5 minutes, here the Merlin 20 series is a better engine under 5 km altitude, and DB 605A is better above 5 km.
If max power of minimum 15 min is required, it is not WER but military power (in US parlance), and then indeed the DB 605A is better at all altitudes, plus it will be doing the required power 30 minutes, not just 15.

Good point, I've seen that one too ... always thought it assumed ram air. The one I've been using is this one, which fortunately is marked clearly as being for static conditions: http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-curve-c1.jpg

Yes, that chart is IMO the best for the 20 series (note that it lists the late Merlins from the same series there, too).

I can't seem to find the supercharger drive gear ratios for the Merlin 20. The Merlin 46 has a 10.85" impeller driven at a 9.089 gear ratio. The Merlin 45 has a 10.25" impeller driven at the same gear ratio, and I understand that the Merlin 20 series impeller is the same as the Merlin 45's, but what are the drive gear ratios?

Low gear was 8.15:1, high gear was 9.49:1 on the 20 series.
Merlin 45 and XX also shared the 'proper' central intake elbow, and used the improved impeller from the Merlin X.

Doesn’t that almost guarantee that the logical choice is an air-cooled radial, almost certainly a R-2800 or Centaurus depending on timing/ year to enter service if maximising performance is also critical?

R-2800, at least as used on the P-47s (granted, witgh help of the turbo from there) was found unreliable between early 1942 and mid-1943. Engine problems, sometimes resulting in mid-air engine fires, are stated on the pg. 286 and 287 in the 'America's hundred thousand' book (an excellent book on it's own), and were part of the reason why no P-47Bs were ever deployed overseas.
Centaurus production before mid-1944 was in ones and twos, will not cut it for early 1943.

I agree that a radial engine might be a good choice, but the Kasei in 1943 has a lot of reliability problems, and the Hercules in that timefrime doesn't provide the kind of power advantage over the inline engines, as far as I can tell. (More Hercules data would be appreciated, I don't have all that much about this engine.)

Problems with Kasei's vibrations were probably much worse on the J2M due to presence of the extension shaft, than on the G4Ms?
However, the Ha-109 seems like a very good alternative, with decent power on required altitudes, small weight, and compact dimensions.

(More Hercules data would be appreciated, I don't have all that much about this engine.)

I haven't looked at the R-2600 yet ... hm, it seems the R-2600-23 (company designation GR-2600-A5B) version used in the A-20C would be available in time.

From what I've read, the engine powers vs. altitude were comparable between the 1942/43-vintage Hercules and the better, B series R-2600s, like the -8 (on Avenger) or -13 (on B-25). Hercules was lighter and of smaller cross section (seen best here), and also using less fuel.

The A series R-2600 (used mostly on A-20s) were a bit down on power at all altitudes (see here), and were still with the bulk, weight and bad mileage of the B series. The Lockland scandal didn't helped the R-2600, either.

 

[Scott Kenny]

Water-injection may be used to meet performance requirements with either 87 octane fuel. Fuel system must be compatible with gasoline/alcohol blends.

Are we seriously stuck with 87 octane?

Because if we are, I don't believe a single Allied engine will meet those performance demands.

 

[tomo pauk]

Are we seriously stuck with 87 octane?

Because if we are, I don't believe a single Allied engine will meet those performance demands.

RR Griffon just might, even with low boost (and hence the lower power at lower altitudes) due to the 87 oct fuel?

 

[HoHun]

Hi Tomo,,

Same as before - a 15 min WER power was as rare as hen's teeth, especially in early 1943.

@Pasoleati - maybe you could clarify whether you really insist on a 15 min War Emergency Rating? I yes, can we still use short-term take-off power for take-off? At which power settings are top speed, climb rate and turn rate to be measured? Are all these data points to be measured with full internal fuel and ammunition? Can we use drop tanks? Can we use higher-octane fuel than 87 octane?

Low gear was 8.15:1, high gear was 9.49:1 on the 20 series.
Merlin 45 and XX also shared the 'proper' central intake elbow, and used the improved impeller from the Merlin X.

Thanks a lot!

From what I've read, the engine powers vs. altitude were comparable between the 1942/43-vintage Hercules and the better, B series R-2600s, like the -8 (on Avenger) or -13 (on B-25). Hercules was lighter and of smaller cross section (seen best here), and also using less fuel.

Do you happen to have a power chart for a suitable B-series R-2600 engine? (I presume the GR-2600-A5B is an A-series engine.)

Would the Hercules XI be a eligible engine for us, based on the timeline? Would it be the best choice from the eligible Hercules variants?

Do you know whether the Hercules can be fitted with individual exhaust stubs, or at least a collector ring with rearward-facing nozzles to exploit exhaust energy for thrust? The power curves are for open exhausts, so fitting jet nozzles will reduce shaft power a bit.

Regards,

Henning (HoHun)

 

[tomo pauk]

Do you happen to have a power chart for a suitable B-series R-2600 engine? (I presume the GR-2600-A5B is an A-series engine.)

Here 'tis:

Would the Hercules XI be a eligible engine for us, based on the timeline? Would it be the best choice from the eligible Hercules variants?

For 1942 and on, the VI is the better (and later) one, despite the nomencature that might mislead us in believing the XI was the better and later.

Do you know whether the Hercules can be fitted with individual exhaust stubs, or at least a collector ring with rearward-facing nozzles to exploit exhaust energy for thrust? The power curves are for open exhausts, so fitting jet nozzles will reduce shaft power a bit.

Bristol started installing the individual exhausts on their engines from the Hercules 100 series (these were also with the much-improved altitude power due to the refined S/C section). Basically every radial engine of note was done with collector-exhausts by 1944, but the engines already installed rarely if ever received the upgrade.

Power curves are probably for, at least, collector exhausts?

 

[drgondog]

Hi Bill,



I don't think it would be possible to catch any subtle differences - many aircraft for which multiple tests are available show considerable variation between aircraft. Analysis of flight test results can provide quite a good framework for understanding the major performance drivers though. I don't know if you're into WW1 aircraft too, but last year Anders Jonsson published a book titled "WW1 Aircraft Performance", which illustrates that quite nicely and might actually provide some new insights into the combat realities of the era. Of course, in comparison to the WW1 era, the test data we have on WW2 aircraft fortunately is both more plentiful and much more detailed!

NEW BOOK: WW1 Aircraft Performance Design, Aerodynamics And Flight Performance

NEW BOOK: WW1 Aircraft Performance Design, Aerodynamics And Flight Performance Books and Magazines

www.theaerodrome.com

For the V-1710-81 on 1/1/1943, it seems this is the relevant engine chart (dated December 18, 1942) ... 3000 rpm @ 57" Hg WEP, for 1480 HP @ 10000 ft (with ram): http://www.wwiiaircraftperformance.org/P-40/P-40N_V-1710-81_specific_engine_flight_chart.jpg

A bit surprising to the 52" Hg take-off power with a time limit of 5 min, but the 57" Hg only labeled with "emergency only".

This later chart has the 57" Hg war emergency power setting with 5 min duration too, but gives the full throttle height at "sea level", confusingly. At also revises the full throttle height in military power downwards by 3500 ft (with ram): http://www.wwiiaircraftperformance.org/P-40/P-40M_V-1710-81_specific_engine_flight_chart.jpg

As an additional data point, an Australian test report for a P-40N, observed a full throttle height at 3000 rpm/57" Hg of 9200 ft in high-speed flight and of 6800 ft in the climb. That's closer to the earlier chart than to the more pessimistic later one, so I'd stay with the earlier one for once.

Then there's this February 23, 1943 calibration chart for the V-1710-81: http://www.wwiiaircraftperformance.org/P-40/P-40N_V-1710-81_Engine_Flight_Calibration_Curves.jpg

It shows a take-off power of 3000 rpm/52" Hg up to 10000 ft, but looking at the chart, I strongly suspect that the 10000 ft limit for take-off power was just a conventional limit set by the USAAF. Eyeballing it, I'd say the engine might actually have sustained the 52" Hg up to 13000 ft.

MIL power critical altitude is 15500 ft, so I assume this is consistent with the December 18, 1942 power chart above, but for a no-ram effect situation. (WEP is not shown on the chart, unfortunately.)

For the V-1650-1 on 1/1/1943, it seems this is the relevant engine chart (dated December 18, 1942) ... 3000 rpm @ 51" Hg WEP, for 1300 HP @ 4600 ft and 12000 ft respectively (both with ram): http://www.wwiiaircraftperformance.org/P-40/P-40F_V-1650-1_specific_engine_flight_chart.jpg

Odd rating, normally you don't get the same power from the same settings at both critical altitudes! Also a bit odd that no time for WEP is given, and time for MIL is limited to 5 min.

To further complicate matters, Pasoleati in the range requirements specified 15 min flight at war emergency rating ... I presume that implies that these 15 min war emergency rating have to be available in a single burst, so we might not be able to use the WEP settings of the US engines at all. Another wrench in the works!

On the V-1710-81 charts, MIL is shown as usable for 15 min, so I think we're limited to MIL then. On the V-1650-1 chart, even MIL is limited to 5 minutes, so I have no idea which power level to use as WEP-in-the-sense-of-the-requiremnts here. The next lower setting on the chart is maximum continuous, which is a much lower power rating.



Our fuel requirement (from https://www.secretprojects.co.uk/th...ign-for-rugged-areas.42705/page-3#post-645390):

"Range 1000 km on internal fuel with warm up, take-off and climb to 6000 m at maximum allowed power, 15 minutes at WER, remaining at maximum air range conditions + 30 minute reserve at maximum endurance conditions."

I presume that implies a 500 km combat radius. Let's say - all of this very roughly just to get the order of magnitude right - 10 US Gals for warm-up/take-off, 20 US Gals for climb, 1 hour at maximum cruise for another for another 65 US Gals, 40 US Gals for 15 min WEP, and another 1 hour at maximum cruise for the way back, 65 US Gals again. Then 30 min of reserve for another 30 US Gals. (Roughly based on V-1650-1, V-1710-81 might save a bit fuel on the way back/in reserve, but need a bit more for WEP).

That a total of 230 US Gals, or 870 L. Not sure if Pasoleati will consider drop tanks acceptable. We might end up with the Fisher P-75 yet! ;-)



Thanks, that would be great! Is it available on ww2aircraft.net somewhere? I only found an announcement thread over there, not sure if there's another more recent one.

Regards,

Henning (HoHun)

A lot to chew on as you have covered the anomalies - some of which are 'first time' for me.

On the erata question. I think I may place the erata document on"P-51 Mustang" site on Facebook as they have provision for files. I may put a duplicate in the Technical section of WW2aircraft and will talk to Mike Williams about Spitfireperformance. I don't want more than two as I expect perhaps a few more 'adds' that aren't included in the book. Will let you (and Tomo) know soon.

I forgot Paseoleati stipulation - but excluding combat tanks doesn't make sense. The reguired fuel fraction (internal) for a high performance WWII era fighter for that range stipulation. For a US 'std' calculation for Combat Radius for a P-51B-1 w/o 85gal fuse tank, no combat tanks was ~ 150+ miles. With 85gal tank (184+85 total), the CR extended to 375mi. All 'straight line' calcs, no consideration for close escort. The Allison V-1710-81 would have been slightly more economical than the V-1650-1 & -3

The curse of the P-47 (IMO) was Kartveli's 'disdain' for draggy wing pylons and refusal to provide for plumbing (or extra tankage) in the wings until brutally confronted with realities of ETO escort requirements. First Lockheed (Dec 1941) then NAA (Sept/Oct 1942) had both in production. It took Republic one more year to start factory pylon introduction in late 1943 with the D-15, and then another several months to roll out the D-25 with the extra 65 gal internal. And then another 8 mo for P-47N wing fuel change.

 

[tomo pauk]

The curse of the P-47 (IMO) was Kartveli's 'disdain' for draggy wing pylons and refusal to provide for plumbing (or extra tankage) in the wings until brutally confronted with realities of ETO escort requirements. First Lockheed (Dec 1941) then NAA (Sept/Oct 1942) had both in production. It took Republic one more year to start factory pylon introduction in late 1943 with the D-15, and then another several months to roll out the D-25 with the extra 65 gal internal. And then another 8 mo for P-47N wing fuel change.

On the other hand, USAAF was free to require that combat drop-tank facility is present on the fighters by some time of late 1941/early 1942, and Republic would've yielded.
A 'flat', metalic drop tank of 150-200 gals was feasible before Pearl Harbor, would've come in handy for the P-47s without requiring the wing racks, but alas. Republic was also free to develop less draggy wing racks, but again - alas.

 

[HoHun]

Hi Tomo,

Here 'tis:

View attachment 717069

Thanks! Do you also have a copy of the preceding page that probably shows the ratings? I'd of course like to derive the climb power figures, and I believe the "naked" chart doesn't provide them.

It's listed here ... https://www.enginehistory.org/References/ModDesig/jpg/I47.jpg ... with 1500 HP @ 6700 ft (2400 rpm) and 1450 HP @ 13000 ft (2400 rpm).

Again, this rating seems a bit odd due to the small difference in power between these settings. The chart you provided shows 1500 HP @ 5900 ft (2400 rpm/37.5" Hg) and 1350 HP @ 13000 ft (2400 rpm/40.5" Hg).

The high altitude data point actually fits the ratings given in the above document for the R-2600-9, and comparing the two lines, there are no less than three obvious typos in the R-2800-8 WEP/MIL column! I guess the "1450" in the continuous power column should really be a "1350" like for the R-2800-9 column. The R-2800-9 is "similiar to the -13" except for the carburettor, and cross-checking that engine, it confirms the ratings given for the R-2800-9, wich has all the same power-relevant parameters as the R-2800-8.

MIL rating according to the R-2800-9 data set is 1700 HP @ 4500 ft (2600 rpm) and 1450 HP @ 12000 ft (2600 rpm). Cross-checking that with your graph, it's 1690 HP @ 3100 ft (2600 rpm/42" Hg) and 1450 HP @ 12000 ft (2600 rpm/44.5" Hg). The take-off rating is also given as 1700 HP in the above document.

Remaining power at 5200 m: 1130 HP (2400 rpm/34.5" Hg) ... which is the same as the Merlin 20 series' 1130 HP at this altitude (chosen because it's the latter engine's full throttle height).

Except for the Hercules which I haven't looked at yet, the R-2600-8 is the engine with the best take-off power, the best power at 2000 ft, and it ties with the V-1650-1 (which according to a scan I found elsewhere could be equivalent to quite a few different 20-series Merlins, so I'll be using this as a generic designation from now on) for best at altitude, too.

Of course, the downside is the drag increase that's the inevitable byproduct of installing a big radial engine in an airframe, so we'll definitely be sacrificing some high-altitude top speed if we chose the R-2600-8 over the V-1650-1. At low altitude, we've got a quite substantial power advantage with the R-2600-8, so it might deliver a superior top speed at 2000 m despite the extra drag. Take-off and turn rate at 2000 m should also be better with the R-2600-8.

Dry weight of the R-2600-8 is given as 1986 lbs "without accessories". Relying on Dean's "America's Hundred Thousand", the data for the P-40F shows for the V-1650-1 "Engine: 1518 lbs" and "Cooling 294 lbs". Ignoring the rest of the engine-related categories as they're most likely not included in the R-2600-8 dry weight either, that gives us 1813 lbs for the V-1650-1 as "dry weight without accessories"-equivalent (though I figure "cooling" includes the coolant weight, as it's not listed anywhere else in that table), so we have a weight penalty of just 173 lbs or about 80 kg for the radial engine.

I've neglected propeller weight, which is 386 lbs on the V-1650-1, compared to 485.2 lbs for the F6F-3's propeller, which I presume is in the same ballpark as a suitable propeller for our R-2600-8. So, another 45 kg weight penalty for the R-2600-8 version of our fighter (total 125 kg).

For 1942 and on, the VI is the better (and later) one, despite the nomencature that might mislead us in believing the XI was the better and later.

I guess you it's implied you don't have any ratings or power graphs for the Hercules VI in 1943 either? ;-)

Bristol started installing the individual exhausts on their engines from the Hercules 100 series (these were also with the much-improved altitude power due to the refined S/C section). Basically every radial engine of note was done with collector-exhausts by 1944, but the engines already installed rarely if ever received the upgrade.

Power curves are probably for, at least, collector exhausts?

When I think "Hercules", pictures of "hedgehog"-style flame dampers come to my mind "Open exhaust" in my opinion means that the indicated data is for an exhaust-less engine, or at least for one with short constant-area exhaust stubs.

Regards,

Henning (HoHun)

 

[tomo pauk]

hanks! Do you also have a copy of the preceding page that probably shows the ratings? I'd of course like to derive the climb power figures, and I believe the "naked" chart doesn't provide them.

IIRC the preceeding page lists the boost values, RPM, altitude and fuel consumption, but it does not list the power figures. There was no specific 'climb power' rating on US-designed engines.

It's listed here ... https://www.enginehistory.org/References/ModDesig/jpg/I47.jpg ... with 1500 HP @ 6700 ft (2400 rpm) and 1450 HP @ 13000 ft (2400 rpm).

Again, this rating seems a bit odd due to the small difference in power between these settings. The chart you provided shows 1500 HP @ 5900 ft (2400 rpm/37.5" Hg) and 1350 HP @ 13000 ft (2400 rpm/40.5" Hg).

Many times, the data sheets do not agreee with each other. Please see here for the -13, the power values align with the power values from the -8 chart pretty nice, unlike the data sheet for the -8 that disagrees alot with the graph for the -8.
The data sheet you've listed (as well as other data sheets from the same doc) need to be approached with caution, eg. they show for the -8 the power rating of 1400 HP at 21000 ft - as it was with a 2-stage S/C.

Of course, the downside is the drag increase that's the inevitable byproduct of installing a big radial engine in an airframe, so we'll definitely be sacrificing some high-altitude top speed if we chose the R-2600-8 over the V-1650-1. At low altitude, we've got a quite substantial power advantage with the R-2600-8, so it might deliver a superior top speed at 2000 m despite the extra drag. Take-off and turn rate at 2000 m should also be better with the R-2600-8.

While I don't like very much the R-2600 family on the fighters, we can recall that the early A-20s, with the A series engines (a.k.a. the 1600 HP versions) were still zippy aircraft, despite the bulk of the R-2600s, dubious amount of the exhaust thrust, big wing, a very thick wing, and deep fuselage - 349 mph. A 1700 HP R-2800, on something like the Fw 190, with 'proper' exhausts would've not been a slow aircraft.
(the planned R-2600-powered Fw 190 - for export? - unfortunately never materialized)

I guess you it's implied you don't have any ratings or power graphs for the Hercules VI in 1943 either? ;-)

Unfortunately, only this, and for 2900 rpm operation:

 

[HoHun]

Hi Tomo,

IIRC the preceeding page lists the boost values, RPM, altitude and fuel consumption, but it does not list the power figures.

As power can be derived from boost, rpm and altitude using the chart you posted, that would not be a problem The most interesting information would be the time limit, of course - maybe I'll have to check some aircraft manuals to see if I can find anything on that in there.

Regards,

Henning (HoHun)

 

[HoHun]

Hi Tomo,

There was no specific 'climb power' rating on US-designed engines.

Sometimes, climb power settings are in fact listed, as on this page from the B-25 manual:



It's interesting that the climb settings are the same as the high speed settings as far as the engine parameters are concerned, but obviously, in the climb case the engine heats up quickly even with cowl flaps fully open, so there's a 5 minute limit for operation at the limiting temperature. I presume if you start with an engine at the cruise temperature of 205 °C, you can add a couple of minutes until you're at the 260 °C limiting "climb" temperature, but I really don't know how long that would take.

Regards,

Henning (HoHun)

 

[tomo pauk]

Hi Tomo,



Sometimes, climb power settings are in fact listed, as on this page from the B-25 manual:

It's interesting that the climb settings are the same as the high speed settings as far as the engine parameters are concerned, but obviously, in the climb case the engine heats up quickly even with cowl flaps fully open, so there's a 5 minute limit for operation at the limiting temperature. I presume if you start with an engine at the cruise temperature of 205 °C, you can add a couple of minutes until you're at the 260 °C limiting "climb" temperature, but I really don't know how long that would take.

Regards,

Henning (HoHun)

The max climb power = max cont power (in this case)?
Going from 2400 to 2600 rpm means using military/take-off power.

 

[tomo pauk]

@HoHun
Perhaps of interest for you - Polish offering the P.24 with 90-rd drums for the Oerlikon cannons.
Whoops - perhaps just 45 rd drums??

 

[drgondog]

On the other hand, USAAF was free to require that combat drop-tank facility is present on the fighters by some time of late 1941/early 1942, and Republic would've yielded.
A 'flat', metalic drop tank of 150-200 gals was feasible before Pearl Harbor, would've come in handy for the P-47s without requiring the wing racks, but alas. Republic was also free to develop less draggy wing racks, but again - alas.

Agreed Tomo. Actually Arnold placed external combat tanks at the top of the Fighter Priorities list at the Fighter Conference February 1942. Gen Muir Fairchild began the FAREP report approx July 1942 which recommended that fighter manufacturers increase internal fuel and provide capabilty for fuselage and/or wing tankage.

At that time the A-36 protoype already had wing rack with dual purpose fuel tank/bomb. Lockheed (via Kelsey back door development) had already installed the pylon and plumbing for Lockheed made 165 and 330 gal fuel tanks (not elf sealed) then made kits for the F-4E, then introduced production articles into P-38F second block.

Crickets from Republic.

George Kenney was irate, then livid that Republic was slow to add external fuel tank capability, and when the 47C-2/D came into SW Pacific, he went out on his own to subcontract streamlined Ferry tanks (IIRC 150-200gal) for the new C/L racks. He was way out in front of 8th AF and Republic. Of course, operationally the 348FG operated at medium altitudes and over long stretches of water - reducing the hazard of interception and bypassing pressurization issues.

The long combat tank gestation problem (IMO) was twofold. First Materiel Command (echols) leadership didn't treat Arnold or Fairchild directives as priority 1. Second Echols was slow to release a P-47 to Eglin Field for range testing. This is mid 1942 timeframe.

Next, MC put out RFPs to develop combat tanks in 52, 60, 75, 110 and 150gal and parcelled them out beginning with smaller tanks first. As a result, the most important (150, 110 and 75gal) were last in line for development and testing. IIRC the 150 still had not passed testing in August 1943.

Greg mistakenly blamed the delay on Bomber Mafia belief that the 'bomber would always get through' when in fact (IMO) it was simply incompetence by Echols, complicated by fierce determination on Echol's part to retain his kingdom and prerogatives of control over R&D, Testing, Services and Logistics embodied in Materiel Command.

If it had not been for Wolfe, Fairchild and Kuter (and Hitchcock perhaps most for going directly to Roosevelt), even the Rolls Royce verson might have been killed in US, at least in context of 8th/12th AF operations pre D-Day.

So back to Kartveli. He saw what NAA and Lockheed were doing in early/mid 1942. He got the memo from Arnold Conference and FAREP report. By that time casualty rates were going up with 8th AF. But because I (and no one else for that matter) are privy to Republic correspondence (due to destruction of records by Fairchild), we don't know much about internal deliberations or communications with War Production Board. Republic may have been trying introduce a better solution than the 205gal Ferry tank, or trying to get internal wing & pylon designs approved.

What did happen, however is that not even the main tank expansion design for D-25 was complete until mid-December 1943. By contrast, NAA solicted, had reviewed and approved by MC (Bradley) the 90 gal SS prototype fuse tank - in 6 days from July 3 to July 8 . It was fabricated and installed and test flown within two weeks (july 17, 1943). During the test flight two 75 gal combat tanks were also installed. Lockheed also moved fast.

 

[tomo pauk]

Greg mistakenly blamed the delay on Bomber Mafia belief that the 'bomber would always get through' when in fact (IMO) it was simply incompetence by Echols, complicated by fierce determination on Echol's part to retain his kingdom and prerogatives of control over R&D, Testing, Services and Logistics embodied in Materiel Command.

Thank you for the very detailed post, Bill.
FWIW, I avoid referencing Greg (the youtuber) wrt. ww2 aircraft.

 

[HoHun]

Hi Tomo,

@HoHun
Perhaps of interest for you - Polish offering the P.24 with 90-rd drums for the Oerlikon cannons.
Whoops - perhaps just 45 rd drums??

Thanks, that's in fact very interesting!

Quickly checking the next few pages, here's mention of "un chargeur de 45 projectiles du calibre 20 mm" ... maybe there's a more specific description elsewhere to confirm it's in fact a drum. I don't remember the capacity right now, but the Luftwaffe also had a small straight magazine for the MG FF that could be used in flexible positions ... no idea what shape the Polish "chargeur" was.

https://muzlot.nazwa.pl/digitalizacja_archiwaliow/katalog/ksiazki/09/pzl_katalog_p.24_i_p.23/7.jpg

I wouldn't mind the MG FF/M as armament for our fighter ... it would save some more weight compared to the MG 151/20. Didn't the Japanese develop a belt feed for their version of the gun? If that fits our timeline, we'd be good to go.

Regards,

Henning (HoHun)

 

[tomo pauk]

I wouldn't mind the MG FF/M as armament for our fighter ... it would save some more weight compared to the MG 151/20. Didn't the Japanese develop a belt feed for their version of the gun? If that fits our timeline, we'd be good to go.

Yes, Japanese have developed the belt feed for their Oerlikons (FF & L), but so did the Germans. Belt-fed MG FFMs were used on some Do 217 night-fighters.
The 90 rd drum was used on many Fw 190s.

 

[HoHun]

Hi Tomo,

The max climb power = max cont power (in this case)?
Going from 2400 to 2600 rpm means using military/take-off power.

I'm not entirely sure. The above page also provides a 2100 rpm "cruising" setting, which doesn't appear to have a special function if it's not "maximum continuous". The next page, which maybe contributes a bit to a better understanding, also has a 2000 rpm "cruising - desired" setting, as well as a 1550 rpm "cruising - long range" setting. The latter is the only one of the three that's not "full rich".

On the GR-2600-A5B-0, "maximum continuous cruising (AUTO RICH)" is given for the 1900 rpm setting, so it's seems not unreasonable to understand the (improved) R-2600-8's 2100 rpm "cruising" setting was the direct equivalent. The GR-2600-A5B-0 also has a "maximum continuous cruising (weak mixture)" setting at 1850 rpm, which I speculate might be the equivalent of the R-2600-8's 1900 rpm "cruising - desired" setting. My thinking is, maybe the automatic mixture control of the R-2600-8 has a wider band in which it can set the correct mixture automatically.

(I think there's a P-51D manual that points out that there are two variants of the mixture control in service, and these also use the terms "Auto Rich" and "Full Rich". I don't remember the details right now, but I suspect that could be a similar improvement as seen on the R-2600 counterpart.)

By the way, the B-25 manual actually addresses the R-2600-8's superchargers as "two-speed turbo superchargers"! Not the first time I see these terms used in error, but certainly the first time I find them like that in an official manual! :-D

Regards,

Henning (HoHun)

 

[HoHun]

Hi Tomo,

Yes, Japanese have developed the belt feed for their Oerlikons (FF & L), but so did the Germans. Belt-fed MG FFMs were used on some Do 217 night-fighters.

Does it fit our timeline, though? I don't really know when it was first used - my impression was pretty late in the war, but that's mainly based on the belt feed never making it into the Fw 190, which is a pretty weak "data point"

Regards,

Henning (HoHun)

 

[Scott Kenny]

(I think there's a P-51D manual that points out that there are two variants of the mixture control in service, and these also use the terms "Auto Rich" and "Full Rich". I don't remember the details right now, but I suspect that could be a similar improvement as seen on the R-2600 counterpart.)

Auto Rich is usually a pressure carb setting, Full Rich is usually a manual mixture setting. Were -Ds getting some engines with standard carbs?