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

Chapter 7: "Destroy the Luftwaffe - in the Air and on the Ground" by D-Day, the Luftwaffe could only fly a few fighters, so WALLIED fighters were unleashed as fighter-bombers to strafe German ground forces in France. This was more a matter of having too many fighters and too few aerial targets, so the RAF deployed Spitfires as dive-bombers, often with just a single bomb and their 20 mm cannons. RCAF Flight Officer Bishop flew ground attack missions from Norman airfields until he was exhausted.
Similarly, USAAF P-47s and P-51s were assigned to strafe and bomb German ground forces. They killed few Tiger tanks, but ruined so many German supply vehicles that hundreds of Panzers were abandoned when they exhausted supplies of fuel, ammo and spare parts.
 
I haven't had a chance to do more than flip through it, but it looks most interesting and in depth. I will say that it appears to be a good companion to the North American history series that starts with The Warbird Factory. The recent Mushroom book on the P-51B also adds some useful information and perspectives.
 
I appreciate your comments - source documentation foundation included over 1000 combined NAA/AAF-Hq/AAF-Materiel Command documents and reports plus a great deal of research at NARA and USAF HRC.

Even though the last trenche of edits were bypassed by Osprey (leaving some glaring errors un-corrected) in their zeal to publish before the Covid avalanche, we are very proud of the Foreward from Bob Gruenhagen.

I'm working on the sequel now. It will have far less discussion of combat/political points and deal with P-51D & D-1 in much more detail, the XP-51F/G/J, explain the P-51L and M and certainly the P-51F. Maybe XP-82

I suspect the Appendices will be heavily focused on not only the 'how and why' the Mustang design was so advanced (3 primary reasons), bu also present table of Model vs Features/changes for each Mustang Version, complete specifications wrt to dimensions, areas, fuel capacity, etcand examples of Analytics for high speed, climb and range estimates.

You comments regarding what you would like to see are welcome.

Regards,

Bill Marshall
 
Bruno Anthony said:
This video provides a definitely different view on the subject of bomber escorts.

View: https://youtu.be/aCLa078v69k
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The only comments I would make is that Greg fatally mis-understood the definition of Combat Radius. Equally he didn't understand the limitations of the unpressurized 200gal Ferry Tank, nor why the P-47 was never adequate for target support in E.Germany or Poland or Czechslovakia until first the D-15 with pylons and fuel feed for wing tanks, then the added 65gal internal fuel was incorporated in the D-25.

As an illustration, the P-51B-5 with 85 gal fuse tank and 2x75gal tank flew escort to Posnan, while the P-47D-15 with 2x150gal external tanks were flying just past Brunswick - well shy of Berlin.
 
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From experience with these video's from just about everyone out there, are made by people who (A lot of them anyway) love the sound of their own voices, basking in the joy of being able to, by prevarication, prove how much they 'know'.

I can tell you left is right but it does not mean it is so, not does making one sentance into war and peace. My little sister, bless. Would read books on phylosophy she had no clue about and then ask dopy questions like "Why do we say grass is green? "Shirley we could say it was black or pink"?

With armchair warfare becoming an international money spinner, it is getting harder to sort wheat and chaff.

Thankfully we have this place.
 
Foo Fighter said:
From experience with these video's from just about everyone out there, are made by people who (A lot of them anyway) love the sound of their own voices, basking in the joy of being able to, by prevarication, prove how much they 'know'.

I can tell you left is right but it does not mean it is so, not does making one sentance into war and peace. My little sister, bless. Would read books on phylosophy she had no clue about and then ask dopy questions like "Why do we say grass is green? "Shirley we could say it was black or pink"?

With armchair warfare becoming an international money spinner, it is getting harder to sort wheat and chaff.

Thankfully we have this place.
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Foo - two question por favor?

I have been asked to do a series on the Mustang, touching on differentiation between all models, the myth or 120 day design to fly cycle, eplaining the different features introduced in the design of the Mustang that contrbuted to performance (such as the wing discussion laying to rest 'laminar flow, but explaining why the airfoil delayed bounday layer adverse pressure gradients).

I have an awful lot of docs and images to souce my comments - but my presentation style is 'tell em' what you are going to tell em', introduce a point/important fact, explain why I bring that up and summarize what I just told you'.

1.) what would cause you to actually sit down and listen to the presentation?

2.) what topics/interests about the Mustang are most important to you?

Regards,

Bill
 
sienar said:
Is Greg the one who thought ram air increased power?
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I'm not sure as I haven't seen most of his stuff. I did see his video stating that the reason the P-51D was faster than the Bf 109 was because of the increased manifold pressure capability of the Merlin engine. That said, I have not seen any explanation during his Mustang Series why the FTH of a P-51B w/1650-3 engine is 29K vs 24K for Bench Test HP.

I asked him why the P-51A on 52" MP was faster than the Bf 109K the deck, but I guess he forgot the question.

Actually I find Greg to be very knowledgeable about engines, but has seriously flawed knowledge base when he dips into performance and drag discussions. Having a copy of Aerodynamics for Naval Aviators is just not enough.

I'm into a discussion right now about his new P-51H video.
 
drgondog said:
Foo - two question por favor?

I have been asked to do a series on the Mustang, touching on differentiation between all models, the myth or 120 day design to fly cycle, eplaining the different features introduced in the design of the Mustang that contrbuted to performance (such as the wing discussion laying to rest 'laminar flow, but explaining why the airfoil delayed bounday layer adverse pressure gradients).

I have an awful lot of docs and images to souce my comments - but my presentation style is 'tell em' what you are going to tell em', introduce a point/important fact, explain why I bring that up and summarize what I just told you'.

1.) what would cause you to actually sit down and listen to the presentation?

2.) what topics/interests about the Mustang are most important to you?

Regards,

Bill
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I will get back to you later Bill, you deserve (Have earned) a properly constructed response and these days I need to cogitate a bit more than has been the case in the past. Have a great day mate.
 
drgondog said:
I'm not sure as I haven't seen most of his stuff. I did see his video stating that the reason the P-51D was faster than the Bf 109 was because of the increased manifold pressure capability of the Merlin engine. That said, I have not seen any explanation during his Mustang Series why the FTH of a P-51B w/1650-3 engine is 29K vs 24K for Bench Test HP.

I asked him why the P-51A on 52" MP was faster than the Bf 109K the deck, but I guess he forgot the question.

Actually I find Greg to be very knowledgeable about engines, but has seriously flawed knowledge base when he dips into performance and drag discussions. Having a copy of Aerodynamics for Naval Aviators is just not enough.

I'm into a discussion right now about his new P-51H video.
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What sources do you think he’s missing?

Where else do you think he’s off base? I like his videos a lot but I never want to become a single source follower.
I do agree with him on treating the official manuals as major sources of not second hand info.
 
Bruno Anthony said:
What sources do you think he’s missing?
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With respect to Drag Discussions?
Well, while a pilot and a serious historian, I think he wants to step into subjects like drag, armed only with cursory aerodynamics as taught in "Aeronatical Enginering for Naval Aviators". His 'performance/Drag analysis examples used to make a point are based on Hoerner's Chap 14 example fr Bf 109G in Fluid Dynamic Drag text - which are examples of building a method to separate Total Drag from Parasite/Form Drag and Induced Drag but makes hugely general assumptions to get to Total Thrust HP delivered (i.e. THP based on 380mph at 22,000 ft plus 'assumed' exhaust gas thrust as percentage of THP). Equivalent 'Flat Plate Drag' between two aircraft, same flight speed, same altitude, same loadout conditions, etc - are achievable for a 'rule of thumb' discusion of 'what' but not 'why'

A good text for a first year aero student - But an impossible approach to calculate meaningfully accurate L/D for all flight conditions, or even cruise or loiter.

With Respect to Sources
With respect to say FW 190D vs P-51D discussion I took him to task for cherry picking the few flight test results he chose from Mike Williams Spitfireperformance.com. With respect to some specifics, he chose P-51B-15-NA 150 octane tests as basis for extrapolating P-51D performance - without understanding the drag effect of the B version wing racks compared to the D, on both climb performance and top speeds. To compound the comparison he chose FW 190D-9 flight tests without ETC racks - which impose 7-10mph drag penalty and perhaps 400 fpm Max ROC. All 8th AF Mustangs (B/C/D/K) were using 150 Octane for 72" MP boost and flew with wing racks attached. His response to my points were 'Well, I couldn't find FW 190D picture with racks, nor could I find a flight test for 150 octane P51D test".

Greg 'seems' to ignore selecting flight test docs which a.) Cite complete take off condition, including load out with respect to Max Gross weight at take off, and wing racks, and b.) special conditions. To the latter he was making comparisons to a stock P-51B with 130octane fuel tested against F4Us but failed to mention that the one most important comparison was the the 'special F4U' operating at water injected 65" MP compared to 59.5".

My favorite discussion regarding sourcing was his elaborate discussion of 'bomber mafia' keeping te down trodden and maligned P-47' from its rightful place as supreme escort fighter - then proceeding down a rathole using the 200gal 'bathtub' tank as the answer to a mother's prayer to save the 8th AF at Schweinfurt'. He proceeded to calculate a 'Greg certified Combat Radius using it - to prove his point'. What he missed, had he not ignored the issues with the tank's useful capacity for escort(vs Ferry), was that he also built in assumptions that also ignored incremental Required use of the internal fuel.
1.) The 200gal tank was modified by Air Tech Services (Cass Hough) by attaching a wood 'elevator' to force the tank down and away after ejection; I haven't put my finger on the doc yet - but the incremental drag estimate was approximately 50mph in cruise and approximately 400 fpm less ROC.
2.) The 200gal tank could only carry ~ 100gal because the tank was not pressurized above 18,000 feet - and totally useless at escort altitudes.
3.) It exended Combat Radius by approximately 30 miles.
4.) The reason the P-47 did not have enough internal fuel or even wing pylons was pretty much because Kartiveli didn't want to do so. The P-51B already had pylon and plumbing thanks to A-36, and added the fuse tank in response to Baarney Giles pressure on NAA, Lockheed, Bell, Curtis and Republic.
5.) NAA (85gal fuse) in flight test July '43. 2. Lockheed (55gal LE) in flight test in July '43. 3. Republic (wing plumbing in D-6 but not until D-15 for production article testing until Jan 1944) and first test of -25 with added 65 gal increase internally until Feb 1944

Last - unless provoked for more. His most recent video citing Fokker (US) as the key to 'NAA rapid rise and ability to build a Mustang in first five years of existance'. He tortuously leads you through the formation of Fokker post WWI, formation of his (US) company, building successful aircraft - then suffering fatal PR blow when Knute Rockne was killed in a Fokker. IIRC GMC purchased Fokker not too long afterwards along with NAA and Berliner-Joyce. Edgar Schmued was at Fokker in this period, when Fokker and Berliner were folded into GAC - then finally NAA.

At this point he doesn't even mention Dutch Kindelberger who was hired by GMC to integrate GMAC (aka GAC), Berliner-Joyce at Dundalk MD, Fokker remnants from Teteboro and Move the key design and mfg to Dundalk. The most important reason o mention Kindelberger in 1935 is that he recruited Atwood (Chief, Engineering), Schweiker (Structures), Rice (Asst Chief Engineer), Smithson (Chief Production), Hanson (Chief Project Management), Baldwin (Project Management) from Douglas where all were integrally involved in DC-1 and -2 among others. Several key production Future managers and supervisors came from Berliner as well as Fokker, including Schmued. Schmued was promoted by Dutch at GAC toproject manage the GA-15 (O-47)
Bruno Anthony said:
Where else do you think he’s off base? I like his videos a lot but I never want to become a single source follower.
I do agree with him on treating the official manuals as major sources of not second hand info.
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Recently he made a comment that the P-51H cockpit was 'moved forward' compared to P-51D. Had he sourced the Three Views with attention to actual location of the 25% Chord line, he would have noted that cockpit stayed about he same, but the wing moved aft about six inches from nose of spinner.
 
drgondog said:
My favorite discussion regarding sourcing was his elaborate discussion of 'bomber mafia' keeping te down trodden and maligned P-47' from its rightful place as supreme escort fighter
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This is a big one for me. Because it’s by far his most controversial video. One of the sources he cites is the ChicagoBoyz. A website that promotes COVID and election conspiracies. Trent Telenko who’s gotten notoriety on Twitter for being the Ukr War “Tire Guy” is on the ChicagoBoyz.

Your overall reply was overwhelming. Any research sites or references you’d recommend?
 
Bruno Anthony said:
This is a big one for me. Because it’s by far his most controversial video. One of the sources he cites is the ChicagoBoyz. A website that promotes COVID and election conspiracies. Trent Telenko who’s gotten notoriety on Twitter for being the Ukr War “Tire Guy” is on the ChicagoBoyz.

Your overall reply was overwhelming. Any research sites or references you’d recommend?
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Gawd, where to start? The single best overview (LONG and extremely well sourced) is USAF Study 136 Development of the Long Range Fighter by Boylon. Free download from USAF HRC.

That said, the timelnes, chronolgies and sourced Combat Radius is well documented in my Appendix focused on Escort Range of P-38, P-47 and P-51 with detailed tables that illustrates each variation from internal fuel to increased internal fuel to different wing stores from 75 to 110 to 150gal.

Dean in America's One Hundred Thousand pulls several AAF-MC Combat Radius Charts together.

Because the focus on my book was the development of the P-51B, I wanted especially to devote a significant amount of ink to detail how politics, vision, 'lack of vision' of AAC, then AAF as Airpower doctrine evolved - and shaped R&D priorities, particularly from late 30s through the Big Week and Regensburg-Schwienfurt crisis for Strategic Bombing doctrine.

There have been so many outright lies told about Arnold/Spaatz/Eaker blind devotion to the 'Bomber Will Always Get Through'. If you don't read any biography other than Arnold's Global Power, would point you in that direction. His 'unease' on clinging to that belief was clearly originated by intelligence reports of Spanish Civil War as well as BoB. He CLEARLY understood that Pursuit was meeting the challenge of Bombardment.

Independent of any other insights, you should look to Asst Secy War Lovett tour of ETO and 8th AF in June and July. The exchange of visit reports, letters, telex's between Lovett/Arnold/Eaker clearly demonstrates the need for LR scort. Eaker requested urgent need for Mustang (P-51B) and P-38s (to be returned to him). Arnold, even recuperating from a cardiac event, made sure that a.) his deputy Giles prioritized long range escort inETO by end of year, b.) re-directed deployment of 55th and 20th FG to ETO, c,) mandated that P-51B go first to 9th AF (they were still tasked for TAC).

The 'doom on the P-47D for LR is that Kartaveli (my opinion somewhat supported by Bodie) was adamant regarding not doing the necessary mods to install wing pylons and plumbing (more drag plus extensive internal mods on wing), or add more internal fuel (redesign of center fuse because kits not feasible). NAA and Lockheed already had operational wing racks. NAA and Lockheed almost immediately resonded to Giles' directives in early July 1943 (just before Big Week) and had working prototype tankage in P-51B-1 (90gal SS Fuse) and P-38J prototype LE. Republic's 65 gal auxilary tank DRAWING was finally approved mid December for P-47D-25. Their 'plumbed and plyon'd' production D-15 was finally in ETO beginning late Feb 1944.

Paul Ludwigs P-51 Long Range Fighter is also excellent
 
Book could have been called "Saved by the British".

The Mustang was built in direct response to a British requirement, and only attained greatness when fitted with a British engine.

Likewise, I wonder how many US naval aviators nowadays could tell you where the angled deck, steam catapult and mirror landing system come from.
 
pathology_doc said:
Book could have been called "Saved by the British".

The Mustang was built in direct response to a British requirement, and only attained greatness when fitted with a British engine.

Likewise, I wonder how many US naval aviators nowadays could tell you where the angled deck, steam catapult and mirror landing system come from.
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I will soon embark onYou Tube series to borrow from Ed Horkey's book - "The Real Story" to address the points you just made.

First, you are correct to the framework, under which the P-509 and thence X73 and then NA-73 Mustang I/XP-51 specifications were were drawn.

Simply BAM/RAE gave NAA The "British Specification, F.18/39 Operational Requirement OR.73" in early 1939. In this respect the subsequent proposal to Anglo France Purchasing Board in mid March 1940 with both NA Report 1592 Specification High Speed Pursuit (Allison) and Report 1593 Performance Estimates for High Speed Pursuit (Allison). The contents presented P-509 complete with side elevation General Assembly displaying the aft of wing Meridith Cooling system as well as engine, wing fuel, and other detailsnecessary for weight and balance calcs to position the CG. The Contents outlined the equipment proposed, the performance improvements to cooling system drag, exhaust gas thrust, top speed and range projections. Also included were the armament proposals incl 4x20mm preferred by RAF as well as commitment to High Speed/Low Drag wing.

The P-509 was the mock up authorized by Kindelberger just before LOI was signed by Lord Henry Self. Te evolution of 'Allison Powered High Speed Pursuit at NAA had its origins with consulting engagement from NAA to Clark Milliken, PhD in spring 1938

The real story however is that key RAF/BAE inputs were sef sealing fuel tanks, efficient cockpit and increasing fuel from 156gal in P-509 to the 170 contained in the future NA-73 Mustang I - not the original or bulk of the NA-73 Mustang I. Additionally, and hugely important, was the guidance and Tech support of the cooling system improvements from Dr Shenstone, RAE in 1941. Later, the RAF led the way with recon mods, cleaning up armament issues, exhaust system improvements, etc.

I would take mild exception that only the inclusion of the Merlin made the Mustang a great plane.

To me that sounds somewhat like dismissing pre-Mk IX Spits because they had ony low/medium altitude rated engines?

I would whole heartedly agree that such made it a great high altiude Escort - but not substantially better below 15000 feet. The two primary features of the Merlin version was the engine and the 85gal fuse tank. The wing, external stores, armament and exceptional handling of the airframe set the tone for future development.

Many innovations incorporated into the Allison airframes were crucial to be considered by USAAF Operations Testing personnel as the 'best sigle engine aircraft - below 18,000 feet. With the P-51-NA it had the heaviest firepower with 4x20mm and was the fastest low/medium altitude fighter, extremely capable CAS/Dive bomber with A-36. It had the longest range with P-51A and A-36, carried the heaviest bomb load or s/e fighter (USAAF, not as much as F4U-1) before the P-47 was equipped with pylons.

The A-36 could be considered the best armed recon a/c through 1943 with the firepower of 6x50cal, and ability to carry one 500 pound bomb and a 75 gal combat tank - for high speed and range.

To dismiss the 'greatness' of the Allison version seems akin to dismissing all Pre Merlin 60 series Spitfires?
 
drgondog said:
1.) The 200gal tank was modified by Air Tech Services (Cass Hough) by attaching a wood 'elevator' to force the tank down and away after ejection; I haven't put my finger on the doc yet - but the incremental drag estimate was approximately 50mph in cruise and approximately 400 fpm less ROC.
2.) The 200gal tank could only carry ~ 100gal because the tank was not pressurized above 18,000 feet - and totally useless at escort altitudes.
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I wonder, what's typical manner of usage the fuel in this fuel tanks - did the pilots "save" them until the aircraft consume all (or most part) internal fuel? Or they used fuel from the auxiliary tanks in the middle of the mission?
Asking the question more broadly: is their a common appoach to the usage of external fuel tanks, say, for the all USAAF fighters in WW2?
 
Silencer1 said:
I wonder, what's typical manner of usage the fuel in this fuel tanks - did the pilots "save" them until the aircraft consume all (or most part) internal fuel? Or they used fuel from the auxiliary tanks in the middle of the mission?
Asking the question more broadly: is their a common appoach to the usage of external fuel tanks, say, for the all USAAF fighters in WW2?
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Good question. Because Cass Hough noted the 18000 feet ceiling to pressurization limit from engine vaccum pump, he issued recommendations that the tank be filled with 100 gallons, enough to switch on after Group assembly over airfield and initiate climb. It was enough to executed climb at GWmax to 17-18000 feet. Simple answer to your question is that only in the interval between takeoff and climb altitude of 18000 feet was the 100/200gal tub use practical.

An aside, but directly appropriate. is that General Monk Hunter CO VIII FC issued Orders that the 200 gal ferry tank be retained after switched off and initiate Mains. To which the three operational FGs (4th, 56th & 78th) basically raised single digit salute by telling their pilots 'use your best judgement - but everybody do the same'. You can imagine one squadron trying to keep formation with a honkig draggy bathtub while the rest are flying 'clean'.

One (of many) points made by Greg that simply wasn't true was the availability of 200 gal of external fuel.
The second is that climb ROC, and climb speed were severly affected by the increased weight and drag of the 'tub'.

I haven't found enough drag data yet to calculate the true advantage that it provided - but one fact is clear. The tank was gone before bomber escort altitude was reached - or initial cruise (at 40kts lower speed and higher optimal fuel consumption at that speed) until fuel gone. The inital cut at an estimate is that it saved the actual internal fuel consumption at Max Continuous Power from formation assy to ~ 18000 feet.

But - from transient ramp assy for take off, you have Military Power until reaching orbit for squadron and group assy, Max Continous for climb to cruise altitude, Cruise settings for MP at auto lean. So, HYPOTHETICALLY much of the Pilot Handbook fuel consumption from internal tanks after take off and achieving 18K altitude is best to be expected to be saved.

Point two - from P-47/Schweinfurt discussion. He founded his range/Combat Radius discussion, not only on have 200 gal, no reduction in cruise speed for added drag - from the operating data hadbook. He never followed the operating assumptions as Defined for Chart Combat Radius, much less factor in ETO additional planning constraints - such as mostly adverse winds aloft up to 90mph, the time it took to warm up, taxi,take off, form up into squadron and group assembly.

Notably he somehow missed that escort, while as a block' were traveling at same cruise speed as bombers, they flew far farther in mission length due to essing above and around the bombers to and from thetargets as long as they were in excort role.

Point three - The more aeodynamic 75 gal tank became available in time for at least one group to employ them. That would get you to Paris - about 20 miles more than the 100/200 gal tank. The combat radius for the 75 gal tank included 20 minutes of combined Military Power and Combat Power and a 30minute reserve for return issues such as weather, lost but 'looking'.

Point four - and MOST Important was that the P-47 through the -11 had only 305gal internal fuel with only a c/L rack for external tank. The -11 with 150gal tank available after the October Schweinfurt strike (January 44) had a combat radius to Bremen and Frankfurt. FAR short of Schweinfurt.

If I had to guess why Greg went down the rathole of magic range extension with external tanks, I might speculate that h was thinking about F4U/F6F ops over non contested water surface where use of several external tanks at low cruise speed and 10000 feet were standard. That was Not 8th AF experience after approx 75 mies into a 500 mile mission.
 
According to Whitney's V-1710 book, P-38 pilots had to be specifically taught how to minimize fuel consumption while cruising (low rpm/high boost). Were P-51 pilots initially any better in this?
 
pathology_doc said:
It's not the Allison version the bomber pilots put their trust in to save them from attacking fighters.
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Well, in the CBI and to a lesser extent the MTO (A-36 occasionally), Allison Mustangs did perform light and medium bomber escort, as well as transport (C-47, C-46) - along with the P-40 and served well. The P-51 served well, though not long before the P-51B/C replaced them. Recall that only the B-17/B-24 operated at high altitude in ETO/MTO until B-29 arrived in CBI/Pacific.
 
drgondog said:
Very true. Same issue applied to P-47D until 1944, and only partially solved unti D-25 entered service around D-Day
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The P-47 didn't really become a long-range airplane until the N variant entered service, which is why some P-47Ns were used that way in the Okinawa campaign near the end of the Pacific war.
 
gatoraptor said:
I think their short range was more the limiting factor rather than engine performance.
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You are missing the point. Even the V-1710-equipped Mustang had long-range while the implication in pathomogy_doc's post was that the Merlin supposedly created that range. In fact, at low power cruising settings the Allison had lower fuel consumption both due to having lower sfc and tolerating lower rpm.
 
Pasoleati said:
According to Whitney's V-1710 book, P-38 pilots had to be specifically taught how to minimize fuel consumption while cruising (low rpm/high boost). Were P-51 pilots initially any better in this?
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Simple answer - yes.
But Complex issue relative to P-38 which had Turbo with finicky' behavior when spooled up too fast at high altitude. IIRC Allison and Lockheed both understood this before Lindbergh went Pacific and Lavier went ETO - both to contradict the Air Services Command manual developed by Materiel Command.

As to Mustang, for both Allison and Merlin, initial instrucions were 60% power and 2200 RM (I have to look up RPM for Allison recommendations). Both Wright Field and Eglin pilots cotinued to refine engine power and prop RPM as a function of altitude and fuel consumption. In the Table below the escort cruise setting is on far right if using 110 gal combat tanks.

at 25K, 32"MP, 2250 RPM, 57gph, 281mph TAS outbound. After dropping tanks at 25K, 29"MP, 2050 RPM, 52gph, 343mph TAS
 

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gatoraptor said:
The P-47 didn't really become a long-range airplane until the N variant entered service, which is why some P-47Ns were used that way in the Okinawa campaign near the end of the Pacific war.
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Actually the Combat Radius of the P-47D-25 & Subsequent - with normal 2x150gal combat tanks had aout the same radius as P-51B/D w/2x75 gal combat tanks. The fundamental distinction from earlier P-47D models was the increase in internal fuel from 305 to 370gal.
 
drgondog said:
Simple answer - yes.
But Complex issue relative to P-38 which had Turbo with finicky' behavior when spooled up too fast at high altitude. IIRC Allison and Lockheed both understood this before Lindbergh went Pacific and Lavier went ETO - both to contradict the Air Services Command manual developed by Materiel Command.

As to Mustang, for both Allison and Merlin, initial instrucions were 60% power and 2200 RM (I have to look up RPM for Allison recommendations). Both Wright Field and Eglin pilots cotinued to refine engine power and prop RPM as a function of altitude and fuel consumption. In the Table below the escort cruise setting is on far right if using 110 gal combat tanks.

at 25K, 32"MP, 2250 RPM, 57gph, 281mph TAS outbound. After dropping tanks at 25K, 29"MP, 2050 RPM, 52gph, 343mph TAS
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60 % power is far too much at lower altitudes (and I have no interest in high altitudes) for maximum air range cruising. The Allison tolerated rpm down to 1200ish rpm*, the Merlin fid not without some modifications** (I am not sure if these mods were ever carried out on Mustangs). If cruising at 25,000 ft., then the most economical setting is full throttle and adjusting rpm to maintain best range IAS. Not 32" and 2250 rpm.

*According to e.g. a report available on www.wwiiaircraftperformance.org.
**According to David Birch
 
Pasoleati said:
60 % power is far too much at lower altitudes (and I have no interest in high altitudes) for maximum air range cruising. The Allison tolerated rpm down to 1200ish rpm*, the Merlin fid not without some modifications** (I am not sure if these mods were ever carried out on Mustangs). If cruising at 25,000 ft., then the most economical setting is full throttle and adjusting rpm to maintain best range IAS. Not 32" and 2250 rpm.

*According to e.g. a report available on www.wwiiaircraftperformance.org.
**According to David Birch
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Auto Rich, 1300rpm is warm up prop speed on the 1650-3/-7. I should look to P-51A Operating manual for more specificity regarding Range tables. That said, the SOP for cruise settings on Allison was "60%" until more testing specifically for max range occurred - maybe as late as 1944.

Perhaps You should look at the report to which was attached the values I showed you.
Max Mpg= 4.91 for 2250RPM/32"MP/281mph TAS at 25K



So, for A-36: SL minimum gph (max loiter?? not necessarily max range) 1650RPM, 29"MP, Auto Lean Mixture, 32gal per hour.
At 5K, 1650 RPM, 28"MP, AutoLean, 35gph. Offhand, I have never seen specificity for 'best cruise Miles/gal' testing for Allison Mustangs.
 
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drgondog said:
Auto Rich, 1300rpm is warm up prop speed on the 1650-3/-7. I should look to P-51A Operating manual for more specificity regarding Range tables. That said, the SOP for cruise settings on Allison was "60%" until more testing specifically for max range occurred - maybe as late as 1944.

Perhaps You should look at the report to which was attached the values I showed you.
Max Mpg= 4.91 for 2250RPM/32"MP/281mph TAS at 25K



So, for A-36: SL minimum gph (max loiter?? not necessarily max range) 1650RPM, 29"MP, Auto Lean Mixture, 32gal per hour.
At 5K, 1650 RPM, 28"MP, AutoLean, 35gph. Offhand, I have never seen specificity for 'best cruise Miles/gal' testing for Allison Mustangs.
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The problem with some manual figures is that they are conservative. Especially those in the early period of the war. For example, that 1650 rpm/29" cannot be the most efficient setting. From a 1943 report concerning Allison Mustangs:"They must run slow speed fuel consumption tests so that they are convinced that it is possible to operate at 200 mph and approximately 20 gal per if they keep the R.P.M. down to 1100."

Another excerpt from the same report:"As has been mentioned before, they have had exceptionally good service out of these engines and due to its smoothness at low RPM’s, they are able to operate it so as to obtain a remarkably low fuel consumption giving them an operational range greater than any single engine fighter they possess (the fact that the Merlin engine will not run well below 1600 prevents them from obtaining an equivalent low fuel consumption and therefore limits its usefulness for similar operations)."
 
I agree with you that they were conservative early on but maximum range is not derived by minimum fuel consumption
Pasoleati said:
The problem with some manual figures is that they are conservative. Especially those in the early period of the war. For example, that 1650 rpm/29" cannot be the most efficient setting. From a 1943 report concerning Allison Mustangs:"They must run slow speed fuel consumption tests so that they are convinced that it is possible to operate at 200 mph and approximately 20 gal per if they keep the R.P.M. down to 1100."
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When you operate at that setting for a Mustang, early or late, there is no practical use for 200mph unless that speed combined with the boost and rpm setting yield a maximum loiter/endurance time aloft or maximum range. The low RPM/low fuel consumption you cite, achieve neither (for Allison or Merlin powered)

As you know 'efficient' cruise is resolved not at lowest flight V for a given altitude, but at dTr/dV =0, where L/D is max. Where the Change in Thrust required with respect to Velocity = 0.

'Best' mile per gallon values are always at setiings well above the 'lowest fuel consumption for level flight'. Without boring all of us wth calculations, imagine the increase in CL required to sustain a 9000 pound airframe at SL at 200mph (CL=0.377) . Same GW At 300mph CL=0.167.
The Induced Drag ratio is (0.377)^2/(0.167)^2
If you want me to show you thecalcs, I will. but the CDi induced drag of the 200mph Mustang is 5.1X of the 300mph Mustang
 
Yes, but the fact is that the best range speed for the Mustang is less than 200 mph IAS. For the F4U it is 135 knots IAS. Hence the quoted figure from the report is likely to very correct.

Edit: According to the Pilot's Notes for Mustang III the best range speed is 185 mph IAS. To maintain this at SL takes maybe 350 hp.
 
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Pasoleati said:
Yes, but the fact is that the best range speed for the Mustang is less than 200 mph IAS. For the F4U it is 135 knots IAS. Hence the quoted figure from the report is likely to very correct.

Edit: According to the Pilot's Notes for Mustang III the best range speed is 185 mph IAS. To maintain this at SL takes maybe 350 hp.
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Pasoleati - first point is that best range= best cruise speeds.

Second point is that cruise speed and range are influenced by both gross weight and external stores, racks, etc.

Third point is that altitude (i.e. density factor influencing Lift Coefficient, which in turn is crucial to Total arasite drag of any specific flight conditon).

Last point is that while IAS speeds are what pilots saw in cockpit, but True Airspeed is what the aircraft sees = most important to this discussionof values for clean, .

This discussion was focused on the in-line engined Mustang, correct? Either Allison or Mustang?

I posted the A-36 as an example, but you didn't like that. I posted both the Range Testing Report for the P-51D and the appendix citing full range of values obtained at SL, 5, 10, 15, 25 & 30K so you could see the spread between Clean (no racks), 110gal combat tanks, 250 pound bombs.

SL for P-51B & D values are the same for the same Boost/RPM
@SL w/racks = 264mph TAS, 1800RPM, 35"MP, 46gph

About near the bottom are summary tables for 110 gal tanks at 5000 and 25000ft

@5K the very best TAS and RPM/Boost/HP(est) = 240mph TAS, 1900RPM, 37"MP, 637HP for 4.81 miles per gallon

@25K the very best settings = 281mph TAS, 2250RPM, 32" boost, 631 HP for 4.91 mpg.

Anecdotally, 8th, 9th and 15th AF Mission Reports occasionally cite 220mph as cruise speed in pilot debriefings - which are all referencing IAS. So, for that day, at 25K +/- 2000 feet, they were cruising inbound at or around 280mph TAS depending on Temp and Pressure variations at that altitude..

@SL w/bomb rack only (i.e return leg after dropping tanks) =303mph TAS, 2050RPM, 29"MP, 52gph

NOTE: Test pilots recorded IAS during the tests, but were converted to True Airspeed on the ground for Reports, often accompanied by calibration error spread for each altitude
 

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