Why didn't the army develop the P-51?

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The planning procedures today have changed rather drammatically since before WWII.

Back then it was seat of the pants and the General did all the thinking about strategy.

Today, when we build a weapon system, we tets it for artic, desert, mountainous, and tropic environments, and throw in blowing sand, blowing dust, temperature, altitude, humidity, salt sry, salt fog, and a host of other thngs that raise the price of testing rather steeply. By the time it gets out of testing, we KNOW it will work in the intended environment.

In 1940, that was not quite the case yet.
 

They tried, the 1st Pursuit Group was based in Michigan (Michigan winters being a pretty good cold weather test) and I believe they sent a few YP-37s to Alaska for cold weather testing.

The intake manifold/"european" fuel problem was anticipated before it happened. Allison was working on the new manifold in the spring/summer of 1943 right after the new fuel was announced. While it was 100/130 fuel different compounds ( or different amounts of certain compounds) were allowed to be used to stretch the 100/130 fuel supply. These compounds were heavier and would separate out at low temperatures or affect the evaporation rate at low temperatures. It just took until the fall/winter of 1943/44 to design the manifold, test it, put it in production and equip both production engines and send some overseas for refit.
 
Shortround6 said:
They tried, the 1st Pursuit Group was based in Michigan (Michigan winters being a pretty good cold weather test) and I believe they sent a few YP-37s to Alaska for cold weather testing.
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I thought the army had a cold weather research lab on the upper peninsula but can find no record of it. Just the current Cold regions lab in Hanover NH
U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) (CN)

From my winters at NAS Glenview IL and NAF Selfridge, MI, they are about as cold as I want these old bones to get. For Michigan, the name even confirms it Sel-FRIDGE!
 
Wasn't Selfridge the first American armed forces person killed in a military a/c?

Dave, how many German test pilots were killed in operational testing and training?
 

The first report from USAAF on the P-51 was on December 21, 1941. The next test April 1942

P-51 Mustang (Allison Engine) Performance Trials so the short answer is that USAAF had zero clue regarding the qualities of the P-51 and didn't wake up with a production contract for another 5 months. In the interim, General Wolfe - Chief of Production Engineering noted that all 'dive bomber/low altitude attack' a/c in the inventory were unsuitable' - this was the stimulus, along with the excitement generated by RAF in the Merlin contemplation, that stimulated the A-36 preliminary design in April and production contract in August 1942.

The A-36 was Huge because it enabled NAA to cost the Tooling for the P-51A/A-36 production line at the exact time NAA was deep in preliminary Design of the P-51B.
 
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In the Allison V-1710, the supercharger discharges into a round tube in the bottom middle of the cylinder bank Vee and goes to mid-engine where it turns upward and splits into two sides that attach to four 3-cylinder intake manifolds that feed the 12 cylinders. Sounds complex but isn't. The Merlin intake manifold takes the same exact route, but has fewer parts. Taken as whole, the Allison has 7,000 parts and the Merlin has 11,000, but the Merlin has fewer intake tract parts. Just two different ways to get the air-fuel charge from the supercharger to the cylinders.

One of the "fixes" was to put a set of concentric-but-shaped rings inside the round tube to direct the charge flow properly, and the other was to slightly change the angle at which the moving air-gas charge stream hit the 3-cylinder manifolds. That eliminated the two outside cylinders in each 3-dylinder manifold from being rich with the middle one lean. Simple.

It would not have taken anywhere NEAR as long if the European fuel issue hadn't been happening at the same time, confusing the troubleshooting. We could not duplicate the European fuel issue in Indianapolis, Indiana and it took some trips back and forth by factory personnel ... until one set of guys brought back some European fuel and suddenly the problem COULD be duplicated. The the light went on and the fix could get started.

By the time it WAS corrected, the P-51 was arriving and there was NO POINT in maintaing two logistics chains into Europe with two sets of mechanics for two fighters doing a similar job, so the Euopean P-38's were released to the MTO, POA, FEAF, and CBI theaters of operations where they had no more fuel or intake problems.

They were successful and became the mount of the two top aces of the USA. Along the way, the pilots learned how to operate them by the book, which helped a LOT. They produced an abbreviated checklist that made the movements to go from cruise to combat settings much easier and less confusing. The same steps were taken, but they pilots got trained on the proper movements and they could do it blindfolded in a short time. After that, very few P-38's were shot down flying straight ahead while the pilot was trying to get from cruise to combat settings when bounced by an enemy.

The cockpit heater issue was simple, too. The cockpit was just too far away from the exhaust heater mufflers for the hot air to remain hot by the time it got to the cockpit. The fix was VERY simple ... an electric cockpit heater in the central boom that eliminated the heater mufflers and solved the issues once and for all. After that, the guys were toasty as they wanted to be at any altitude, and maybe toastier than they wanted to be in the tropics ... but at least they could turn the heat up or down when they got to altitude and have the cockpit stay comfortable.

Once that was all done, the only real issue they had was the relatively low limiting Mach number of the P-38 ... which COULD have been fixed, but was never GOING to be fixed because newer designs were already coming down the pike. They settled for the dive flaps / brakes and put up with the issue. It didn't have much of an effect in the Pacific Theater. Toward the end of the war, the P-38's were being replaced by the P-47N that was quite fast and quite good way up high, and faster at medium altitudes too, though it had nowhere NEAR the acceleration of the P-38 from low-to-medium speeds on up.

Naturally, some pilots are loathe to transition from a popular mount to a new one while others take right to the new mount and love it. I'm sure the transition from tricycle gear back to conventional gear was a major step backward in some minds, but other guys had no trouble, having already mastered the taildragger years before. You can still find that today with many pilots never having flown a conventional-gear aircraft. EVERYONE flew conventional gear aircaft back then becuase that's what they had for trainers. But some guys had gotten rusty and had to reacquaint themselves with the basics in the new P-47N's.
 
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davebender said:
Why didn't P-38 use fuel it was originally designed for until new engine and higher octane fuel were perfected?
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What higher octane? or what fuel was it designed for?

Between 1937 and 1943 the US went through plain 100 octane, ( no rich mixture measure) 100/125 fuel, the original 100/130 spec and the "relaxed" 100/130 spec fuel. And ALL Allisons had problems with the so called European blend, just not any where near as bad as the P-38 and ALL Allisons got the new manifold after it was introduced into production.

Trying to separate out the fuel would have been a real problem. The allowable fuel blend was changed, once fuel meets the spec it is accepted for distribution through the supply system. They didn't keep track of blend "A", "B" and "C". There were dozens of allowable blends, as long as they meet the specs they were considered interchangeable.
 
Why did that take so long?

Zillions of American cargo ships were steaming to Europe loaded to the gunwales and steaming back empty. Transporting a few thousand gallons of aviation gasoline from Liverpool to New York should have been simple.
 
US grade 100 fuel had about 2% aromatics in it. European fuels had about 20% aromatics with the same fuel performance grade. Since the Allisons were jetted in the USA at the factory, they arrived in Europe with incorrect jetting for the 20% aromatic fuel. Stated simply, the Euroean fuel was better at vaporizing, so it ran a bit differently, especially at altitude.

Naturally, European engines, like the Merlin, were developed on European fuels, aso they had no such issues. It just happened that the Allison was much more sensitive to it than the US radials were (they had a MUCH shorter intake from supercharger to cylinders). So, it showed up particularly at higher altitudes where the range of mixture control proved to be slghty insufficient for the large difference in aromatics in the fuel over the longer intake tract. Once they figured that out, the fix was a simple jet chage and expansion of the mixture range to account for using both fuels.

Once this was known and communicated to Europe, any flying on US-supplied fuel would have been investigated and the issue ironed out before it happened. Allisons tended to run lean on European fuel and the Merlins tended to foul plugs on US fuel until the mixture ranges were adjusted.

When I was working with Joe Yancey, we had a shelf of early intake tracts that were pretty useless. They were really only useful if we built a cutaway or mockup engine that was going on display and would never be run. We have one of those at the EAA museum in Oshkosh and several others around. Most don't even have a full set or parts in them, and only the cylinders that were cut away have rods and pistons. One doesn't even have a crankshaft, but you can spin the propshaft since it is connected to the nose gears and has its own bearing. Likewise, the supercharger has its own bearing and also can spin whether or not it is connected to the crankshaft except fopr one supercharger that was used in a cutawy because it had a failure while running at normal speed. That one won't rotate even you try VERY hard to make it move.
 
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My problem with the published record you quote here is that, except for a relatively brief 2 month hiatus due to an accident, we know there was the NA-73X Prototype flying from October 1940 up to the initial production Mustang I flight in late April 1941. Joe Baugher at North American NA-73 implies that the NA-73X demonstrated a top speed 25 mph above that of the P-40 with essentially the same engine.

"Test pilot Vance Breese flew the NA-73X for its first time on Oct 26, 1940. It was a clear 25 mph faster than the P-40, despite being powered by the same engine."

I assume there was an RAF rep on scene for the flight and I'd bet there was a USAAC officer as well.

That's the only evidence I have found so far of the early demonstration of Mustang superiority. I am sure there is more out there somewhere...

Another site lists some interesting tidbits:

P-51 Mustang Timeline

The USAAC puts a 2nd LT in charge of the program! (is this in line with Dave Bender's reference to military Bone-Head moves or something more sinister?)

On March 16, 1941, A USAAC pilot named Captain M.J. Lee flies the repaired NA-73X. No record of his impression of the aircraft is ever found. there is a reference provided for this anecdotal story. Conspiracy or just bureaucratic bungling?

"Beginning on October 8 and running through December 22nd, performance tests were conducted at Wright Field on XP-51 41-038. With a full load of ammunition for its eight guns and 170 gallons of fuel, it weighed 7,934lbs. Top speed was 382 mph at 13,000 feet. (The contract performance guarantee by NAA had been 375 mph. ) Range was 750 miles at 325 mph cruise. (5)"

I assume this series of tests to be the source of the performance report you quote.

Let's return to Baugher who says in his monograph on the Mustang:

"Testing of the two (USAAF XP-51/Mustang Is) was rather slow at first, almost as if the Army didn't really want to bother with these airplanes and that they were some sort of nuisance. Some authors have suggested that there were dark and evil motives behind the Army's reluctance to test the ships; however, the slow pace can probably be blamed more on bureaucratic inertia than on anything all that sinister.

At that time, Wright Field was overloaded with test programs, with the Lockheed's P-38 Lightning, Bell's P-39 Airacobra, and Republic's P-47 Thunderbolt being thought to meet all the Army's requirements for fighter aircraft. Nevertheless, once testing of the XP-51s did get under way, the Army's test pilots reported very favorably on their performances.
Despite high scores in the tests, strangely no Army orders were forthcoming. Much later, a Senate Special Committee to Investigate the National Defense Program (the "Truman Committee") looked into the system under which military production contracts were awarded during wartime conditions. They sought specifically for the reason why the Army had sat on its hands for so long before ordering any examples of the P-51, an airplane with demonstrably superior performance.

Some insiders claimed that NAA President "Dutch" Kindelberger had been asked to pay bribes in exchange for a production contract, and that he had refused all such demands in no uncertain terms. The primary cause of the Army's stall is likely somewhat less sinister. The Mustang could have been the victim of the "Not Invented Here" (NIH) syndrome, in which the Army looked askance at an upstart aircraft that had not been designed in response to any of its official requirements or specifications, and was therefore way down on their list of priorities."

I have to admit, to me, if it looks and smells like a dead fish, it probably is one... The calling of a senate committee seems a bit over the top for simple bureaucratic bungling. But then again, perhaps that's just how we do things in the good ole' USA.

While I appreciate the military doesn't procure an aircraft without comprehensive testing, the XP-51 despite its X designation was a warplane already in production and was a US built aircraft that I believe entered combat before the P-38, P-39 or P-47. Didn't it?
 
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Allison ( and every other maker of engines) was aware of a change in the specification for AN-F-28 grade 100/130 fuel in the winter of 1943, This was the use of the heavier compounds to stretch the fuel supply. By this time US fuel had about the same amount of aromatics as British spec fuel. It was back in 1940/41 that the British and American 100 octane showed the big difference in aromatics. (and the chances of getting 100/130 fuel without a lot more than 2% aromatics are pretty slim.) Once the US and British agreed on a common fuel specification the US had to change the composition of some of it's self sealing tanks and gaskets/seals in the fuel systems to stand up to the high aromatic content fuel.

Aromatics are type of hydrogen-carbon compound and there are a number of them. There are about 400 different compounds that can be found in aviation fuels ( both piston and turbine) at least in trace amounts. Most fuel will have nowhere near that number in any one sample. On a short list of 73 compounds in a booklet by the Ethyl corporation prepared by Sam Heron aromatics there are 11 aromatics listed ( some useless for aviation fuel like Naphthalene/mothballs) so while saying a fuel had aromatics it tells us something but not a whole lot. Fuel has to be blended to give ALL the desired properties. Benzene is another aromatic and while it raises rich mixture response it lowers lean mixture performance ( cruise). it has about 1400 btus less per pound than blended gasoline and it freezes at +42 degrees F. Benzene was used as part of a number of racing fuels in the 20s and 30s but has some obvious problems as a general aviation fuel component.

What was known about fuel in 1940 was a lot less than what was known in the early 50s. And what was known in 1940 was a whole lot more than what was known in 1925/26 ( pre-octane rating).

There may very well have been some bad batches of fuel in Europe in 1943/44 but since both American and British fuel was supposed to be inter-changeable at this point in time (unlike 1940/41) and since the change in the allowable compounds was agreed to before issue.

P-38s in other theaters were also having problems, just not to the extent they were having in Europe.

From "Vee's for Victory" pages 374-375.

"the early Allison test engines were rated on 92 octane fuel per Army specification 2-95. The first engine to be rated on 100 octane fuel was the first altitude rated engine, the XV-1710-19(C13) for the Curtiss XP-40.................With the 1941 introduction of the V-1710-F5 series of sea level engines for the Lockheed P-38, Allison began to rate engines using the lean/rich grade 100/125PN fuel to specification AN-F-27. However because of quality and supply problems, they used only grade 125 for rating engines prior to the V-1710-89/91 (F17R/L), which begain delievers in 1943. These and all V-1710's deleivered through the end of the war were rated on Grade 100/130 produced to military specification AN-F-28."
Some later engines were rated on Grade 115/145 (specification AN-F-33).
"Through most of the war, the aircraft being flown within the Continental U.S. in vaious training and liaison roles were operated on 91 octane fuel. This was a fuel that was not suitable for combat. The reason was simply the critical fuel supply situation. It was standard practice to retard the fixed timing of the magnetos in such service as a way to protect them from detonation damage, particularly during take-off. For the V-1710, the revised timing was 29 degrees BTC for the exhaust and 23 degrees BTC for the intake plugs. At the same time the maximum manifold pressures were reduced by 5 inHgA, meaning somewhat reduced power was available............While official Air Force technical orders required resetting the timing on any engine being sent to foreign theaters, a number of engines with retarded timing reached England in 1944 and were installed in P-38s without having been reset for full power operation on Grade 100/130 fuel. The Material Command took immediate action to ensure this situation was rectified.
 
Most interesting Shortround6 and GregP on the P38 fuel problems.
After some searching on the internet, I came across a document concerning carburetor settings. Dated Feb. 1944. Number AA 449966. Does anyone have this document and can post it here? I would like to read it.
 
Very interesting info in your post #33 Oldcrow - good stuff and food for thought.

I still think that the fact that the USA was not at war had some bearing on the pace of interest in future planning within the USAAC/F at that time, with development of the P-38 and P-47 occupying procurement departments' time, a fighter being built for the British and barely out of the box as prototypes only might not have raised more than a few eyebrows - good performance notwithstanding. After all, being a British fighter (albeit designed and built in the US) being built in California - which is a long way from the beauracrats in Washington, about which very little was known might even raise the question, "why would the US military take it seriously at that point in time?" A question I have is; could the fact that all NAA had done up to that point was the T-6 and developing the B-25 and therefore was not taken seriously as a design team capable of producing good fighters have had some bearing on a reluctance to place any degree of priority on the Mustang/P-51 by the USAAC?
 
I have participated in over 15 Allison overhaus with Joe Yancey. All have resulted in smooth running Allison V-12's. He has several with over 1,200 hours on them running just fine. No result of mine. Find me ANY Merlin with over 600 hours on it and you wil have found the holy grail of Merlins.

Merlins are GOOD engines but not exactly long lasting. You can fly an Allison farther than you can ship a Merlin.

But the Merlin is reliable and will GET you there and back unless combat dictates otherwise.

Both were good engines and accomplished yeoman service.

In WWII, the Merlin did more for the war effort, but was also the weaker mechanical unit and did not hold a tune as lomg as a Allison did.

In retrosect, the Merlin was better due to the two-stage supercharger (the result of Sir Stanley Hooker), not for any ineherent defects in Allison design.

By the end of the war, the Allison was making the power of any Merlin, at altutude.

Little to chose indivually initially, but the momentum of the Merlin took over, just before the jets cancelelled everything in the piston category.

And pistons died along with the Allison AND the Merlin. Two very good engines.

Wish we had more running ...
 
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The Basket said:
Low priority was better than no priority I suppose
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These seem to me to be persuasive and/or compelling points suggesting the P-51 moved about as fast into US operation as could be reasonably expected.

The US was not yet at war and I am sure many people in influential government and military positions were in denial. It may also be that the push to get ready for the coming war which was also a part of 1939-41 American aeronautical and arms industry, simply moved the accepted standard bearers (P-38, P-39 and P-47) to the head of the line.

However, bribery and industrial espionage have been a part of the US aeronautical industry since the time of the Wright brothers and Curtiss had a lot too lose with an emerging NAA.

I expect CW was relying on the evolutionary growth of the P-40 to retain the lion share of the fighter market in the coming war years. Who would have bet against the ultimate ascendancy of CW with a follow-on to the P-40?

Moreover, while the Mustang was in production, USAAF Squadrons were already receiving early P-38s with performance comparable to the NA-73X, so perhaps a lack of urgency did characterize the Mustang's 'slow' adoption.

Two other items from the previously mentioned timeline:

"April 7, 1941: NAA receives contract for 150 P-51s (NA-91) from AAC four months before 1st XP-51 arrives at Wright Field for testing. This may have been a preliminary to the BPC order for Mustang Mk IAs on 06/30/41. The USAAC designation of P-51 was for the cannon equipped Mustang. (6)"

The latter comment must be true as the next comment would make even less sense:

"Oct 21, 1941, NAA test pilot Bob Chilton arrives at Wright Field to check out a Spitfire V and Hurricane II. Upon checking the first XP-51's logbook, he found only one hour of flight time had been accrued since its arrival back on August 24, 1941. The XP-51 Project Officer was a junior Second Lieutenant Winthrop Towner. (5)"

Presumably Chilton is citing the log book up to October 8 when XP-51 testing at W-PAT commences.

Finally, there is the iconic moment probably worth repeating in the context of this thread:

"Nov 11, 1941: AG346 is first flown in Britain. Test pilot reports are positive as the Commander, Air Fighting Development Unit describes the Mustang as "an excellent low- and medium-altitude fighter...pleasant to fly...extremely stable...far smoother in all maneuvers" than the Spitfire. Test pilots report the Mustang was "definitely the best American fighter that has reached England." (5)"

I wonder whether this early comment by RAF test pilots is correctly dated? In the previous post, tests at Boscombe Down commenced in January 1942.

Perhaps the bottom line is that, with or without possible Curtiss interference, bribery or influence peddling, the P-51 progressed about as fast as it could and its development owed much to the foresight of some influential advocates like General Wolfe?

Drgondog, was Wolfe a Texan?
 
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You are giving too much credit to the P-40 and not enough to CW planning it's replacement.
The USAAF issued a contract for two prototype XP-46s on Sept 29, 1939.
The USAAF issued a contract for two prototype XP-53s October 1, 1940. First flight of the XP-46 isn't until Feb 1941.
On June 22, 1940 the Army had placed a contract for engineering data and a wind tunnel model of the XP-55. last Curtiss design by Donovan Berlin.
Within 6 weeks of the XP-53 contract it was modified so the 2nd airframe would be Merlin powered and not use the Continental engine and so started the XP-60 saga.
Army was also fooling around with 3 other "unorthodox" fighters at the same time as the XP-55. The XP-52, XP-54 and XP-56, all to the same requirement as the XP-55 and the requirement dated back to the fall of 1939.
Throw in a few other projects like a Continental powered P-38 (XP-49) and I think the Army was running in too many different directions at the same time. Trying to pick a "winner" out of this mess to be used in combat 2 years down the road is going to be hard.
Design work started on the P-61 in the Fall of 1940. Formal contract signed in Jan 1941.

There was an awful lot going on "behind" the scenes.

oldcrowcv63 said:
Moreover, while the Mustang was in production, USAAF Squadrons were already receiving early P-38s with performance comparable to the NA-73X, so perhaps a lack of urgency did characterize the Mustang's 'slow' adoption.
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Perhaps but it seems more like a mad scramble than a lack of urgency. It may be a good thing that the USAAF had a lack of interest in the Mustang in it's early life. They may have tried to stick a Continental IV-1430 in it and screwed the program up for months

From Joe Baughers web site. "On April 10, 1941, two P-39Ds were ordered modified and flight tested under contract AC18373 as flying testbeds for the experimental Continental V-1430-1 supercharged inverted-Vee engine that was expected to deliver 2100 hp. These aircraft were assigned the designation XP-39E."

Without any clear evidence of bribery I think it can be discounted.
 
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