USAAF procurment system in WW2

[Koopernic]

How did the USAAF acquire an aircraft during and before WW2?. Did manufacturers approach some section within the USAAF or did a certain section develop a specification in accordance with a need. How did it interact with the Dept of Defense and develop an aircraft that 'might be required'

I know that by 1945 something called "air material command" existed. I am not an American (happy 4th July incidentally) and I suppose am after a few pointers and references.

The UK system seemed to involve the Ministry of Defence and the Air Ministry. The Germans had the Armaments Ministry, the RLM (Reich's Luftfahrts Ministerium and the Luftwaffe itself which had offices such as the "Technisches Ampt" a system that didn't always go well.

This came out of search for how the "Amerika Bomber" and the B-36 Intercontinental Bomber (The Germany Bomber?) came into being; independent projects designed to be intercontinental bombers. Did Roosevelt for instance say that we might need an aircraft that can bomb Europe since presumably only he and a few knew what policy direction he was manoeuvring towards. How did proto Intercontinental Bombers such as the Douglass B-19 and Boeing B-15 come about.

It also occurs to me that with excellent engineers on all sides that this aspect can be extremely important in addition personal opinions of the officers often stifled promising aircraft and technology while promoting things that just didn't work out.

 

[wuzak]

The Air Materiel Command existed throughout WW2 and before. It was a division of the USAAC/F. I believe they were controlling the purchase of equipment, but not setting requirements.

 

[Shortround6]

The USAAF (Or USAAC depending on year) formulated a requirement and put it out to the manufacturers. Sometimes a restricted list and sometimes more of an "open call" at which anybody was welcome. The Manufacturers (those that were interested) responded with a bunch of paper proposals, often one manufacturer would submit several different proposals to the same requirement. Engineering officers in the Army dept would evaluate the proposals and rank them for suitability. The Army might (or might not) select a few of them for more detailed 'engineering studies' which the Army would pay for. The results of the engineering studies belonged to the Army and the results could be shared with other manufacturers. Next step might include mock-ups or go right to prototype construction (although a mock-up construction and inspection would be part of the deal), Sometimes more than one type of aircraft was selected for prototype construction for a "fly off".
In some cases the Army took into consideration a companies experience when evaluating the paper proposals, like Boeings experience with large multi-engine planes when the B-29 came along or a companies work load and engineering staff. A company with a number of projects under way was less likely to get a new project because it was felt that their staff might already be stretched thin and the new design might not be completed in a timely manner.

A lot of times the officer/s formulating the requirements did have pet theories which did affect decisions. But please remember that a lot of times the "requirements" listed in many books do NOT include ALL the requirements. The US for instance had a small book of "requirements" that ALL new aircraft had to meet that included "G" loadings for different classes of aircraft. Construction details or materials and other things. The British specifications for ALL aircraft in the 1930s including a "ground loading" of sorts to prevent rutting the grass fields. Max tire pressure could not exceed either 35 or 38lbs per square in. Didn't matter if it was a trainer, fighter or 40,000lb bomber. For instance ALL US fighters of the time were stressed to an 8 "G" service load with a 50% safety factor for a 12 "G" ultimate load. This made them fairly sturdy but also made them heavier than many other countries fighters. The "G" loading was not spelled out in individual fighter specification requests but was in the the small "hand book" of general design requirements.

Any company that ignored the general requirements stood a good chance of it's submission being thrown out or put at the bottom of the pile regardless of how good it's paper performance specifications were.

 

[FLYBOYJ]

In addition to SR's post you also had to consider if the contract was going to be "cost plus" or "firm fixed price." Usually when an item was being developed cost plus was in effect (with government contract officer(s) monitoring the way the money was being spent). Once in production contracts were let firm fixed, keeping a cap on cost overruns. Price increases had to be explained, justified then approved. The same situation exists today.

 

[gjs238]

ALL US fighters of the time were stressed to an 8 "G" service load with a 50% safety factor for a 12 "G" ultimate load. This made them fairly sturdy but also made them heavier than many other countries fighters. The "G" loading was not spelled out in individual fighter specification requests but was in the the small "hand book" of general design requirements.

With hindsight, would the US have been better off reducing its "G" load requirements?

One can wonder how more competitive the lighter US planes would have been.

 

[wuzak]

With hindsight, would the US have been better off reducing its "G" load requirements?

One can wonder how more competitive the lighter US planes would have been.

Isn't that what they did with the P-51H?

 

[Shortround6]

The P-51H was built to a reduced "G" load standard I believe as was the Grumman Bearcat.

It maybe a trade-off, better performance means fewer planes shot down (and/or more kills?) but less rugged planes means more of them written off as un-repairable due to combat or landing damage?

I have no idea were the 'break point' would be, 7.5 "G"s instead of "8" or 6.5 "G"s ?

Europe was 3-6,000 miles from the factories and the CBI theater was well over 8,000 miles from the west coast factories which means replacement aircraft/pats are going to be a problem no matter what the cause of damage was. Granted the 8 "G" requirement existed long before the war started.

The US navy also a few strange requirements during the 1930s. EVERY Navy plane was supposed to do a terminal velocity dive. A Dive that reached the max dive speed of the aircraft due to aerodynamic limits (drag) and not structural limitations. This lead to some heavier than needed biplanes but was quickly changed when they found that monoplanes could go fast enough that leaving enough room for a safe pull-out was a problem. Navy planes were also 'supposed' to be able to do a 10 turn spin both to the right or left and be recoverable. Again it worked fairly well with biplanes but some monoplanes could loose a couple thousand feet of altitude per turn. They just ran out of room (altitude) to perform such tests and the tests had lost some of their meaning anyway. Ensuring enough reserve of strength in a 200mph airplane is one thing but a 400 mph airplane has 4 times the structural loads being put on it just in level flight. Trying to come up with tests to ensure the same safety margin became a bit difficult. That and aircraft structure design had progressed to the point where destructive testing in flight was no longer needed as much.

 

[Koopernic]

With hindsight, would the US have been better off reducing its "G" load requirements?

One can wonder how more competitive the lighter US planes would have been.

My recollection was that the RAF standards were to the same G requirements as USAAF but the requirement was relaxed on some axis where it was presumably thought the strength was not needed.

These are engineering standards of course but do not tell us how a requirement for a particular type of aircraft comes into being. One story has Hap Arnold instigating work on what would be the B-36 in 1938 after at Lufthansa Focke-Wulf Fw 200S flew 3700 miles from Berlin to New York. It wasn't a threat of course since the range would need to more than double to undertake a practical return mission with military loads. Lufthansa had wanted to make regular currier flights but Roosevelt banned them. The USAAF of course already had the impressive Boeing XB-15 in the air and Douglass XB-19 underway.

At some point there must be a kind of think tank where the strategists meet with technocrats to put together a requirement for something like the B-25/B-26 or B-29. Clearly in the case of the B-29 its priority must have increased when it became a carrier for the A-bombs.

The strategists must have a fair idea of emerging threats and opportunities from intelligence to correctly formulate a specification for an aircraft and to decide to procure it in numbers. For security and diplomatic purposes the technocrats might need to be kept in the dark somewhat. Someone decided that the P-40 was going to be a low altitude army support fighter while the P-47 and P-38 the high. What happened is that the latter weren't ready.

 

[wuzak]

When the design load was reduced for American aircraft, was it a reduction in the nominal "G" design limit, or a reduction the in the safety factor?

I thought it was the latter, so that the design limit was still 8g, but the ultimate limit was 10g (approx) rather than 12g.

I also thought that was what they British had - a lower ultimate limit.

 

[Shortround6]

Someone decided that the P-40 was going to be a low altitude army support fighter while the P-47 and P-38 the high. What happened is that the latter weren't ready.

While the latter part is correct the first part isn't. The First 524 P-40s were ordered because the P-38 and P-39 were not ready and the P-40 could be put into production about 1 year sooner. It was a question of P-40s or nothing (Ok maybe a hybrid P-35/P-43 without the turbo and in smaller numbers?).

The XP-40 and very first P-40s were lousy ground attack planes. This is also ignoring an Army decision made years earlier that ground attack planes would use air-cooled engines for less vulnerability to ground fire. Early P-40s had a much smaller bomb load than the P-35. Now this may have been a "trick" to get more government funding for attack planes as the export Hawk 75s were certainly equipped (or had options for) a rather substantial bomb load for the time. Tell Congress that the new fighter can carry 700-800lbs of bombs watch funds for new attack plane disappear
XP-40 had two .50 cal guns with 200rpg which is poor armament for strafing. This was improved somewhat rapidly but the engine used in the early P-40s had the second best altitude performance (for a production engine) in the world at the time second to the Merlin so it is a little hard to figure out were the "low altitude army support fighter" comes from.
Granted they were used for that several years after they were ordered but the intention in 1939/40 was???

 

[vikingBerserker]

Before WW2, sometimes a manufacturer would approach the military with design proposals.

 

[GregP]

Aircraft were designed for a mission, with secondary characteristics to be determined by mission requirements. It sometimes happend that a particular design would excel at a secondery mission almost by accident. The P-47, for instance, was designed as a high-altitude figher and exhibited it's best performance above 30,000 feet. It turned out to have a great capability for ground attack ... a somewhat unexpected development.

The P-51 was designed as a P-40 replacement and ALSO was able to develop a long range for escort duties. It was never designed with particularly long range in mind initially, but was modified to have it. It often flew with drop tanks made of paper!

The P-39 was designed as a high-altitude fighter but the turbocharger was deleted and it became a ground-attack specilaist by necessity.

So the procurement process was flawed, but did not produce many unusable aircaft for the most part. If they had stuck to the turbo-P-39, it might have been a real performer as developed. They didn't and it became synonymous with a dog. The best pure dogfighter we had was the Hellcat, but it played a very minor role in the ETO. The initial flaws in the P-38 got it a bad reputation in the ETO but, once fixed, it became the mount of our two top aces (Bong NcGuire) in the PTO. The third place finisher was the F6F (McCampbell) in the top score department, followed by the P-47 (Gabreski). The P-51, despite its high praise in general, had it's best US pilot come in fifth in score (Johnson).

My conclusion is that the best fighter depends on what aircraft is deployed where, and is flown by whom, against which opponents.

In WWII, the best combination for ACE in the US Armed Forces was the P-38 followed closely by the Hellcat and P-47, with the P-51 coming in a very respectable fifth in overall scoring but forth in type (2 P-38Aces).

Had the opponents or geography been different, the results may well have changed drammatically. A twin will almost always be safer over water (P-38) and the plane with a lot of wing area will almost always be very maneuverable (Hellcat).

Everything else gets accomplished by the luck of the draw depending on who you face off against flying what aircraft, what is required of the troops, and how well they plan it. It might be better to have 15 Skua's attack a single ship unexpectedly than 3 Lancasters that are expected and planned for.

Tough to say until you DO it.

 

[wuzak]

The P-39 was designed as a high-altitude fighter but the turbocharger was deleted and it became a ground-attack specilaist by necessity.

I thought that was a myth. The Russians used the P-39 as a low altitude fighter.

 

[michaelmaltby]

"....If they had stuck to the turbo-P-39, it might have been a real performer as developed...."

For whom ....? It WAS a real performer for the Soviets .... a turbo would have been a disadvantage for front line Soviet Cobra units.

For wider acceptance - USAAF combat squadrons for instance - a turbo would give users better climb to combat altitude and performance but the P-39 lacked range, IMHO. In Europe I don't see Cobras escorting ram rod missions to Berlin or Schweinfurd (sp).

Beauty is in the eye of the beholder, , and those who liked the P-39, liked it a LOT. Those who didn't like it, called it a DOG.

AFTERTHOUGHT: A turbo P-39 would have been right at home in the air battles above Guadalcanal and a definite performance improvement. But I think the fight out of Henderson Field is unique in USAAF/USMC/USN WW2 history. Akin to a mini BoB.

And we always forget about this theatre ...

http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=477

 

[Shortround6]

Nobody yet has figured out where the turbo and intercooler where supposed to go. The setup they had didn't work.

Especially for later, higher powered versions. P-38s suffered from increasing cooling problems with intercoolers which restricted FTH on the later engines until they got to the J model with the new intercoolers. They also had to fit larger radiators starting with the H (?).

The Guys at Bell were not complete dummies. There was a reason the P-39E/P-76/P-63 fuselage was about 2 feet longer than the P-39 and it still didn't have an intercooler.

 

[GregP]

The turbo setup they had in the XP-39 required some debugging. The people in charge elected not to develop the system and instead dropped the turbo. Had it been developed, things might very well have changed.

Don't tell me there was no roon ... the prototype HAD the system in it. It did need some development, but it flew, so there WAS room.

 

[Shortround6]

Yep, the Prototype had the "system".

only trouble was the "system" created a LOT of drag.

AND the NACA found that the original radiator set up required 10,250 scfm to cool the engine properly, in a 160mph climb it was only getting 7,880 scfm and at 350mph in level flight it was getting 16,900 scfm. Too little cooling in the climb and too much drag in level flight. Note that these are the coolant radiators/oil coolers. The intercooler was only flowing 1,600 scfm at high speed while 5,000 to 7,000 scfm was needed for full power without detonation (height not given).

Assuming the 5000 scfm is correct ( and it may very well be different at different altitudes/temperatures) the intercooler was about 32% the size in needed to be ( or needed bigger scoops/ducts) for high speed level flight. For climb with much less airflow through the intercooler things (actual available power) get much worse.

And if there was so much room INSIDE why did Bell resort to this?

There was another version that was even uglier. A "saddle" pack that sat over the engine (took out the rear part of the canopy and the normal air intake) and was wider than the fuselage.

If "development" means you need more cubic ft of space INSIDE the fuselage you have a problem.

I would note that the solution for the radiator cooling problems in the prototype including routing the airducts from the wing root leading edges into the center of the bottom of the aircraft underneath the engine, just about where the the Turbo was located on the prototype.

and http://www.ww2aircraft.net/forum/at...pilots-flight-operating-instructions-p-39.pdf

See figures 4, 10 and 11 for cooling system diagrams.

 

[FLYBOYJ]

From Wiki...

"As originally specified by Kelsey and Saville, the XP-39 had a turbo-supercharger to augment its high-altitude performance. Bell cooled the turbo with a scoop on the left side of the fuselage. Kelsey wished to shepherd the XP-39 through its early engineering teething troubles, but he was ordered to England. The XP-39 project was handed over to others, and in June 1939 the prototype was ordered by General Henry H. Arnold to be evaluated in NACA wind tunnels to find ways of increasing its speed, by reducing parasitic drag. Tests were carried out, and Bell engineers followed the recommendations of NACA and the Army to reduce drag such that the top speed was increased 16%. NACA wrote, "it is imperative to enclose the supercharger within the airplane with an efficient duct system for cooling the rotor and discharging the cooling air and exhaust gases." In the very tightly planned XP-39, though, there was no internal space left over for the turbo. Using a drag-buildup scheme, a number of potential areas of drag reduction were found. NACA concluded that a top speed of 429 mph could be realized with the aerodynamic improvements they had developed and an uprated V-1710 with only a single-stage, single-speed supercharger.

At a pivotal meeting with the USAAC and NACA in August 1939, Larry Bell proposed that the production P-39 aircraft be configured without the turbocharger. Some historians have questioned Bell's true motivation in reconfiguring the aircraft. The strongest hypothesis is that Bell's factory didn't have an active production program and he was desperate for cash flow. Other historians mention that wind tunnel tests made the designers believe the turbocharger installation was so aerodynamically cluttered that it had more disadvantages than advantages.

The Army ordered 12 YP-39s (with only a single-stage, single-speed supercharger) for service evaluation and one YP-39A. After these trials were complete, which resulted in detail changes including deletion of the external radiator, and on advice from NACA, the prototype was modified as the XP-39B; after demonstrating a performance improvement, the 13 YP-39s were completed to this standard, adding two .30 in (7.62 mm) machine guns to the two existing .50 in (12.7 mm) guns.Lacking armor or self-sealing fuel tanks, the prototype was one ton (900 kg) lighter than the production fighters.

The production P-39 retained a single-stage, single-speed supercharger with a critical altitude (above which performance declined) of about 12,000 feet (3,660 m). As a result, the aircraft was simpler to produce and maintain. However, the deletion of the turbo destroyed any chance that the P-39 could serve as a medium-high altitude front-line fighter. When deficiencies were noticed in 1940 and 1941, the lack of a turbo made it nearly impossible to improve upon the Airacobra's performance. The cure for the drag problem was worse than the drag itself. In later years, Kelsey expressed regret at not being present to override the decision to eliminate the turbo."

 

[FLYBOYJ]

Before WW2, sometimes a manufacturer would approach the military with design proposals.

That's called an "Unsolicited Proposal." It's still done today, this is one of the more recent ones that are known.

 

[Balljoint]

The P-51H was built to a reduced "G" load standard I believe as was the Grumman Bearcat.

It maybe a trade-off, better performance means fewer planes shot down (and/or more kills?) but less rugged planes means more of them written off as un-repairable due to combat or landing damage?

I have no idea were the 'break point' would be, 7.5 "G"s instead of "8" or 6.5 "G"s ?

Europe was 3-6,000 miles from the factories and the CBI theater was well over 8,000 miles from the west coast factories which means replacement aircraft/pats are going to be a problem no matter what the cause of damage was. Granted the 8 "G" requirement existed long before the war started.

The US navy also a few strange requirements during the 1930s. EVERY Navy plane was supposed to do a terminal velocity dive. A Dive that reached the max dive speed of the aircraft due to aerodynamic limits (drag) and not structural limitations. This lead to some heavier than needed biplanes but was quickly changed when they found that monoplanes could go fast enough that leaving enough room for a safe pull-out was a problem. Navy planes were also 'supposed' to be able to do a 10 turn spin both to the right or left and be recoverable. Again it worked fairly well with biplanes but some monoplanes could loose a couple thousand feet of altitude per turn. They just ran out of room (altitude) to perform such tests and the tests had lost some of their meaning anyway. Ensuring enough reserve of strength in a 200mph airplane is one thing but a 400 mph airplane has 4 times the structural loads being put on it just in level flight. Trying to come up with tests to ensure the same safety margin became a bit difficult. That and aircraft structure design had progressed to the point where destructive testing in flight was no longer needed as much.

The P-51-H was largely the result of a study by Schmuel of the Spitfire design specs including a lighter gauge skin.