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You are asking questions that I doubt younger people can answer. There are a few in here who stubbornly think the U.S.A. should have bought foreign weapons, particularly the DH Mosquito.
But the attitudes of the time would preclude that from ever happening at the time when it might have been really useful. That being said, even if we could post the real-world reasons for the items above, very few people today would acceot the reasoning behind them. Everyone wants to take apart the decisions and replace them with whatever decision seems best using the infallible power of hind-sight and knowledge of everything we know today after years of digging and changes in attiudes.
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The valves in an Allison were sodium-filled Stellite, and that required tungsten and molybdenum. The supplies weren't unlimited and ALL military piston engines needed valves, so they got first priority for the alloys. Turbine wheels came further down the food chain. Other makers also needed wear-resistant valves, and Allison was forced to share that with Rolls-Royce and, eventually, commerical competitors. That was NOT a welcome decision by Allison or GM, but helped the war effort overall.
I don't know why the engine makers didn't experiment more with 2-stage superchargers, but it most likely is due to their primary customers wanting turbochargers instead. Everyone was sort of waiting for the "breakthough" in turbocharging and it never did get to a stage of development that was as reliable as 2-stage superchargers. I think charge coolers were a big issue: inter / after coolers that could drop the etemperature of the compressed air and/or air/fuel mixture and delay detonation.
If you go look up the history of the R-2800, you will find a LOT of master-rod designs, a lot of failures before "getting it right," a lot of cooling fin designs, and a lot of hard work. Early R-2800s weren't necessarily great engines. The White book, "R-2800 Pratt and Whitney's Dependable Masterpiece" is a great source. The timeline doesn't exactly allow for early use in large numbers. "B series engines were built from 1943 and "C" series were from 1945. An "A" series engine has very few parts in common with an "E" series engine.
The R-2800 first flew in 1940, but the "B" series is what started them down the right path. That said, actual development times for the Grumman Cats wasn't bad at all.
You are asking questions that I doubt younger people can answer. There are a few in here who stubbornly think the U.S.A. should have bought foreign weapons, particularly the DH Mosquito.
The valves in an Allison were sodium-filled Stellite, and that required tungsten and molybdenum. The supplies weren't unlimited and ALL military piston engines needed valves, so they got first priority for the alloys. Turbine wheels came further down the food chain. Other makers also needed wear-resistant valves, and Allison was forced to share that with Rolls-Royce and, eventually, commerical competitors. That was NOT a welcome decision by Allison or GM, but helped the war effort overall.
Item 2 is wrong re. USAAF wanting a long-range escort fighter with XP-65 - doctrine for long range escort did not existed in 1941 in the USA....
From what I remember
....
- The USN issued a requirement for an interceptor program: This produced the XF5F, XFL-1, and F4U, of which the latter one.
- The USAAF procured a long-ranged escort fighter in the form of the XP-65 which was to use 2 x R2600 with either a twin-stage supercharger or turbocharging, a pressurized cockpit, and 37mm cannon; they also procured the XP-50, which was an XF5F with a nose-gear and turobcharging.
What I'm curious about is the following
- Why didn't they just use R-2800's with either 1 stage supercharging (F7F), or two-stage supercharging, or a turbocharger?
- Why did the USAAF want 37mm cannon: They were brutal when they hit, but fired slowly, had bad ballistics, and permited only 40-45 rounds; the 20mm hit greatly harder than the 50 calibur, had similar refire rate, ballistics were a little inferior but acceptable at 400-yards for most purposes
- Why did the USN just put 4 x 20mm in the nose and disregard the 0.50? That was more than enough...
Other makers also needed wear-resistant valves, and Allison was forced to share that with Rolls-Royce and, eventually, commerical competitors. That was NOT a welcome decision by Allison or GM, but helped the war effort overall.
True, but shooting is only one part of the equation... anybody can shoot a gun, not everybody can make it hit something.wuzak said:The USAAC/F did have a fascination with the 37mm cannon. Probably because of its destructive power.
I guess there was the P-67 too...tomo pauk said:The US 20mm was not a done deal by 1941, while the 37mm was, and it had a role for the primary purpose of USAAC fighters of 1941 - killing the enemy bombers close and above the USA and it's territories.
wuzak
I didn't realize the R-2800 and R-3350 were concurrent designs. I thought (for some reason) that the R-2800 and R-2600 were concurrent.
The RAF early on had 8 x 0.303's in the Spitfire and Hurricane, followed by 12 x 0.303's for the Hurricane and Typhoon, followed by 4 x 20mm for the Hurricane, Typhoon, and Tempest.
I think we have answered most of the questions. I would add in regards to the engine question that it was not so simple to ADD two stage supercharging to an existing fighter design. One text book claimed about 10 cubic feet of volume was needed for a 1000hp engine for the supercharger AND intercooler AND ducts. Since horsepower is pretty much a function of airflow a 2000hp engine is going to need nearly double the volume, there is some savings in scaling up but no, you are not going to cram 2000hp worth of airflow into 12-14 cubic feet. On bombers with large wings and engine nacelles there was a lot of room to put things. On fighters you pretty much designed for one type of engine from the start. Please note that the Spitfire and P-51 and Mosquito all used substantially larger radiator sections to fit in the intercooler radiators than the single stage engined planes.What I'm curious about is the following
- Why didn't they just use R-2800's with either 1 stage supercharging (F7F), or two-stage supercharging, or a turbocharger?
- Why did the USAAF want 37mm cannon: They were brutal when they hit, but fired slowly, had bad ballistics, and permited only 40-45 rounds; the 20mm hit greatly harder than the 50 calibur, had similar refire rate, ballistics were a little inferior but acceptable at 400-yards for most purposes
- Why did the USN just put 4 x 20mm in the nose and disregard the 0.50? That was more than enough...
The Madsen was a 23mm cannon, if I recall correctlyA few observations for now.
1. On the subject of guns. The US Army was enamored of the 37mm gun for a number of reason, part of it was because it was home grown, although they certainly did at least test several other options including Danish Madison cannon.
I see your pointThe actual truth is that a LOT of the pre-war cannon promised a lot more than they delivered in regards to reliability. Also most of the cannon on offer had rather low rates of fire in the mid to late 30s. It was only in the very late 30s that the Hispano got to 600rpm. So.... a 37mm at 140rpm or a 20mm at 400-450rpm?
By 1937 or 1938 weren't we aware what the Germans were doing at all?Another reason was the size of anticipated targets. The USAAC having built the XB-15 and XB-19 and with America's isolationist policies one theory was that any air attacks would be from similarly sized aircraft.
Infamous?As a further note on the Army and Navy on guns, they did not always play well together. During the 1930s when the need for light automatic cannon for AA use was becoming glaring apparent the Army proceed with their own 37mm AA gun while the Navy designed and built the infamous 1.1 in (28mm) machine cannon.
40mm would have been better as I think it had a higher muzzle velocity...However the Navy changed direction sometime after summer of 1940 when they got their hands on a twin mount 40mm Bofors and started plans for production even before getting a licence, I don't know when the Army joined in but by 1943/44 the 40mm Bofors was in widespread Army use and the Army 37 AA gun was on the way out.
Wait, I can't speak for the R-2600 but the R-2800 could do around 23,800...The engine question R-2600 vs R-2800 vs R-3350 gets really convoluted but lets try to sort through things.
1. None of these engines were worth much at high altitude without an auxilary or two stage supercharger. Even with a two speed supercharger FTH was around 12-14,000ft and engine power was several hundred HP below take-off power.
OkayIf you want a low altitude plane you are all set, if you want to escort turbocharged bombers then single stage supercharged radials won't work.
That was teething trouble...Please note that for the R-3350BA it took from 1938 to the end of 1942 to build 77 engines. Lack of demand or lots of teething troubles?
You would want that there from the startI would add in regards to the engine question that it was not so simple to ADD two stage supercharging to an existing fighter design. One text book claimed about 10 cubic feet of volume was needed for a 1000hp engine for the supercharger AND intercooler AND ducts.
I think I understand, you could make an airplane with a wildly varying CG...Finding information on the thinking of the Navy on the armament is hard. However sticking four 20mm cannon in the nose requires a bit of thought. The F7F as designed carried the 20mm guns and ammo pretty close to the center of gravity. 800 rounds of 20mm ammo weighs around 560lbs so you have to be careful where you put it or the flying characteristics of the plane change as the ammo is used.