Supercharger Development & Aircraft Design Policy (USAAC)

[tomo pauk]

It was the first 400mph fighter.
.... It had a much lower bomb carrying capability. And of course, one hit anywhere in the cooling system and it wasn't likely to make it home.

Oh, no, the P-38 was not the 1st 400 mph fighter.
One hit in the oil system of, say, Corsair also means an aircraft lost. There was a reason why F7F, F8F, FM2 and AU-1 have received oil coolers that were armored/convoluted/protected by engine.

...
None of these specs had been achieved previously, and the only engine available in '38 when Kelsey wrote the spec was the V-1710, and both he and Johnson recognized that two engines would be required to do the job. I'm curious-just when did the R-2800 become available, and when/how did the turbocharger development with it take place? I'm assuming it was a little behind the 1710, but honestly don't know. One point of interest-according to Kelsey, the '38 was designed as a versatile fighter right from the start, not as an "interceptor". He created the interceptor name/classification as a way to get around the AAC limits and restrictions of the day.

The R-2600 was powering the prototype of the Boeing 314 in 1938, 1500 HP. 1st run in 1935.
The 2-stage supercharged R-2800 propelled XF4U-1 in late May 1939. 1st run in 1937.

Turbocharging offered a number of advantages over mechanical supercharging (along with disadvantages). Mechanical superchargers take a lot of power to drive-I believe I've seen around 250hp discussed for the Merlin (correct me if I'm way off base-could well be). Lets assume for the sake of argument that that is true-for a net output of 1400hp, you need the engine to produce 1650 (to provide the power to drive the SC). Which means the engine is stressed more. The intake charge has to be compressed that much more, heating the charge more. The structure of the engine needs to be built around that. And of course you burn the fuel of a 1650hp motor, not a 1400hp one. The turbo, being powered from "waste" energy, doesn't have those issues-your 1400hp engine puts out 1400hp. Fuel economy is theoretically better. Mechanical SCs were typically gear driven with a transmission to shift gears (at least in 2-speed ones). That gave peak power at the point where you shifted into the next higher gear-with power dropping off as altitude increased (and boost of the fixed-speed SC decreased). Turbos were infinitely variable in terms of compressor output. (poorly worded, let me explain). The turbocharger's boost was set by a wastegate, which adjusted the exhaust "energy" driving the turbine blade. Fully closing the wastegate drove all exhaust gas through the turbo, opening it bypassed it. Boost was regulated by the degree to which the waste gate was opened. In theory at least, peak power could be maintained from sea level up to the maximum altitude where the turbo could still produce rated boost (assuming no other limitations, such as intercooling capacity).

Aircraft were pushed through air by thrust. The exhaust thrust was there on mechanically-supercharged engines, not so much on turboes.
If designer did it's homework right, the mechanically-S/Ced engine will make a good use of ram effect (pushing up the rated altitude by 4000-5000 ft), again the turbocharged engines will gain perhaps another 1500 ft in rated altitude - all figures for max speed. That is not some academic question, since the good use of ram effect = gain in power. See here - a gain up to 400 HP due to ram effect; almost 300 HP at 30000 ft. Calculate in the gain due to exhaust thrust (10 to 12% gain above 20000 ft, greater percentage as altitude increases = 'free thrust'), and a good 2-stage engine is no worse than a good turboed engine power-wise, while being easier to install, lighter, and requiring less volume = less drag.

 

[GregP]

Regarding post #25, Wuzak.

Allison did not develop the external auxiliary supercharger because they preferred their engines to be as modular as possible.

They developed their auxiliary supercharger that way because they tried and failed at least three times to get the government to fund the development of an integral, 2-stage supercharger and were contractually bound to deliver V-1710 engines per an approved drawing set. Since they were denied funding for that development, they developed a bolt-on supercharger that worked but was less than what might have been developed had the effort been approved and funded. Allison did not have deep pockets and even General Motors was reluctant to develop a major improvement on their own money that was repeatedly denied funding by the government. They were pretty sure, and I'd have to agree with them, that any such development would be eagerly used by the government, but no payment for development would be forthcoming.

The government didn't fund the Northrop F-20 either and didn't support it when Northrop tried to market it. In the end, that VERY promising aircraft's full development effort was funded by Northrop. Considering that event, I doubt very seriously that any current US warplane maker will EVER develop a warplane on their own, without at least some overt government interest. The French firm Dassault-Breguet learned all about that one when they developed the Super Mirage 4000 on company funds and nobody bought it. They flew it for years at airshows, and everyone was impressed, but not enough to be the first customer.

As an added note to post #61, the P-38 WAS the first 400 mph fighter in service. The XP-38 went over 400 mph in 1939. The F4U Corsair was the first single-engine, 400 mph fighter in development. The XF4U-1 went over 400 mph on 1 Oct 1940 at an average ground speed of 405 miles per hour (652 km/h) from Stratford to Hartford in the U.S.A. . The Fw 190A didn't see service until March 1941. They could just hit 400 mph when they weren't having engine problems. I believe the first Spitfire to exceed 400 mph in level flight was the LF Mk. IX, which did that in 1942. The Typhoons were still having structural failures in 1941 and were not reliable 400 mph aircraft. In fact, one broke up on a speed test and killed pilot Phillip Lucan in August 1942, which resulted in adding structural plates to the tail to prevent failure at high speed. Perhaps there is one or more that I am missing?

I am only talking about aircraft that went into military service, not prototypes or other "special" aircraft. We all know the Supermarine S-6 could hit over 400 mph. but it was hardly able to attack anything. It was sometimes hard pressed to survive a landing in a smooth harbor, much less kill anything. But id DID pave the way for the Spitfire that we all know and love.

 

[Admiral Beez]

If most superchargers weren't that good -- why did the USN go for two-stage and the USAAC just go for turbos

IDK if superchargers are good or not, but this Japanese Ki-87 one looks impressive.

 

[P-39 Expert]

IDK if superchargers are good or not, but this Japanese Ki-87 one looks impressive.

View attachment 564629

Well, it looks better than the one on the XP-39.

 

[GregP]

The F4U Corsair was nicknamed hose-nose because the cockpit was far back on the fuselage and the visibility wasn't very good over the nose.

The Ki-87 looks to be right in there with the Hose Nose as difficult to see to lead the target ... or land or take off or taxi in.

 

[fubar57]

I thought it was "Hog-nose"

 

[wuzak]

They developed their auxiliary supercharger that way because they tried and failed at least three times to get the government to fund the development of an integral, 2-stage supercharger and were contractually bound to deliver V-1710 engines per an approved drawing set. Since they were denied funding for that development, they developed a bolt-on supercharger that worked but was less than what might have been developed had the effort been approved and funded. Allison did not have deep pockets and even General Motors was reluctant to develop a major improvement on their own money that was repeatedly denied funding by the government. They were pretty sure, and I'd have to agree with them, that any such development would be eagerly used by the government, but no payment for development would be forthcoming.

The external auxiliary supercharger needed funding too.

 

[Shortround6]

the first 400mph fighter was the Hawker Hurricane
Set on a flight in 1938?
Carefully planned to make use of very strong tailwind.

The claim for the XP-38 is based on an estimate that Kelley made based on data recorded on the cross country flight that ended in the crash. There Is no evidence that the XP-38 ever flew close to 400mph before it was destroyed.

The record for the Corsair gives no details of how the start and stop times were recorded, it is about 48 miles from Stratford to East Hartford (if it was Hartford Airfield then it is a few miles shorter) but the P & W plant and airfield are in East Hartford. Other side of the river. the flight was in North East or North North East direction and guess which way the wind blows most of the time, no prize given for correct answer. The flight at 400mph should have taken about 7.2 minutes. Most accounts make no mention of altitude or any other details. (started at 20,000ft over Stratford and finished at 5,000ft over East Hartford? )Maybe they did do it on the straight and level but this was the aircraft.

The R-2800 X2 and R-2800 X4 engines used in the XF4U-1 (with it's short nose) were rated at 1850hp for take-off. and ran at 2600rpm max. any given altitude they were 100-150hp down on power from the production R-2800-8 engines used in the production F4U-1 aircraft.

 

[XBe02Drvr]

IDK if superchargers are good or not, but this Japanese Ki-87 one looks impressive.

Sure looks like a turbo-, not a super- charger to me!

 

[Admiral Beez]

Sure looks like a turbo-, not a super- charger to me!

Yes, that's why I was posting a reply to Zipper's note on turbos. But I could've been clearer, clearly.

 

[Deleted member 68059]

Also note that the US was just introducing 100/100 fuel (not 100/130) in the very late 1930s and 1940..

Your post is a good one, just pointing out that 100/130 IS basically 100 grade, its just the designation which was adopted after the US methods of fuel testing were improved mid-war to show octane at both lean and rich ratings. Fuel was tweaked all the way through the war, but essentially 100/130 is just 100 grade with an additional measurement step taken, to describe its performance more fully (130 is rich rating, 100 lean). Some alterations were needed to make sure that the rich and lean always met the new spec, but for the most part 100 = 100/130, they just only measured it at one point in the air/fuel scale before about early-1942 ish (not got the exact date sitting here right now), which was why it only had one number in the name.

The compositions changed more discerrnably with 100/150, and 115/145, which are actually chemically different fuels.

 

[Shortround6]

According to a few books I have U.S. 100 octane fuel in the late 30s or 1940 and ???? was 100 octane lean and anywhere from 97 to 103-4 "octane" running rich. Please remember that the US 100 octane fuel could contain NOT MORE THAN 2% aromatic compounds compared to the British 100 octane which could contain NOT LESS THAN 20% aromatic compounds at the time of the BoB. The British fuel was later measured at 100/115-120 depending on the batch. Once they knew how to measure the rich rating (or developed a scale to measure it with it was a lot easier to "tweak' the fuel to give the 100/130 performance level.
It is the aromatic compounds that give the much improved performance at the rich mixture conditions.

The US for short period of time specified a 100/125 fuel but standardized with the British on the 100/130 specification (which was changed twice to allow different amounts of lead in addition to other changes, the infamous "British fuel" in P-38s story.) perhaps some time in late 1941 or early 1942? the 3rd (?) specification for 100/130 is what caused the problem and it was issued in very late 1942 or early 1943. It allowed up to 4.6cc of lead per US gallon. the original 100/130 specification only allowed for 3.0 cc of lead per US gallon, the intermediate one allowed 4.0cc

The US often abbreviated the 100/130 fuel designation to 100 which doesn't help things.

The Books are By Samuel Heron who, as I am sure you know. invented/developed the performance number scale used to measure the fuel.

"Development of Aviation fuels" by S.D. Heron

and "Aviation fuels and their effects on engine performance" also by S.D. Heron. This last 'book" has a Navaer number of -06-5-501 and a USAF T.O. No 06-5-4

Neither book gives the full specification/s for the fuel.

and yes, the book specifically mentions that some batches of the early american fuel actually measured under 100 octane when tested under rich conditions.
There could be literally hundreds of different combinations of fuel, as long as the "blend" met the performance specifications (including vapor pressures and gum tests and so on) it was OK for purchase/use.

 

[Shortround6]

My Apologies gentlemen. I started to skim through the first book mentioned and it seems my memory isn't what I thought. I may be in error on a few points, I will try to read some more and get back to you.
for instance the British did have a short lived specification for 100/125 fuel before the 100/130.

 

[P-39 Expert]

Regarding post #25, Wuzak.

Allison did not develop the external auxiliary supercharger because they preferred their engines to be as modular as possible.

They developed their auxiliary supercharger that way because they tried and failed at least three times to get the government to fund the development of an integral, 2-stage supercharger and were contractually bound to deliver V-1710 engines per an approved drawing set. Since they were denied funding for that development, they developed a bolt-on supercharger that worked but was less than what might have been developed had the effort been approved and funded. Allison did not have deep pockets and even General Motors was reluctant to develop a major improvement on their own money that was repeatedly denied funding by the government. They were pretty sure, and I'd have to agree with them, that any such development would be eagerly used by the government, but no payment for development would be forthcoming.

The government didn't fund the Northrop F-20 either and didn't support it when Northrop tried to market it. In the end, that VERY promising aircraft's full development effort was funded by Northrop. Considering that event, I doubt very seriously that any current US warplane maker will EVER develop a warplane on their own, without at least some overt government interest. The French firm Dassault-Breguet learned all about that one when they developed the Super Mirage 4000 on company funds and nobody bought it. They flew it for years at airshows, and everyone was impressed, but not enough to be the first customer.

As an added note to post #61, the P-38 WAS the first 400 mph fighter in service. The XP-38 went over 400 mph in 1939. The F4U Corsair was the first single-engine, 400 mph fighter in development. The XF4U-1 went over 400 mph on 1 Oct 1940 at an average ground speed of 405 miles per hour (652 km/h) from Stratford to Hartford in the U.S.A. . The Fw 190A didn't see service until March 1941. They could just hit 400 mph when they weren't having engine problems. I believe the first Spitfire to exceed 400 mph in level flight was the LF Mk. IX, which did that in 1942. The Typhoons were still having structural failures in 1941 and were not reliable 400 mph aircraft. In fact, one broke up on a speed test and killed pilot Phillip Lucan in August 1942, which resulted in adding structural plates to the tail to prevent failure at high speed. Perhaps there is one or more that I am missing?

I am only talking about aircraft that went into military service, not prototypes or other "special" aircraft. We all know the Supermarine S-6 could hit over 400 mph. but it was hardly able to attack anything. It was sometimes hard pressed to survive a landing in a smooth harbor, much less kill anything. But id DID pave the way for the Spitfire that we all know and love.

Regarding the FW190 engine problems, can you elaborate? I have read many times about that engine running rough from captured 190 pilots, allied test pilots flying captured 190s and videos of 190s. This rough operation supposedly destroyed any "feel" coming up through the stick making normal stall warnings impossible to detect. Were these the engine problems you were alluding to, or were there more? Thanks.

 

[tomo pauk]

Regarding the FW190 engine problems, can you elaborate? I have read many times about that engine running rough from captured 190 pilots, allied test pilots flying captured 190s and videos of 190s. This rough operation supposedly destroyed any "feel" coming up through the stick making normal stall warnings impossible to detect. Were these the engine problems you were alluding to, or were there more? Thanks.

If I may. BMW 801C was pretty temperamental engine, the problems going up to the engines starting fire. There is a few pictures where the crewman stand with fire extinguisher at the ready next to the Fw 190s in 1941.
A quote from German Wikipedia:
Technische Berichte aus dieser Zeit zeigen, dass die Kühlprobleme des Motors BMW 801 C-2 immer noch nicht vollständig ausgeräumt waren. So kam es auch in dieser frühen Einsatzphase immer wieder zu Überhitzungen, insbesondere der unteren Zylinder des hinteren Zylindersterns, sowie gelegentlich zu Motorbränden.
that translates into:
Technical reports from this period show that the cooling problems of the BMW 801 C-2 engine were still not completely eliminated. In this early phase of operation, overheating occurred again and again, especially the lower cylinder of the rear cylinder star, and occasionally engine fires.

Despiet that, already by winter of 1941/42, the engine was succesfully tested with revs up to 2700 in high gear (previous limit was 2550 rpm) - here, pg.3.

The uprated 801D was also with it's set of problems. I don't want to copy/paste more than necessary, so if anyone wants to read, here is my understanding of it: link (about 801D having issues is at post #28 there)

 

[GregP]

Regarding post # 68, where do you get this stuff, Wayne? The XF4U-1 has been recognized as the first single-engine fighter to exceed 400 mph for nearly 80 years. You ain't gonna' change that because you have an agenda. The Planes of Fame actually flies the oldest Corsair in the world, and IT can hit 400 mph in a straight line if Steve Hinton would allow it.

The XP-38 has also been acknowledged as the first fighter to exceed 400 mph in level flight for going on 80 years and you ain't gonna' change that, either.

Better think again, buddy.

 

[Shortround6]

A lot of books and articles over the last 80 years claim the XP-39 did 390mph too.
Does that mean it is right?

The XF4U is iffy, maybe it did and maybe it didn't. however the details that would prove it one way or the other are lacking.
The difference in time over the distance flown between 395mph and 400mph is under 4.5 seconds out of 7.2 minutes. about 1%
Perhaps you have the details and would care to enlighten us?


As far as the XP-38 goes, when did it fly 400mph? what date? At what altitude?

There was a lot of public relations hoopla (propaganda) going on at the time in several different countries, let alone companies.

There were a number of planes 'designed" to fly at 400 mph (Typhoon being one of them), actually achieving 400mph was a bit harder.

My agenda is trying to figure out what really happened, not swallowing the propaganda.

 

[Shortround6]

A bit more on the XP-38
First flight Jan 27th 1939.
by the 4th flight Lockheed aerodynamicists had figured that elevator buffet at high speed was more than likely the result of high activity prop wash and a change in propeller rotation would solve the problem, (swap engines left to right). This apparently was NOT done before the prototype crashed. A One account says there was only about 5 hours in the air before the cross country flight. There were a few minor changes in some of the inlets and outlets

Note adjustable (?) scoop fir oil cooler under the nacelle. The slots for cooling the exhaust manifolds were supposed to have been changed and pictures of the crashed aircraft show a cover with a scoop. the air intakes are just under the wing flaps, the radiator scoops are on the the sides of the boom but the radiators are inside and the exhaust gas from the radiators goes out through the chutes (adjustable) in the top of the boom.
I have no idea if the later changes helped or hurt, just saying there were changes and at least one of them was in the first 5 hours of flight testing.

accounts are bit confusing, the engines were rated at 1150hp at 2950rpm to 25,000ft.
One account (or more? Daniel Whitney quoting Warren Brodie) says that after the loss of the XP-38 LT Kelsey prepared a report based on the partial data form the few hours of testing that had been completed. He estimated that when using 1150hp from both engines the XP-38 would have been able to cruise at 394mph at 20,000ft.

Now maybe it is just me and my agenda but I am not sure how you cruise at the full rated power of the engine?

The XP-38 was designed to fly at 400mph, that was the goal and the contract specification, the question is did the XP-38 ever fly that fast or was that left to a YP-38 at a later date?

 

[DarrenW]

We can take a look on the cross-section and cutaways of the F6F, in order to compare. Where the P-47 have had turbocharger and intercooler, the F6F have had basically nothing (bar radio and wires/bars for control of empenage). The F6F also featured long 'beard', needed for ram air intake, intercoolers and oil cooler. Add the thick belly, too, while the wings were of greater area by 11%.
On the other hand, the P-47 carried more fuel by a large margin (even before we facture in the P-47N), and more firepower.

The rather thick fuselage of the F6F can be attributed to Grumman's design philosophy and comments made by BuAer's Lt Cdr A. M. Jackson, who directed the manufacturer to raise the height of the cockpit even further than what was seen on the F4F. His goal (along with Grumman's) was to increase pilot visibility, where he's famously quoted as saying "you can't hit 'em if you can't see 'em". There was never a need to use the spare fuselage space for additional fuel because the airplane more than met the design criteria for range set forth by the US Navy.

 

[GregP]

There are thousands of civil aircraft today that cruise at relatively high altitudes (for normally aspirated engines) at what is essentially full power, at just a few rpm less than full rpm. One example is a Cessna 172. Max rpm is 2,650 and cruise is as high as 2,500 rpm.

Asking questions doesn't disprove the 400 mph claim. Shortround. Asking ME to prove it also doesn't disprove the claim. It isn't MY claim, it is widely reported by various publications at the time. As you can imagine, everyone knew there was a war about to happen, and they didn't routinely publish the exact figures to include the rpm, manifold pressure, or other flight data. The Germans, when Fritz Wendel set the new world speed record with the Me-209R on 26 Apr 1939 at 468.9 mph, ALSO didn't publish the rpm, manifold pressure, power developed,m or technical information about the aircraft.

If you want to make a claim about the P-38 NOT hitting the often-quoted 400 mph, the burden of proof is all on you, not me. I am not taking pot shots at you, Shortround, far from it. I'm just not getting involved in a rush to prove or disprove that the two fighters widely regarded as being the first to hit 400 mph did or didn't do it. I have no access to original period material and also do not have the time to dig into it at this time. It is more of "don't have time" than "don't have interest."

But, please pursue it if you HAVE the time and interest. You posts are generally well thought out and I don't question your ability to do so. I am of the opinion that original data about the XP-38 will prove very difficult to find, but it could be out there. I predict it will be easy to claim the XP-38 and XF4U didn't make 400 mph at this late date, but it will be difficult to prove. Good luck to you!