XP-39 and the Claims

Shortround6 · Apr 17, 2020

Greg, please go over the time line for the P-38. There are two different issues with fuel at different times.

The early US fuel had little or no aromatics, this was in 1940 or so, If you want 100/125 or 100/130 you have to use aromatics. At least if you want to make fuel on a large scale.

When the Americans started to use the 20% (max it could be less) fuel there were all sorts of problems, including dissolving rubber parts in the fuel systems and self sealing tank liners, Jetting may very well have been a problem but the other problems were bigger. ALL of the problems were eventually solved. This is in regards to the early 100/130 fuel.

Early 100/130 fuel was limited to 3.0ccs of lead per US gallon and while there could be 20% aromatics in the fuel the types of aromatics may have been restricted. Use of aromatics is also restricted by the standard of BTUs per pound of fuel (18,700?) and most or all of the aromatics are lower than that so if you use too much of the aromatics in the blend you have somewhat lower than requirement heat value per pound.

At some point in 1942 (early?) they decide that if they use 4.0 cc of lead per US gallon they can get a lot more 100/130 fuel from the same amount of base stocks so that is approved (after testing to see about lead fouling) and in late 1942 or early 1943 they decide they need a lot more 100/130 fuel and the way to do that is to allow 4.6cc of lead per gallon and allow more of the heavy aromatics but still not exceeding about 20% total. everybody knew that this "new" 100/130 might cause problems and the engine makers began testing it with the engines at the beginning of 1943. Allison found they did have troubles under certain conditions and started working on a new intake manifold in the spring of 1943. It was being fitted to engines and P-38s in either November or December of 1943 but since it takes weeks to get a P-38 From California to Europe all the planes in theater had the old manifolds.
There may have been bad batches of fuel supplied to units in England, or batches of fuel that gave more trouble in P-38s than other aircraft.

However the constant referral to "British" fuel may be a bit unfair. The Entire 8th and 9th Air Force were using British fuel? America was shipping no 100/130 fuel to England at this time?

In any case, the switch from US 100 octane 2% aromatic fuel to the 20% aromatic fuel happened 1-2 years before the P-38 was used as escort by the 8th Air Force in 1943/44.
In fact the British and Americans were on their 3rd joint specification for fuel (1=100/125, 2=100/130 3cc lead , 3=100/130 4cc lead) using 20% aromatic fuel when the P-38s were England before being sent to North Africa at the end of 1942.

What the US was doing with old stocks of the 100 octane fuel with 2% aromatics at this time I have no idea, using it for training? sending it to engine makers to run in the engines with?
Was it all used up by the end of 1942? I don't know and won't guess. There is certainly a possibility that engines were being jetted wrong.

There is also the fact that engines that were used for training in the US were jetted for (and used different ignition timing) to suit them for 91 or 91/96 fuel used the training commands. Strict track was supposed to be kept of where these engines went but........ who knows????

There is certainly room for confusion as there were so many different fuel blends all with the same "name"

Venturi · Apr 17, 2020

Single stage V-1710: options for improvements?

I like this post.

tomo pauk · Apr 17, 2020

Venturi said:
Single stage V-1710: options for improvements?

I like this post.

Cheers, Venturi.
Note that a lot of points (all of them?) listed there were not substantiated by a source.

Venturi · Apr 17, 2020

I don't think I see many sources posted on here. If you were made to post with reference sources such as in the scientific literature, then surely less unsubstantiated claims would be routinely made. But also, those who have knowledge and not too much time, would be posting less.

Cheers

tomo pauk · Apr 17, 2020

Venturi said:
I don't think I see many sources posted on here. If you were made to post with reference sources such as in the scientific literature, then surely less unsubstantiated claims would be routinely made. But also, those who have knowledge and not too much time, would be posting less.

Cheers

I'll wish you a good day then.

Shortround6 · Apr 17, 2020

Sources include.

Development of aircraft engines by Robert Schlaifer
Development of Aviation fuels by S.D.Heron
Aviation fuels and the effects on Engine Performance S.D. Heron
this last is also Navaer-06050501/USAF T.0. No. 06-5-4

and a few other books that mention aviation fuel.

gjs238 · Apr 17, 2020

varsity07840 said:
Climb rate aside, what was the max speed of the P-39N vs. the P-47D, P-51B/D/K, P-38J/L at the altitudes required for bomber escort? What was the P-39N's radius of action after getting to escort altitude? With regard to weight savings on earlier models, given the P-39's poor air to air armament, one would think that removal of the 37mm gun the archaic sychronised .50s and the would be the first step. But that wasn't possible because the aircraft was designed around nose armament particularly the cannon. Removal would affect the cg, just the way expended ammo did. Removal of the nose guns on the P-40 caused no such problems. So, what you would end up with is two slow firing .50 cal guns and a cannon that was totally unsuited for fighter vs fighter combat. Yes, the Russians made good use of the P-39 in that configuration, but I doubt if you could have found an American pilot of that era who would prefer to fight with that type of armament.

RE: removal of the 37mm gun

From Bell P-39 Airacobra - Wikipedia
In 1940, the British Direct Purchase Commission in the U.S. was looking for combat aircraft; they ordered 675 of the export version Bell Model 14 as the "Caribou" on the strength of the company's representations on 13 April 1940. The British armament was two nose-mounted 0.50 in (12.7 mm) machine guns, and four 0.303 in (7.7 mm) Browning machine guns in the wings; the 37 mm gun was replaced by a 20 mm (.79 in) Hispano-Suiza cannon.

varsity07840 · Apr 17, 2020

GregP said:
Never said British fuels were to blame for late-model P-38 issues, Wayne, and you damned well know it. We've had this conversation before. The early P-38's had issues with the intake that was fixed with the turbulator-venturi inside the intake. They had issues with the 20% aromatic fuels. The fix took some 6+ months to iron out because the issue wasn't recognized at first. They had issues with the cockpit heater. The fix was a simple electric heater in the cockpit. And we had issues with training. That took experience and not flying into a combat zone with the engines at low cruise and the gunsights cold. They never DID fix the low critical Mach number.

You really need to stop trying to put words in other people's mouths, at least mine. If I'm trying to say something, I'll say it. If you want to say something, say it and take credit for it, but don't attribute it to me, OK?

As for when we made Merlins, the XP-51B didn't fly until Nov 1942 and the P-51B/C wasn't in production until after that. Meanwhile, the Merlins that were built here were built to British specifications until the USAAC/F started acquiring the P-51B/C. The P-51As didn't cause any issues at home because we were flying U.S. gasoline and didn't see the issue at all. There were many issues with making Merlins in the U.S.A., but the aromatic fuel thing wasn't really one of them. The Merlin issues were largely with transferring production and associated drawings ... normal start-up things for a new factory tooling up for an existing design.

Did you or did you not say that there was problems with the Allison in Europe relative to British fuel. Where did I say that you said that British fuel was responsible for the P-38's problems.

GregP said:
Never said British fuels were to blame for late-model P-38 issues, Wayne, and you damned well know it. We've had this conversation before. The early P-38's had issues with the intake that was fixed with the turbulator-venturi inside the intake. They had issues with the 20% aromatic fuels. The fix took some 6+ months to iron out because the issue wasn't recognized at first. They had issues with the cockpit heater. The fix was a simple electric heater in the cockpit. And we had issues with training. That took experience and not flying into a combat zone with the engines at low cruise and the gunsights cold. They never DID fix the low critical Mach number.

You really need to stop trying to put words in other people's mouths, at least mine. If I'm trying to say something, I'll say it. If you want to say something, say it and take credit for it, but don't attribute it to me, OK?

As for when we made Merlins, the XP-51B didn't fly until Nov 1942 and the P-51B/C wasn't in production until after that. Meanwhile, the Merlins that were built here were built to British specifications until the USAAC/F started acquiring the P-51B/C. The P-51As didn't cause any issues at home because we were flying U.S. gasoline and didn't see the issue at all. There were many issues with making Merlins in the U.S.A., but the aromatic fuel thing wasn't really one of them. The Merlin issues were largely with transferring production and associated drawings ... normal start-up things for a new factory tooling up for an existing design.
[
You really need to stop trying to put words in other people's mouths, at least mine. If I'm trying to say something, I'll say it. If you want to say something, say it and take credit for it, but don't attribute it to me, OK?

As for when we made Merlins, the XP-51B didn't fly until Nov 1942 and the P-51B/C wasn't in production until after that. Meanwhile, the Merlins that were built here were built to British specifications until the USAAC/F started acquiring the P-51B/C. The P-51As didn't cause any issues at home because we were flying U.S. gasoline and didn't see the issue at all. There were many issues with making Merlins in the U.S.A., but the aromatic fuel thing wasn't really one of them. The Merlin issues were largely with transferring production and associated drawings ... normal start-up things for a new factory tooling up for an existing design.

Did you or did you not say Allisons had detonation problems attributed to British fuel? No, you didn't say British fuel was responsible for P-38 issues, and I didn't say you did. You note the detonation problems and suggested that issues with British fuel were resolved before the Packard Merlin went into production, so Merlins produced weren't mis jetted in the factory. I take that to mean that based on experiences with the Allison, Packard took measures to ensure that they didn't have the same problems, what you refer to as mis jetting. That's just not the case, as I pointed out since V-1650s were in production well before the P-38H and J flew their first missions in Europe. How is that putting words in your mouth?

Venturi · Apr 17, 2020

Nose-mounted armament is inherently superior to wing mounted, from multiple points of view. Centerline-mounted weapons have no horizontal convergence issues, additionally wing-mounted weapons have significant dispersion when under any g loading which the centerline weapons do not Wing mounted weapons also increase the aircraft's rotational intertia, (about the longitudinal axis) leading to slower aileron response. Yes, close inboard wing mountings reduce these problems, but only serve to prove the point.
Advantages with wing mounted weapons include greater space for multiple weapons and associated ammunition, less adverse CoG effects when ammunition is expended (variable), and no need for propeller synchronization.
By the way, the Germans found no issues with RoF reduction in centerline synchronized MG17 mounts... RoF somewhere around 1200RPM.

varsity07840 · Apr 17, 2020

gjs238 said:
RE: removal of the 37mm gun

From Bell P-39 Airacobra - Wikipedia
In 1940, the British Direct Purchase Commission in the U.S. was looking for combat aircraft; they ordered 675 of the export version Bell Model 14 as the "Caribou" on the strength of the company's representations on 13 April 1940. The British armament was two nose-mounted 0.50 in (12.7 mm) machine guns, and four 0.303 in (7.7 mm) Browning machine guns in the wings; the 37 mm gun was replaced by a 20 mm (.79 in) Hispano-Suiza cannon.

The 37mm gun was replaced by a 20mm in the "Caribou"/Airacobra/P-400 and the P-39D1. That's a given. The nose cannon wasn't eliminated. It was replaced with a different one in those versions, again because cg issues demanded a gun or ballast be installed. In that case, you might as well install a gun.

varsity07840 · Apr 17, 2020

Venturi said:
Nose-mounted armament is inherently superior to wing mounted, from multiple points of view. Centerline-mounted weapons have no horizontal convergence issues, additionally wing-mounted weapons have significant dispersion when under any g loading which the centerline weapons do not Wing mounted weapons also increase the aircraft's rotational intertia, (about the longitudinal axis) leading to slower aileron response. Yes, close inboard wing mountings reduce these problems, but only serve to prove the point.
Advantages with wing mounted weapons include greater space for multiple weapons and associated ammunition, less adverse CoG effects when ammunition is expended (variable), and no need for propeller synchronization.
By the way, the Germans found no issues with RoF reduction in centerline synchronized MG17 mounts... RoF somewhere around 1200RPM.

Any synchronized gun will have a reduced rate of fire. The MG17 had a 1200 RPM rate WITHOUT synchronization. Axis fighters that retained synchronized weapons did so because their original wing designs prevented added guns or larger frame and or caliber guns from being installed without major redesign. The Bf-109 is a perfect example as was the P-39 for the allies. The Idea of a gondola mounted .50 on an American fighter in 1943 is ridiculous. And they were combined with synchronized nose guns and mandated cannon due to cg issues. The Germans and Russians did have better success with centerline cannon because their guns had a much better ROF.

gjs238 · Apr 17, 2020

varsity07840 said:
The 37mm gun was replaced by a 20mm in the "Caribou"/Airacobra/P-400 and the P-39D1. That's a given. The nose cannon wasn't eliminated. It was replaced with a different one in those versions, again because cg issues demanded a gun or ballast be installed. In that case, you might as well install a gun.

Uh, yeah, that's what it says.

wuzak · Apr 17, 2020

GregP said:
Never said British fuels were to blame for late-model P-38 issues, Wayne, and you damned well know it. .

Maybe you didn't say it, but others have, evidenced by the article I quoted above.

GregP said:
As for when we made Merlins, the XP-51B didn't fly until Nov 1942 and the P-51B/C wasn't in production until after that. Meanwhile, the Merlins that were built here were built to British specifications until the USAAC/F started acquiring the P-51B/C. The P-51As didn't cause any issues at home because we were flying U.S. gasoline and didn't see the issue at all. There were many issues with making Merlins in the U.S.A., but the aromatic fuel thing wasn't really one of them. The Merlin issues were largely with transferring production and associated drawings ... normal start-up things for a new factory tooling up for an existing design.

To be clear, Packard Merlins, at least the main production variants, were always built to Rolls-Royce specifications, and their power ratings were the same as the equivalent Rolls-Royce model.

Venturi · Apr 17, 2020

varsity07840 said:
Any synchronized gun will have a reduced rate of fire. The MG17 had a 1200 RPM rate WITHOUT synchronization. Axis fighters that retained synchronized weapons did so because their original wing designs prevented added guns or larger frame and or caliber guns from being installed without major redesign. The Bf-109 is a perfect example as was the P-39 for the allies. The Idea of a gondola mounted .50 on an American fighter in 1943 is ridiculous. And they were combined with synchronized nose guns and mandated cannon due to cg issues. The Germans and Russians did have better success with centerline cannon because their guns had a much better ROF.

I looked it up, since you're so stuck on this one point and did not address anything else. The unsynchronized MG17 rate of fire is 1100rpm. Synchronized is 1000rpm. Significant drop? Hardly.

I guess you're not counting the FW190A series or Bf109E, are you?

Your original argument was that the P-39 nose mounted armament was insufficient. I think both the Soviet success with the type as well as general principles which I illustrated above, say otherwise.

P-39 Expert · Apr 18, 2020

varsity07840 said:
Climb rate aside, what was the max speed of the P-39N vs. the P-47D, P-51B/D/K, P-38J/L at the altitudes required for bomber escort? What was the P-39N's radius of action after getting to escort altitude? With regard to weight savings on earlier models, given the P-39's poor air to air armament, one would think that removal of the 37mm gun the archaic sychronised .50s and the would be the first step. But that wasn't possible because the aircraft was designed around nose armament particularly the cannon. Removal would affect the cg, just the way expended ammo did. Removal of the nose guns on the P-40 caused no such problems. So, what you would end up with is two slow firing .50 cal guns and a cannon that was totally unsuited for fighter vs fighter combat. Yes, the Russians made good use of the P-39 in that configuration, but I doubt if you could have found an American pilot of that era who would prefer to fight with that type of armament.

Max speed of the P-39N at 25000' was 370-375mph depending on the test. Competitive with the 109G and 190A but certainly well below the two stage P-38, P-47 and P-51.
Radius of action at 25000' was about like a Thunderbolt when each plane had the 110gal drop tanks available in the ETO at that time, on the order of 350-400 miles at about the same speed 280mph TAS. Please remember that the P-39N had completed its production run before the P-47 got into combat in May '43.

Regarding armament, the 37mm cannon wasn't nearly as bad as most people think. Trajectory drop was within 21" of the twin .50s at 400 yards and that was about the outside limit for air-to-air. There were separate buttons on the stick for the .50s and the cannon so you could use just the cannon beyond 400 yards. Rate of fire at 2.5 rounds per second wasn't bad considering the destructive power. One hit was enough to bring down most anything with two engines or less. Reliability was spotty until the L model in mid '42 introduced the little exit vents just aft of the reduction gear. These exhausted the warm cockpit air that was ducted up from the rudder pedal wells onto the breeches of the cannon and twin .50s. This kept the guns from freezing at altitude which was the main cause of jams/interruptions.

According to what I have read AAFpilots were pretty evenly split between preference for the 37mm and 20mm. Biggest problem with the 20mm was only 60 rounds in the drum which was about 6 seconds of firing time. Spitfires held 120 rounds per gun and an increased magazine for the American 20mm would have been the ideal solution but that was not to be.

The Russian solution was to delete the useless .30 caliber wing guns and the IFF radio using the weight savings to further improve performance. They maintained that the 37mm cannon was much more reliable than the 20mm cannon. They also reportedly used the twin .50s against fighters and the 37mm cannon against bombers. Four of the top five Russian aces and scores of 20+ victory aces flew the P-39 and were enthusiastic proponents.

eagledad · Apr 18, 2020

Venturi

While the ROF of the MG 17 did not suffer too much from synchronisation, it appears the Brownings did. According to Anthony Williams,

"It is however difficult to find many actual examples of the effects of synchronisation on rate of fire. The Soviet 12.7 mm UBS was stated to fire at 800 rpm instead of 1,050; a reduction of 24%. It also appears that the ShKAS was slowed from 1,800 to 1,300 – 1,500 rpm (17 – 28%) depending on the installation, and the ShVAK from 800 to 700 (12.5%). Some installations appeared to be even worse than this; tests of cowling-mounted .50 M2 in US aircraft revealed RoFs of 400–450 rpm, and anecdotal reports of the Japanese 12.7 mm Ho-103 (which shared the M2's Browning short-recoil 7 mechanism) indicate a similar problem."

Williams gives a normal ROF for the ,50 Browning M2 at 13 rounds per second. (780 rpm).

FYI

Eagledad

Source: http://quarryhs.co.uk/Synchro.pdf

varsity07840 · Apr 18, 2020

Venturi said:
I looked it up, since you're so stuck on this one point and did not address anything else. The unsynchronized MG17 rate of fire is 1100rpm. Synchronized is 1000rpm. Significant drop? Hardly.

I guess you're not counting the FW190A series or Bf109E, are you?

Your original argument was that the P-39 nose mounted armament was insufficient. I think both the Soviet success with the type as well as general principles which I illustrated above, say otherwise.

In the cases of the FW190A and Bf109E neither design was able to accommodate increased/improved wing armament to replace the MG FF cannon in subsequent models. I acknowledged that the Soviets had success with the P-39, but apparently the AAF was of a different mindset since the P-39 was the last nose gun fighter to see combat. One has to wonder why Bell pursued the same design in the P-63.

drgondog · Apr 18, 2020

varsity07840 said:
In the cases of the FW190A and Bf109E neither design was able to accommodate increased/improved wing armament to replace the MG FF cannon in subsequent models.

????? the 109K-6 with Mk 108 was a 'pretty good improvement' and so was the MG 131/20 underwing. As for the Fw 190, the MG FF was replaced by MG 131/20 or Mk 108 internal to the wing.
I acknowledged that the Soviets had success with the P-39, but apparently the AAF was of a different mindset since the P-39 was the last nose gun fighter to see combat. One has to wonder why Bell pursued the same design in the P-63.[/QUOTE

Center of Gravity issues dictated the heavy gun up front, or as previous poster noted 'load it up with ~300+ pounds of useless ballast'

Shortround6 · Apr 18, 2020

varsity07840 said:
One has to wonder why Bell pursued the same design in the P-63.

Because work started on what would become the P-63 in Feb 1941. They changed the airfoil (tried for laminar flow), lengthened the fuselage to accommodate different engine or engine with 2 stage supercharger, They moved the wing and got rid of the CG problem/s or at least the worst of them.

Somewhere in there is the P-39E and P-76 This is all started before the P-39 actually sees combat or even regular squadron service (not counting the YP-39s)

For some reason both Bell and the AAF were enamoured with the 37mm cannon and while the P-39 may have been the last US fighter with nose armament (need better definition of that) to see combat in US service (Russian P-63s?) there were a number of projects that used the 37mm cannon, sometimes in multiples. XP-54 and XP-67 come to mind offhand.

varsity07840 · Apr 18, 2020

Shortround6 said:
Because work started on what would become the P-63 in Feb 1941. They changed the airfoil (tried for laminar flow), lengthened the fuselage to accommodate different engine or engine with 2 stage supercharger, They moved the wing and got rid of the CG problem/s or at least the worst of them.

Somewhere in there is the P-39E and P-76 This is all started before the P-39 actually sees combat or even regular squadron service (not counting the YP-39s)

For some reason both Bell and the AAF were enamoured with the 37mm cannon and while the P-39 may have been the last US fighter with nose armament (need better definition of that) to see combat in US service (Russian P-63s?) there were a number of projects that used the 37mm cannon, sometimes in multiples. XP-54 and XP-67 come to mind offhand.

Last single engine fighter with synchronized nose guns.

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