Improvements to the P-39

Just Schmidt said:

On the other hand an extensive redesign could also be problematic. The moving forward of the pilot might not only create trouble for the fuselage mounted armament, but also for the nose wheel and the transmission from the engine drive shaft. I don't have my books 7cutaway here, and haven't tried modeling a solution, but I am not optimistic on that count.

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Trainer versions of the P-39 had a forward cockpit.



I believe these were modified from standard P-39s.

My thought is that they could mount the guns either in the wing, or in the fuselage flanks, synchronised.

that is the first I have ever seen that configuration!!

Ditto! Not as "clean" of a design as the single seat version...

Looking at this graph, there was a significant lack of power in two nominally equally powered aircraft, the P-39N and P-40N - the - 39 has maybe 6-8% less HP. The location of the ram air intake is really a bad choice? Still, the P-39 is faster by 20 mph, almost making 400 mph. Granted, 385 mph is the figure more often encountered.
Another thing about the V-1710s - late 1-stage engines were rated to 1480 HP on the P-51A and P-40N, but just 1410 HP on the P-39, not sure why.

Also this report (pdf), the P-39C making unbelievable 406 mph!! A curious thing is that it's engine's supercharger is driven via 9.6:1 gearing - an experimental engine sub-version preceeding the series-produced engines with such gearing?

A collective 'thank you, Mike' is mandatory

I've never seen any Allison rated at 1,480 Hp normal, military, or WER, so that makes me curious.

I thought I might share a file I put together about Allisons. Find it attached. If you spot any errors, I'd appreciate hearing about it. As most of you undoubtedly know, I'm not a candidate for the world's best typist. The sheets are protected, but without a password. If you choose "Unprotect Sheet," it will do so.

I concentrated on the E, F, and G series since the early Allisons aren't all that interesting to me. I say not all that interesting only because there are so few running.

I'm not a fan of the long skinny nosecase ... too delicate. Most all of the ones I worked on were either E or F engines. We did work on a couple of G-series, but they weren't stock. We didn't use any of the original smooth intake manifolds, either. We used on t the manifolds with the turbulators in them ... the ones that corrected the original mixture issues. I've seen the very early intakes manifolds (actually a complete set), and don't know how they work in service, but they LOOK good.

If I were flying an Allison-powered warbird today, the internals would all be -100 series components regardless of the dataplate. That is, I'd want a 12-counterweight crankshaft, late intakes, late lifters / distrubutors, etc. If I had my choice, it would be a V-1710-111, which is an F30R or the E-series equivalent if I wanted to fly a drivehshaft airplane. I'd probably stick with an F since the supply of spare parts for the driveshaft units is rather low.

I know one fellow, Bob Deford, who has a Yancey Allison in a Marcel Jurca Spitfire replica and he outperforms the Rolls-powered real Spitfires down low, which is where most of the warbirds fly today. Actually he SHOULD since the Jurca kit has a wood wing and Bob's finish is better than any real Spitfire wing I ever saw.

Here is Bob's airplane:



The cockpit has a stick assembly and cockpit bits from a real Spitfire and the fit and finish of Bob's work is beyond excellent.

In the attached spreadsheet, check out the tab titled "Specifications." It shows most of the Allisons ever built or put down on paper as a serious proposal. Allison actually proposed an integral 2-stage engine to the USAAF on two or three occasions. I know they proposed it twice and have heard three times from a couple of sources, but I make no claim about the third proposal as I have never seen primary source for it.

I've seen the proposal for one of them (well, 2 sheets of it anyway) and I don't know which one it was (first or second, etc.). It wasn't designed or assigned a series number because the proposal was turned down, but they DID consider it. The proposal I saw used a standard V-1710 case / nose (E or F), and had a new accessory case (with the superchargers, starters, generators, etc.). Since I didn't see an intercooler, I am assuming an upstream pre-cooler or ADI or both. Might or might not have been needed, depending on the level of boost.

However, if your primary customer says no, and you are involved in wartime production of running engines that sell, you don't assign much manpower to it if you are small company, even if you like the idea, unless management is willing to fund the effort and the manpower is available. In a small company, design manpower is usually always accounted for and isn't "freely available." The Allison had to have a few issues worked out, and that might well have been the case for a 2-stage V-12, too. Perhaps the thought of a prolonged development is what prompted the USAAF to say no in the first place, I don't know.

While I was at Joe Yancey's we had visits from several former Allison employees, but never discussed the potential 2-stage engine. It was more of a visit by them to see the engines they used to work on than a history lesson for us.

We DID overhaul the Allison engine in Art Arfons' old Green Monster dragster, and Joe fabricated the adapter plate for the clutch and gearbox. When I say "We," I mean Joe. I helped with assembly / disassembly, part prep, cleaning of parts, and some assembly / painting (engine painting, not car painting). Joe and Pat Yancey did the engine building and Pat made the new wiring harness. Her wiring harnesses almost qualify as works of art in their own right.

Here is a pic of that car.





A friend of mine, Bob Velker, and I made the fin and the fin attach setup. It was fun! Basically, the original fin was a swept fin from some unknown jet fighter of the time, and all we had to go on was a cardboard outline of the profile shape. So, if you take a typical swept jet fighter fin, reverse it and then stand it up on the rudder hinge surface, you get the shape above. It LOOKS like an F-86 fin to me, but I didn't check it with the template. We just took it and ran with it. We scratch-built everything from 0.040" 2024-T3 Aluminum and it actually came out straight and stood up at 90° the FIRST time we mounted it. Talk about serendipity, we had it that day. Since it was never going to fly, we only put in 4 - 5 ribs (I forget which), but it still came out strong and stiff.

The owner runs it at vintage drag races and "cacklefest" events. You can probably tell it uses P-38 exhaust logs.

This pic is from a Planes of Fame airshow, as you can probably tell from the aircraft in the background. That's our Northrop N9M-B and P-40N. The Green Monster owner (John Rolley) was coming over for a drag race event about the same time and agreed to display it at the airshow next to the VIP tent. John Rolley did a great job restoring this car! He runs a quality, first-class race team with vintage digger dragsters and the occasional land speed record run on the salt flats.

I would like some more info on that dual 39....when were they built. I know 39 outfits that were in place before ww2 and have read stuff read by the guys who were in them. none of them ever mentioned their first check ride or familiarization ride in a dual control ac. from all accounts I have read they went from an AT6 right into a single seat 39 and were on their own. that plane does intrigue me...I don't have the time to research it at the moment

If there was ever a gorgeus aircraft, it is surely Spitfire.
The E-19 (V-1710-85) is with 9.60:1 S/C ratio, but I indeed congratulate you for the effort

The -81 rated at 1480 HP @ WER; note that same power is listed on the Mike's side in several instances:

bobbysocks said:

I would like some more info on that dual 39....when were they built. I know 39 outfits that were in place before ww2 and have read stuff read by the guys who were in them. none of them ever mentioned their first check ride or familiarization ride in a dual control ac. from all accounts I have read they went from an AT6 right into a single seat 39 and were on their own. that plane does intrigue me...I don't have the time to research it at the moment

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From https://en.wikipedia.org/wiki/Bell_P-39_Airacobra

By the time of the Pearl Harbor attack, nearly 600 P-39s had been built. When P-39 production ended in August 1944, Bell had built 9,558 Airacobras, of which 4,773 (mostly −39N and −39Q) were sent to the Soviet Union through the Lend-Lease program. There were numerous minor variations in engine, propeller, and armament, but no major structural changes in production types, excepting a few two-seat TP-39F and RP-39Q trainers. In addition, seven went to the U.S. Navy as radio-controlled drones.

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They were based on later model P-39s.

Thanks Tomo!

I think I might need to add a WER column to my specification page in the attached spreadsheet above. The data source I used was from Allison and they didn't give all of the ratings, apparently. They gave takeoff, one altitude rating, and continuous. The thing is, 57 inches is about the max rating for almost all of the Allisons in stock configuration, and the Allison table gave a lot of data ... but no simultaneous MAP numbers to go with them.

I can only be frustrated at the necessity to look at multiple sources to get complete data. Keep up the great references!

One last comment, I went back and added some text to the effect that the sheets are protected, but I didn't use a password ... on purpose. So if you go to Excel Home tab (Excel 2010+) and choose Format, Unprotect Sheet, it will unprotect and you can make any edit changes you like.

I protected it just to prevent inadvertent edits on my own part since I'm such a great typist.

From Bell P-39Q Airacobra

A few P-39Qs were modified into two seaters with dual controls for use as advanced trainers under the designation RP-39Q (redesignated TP-39Q after 1944). All armament was removed. The second cockpit was sort of "grafted" in front of the original cockpit, and the pilot in this extra cockpit sat under a hinged canopy. The extra cockpit was fitted with only rudimentary controls. The original cockpit retained the same controls and instruments as the standard P-39Q. The instructor sat in front in the extra cockpit, the student in the original cockpit, and the two communicated via an intercom telephone. The tail fillet was enlarged and an additional shallow ventral fin was fitted under the rear fuselage. These modifications produced one of the most grotesque aircraft I have ever seen. . The first example, converted from P-39Q-5 42-20024, was rolled out for the first time on September 16, 1943. It was designated TP-39Q-5. 12 two-seater fighter trainers were converted from P-39Q-20s, and were designated RP-39Q-22. The ventral strake was somewhat different in shape from that of the ventral fin of the original TP-39Q-5. Serials were 44-3879, 3885/3887, 3889, 3895, 3897, 3905, 3906, 3908, 3917, and 3918.

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The V-1710-35 (E-4) was not very good at altitude, at least in the time of introduction, not capabe to attain the 12000 ft with 1150 HP (no ram); situation changed with -63 (E-6) that used, among other improvements, the rotating guide vanes prior the impeller.

Table from Oct 1941, not sure when/if the engines were modified to the new standard aferwards:

by sept 43 everyone I know that trained and flew 39s were on their way to England. thanks to everyone for the info

That engine wasn't used much I'd bet. If you look on the 3rd line, the specs are with backfire screens installed. From many conversations with WWII Allison crew chiefs, Joe Yancey has been apprised numerous times that these were rather instantly removed when the planes got to the front lines. After the pilot knew how to start an Allison, they weren't needed.

Backfire screens were needed in pilot training, but not once you had any experience to speak of. Some time back I posted a pic of one that I have, but here's a re-post.



Looking at it, you can imagine the back pressure it would cause ... and it sits right in the intake manifold to cylinder head junction, so it's right in the way of incoming air-fuel mixture. I believe a pretty decent drop in power would be anticipated ...

But, again, I appreciate the spec page. Most that I see agree, but the one earlier is not an Allison page, it is from a USAAF manual, and I hadn't seen it before. It doesn't disagree with Alison's spec, but it gives more data points, which is always welcome.

I know Joe can get about 2,850 HP or so to the prop if he builds a racing Allison for Reno using the stock supercharger and G-series rods. The extra power comes from added rpm coupled with more boost (up to 110" MAP). There might be more there with a new cam and a few other goodies, but finding out requires a bucket of money and someone who wants to actually DO something with the resulting engine. Doing it for fun isn't in the cards or the bank account.

drgondog said:

Placing a 'saddle' extra fuel tank between back of pilot's seat and in front of the Allison is impossible without altering airframe.

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Obviously there would be some alterations required to the airframe to have the forward cockpit solution, but based on the 2 seat conversions I should think it would be quite possible.

The idea of putting a fuel tank between cockpit and engine is to increase capacity and have that extra capacity as near as possible to the CoG. The extra capacity would not be huge, but useful.

Tomo's mock-up of what such an aircraft might look like:

tomo pauk said:

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GregP said:

...
But, again, I appreciate the spec page. Most that I see agree, but the one earlier is not an Allison page, it is from a USAAF manual, and I hadn't seen it before. It doesn't disagree with Alison's spec, but it gives more data points, which is always welcome...

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The table comes from the document attached, along with tables for the rare -37 engine, as well as for the prolific -39 (P-40, P-51) where altitude data is with ram. Same data is repeated in this blurred, yet very usable table about P-39s and early P-63s.

edit - hmm, 11800 ft is there for -35 and -63 - end of edit

On the other hand, the graph on the Vee's, pg. 255, shows 1150 HP indeed at 12000 ft, dated 10th Jan 1941. Altitude performance decreased with backfire screens installed, that allowed for greater boost in lower altitudes?
Note that I'm going after what was done back then, not 50-75 years later

That really IS a very usable table, Tomo.

Once again you are the Galactic Overlord of Finding Interesting Stuff.

The screens robbed performance everywhere since they restricted the intake. What they did that was beneficial was to help prevent neophyte pilots from backfiring the engines and blowing out head gaskets on startup from use of improper starting technique.

Personally, after 3 - 4 startups, I was having no trouble with it myself. You operate the manual fuel pump for 2 - 4 pumps until fuel runs out for about 1 second, put the mixture in auto-rich, run the throttle open about 1 inch, run the starter until it gets as fast as it will, and engage the solenoid. When it catches, release the starter, set the rpm at about 850 - 1,000, and wait for the temps to come up. Once near the green you can increase to 1,500 rpm or so and wait until warm enough for normal operation. That can all be done on the engine stand easily.

Setting the mixture is correspondingly easy. See the middle 2 pages below.



It LOOKS complicated but is easy on the engine stand. Moving the mixture adjusts the flame easily and quite clearly. Once proper, look at the EGT/cylinder head temp and you can probably set it by EGT/CHT just as well after that, especially if you are at the same altitude. I'd think you would use the recommended method from the manual since seeing the exhaust might not be simple in a P-39 and is impossible in a P-38.

It is simple in a P-40; just look at the exhaust (in daylight, anyway). Might not want to do that at night.

A few considerations for this "plan".
A .50 cal machinegun was 72.4 in long from muzzle to rear of buffer and that is with the 36in aircraft barrel. Front of the ammunition feedway was about 41-42in from muzzle.
.50 cal ammo is large.

Each ammo container on this mount held 200 rounds. I used this photo to show the soldier for scale. You need two (or three?) containers stuffed in the nose of the forward of the pilot, but at least 3 1/2 feet back from the propeller.
Someone suggested putting the guns in blisters on the fuselage sides behind the pilot but then the ammo is competing for space with the new fuel tank.

A few notes on the racing Aircobras.
They were equipped with Allison V-1710-135 engines that were modified from stock. They used lower compression pistons to allow more boost to be used and were fitted with 100 gallons of water/alcohol storage (among many other things) and propellers from P-63s. The engines were good for 2000hp so race performance vs combat performance needs a bit of healthy skepticism.
The Aircobra's in the 1946 being as close to a "factory" effort as you were going to get in those days. The Pilots were Bell factory test pilots and the "corporation" that "owned" the planes contracted with the Bell factory to provide hanger space and labor to perform the modifications.
One thing that some people might want to note is that the original oil cooling system could in no way keep up with the increase heat load and not only was the oil tank increased in size but an oil cooler from a P-40 was added to the system and housed in duct under the fuselage.

Air intake was also larger than stock and used parts form a P-63 to get it out of the boundary air flow.

Surely the best way of improving the P-39 is at the beginning of the process. When Larry Bell responds to the circular for a turbocharged high-speed interceptor with a design that simply cannot ever meet the spec, just punch him in the face and give the P-39 designation to something else.
If you want a fast low-altitude fighter with tricky handling there have to be better ways of doing it than fiddling with the airacobra.

nice pic of cobra II. cobra 1 flown bylegendary pilot Jack Woolams is resting somewhere at the bottom of lake Ontario.. even though they have a rough estimate of where he went down ( during a shake down flight after getting his plane fixed for the Cleveland air races ) no trace has been found. woolams body was found and some debris but that is it. maybe finding it will be my hobby when I retire...

tomo pauk said:

Looking at this graph, there was a significant lack of power in two nominally equally powered aircraft, the P-39N and P-40N - the - 39 has maybe 6-8% less HP. The location of the ram air intake is really a bad choice? Still, the P-39 is faster by 20 mph, almost making 400 mph. Granted, 385 mph is the figure more often encountered.
Another thing about the V-1710s - late 1-stage engines were rated to 1480 HP on the P-51A and P-40N, but just 1410 HP on the P-39, not sure why.

Also this report (pdf), the P-39C making unbelievable 406 mph!! A curious thing is that it's engine's supercharger is driven via 9.6:1 gearing - an experimental engine sub-version preceeding the series-produced engines with such gearing?

A collective 'thank you, Mike' is mandatory

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I never understood that graph either. Contemporary E and F engines had the same ratings, yet the graph shows the F model to be more powerful. P-39 was still faster.

The 9.6 gears in that P-39C were pre production experimental. Allison planned for the SC gears to be interchangeable from 6.44 up to 9.6 (even 11.6!) but the 9.6 gears wouldn't pass the 150HR test and had to be widened putting the 9.6 program back almost a year.

The only thing that needed to be done to the P-39 was lose the wing guns. And lose the 100# nose armor but the radios would need to be moved up above the engine behind the pilot to restore balance. At 7100# the P-39 was a tiger, see the performance graph for the P-39C in wwiiaircrfaftperformance. Speed increased only about 10mph to 379mph but climb increased about 1000fpm making it very competitive with any other 1942 axis fighter. The P-39F would weigh 7100# without wing guns and nose armor. These were in production when the Japanese attacked Pearl Harbor.

Without the wing guns (which didn't provide much firepower anyway) that space could be used for additional fuel (say 50gal) if necessary.