Improve That Design: How Aircraft Could Have Been Made Better

GregP · Jan 15, 2021

When I was in the military weapons business, the MINIMUM testing we did was five units. Then we'd throw out the high and low readings, and average the other three. Mostly, it was more units than five, sometimes ten or fifteen. That was non-destructive testing.

For destructive testing, the number of units expended was dependent upon cost. One doesn't fire ten Navy Standard Missiles just to check performance. But bench-tesing the proximity fuze was non-destructive and could be run as many times as you wanted, and the test unit could still be delivered to the fleet.

Also, Shortround6, by the time the P-39N came along, the P-39's reputation in the USAAF was already well established, and making it sound better wasn't going to work with the rank and file pilots. They already knew people who had flown them, and they had their opnions. Forcing P-39s on them wasn't gling to help morale. The first time a P-39N shows up is Nov 42, and pilot morale was IMPORTANT at that time. Also, the P-39N had a smaller fuel tank that decreased the already-too-short range. Nov 42 was contemporary with the Fw 190A-5 and the P-40M.

The P-40M was basically a purely export version of the P-40K although many ended up in US units. The Allison had 1,325 hp and gave noticeably better performance than the P-40E, particularly at low altitudes. The Fw 190A-5 needs no introduction; it was one of the finest fighters at the time, if not the BEST. If you had a choice, almost everyone would choose the Fw 190 or the P-40 over the P-39N, if only from reputation.

The P-40 flew 67,059 sorties and had 521 claimed kills against 553 combat losses. That in the ETO. That's 1 kill every 129 sorties. Much better than the P-39's 1 kill every 955 sorties.

Update from above: My P-39 numbers were from the ETO 1942 - 1945, not the Pacific, as are the P-40 numbers above.

P-39 Expert · Jan 15, 2021

Shortround6 said:
Facts
1. The P-39N was running clean except for the drop tank shackle (no sway braces). Correct.
2. The F6F-3 was running with fuselage bomb rack and "T" braces, also wing bomb rack fairings and sway braces. In Clean condition the F6F-3 was supposed to be good for 321mph at sea level and 384mph at 18,000ft, not the 372mph shown on the chart. Agree. The F6F-5 chart showed 382mph top speed but 300fpm less climb. Take your pick, 10mph is negligible in the grand scheme of things.
3. The P-39N was running light. 3-400lbs below normal clean gross weight. Reduced fuel? Now don't act like you and I haven't beaten this to death in previous threads. All the AAF fighters tested at less than published gross takeoff weight. All planes weigh less at the end of their mission than the start due to fuel burn. The test weight was the average weight of the plane for that flight. P-39 normally carried 720lbs internal, 360lbs is half. That's just how the AAF tested their planes. The British used a flat 95% of gross takeoff weight as tested weight. P-39N test 7274lbs divided by 95%=7656lbs, almost exactly gross weight.
4. The F6F-3 is rated at full clean gross weight. Full internal fuel.
5. A minor consideration. (sarcasm) the P-39N was running above (well above?) the the AIr Corp standards for cooling temperatures.
6. This P-39N seems to show an amazing deviation from other P-39s. Performance at 5,000ft
.......................................P-39M.........................P-39N........................P-39Q
Weight...........................7430lbs.........................7301lbs.....................7871lbs Look at the weights.
Horsepower..................1395.............................1375............................1382
Climb ft/min.................3840..............................4240...........................3770 Look at the weights.
Speed at 9,500ft..........385.5............................398.4*.........................374 Q had the underwing gun pods, cost about 14mph. M had the 2.0 reduction gear and bomb shackles.
All at 57in MAP and 3000rpm except the speed of the P-39N.
P-39N used 59.8in MAP at 9700ft.

P-39Q speed was at 10,000ft. P-39Q had the under wing gun pods. See above.
Notes the test of the P-39-Q-5 (different pane than above) state that the external gunpods on the XP-63 were worth about 110ft/min climb. This was noted as the test P-39Q-5 engine was not running properly and so could not be compared to the P-39Q-1 test. P-63 gun pods appeared much more aerodynamic to me, and rough engine. Hard to compare.

Yep, let's pick and choose our facts very, very carefully and then accuse others of being unaware or failing to see the brilliance of the concept. I'm really not trying to pick and choose, use whatever speed for the F6F that you want. Use the -5 speed with the -3 climb if you want. F6F was the best Navy carrier plane of WW2 and unquestioned master of the Japanese. But the P-39N was a better performer AT ALL ALTITUDES and was out of production before the Hellcat even got to combat.

rapid climb by P-39 ending with overheated engine in tropical/desert conditions. Great way to start combat, engine already cooking itself. All the AAF WW2 fighters overheated in tests, except the P-40. Apparently, like the CG problems, symmetrical airfoil, the disconnected driveshaft and all the other imagined P-39 maladies, the AAF managed to live with the P-39, warts and all. And the Russians won the war with it.

I would really love to see the different P-39 model's performance on a chart as I think this P-39N would be in a class by itself. Agree, but compare apples to apples. The D/F/K/L/P-400 had lower rated engines (-35 and -63). Compare the M/N/Q with the -83/-85 engines. The M didn't have the larger propeller and the Q had the underwing gun pods. As always I enjoy our discussions.

Please expand above.

P-39 Expert · Jan 15, 2021

GregP said:
When I was in the military weapons business, the MINIMUM testing we did was five units. Then we'd throw out the high and low readings, and average the other three. Mostly, it was more units than five, sometimes ten or fifteen. That was non-destructive testing.

For destructive testing, the number of units expended was dependent upon cost. One doesn't fire ten Navy Standard Missiles just to check performance. But bench-tesing the proximity fuze was non-destructive and could be run as many times as you wanted, and the test unit could still be delivered to the fleet.

Also, Shortround6, by the time the P-39N came along, the P-39's reputation in the USAAF was already well established, and making it sound better wasn't going to work with the rank and file pilots. They already knew people who had flown them, and they had their opnions. Forcing P-39s on them wasn't gling to help morale. The first time a P-39N shows up is Nov 42, and pilot morale was IMPORTANT at that time. Also, the P-39N had a smaller fuel tank that decreased the already-too-short range. Nov 42 was contemporary with the Fw 190A-5 and the P-40M.

The P-40M was basically a purely export version of the P-40K although many ended up in US units. The Allison had 1,325 hp and gave noticeably better performance than the P-40E, particularly at low altitudes. The Fw 190A-5 needs no introduction; it was one of the finest fighters at the time, if not the BEST. If you had a choice, almost everyone would choose the Fw 190 or the P-40 over the P-39N, if only from reputation.

The P-40 flew 67,059 sorties and had 521 claimed kills against 553 combat losses. That in the ETO. That's 1 kill every 129 sorties. Much better than the P-39's 1 kill every 955 sorties.

Update from above: My P-39 numbers were from the ETO 1942 - 1945, not the Pacific, as are the P-40 numbers above.

GregP · Jan 15, 2021

So, pretty much the entire Allied aviaiton world thought the Fw 190 was the best fighter in the world when it came out, even the Spitfire V guys, but you are saying the P-39N was a match for it?

Am I interpreting that right? Just making sure before I reply to an incorrect assumption.

If you look at the Pilot's Operating Handbook for the P-39N-0 and N-1, the rate of climb at 3,000 rpm and 44.5" MAP (listed as Military Power), at 3,000 ft. and 5,000 ft. is shown as 2,250 fpm at 8,000 lbs gross weight and 2,900 fpm at 7,100 lbs. That won't outclimb an Fw 190A-5. This is from the Pilot's Operating Handbook straight from the USAAC.

The test in wwiiaricraftperformance are at 57" MAP. So, exactly WHEN did 57" MAP get approved? I don't know, but the coolant was overheating at this power setting, as indicated in the report. Definitely NOT as described in the Pilot's Operating Handbook, which is generally "the bible" on a military airplane.

Google P-39N POH pdf.

P-39 Expert · Jan 16, 2021

GregP said:
So, pretty much the entire Allied aviaiton world thought the Fw 190 was the best fighter in the world when it came out, even the Spitfire V guys, but you are saying the P-39N was a match for it? A little slower at higher altitudes, better climb rate. P-39N had better performance than a Spitfire V.

Am I interpreting that right? Just making sure before I reply to an incorrect assumption.

If you look at the Pilot's Operating Handbook for the P-39N-0 and N-1, the rate of climb at 3,000 rpm and 44.5" MAP (listed as Military Power), at 3,000 ft. and 5,000 ft. is shown as 2,250 fpm at 8,000 lbs gross weight and 2,900 fpm at 7,100 lbs. That won't outclimb an Fw 190A-5. This is from the Pilot's Operating Handbook straight from the USAAC. Pilot's handbook rate of climb was less than the tested rate of climb on virtually all AAF fighters in WW2. Pilot's handbook was advice to a pilot, test results were documented tests.

The test in wwiiaricraftperformance are at 57" MAP. So, exactly WHEN did 57" MAP get approved? I don't know, but the coolant was overheating at this pwoer setting, as indicated in the report. Definitely NOT as described in the Pilot's Operating Handbook, which is generally "the bible" on a military airplane. 57" was WEP, you are looking at the WEP climb test. Right above that in wwiiaircraftperformance.org is the military power test at 50.5", which is what I used in the comparison. Comparison was test to test, not pilot's manual to pilot's manual.

Google P-39N POH pdf. I already have a P-39N pilot's manual, as well as a P-39K/L/Q manual, a P-38F/G/H/K/L, P-40-E/F/N, P-47B/C, P-51D, FM2 Wildcat, F4F and F6F, thanks.

Expand above.

GregP · Jan 16, 2021

Yeah, right. Better than a Spitfire Mk.V. The numbers you are reporting are twice what is in the POH. Sorry, but another couple or three hundred hp just doesn't DO that, and neither did operational P-39s.

I'm not biting again for any reason. You're on your own. It's a good thing I'm not a moderator I suppose. Cheers.

P-39 Expert · Jan 16, 2021

GregP said:
Yeah, right. Better than a Spitfire Mk.V. The numbers you are reporting are twice what is in the POH. Sorry, but another couple or three hundred hp just doesn't DO that, and neither did operational P-39s.

I'm not biting again for any reason. You're on your own. It's a good thing I'm not a moderator I suppose. Cheers.

Just an official Wright Field performance test. What did they know?

Milosh · Jan 16, 2021

57" was WEP, you are looking at the WEP climb test. Right above that in wwiiaircraftperformance.org is the military power test at 50.5", which is what I used in the comparison.

P-39Q-5, AAF No. 42-19615 57" boost 4 August 1943
P-39Q-5, AAF No. 42-19615 55" boost 9 October 1943

P-39 Expert · Jan 16, 2021

Milosh said:
57" was WEP, you are looking at the WEP climb test. Right above that in wwiiaircraftperformance.org is the military power test at 50.5", which is what I used in the comparison.

P-39Q-5, AAF No. 42-19615 57" boost 4 August 1943
P-39Q-5, AAF No. 42-19615 55" boost 9 October 1943

We're talking about the P-39N, not the P-39Q.

jmcalli2 · Jan 16, 2021

GrauGeist said:
You and your smartass comments are growing tiresome.

Any halfwit can look at a P-39's cutaway and see CLEARLY that the driveshaft is NOT SUPPORTED by any other means than the 1) Engine Output, 2) Carrier bearing assembly at the coupling (at the halfway point) and finally, 3) Gearbox situated at the nose. It was a 102 inch spinning shaft - it wasn't going to be attached to anything other than components that required it's energy transfer.

Perhaps you should go look under your car for a rudimentary idea of what the grownups are talking about here, or find a topic better suited to your limited abilities.

That bearing just sort of floats on air...

You morons have a problem.

You hate the P-39, but that's not your problem.

When someone posts documentation that the P-39 didn't suck, you go out of your way to invent "design flaws" that never existed.

When people post documentation that you were wrong, you say without evidence that people (such as the AAF flight test reports and designers such as Robert Woods and writers of the time like Martin Caidin and Eugene Miller) were wrong or lying.
Because you "KNOW!"

When asked to produce documentation of your positions, you change the subject or simply state, "I KNOW!"

Had you read ANYTHING about the P-39 structure, including the design analysis I posted, you would clearly see that "the airplane fuselage beam assembly was to all intents and purposes a part of the engine assembly since it was really a crank case extension and acted as a housing and support for the extension drive shaft and independent gear box assembly and propeller."

NONE of you have demonstrated ANY understanding of there P-39 structures. You even missed the fume-proof armor bulkhead that separates the cockpit from the gun compartment.

You don't understand the P-39 because your egos won't allow it.

When presented with documentation you turn off and fall back on "I KNOW!"

I know you.

And I feel sorry for you.

jmcalli2 · Jan 16, 2021

XBe02Drvr said:
A couple of the attachments people put up on this thread refused to open on my Android, but I haven't seen anything contradicting what I posted. Explain yourself.

Still waiting for ANY documentation from you...

You morons have a problem.

You hate the P-39, but that's not your problem.

When someone posts documentation that the P-39 didn't suck, you go out of your way to invent "design flaws" that never existed.

When people post documentation that you were wrong, you say without evidence that people (such as the AAF flight test reports and designers such as Robert Woods and writers of the time like Martin Caidin and Eugene Miller) were wrong or lying.
Because you "KNOW!"

When asked to produce documentation of your positions, you change the subject or simply state, "I KNOW!"

Had you read ANYTHING about the P-39 structure, including the design analysis I posted, you would clearly see that "the airplane fuselage beam assembly was to all intents and purposes a part of the engine assembly since it was really a crank case extension and acted as a housing and support for the extension drive shaft and independent gear box assembly and propeller."

NONE of you have demonstrated ANY understanding of there P-39 structures. You even missed the fume-proof armor bulkhead that separates the cockpit from the gun compartment.

You don't understand the P-39 because your egos won't allow it.

When presented with documentation you turn off and fall back on "I KNOW!"

I know you.

And I feel sorry for you.

buffnut453 · Jan 16, 2021

My-oh-my, we're getting passionate about this topic! I'm pretty sure nobody on this forum "hates" any aircraft. We are all interested in learning more about aviation and to explore the reasons why things happened.

Personally, I find it frustrating that the P-39 seems to crop up in every bluddy thread on this forum...and it's the same people having the same arguments on all the threads. Nobody's pre-existing perspectives are getting swayed by arguments in either direction. There's a lot of transmitting but not a lot of receiving going on.

Frankly, it's getting boring.

P-39 Expert · Jan 16, 2021

buffnut453 said:
My-oh-my, we're getting passionate about this topic! I'm pretty sure nobody on this forum "hates" any aircraft. We are all interested in learning more about aviation and to explore the reasons why things happened.

Personally, I find it frustrating that the P-39 seems to crop up in every bluddy thread on this forum...and it's the same people having the same arguments on all the threads. Nobody's pre-existing perspectives are getting swayed by arguments in either direction. There's a lot of transmitting but not a lot of receiving going on.

Frankly, it's getting boring.

I hate the Brewster Buffalo. I'll show myself out...

Simon Thomas · Jan 16, 2021

nuuumannn said:
Part of the problem with the Stirling was that construction of the prototype was begun before trials with the small scale aircraft had been completed, which meant Short didn't foresee that the wing's angle of incidence was too shallow, which meant it would have had an inordinately long take off run fully loaded, so its gangly undercarriage was lengthened to steepen the angle at which the wing began to produce adequate lift to get the thing off the ground.

I don't buy that. The Empire wing incidence was spot on, as the aerodynamics and hydrodynamics of the TO run of a flying boat is rather critical. Arthur Gouge had already designed a flying boat that was incapable of lift off from the water. After learning his lesson, he didn't suddenly forget how to angle airfoils when he worked on the Stirling.
The incidence problem was not identified by Parker when he was running the factory tests, rather it was a complaint from the pilots at RAE when the factory testing was well advanced.
If Shorts was able to "correct" the wing incidence wrt the airframe, the cruise angle of the airframe would have been sub-optimal.
Any pilot can lift off at the correct airspeed - having to add a few more degrees nose up is not that complicated or time-consuming. Having said that, the Cessna Cardinal is an interesting example of having to re-design an aeroplane due to pilots failing to follow the manual .

GrauGeist · Jan 16, 2021

jmcalli2 - I'll (once again) post an actual Bell Aircraft image of the propulsion unit for a P-39Q.
In the image, is shown the Allison V-1710-85 (which was obviously mounted to the airframe), the 60" rear shaft, the carrier bearing/coupling (which was mounted to the airframe), the 60" foreward shaft and the gearbox/propeller mount (which was mounted to the airframe).
Now, there were only THREE points of contact for this assembly:
1. Engine
2. Carrier bearing
3. Gearbox.

That's it - nothing more. Period.

So calm the eff down.

Glider · Jan 16, 2021

That shaft only weighed 10 pounds?

GregP · Jan 16, 2021

The Allison V-1710 has exactly four points of attachment. There is no "crankcase extension, " and the driveshaft simply bolts to the extension shaft flange sticking out of the front of the gearbox. I have personally worked on some 15 of them and worked in a shop that has 150+ of them, a mixture of E's and F's and a few odd G's.

Here's a F-series engine:

Note it has a propeller shaft sticking out of the gearbox where the propeller mounts.

Here's a turbo compund E-series:

It has an extension shaft sticking out of the front (left side) that is very short compared with the F-series.

There is no magic here. You can make an E-engine by simply removing the nosecase from an F-engine and bolting on an E-engine front case. And there is no "stucture" supporting the driveshaft. The only point of connection to the engine is the extension shaft.

Honestly jmcalli2, if you're going to fuss at the entire forum, you at LEAST should go look at the airplane or engine you're fussing about.

War Emergency performance numbers are not very interesting because they very seldom ever got used. If they DID get used, the engine usually had to be pulled and changed, depending on group policy. Pilots were very unlikely to use WER when far from home because abusing your engine when you were several hundred miles from home was not every smart and not very good for survival. If you were going to have engine issues and bail out or were forced land, it didn't make sense to court disaster unless your life was in immediate danger.

The P-39N-1 performance test dated 17 Oct 42 used 50.5" MAP and the max rate of climb was 3,920 fpm at 11,000 ft. It dropped off pretty steeply from 11,000 ft. upward and was down to 2,630 fpm at 20,000 ft. 50.5" MAP was takeoff power and 52" MAP was approved just for takeoff and up to 5 minutes after takeoff. Military power was 44.2" MAP and it was approved for up to 15 minutes. Max continuous power was 39.2" MAP. 55" or 57" MAP wasn't even approved when the Pilot's Operating Handbook was written, and it was released in 1 Feb 1943.

The gross weight for the test from wwiiaircraftperformance was 7,274 lbs. . Normal load was 7,500 lbs. or more, so I guess the test was conducted without the center fuel tank ... which was generally needed in the Pacific since the range was nothing spectacular without it.

Wing tanks held 87 gallons and aux tank held 75 gallons. You needed a reserve of fuel, so if you had no aux tank, you'd generally plan for 70 gallons. If you were cruising at 2600 rpm, you had from 210 to 255 miles range. You COULD get up to 430 miles, but you'd be cruising at 2200 rpm and 215 mph or so at low MAP. Without the aux tank, you don't get many places in the Pacific, so they all generally hauled the aux tank. Gross weight was higher than 7,274 lbs. for Pacific operations unless you were doing CAP for the home airfield.

The rate of climb for the P-39N-0 and N-1 was 2,700 fpm and 44.5" MAP (15-minute limit for combat) at sea level, and it went down from there. Ferry climb was 1,350 fpm at sea level, again for 15 minutes. The performance charts note you increase the time to climb by a set percent for each 10°C above 0°C free air temperature. In the Pacific, there were damned few days when the temperature was 0°C, so NONE of the Pacific P-39N's likely climbed as well as 2,700 fpm right off the runway. That's an estimate, of course, but I never saw 0°C in the South Pacific any time I was ever there personally.

If you flog the engine and run it up to 57" MAP, you have a very short duration experience with good climb rates. The Soviets used them at 70" MAP and more, but they didn't fly in the USAAC/F where that would likely get you grounded if it happened very many times. The crew chief could tell because the wire across the throtte quadrant would be broken and it had to be reported.

Moral of the story is that yes, you CAN get 3,900 fpm climb rate from the P-39N in a test of WER climb for a short time, but the operating airplanes in-service in the Pacific and the ETO generally didn't get anywhere NEAR that performance when they were operated by the book at usual weights. Most were.

You two spouting about the P-39 won't change the FACT that the U.S.A. never embraced the airplane and it wasn't anywhere NEAR as good as a Spitfire V or an Fw 190A-5. It could have been the best fighter in the world (wasn't) and the U.S.A. would still not have embraced it due to the solidly mediocre performance of the first several thousand of them. After that, nobody wanted them. Oh yeah, it also had a solidly anemic combat record in U.S. service. The Soviets operated them in cold weather and ran the engines hard, and the P-39 seemed to thrive there, but not when and where the U.S.A. operated it.

In actual history, it ranks down near the bottom of the WWII fighters in U.S. use, right close to the Buffalo but definitely above the Buffalo. Much ado about nothing doesn't change that.

Jugman · Jan 16, 2021

GrauGeist The shafts were only 48.5625" long. overall length of a single-stage E was 194" vs 85.625 for an F.

Glider total additional weight for an E was 90lbs. most of that was the drive shaft

buffnut453 · Jan 16, 2021

P-39 Expert said:
I hate the Brewster Buffalo. I'll show myself out...

There's no accounting for taste...or even lack thereof.

Truth be told, I'm really, REALLY struggling with the concept of anyone hating an inanimate object. It has to be the most futile of actions given that the object, being inanimate, has no conception of the feelings anyone may have about it.

pbehn · Jan 16, 2021

GregP said:
So, pretty much the entire Allied aviaiton world thought the Fw 190 was the best fighter in the world when it came out, even the Spitfire V guys, but you are saying the P-39N was a match for it?

.

This is my issue with the discussion the timing, the first P-39s to enter RAF service were not at all sorted and more of a danger to its own pilots than the enemy. These aircraft were contemporaries of the Fw-190. By the time 601 squadron packed these early versions off to Russia the Spitfire Mk IX and the Mustang Mk Is were starting to appear and the Fw 190 was a beast.

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