Improve That Design: How Aircraft Could Have Been Made Better

GrauGeist · Jan 13, 2021

And to touch on the P-39 armor "thing" - I appreciate the exhaustive attempts to try to reimagine the P-39 into a world beater by moving this and eliminating that, so it would maybe, somehow, be better than it was.

So let's do this:
We'll remove the gearbox armor and while we're at it, let's remove the 2 gallon oil tank, too. Then let's get rid of the Olds 37mm cannon, way too heavy.
It seems to me that the driveshaft assembly is extra weight we don't need, so that goes.
What's next - oh yeah, CoG issues, so let's move the engine to the front where all that empty space is and maybe adjust the mainwing a bit to balance things out. Nice.
Now the two cowl .50MGs will have to go in the wings with the others, of course.
Ahh yeah, let's get rid of the nosegear, way too heavy - a tailwheel will do just fine, less weight, you know.

So now we get to see the what we've created and...what do we have? A P-40 - that's what we have.

Someone better get the DeLorean and go back and tell Bell!

P-39 Expert · Jan 13, 2021

Find one instance where the driveshaft gave way. One. 9500 examples produced, in combat all over the world in all kinds of weather.

Find one instance where a P-39 took a round in the nose armor. One. In all of history.

Dead men tell no tales? Well you're telling a big one right now.

pbehn · Jan 13, 2021

P-39 Expert said:
Find one instance where a P-39 took a round in the nose armor. One. In all of history.

With all those produced and used in combat, an absence of any plane that took a hit in the nose armour and returned is evidence that it was fatal not that it didn't happen, that is survivorship bias The Statistics That Kept Countless Allied Fighter Planes In The Sky . I don't know about the P-39 history, just stating the general principle.

pbehn · Jan 13, 2021

GrauGeist said:
So now we get to see the what we've created and...what do we have? A P-40 - that's what we have.

!

Or a P-51 or that very rare Allison engined Spitfire.

XBe02Drvr · Jan 13, 2021

pbehn said:
Or a P-51 or that very rare Allison engined Spitfire.

Or a P51? Larry Bell may have had some experience at Consolidated, but he was no Dutch kindelberger. Not by a long shot.

pbehn · Jan 13, 2021

XBe02Drvr said:
Or a P51? Larry Bell may have had some experience at Consolidated, but he was no Dutch kindelberger. Not by a long shot.

Just a joke on the general principle.

swampyankee · Jan 13, 2021

pbehn said:
With all those produced and used in combat, an absence of any plane that took a hit in the nose armour and returned is evidence that it was fatal not that it didn't happen, that is survivorship bias The Statistics That Kept Countless Allied Fighter Planes In The Sky . I don't know about the P-39 history, just stating the general principle.

Since there's no evidence, there's no evidence that it happened, either. One way to see how likely gearbox damage is to examine the damage records of twins, especially twin fighters.

XBe02Drvr · Jan 13, 2021

GrauGeist said:
So now we get to see the what we've created and...what do we have? A P-40 - that's what we have.

No, we have a smaller, lighter, P40 wannabe that probably can outperform the P40 in the interceptor role, but is nowhere near as versatile, and can't hold a candle to it in attack and CAS modes. That small wing with its symmetrical airfoil impairs its ordnance lift capacity and increases its runway length requirements.

GrauGeist · Jan 13, 2021

XBe02Drvr said:
No, we have a smaller, lighter, P40 wannabe that probably can outperform the P40 in the interceptor role, but is nowhere near as versatile, and can't hold a candle to it in attack and CAS modes. That small wing with its symmetrical airfoil impairs its ordnance lift capacity and increases its runway length requirements.

Of course, I was being facetious, but in reality, there was only a few feet difference (length/width) between the two.

Now Bell's XP-77 was most certainly smaller - but definately no better than the P-39's spin-offs: XFL, XP-76.

jmcalli2 · Jan 13, 2021

tyrodtom said:
To be .30 caliber proof is just how useful when all Bf-109s from the late F up had two 20mm wing cannon in addition to the usually .50 cal. cowl guns.
The armament situation for the Bf109 is so confusing, late B's had 4 .30s, middle E models had 2 .30s, and 2 20mm, the F model had so many configurations, 15mm, .50 caliber, 20mm, and ???
But once the G model came out I don't think there were any more .30 armed Bf109s.
The F model was just coming into service when Germany invaded the USSR.
Then the Fw190 had wing cannons from the beginning, in addition to the cowl .30s.

So just how useful is .30 caliber proof, when almost any opponent you're going up against has heavier armament ?
I think you're being deliberately obtuse about the realities of most of the actions the P-39 was involved in, especially the war on the eastern front. .
Planes lost in action , for any cause, very seldom could have any investigation, the most intense conflict the world has ever seen was going on.

Again YOU HAVE NO IDEA WHAT THE CONVERSATION IS ABOUT!

It is about the armor in front of the gearbox.

ARMOR THAT WOULD NOT STOP A 20mm SHELL.

jmcalli2 · Jan 13, 2021

XBe02Drvr said:
No, we have a smaller, lighter, P40 wannabe that probably can outperform the P40 in the interceptor role, but is nowhere near as versatile, and can't hold a candle to it in attack and CAS modes. That small wing with its symmetrical airfoil impairs its ordnance lift capacity and increases its runway length requirements.

The P-40 had two advantages over the P-39:
1. longer range on internal fuel;
2. early production. 7,478 P-40s and 2,912 P-39s were delivered by the end of '42.

As for being "more versatile," P-40 production began in May 1940 and stopped in November 1944 with 13,738 built.
Nothing replaced it on Curtiss assembly lines.

P-39 production began in December 1940 and ended in August '44 with 9,588 built; P-63 production began in January '44 (31 P-63s were delivered in '43) and continued through June '45 with 3,303 built (including 30 delivered between September 1945 and April 1946) for a total of 12,891 'Cobras built.

Both lines slowed down from peaks of 463 P-40s in August '43 and 503 P-39s July '43 to 200 P-40s in May '44, with 201 P-39s and 110 P-63s the same month.

The US didn't need the P-39/63 by early '44; they were built for the USSR.

The USSR wanted P-39s and P-63s.

The US didn't need any P-40s by early '44 and the USSR didn't want anymore P-40s; so P-40 production ended.

Being "more versatile," whatever that means, didn't keep the P-40 in demand as long as the P-39/63 line.

jmcalli2 · Jan 13, 2021

P-39 Expert said:
A few corrections need to be made (as usual).

The first D is actually a D-2.

The second L is incorrect, I don't believe a production L had a -83 engine, just the -63.

The M had the -83, 1125HP@15500'.

The N had the -85, same rating as the -83, just a different reduction gear from 2.0 to 2.23.

All Qs had the -85 like the N with 1200HP for takeoff and 1125@15500'. Or 1150HP@15000', take your pick.

The 11800' models are often listed at 12000' and have the earlier 8.8 supercharger gears. The 14600' models have the later 9.6 supercharger gears but these engines still had the port backfire screens which would be deleted from all V-1710 models with the introduction of the aluminum intake manifolds in mid-'42. The production 9.6 models (-83 and -85) never had the backfire screens since they were gone before the 9.6 models started production in August '42. Backfire screens were a real nuisance since they clogged quickly and getting rid of them improved critical altitude by 900' (14600' to 15500').

The -59 in the P-39J was an early attempt (Dec '41) at the 9.6 gears but they couldn't pass the 150 hour test and were converted back to 8.8 geared models. Only 25 -J models produced so basically disregard this model. The accessories drive was redesigned for wider 9.6 gears that would pass the 150 hour test but that set the program back about 8 months in 1942 (Dec-Aug). The M was the first user with production of that plane beginning in October 1942.

Simple, eh? It was pretty much chronological with the -35 in the P-400, D, D-1, and F, the -63 in the D-2, K and L, the -83 in the M and the -85 in the N and Q. The -35 and -63 had the 8.8 gears and the -83 and -85 had the 9.6 gears.

I got my engine model info from USAF Engine Models

The chart does not say how many of a specific model carried the specified engine; could be one, could be more of the production run.

jmcalli2 · Jan 13, 2021

XBe02Drvr said:
QUOTE="jmcalli2, post: 1609575, member: 45349"]Once again, a bullet would not shake the drive shaft loose

It wouldn't need to. What's going to happen when a hollow tube carrying the torque from 1150 HP in walls .020" thick at 3,000 RPM, carefully balanced and tuned to avoid resonances, is holed or furrowed by a 7.7MM round, upsetting all that balancing and tuning? I suspect the shaft would shake itself loose, possibly ripping the intermediate coupling loose from its supporting structure.

Actually, it is. Imagine you're in a dogfight, pulling 3,000 RPM and all the MP the supercharger will give you, plus fluctuating G and gyroscopic loads from your gyrations, and your reduction gearbox is disabled, suddenly unloading that engine right behind your seat. Wide open throttle and no load on the crankshaft, what do you think is going to happen? Right, it's going to come unglued. Spectacularly. The only question is how many revs it'll hit before it does. 3,500? 4,000? Who cares? You won't. The scalding glycol and engine oil will have seen to that. And nobody will be around to tell the tale.
Reduction gearbox armor was essential.[/QUOTE]

I disagree.

Because the drive shaft is supported front and midsection by the main structural beam of the aircraft.

Because if your "I KNOW" scenarios were true, EVERY Sikorsky helo would have had that problem; radial engine with drive shaft going through the cabin.

So, once again, show me some documentation OTHER THAN "Oh, I KNOW."

I'm still waiting.

As for hot glycol, that is BELOW and BEHIND the pilot int the P-39;

Perhaps you are confused by the P-40, with the coolant and oil radiators in front of the pilot, where one little bullet could scald him?
Then the P-40 was a deathtrap! It should have had foot-thick armor in front of those radiators!

P-39 Expert · Jan 13, 2021

I'll s

jmcalli2 said:
I got my engine model info from USAF Engine Models

The chart does not say how many of a specific model carried the specified engine; could be one, could be more of the production run.

I'll stick with my answer.

GrauGeist · Jan 13, 2021

jmcalli2 said:
Because the drive shaft is supported front and midsection by the main structural beam of the aircraft.

Nothing supported the drive shaft between the engine and gearbox except the carrier bearing assembly that was situated at the 60" mark, where the two shafts joined.

tyrodtom · Jan 13, 2021

jmcalli2 said:
Again YOU HAVE NO IDEA WHAT THE CONVERSATION IS ABOUT!

It is about the armor in front of the gearbox.

ARMOR THAT WOULD NOT STOP A 20mm SHELL.

I'm beginning to wonder if you do.
I'm pointing out that .30 caliber proof armor is minimum armor, no aircraft I'm aware of carried a smaller caliber weapon, while almost any axis aircraft you would meet ( with the exception of the Ki-43 early in the war) had additional guns that were bigger than .30 cal.
So just what good did the armor do?
What Larry Bell did IMO was create a aircraft that was so different from other aircraft it was dangerous.
Right at the end of a combat mission when the ammo is low or out, and the pilots flying skills aren't the best because he's probably dog tired.
Most aircraft handle the best at the end of the flight, if there's no battle damage, lower total weight, lower stalling speed, etc.
But in the P-39's case that's when it's most sensitive, with close to aft CG.
Pull that turn to final a little too tight, or rough, and you'll end up in a stall/spin that'll take more altitude to recover from than you've got.

Most aircraft destroyed in combat in the WW2 era would get no investigation under most conditions.
The pilot, if he survived, sometimes might have a clue. His squadron friends might see it, but are likely too busy with the mission, or their own survival , to really concentrate on exactly what happened.
And even if they could find a secure crash site, no one had the time to do a complete forensic investigation on a smoking hole in the ground, like modern crash investigations .

I feel like this is a waste of time trying to have a adult conversation with someone who evidently has no knowledge beyond what he reads, and has no real experience with anything mechanical.

GregP · Jan 13, 2021

The P-39L was built with both -63 and -83 engines. Basically, the P-39L was a P-39K with a Curtiss Electric propeller and a modified nosewheel.

The -63 has 7.48 : 1 supercharger gearing. It had 1325 hp at S.L. and 1100 hp at 13,800 ft and 44.2 in. Hg.

The -83 had 9.60 : 1 supercharger gearing. It had 1200 hp at S.L. and 1125 hp at 15,500 ft. and 38.8 in. Hg.

Both airplanes were likely flown at considerably higher power settings than 39" - 44" Hg by the Soviets, so they likely got sprightly performance that another 300 - 400 hp would offer.

So, the -63 was better way down low and the -83 was better a couple of thousand feet higher than the -63 airplane ... but neither one should have had a decisive difference in flight performance except for shorter takeoff in the -63 airplane and slightly better very low-altitude climb performance.

In service, there was no problem with drivehsaft failures. There wll might have been combat drivehsaft failures, but there were NONE in-service in airplanes that returned from combat.

GrauGeist · Jan 13, 2021

Interesting - I've seen photographs and guncam footage showing aircraft being attacked and in the process, engines falling away, landing gear dropping, control surfaces flying off, canopy structures blown out and a whole host of other indications of deadly fire.

But aparently Bell was a genius and built an indestructible machine that can defy the laws of physics...

XBe02Drvr · Jan 14, 2021

jmcalli2 said:
Perhaps you are confused by the P-40, with the coolant and oil radiators in front of the pilot, where one little bullet could scald him?
Then the P-40 was a deathtrap! It should have had foot-thick armor in front of those radiators!

The P40 had a firewall between the propulsion compartment and the rest of the airframe, as front engine planes generally do. They are made of stainless steel, ruggedly constructed to take the stresses of the engine mounts bolted to them, and generally do their job well, keeping engine related fluids and risks out of the rest of the plane. Anyone who's had grease under their fingernails from working on airplanes knows this.

jmcalli2 said:
As for hot glycol, that is BELOW and BEHIND the pilot int the P-39;

In all the drawings and photos I've seen of P39s in service, being maintained, or under construction, there doesn't seem to be any sort of a solid secure firewall between the engine compartment and the cockpit, and the radiator and oil cooler plumbing run right under the pilot's feet. The engine mounts appear to be supported by the lower fuselage "backbone" beams rather than cantilevered from a firewall in the usual manner. This means that cockpit and engine compartment form a cocoon that will confine and contain any escaped hot fluids, frying the pilot. Not my favorite way to go.

P-39 Expert · Jan 14, 2021

GregP said:
The P-39L was built with both -63 and -83 engines. Basically, the P-39L was a P-39K with a Curtiss Electric propeller and a modified nosewheel.

The -63 has 7.48 : 1 supercharger gearing. It had 1325 hp at S.L. and 1100 hp at 13,800 ft and 44.2 in. Hg.

The -83 had 9.60 : 1 supercharger gearing. It had 1200 hp at S.L. and 1125 hp at 15,500 ft. and 38.8 in. Hg.

Both airplanes were likely flown at considerably higher power settings than 39" - 44" Hg by the Soviets, so they likely got sprightly performance thath another 300 - 400 hp would offer.

So, the -63 was better way down low and the -83 was better a couple of thousand feet higher than the -63 airplane ... but neither one should have had a decisive difference in flight performance except for shorter takeoff in the -63 airplane and slightly better very low-altitude climb performance.

In service, there was no problem with drivehsaft failures. There wll might have been combat drivehsaft failures, but there were NONE in-service in airplanes that returned from combat.

The -63 engine had the same 8.8 supercharger gears as the -35. The 7.48 geared engines were all two stage.

The 9.6 engines developed the same 1150HP as the 8.8 engines, just at about 3000ft higher critical altitude. At the same altitude, the 9.6 engines developed about 100HP more than the 8.8 engines above about 9000ft. Gave the P-39N a big performance edge over the D/F/K/L at the same weights. See attached chart.

I don't know of any L models with the -83 engine, otherwise they would be Ms.

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