Improve That Design: How Aircraft Could Have Been Made Better

[XBe02Drvr]

A hit in the reduction gearbox is the same whether it was mounted on the engine or remotely like the P-39. No other reduction gearboxes were armored

YOU STILL DON'T GET IT!
On WWII era engines, the reduction gears weren't "mounted on" the engine, they were integral to it. A hit to the nosecase was a hit to the engine and would generally lead to failure, whether immediate or delayed. A "straight drive" engine, with no reduction gears like the P39 had, was an anomaly, not the norm. P39/P63 was different in that a hit to the reduction box could "unload" the engine, causing it to overspeed to destruction, with perhaps a catastrophic driveshaft failure, to boot. Not good for pilot survival.

 

[P-39 Expert]

YOU STILL DON'T GET IT!
On WWII era engines, the reduction gears weren't "mounted on" the engine, they were integral to it. A hit to the nosecase was a hit to the engine and would generally lead to failure, whether immediate or delayed. A "straight drive" engine, with no reduction gears like the P39 had, was an anomaly, not the norm. P39/P63 was different in that a hit to the reduction box could "unload" the engine, causing it to overspeed to destruction, with perhaps a catastrophic driveshaft failure, to boot. Not good for pilot survival.

I think I get it all right, in either case a hit to the nosecase, whether mounted on the engine or mounted remotely would result in failure of the engine. The nosecase mounted on the engine was not armored, why armor a remotely mounted nosecase? It was redundant and therefore not needed.

 

[XBe02Drvr]

The supercharger and weight advantage you allude to would be operating in the same atmosphere as the P-39. If the P-39 was faster than the A6M2 in tests it would still be faster in theater since both planes would be at the same disadvantage. By the way, what supercharger advantage are you speaking of? Both planes had about the same critical altitude and speed bled off above that at about the same rate. See attached chart.

I don't have a computer to hand at the moment, but on my tiny cellphone screen I can't make much sense of that chart. But this I did notice; the P39s in question were Ds, but the chart depicts Ks, which, IIRC, had more power and different supercharger gears. The A6M2 data, if derived from the Akutan Zero, is not accurate, as that plane was not perfectly restored and not performing to spec. (Issues with airframe rig, carburetor configuration, unknown "actual" engine limitations, reluctance to damage a valuable intelligence asset, etc). It's impossible to restore a damaged aircraft to spec without the proper documentation.

 

[jmcalli2]

In post #703, you stated:
"Extra boost would only be available up to the critical altitude of around 14000' with ram."
And I replied in post #711:
"And that density altitude would be at a much lower MSL physical altitude in a tropical climate."
To which you replied in post #714:
"Yes and your opponent would be flying in the same atmosphere."
And my reply was, in post #716:
"Yes, but with a significant supercharger advantage and a super lightweight and high lift airframe. Superior power giving superior thrust/weight, and superior L/D at altitude."
Which you either ignored or didn't comprehend. The Zero (ignore Koga's plane; it wasn't performing to capacity) has all the advantages enumerated above in any atmosphere, making the P39 of the time a LOSER any way you slice it. The only factors, as I see it, that allowed the New Guinea P39s to establish any sort of a win/loss record was the occasional tendency of teenage IJN pilots to exuberantly ignore their hard learned lessons of combat and play to the P39's strengths, as well as the ability of American pilots to un-learn their trained tactics and adapt to the new reality.

I agree except for the "loser any way you slice it."

Give the P-39 pilots the AVG early warning and tactics, and they would do at least as well by your own standards; the P-39 had the same engine and supercharger, a higher rate of climb, a lower wing loading, and a higher power/mass ratio than the P-40 of similar models.

Even with the poor tactics, the P-39 was even in wins/losses with the Zero.
( reference Claringbould "P-39/P-400 vs. A6M2/3 Zero-sen New Guinea 1942 )

Or, should it be said this way: the vaunted Zero could do no better than fight the Airacobra to a draw over New Guinea.

 

[XBe02Drvr]

I think I get it all right, in either case a hit to the nosecase, whether mounted on the engine or mounted remotely would result in failure of the engine. The nosecase mounted on the engine was not armored, why armor a remotely mounted nosecase? It was redundant and therefore not needed.

Do you relish the thought of an engine exploding ten inches behind your precious posterior? Have you ever seen an engine that has come unglued due to an "unloaded" overrev at full throttle? Not pretty! Internal parts come right out through the engine crankcase. Scalding hot oil and coolant flying everywhere. Not healthy.
A hit to a front mounted engine's nose case is likely to continue on into the crankcase proper, as there's not much to stop it, bringing the engine to a halt without the "unloading" scenario described above.

 

[P-39 Expert]

I don't have a computer to hand at the moment, but on my tiny cellphone screen I can't make much sense of that chart. But this I did notice; the P39s in question were Ds, but the chart depicts Ks, which, IIRC, had more power and different supercharger gears. The A6M2 data, if derived from the Akutan Zero, is not accurate, as that plane was not perfectly restored and not performing to spec. (Issues with airframe rig, carburetor configuration, unknown "actual" engine limitations, reluctance to damage a valuable intelligence asset, etc). It's impossible to restore a damaged aircraft to spec without the proper documentation.

K model engine was the -63 with the same 8.8 supercharger gears as the -35. It was strengthened and developed 1325hp at takeoff vs 1150 for the -35, but HP at critical altitude was the same 1150hp at 12000ft. So above 12000ft they made the same power. Performance of the D and K were virtually identical. I use the K chart because that's all I have.

 

[P-39 Expert]

Do you relish the thought of an engine exploding ten inches behind your precious posterior? Have you ever seen an engine that has come unglued due to an "unloaded" overrev at full throttle? Not pretty! Internal parts come right out through the engine crankcase. Scalding hot oil and coolant flying everywhere. Not healthy.
A hit to a front mounted engine's nose case is likely to continue on into the crankcase proper, as there's not much to stop it, bringing the engine to a halt without the "unloading" scenario described above.

And either way both engines stop working. Immediately.

 

[P-39 Expert]

I agree except for the "loser any way you slice it."

Give the P-39 pilots the AVG early warning and tactics, and they would do at least as well by your own standards; the P-39 had the same engine and supercharger, a higher rate of climb, a lower wing loading, and a higher power/mass ratio than the P-40 of similar models.

Even with the poor tactics, the P-39 was even in wins/losses with the Zero.
( reference Claringbould "P-39/P-400 vs. A6M2/3 Zero-sen New Guinea 1942 )

Or, should it be said this way: the vaunted Zero could do no better than fight the Airacobra to a draw over New Guinea.

You are correct, no P-40 was as fast or climbed nearly as well as any contemporary P-39. Being 750lbs lighter had its advantages.

 

[XBe02Drvr]

And either way both engines stop working. Immediately.

Front engine: pilot survival likely.
Rear (driveshaft) engine: not so much.

 

[P-39 Expert]

Front engine: pilot survival likely.
Rear (driveshaft) engine: not so much.

In your opinion. A round into the nosecase of a P-40 will cause the engine to slowly stop itself while a round into a P-39 nosecase will cause the engine to explode? Okay, if you say so.

 

[XBe02Drvr]

In your opinion. A round into the nosecase of a P-40 will cause the engine to slowly stop itself while a round into a P-39 nosecase will cause the engine to explode? Okay, if you say so.

In the P40's case the round will likely stop the engine, as it will continue on into its internals. In the P39, if it shatters the reduction gears or the driveshaft, it will likely "unload" the engine resulting in an over-rev catastrophic failure. An over-rev failure ten feet out in front of the cockpit (if it occurs) is more likely survivable than one ten inches behind.

 

[Shortround6]

P-40 doesn't have 10 feet of drive shaft running through the cockpit and nose.

One reason the XP-39's claim to 390mph top speed is so suspect is that the engine in initial testing was limited to either 2600 or 2700rpm due to fears about the drive shaft having vibration problems should the engine misfire. A heavier drive shaft (larger diameter and heavier walls) was designed and fitted but not until the Plane had gone to Langley,
Gearbox doesn't need to have a catastrophic failure, Not much you can do about the propeller but anything that throws the reduction gears out of wack balance wise will affect the vibration patterns.

 

[GrauGeist]

A good comparison would be when a top-fuel funny car grenades it's rear-end.
The engine and driveline are no longer under load and catastrophic failure is the result.
Granted, the driveshaft loop and transmission shield help reduce the chance that the driver won't be injured or killed, but not always.

The P-39 did not have the benefit of modern drag racing safety protocols...

 

[jmcalli2]

A good comparison would be when a top-fuel funny car grenades it's rear-end.
The engine and driveline are no longer under load and catastrophic failure is the result.
Granted, the driveshaft loop and transmission shield help reduce the chance that the driver won't be injured or killed, but not always.

The P-39 did not have the benefit of modern drag racing safety protocols...

That's why no other aircraft has ever been designed with a drive shaft or counterrotating props since...

Except for:
many autogyros
XF5U
N-1M
FM-1
XF-84H
P-75
XB-42
B-35
B-36C
Do-335
J2M
A2D
Bristol 167
V-22
R-4
H-5
H-19/34
CH-47
plus many more helicopter designs, not to mention every turboprop design where the airscrew shaft is offset from the turbine shaft. All use driveshafts and remote gearboxes of varying lengths and configurations and with various degrees of success.

I've never heard of a P-39/63 drive shaft being a problem until these last few posts. That doesn't mean it wasn't a problem, but it does mean it's unlikely such problems were anything but a rare issue.

Could you be confusing armor with adequate structural strength?

 

[XBe02Drvr]

I've never heard of a P-39/63 drive shaft being a problem until these last few posts. That doesn't mean it wasn't a problem, but it does mean it's unlikely such problems were anything but a rare issue.

Quite likely it wasn't, because of the gearbox armor, and because in whatever cases may have occurred, there may have been no one left to tell about it.

 

[GrauGeist]

A production P-39 off the assembly line is not likely to suffer a driveshaft/gearbox failure.
Once it's in combat, things change.
A bullet or cannon shell can alter the manufacturer's design specs in a fraction of a second.

And regarding the list, most of those types never left the prototype stage. The XF5U for example, which never flew because of dangerous vibrations at higher RPMs - the V-173 did, however.
The FM-1 had a radial engine mounted the same as the F4F/FM-2, not sure why it's on the list - same goes for the J2M. Perhaps you meant "YFM-1"?
And the B-36 didn't have a driveshaft.

 

[jmcalli2]

Quite likely it wasn't, because of the gearbox armor, and because in whatever cases may have occurred, there may have been no one left to tell about it.

If that were a problem, then why don't we see P-39s that belly landed torn up by driveshafts whipping around? The props stopping suddenly when hitting the ground would add as much if not more stress than a bulett hitting gears engineered to withstand huge amounts of stress.
Again, the structure wouldn't allow it, with or without the armor.

 

[eagledad]

P-39 Expert

Attached is a graph for the P-39D-2, powered by the Allison V-1710 E-6 (Military designation V-1710-63).
For your use and information.

Eagledad

 

[Glider]

Suggest you take a P39. Put the engine in front of the pilot, saving the weight and complexity of the drive shaft, its supporting structure and making it less twitchy on COG issues. Move the guns to the wings with uniform 0.50.
It would weigh a lot less than the P40 with similar power equalling a better performance.

 

[Zipper730]

P-39 Expert

Attached is a graph for the P-39D-2, powered by the Allison V-1710 E-6 (Military designation V-1710-63).
For your use and information.

Eagledad

View attachment 608389

This is a good graph, and honestly it'd be a good idea to create more graphs of that detail.