Improve That Design: How Aircraft Could Have Been Made Better

[Ascent]

As a job I work in an engine test house doing development work for various manufacturers. One time while doing an acceleration test on an engine the propshaft connection to the Dyno failed, this resulted in the propshaft destroying the solid metal guard mounted around it for just such an occasion. Fortunately most of it was contained but one end of the shaft spun around the test cell like a top and large metal bearings from the universal joint scattered around putting some big dents in a couple of pipes.

This was just a 2L, 4 cylinder engine, although it was around 6,000 rpm which an aero engine wouldn't achieve. Fortunately we have all sorts of control software to shut the engine down when they lose the load suddenly like that, but even so they massively over rev. That's not something you'd have in a WWII aircraft.

 

[Koopernic]

I would have liked to have seen the Spit reach it's full potential. The interim models were needed, MkV-IX-XIV but I can't help but think the blooding of the spit in 1941-42 by the likes of the FW190A would not have happened if the MkIII running 2 stage Merlin XX's could have been made.

The Merlin XX had a two speed supercharger drive but still single stage supercharger. The Merlin 60 with two stages, after-cooling and two speeds came much latter.
Pretty much the ideal spitfire was the Mk VIII with the lower fueselage tank increased from 36 to 48 gallons and 2 x 12 gallon wing tanks and retractable tail wheel. If the tail tank used as a ferry tank in the simpler IX were added it would have impressive range though the tail tank would need to be half burned of before combat. Probably some machine tool company in Cincinnati saved the day with gear cutting machines to allow more gearboxes to be built.

 

[jmcalli2]

The gearbox and reduction box at either end were armored for a reason.

The driveshaft transferred a great deal of energy and if either gearbox was damaged, then all that energy stored in the shaft under load has to go somewhere.

A bullet through the prop was not enough to stop the aircraft - a P-47 took a 20mm round through a prop and flew back to England. Matyer of fact, a P-47 flew through an Olive grove, bending back all four of the props (amongst other things) and still flew over 100 miles back to base.

So back to the core of the issue:
Is the armor at the prop's gearbox nessecary? Yes.
Is the armor at the engine's gearbox nessecary? Yes.
Reason for the armor? To prevent catastrophic failure if struck by projectiles while in combat.

More like the AAF decided to armor everything on the P-39. Almost 250lbs worth for the smallest operational fighter since the P-26.

Once again, a bullet would not shake the drive shaft loose:

LiTOT: P-39: Why a Rear Engine Installation

 

[jmcalli2]

No u-joints maybe, but if the front gear box took damage that locked it up solid.
That's where you get those fantastic pictures of the whole prop coming off.
What ever was weakest would fail, if it happened at the front of the drive shaft, coming out of the front gearbox, you'd have the drive shaft whipping around like a giant weed eater.

It was designed and tested for that.

LiTOT: P-39: Why a Rear Engine Installation

 

[GrauGeist]

Once again, a bullet would not shake the drive shaft loose:

So you're saying that a bullet or cannon shell, which could tear apart aircraft engine blocks, was incapable of damaging either gearbox of a P-39?

Interesting...

 

[jmcalli2]

So you're saying that a bullet or cannon shell, which could tear apart aircraft engine blocks, was incapable of damaging either gearbox of a P-39?

Interesting...

Of course a bullet could disable the gearbox. That is not the discussion.
Remember the "reason" everyone gives for the armor in front of the gearbox; a bullet in the gearbox would cause the gearbox to explode and the driveshaft would then whip around and destroy the aircraft; that the same bullet hit on a P-40 gearbox would only kill the gearbox, not destroy the pilot via said whipping driveshaft; and what that armor could do: stop a .30cal bullet.
A "cannon shell" on a trajectory to hit the gearbox would not be stopped by the armor installed.
Therefore all the arguments were about a .30cal bullet causing the driveshaft to destroy the aircraft.
As can be seen here, the driveshaft/gearbox assembly was run for 20 hours in a way some believe would cause the driveshaft to whip around:

LiTOT: P-39: Why a Rear Engine Installation

 

[GrauGeist]

I'm sure that pages upon pages of test results, graphs and illustrations are interesting, but as has been stated before: this is not under combat conditions.

If a standard fighter (radial or inline) suffers catastrophic failure of their gearbox, the result is the propeller coming free from the front of the engine - the point being that the P-39's gearbox was not impervious to damage, which is why it was protected by armor plate.

A .30 caliber bullet (7mm) can and will penetrate cast-iron, mild steel plate and so on. So will .50 caliber (13mm) and 20 and 30mm goes without saying.

A basic grasp of physics and a close look at the P-39 will make it clear that a failure of the shaft's gearbox (on either end) can wreak havoc on the interior of the fuselage in the event it comes free under load.

No one has implied the shaft will fail during testing, normal flight and so on, the conversation is about the need for armor and what can happen if the aircraft is in combat and suffers damage from enemy aircraft without the armor protection.

Evidently, Bell thought it was needed...

 

[tyrodtom]

Of course a bullet could disable the gearbox. That is not the discussion.
Remember the "reason" everyone gives for the armor in front of the gearbox; a bullet in the gearbox would cause the gearbox to explode and the driveshaft would then whip around and destroy the aircraft; that the same bullet hit on a P-40 gearbox would only kill the gearbox, not destroy the pilot via said whipping driveshaft; and what that armor could do: stop a .30cal bullet.
A "cannon shell" on a trajectory to hit the gearbox would not be stopped by the armor installed.
Therefore all the arguments were about a .30cal bullet causing the driveshaft to destroy the aircraft.
As can be seen here, the driveshaft/gearbox assembly was run for 20 hours in a way some believe would cause the driveshaft to whip around:

LiTOT: P-39: Why a Rear Engine Installation

I read that information BEFORE I entered this discussion, You seem to think it says something that it simply does not say.
They only tested it in a mock-up fixture that simulated a severe air frame distortion, but within it's design limits, but much longer that it was ever likely to occur.
They never tested it in a failure mode, such as the front driveshaft becoming detached from the gearbox.
They probably never tested it for that because they knew it was catastrophic .

 

[jmcalli2]

I'm sure that pages upon pages of test results, graphs and illustrations are interesting, but as has been stated before: this is not under combat conditions.

If a standard fighter (radial or inline) suffers catastrophic failure of their gearbox, the result is the propeller coming free from the front of the engine - the point being that the P-39's gearbox was not impervious to damage, which is why it was protected by armor plate.

A .30 caliber bullet (7mm) can and will penetrate cast-iron, mild steel plate and so on. So will .50 caliber (13mm) and 20 and 30mm goes without saying.

A basic grasp of physics and a close look at the P-39 will make it clear that a failure of the shaft's gearbox (on either end) can wreak havoc on the interior of the fuselage in the event it comes free under load.

No one has implied the shaft will fail during testing, normal flight and so on, the conversation is about the need for armor and what can happen if the aircraft is in combat and suffers damage from enemy aircraft without the armor protection.

Evidently, Bell thought it was needed...

Well then we have the P-51s that disappeared due to entering a spacial anomaly from high diving speeds.

There is absolutely no evidence of this at all, but of course it happened on every mission a P-52 never came back from.

We know because those P-51s never came back.

 

[jmcalli2]

I read that information BEFORE I entered this discussion, You seem to think it says something that it simply does not say.
They only tested it in a mock-up fixture that simulated a severe air frame distortion, but within it's design limits, but much longer that it was ever likely to occur.
They never tested it in a failure mode, such as the front driveshaft becoming detached from the gearbox.
They probably never tested it for that because they knew it was catastrophic .

Translation:
"You can cite page after page of studies, but I KNOW."

"To argue with a person who has renounced the use of reason is like administering medicine to the dead."
Thomas Paine

 

[GrauGeist]

Well then we have the P-51s that disappeared due to entering a spacial anomaly from high diving speeds.

There is absolutely no evidence of this at all, but of course it happened on every mission a P-52 never came back from.

We know because those P-51s never came back.

To be honest, that's an asinine analogy

Then it's up to YOU to prove the facts otherwise.
Start by sorting through USAAF, RAF and VVS loss reports and discount any catastrophic failures by enemy contact.

Take your time, we've got all day

 

[swampyankee]

Did the P-39's driveshaft have any intermediate bearings?

 

[jmcalli2]

To be honest, that's an asinine analogy

Then it's up to YOU to prove the facts otherwise.
Start by sorting through USAAF, RAF and VVS loss reports and discount any catastrophic failures by enemy contact.

Take your time, we've got all day

It is an exact analogy of the argument of everyone claiming that a bullet in the gearbox would cause the drive shaft to whip around and destroy the aircraft.

I provided exactly as much prof for the P-51 time warp as they did for the P-39 drive shaft.

As for the P-39 drive shaft, I have posted several references backing up my position. those who disagree have provided zip, zero, nada to back up their claims.

So, some one, anyone show some documentation of an aircraft destroyed by a drive shaft gone wild after a bullet hits the remote gearbox.

No one has.

 

[tyrodtom]

Translation:
"You can cite page after page of studies, but I KNOW."

"To argue with a person who has renounced the use of reason is like administering medicine to the dead."
Thomas Paine

That's your translation of what I'm trying to get across.
I and several other people on this forum have seen what a powered loose drive shaft can do, and you refuse to accept that we saw what we saw.

 

[GrauGeist]

It is an exact analogy of the argument of everyone claiming that a bullet in the gearbox would cause the drive shaft to whip around and destroy the aircraft.

I provided exactly as much prof for the P-51 time warp as they did for the P-39 drive shaft.

As for the P-39 drive shaft, I have posted several references backing up my position. those who disagree have provided zip, zero, nada to back up their claims.

So, some one, anyone show some documentation of an aircraft destroyed by a drive shaft gone wild after a bullet hits the remote gearbox.

No one has.

It appears you don't understand the difference between a P-39's power train versus other conventional types.
A typical radial powered fighter (Fw190, F6F, P-47, A6M, etc.) has the propeller assembly attached to the front of the engine, which is mounted foreward of the cockpit.
A typical inline powered fighter (Spitfire, P-40, Bf109, Yak-9, etc.) has the propeller assembly attached to the front of the engine, which is foreward of the cockpit.

The P-39 and P-63 as the engine mounted behind the cockpit, with a driveshaft extending 120 inches to the front of the aircraft, connecting to the propeller assembly via a gear reduction box (which is normally directly between the propeller and engine). It is this shaft, that carries a considerable amount of energy when under load.

As has been carefully explained by several people here, a shaft coming free under load can cause considerable damage and to think that the 120 inch long shaft in a P-39, under load, driven by over 1,000 horsepower cannot fail, nor ever did, during combat is a little odd.

That's like saying that a bullet could not possibly destroy a jet engine on the Me262...

 

[ThomasP]

Hey Swampyankee,

re"Did the P-39's driveshaft have any intermediate bearings?"

 

[XBe02Drvr]

Hey Swampyankee,

re"Did the P-39's driveshaft have any intermediate bearings?"

View attachment 608535

Now we see "center bearing support for flexible splines coupling", and a whole new arena of potential disaster scenarios opens up. I hope that center bearing support is bolted to some mighty robust structure, or I see a potential wrecking ball.

 

[XBe02Drvr]

to think that the 120 inch long shaft in a P-39, under load, driven by over 1,000 horsepower cannot fail, nor ever did, during combat is a little odd.

That's like saying that a bullet could not possibly destroy a jet engine on the Me262...

Almost certainly there would be no documented proof of its happening, if it occurred in a combat scenario.

 

[XBe02Drvr]

Evidently, Bell thought it was needed..

...to keep the CG within limits, even if for no other reason.

 

[XBe02Drvr]

"To argue with a person who has renounced the use of reason is like administering medicine to the dead."
Thomas Paine

EPITAPH FOR A NATION.