Improve That Design: How Aircraft Could Have Been Made Better

[jmcalli2]

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.

You saw a drive shaft on a CAR.

My point is that the P-39 drive shaft is secured in a way the car's drive shaft is not.

AND that a .30cal bullet would NOT sever that driveshaft.

Your argument is back to, "I KNOW."

Show me where it happened to a P-39.

I'll wait.

 

[Shortround6]

Yanking a pair of 24lb guns and about 80lbs of ammo (600rpg ? 1200 rounds total) isn't going to do much for the bomb load.

The 905 HP Perseus made the 905hp at 6,500ft.
The Production Taurus engines were mostly rated at 3500ft. using 100/130 fuel. (1130hp?)
Of course it took a while to solve the Taurus engine overheating problem/s.

You could get a single speed Pegasus to have 1,010hp for take-off and 890hp at 6,500ft using 87 octane fuel and be about 165lbs lighter than the Taurus.
A two speed Pegasus offers a lot of improvement without the sleeve valve troubles.

 

[jmcalli2]

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...

It appears you haven't bothered to read my other posts.
Start with Improve That Design: How Aircraft Could Have Been Made Better

Notice that the drive shaft is supported in the front, rear, and center by the P-39's main structure,

Then read Improve That Design: How Aircraft Could Have Been Made Better

Notice that the P-39 driveshaft installation was tested extensively.

A .30cal bullet hitting the gearbox would NOT cause the P-39 driveshaft to whip around.

Show me some documentation that it ever happened.

I'll wait.

 

[GrauGeist]

There may have been 3 different shafts used between the XP-39 and production P-39s.

The XP-39 was fitted with shafts of 2.500 diameter and 0.156 wall thickness to begin with but new shafts were fabricated while the XP-39 was at Langley.
The New shafts (weight increase 11-15lbs but not specified as to each shaft or both shafts) were 2.550 in diameter and wall thickness 0.200.

Production P-39s got 3.000 diameter shafts that were only 5 lbs heavier (book doesn't give wall thickness.) all in the larger couplings and flanges.
The 3 in shafts were supposed to have the same torsional characteristics as the 2.550 in shafts.


a 60 in solid shaft 3 in in diameter would weigh about 118lbs (?) depending on exact alloy.

BTW the Shaft is one of the reasons there is considerable doubt about the XP-39 ever coming close to 390mph in it's original form (pre Langley) as the engine was restricted to either 2600rpm or 2700rpm due to potential vibration problems should the engine misfire at higher RPM.

The 2nd shaft was supposed to be about 30% stiffer and raised the vibration problem area by 400rpm which was above the normal operating range of the Allison at that time.

The entire drive shaft may have weighed 100lbs? (or 50lbs plus the fuselage weighing another 50lbs more than a front engine plane due to extra stiffening?)
I can't remember were I read that or the exact numbers assigned to each part (shaft/s and fuselage)

The drive shaft (the the flexible coupling in the middle) was designed to accommodate +/- 1 degree of misalignment between the engine drive flange and the gearbox input flange.
This was supposed to be a total of 3.64in of possible travel over 10 ft.

I recall reading (ages ago) that they tested quite a few different types (hollow, solid, fluid filled, etc.) and different alloys to address a host of potential issues.
The division General Motors created just for this project did come up with a winner, though.
The P-39 may not have been all it was expected to be, fighter-wise, but it was certainly one hell of an engineering job.

 

[tyrodtom]

It appears you haven't bothered to read my other posts.
Start with Improve That Design: How Aircraft Could Have Been Made Better

Notice that the drive shaft is supported in the front, rear, and center by the P-39's main structure,

Then read Improve That Design: How Aircraft Could Have Been Made Better

Notice that the P-39 driveshaft installation was tested extensively.

A .30cal bullet hitting the gearbox would NOT cause the P-39 driveshaft to whip around.

Show me some documentation that it ever happened.

I'll wait.

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.

 

[tomo pauk]

That's probably where the Skua needs help the most, where its 905 hp Perseus (55" dia, 1,025 lb) engine needs a replacement. What pre-Hercules options do we have? The Bristol Taurus is rated at 1,050 hp and at 46" wide and 1,301 lb. it could allow the Skua's engine bay to be narrowed and more streamlined, but it's 30% heavier.

If we're keeping the Perseus, reject the fighter role and remove two of the forward .303 guns to allow for a heavier bombload.

As noted by SR6, a 2-speed suprcharged Pegasus is probably the best choice for the Skua - engine is light enough, reliable, no-nonsense and in production, can do another ~100 HP for take off, while also offering much more power at altitude.

 

[Milosh]

But once the G model came out I don't think there were any more .30 armed Bf109s.

That should be G-6.

 

[XBe02Drvr]

the shaft (each one) would have weighed at least 75 pounds. They weren't hollow like an automobile, but rather turned from solid stock (much like a hydraulic ram) in order to handle the torque between the engine and the prop's loading

The XP-39 was fitted with shafts of 2.500 diameter and 0.156 wall thickness to begin with

The New shafts (weight increase 11-15lbs but not specified as to each shaft or both shafts) were 2.550 in diameter and wall thickness 0.200.

Production P-39s got 3.000 diameter shafts that were only 5 lbs heavier

We seem to have a contradiction here. First, it's a solid shaft, then it appears to be a hollow shaft with various specified wall thicknesses. Which is it? A solid shaft seems rather unlikely from a weight standpoint, but then a 1/5" thick wall hollow one seems rather delicate for the forces involved. I'm no engineer, but that doesn't feel right "in the gut".

 

[Koopernic]

That should be G-6.

The Me 109G1 was as clean a machine as the Me 109F4. However by the time time of the Me 109G5/G6 had
1 Developed bulges over the engine where the large 13.2mm MG131 replaced the rifle calibre MG81
2 Bulges over the wings to incorporate enlarged wheels
3 Lost its retractable tail wheel
4 Didn't have wheel covers.
These problems were probably mostly fixed by the Me 109K1 but it was delayed at least 7 months due to bombing and loss of plans we didn't see them fixed till the Me 109K4 in October 1944.

The major issue of the Me 109G was the lack of range. A small tank (about 100L) was added to the rear but although it was meant to be plumbed for Nitrous Oxide, Methanol-Water or Extra Fuel seems to have carried MW50 most of the time.

A secondary issue was the lack of fire power for engaging 4 engine bombers. This was partially remedied by removable underslung gondola weapons. Latter in the Me 109K6 30mm MK108 canon were to be integrated within the wing.

Why not fit MG131 13.2mm within the wing in 1942? The rifle calibre guns can remain in the cowling without bulges.

 

[Admiral Beez]

As noted by SR6, a 2-speed suprcharged Pegasus is probably the best choice for the Skua - engine is light enough, reliable, no-nonsense and in production, can do another ~100 HP for take off, while also offering much more power at altitude.

Sounds like a good plan.

Can we get heavier bomb load? It's more than engine power, but also the weight of the bomb cradle and mounts. We also need a reasonable takeoff speed for carrier ops. Also, can the undercarriage and hook hold up if we're carrying a full load and for example a 1,000 lb. GP or AP bomb (we'll need to design the latter) and need to return to the carrier? We don't want to be dumping ordinance into the sea after every patrol.

 

[special ed]

Not wanting to derail the thread, I would still like to know how the flexible splines coupling worked. If as suggested a spherical end within tubed splines, then lubrication, especially in a combat aircraft, would be critical. The spherical splined part would not have full contact with fixed splines. Perhaps an expert on the P-39 may have the answer.

 

[GrauGeist]

The shaft at either end (engine/gearbox) would pass through a seal in the housing, much like the front and rear seal on your car's engine where the ends of the crankshaft emerge for the crank pulley and the transmission drive.
The P-39's gearbox (in the nose) had a 2 gallon oil tank that provided lubrication and the shaft's coupling would have been lubricated along with the reduction gears and prop coupling.
The rear of the shaft entering the engine's output coupling would have been lubricated by the engine's oiling system.
The shaft's center carrier bearing assembly would have been greased like your car's driveshaft U-joints or other joints, either by packing or via "zirc fittings" (I'm not sure which).

 

[GregP]

The P-38 was the ARMY fighter that shot down the most enemy aircaft in the Pacific Theaters, not the single aircraft, regardless of service, that shot down the most enemy aircraft for the entire war.

 

[swampyankee]

Torsional stress on a shaft is torque time radius divided by second moment of the area. For a thin-walled tube, this reduces to torque divided by (twice the thickness times the tube area). See Torsion Equations - Roy Mech

 

[P-39 Expert]

The V-1710-63 had a 1325hp rating on take off, the rest seems right.

http://www.enginehistory.org/References/ModDesig/jpg/I30.jpg

What I find fascinating about P-39 models is the seemingly haphazard manor of engine choices.
Some models have engines with critical altitudes of 11 or 12,000 feet, and still others were 14 or 15,000 feet.View attachment 608436
The choices seem to overlap P-39 models.

Data source: USAF Engine Models

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.

 

[XBe02Drvr]

A bullet would not sever the drive shaft!

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

Of course a bullet could disable the gearbox. That is not the discussion.

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.

 

[P-39 Expert]

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]

_________________________________________________________________________________________________________________________________________

All the reading I have done on the P-39 I've never read of a driveshaft problem, never read that the shaft was struck by a bullet, never read that the shaft came loose, no Bell tech reps ever heard of the reduction gears being struck. The nose armor would be unlikely to stop anything larger than a .30cal round anyway, and maybe not even that. Nose armor was useless redundant weight mostly for ballast pending expected larger, heavier propellers. No other planes had nose reduction gear armor.

 

[swampyankee]

While I am far from a big fan of the P-39 -- I feel there were far more disadvantages to the mid-engine location than advantages -- in fighter-vs-fighter combat the vast majority of hits will be from the rear aspect, where the drive shaft and reduction gearing is well-protected by the bulk of the airframe. From the front aspect, a P-39 would likely be targeted by flexibly-mounted guns. The gearbox will be a small target and will also shield the drive shaft.

Alas, I've no access to detailed causes of P-39 and P-36 combat losses.

 

[XBe02Drvr]

All the reading I have done on the P-39 I've never read of a driveshaft problem, never read that the shaft was struck by a bullet, never read that the shaft came loose.

You wouldn't. Dead men tell no tales. Combat losses are generally not accessible for investigation.

 

[GrauGeist]

It's not the shaft being hit by a bullet that's cause for concern, it's the gearbox being damaged.

Plenty of people have pointed out that if the gearbox is damaged, the shaft will bind and let go (just like the Camaro video posted), which is WHY it was protected by armor.

Not sure how many times this point needs to be repeated, but, here we are once again...

And this:
"No other planes had nose reduction gear armor."
Seriously?? How many other fighters had 10 feet of driveshaft between their engine and prop?
As has been said over and over and over and over: conventional fighters (radial and inline) did not need armor on their gearbox because if it took damage, the very worst that would happen is the engine would bind and worse-case scenario, the prop would come apart - at which point, the pilot would most likely want to bale out.

The P-39/P-63 was the only production fighter with 10 feet of spinning steel underneath the pilot, who would be beat to death by the shaft in the event the gearbox was damaged.

I thought this was a fairly straight-forward point being made - but it appears I was wrong...