Because in a belly landing the engine and prop would be turning at minimum power, if not at idle, the prop would be out of its governing range, and if the pilot had any sense at all, he would have killed the engine just before touch down and the prop would be wind milling down at time of impact. This would mean minimum stress on the entire drivetrain when the prop starts hitting the ground, especially since the high wing loading in a power off condition would result in a nose high touchdown so the prop blades get curled inward from the tips in a series of glancing blows instead of a single blade sudden stop.
Improve That Design: How Aircraft Could Have Been Made Better
- Thread starter Zipper730
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Zipper730
I can't take credit for the graph, as I found it in the Wisconsin State Historical Library nearly 50 years ago! Been looking for performance graphs ever since. Found Nirvana with AHT. Mike Williams and Neil Sterlings web site and TAIC manuals.
Eagledad
I can't take credit for the graph, as I found it in the Wisconsin State Historical Library nearly 50 years ago! Been looking for performance graphs ever since. Found Nirvana with AHT. Mike Williams and Neil Sterlings web site and TAIC manuals.
Eagledad
- Thread starter
- #803
It's hard to find graphs for certain aircraft, isn't it?
Regardless, I do like the way everything is laid out very well on one graph.
I am familiar with a case where a OH-6 tail rotor drive shaft come free from the tail rotor transmission, It whipped around,destroyed the tail boom, then got into the main rotor. It evidently happened so quick no mayday message got transmitted, Both occupants died.
It took a few weeks before the investigation determined the order of the failure from the scattered wreckage left.
And that was from a drive shaft that had only a fraction of that engine's power going through it.
Imagine in the P-39, the driveshaft going beneath the pilots butt, and then going forward right between his legs, and it's transmitting over 1000 hp.
Can you guess what would happen if the forward transmission failed and that driveshaft did detach from it. There would be no survivor, and scattered wreckage.
Under WW2 conditions, just how much investigation would there be ?
Maybe that's why that isolated forward gearbox was armored, some failure modes of it could be catastrophic .
There were tons of rumors in the military.
I remember one I heard in basic.
They put saltpeter in our food to make us impotent.
The infamous "buzz balls" theory.
The point I've been making all along. Now convince our favorite Ex-spurt.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Okay, you convinced me.
davparlr
Senior Master Sergeant
I'm having a hard time biting on the driveshaft issue. First, while I haven't read much about the P-39, and, while there are a lot of complaints about flying the plane, driveshaft issues and failures does not seem to pop up much. And this issue of getting a bullet through it causing catastrophic failures, how about a bullet or shell through a propeller blade, or hub, a fuel line, the pilot, or a control line. In wartime, an aircraft is not a safe place to be.
If you get a bullet through the propeller blade, it would depend on what size bullet, either a hole with a whistle and slight imbalance, keep flying.
Big shell through propeller, you'd might loose the blade outboard of the hole. Big imbalance that could shake the engine right out of it's mounts if you didn't shut the engine down in time.
Bullet in the hub, same thing , same as above..
Bullet in the fuel line ? Obvious result, reduced flight time, maybe fire.
Bullet in the pilot ? Maybe that's why they try to put a lot of armor around him. Of course something might get through with obvious results.
Bullet in the control line ? That's why they're made of cable, it takes a solid hit to sever the cable clear thru. If it does cut the control cable, or tube, or whatever, reduced control ability.
All those are not instant catastrophic failures, except maybe a bullet in the pilot's heart, or brain.
I've circle track raced for over 20 years, I've seen a loose drive shaft, from a broken back u-joint, flip a 3500 lb car instantly.
That's why most car racing associations require driveshaft hoops, front and rear, made from 1/4 in. steel.
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Wouldn't that be a front U joint, which would act like a pole vault pole as the shaft dropped and dug in?
Simon Thomas
Senior Airman
From "Short Stirling, The First of the RAF Heavy Bombers – Pino Lombardi"
IIRC, one reference quoted 15,000 lbs of extra weight. To put this in context, it is roughly equivalent to the Stirling having to carry an empty de Havilland Mosquito or fully loaded Hawker Tempest. I am sure you could imagine the impact if the Stirling was ~15,000 lb lighter on every mission would have a significant impact on cruising altitude and speed. [Is there an easy way to determine the increase in cruise altitude with a weight reduction of 15,000 lbs?)
The 100 ft limit on the wing span was not related to hangars. I have read a few books on the Stirling, and there is no clear answer however most point to the Air Ministry using it to limit the all up weight. Which is rather ironic, considering the plethora of mandatory requirements which drove the weight so high in the finished product.
I have a WAG that watching the Stirling go from a reasonable aeroplane to an overweight underperformer may have taught the Air Ministry officials to not interfere as much. They did not allow Shorts to use the 112' wing they had already designed, and they were refused permission. Not that much later Avro and Handley Page wanted to add extra engines, and that was allowed. Adding extra engines would take considerably more time to engineer and get into production than using a wing design that already existed.
Mind you, this still happens today. The Royal Australia Navy wanted to buy helicopters, and then drowned them in specifications to the extent that they were incapable of entering service. Seasprite - The Billion Dollar Blunder
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.
The choices seem to overlap P-39 models.
Data source: USAF Engine Models
The race car didn't have the heavy bearings bolted onto the frame the way the P-39 did. The race car's drive shaft has to take suspension movement into account. The P-39 didn't have universal joints.
Attachments
The stress of stopping would be more immediate on a belly landing.
A bullet would not sever the drive shaft!
Or, if it was big enough to, it would obliterate the aircraft and ANY armor it could carry.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
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.
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.
No in this particular case it was the rear u-joint, it hit the pavement hard enough to turn the car over, then the driveshaft slide out.
The front U-joint was still on the shaft, the rear broken U-joint half was still on the rear end.
Though I've seen it happen more often the way you describe.
After a few years of those types of mishaps, they started requiring drive shaft hoops on all RWD cars, no matter how little HP they have.
The rear U-joint breaking is by far the most destructive of the 2 failure modes.
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.
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GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Back in the 80's, I saw a Pro-street Charger blow his pumpkin on the launch and the driveshaft ripped free of the loops, launching it sideways through the fence and into the crowd.
No one was killed, but seeing that beast hurling into the crowd while we were dodging ring-gear, pinion and spline debris left a lasting impression.
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