Propeller breaks at 13,000 feet

[ayavner]

wow:

 

http://www.cnn.com/video/data/2.0/video/us/2014/09/22/dnt-plane-crash-survivor-speaks.ktvu.html

 

I wonder - shouldn't he have killed the engine and glided it in rather than attempt to fight a bucking plane with a broken prop?

 

Good outcome, and they actually got the model right this time!

 

 

[Teckair]

I wonder - shouldn't he have killed the engine and glided it in rather than attempt to fight a bucking plane with a broken prop?

Yep I think so, I would be worried the engine might rip itself off the plane and that would be the end then.

 

 

[ayavner]

i've thought about that often, and i am pretty sure that would be my instinctive response would be to kill the engine asap.

 

 

[flyerme]

Yep I would definitely have killed the engine. My old bunyip had safety wire wrapped around engine and mount, as the old owner lost a blade once and cracked the engine mounts ( yes he shut it down) So when he replaced the mount he also put the wire around the lot to be sure I guess.

 

 

[rgmwa]

So when he replaced the mount he also put the wire around the lot to be sure I guess.

That doesn't sound like it an AC43.13 approved method of aircraft construction. He wasn't a farmer by any chance was he?

 

 

[flyerme]

Loo

 

That doesn't sound like it an AC43.13 approved method of aircraft construction. He wasn't a farmer by any chance was he?

yep farmer that used it for mustering , still had air horn fitted( which was fun)lol

 

 

[rgmwa]

Looyep farmer that used it for mustering , still had air horn fitted( which was fun)lol

Ah yes. So it would have been baling wire then, not safety wire.

 

rgmwa

 

 

[Teckair]

Ah yes. So it would have been baling wire then, not safety wire.rgmwa

I have only seen hay bales held together with twine, so might be best to use double thickness for this job.

 

 

[Old Koreelah]

I've heard of Rotax engines, after throwing part of the prop, vibrating so badly that one or both carbies came off their rubber mounts, stopping the engine before it broke free. Seemed a damned good design feature for carbies to be so loosely attached. Inspired by this, I ran a slightly loose steel cable around my Jab. engine's Bing, in the hope that it would be yanked free in a similar situation.

 

 

[rankamateur]

I have only seen hay bales held together with twine

You are showing your (young) age, I may be even younger than you but have seen a few wire tied bales from an ancient baler. The wire used is some of the most user friendly wire you are likely to encounter. Might be a good thing if he did use baling wire.

 

 

[flyerme]

Here's a pic of my old redneck farmer bunyip engine frame! With safety wire lmfao. Ok I will be honest it really part of the new hangar I'm building

 

 

[frank marriott]

You are showing your (young) age, I may be even younger than you but have seen a few wire tied bales from an ancient baler. The wire used is some of the most user friendly wire you are likely to encounter. Might be a good thing if he did use baling wire.

Wire tied bales (rectangular shape prior to the large round ones) was common in the 60s. From a carrier's point of view they were better to cart, no string breaking, and you could load them using "wool hooks" - easier on the hands.

 

 

[johnm]

photo's attached are a broken in flight prop ................ in the circuit

 

Carbs were pulled out by vibration !

 

 

 

[nong]

[Dafydd Llewellyn]

OK, you have, say, a 60 inch fixed-pitch wood propeller that weighs four pounds, turning at 2700 RPM. The centre of gravity of each blade will be somewhere about one foot (300 mm) from the axis of rotation. What's the centrifugal force at the centre of the propeller hub?

 

The formula for the centrifugal acceleration is radius x (speed of rotation squared); the speed of rotation in radians per second.

 

2700 RPM = 45 revolutions per second. There are 2 pi radians per revolution, so that's 283 radians per second.

 

So the centrifugal acceleration is 1 x (283 squared) = 80,089 ft/sec^2. 1G = 32.2 ft/sec ^2, so that's 2487 G acting on the blade - so the force will be 2487 x the mass of the blade (2 lbs) = 4974 pounds force, i.e. 2.2 tons.

 

The engine mount is stressed for 1.5 times the engine weight, acting sideways - so for a 180 lb engine, the mount will be designed for a limit side load of 270 lb Force; and the required factor of safety is 1.5, so it will break at a bit over 405 pounds force, i.e. a bit less than 1/4 of a ton, under the side load. It's also stressed for around 6 times the engine weight, vertically down, i.e. around 1080 lbs force.

 

Either way, if half the propeller departs and the other half stays on the engine, the engine is almost certain to part company with the aircraft. This tends to result in the CG being not where the designer intended, so you get a short and very interesting ride.

 

Fortunately, when a fixed-pitch wood propeller fails, it almost always does so in the middle in such a way that both blades depart virtually simultaneously. This is one of the reasons I like fixed-pitch wood propellers, especially certificated ones.

 

 

[facthunter]

When a prop chucks a blade you have a problem for sure. It's something we should pay more attention to. If you don't run a certified prop/engine aircraft combination, run a wood prop, or something that has proven itself extensively in the field and do all required inspections, and LAND if any vibration changes and check why. Most times you won't get a lot of warning. The Allison turboprops on the Electra and C-130 have vibration meters on each engine and you shut them down quicktime if they don't read right. They have hollow steel blades and get a lot of cracks. Nev

 

 

[Old Koreelah]

When a prop chucks a blade you have a problem for sure...Most times you won't get a lot of warning...

Sobering thought, Nev. That's why some sort of "automatic" shutdown is needed; it takes a normal human a couple of seconds to recognise the problem and react. By then the engine may have shaken loose, leaving an uncontrollable aircraft.

Jabiru engines normally shutdown by shorting out the coils, but those flimsy wire connections could be instantly pulled out by a badly-vibrating engine.

 

 

[facthunter]

You have an instantaneous overload to an over the design limit level. It might help if the engine has dislodged and is rattling around loosely restrained by part of the structure.

 

A Chipmunk chucked a blade (Fairy Reed aluminium prop) over Lake Macquarie. The engine fell out and the very markedly tail heavy ( but much lighter,) aircraft spun in without serious injury to the pilot (if my recollection is correct).. You normally don't survive a Chippie spin in. as the ROD is high. Nev

 

 

[Dafydd Llewellyn]

When a prop chucks a blade you have a problem for sure. It's something we should pay more attention to. If you don't run a certified prop/engine aircraft combination, run a wood prop, or something that has proven itself extensively in the field and do all required inspections, and LAND if any vibration changes and check why. Most times you won't get a lot of warning. The Allison turboprops on the Electra and C-130 have vibration meters on each engine and you shut them down quicktime if they don't read right. They have hollow steel blades and get a lot of cracks. Nev

Yes, indeed. In recreational aviation circles, some people seem to regard the propeller as some sort of fashion accessory. The reality is that propeller failure is just one notch less disastrous than losing a wing.

 

 

[pmccarthy]

Could we have a piece of 5 tonne capacity steel cable between the engine and airframe? It might hold the engine where it needs to be for ballast after the electrical and fuel lines are torn out and the engine stops. Assuming there is a suitable attachment spot on the airframe.

 

 

[facthunter]

Be a problem when landing. An Ansett DC-6b shook an engine out over Port Phillip bay rather than risk it coming out during the landing. It would have fouled a landing wheel if that had occurred. Nev

 

 

[PA.]

Ballistic Chute anyone?

 

 

[Dafydd Llewellyn]

Compliance with a suitable design standard - e.g. FAR Part 35 - or CASR Part 35, for that matter - and the appropriate maintenance requirements - provides adequate safety as far as most people are concerned. Discussing ways to compensate for sub-standard propellers by such measures as ballistic parachutes is about as sensible as debating the merits of various shark repellants, to allow one to swim off Victor Harbour when the Great Whites are about.

 

A sane person who understands the risk, simply avoids the problem. There are at present a considerable number of manufacturers who market composite-bladed propellers. You can count the ones who have put their product through Type certification on the fingers of one hand.

 

Attached is a typical GA propeller Type Certificate Data Sheet. The most interesting part of it is the table of engines for which the propeller has been cleared (in single-engine tractor applications) in regard to vibratory stress (which causes blade fatigue failure in a metal propeller, and can cause delamination in a composite propeller.) It starts about half way down page 6. The "crankshaft damper configuration" refers to the use of tuned pendulous counterweights on the engine crankshaft, to reduce the propeller blade vibratory stress.

 

Now, go see if you can find this sort of information for any composite propeller for recreational aircraft. If you do, please let me know.

 

McCauley2A34 series.pdf

 

McCauley2A34 series.pdf

 

McCauley2A34 series.pdf

[Dafydd Llewellyn]

Could we have a piece of 5 tonne capacity steel cable between the engine and airframe? It might hold the engine where it needs to be for ballast after the electrical and fuel lines are torn out and the engine stops. Assuming there is a suitable attachment spot on the airframe.

You have answered your own question. What suitable attachment spot?

 

 

[facthunter]

I think I would be happy to see the engine go if there is a lot of damage. Once you lose the weight the plane will probably flat spin at a vertical speed that you can live through. The big worry is with pushers. You are likely to sever the boom. Nev