How Dangerous are Propellers?

[jdermody]

Assume a propeller came free of its mount while a plane was happily flying along. What would be the motion of the propeller?

Assuming the blades are rotating clockwise, would the propeller move in any way towards the right? (i.e would a detached propeller on the left wing impact the cabin?)

Would the motion of the propeller differ if the plane was climbing or descending? (i.e. if the propeller was not aligned with the downwards force of gravity)

And finally, does anyone know of any instances where a propeller has indeed fallen off while the plane was flying?

[Berkut]

@jdermody

Assume a propeller came free of its mount while a plane was happily flying along. What would be the motion of the propeller?

I guess it depends on if you lost a blade or the whole thing. I personally know of one whole assembly that was lost in flight, and he said it came loose and took off straight ahead, leaving him behind. They never found it.

Assuming the blades are rotating clockwise, would the propeller move in any way towards the right? (i.e would a detached propeller on the left wing impact the cabin?)

It could. Certification requirements in the US only call for an inch of clearence between a propeller and the fuselage.

Would the motion of the propeller differ if the plane was climbing or descending? (i.e. if the propeller was not aligned with the downwards force of gravity)

Assuming you lost the whole thing, it would probably have a tendency to veer to the left or right, at least initially.

And finally, does anyone know of any instances where a propeller has indeed fallen off while the plane was flying?

It happens every once in a while. Cracks can cause the loss of a section or the whole blade. Wood props that aren’t torqued properly may detach in flight. We operate nine Diamond DA-20-C1s that have to have the props torqued every 50 hours or we risk losing them.

Here’s one I remember reading about a while back.

[Johnny_L.A]

It could. Certification requirements in the US only call for an inch of clearence between a propeller and the fuselage.

That would be for a multiengine aircraft.

If a part of the prop broke off on the port side, then it would fly off in that direction. The only reason the tip of the prop is going around in circles is because it’s attached. Once it’s released, it will fly off in a straight line, which will be a vector formed by the outward-force vector and the rotational vector. It would be unlikely for it to “come back”, although it certainly can (almost certainly well aft of and below the aircraft) because it has some aerodynamic qualities.

What happens if the whole thing comes off? I don’t know.

My dad bought a six-year-old Cessna 172 in 1976. It was being flown up to him from San Diego to Lancaster, and six inches of prop flew off over MCAS El Toro. The pilot shut down the engine and made an emergency landing at El Toro. The seller provided a new cruise prop for it, and the engine was magnafluxed.

[Berkut]

I assumed having an engine on the left wing would make it a multiengine aircraft. Unless it’s a Rutan design.

No matter the direction of rotation of the engine, if it lets go in the right spot it could hit the fuselage. It’s a little disconcerting in some aircraft to be within a couple of feet of the plane of rotation, especially when ice starts flinging off the prop and hitting the side of the airplane. I (and my shorts) wouldn’t want to think of the racket a prop blade hitting the fuselage would make.

[Johnny_L.A]

Incidentally, propellers and rotors are very dangerous on the ground. They spin so fast that they are sometimes difficult to see. Many people have walked into them. My dad told me that when he was in the Navy someone was blown into the prop of the plane behind another one that just ran up its engine. If you’re walking around the ramp, be sure to give the aircraft a wide berth, and always approach them from a safe direction.

[Johnny_L.A]

I assumed having an engine on the left wing would make it a multiengine aircraft.

You’re right. I mis-read the “would a detached propeller on the left wing impact the cabin?” part.

[Squink]

@Johnny L.A.

The seller provided a new cruise prop for it, and the engine was magnafluxed.

Hey, that’s pretty cool. I didn’t know about magnafluxing.

Magnetic particle inspection is based on the fact that a crack in a magnetized ferromagnetic part creates a small magnetic field on the surface of that part. When iron powder is sprayed onto the part, the field acts as a little magnet to attract the powder to the crack. You may not be able to see a crack, but you are able to see the iron powder collecting at the magnetic field in and around the crack.

[Broomstick]

@jdermody

And finally, does anyone know of any instances where a propeller has indeed fallen off while the plane was flying?

I have a flying friend who lost about a 1/2 inch of a prop blade while in flight. Caused an imbalance in the prop and some serious vibration problems - said it was like riding one of the paint-shakers at the hardware store. He had to shut down the engine completely, then glided to a landing.

I guy I knew from an e-mail list had an entire prop depart his airplane while in flight. Said it left and flew ahead of him and the airplane briefly, then descended. Presumably, it is still on the bottom of the Ohio River. Again, he glided down to a safe landing.

So yes, it can and does happen.

[Sam_Stone]

If you lose the entire prop in flight, the only effect on the aircraft will be A) loss of thrust, and B) a rearward movement of the center of gravity. Whether that rearward movement of the Cg effects the flying characteristics of the plane depends on how heavy the prop is, where it’s mounted, and how heavy the airplane is.

But most prop failures involve the loss of part of one blade. A nick in the prop blade can create a stress riser that causes cracking and eventual failure. Loss of part of the blade is a far more dire situation that losing the entire prop, because the force imbalance can tear the engine right of its mounts, and that will almost certainly make the aircraft unflyable (in a single engine plane, anyway).

[chukhung]

For a real world example of what happens when a propellor blade comes off a plane, you may be interested in reading the National Transportation Safety Board’s report on the crash of Atlantic Southeast Airlines Flight 529 on August 21, 1995.

From the Executive Summary section:

On August 21, 1995, about 1253 eastern daylight time, an Empresa Brasileira de Aeronautica S. A. (Embraer) EMB-120RT, N256AS, airplane operated by Atlantic Southeast Airlines Inc., (ASA) as ASE flight 529, experienced the loss of a propeller blade from the left engine propeller while climbing through 18,100 feet. The airplane then crashed during an emergency landing near Carrollton, Georgia, about 31 minutes after departing the Atlanta Hartsfield International Airport, Atlanta, Georgia.
…
The captain and four passengers sustained fatal injuries. Three other passengers died of injuries in the following 30 days. The first officer, the flight attendant, and 11 passengers sustained serious injuries, and the remaining 8 passengers sustained minor injuries.
…
The National Transportation Safety Board determines that the probable cause of this accident was the in-flight fatigue fracture and separation of a propeller blade resulting in distortion of the left engine nacelle, causing excessive drag, loss of wing lift, and reduced directional control of the airplane. The fracture was caused by a fatigue crack from multiple corrosion pits that were not discovered by Hamilton Standard because of inadequate and ineffective corporate inspection and repair techniques, training, documentation, and communications.

Contributing to the accident was Hamilton Standard’s and the Federal Aviation Administration’s failure to require recurrent on-wing ultrasonic inspections for the affected propellers.

Contributing to the severity of the accident was the overcast cloud ceiling at the accident site.

[GusNSpot]

Lost both tips off a Beech Robie prop on my 85HP Swift GC-1a in 1967. The prop was still balanced enough that during the power application and subsequent landing it was not noticed until I shut the engine down. A friend saw it and found the tips and brought them to me.

Same friend had an PT-22 and one time coming back from Oshkosh, one half the wood prop left. It tore the engine off the mounts and it was hanging down between the landing gear. The fuselage had a 30 degree kink in it behind the aft cockpit. He crashed in a corn field and him and his wife both survived. She got a cut on her head when she released her seatbelt and fell out of the upside down aircraft. ( only injury )

I lost about ½ an inch from a Cessna 180’s prop and managed to shut it down before there was damage. SWO was near enough for an un-powered landing.

Made another precautionary landing at SWO when the spinner and spinner bulkhead disintegrated on that same 180 a year later.

A T-craft had a prop fly off on the ground at Harvey Young airport in Tulsa one time. Looked kinda like that shot on Tora, Tora, Tora where the prop chased that guy. This one did not chase anyone but it was during ‘run-up’ and it looked much the same.
Any of you pilots remember when the ‘Gold Bug’ went to Oshkosh?

[Berkut]

Dang. Have you considering switching to jets?

[jdermody]

Thanks for all your answers.

While I agree it’s really unlikely, I was just mainly curious about the actual motion of a propeller that cleanly separates from the wing. I mean, do the things just drop when they fall off, or do they fly all over the sky due to their massive rotation?

It’s seems that everyone I’ve asked has a different “intuitive” answer on what they think the actual motion would be.

I think if you look at the forces involved then things can get a little confusing. There’s gravity, which may or may not act on the edges of the propeller as they spin, which may or may not induce changes in the propeller’s direction, which may or may not cause the propeller to move in sideways motion.

My maths are really not up to the standard required here, so I was hoping that someone knew of an example where this had actually happened or could figure out off-hand the aerodynamics involved.

I guess it’s not a very practical piece of knowledge but it’s really bugging me trying to figure it out.

[Race_Bannon]

There’s another aspect to consider - what happens to the pitch of the blades after your prop departs the engine? Some propellers (like on small planes) are “fixed pitch”, meaning the pitch of the blades is, well, fixed in place. If such a prop came loose from the engine, and the blades stayed in place, then it would briefly continue producing thrust (from it’s own inertia) and take off ahead of the airplane like one of those toy spinners. After it slowed down (due to drag) it would then just fall to earth.

But, may propellers (especially on larger airplanes) have “constant speed” props, in which the pitch of the blades can be varied to increase performance. If one of those departed the driveshaft, it might be anybody’s guess as to how the pitch of the blades would behave. If the pitch stayed where it was when it broke loose, then it would behave as above. But if the pitch went flat, then the prop would stop producing thrust, and probably just fall edgewise to the ground. It’s gyroscopic inertia would keep it more or less in the same plane (that is geometric plane) as when it left. I see no reason that it would go sideways.

If the blade pitch became unstable, then the thing could flop around in any crazy way till it ran out of inertia.