Damaged Propeller in Flight

[Rotor-Head]

On February 20, 2004 after a short successful flight around the valley I landed to double check all the critical nuts and bolts on the gyro before going on a longer flight.

I then proceeded to start the gyro back up and taxi out for take-off. I applied the pre-rotator gently and slowly got the blades up to roll speed. Right as I lifted off the ground, I heard a soft "clunk" and felt a very mild vibration on the engine. I proceeded to do a 180 degree turn and land. Right at touch-down, the vibration got really bad and I heard the prop crack and shatter. I imediately shut the engine off (I was on the ground just rolling by this point).

Upon inspecting the propeller, I saw that the 2 bolts that hold the pre-rotator on had stripped and came out. The entire pre-rotator rubber wheel assembly had moved back into the propeller causing the initial damage. When I landed, it must have shifted back again doing the bulk of the damage to the propeller.

It was a bit frightning, but I stayed fairly calm and collected. Right when it happened I knew it was the propeller, and I was in a good place to get the machine down quickly and safely.

For more pictures, go to: http://www.rotor-head.com/stories/broken_prop/index.html

[Victor Duarte]

Wow,
you took the good decision, what is it due to ?
well... glad to read that..from you in person ;)

[birdy]

Woz it the thread on the rodends that stripped ???

Sh1t happens.

[barnstorm2]

Wow! Glad to hear you are ok! Good recovery!!

[Rotor-Head]

Woz it the thread on the rodends that stripped ???

Sh1t happens.

They were only threded about 2/3" inch in. The bolt threads didn't strip, the mount threads did... I am thinking that perhaps the rubber wheel somehow stayed slightly engaged after I released the pre-rotator handle and it worked out from just spinning at 3000 rpm. I'm not sure though.

[birdy]

There'd be alot of 'bending 'stress on those bolts/threads when your prerotating.
Longer threads and a lock nut on the protruding thread would be much more secure.Better still, drill out the remaining thread and use lock nuts on both sides of the mount.
Most rodends are only designed for tension/ compression, not shear or bending .

[Jerseywing]

That sucks... At least you were close and got down to terra firma before it went away.
Good work flying, I hope it won't be too expensive to fix, but like I've said before it's only stuff and can be replaced. You can't

Mike

[bones]

Man bad luck ive given mine a fair hammering over the time and its held together so far but i think i'll chexk it a bit more often

[animal]

[QUOTE=Rotor-Head]On February 20, 2004 after a short successful flight around the valley I landed to double check all the critical nuts and bolts on the gyro before going on a longer flight.

I then proceeded to start the gyro back up and taxi out for take-off. I applied the pre-rotator gently and slowly got the blades up to roll speed. Right as I lifted off the ground, I heard a soft "clunk" and felt a very mild vibration on the engine. I proceeded to do a 180 degree turn and land. Right at touch-down, the vibration got really bad and I heard the prop crack and shatter. I imediately shut the engine off (I was on the ground just rolling by this point).

Upon inspecting the propeller, I saw that the 2 bolts that hold the pre-rotator on had stripped and came out. The entire pre-rotator rubber wheel assembly had moved back into the propeller causing the initial damage. When I landed, it must have shifted back again doing the bulk of the damage to the propeller.

It was a bit frightning, but I stayed fairly calm and collected. Right when it happened I knew it was the propeller, and I was in a good place to get the machine down quickly and safely.

man glad you made it down safely. I some times think rod ends are used in to many places where a bracket would be safer,I have seen them used for everthing from mounting control sticks ( guilty my self on that design idea) to mounting landing gears. and when testing the dusty2 Prototype,learned they can break easyer then you might think.and that you can over torque and strip the threads on a/n nuts and bolts. I may not have gotten the Dusty2 to fly, but I sure learned alot, 6 years of designing and testing. if i had at the time had a backer I probably could have made it fly,but at the time it was all self funded and i was going thru a bad time,bad marriage and devorice. I won't make that mistake again. but from the pic of the way it mounts I can't help but wonder why they did not machine a simple bracket with some needle bearings insteady of rodends.again glad you made it down safe and brought this to everyone attention. stress on parts do starnge things to metal.when i tore down the Scorpions rotorshaft and head to do my mods I noticed the solid rod part of the flex cable where the rod end screws onto was bent at a 7 degree angle,needless to say if I had tryed to fly with that, you would be reading about me and not in a good way.

fly safe.
Tim

[Doug Riley]

Shawn, I have an '80's Air Command nearly identical to yours. That's an older model of the Wunderlich lower unit. There's a newer, beefier version that doesn't use rod ends. Both the stationary half and the moving half of the hinge on the newer model are solid aluminum castings.

Ed Alderfer had one of these lower units come loose and get into the prop back about 15 years ago. The flex shaft caught in the prop right on takeoff, jammed and caused the gyro to do a snap roll into the ground. Fortunately, Ed wasn't hurt. Such an accident is a recipe for a broken neck at ground level and a near-certain fatality at altitude.

After hearing Ed tell this tale, I started safety-wiring the whole lower end unit with a "cable" made of four strands of .040 safety wire twisted together and encased in a piece of fuel line. The wire forms a loop around the lower end unit and flex-shaft housing and is attached to the engine. The idea is to keep the unit from sliding back into the prop if it comes loose thanks to a cracked casting or similar failure.

A more professional-looking safety retainer could be made up from aircraft cable, Nico sleeves and thimbles. It wouldn't hurt to put one at the upper end of the flex-shaft, too, since that end also is secured by light pot-metal castings that crack fairly easily.

[Rotor-Head]

Doug, I was actually thinking of putting a backup harness on it of some sort to keep it from ever impacting the prop again.
Do you know where I can get one of these newer systems? Everything from my Flex Shaft and higher was not damaged (just the rubber wheel assembly was bent). I am about to put my CLT kit on and it would be a good time to do the re-rotator right!

[Doug Riley]

Dick Wunderlich, the manufacturer of the prerotator, sold me the newer style unit. He doesn't use the Net, but he can help you over the phone. He's listed in the PRA magazine. Maybe someone has his number handy...?

[CLS447]

Once , while prerotating something didn't feel right. One of my rod ends had broke. No flying that day. I replaced them both & I was back in business.
I look closer at this when I preflight now, of course.

Please keep us posted on your PR upgrade & your CLT upgrade progress!

[Doug Riley]

Wunderlich's: (815) 838-0450, FAX 838-0630.

Birdy's right: Rod end bearings can't take bending loads applied to the stems. It's best to get rid of the rod-end type of lower unit.

[Udi]

...The flex shaft caught in the prop right on takeoff, jammed and caused the gyro to do a snap roll into the ground...
Is there enough momentum in the engine and prop to actually cause a snap roll if jammed in flight??? I guess the momentum comes from the prop and the flywheel, if there is one. Wouldn't the prop/shaft/gear break before they can transmit that kind of torque back into the frame?

Udi

[Doug Riley]

I didn't see it happen. Ed's a pretty honest guy and a high-time gyro pilot. I believe him when he reports that the gyro flipped out of control as a result of the flex shaft's tangle with the prop. The machine was a first-generation Air Command that was intended for Ed's wife, Bernadine.

The one time I had a similar experience (BRS cable in the prop) was in a FW U.L. plane and the wooden prop just shattered into toothpicks. The pusher engine was ripped completely out of its mounts and was left dangling off the craft, suspended only by the choke and throttle cables. I didn't notice much rolling reaction, just a noise like hitting a log with a rotary lawnmower, followed by instant silence.

Putting a thick steel cable into the prop at full throttle is just not a good thing.

[Rotor-Head]

I guess I got off easy. No other damage except the pre-rotator lower assembly and a prop....

[mceagle]

Good point Udi. I have seen two instant engine lockups and though there was a considerable torque reaction, it was controllable and both Gyroplanes landed successfully.

[Timchick]

Shawn,
Sorry to hear about your prerotator mishap. That's a real bummer with you just getting in the air and everything. It's good it didn't do any more damage and you didn't get hurt.

My friend is letting me take his 3 chip Panasonic mini dv camera to Bensen Days. I would've rather taken one of his Sony's but beggers can't be choosers.

[Rotor-Head]

Here is my new prerotator. Notice I have some wire securing the bottom assembly to the engine mount and I have added a pipe fitting to the flex cable and secured that to the flex cable locking screw. I don't think this one is going to be a problem.

[CLS447]

Wow, that was fast. Just how much was that beauty? I still have the old one. Thanks for the picture. I see several improvements..... heavy cast pivot points, where the flex shaft goes in not only is there set screw, but a pinch bolt also. The return spring is connected to the casting instead of a small angle tab. Also, the activation cable stop looks to be better than the small steel tab that I have.


Do you see any other things that you like about it better than the old one? Does it work the same or better? What all did you buy and how much was it?

Thanks

PS Your pipe fitting looks to be an aviation clamp !

[Rotor-Head]

Yeah, it's a lot beefier. On my old prerotator, if you grab the flex shaft, the entire lower assembly would move, now it is totally solid... and in engages smoothly...

[Rotor-Head]

Do you see any other things that you like about it better than the old one? Does it work the same or better? What all did you buy and how much was it?


This one is much better, smoother and stronger. It was $195 (just for the lower assembly). Well worth it, not just in parts, but peice of mind.

[scott heger]

Shawn, why not safety wire that silver spring on the end? If it breaks from vibration, the prop is not going to be very happy either. I have broken 2 Rotax exhaust springs so far, and because they were safety wired, no damage occured. Just something to think about.

Scott Heger, Laguna Niguel, Ca N86SH