Who knew? Prop balance.

I kept hearing a plane rev up for a minute and then shut down out behind the hangar. After four or five cycles I peeked around the corner, one of our members was hopping in and out of a plane, tweaking, revving.

Airplane engines are balanced like car engines, drilled holes in the flywheel. The prop is bubble balanced.

The mechanic-technician-A&P has a computer program that identifies the 12 bolts holding the nose cone on as clock positions. You rev it up and the computer identifies which position needs to have weight added. You remove one of the bolts, add a washer under it, run it up again and check the balance.

He was doing a Bonanza when I walked over, he said the after doing his Citabria (small tandem two seater) he could feel the difference via seat-of-the-pants just sitting on the taxiway.

I don't know the cost, but it seems like a worth while investment saving on bearings etc.

Dan

That's really cool. It's one of those things that probably happens around me daily that I never knew about.

That says a LOT for the state of propeller manufacture when a large-diameter unit can be balanced by adding or subtracting a flat washer just slightly outside the center of it's rotational axis.

Amazing stuff! I would LOVE to get into that!

I am guessing it is important to properly torque those bolts!

In reply to pinchvalve:

Safety wire!

In reply to Kenny_McCormic:

Properly installed too.

I have seen what can happen if a prop goes suddenly out of balance. Cessna 3xx, twin engine, one in front, one out back. Pilot started his take off and at about 15 feet up, declared an emergency and requested, and got, clearance for an emergency landing. Came down OK. Turned out that a piece of debris had hit the rear prop and put a 1/2" hole in it. That imbalance took out the main bearings in the front of the engine and dumped all his oil. Could have been a lot worse. This was in Nassau during the Haiti earthquake relief efforts, and this pilot was Canadian. 40K for repairs, and what pissed him of most was that he would have to fly commercial back home.

Out of balence props can and will rip an engine off a plane.

We used to have to do this on the Hercules...that was scary when they were out.

My recollection from when I had a dynamic prop balance done was that it was in the $150-200 range.

Bolted one or two accelerometers to the case and used a strobe on the prop to verify the RPM-- pretty cool.

We've been using automated track & balance on rotor systems on helicopters for years. Getting more refined as technology gets better. Similar to what you mentioned but a bit more involved on helicopters. Can tell you where and how much to add/subtract balance weights and track adjustments. Track is blades/props travel on same path/pitch. Makes a difference. Especially on the long rotor blades on helicopters. Starting to rely on vibration analysis for component life requirements also. Tells us when and which component is going bad before it fails.

Appleseed wrote: Out of balence props can and will rip an engine off a plane.

Very quickly too

When they go, they GO.

Listen to that sound!:

https://www.youtube.com/watch?v=DhyEnqudx8M

We used to balance the fan blades individually on a PW4K-112" then produce a chart to note which blade went in each hub position.. Also, each blade(and there were 22) cost over 6 figures.

Easier than experimentation.

More involved than balancing the blade of a lawn mower.