[Desert Rat]

I should probably know the answer to this, but I don't recall the last time I flew a 4 cylinder with a 3 bladed prop, or how it behaved at shutdown. Of the 2 ways you can index a prop on a 4 cylinder Lycoming, which way is more likely to have a 3 blade stop with one blade pointed straight up at shutdown?

W.W. says their prop doesn't care which way it goes, and that the engine will just stop wherever it stops, but based on the fact that 2 blade props almost always stop at 10:00 and 4:00, it seems like there must be a sweet spot.

The options are to have a blade aligned with the TDC mark on the back of the flywheel, or 180 degrees out from that.

 

[rockwoodrv9]

I should probably know the answer to this, but I don't recall the last time I flew a 4 cylinder with a 3 bladed prop, or how it behaved at shutdown. Of the 2 ways you can index a prop on a 4 cylinder Lycoming, which way is more likely to have a 3 blade stop with one blade pointed straight up at shutdown?

W.W. says their prop doesn't care which way it goes, and that the engine will just stop wherever it stops, but based on the fact that 2 blade props almost always stop at 10:00 and 4:00, it seems like there must be a sweet spot.

The options are to have a blade aligned with the TDC mark on the back of the flywheel, or 180 degrees out from that.

If there is a clocking stop position on a 3 blade, I didnt know that. I have a CATTO and it sort of stops wherever it wants. At least I think! I will pay more attention and see if it does stop in the same position.

 

[Mel]

With a 2-blade prop, you are dealing with an even number of compression strokes per revolution and an even number of blades.

With 3-blades (odd number) relative to an even numbered compression strokes, the prop will stop at random positions. There is no practical clocking of the prop that will accomplish what you want that I know of.

 

[Desert Rat]

With a 2-blade prop, you are dealing with an even number of compression strokes per revolution and an even number of blades.

With 3-blades (odd number) relative to an even numbered compression strokes, the prop will stop at random positions. There is no practical clocking of the prop that will accomplish what you want that I know of.

I guess that makes sense. I'm thinking of all the 3 blade props I've flown over the last few years and they are all 6 cylinders, which makes the calculus different.

Thanks!

 

[dmattmul]

I guess that makes sense. I'm thinking of all the 3 blade props I've flown over the last few years and they are all 6 cylinders, which makes the calculus different.

Thanks!

It's a guess. Prop stops in a variety of positions. When I installed my 3 bladed prop I measured each blade tip tolerances at the bottom. (Initially 3/16th of an inch difference) Then using Vibrometer app measured static readings at 2,400 RPM. Flew the airframe for 2 to 3 hrs. Then re-clocked the prop 180 degrees. Tip measurement's now 3/32nds and vibration app improved. Very smooth. I am not sure of a better method. If you find one let us know. Trial and error.

 

[riseric]

Interesting question,
I confirm that the prop stops either as a "Y" or 180° opposite, ramdomly.

 

[Dan 57]

I confirm that the prop stops either as a "Y" or 180° opposite, ramdomly

More or less the same here, my 3 bladed MT stops about 67.9% of the time in the Y position, the rest with one blade pointing skyward

 

[John RV8]

More or less the same here, my 3 bladed MT stops about 67.9% of the time in the Y position, the rest with one blade pointing skyward

Interesting…. My MT 3 blade stops 74% of the time with one blade straight up. Even more interesting is that the SAME blade usually ends up at the lower right location. I know because that is the only blade that has a blemish (came from the factory that way).

 

[Mel]

Interesting…. My MT 3 blade stops 74% of the time with one blade straight up. Even more interesting is that the SAME blade usually ends up at the lower right location. I know because that is the only blade that has a blemish (came from the factory that way).

Possibly because one particular cylinder has slightly higher compression than the others.