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Hayes disc brake stops Larrys Jet engine propeller.

I flew my ultralight turboprop ultralight up to about 4000 feet AGL and shut off the turbine engine just to see how well it glided. I measured the glide slope using a Garmin GPS-60CS and a Garmin GPSMap 276. But what happened next scared me. The free wheeling prop (an IVO 372) spun up to a high RPM with a shuddering vibration as if it was out of balance. And my glide rate decreased as it spun up. This was not cool. I re-started the engine and flew home, after a couple of wing-overs to lose altitude (and extra fun:-))

I found a Thesis by Peter Sprunger, Goshen College, on windmilling propeller drag. His data shows that it depends a lot on the pitch of the prop. Of course a feathered prop will have the least drag, but I cannot feather my fixed pitch prop and because the pitch is very little I'm convinced the best thing to do is stop the prop and prevent windmilling in an engine out condition.

A normal internal combustion engine on an ultralight has enough compression to stop the prop from windmilling however my gas turbine has zero compression and whats more - it's "two spool" turbine which means it has a free turbine - which spins free - which means windmill city big time. It's like draging a 6 foot diameter parachute behind! It wrecked my 7 to 1 glide ratio.

What to do?

In addition to that, I now have an amphibious aircraft. How can I stop in the water without stopping the engine? --- duh, how about I stop the prop?

I shopped a bit and found a fairly low cost Hayes GX-2 Mechanical Disc Break for about $45.

I attached the brake to the propeller shaft. A brake made for bicycles.


I didn't think it would work and it took a lot of effort to find out. I had to modify my hub to accept the disc and make a very strong bracket to hold the caliper. So I was very happy to discover it works really well. I have enough control to position the blades out of the hot jet exhaust. I don't know what happens to an IVO prop when it's cooked. Hmmm, I have some old blades - maybe next time I run the engine I'll hold one in the exhaust and see. It would be very cool to know how hot it gets and if it's not a cool thing to do, and exactly how un-cool it is.

Gas turbine engines you know don't idle down very well but this one will idle low enough that I can taxi around OK after adding good breaks to my two main wheels. But in the water I'll be having some big problems, and of course there is that worry about an engine-out and the windmill problem.

This brake idea solves a lot of problems and introduces no new ones that I have thought of - and the added weight is very little.


IPO: 7Jan96