Thorp Air Command - T18.net

I searched both forums but came up empty. Has anyone tried an Aeromatic propeller? Variable pitch in flight while being much lighter than a constant speed seems like a good idea but the blades may be too long (74 inch diameter according to the Type Certificate).

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

That's interesting. It appears they are able to be used on a pretty good list of certified airplanes. I must admit, the idea of the prop changing angles without my control is at first blush a little uncomfortable, especially if it became a runaway situation, but I guess you could have a prop governor failure as well.

A constant speed prop is constantly changing pitch without input from the cockpit to maintain the RPM you selected to run. The Aeromatic doesn't work much different in theory except that it sets the RPM for the conditions and you can't flatten it to slow down or over square it for a little more speed. It automatically gives low pitch for takeoff and automatically adjusts itself for cruise but the way it works is self limiting to the altitude window it was set up to run in. Manifold pressure is still used to set power. I don't think it be a good option for someone based at sea level who frequently flies above 5 or 6 thousand feet. Someone based at 5,000 feet msl would have to be careful not to over rev the engine when flying from lower elevations but would be good to higher altitudes.

I witnessed a governor failure from the ground at the air races one year. The engine screamed then seized, breaking the prop in the process. The pilot was able to land the aircraft.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I tried one of these props on my Stinson 108-3. It worked ok but it had a vibration that I did not want to have to put up with especially with the NOS crank I had I in the 165 Franklin. The Franklin engine is the smoothest engine I have ever flown behind so adding a prop that vibrated seemed to defeat the purpose. The blades are wood and the support for the prop at the time was questionable.

regards,

Jim

Jim,
Franklins are smooth. It is a shame they made the bottom spark plugs so hard to get to. Do you know if the prop itself was vibrating or if you had a mass imbalance that could have been corrected with a few grams of well placed weight and/or by re-clocking the prop?

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Jeff,

We did take it apart and found that there were Allen head lag bolts on one blade and regular hex head bolts on the other blade. These bolts retain the wooden blades into a steel shank. I suspect that this was the reason for the imbalance. The prop did work well and allowed the Franklin to wind up on take off. I also had the 220 HP manifolds on it so it was a good performer to start with. It was the best flying aircraft I have ever flown. It was fabric and it looked like the fabric would be due about the time I was planning on retiring. That would not have been a good conversation to be having with the wife at that time, hence the Thorp entered the picture. The Thorp has turned out to be a plane that has made me a better pilot. It's also been a lot cheaper plane to keep flying. I don't miss the $1000.00 CDN spark plug changes.

Regards,

Jim

Thanks Jim. I had read there was some problems with one of the overhaul shops but nothing specific. Mismatched hardware may or may not have been one of the issues.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson