Thorp Air Command - T18.net

Building a 200-215 hp 360 with a throttle body.
With that hp , anyone out there with a reccomendation on the pitch. I hear 68x76 alot.. but seems those are lower HP units.

Thoughts?

I have a metal prop off a grumman cheetah. Im going to cut and have a prop ship pitch it. Where do i Start with the pitch and that HP.
Appreciate input from others with 200+HP.

I’d say 68/85. Somewhere close to that.
Cubes

My O-360 makes 196hp and it has a 68X80.

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Scott Hinton
N149RH
KECG
Elizabeth City, NC

Make sure you read all the written in blood history of cut down metal props before you go much further.

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Bob Highley
N711SH
SN 835
KLAL

Me personally, I wouldn't re-pitch a metal prop except to fine tune a degree or two and I would not cut a metal prop down, but that's me. That said I'm running a Whirlwind ground ajustable prop on my O290 68" dia and love it. You can get them in 68" 70" and 72" dia. If you have the long gear you could use the larger dia prop. My prop was $2500, cheaper than a Catto . I would give them a call and see what they have to say about a 200 HP engine installation.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

To Bob's point there are only 2 metal props that will not kill you in a Thorp .. 1970-80s era Sensenich M76 is considered 'safe'. That being said even the M76 should be harmonically tested before use. If the prop you're considering using came off a Cheetah ... it's not safe. The only other metal prop considered safe right now is the type developed for the RV ...

http://www.sensenich.com/product-catego ... l=aluminum

maybe consider one of the ground adjustable Sensenich composite props or a Cato?

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I never knew that about only two props. Why are the metal props so problematic on a Thorp, Lee?

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

Here's the warning on our SDR list ...

"5. Cutdown Metal Propellers- If your airplane has a cutdown metal prop, especially an M74, replace it immediately. The M74 will fail (every time ), usually with a low number of hours. The M76 is supposedly "safe" for being cut down, but should also be viewed as a risk, especially if it has not been thoroughly tested by a qualified prop shop. Newsletter 79 has a lot of data on these props. If you are looking to buy a new metal prop, check with www.Sensenich.com for new props that are designed for T-18/S-18 engines and flight speeds. Also see NL 47. Recommended Sensenich wood props: W66LM for 125-179 hp, W68LY for 180 hp. (Note: These may no longer be readily available.)"

Here's a link to an article written by Lou Sunderland .. still relevant to date for our airplanes ... in short harmonics.

http://thorp18.com/thorp_files/1972_11_09_.pdf

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

THANKS GUYS,
WILL GO WOODEN :!

Hi All,
I have bought an IO360B1A2 engine for my S18. I would like to hang a constant speed prop on it. Some of the comments here give me pause. Any recommendations?

Thanks,
Pancho

If I were looking for a constant speed prop I'd start with the ones from Whirlwind, they are designed for the RV series of aircraft so I would think they would be very compatible with a Thorp. Note: they just started selling a 3 blade version. Full disclosure I'm currently flying with a Whirlwind ground adjustable prop and am very happy with it.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

Those comments are for fixed pitch metal props. The Hartzell CS units have been fully tested.
Cubes

I liked the Airmaster electric constant speed prop. But it's expensive and in testing it showed vibration problems with the IO360 engine, so not advised. I ended up buying a Sensenich three-blade ground adjustable prop. Should suit me fine.

Catto makes a nice three blade fixed pitch that seems to work well. They will also work with you to re-pitch if it is not quite right and all you pay is the shipping.
Speedbird 1

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N872DD
200hp Lycoming