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Jwsteele1981
PostPosted: Sat Aug 08, 2020 5:53 pm 
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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.


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James Grahn
PostPosted: Sat Aug 08, 2020 7:35 pm 
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I’d say 68/85. Somewhere close to that.
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ScottECG
PostPosted: Sun Aug 09, 2020 5:19 am 
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My O-360 makes 196hp and it has a 68X80.


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fytrplt
PostPosted: Sun Aug 09, 2020 11:46 am 
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Make sure you read all the written in blood history of cut down metal props before you go much further.

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bfinney
PostPosted: Sun Aug 09, 2020 4:30 pm 
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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 8). I would give them a call and see what they have to say about a 200 HP engine installation.

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leewwalton
PostPosted: Tue Aug 11, 2020 8:48 am 
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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
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jtwigg
PostPosted: Thu Aug 13, 2020 1:25 pm 
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I never knew that about only two props. Why are the metal props so problematic on a Thorp, Lee?

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leewwalton
PostPosted: Thu Aug 13, 2020 2:03 pm 
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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
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Jwsteele1981
PostPosted: Sun Aug 30, 2020 9:12 pm 
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THANKS GUYS,
WILL GO WOODEN :!


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PanchoGA
PostPosted: Mon Mar 29, 2021 7:14 pm 
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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


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bfinney
PostPosted: Mon Mar 29, 2021 9:15 pm 
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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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James Grahn
PostPosted: Tue Mar 30, 2021 10:54 pm 
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Those comments are for fixed pitch metal props. The Hartzell CS units have been fully tested.
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