Thorp Air Command - T18.net

Guys,

I was out last night turning gas into noise and at one popint noticed that my speed dropped about 5 mph with no changes to power, rpm or fuel burn and perhaps a slight vibration. I landed and noticed that my spinner was drastically different from what it was when I took off.
A large portion had started to separate.
I have attached a picture. I suspect that this occured as a result of my previous prop, which was shorter than what Hartzell recommended.

Jim

Maybe you can JB-Weld it.

D

Might make a nice lamp ? I would add it to the aluminum can recycle bin .

RB

I tried 2 aluminum spinners and both cracked. I'm sure it was my fault for not cleaning up the edges or holes good enough, and that's why it cracked. I switched to a fiberglass spinner and haven't had a problem since.

I have a van's spinner on mine, and it just doesn't look nearly as good as a Thorp spinner, but I don't mind since it seems to be holding up for me.

The aluminum T18 spinner has a lot of mass to it and requires a forward bulkhead and two re-enforcement plates at the base.
`

Jim,

It appears from the picture that it is missing a piece that broke off at the corner edge of the propeller cut-out? A couple of thoughts... the structure/attachment at that point probably failed first, maybe from a crack which propagated from the hole(s) in that area. From there, maybe centrifugal force & vibration caused the large crack & outward bending of that section. It also looks like you had screws attaching the spinner to the front bulkhead, which experience over the decades has shown to be problematic. A spinner set up to run true, with only a nice tight fit to that bulkhead is much more reliable based on experience. Also, I see that your screw holes have been countersunk. That also greatly increases the possibility of stress risers and cracks developing. Were you at least using countersunk tinnerman washers with the screws? A more reliable setup would be to use low profile head screws with non-metallic fiber washers & nice clean holes, carefully de-burred & nick-free. Just my humble 2 cents worth. I'm sure glad you got down before it got worse!

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

John,

Yes the holes are countersunk and I use the SS countersunk Tinnerman washers. Looking back on it, the plane was telling me what was happening but I wasn't listening. When I bought the plane it had a C/S prop on it that was shorter than the minimum 70". It was 68 5/8". I was frequently tightening the spinner screws and the Tinnerman washers were wearing into the aluminum around the holes. I brought the prop in over the winter to have a small seal leak fixed and this is when I found out about the length issue. I replaced the prop with an overhauled one set up for an RV6 and it is running much smoother. It is 72" in length. I suspect the damage was done with the last prop and the failure started from a mounting hole. Are you suggesting that I not use screws in the front bulkhead, just a snug friction fit?

Best regards,

Jim

I do not use screws in the forward bulkhead. A little anti chafe tape is all it has. It been on for over 1000 hours.
Cubes

Jim,
I still make carbon fiber Thorp spinners if you would like to go that route.
Lee

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

No screws on my fwd bulkhead . I attached a rubber strip with 3M heavy duty trim adhesive . A nice snug fit with no movement . I had an ACS spinner crack at one of the curved portions of the cut out . Had a local guy with aerospace welding experience put a bead on it . After he blended it in you would be hard pressed to tell where the weld is .

RB

Guys,

My Thorp has a new spinner. Many thanks to Cubes for the excellent response in shipping and my many questions. It's great to have this forum and great suppliers to support the brand.

Best regards,

Jim

In the previous forum there was a note about Brock spinners being 1" shorter for fixed pitch props compared to spinners for constant speed props. (Consequently there was a slight difference in back plate diameter.)

Does anyone know the proper ABSOLUTE length of the Thorp spinner for a FP prop?

D

Looked at drawings 639,640,and 641 spinner. It appears the drawings are for a FP. The length is 14.630" and 12" diameter

I only stock one length. I'll measure them when I get off this trip from hell. I know Texas needs rain, but wow!
Cubes

Awful trip. My spinners are 16.25 by 12.5".
Cubes