Thorp Air Command - T18.net

Have read much about the efficiency and beauty of the original metal cowling built by John Thorp. Have searched this and the prior site but haven't yet been able to find any pictures. If someone has a pic or two can you share?
Thanks,
Chris

Here is my version of it.

_________________
Bob Highley
N711SH
SN 835
KLAL

My aircraft has the drop hammer formed cheak cowls. The ugly photo is when I stripped the paint in 2013, the slimey green stuff is zinc cromate primer, it didn't want to come off had to use multiple coats of paint stripper. There are multiple parts forward of the seam that are welded, hard to see in the photo.

Here is how it looks with new paint.

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

Here's mine

This is Bob's and I just after we completed making the metal cowls on our Thorps. We found that the temperatures dropped 50 plus degrees as opposed to the fiberglas cowls

Thank you all for sharing the cowl pictures. Has anybody measured the intake and exit size of the metal cowl? Curious is the efficiency is due to shape, ratio of air entering and exiting the cowl, what goes on with the baffles or plenum underneath or all of the above?

Bob and I made our "buck" using the old fiberglass cowl, never really took a measurement though. If you look at a Thorp cowl the intakes are slanted back a few degrees at the bottom. This yields a bigger opening in climb and closes down slightly in cruise from the tail high attitude in flight. For the cooler temperatures, I believe this is a result of aluminum transferring the heat better than glass, remember they use glass as an insulator on exhaust.

Bob/Bill, just for curiosity, can you post a picture of the cowl bucks?

How many pieces is the inlet made of? Just two?!

D

PS... no guys, I'm not going to make a metal cowl.
Maybe some winter when I'm retired, but not now.

I'll dig the buck out of the back of the hanger and post a picture. The front "bowl" is three pieces. We made the complete front bowl, and cut it in two after it was welded. As a side note, the top, bottom and cheeks are a flat wrap. There is some forming around the spinner area and lower cowl panels. Considerable annealing was done to form the parts from 6061 and 5052 aluminum. We used a 1" wide magic marker to paint the metal and using a torch burned it off. It will go back hard in a day or two.

This is a simplified explanation, but for whatever it's worth (probably not much), 5052 is a non-heat-treatable alloy. It will harden as it is cold worked, but I believe it won't age-harden after annealing. 6061 can be much the same, although it is heat-treatable. When annealed to a certain temperature (I don't remember exactly... something over 500 deg.) it will not age-harden unless it is quenched after heating. It too can be cold work-hardened of course. More than you wanted to know, I'm sure.

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

We used 3003-0 for the really hard to form parts.



This picture shows the piece next to the spinner and the inlet as formed (on floor) before we cut it apart.



This is the annealing method Bill talked about.



Fitting the cheeks before welding.

Some fun! Brings back memories.

_________________
Bob Highley
N711SH
SN 835
KLAL

Pictures of the buck Bob made for making our metal cowls
It was made in four pieces and welded, the front ring one piece. After welding we cut it in half

Nice. You guys are artists.

Wow....I'm not sure if the buck (that's a new term for me so I learned something) or the final product looks more impressive. Man, I can see that if I ever have to replace my metal cowl/cheeks, I'm going to just have to buy the fiberglass cowling from ACS.

Metal cowls will never wear out. And ACS does not have a Thorp cowl setup, be ThorpCentral does.
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