Thorp Air Command - T18.net

Hey Gang,
We recently bought an older T-18 (N312LL). The VSI, Altimeter and Airspeed indicator seem to be very erratic. The static ports are on the pitot tube. I'm thinking that is not the correct placement. Where has everyone found to be the best spot for the static port.
Thanks
Tim

Are you sure about the static port being on the pitot tube ? Some folks just vent from the back of the panel and that can cause "erratic" readings. If it is on the pitot tube I would also check the connections all the way to the instruments. There may be a common "T" than has a leak ? Doesn't take much.

I placed my flush static ports on the sides of the A/C. One on the left for the instruments and one on the right for the autopilot.

RB

I just chased a static leak for several hours before I switched the "T" out on the back of the instrument because I had run out of ideas of where the leak was coming from. It solved the problem. I still cant figure how it was leaking but it sure stopped it once I switched it out.

Yep thought about leaks too. I ran across an article that Lee sent me a while ago & re-read it. It was from the '80s and in reference to our plane specifically. It talked about the same problems we're still having. Makes me think the placement has been wrong from the beginning. I was thinking that side of fuse would be best. Just need to figure out exactly where.

Now that I think back when I did my pitot static system leak check (using a balloon/modeling clay and a large syringe) I did find (2) leaks on the back of 2 instruments where the nylon fittings screwed in. I applied a little EZ turn to the threads and problem solved. When I had the pitot/static system ground checked for the transponder Mode C, he ran a leak check using one of those very expensive black boxes and it was a very tight system.

RB

Try the Thorplist Archives and search static port location.

RB

The side mounted static lines are supposed to be connected to balance out side slips, etc.

According to my news letter index the following have articales on the static ports (news letter-page no.):
19-3, 44-4, 61-5, 91-9, 100-17, 105-10

Of this list I only have 91, it has a drawing on how to position the static ports on the side of the fuselage. I have not verified it but I believe my static ports are farther aft than what is shown in the drawing.

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

A few Australian T18s have their static ports located further aft than the position indicated in the newsletters with apparent good results. My other post on the topic of side skins had a drawing showing the static location.
Stuart

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Stug