Thorp Air Command - T18.net

I noticed I have quite a bit of play between the jack screw and the nut. The assembly the builder used does not match the drawings. I have the tools to fabricate the nut and could use some practice using them so I figure I will give fabrication a shot. The drawing calls out aluminum plate for the nut but mine appears to be made from brass. What is the most popular metal being used to make the nut?

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Mine is made from aluminium bar stock as called out on the plans. How do I know this you ask? I recently made a new one cause I had what I thought was excessive play in my trim system.

Merry Christmas to all and to all good night.

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

Per Plans...in stock.
Cubes

An old newsletter talks about putting a thrust washer in the bearing block to take out the end play in the jackscrew.

_________________
Bob Highley
N711SH
SN 835
KLAL

My first thought was to call Cubes but when I saw how the assembly differed from the drawings I decided to look at making my own. I already have a couple of extra parts I ordered that don’t fit because of deviations from the drawings. I may still call Cubes if the dimensions match up or I decide I can’t make the part. I have other things I am considering and need to call him anyway. I have aluminum I bought to practice welding and machining on hand although I am not fond of using it for this application because aluminum is abrasive. I don’t use aluminum rods to clean my guns for the same reason.

There is a little slop throughout the system but the bulk of the movement is between the nut and the jackscrew. There is more slop in the pins holding the assembly than end play in the screw.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Jeff,

As I believe John Thorp himself pointed out, aluminum and steel actually make a pretty good bearing pair, with proper lubrication of course. I don't remember what alloy is called out on the print for that "nut", but I believe it is 2024-T3. That's what you should use, IMHO. You also should have the proper thread type. Like you said though, your assembly is obviously not built to plans, based on the picture.

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

I don’t have the drawings handy but I remember thinking the thread called out was a standard bolt thread. If it isn’t, then I cannot fabricate as I don’t have what I need to turn an internal thread. All I have for cutting threads is a standard tap and die set.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

It’s been so many years since I built my T-18... I was building in the 70’s and 80’s, and I no longer have the prints to check, but a jack screw like that is frequently an acme thread. Anyway, Cubes has the right part I’m sure. I didn’t mean to muddy the waters, Jeff. That thread may indeed be a “standard” thread, but I believe I may have borrowed an acme tap to make mine. I could be wrong.

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

Per plans, drill 5/16" tap 3/8-16 NC, this is how mine is made works fine, so far.

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

Look at the 694 drawing. It is 2024t3. It’s made from .500 bar.
Cubes