Turnbuckle for helicopter towing

We have a prototype Bristol Belvedere at the museum, not much more than a shell, and sometime next year will be getting a complete one from the Manchester museum.

They have fixed rear wheels and castering front wheels, so provision has to be made for steering both front wheels when being towed. The towing arm is in line with one front wheel and a linkage similar to Ackerman steering turns the other wheel. This design was probably used to make steering easier than just steering one wheel and having the other follow.

When I saw how it was set up, what worried me was that the suspension height affected the width of the track and the two helicopters might not match. The link between the two wheels was not adjustable, ours was made from a bit of scaffold pole and not original.

I decided that a turnbuckle adjustment in the link would be a good idea, and Mike, Alan and Greg helped me make it. The nuts were from steel laying about, but the rod was EN1A 1 1/4" by 500mm long. I managed to get it uncut into the Smart & Brown model A which is a 9 x 20 lathe, and made left and right hand 1 3/16" x 8 ACME threads, with a bored out 1" UNF nut pressed into the centre which was left slightly bigger than 1 3/16". The nuts have 1 1/2" of thread in them. The link can be 4 1/2" shorter and 10" longer than originally made.

Edited By old mart on 18/12/2021 20:29:50

Edited By old mart on 18/12/2021 20:31:43