Glass fibre push rods advice

[Chris Walby]

Hi,

I have a Ripmax slim twin kit that came with 4mm GF pushrods and there are no details on how the clevis rods (2mm) are actually attached to the GF rod at each end?

I was thinking of laying the two in offset parallel (1 inch overlap) and binding with cotton thread, then covering with 5 min epoxy. lastly covering with a bit of heat shrink sleeving.

Would this be okay for a twin 46 size IC model or should the clevis rods be better secured, if that's the case how?

I do have some carbon tube and thought I could epoxy the clevis rod inside the carbon tube or drill a hole in the carbon tube, then bend the clevis rod with a hook and epoxy/sleeve.

What's the collective advice?

PS the GF rod is 2ft long and supported in a couple of places along its length.

[Allan Bennett]

I've had a couple of kits with balsa pushrods, and the connection method recommended was as you suggest, with the addition of the end of the clevis rod (metal, I presume) being bent at 90 degrees and inserted into a hole drilled through the balsa. For round rod I would file a slight flat on it for the length of your clevis rod overlap. That will help with drilling the hole, as well as keeping the clevis rod in place better while you bind it.

[Bruce Collinson]

Whilst I claim no expertise, I built a Maxford Mentor, big 84” highwing “trainer” behind a Zenoah 20, with M3 clevises. I thought it would look more elegant with carbon tube pushrods.

I used an I/d slightly smaller, bound the end inch with Kevlar fly tying thread, then cyanoed the thread, then covered with heat shrink, all to keep the Kevlar thread in situ. Then I cut an M3 thread inside (supposed to be impossible) which gave some grip for the threads. The Kevlar whipping stops the carbon tube from splitting whilst tapping the thread.

Then thoroughly cleaned up the threads with meths and cyanoed 2” of M3 studding into the carbon tube, then pulled like hell. Light, stiff, looks tidy.

Carbon may well obviate the need to support midspan. Works with a Wot 4.

Don’t t try breaking Kevlar thread, it is very thin with terrific tensile strength. Makes good floss too. Hope this helps.

Ought to work with your g/f tubes if the inside diameter stacks up.

BTC

[Ron Gray]

With carbon pushrods I use these SLEC fixed with epoxy.

[Martin Harris - Moderator]

I followed the kit instructions with mine and bound wire pushrods with thread, epoxied as you suggest. I used Kevlar thread because I had some handy and they have survived a mid-air resulting in a major crash, a write off due to a failed recovery from a flat spin and were used in my later re-creation from a standard Extra Slim kit. They survived this model too!

[Chris Walby]

Thanks guys for the advice and all helpful for this application or elsewhere in my attempts to build models.

The GF is rod so limits an option, but I do have some carbon fibre tube so will have a quick look in the shed for other bits to go with that as Bruce/Ron suggested.

If that proves inconclusive I'll go with Alan's suggestion, file a slight flat, bind, epoxy and head shrink sleeve as a 2mm hole in a 4mm rod does not leave much "meat" + I suspect the LA's will vibrate a bit!

Thanks to all, keep well and stay safe.

[Robert Welford]

Chris, when I have used carbon for pushrods it is tube not rod. I insert a threaded fitting (either threaded rod or threaded adaptor) to each end bonded with JB Weld (better than other epoxies for this purpose).

I think it was Macgregor's who used to sell carbon pushrod kits that included the end fittings and quick links.

I know people use carbon tube over a metal pushrod. For larger models use M3 threaded rod, but sleeve it with >3mm ID carbon tube. This provides additional stiffness.

Edited By Robert Welford on 30/04/2020 09:35:41