Silicone in uc torque boxes

[Matt Carlton]

I had an idea, wondered if anyone had tried the same thing. 

In a traditional uc arrangement with the inner end of the leg bent up into a hardwood torque box, I pondered drilling the hole out oversize and squeezing aquarium sealant or similar in the hole. Smear the uc leg stub with vaseline and fix in place. The silicone would then provide a slightly 'soft' mount to absorb a bit of landing shock. 

Pointless? 

Some of the wheels I have seen are less than shock absorbing, especially when it is cold! 

[Andy Gates]

The leg should be twisting between the inner end and the leg down to the wheel, that should be more than enough if sized up and designed correctly.

[Denis Watkins]

Dubro Air wheels have shock absorbing tyres that can smooth out landing more than regular low cost wheels.

The torque box is a popular simple design solution

But all manner of shock absorbing legs can be obtained but are costly

[Matt Carlton]

Thanks chaps. I put it together "as is" this evening and it seems ok. The single wire legs look awfully spindly though, so some fairings are needed. 

Its a shame you can't get streamline section balsa like you used to! 

[Christopher Wolfe]

I have mounted some u/c legs in a slightly wider than normal channel in the hardwood u/c block filled with Silastic silicone sealer with a couple of conventional straps added for security.  Worked quite well for pylon racers.

 

Press the legs in, wipe away excess with a plastic squeegee (credit card), add the straps and the job is done. Has always outlasted the models.

 

Regards * Chris *

[Mike T]

Interesting idea.  You could get much the same effect with less mess by sleeving the leg with fuel tube. 

 

My last torsion legs got cut short at the outboard end and had 'oleo' struts fitted, which seemed to work well.

[Matt Carlton]

I did contemplate sleeving as an option but I thought the relatively thin wall thickness would make little difference but maybe enough just to absorb a slightly iffy landing. 

I do use a bit og fuel tube on the uc legs on the inside of the wheels instead of a soldered washer though. 

[Nigel R]

I've always found piano wire torque gear to be surprisingly resistant to arrivals.

 

If you're after a bit of extra spring, you could try using a pair of the light sponge wheels. They're very soft. And light.

 

That said, I just use standard wheels as sold by SLEC. They seem to last quite well and don't melt when you get fuel/exhaust on them. I fly from grass though.

 

 

[Matt Carlton]

I fly from a combination of grass and molehills so a bit of extra bounce isn't a bad idea. I did have a test sproing this evening and the 10G wire is surprisingly resilient. Not sure about the box in the wing but there's a reasonable amount of rake forward on the legs. Should ok. If it isn't, I'll find out quite soon I imagine. 

[Colin Leighfield]

To solve the problem of creating a scale looking Dowty type undercarriage for my Bryant Hawker Fury (modified to represent the Spanish Civil War version), I have made a ply box that the rear cross member at the top of the leg sits inside and filled it with a two-pack synthetic rubber compound. With the front cross member hinged, the rear one in effect “floats” inside the rubber.  It looks very promising, giving some resilience while still being robust. Not flown yet, but I’m confident. 

Edited July 1, 2021 by Colin Leighfield
Missing information.

[Matt Carlton]

Sounds like a neat solution. Fury looks really nice, what is the covering? 

[Colin Leighfield]

Hi Matt. Wings and tail are Solartex, which I then ran out of. Fuselage is Diacover 100 from Sarik, it looks promising so far. 

[Don Fry]

On 30/06/2021 at 19:14, Matt Carlton said:

I did contemplate sleeving as an option but I thought the relatively thin wall thickness would make little difference but maybe enough just to absorb a slightly iffy landing. 

I do use a bit og fuel tube on the uc legs on the inside of the wheels instead of a soldered washer though. 

I initially thought the same, but if the thing lasts long enough, a problem in end of life airframes, is you end up packing undercarriage grooves, as the wires compress it. A bit of silicone tube  might just protect the groove. And provide a bit of movement between. Might try it.

[Allan Bennett]

On 29/06/2021 at 20:52, Andy Gates said:

The leg should be twisting between the inner end and the leg down to the wheel, that should be more than enough if sized up and designed correctly.

 

I remember when I was learning to fly, the underside covering of my wings was forever being punctured by the legs twisting so much during my landings that the wheels contacted the wings ?  No need for any further elasticity.