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143. Wheely Interesting

30/10/2014

If you’ve been paying attention you’ll know that back in September we nearly lost the whole fuselage when a wheel hub broke when it was on the trailer on the way to the LAA Rally at Sywell.

We’ve had new hubs made up, and as you can see, they are significantly thicker than the old ones, in order to reduce the stresses a bit. But it’s amazing how the consequences of a tiny change like this filter through the system and throw up unexpected challenges down the line.

The new hubs were beautifully machined, but the drawing called for steel of 50 tons/sq in strength, and it wasn’t until after we’d had them made that we got a sample tested and found that it was only about 42 ton/sq in.

Wheel hub flanges - the old, broken one on the left and the new, much thicker one on the right

Wheel hub flanges – the old, broken one on the left and the new, much thicker one on the right

We could have got them hardened and tempered, which would have brought them to the required strength and ductility, but because of the date with the BBC, and the need to get on with the rest of the build, we’d trusted to the additional thickness to do the job.

Reassembling the hubs was fine – just Loctite and a good strong vice to press the flanges onto the tube – and I took them to be rebuilt by a specialist wheel builder, having first got the rims shotblasted and powder coated, as there was significant rust inside them when we took the tyres off.

And then the local tyre depot put the tyres back on (amazing to watch him wrestle with them; beaded tyres don’t need any tools at all, just strong arms) and I was all set to pop them back on the axle.

But they wouldn’t quite fit. Why not? The additional flange width had widened the wheels by about 5mm and there wasn’t any spare length on the axle. Well, I managed to alter the hole for the inner sleeve, but the bungees are slightly out of line and there’s a bolt that’s threatening to chew up the undercarriage legs, but I think we’re still okay, and stretching the bungees into place was much easier the second time around now we know what we’re doing.

And that was okay for the BBC’s visit, but we still needed to carry out a load test on the wheels to make sure they were strong enough, and this required me to take the wheels and axle off the undercarriage again. The load test required us to exert four times the normal maximum load, and we set up a system of levers to achieve this, with yours truly hanging off the end of the lever to provide the necessary avoirdupois.

Load test

Interestingly, during the test we ended up raising the tyre pressure to 90psi to limit tyre distortion.

The next job was to apply the wheel covers, and on that first wheel I managed that after a bit of experimenting.

Sewing the wheel covers in place. Originally they were secured to strips of fabric threaded under the tyre, but we felt they would have made the tyre bead less secure in its groove, so we've made up ply discs, doped the fabric to them, and sewed the to discs together through the wheel spokes. Well let you know if it's a success!

Sewing the wheel covers in place. Originally they were secured to strips of fabric threaded under the tyre, but we felt they would have made the tyre bead less secure in its groove, so we’ve made up ply discs, doped the fabric to them, and sewed the to discs together through the wheel spokes. Well let you know if it’s a success!

Then I put the axle – and the bungees – back on again. By now I’m getting really pretty slick at yanking the bungees taut.

When I came to look at the second wheel, I first of all tightened up the securing nut for the valve, as I ‘d done on the other one. As I did so, there was a phhhhhhhft, and the tyre deflated. It was reasonably clear that I’d pulled the valve out of the inner, so I wrestled the tyre off the rime and popped into the local tyre depot and managed to get a replacement inner tube.

Back to the airfield again, where I got to wrestle the tyre back on again – successfully – and was just pumping it up to 90 psi to match the first one when there was a large BANG, and the bead jumped out of the groove at one point and the inner tube exploded…

And of course if the flange hadn’t broken, none of this would have been necessary!

 

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From → Building, Technical

3 Comments
  1. Peter Bond permalink

    Hello David,

    Good progress.
    I’m looking for a wheel builder to make the wheels for my Camel. Can you recommend anyone?

    Regards,
    Peter

    • We used Central Wheel Components in Coleshill. They supplied spokes and rims (ours are standard vintage motor cycle ones) and built them round our hubs. If you have beaded tyres, we are still learning about the process of fitting the tyres and inner tubes correctly. I may be able to get you more advice next week!

      • Peter Bond permalink

        Thanks David, I will contact Central.
        I plan to use wired on tyres rather than beaded, as they should give better side load resistance.

        Looking forward to more updates.

        Peter

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