Back to the beginning: Project Tiger Cub Story part 13b

Thinking about legs

After cleaning and checking the undercarriage legs I notice a difference between the later ones that came with Kit SU208 and the ones supplied with GMJSU (Kit SO175).

While both are fitted with the nylon anti crush insert at the top the earlier legs are single tube at the lower end the later ones are doubled by having another tube inside for the area though which the plates that form the attachment to the axle. Sure enough there is a small damaged area to the lower ends of the earlier legs. I am a bit puzzled by this until I notice that the end of the doubled units are not cut straight as are the older ones but are eased to prevent contact with the axle itself. While they don’t actually touch in either case they are very close on the straight cut tubes. So it would seem that under landing loads it is possible for them to come in contact in the older model. As the legs are angled up to the attachment point this would place them in bending rather than as designed having the load though the two bolts that are in shear and from them straight up the tubes to the main front fuselage framing. It’s bit like a detective story piecing together the development although sometimes it feels almost a form of witchcraft. Well it seem like it at times as I shuffle my Tarot cards (the accumulation of service bulletins and circulars) and cast the Runes of assorted bits a pieces in the workshop the whole thing woven though with the myths and legends from the elder days of microlighting. It is satisfying though as the bits fall into place, SP starts to take the shape of an aeroplane again and end of the rainbow gets a little closer.

Removing the side plates and cleaning up the bits involves removing a peculiar gunk from the undercarriage legs for SU. Strange stuff that has left a golden translucent film over the alloy that while it is not unattractive has to come off so that I can crack test all the bits.

After cleaning I check all the bolt holes and discover that one of the undercarriage legs and one side plate from kit 208 have the holes elongated. Red labels for those and red penitrant dye for the others. As ever it is very satisfying when the developer shows a pristine white surface.

Moving on the main undercarriage axle I clean to the accumulated grime of years to find the wheel bearing surfaces in surprisingly good nick. My luck seemed in as all the holes were still round and the right size then I struck trouble, the darn thing wasn’t straight. Blast it, I laid it on a flat surface and measured, it was certainly not straight, but then I remembered reading somewhere that there was an allowable amount of deflection, trouble was I couldn’t remember where I’d read it or how much was considered acceptable. So, I read again the Kit Build Instructions, nothing there then though the Service bulletins and news circulars, zilch before finding it in the Maintenance Manual. Maximum allowed deflection 1”, that’s right, 25mm; deflexion on my axle? 1.5mm, phew! I sat down and poured myself a glass of wine, it felt as if I deserved it.