Oleo strut - Part 2
Thursday, 7th May, 2015
I began the detailed work on the oleos by making the two sets of four landing gear door-retaining lugs. These differ from the scissor lugs in three respects: they are a lot smaller, there are twice as many of them and because I would be making them of aluminium I could not use solder*. Taken together, this led me to risk a short cut: Rather than mill them as D-shapes like the scissor lugs, I decided to make them cylindrical to so they would bed into small matching channels milled in the strut body.
Because of their split shape, I would be able to secure each lug to the oleo cylinder with a small alloy rivet, which in combination with cyanoacrylate glue and the abovementioned grooved bed should render them well capable of bearing the weight of the gear doors. Photos 1 and 2 help explain this. The little lugs look neat and at some later stage, probably when the oleos are in primer, I propose to finesse them further with a touch of metal filler.
Up lock lug
I used 3mm thick alloy for the up lock lugs, first drilling the big locking hole, then milling the taper that occurs along half its length and finally filing the profile. Next I set the oleo barrels up on the bed of my milling machine and cut a 3mm slot right through each one (Photos 3 – 5). The lugs fit their slots tightly, so that with the addition of a little thin cyanoacrylate the bond became very strong indeed. Consolidated by the two flanking alloy flanges with their steel bolts and more cyanoacrylate glue, I don’t think I could brake the joint should I wanted to – proof that, dependant on the stresses involved, the lack of a soldering option need not be an impediment when working in metal.
This was easy to turn in the lathe from two sizes of brass hexagon. It required three interlocking pieces to create the shape, plus the little shield-shaped locking washer, which I cut from 0.5 mm brass sheet (Photo 6). In my model this relatively minor, almost hidden feature serves the important practical function of a 4BA bolt through the alloy oleo cylinder, its underlying brass support and also the innermost chrome-plated steel ram, thereby locking the entire strut assembly together.
An associated detail is the safety rod, which prevents ground crew from dismantling the strut before bleeding off the pressure in the system. This again required three brass pieces: the small tear-drop shaped mounting plate drilled for an 8BA ‘bleed’ bolt, the rod itself, which is soft soldered to the plate, and the tiny cylindrical retaining lug attached near the bottom of the oleo cylinder. Those in the know will remind me that the rod is made of steel, but I avoid rust prone ferrous metals wherever I can reasonably do so.
This required little additional detail except for some plastic metal padding to flesh out the shape where the parts are joined, thereby creating the impression of a real metal casting. There are also included two 10BA retaining bolts to mimic the real thing, although only the upper of the two is functional in my model. For belt and braces I drilled and tapped through the base of the scissor lug to take an additional hidden countersunk retaining screw (this can be seen in Photo 8).
*There are materials available for soldering aluminium alloy, but I have never used them even though I have a kit. One reason is that I suspect the process to be too cumbersome and the heat needed too severe for use on small parts. I may be wrong.