Recent content by Jeremy


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  1. J

    Foam/Plywood wings

    This old thread you've dredged up has nothing whatsoever to do with the Affordaplane and the implication that I didn't know what I was doing with the Mayfly design several years ago is just plain wrong. The wing sample turned out fine and exceeded BCAR Section S when tested, although I never...
  2. J

    aluminum fuel tanks, welded vs. riveted/prosealed.

    I agree, 0.090" is going to be a bit heavy. I've made welded wing tanks in the past from 1mm (0.040") and found them to be fine. The technique I used was to fold the tank up (with hand formed end plates that conform to the wing section) and pop rivet it together, using alloy rivets. The tank...
  3. J

    Freewing construction

    Sorry to resurrect this old thread, but my interest has been once again piqued by the controlwing concept. I've spent some time looking at the Spratt 103 photos and reading all I can find on the original Spratt designs, patents etc. Unless I'm mistaken, Bernard Geffray seems to have missed one...
  4. J

    Horizontal Tail Proof Load

    That simplified method in Appendix A is so useful that it's been copied pretty much directly into the Euopean codes, as is. I found this out the first time I used it, as the author of CS-VLA (the sub-750kg MTOW code over here) translated the formulae into metric units, but only changed the...
  5. J

    Leading Edge Sheeting

    I experimented with 1/16" thick balsa sheet, covered with thin glass/epoxy. It makes a good leading edge, as the grain of the balsa adds a fair bit to the stiffness between the ribs. I used the 4" wide, 4' long balsa sheets from my local model shop, that I joined together into useful widths...
  6. J

    Horizontal Tail Proof Load

    It's a bit more work, in my view, to build a whiffle tree and use hydralic jacks, as the loads are pretty high, so substantial bits of test structure need to be built. Sand bags (or better, in my view, lead shot bags) are certainly simpler to use for most amateurs. I use gravel, rather than...
  7. J

    Horizontal Tail Proof Load

    That depends very much on where you live, I'm afraid. The US is lucky, in that it has an Experimental category that places the onus for airworthiness primarily on the builder, but many (perhaps most?) countries in the world aren't quite so obliging. Here in the UK, for example, a homebuilt...
  8. J

    Razorback Freewing progress

    I can fill in some blanks on the BMW R100 engine, as I've converted one. Weight, complete with centrifugal clutch and Rotax C type gearbox is around 76kg. Power is around 70hp. With a 2.62:1 gearbox it swings a 70" 2 blade Powerfin very nicely. Fuel consumption is very airframe dependent...
  9. J

    Horizontal Tail Proof Load

    Gary, You need to calculate two numbers, the tail balancing load and the tail manoeuvring load, and then take a look at the code you want to use (most probably CS-VLA for the EU, or maybe FAR 23 for the US) to determine some reasonable factors to take into account. The tail balancing load is a...
  10. J

    Trailing Link Landing Gear

    I haven't done the sums yet (too early in the morning here for math.......) but I would guess that some of the motorcycle spring/dampers used for off-road stuff might be up to it. A typical 3g undercarriage free-fall certification drop test is from a quite modest height, often only a foot or...
  11. J


    It's worth noting that stainless steel braided brake lines are actually just plastic pipes with a bit of stainless braid over them to provide abrasion resistance. The stainless braid doesn't make the pipes any stronger, or withstand higher operating pressure, it just makes them look pretty and...
  12. J

    Geodetic structural design

    An interesting idea. What about using off-the-shelf composite pultrusion instead of wood or metal? This stuff is very light, stiff and readily bonded, plus it's available quite easily too. Jeremy
  13. J


    Hi Duncan, I think this is pretty easy to estimate. The wing AoA will be dependent on the lift it has to generate, so will vary with airspeed. The lift requirement is fairly straightforward to work out; in straight and level flight for the control wing (no tail down force assumed) it will...
  14. J


    If you take a look at the Phantom link I gave earlier, then you may get some ideas about how to attach the rotor. Jeremy
  15. J


    Bicycle disc brakes work very well indeed and are a good idea. Bicycle wheels are not such a good idea, as unless rebuilt with stronger rims and spokes they tend to buckle when exposed to the typical side loads from a cross wind landing. For a supplier of nice light wheels, already fitted with...