WMAC Group build - Impressivo

With regards to push rods why not use some 2mm helicopter ball link's with 2mm threaded rod sleeved with some carbon rod and lock nuts?

can buy one carbon rod split the cost and I would of thought there would be enough for several models?
same with the threaded rod I guess!!!

DavidTappin wrote: As a matter if interest, did all three have their elevon horns on top like Jon's? I was a bit concerned about how weak the push rods seem and worried about them flexing in compression and allowing flutter. Mine are underneath like Mike's which has been reported as the fastest and, presumably, flutter free, but I'll be sleeving them with carbon tube to make sure they keep straight.

The top horn point could well be valid, you are losing some mechanical advantage for sure. It is impossible to be sure if flutter caused the hinge to fail, or the other way round. When I rebuild mine, I am going to change to a bottom horn, with robart hinges and still seal the hinge line with film. Also the rods will be changed or stiffened with carbon tube. If it happens again after all that, it's going in the bin

I will be changing my linkages to 2 or 2.5 mm. I don't see why top or bottom makes any difference to strength (can somebody explain this?) Seems to me that if one linkage buckles while pushing in compression in a high speed manoeuvre, then, when the controls return to neutral, one of the surfaces goes too far the other way pulled by the bent rod, hence a rapid flip over and spin down. In Simon's case, spin not apparent due to low altitude. Clearly a design fault.

Phil-C wrote: I don't see why top or bottom makes any difference to strength (can somebody explain this?)

Phil, it's about mechanical advantage, with the horn on top the distance of the drive position from the hinge point is the length of the horn, when on the underside, it is the horn length plus the depth of the aileron, probably an additional 10mm. Does that make sense?

Just checked my photos, Simon's linkages appear to be on the underside, mine and Dave's on top. I didn't hear any flutter from Simon's, it just rolled in, so that might have been a different cause??

Jon, understand now, thanks. Doesn't apply to my top mounted horns because the Kavan hinges are on the neutral axis of the wing.

Still going to thicken the links. Also try to remove the prop driver eccentricity

I didn't use the linkages supplied, I used thicker ones with adjustable end, even with a dodgy servo mine survived to live again however I will be adding proper hinges! Had a good laugh Saturday, just a shame it was windier than would have liked.

I seem to have made the prop driver concentric. Used a Manchester Screwdriver.

I also tried these HK 5x5 props for balance. Both the ones I have left were way out. When balanced and refitted, there is still a resonance at just over 1/2 throttle, but much less than it was. I guess there is bound to be resonance at some rpm-s.

Phil, if you got your prop adaptor from HK (secured with one Allen grub screw with a very sloppy fit on the 4mm motor shaft), they are useless. Impossible to get balanced and likely to shake the poor airframe to bits at the revs we are getting on those small props. I've just ordered a couple of good quality 4mm collet type adaptors.

I'll let you know how they fit when they arrive, if they are any good you are welcome to one.

Regards, David

DaveBright wrote: I'll admit, my hinging skills with film weren't great which was a major reason why mine went in. And yes, I believe all three of ours had top mounted servo linkages. We did comment yesterday on the fact we were asking a lot from a little piece of wire. Proper hinges and a more substantial servo linkages can't go a miss.
I thought I was safe having let everyone else bug fix last week! Combination of factors caused the high attrition rate...

Sorry to hear about the fatalities on Sat. (currently away in motorhome) . Don't know what went wrong with the film hinges as several members including me have used this models on petrol models without failure. My method was to use 20mm wide strips of Solartex. I believe the secret is to ensure there is a 1 to 2 mm gap before shrinkage tallow the top / bottom strips to bond. I also augmented the bond of the solartex to wood with good smear of Balsaloc.