Aileron Flutter

[Paul Harlow]

Hello,

A while ago, I started learning to fly with a "Bobcat II 40" trainer and discovered that taking off and flying about were pretty easy - landing, though, wasn't...

After ripping the undercarriage off my trainer and pretty much ripping out the whole bottom of the fuselage in one, glorious high speed ground encounter, I decided that trainers just weren't built for my style of "landing"...so I designed and built my own trainer with enthusiastically belting into the ground in mind :)

I have a problem with my ailerons, though - I built the wings up to use a single, central servo and torque rods, a la stock trainer, but this has left the ailerons really pretty sloppy and they flutter about like anything with the engine running :( Is there an easy way I can improve their rigidity without having to ditch the centre servo and put servos in the wings?

I haven't actually tried flying this thing yet, but I'd like to give it the best chance possible of getting back down in one piece...

Thanks,

Paul

[001]

Paul, if the problem is that the rods are loose in the ailerons, I have done the following with success, locate where the forward facing part of the rod is in the aileron, with a pin or similar. Using a small abrasive tool with a flat end, say 6-8mm dia, grind down halfway through the wood until the rod can be seen, fill the hole with 5 minute epoxy,making sure that it soaks around the rod. Cover the resulting scar with film (not essential.)

[Paul Harlow]

Hi Richard,

thanks for that - I should have explained the problem a bit better, really - there's just loads of play in all the pivot joints. There's play at the servo clevis' and play at the torque-rod ends...plus, I think the hinges I've used (metal pin hinged type) aren't holding the ailerons tightly enough to the wing...

I wondered if one solution would be to get rid of the hinges altogether and fix the ailerons to the wing using tape along their entire length...it seems like a bit of a bodge to me, though...

Thanks for your help,

Paul

[001]

Paul, in that case, I would replace all the offending parts, including all the hinges, a pain I know. Tape only is not appropriate or safe for a 40 size I. C. type although you can seal the gap with tape after hinging.

[Paul Harlow]

OK, thanks for that - if I was to take the ailerons off altogether, do you think it would be worth the effort of having a seperate servo in each wing?

Paul

[001]

Yes, I have done this to a number of my models.In that case you can use a smaller good quality servo, such as a Hitec HS 81, which helps keep the weight down.You can also, if you have a computer radio mix in some flap if you want..

[Alistair Taylor]

Paul

with a separate servo for each Aileron you could set them up as flaps, and hopefully achieve some slightly slower landings (test the response at 3 mistakes high altitude before attempting to deploy them on landing).

Also - with the aileron driven from a horn that is central (or slightly offset) to the aileron itself, control should be more positive;

With a torque-rod driven aileron,the wingtip end of the aileron is a long way away from the bit of the aileron that is connected to the servo (i.e. where the torque rod is).

As a result the aileron tip can flex more freely than with the central horn, where the inboard and outboard aileron tips are both closer to and, more or less, equidistant from the horn, and so less prone to flexing.

Hope this helps


AlistairT

[Paul Harlow]

Thanks for that, chaps - I think that's my weekend project sorted, then...I'll get this thing in the air one day :)

Paul

[Steve Hargreaves - Moderator]

If the flutter is down to play in the linkages maybe a move to heli-style ball joints on servo arms & torque rods might be the answer

[winchweight]

I have found pin type hinges have quite a bit of play. On a trainer I just use simple mylar strips which can be pushed together quite tightly. The clevises, are they on metal pushrods? Do they have tiny nuts behind them? If not, try fitting some to pinch up against the cleavis nice and tight. This will stop some play. Then be sure to use a small peice of fuel tube over the clevis jaws to stop them opening accidently and releasing the torque rod.

[Paul Harlow]

Hi chaps,

thanks for all this advice - I like the idea of trying to tighten up the linkages, although I'm quite taken with the idea of independent servos in the wings - I'll have a go at combining both ideas...

Thanks for your help,

Paul