brunobl

Hi All,

Flying in a tight area here, so I'm thinking of modifying an existing electric glider's wing to incorporate Fowler flaps, ailerons and spoilerons.

The idea behind the spoilerons in this case is not so much work as spoilers (I might not even use them this way at all), but to augment the ailerons during slow-speed flight, as the flaps will take up most of the wing's trailing edge, leaving small ailerons. Also, this arrangement suits itself nicely to the concept of providing only a small amount of "up" force from the down aileron and much larger "down" from the spoiler going up. Differential aileron could help, I know, but again most of the available trailing edge will be used up by the flap. Flaperons won't be an option either, as the huge Fowler flaps would induce a lot of adverse yaw.

One benefit from this arrangement is the hefty down force from the spoileron compared to the small increase in lift from the opposite aileron, which should help avoid tip stall at low speed.

That is the idea. Now for the problem.

How can I program a Spektrum DX7 / AR7000 to make the spoiler go UP in association with its aileron, but sit still (i.e, not dig into the flap below it) when the associated aileron goes DOWN? If this didn't make a lot of sense, think of an airliner's spoilerons & ailerons. That's exactly what I'm trying to achieve.

I guess could mechanically link the spoiler to the aileron, and by any of a number of ways allow only the "UP" half of its movement reach the spoiler (which would be in this case spring-loaded to DOWN), but all this sounds much too complicated, heavy and would probably have too much slop. What I really need is some kind of aileron->[another channel] mix.

Any ideas?

AH1G

This is "old school" but forget the fowler flaps, make them into full length flaperons and just mix the alieron and flaps and add the spoilers on a seperate channel. We used to use a very simple setup for the spoilers, a seperate servo that deploys the spoilers using light nylon string. The air flow over the wing will "retract" them. We used a small piece of plastic magnet to hold the spoilers from deploying on there own. I suppose that the spoilers could be mixed the another channel too.
We used the same basic technique for dropable ballast.

BMatthews

The style of spoilerons you seem to be suggesting is different from the usual model style of spoileron. For most of us spoilerons are regular ailerons used with a mix from a second channel so the ailerons themselves move up together in spoiler mode. But it sounds like you want to do the airliner style of spoilers as a roll control instead of just reflexing the ailerons.

Getting back to your wing mod. For a model I think you're going way over the top on this. I've seen many a competition glider with normal sized ailerons and simple hinged ailerons and flaps. When used with crow where the flaps are down at 90 degrees and the ailerons are up at about 30 degrees the safe and steady descent angle is around 30 degrees. And it's still possible to turn at this angle and spiral down into an area about the size of a baseball diamond easily if that is what you need to do. If your landing area is tighter than this then I'd say you need a helicopter instead of flaps....

Aileron differential should be easy. You'll have servos out at the tips to operate the ailerons so just angle the output arm to provide physical geometry differential. If you need more than this then the DX7 likely has Adjustable Travel Volume where you can set the amount of servo travel on each side of neutral separately. I would not recomend the increase in complexity and weight that comes with coupling a set of spoilers to the ailerons like the airliners do. It's just not needed on a sailplane. But you're right about differential and it's well worth using some.

Producing a proper fowler flap mechanism at our model size is going to be difficult. The need for precision tracks and precision shaping of the wing and flap joint and the need for an activating mechanism that pushes at two or more places at once in concert is going to introduce a LOT of complexity that is just not needed for our model size and weight. And then there's the aspect that at our sizes there is no guarantee that the scale size air gap is the right size for our reynolds numbers. So all in all I would suggest just go with simple plain flaps and decent sized ailerons and use a crow mix to throw out the anchor.

brunobl

Hey guys,

Thanks for your thoughts.
I am well aware that this whole flap/spoiler/aileron thing is far from optimal or even practical for model gliders. But this has been a pet desire for many long years and I now seem to have found just the right excuse to try and do it - a short field! This does not even need to be (and won't be, I know!) anywhere near a high performance glider. It will be great if just it flies around a while and then lands on a dime.

The "field" is really my house, I have a rather large front yard some 400 ft long. This may seem long for landing but isn't really, considering the obstacles around and that my current glider is not not awfully maneuverable. A month ago I worked up the nerves to fly it here, and given the available approach path and restrictions (trees, not going over anybody's house, etc), I can consistently get this rudder+elevator glider on the ground in about halfway the available grass strip if there is a steady breeze. If I am to continue flying here, I really need a more maneuverable/steeper approach model.

My first idea was to initially build not a glider but a smaller, 600sqin or so, trainer-sized electric model as a testbed for this crazy idea. If/when I iron out the inevitable difficulties, I'd then attempt to apply the concept to a glider.


AH1G, the nylon string is one of the alternatives. I did this in the past just this way - with no mixing, just plain spoiler it was back then, circa 1978. Time flies!

BMatthews , I hear you about the complexity, specially the flap tracks, etc. One possible way around this might be not using tracks at all, but pivot the flaps some 2-in, or more, below the wing, MD11/DC10-style. If this proves rigid enough, it might be then possible to have only one actuating mechanism per flap. This is really only for fun-flying, I can live with the drag (I think).

After talking to you guys and thinking this over, here is what I might end up doing: I'll look to buy a proper flap+aileron glider kit and rig it with the Crow-style control system (or build one along those lines myself), and in the mean time satisfy my curiosity for the airliner-style flap+spoiler+aileron solution with a longer-term design/build process. For this, I'll still need to figure out all the channel mixing (which I see might be the least of my worries anyway).

Thanks for all your ideas, guys.

AH1G

Go for it Bruno!
Let us know how it works out.