MiL

First of all, hello! I'm back after about a 2 year absence. I'm moving soon and may once again have the room to participate in the hobby. I'm hoping to jump right back in where i left off, i had just completed my first self-designed and scratch built plane (Taco .25) and found that i enjoyed the design/build as much or more than flying. So I want to design another. I'm thinking that i'd like to either build a funky lookin pusher similar to the push-pull cessna (210 is it?) or build a more traditional looking plane, but one that will fly ultra slow.

Right now i'm leaning toward a slow flyer, and that's what this thread is about.

Were i to go this route, what sort of airfoil shape would be best? The things i'm thinking about are a super fat (wow, i can't even remember the terminology) wing like on a fun-fly plane, which gives a lot of drag (good in this case) and provides a lot of lift (also very good) but a much less symmetrical shape since i'm concerned with providing maximum lift while upright and am not really concerned at all with inverted performance.

Keeping weight to a minimum will also pay huge dividends in keeping flight speed low, correct? I'm planning on a stick-frame fuse built for soft flight and not crash survivability. Also, would a lifting-stab design help significantly? I'll probably need fairly large control surfaces to maintain control at very low speeds.

I'm planning on using a .25 FP engine and HiTec mini servos. I want a rediculously slow flying plane.

BMatthews

If you want super slow you will need to keep the weight super light, go for lots of wing area and go for a moderatley thick but highly undercambered airfoil.

For the 25 I would suggest 600 to 700 sq inches, keep it to no more than 48 oz and use an airfoil from the free flight world. For super slow at the expense of virtually NO high speed flying the super high undercambered old school A-2 Nordic airfoils will provide you with a shape that looks like someone designed it with the flaps already down. The only problem with that is that you cannot fly even moderatley fast without straining the wing structure. Some better alternates would be Gottingen 500 or 501, MVA227, MVA301M. What you want is something with a mean camber around or more than 6% and a thickness of about 10 to 14%. Anything in that range will have a stongly concave lower surface.

MiL

Ooh, cambered underside, i hadn't thought of that, i'd just assumed a flat bottom. Is it difficult to cover concave surfaces without the film wanting to bridge the gap and go straight across (making it a flat bottom wing), or coming loose?

Thanks a ton for the airfoil suggestions, i will check them out.

Tall Paul

If you put enough spars on the underside, the covering can follow the rib curve well.

BMatthews

It's not hard but it is different. You start from a central spar or the middle of the ribs and iron (assuming Monokote or equivalent) the covering to the spars and ribs from the center forward and back and leave the leading and trailing edges until last. Some extra care needs to taken to avoid wrinkles and I would suggest using low heat, just enough to tack it, at first so you can pull it all up if required. When happy with the light tacking then seal 'er down well with extra heat. Some extra spars like Paul suggested helps but it's not essential. You stil need to iron the covering from the middle of each rib or spar. Doing it this way avoids the covering just spanning the hollow areas.

Needless to say it takes some extra care to shrink as well. Use the sealing iron rather than the heat gun. And try to avoid the ribs to prevent loosening the seal to the hollow curves of the ribs. Just shrink it in a series of little rectangles.