cheap contest thermal plane, I need advise

[e-sailpilot86]

Our local club is having a build it, fly it contest, we've held them before, and all of them turn out great. Although, this is our first "thermaling" build it fly it contest. We've got many things covered already, but these things:

The wing needs a strong stiff high-start(able) wing, that is fast and easy to make, like in 5 to 10 minutes? We use strapping tape on shorter span slope planes, but these are 60" ers. 7" constant chord I'll bet. Advise?

We need a way to make the plane balance out easy and fast. We'll just throw on the servos, and strap them down, just like the Reciever. We might have trouble balancing, not much time for lead either. We're going to have a long tail, so the plane can still thermal effectively, target weight is fairly low, maybe 12-18 oz. Advise?


Record time for a flyable plane is about 20 minutes. There was one that was done in like 7, but it flew apart instantly, most interesting flight, "we're having a slight malfunction!"


Most importantly, I would like to see some planes that are truly able to be thrown together, such as a floyd. I would like to see other designs too.


I'm sure I can make this a whiz without help, I just want some other's thoughts. Thank you

[francois]

What are the rules? Can you use anything or do they hand you a set bag of parts?

-Bernard

[e-sailpilot86]

the rules are pretty basic. You use whatever servos you want, standard or micro, and the parts for like control horns, etc. are pre-attached. For pushrods, we use some real cheap copper like stuff, taped onto a bamboo stick. We slap on the wing using double-sided fiberglass tape, reinforced with fiber tape to be held on. The rules that are very restricted, is that you cannot have prefabricated parts, like a fuselage that's already built. Basically, you just have to show up with your gear, and slap it on a pink plane. There's a lot of exposed pink foam on the plane, but they last. I've still got the same plane with all the cheap parts attached, I just change the fiber tape on the connections once in a while, still a blast to fly.

I'm sure you're concerned about the difference in performance in these planes...only weight really effects it, and the strength of your plane for combat (while doing slope combat). They are ugly, in a cute way. This is far from being pylon competition! ;) No matter how well you build it, or poorly you build it, they all fly the exact same way.

After a few years, the wings will finally give up and fold in flight, but hey, the whole plane only costs a few bucks. True cheap fun. I could post rules, I'm likely going to be the CD. That'll take a while, and I know the rules will work fine, so I don't really need any recomendations...:D

Referring back to the original Q...do you know of any cheap and fast way to build a stiff wing? It would REALLY HELP!!!!

[steelhead]

Our club has had a couple of these contests- they are super fun and get the whole club and a bunch of new members to join in for cheep. I will be holding another one this summer. Anyone else?

Dean@steelheadproducts.com

[steelhead]

Oh- and PS

We have even thermalled the FLOYD- and that takes less than 2 hours to build at the field.

Dean@steelheadproducts.com

[tim hooper]

Hmmmmm....

Not sure if this really belongs in Electric Sailplanes.

I'll move it to Thermal.

tim hooper

[Ollie]

A good histart launch requires a pull on the line of at least three and preferasbly four times the weight of the model. The maximum pull is at the beginning of the launch (unless there is a lot of wind) and lessens as the rubber shortens. In a good wind the plane can even stretch the rubber more and that incresses the pull.

With a central tow hook, the bending load on the wing is greatest at the center and that is usually where the wing folds under load. The maximum bending load on the wing can be reduced by a factor of four by using a launching bridle and locating a pair of tow hooks under the wing, one on each side, about 43% of the way from the wing center to the tips. The bridle consists of a piece of line about twice the wing span with a ring on each end to engage the tow hooks. The line should slide freely through another ring attached to the end of the tow line or parachute top.

The wing is still subject to bending loads but they are now maximum at the tow hooks during launch, zero at the wing tips and near zero at the wing center. The bending loads produce tension forces on the bottom of the wing and compression forces on the top of the wing. The strapping tape will carry the tension forces well on the bottom of the wing. This leaves the compression forces for the wing structure to cope with. Foam and strapping tape do not carry compression forces well. The tape buckels and the foam crushes easily. What is needed is a small wood spar imbeded in the foam at the top of the wing. it can be glued into the foam with foam compatible CA or a small amount of 5 minute epoxy. You could also use polyurathane (Gorilla brand) wood glue mixed with a drop of water to speed the curing. The tow hooks should be tied into the wood spar to prevent pull out.

The lighter the wing loading, the better the model will thermal so use micro servos, small receiver and battery pack. Every gram you can save will improve performance. To save nose weight, balance the model by sliding the wing to the best position on the fuselage before strapping it in place. Also, the less the model weighs, the less histart tension that will be required to launch it well.

[BMatthews]

You've obviously already got a proven design and construction method for making models. What you may not have had in the past was a wing that is strong enough to take the launching forces of a high start. There's two ways to get that. Carbon tube(s) to act as spars and possibly added flying wires to help the model withstand the launch forces. If the carbon tubes are large enough in section thats all you need as long as you can figure out a way to join them at the root. Or better yet, use ailerons with no dihedral and close to full span single length tubes. If carbon tubes are not an option then mount the wing up on a bit of a pylon or depen the fuselage belly and use some for of compression spar, dowel or spruce sticks, and use flying wires to carry the load. Used this way the wood only carries the local bending loads but the center section is relieved by the flying wires carrying the major portion of the wing loading.

My only other advice is to choose a thinish airfoil with decent lift charactaristics. For simplicity the ClarkY can't be beat but I'm talking a PROPER ClarkY and not just a curved top "thing". For thermalling you need at least SOME aerodynamic advantage.

In fact another option would be a wing from the corrugated plastic stuff used for SPAD's. But you need some way to add a little camber curve to the wing.

[e-sailpilot86]

Hey Dean, that contest was at your club! Note the post was made in September of 2001.

I'm not sure about Tim Hoopers moving of the thread... I think I made the post in here about, oh, two years ago! :D

[e-sailpilot86]

Btw, the planes were very sucessful. After about five high starts the wings started to flex to a 45 degree angle on launch. All of them have failed by now, but they flew real well for a flat nosed plane. Close to a Gentle Lady, and they were real floaters. I'll draw up a picture of one.

[e-sailpilot86]

...okay, not quite a thermal thug anymore! I put a hairdryer fan on it to see if it would work at all, that was about a year ago. The wing was suffering from major flexing on launch, so I saved it for an experiment. Nothing more than an extended glide was attained.

RTF weight was only a pound with standard equipment, I'm trying to get my new club at SASS to try it, it's so much fun. It's going to be hard though, this club is very competitive.

[steelhead]

YEah- I remember hahaha

Why dont you make sure I have your email?

Dean@steelheadproducts.com

[geekykiddo]

Once I just sanded some foam into a TLAR shaped wing, and stuffed a spar in it. The i took a couple of slabs of balsa with scotch tape for hinges, and a CF spar for fuse. flew it free flight, marginal performace.