single surface wing sloper

[shaneyee]

http://pachome2.pacific.net.sg/~shaneyee/slopesaurus.bmp Sloping season is coming up in a month and I am coming up with a sloper with a new concept.

1. Pterosaur look....4m wingspan

2. Single surface Wing from ripstop nylon. carbon or glass fishing rod blanks for leading edge, kevlar line for trailing edge ( or luff line if you prefer ). Plan view above.

3. Control by wing warping

What are the pitfalls of this kind of construction? Rigidity? High drag? flutter?

What do I need to pay attention to?

Thanks

[Ollie]

You need a S-shaped airfoil for pitch stability or/and attack angle twist along the span and for the lift distribution and for pitch stability. See the Horton lift distribution for pitch and yaw stability. The forward sweep of wing needs for yaw stability for a vertical tail. The crank of the planform has part forward sweep and part for sweep back.
http://www.nurflugel.com/Nurflugel/nurflugel.html
http://www.b2streamlines.com/OTW.html

[Work in Progress]

How are you going to persuade your CF leading edges to adopt and maintain that swoopy curve?

[BMatthews]

How are you going to persuade your CF leading edges to adopt and maintain that swoopy curve?

Windsurfing rigs have done this for years. A straight cabon or fiberglass mast is compressed axially into a curved pocket in conjunction with some outhaul pull on the boom along with a few battens and a highly controlled airfoil results. These days the upper portion is often kept loose to twist off for gust control but the cut of the rig was designed for this. A few years back the same sails used a different cut that had a lot less twist built in. So by cutting the sail cloth and pulling it over a frame correctly you can do amazing things.

Shaneyee, you may need to do a bit more research and trials for such a solution to work but if you follow this path then it'll be highly flutter resistant and could concievably result in a wing that is just as efficient as some built up airfoils. Ripstop nylon won't do the job though. You'll need to look into low stretch sailcloth.

[shaneyee]

Ollie,
I will build in reflex into the tips and the legs will also flex up. The legs will have exagerated claws in the form of a wide crescent to provide vertical area aft. I tried using Profili to plot the L/D for a Jedelsky airfoil but it gave an error halfway.... Any experience with this type of wing?? Will I have to ballast it to penetrate? Hang Gliders are a much higher wing loading than models do...

Work In Progress,
Bruce is correct. It is really a pair of old fashioned unbattened windsurfer rigs. The function of the windsurfer wishbone is played by the legs of the pterosaur.

Bruce,
I intend to control the pterosaur by the flex in the legs. Eg Looking from the side, if legs flex downward, the pterosaur will pitch down and vice versa. Roll control will be done by having one leg flex down and the other flex up. My worry is the roll effectiveness will be poor because the shape change is mostly inboard. I intend to make the tip of the wing more bendy so it will follow the flex of the leg more closely than the rest of the wing.

Why do you think ripstop nylon wont do the job? Sailcloth ( dacron ) is harder to obtain in light weights.... I dont intend to have a highly cambered wing...L/D will be poor and the wing loading is very low anyway so I will go for a flat wing and let the stretch of the material provide a little camber.

Thanks all

[Ollie]

The problem with woven cloth is the stretch at 45 degrees to the threads. Also, the nylon stretch is too much compared to decron. Some sails are made with decron fabric and mylar film ply to stiffen the sails so the have the best shape. Consider changing the nylon with mylar film.
See:
http://www.modelresearchlabs.com/using_mylar_covering_materials1.htm

Perhaps 0.0015" or 0.002" thick mylar film would do your job. You could put kevlar tows or threads between two plies of mylar so the kevlar carries the high loads.

The roll control using the feet won't have much leverage and it be not effective enough.

You haven't solved the yaw stability or control. Just work out that solution.

[BMatthews]

What Ollie said... :D

The legs are far too inboard for good roll control and the transfer of the bend out to the tips will be hampered by the curve of the trailing edge. If it was straight or near straight perhaps more flex would make it to the tips but as shown there won't be any roll control even at the mid point let alone the tips.

And it's because you do not intend a highly cambered wing that I suggested some research into the highly loaded spars and membrane. Normal ripstop will stretch into some odd shapes as suggested already and likely flutter as well during any attempts at higher speed flying. It is just far too flexible to control the shape accuratley.

You have also not mentioned anything about a fin to control the yaw. Some small test gliders made from sheet balsa would be a good idea before you get too far into this project.

[shaneyee]

How does this pterosaur do it....??? How much control do you get from flexing your fingers?

http://pachome2.pacific.net.sg/~shaneyee/Pteronodon2.jpg

Answering questions solved 6 million years ago .....as far as I know, all the pterosaur models constructed used rigid fiberglass/ carbon wings....

Shane

[Ollie]

See:
http://www.twitt.org/QNStory.html

The head had vertical area (like a canard rudder) and it was used for yaw control but it was unstable in yaw and it used a gyro for yaw stability.

If you don't use a gyro, you could fly it backwards (feet first).

[BMatthews]

I didn't know the dinosaurs had developed gyros that long ago.... :D

Paul McReady's team did a pterosaur or pterodactyl or something a number of years ago. They had a TON of problems with the head thing. Basically they used heli gyros as well IIRC. The model was totally unstable without them.

[shaneyee]

There are wings that fly without rudders. The Northrop wings and Rogallo hang gliders come to mind. Perhaps I shouldn't look at having a tight wing.... the Rogallo hang glider has a loose covering that billows in flight and the shape provides yaw stability.

[BMatthews]

All those wings have drag centers behind the CG though. The Pterodactyl shape goes against that.

A very easy and inexpensive way to work on your options is to make up a simple little all balsa sheet test glider of about 16 inch span from 1/16 wings and 1/8 body. Include the head and any other bits you planned on. If you can get it to fly more or less stably then great. If it wants to swap ends or fly sideways then you need to work on some fixes. Cut, glue and try until it's stable or at least does not want to diverge from normal flight.

[Ollie]

One way to have yaw stability (and no vertical area) is use enough sweep angle and Horton lift distribution. In the Horton lift distribution, the wing tips lift down. It means lots of twist (washout) in the wing.

Back and read post #2 and study it about tailless aerodynamics.

[shaneyee]

This is certainly a learning experience! It does look like I have to modify the planform a little since the plane will not have the internal gyro that the pterosaur had.... pretty advanced for a 6 million year old design!

Shane