Suitable aerofoils with long thin wings.

[Ado]

Hi,

I want to try and make a scale glider but with a 1.8m EPP wing. The plan was to use a MH-32 foil but the root is only 110mm and the tip is about 50mm. The foil is then pretty thin and gets a bit hard to put a decent spar in there to stop flexing and fit servos. Some gliders scaled down to 1.8m the root is only 80mm and the tip 30mm :eek:

Ideas.. solutions? Is it worth it or best to leave the scale ships to the moldies with 4-6m spans?

Cheers,

Ado

[Ollie]

"Is it worth it or best to leave the scale ships to the moldies with 4-6m spans?"

Yes!

Bad: EPP plus 22.5 AR plus, 0.45 taper plus, 0.08 thickness and very wing loading.

Better: stiffer foam plus, lower AR plus, bigger tip/root chord plus, carbon spar plus, more span plus, allowed low wing loading plus, airfoil allowed thickness.

How much you want more L/D and low sinking speed?

Use:

http://my.athenet.net/~atkron95/pcsoar.htm

[BMatthews]

The trick is to cheat and make the wing wider than scale so you get chords and airfoil thcknesses you can work with. I'd suggest about 7.5 to 8 inch chord at the root with no narrower than 5 inches at the tip. You'll need to increase the size of the horizontal tail as well. The fin will probably be fine or may benifit from only a slight enlargement.

This is still less area than is optimum for a 2 meter model and it'll need to fly faster than other 2 meters to keep the efficiency up in the wing (Reynolds numbers and all that stuff) but it should be doable and still look pretty darn good as well. The other stumbling block against efficiency is the cross section size of the fuselage. But it's also what makes the model look great in the air. Scale can't compete with the winged broomhandles anyway but for the joy of flying it's a lot more fun.

[Ado]

The planes will be designed for slope only... not for flat field thermalling or X-country flying... I should have mentioned this at the start.. sorry.

Im currently in the throws of building up a DG-1000 out of EPP. I have worked out some design issues(T tail strength and pushrods).. the DG-1000 wing(1.8m) was a little small so we lengthened the root and tip a little(150mm,70mm) and will probably use a MH-32(12%) foil. Im not up to speed with RNs and "AR"s .. sorry..again.

Would there be a thicker and possibly better foil for the job? a little thicker would help with the placing of spars and servos I think too. Thicker foil would help with strengthening the wing too... more meat to so speak.

Im I still in the world of make believe? Is my dream of nice scale EPP ship going to remain a dream? hehe

Thanks for the help ;)

Cheers,

Ado

[Ollie]

All-up weight? With a 12% thick airfoil and fast air speed the plane will not able to fly slowly. You need very strong lift. You will not get it to fly at weak lift. The span divided by the average chord is the aspect ratio (AR). The EPP wing will be floppy in bending and twisting at an AR of 16.36 (skinny). That is your main problem.

The average chord of the wing will have the fuselage tail length about 320 mm to 400 mm and the horz. tail area between 8% and 12% of the wing area.

[BMatthews]

Ollie is right about the twisty problem. You can add a spar but the EPP will still twist like a wet noodle and the chord isn't wide enough to rely on filament tape for this one.

A bunch of years ago there was a really nice looking sloper with high aspect ratio wings that used solid sheet for the wings. You may want to consider that as well. 3/8 sheet for the wings with inset carbon strip spars. Use a tool made from a block of wood with a 3/8 wide strip of sandpaper glued on to cut a spar slot and glue in some .007 x 3/8 carbon strip top and bottom. Carve the wing like a big hand launch chuckie. But use lines and cut away bevels with the lines as a guide to form the basic shapes. You may need to do some CAD or sketching to figure out the best way. Then cover the wing with .5 ounce glass cloth using polyurethane varnish as the bonding agent. Cut the cloth and cover with strips such that the weave lines are at 45 degrees to the span so you get the most torsional stiffness from the glass cloth. Primer, sand and paint. A piece of 1/4 sq spruce or very hard balsa for the leading edge will help resist dings. Or if you can cut a nice groove a 1/16 carbon rod would do much the same thing. Just be sure you filler in aroung it to maintain the shape of the airfoil.

For such a small chord and low reynolds numbers thin is in. This Hannes Delago offering would be fast and easy to shape....