Questions on double delta design

[1987tc]

I am working on a Parkflyer design that will be around 200" square. What is the best way to determine the cg? And also I am thinking of either a flat plate wing or one that has an airfoil. What would be the +s and -s of each?
Wes

[Ollie]

Park fliers tend to be light weight and have good strength for their weight. this makes it very practical to test glide the new model over tall grass so that even if it stalls tail first into the grass or noses in, it is unlikely to be damaged. Just keep moving the CG, adjusting the decalage and regliding until you are satisfied with the CG position and decalage.

Flat airfoils can't develop as high a lift coefficient as cambered airfoils. Therefore cambered airfoils can fly slower, other things being equal. Planes that can fly slower can also turn tighter.

Use a thin, single surface airfoil with a camber of about 1/30 of the wing chord and a high point at about 25 or 30% of the chord back from the leading edge. The wing can be made from a 6 inch wide piece of 1/16 or 3/32 inch sheet balsa of medium light density. The balsa sheet is curved to the desired camber and held there with ribs under the wing every 3 inches or so.

[1987tc]

Out of balsa. It is 1/8" because I had some laying around. I am thinking og building a bigger version out of blue foam for radio control tests and then a final model out of a composite of foam,balsa and a litter carbon fiber.
Not really looking for speed with any of them. I know that if the wing loading and power loading are low that a clean airframe will have reasonable speed and be able to slow down.
Also going to toy around with vertical stab(s) position and size as well as number.

Also thinking that it might be interesting once the design is flying well to try and develop a blended wing structure and power it with EDF(s) burried in the wing.
Wes

[BMatthews]

1/8 is a lot heavier than you really need for this model. Especially if you use struts or other support.

Think of that same 200 sq inches of area as two layers of 1/16 and 1/8 sheets sitting on your bench. Now think about cutting spars and ribs from that sheet. There'll be a LOT of lumber left over with the built up option.

There's no reason why a 200 sq inch model built of sticks and jap tissue covered can't weigh only 1 1/2 oz. Weigh your 1/8 wing wood alone and I think you'll see what you SHOULD do.

But I know how attractive it is to build an "instant" airplane. Just be sure you're not going to save a 1/2 hour and $2 now and suffer 12 hours of frustration with poor performance later.

[1987tc]

The 1/8" is sheet wood and was only used to build a 1/4 scale free flight glider. I am building another out of blue foam now that is bigger. It will start out as free flight and maybe radio control later. The final version will be built with lightness in mind. Nice thing about the fan fold blue foam. You can wip something out cheap and fast!

The balsa model mentioned above flies pretty well but did show the need for more vertical stab area.

It will be interesting to see what the bigger one does.
Any thoughts on a motor size for the first powered version? It will be a pusher prop foam before the ducted fan version is built.

Wes

[1987tc]

this is just the Balsa test glider.

[Ollie]

About 40% of the weight cam be saved by using contest balsa instead of average density medium balsa. Another 40% of the weight can be saved by properly tapering and rounding to a streamlined shape before cambering.
The trailing edges should be no more than 1/64 inch thick and taper in a straight line to about 25 or 30% of the chord.

Use a program like MotoCalc to size the motor, battery, gear ratio and prop for the desired performance. There is no substitute for harmonizing all the components to the size and weight of the model and its intended use.

[1987tc]

Can some one post a link or point me in the right direction for a cad program I can down load to work on the plans with?
Doesn't need to be anything fancy.
Wes

[propfan]

www.turbocad.com - TurboCad LE is pretty good and, more importantly, free

[1987tc]

Ah you said the magic word! FREE!!!!
Thank you I will check it out.
Wes