Wing shape, drag and CG on Delta
 

I have decided to build a Delta similar to a Diamond Dust. My goal is to make it a very clean and fast aircraft by having a slightly raised center section to keep things like the fuel tank and servos out of the air stream. I also have some ideas for an engine cowl. To give it a little different look I angled the trailing edge corners. My question is will these angled corners create more drag then a 90* corner? Will the tip cord marked be satisfactory for figuring the CG?

I plan on staying as close to a NACA 0006 airfoil as the size permits with a fairly sharp leading edge. One person I know did put a sharp leading edge on a Dust and did not experience the nasty accelerated stalls like many get with the Shrike. Any thoughts on sharp leading edges on a Delta?

Thanks

RE: Wing shape, drag and CG on Delta
 

You could increase the section thickness percentage at the centre enough to hide the tank etc and still use the 6% tip. Your tip mods will make little if any difference to the handling. Leading edge radius affects the handling the same as any wing, increasing the radius at the tip will make for a more gentle stall at low speeds even on a delta. But on one this small, how slow do you want to go?
Evan, WB#12.

RE: Wing shape, drag and CG on Delta
 

Thanks for the reply. I was concerned my tip mods may cause unwanted vortices but wanted a different look. Speed is the goal. Slow is for landing.

I was only going to increase the center section thickness as shown in the picture. Slight mods will be needed to the airfoil so the trailing edge will end up at 3/8".

RE: Wing shape, drag and CG on Delta
 

Deltas have a lot of votex flow at higher angles of attack. In effect they are practically all wintip at those angles. A sharp leading edge creates a lot of turbulent flow and it may be helping your model by controlling and stabilizing this vortex flow or the formation of separation bubbles on the upper surface at higher angles of attack.

The "problem" is that delta wings just do not work the same at higher angles as "normal" wings. The vortex flow becomes dominant. Ever see the shots of the Concorde at landing if there was fog or dust in the air? Huge curlicues of circular vortex flow over the entire span of the wing.

RE: Wing shape, drag and CG on Delta
 

Are you saying that, because my model is a delta, the sharp leading edge may help stability at a high angle of attack? I would like a balance of high and slow speed handling with low resistance for top end. A rounded leading edge would be just as easy but thought I may be giving up speed with out a good reason.

Why is it a "problem" that the vortex flow becomes dominant?

Thanks for your input

RE: Wing shape, drag and CG on Delta
 

I probably should have said charactaristic. It's just part of delta wing flying.

And depending on the overall airfoil and other things yes a sharp leading edge may help with a delta. Especially if you found on previous deltas that you had a non stable low speed sort of pumping going on where the model would not stay in a stable mode of flight. It's the sort of thing that would benifit from a lower powered quickie build test version.

RE: Wing shape, drag and CG on Delta
 

"Characteristic". That sounds better. I have found deltas to be very stable at all speeds so far. My Shrike, not really a delta, with a sharp leading edge would snap roll in a tight hi speed turn.

I just downloaded Profili and printed out my wing rib templates. It looks like every rib will have to be modified slightly to have a 3/8" trailing edge. Hope that doesn't have a negative impact on this high speed airfoil.

RE: Wing shape, drag and CG on Delta
 

Mike,
By the looks of your plan it seems that your COG is around 30% of MAC.

If that in indeed the case you might want to shift it forward to the 15% - 20% range if you are shooting for speed, as well as stability.

RE: Wing shape, drag and CG on Delta
 

I plugged in the #'s again and and my CG is 10% - 15% of MAC. How did you come up with 30%?
http://www.coloradogliders.com/cente...calculator.htm

RE: Wing shape, drag and CG on Delta
 

Never mind just did the math, should not just go with the visuals...

BTW What do you power your Miss Dara Formula one with?
Nice looking airplane!

RE: Wing shape, drag and CG on Delta
 

I had the Miss Dara back in the early 80's and used it for a sport plane. There was usually some damage on landing on most flights using a 300' runway but did fly it about 50 times before selling it. It was powered by an OS 45 FSR and was considered fast for a sport plane. It did look nice.