Sweep and taper Questions???

[Butch777]

Hi,
I'm trying to desigh a plane like the Projeti. It is a flying wing with a pod type fuselage. I'm going to lengthen the fuselage to move the motor back and the battery forward. Also lower the motor to centerline thrust. But its still tail-less, with elevons.
What would be the best Sweep and taper for mediun to high speed? And for low speed as well? Any help would be appreciated, Butch

[dayhead]

Don't know much about the higher speeds but I've had problems using excessive taper on swept-back wings at low speeds. Lengthening the fuselage and increasing the separation of the two heaviest components (motor & battery) will increase angular momentum/rotational inertia or "fly-wheel effect" and may have detrimental effects on pitch stability/handling qualities, especially on close-coupled aircraft designs like flying-wings. But the beautiful thing about model airplanes is the ability to experiment and learn at relatively minimal expense and risk. Go for it and let us know how it went!

[uav51]

Based on some old NACA reports, it seems a taper ratio around 2 to 1 provided the best results, higher ratios led to early tip stalling and a reduction in cl max (or overall lift). The only data I have is for a sweep back angle of 15 degrees measured from the 1/4 chord line for various aspect ratios and taper ratios. That may be a good starting point for your sweep back. Whatever sweepback angle you use, higher aspect ratios will give you a longer tail moment arm which will give you better longitudinal stability. From the above results, a higher sweep back angle would obviously do the same, but with an overall loss of lift. At higher speeds you need to make sure to build it stiff (especially if you have a high aspect ratio), and some washout towards the tips would probably help things at the slower end.

[biber]

Since I doupt you are going for a higher aspect ratio than 5 or so the taper won't be too critical. If you do an at least about 30 degrees swept wing it will develop deltaish characteristics and the actual amount of taper becomes almost meaningless (but much taper looks much faster ;) ). Even a Projeti basically is a delta, as I recall it, despite it's quite some time ago that I have actually seen one. Deltas are easy to build stiff and light, don't need washout, don't need a sooper-dooper-laminar special airfoil offer a huge amount of lift for landing and are easy to control. Use a simple symmetrical naca000watever airfoil and for speeds sake make it thin. Everything between 9% thickness and a flat plate will do it. Delta is lots of fun, but needs therefor lots of power (otherwise it's not much fun).

Do it! have fun! ;)

biber