Razorback Wing layout
Hi again,
Alan (HITC) had some extremely useful advice/insights to share regarding the Razorback when he visited on Christmas day, and I have taken most (except one) on board. He didn't think (given how far back the wing is positioned) that a high wing would be very practical considering that all upward vision would be lost. So I think a low wing is probably the only feasible option.
I like the idea of a mid-wing configuration, but the spar is not coming to the party, and so that's out. However, a low wing is do-able. I have been playing around with wing plan layout for months, and have oscillated from very high AR to swept back, to inverted gull wing, to tapered, hershey bar and elliptical. Every time I think I have hit on the ideal wing, I lose interest in it and draw something else.
At the moment, I'm inclined to give the plane a low wing, inverted gull forward sweep. And a reasonably low AR.
Something like this.
The various lines on the wing are (from R to L) 1/4 chord line, 37% line (spar), 50% chord. The wing has 8.25 deg forward sweep as measured along the 1/4 chord line. .35 taper ratio, 19.15ft span, AR=6.07, Area = 60.3 ft^2. With big extending split flaps I'm aiming for a stall speed of 38kts
The reason for the inverted gull configuration is to improve the otherwise rather poor downward visibility. And to make the plane very visually attractive. Of course.
Duncan
PS I have researched just about everything I can find on the web regarding FSWs, and most posts seem to be rehashes of a very few basic observations:
(1) FSWs tend to tip divergence. Extra uni Carbon cloth laid in line with the tip twist (ie at about 45 deg) will make the tips rigid enough to withstand the tendency, without much weight penalty. Some details also on exactly how to do this are also available.
(2) FSWs are not affected by tip stall, since the airflow is inwards from the tips into the root of the wing. This gives greater CL at high AoA. However, I can't see this being much of an advantage for the sort of flying I want to do.
(3) Some yaw instability. But this can be overcome by ensuring a larger than "usual" rudder. The Razorback has a HUGE rudder (I like the look), so that would seem to be taken care of already.
And in essence, that's about it.
What remains, for me, is to determine how much forward sweep is too much. The X-29 was highly unstable. On the other extreme is the LET-13 glider, which has a very slight forward sweep, and is very well behaved. I notice that the Rutan Boomerang has about 13.5 deg FS on the main wing, and about a degree more on the smaller wing. I have not read that this plane is at all difficult to manage.
So how much is too much? I've gone for 8.25 deg, and lost about 5% of possible lift because of this. So I raised the wing area accordingly to ensure my stall target is met.
Comments?