Flat sheet Delta in a spin
 

Hi all,
I got a Weston Uk Tigershark delta for Christmas. Its basically a flat sheet of light ply with a fus' and a fin (no rudder). I set up the CofG, lateral balance, elevons, etc as specified in the manual. The first flight was pretty scary, as the controls were pretty unresponsive at low speed, and very sensitive at high speed - it needed a bit of right trim to get it flying level.
Putting it into a loop resulted in a skew off to the left - I think this was because the left aileron had slightly more travel than the right after setting the trim (should be able to fix this on the TX).
However, the second flight was more horrific, I put the nose up and let it go into a stall. One wing and the nose dropped, it then proceeded to pirouette with the whole wing rotating around the nose (a bit like a flat spin, but with the nose down). Nothing I did seemed to make any difference to the spin, and eventually I ran out of airspace and just shut the motor and let it crash.
Amazingly, it landed in mud and only the prop broke, but I am now too scared to fly it again.
Is this what flat sheet deltas are meant to do, or have I got the set-up wrong ?
Is there any way from recovering from said spin ?
I look forward to any advice or anecdotes on this subject.
Best regards to all,
Dorset

RE: Flat sheet Delta in a spin
 

You may have to add a functioning rudder. On this one I had to do that, as I love spins...

RE: Flat sheet Delta in a spin
 

Two things:

1. Sand in some leading edge twist - your leading edge tips should be at least 1/4 inch lower than the nose (this prevents the tips from stalling first).

2. Check your CG - I use the Palos CG calcluator here - http://www.palosrc.com/instructors/cg.htm
Set your CG up for 18%

Report back to us and let us know how these help.

CrazyHerb

RE: Flat sheet Delta in a spin
 

I agree with both posts, particularly -- add a rudder. Did you apply full down elevator in your recovery attempts?

RE: Flat sheet Delta in a spin
 

Thanks for the tips. I tried all points of the compass with the elevon control, but with no airflow over the control surfaces I might as well have been stirring porridge. Given a bit more time maybe I might have got some response, especially if I could have build up some airspeed, but with the nose pointing downwards, opening the throttle just shortened my thinking time, gravity is a hard task-master.
I too have fitted a tricycle undercart and didn't fit the supplied central landing skid, could this affect the stability because of uninterrupted airflow across the underside of the wing ?
The wing sheet is very thin so there is not much scope for sanding-in washout on the leading edge, can I add washout with a twist instead ?
I will also go with the suggestion of fitting a rudder, would it be best to cut the rudder into the existing fin, or add it to the fin (increasing the vertical stab area), on Tall Paul's plane it looks like the rudder area is quite small ?

RE: Flat sheet Delta in a spin
 

I suggest adding the rudder to the existing fin, if possible. The increased area will be beneficial, as will the greater mechanical advantage of the rudder further aft.

I don't think that your landing gear created the problem -- it would add a bit of nose-down pitch, but it probably didn't affect spin recovery. Flying wings without rudders are often real bears to recover from a fully developed spin.

RE: Flat sheet Delta in a spin
 

I put the landing gear on my Shark because of the fear I had of handlaunching something that powerful.
That plane used a 5/16" sheet balsa wing, with an elongated S-curve for camber; essentially a drooped leading edge and reflexed trailing edge.
It was c.g. sensitive, and managed to spin in all by itself, both upright and inverted.