Fast airfoil for a Delta
I have recently put together a spad delta. The span is 30inches with a 45 degree sweep, and length is 22 inches. I put a MVVS Q500 .40 with GRRT pipe on it. MVVS turns APC 8x7 at 20K static. Has one vertical stab. Tank/radio/servos all cowled in. Didn't build cowl for engine and pipe yet. Model weights about 3 lbs. I decided to put a flat bottom on this one to cut down on drag. The model balances at 11% MAC. No down thrust on engine mount.
No relfex built into airfoil.
Flying:
This model needs slight up elevator to hold level flight at about 140 to 150Mph. It need very little travel on ailerons, with 75% exponential.
Comparison to my Spad Diamond Dust Clones:
I had designed other fully symmetrical airfoil deltas, and they flew level at 110mph with no up elevator. This new model however has it maximum wing thickness of 1 inch well behind the balance point. ( A good 3 inches.)
Why do I need up elevator on this model? Could it be a balance problem? (Doesn't drop or climb in corners)
Is this maximum thickness point the aerodynamic center?
Is this aerodynamic center back so far as to push the nose down?(i.e. lift the ass end up)
Should delta AC be at %25 of the cord as other models?
Should the maximum thickness point/AC be at my balance point?
Can anyone offer some insight into these questions.
My ultimate goal is to break 200mph with a delta. I'm not going to do it with this setup however.
Thanks in advance for your help.
Todd Murray
Ottawa, Canada