rsieminski

I've built a scratch, foam delta. WS 42", root chord 23", total area ~693 in2. Where should the cg be? I think the mac is 15.5".
Thanks,
Rick

matchlessaero

Rick, I would start with 20% of the main chord. (I have also heard suggestions of 11% of Mean Aerodynamic Chord, but I have not yet learned how to figurer the MAC)

Start with the CG forward. You may have to put more reflex (up) in the elevons to get it to fly, but it will fly. You can then slowly move the CG back slowly until the performance changes. As the CG moves back, you should need less reflex (which causes drag).

Put a pic up of your delta so we can see.

Cactus.

My Feedback: (1)

my rule of thumb, never failed me yet
work out the CofG as per normal planes. all flying wings must be forward of this point. work out 5% of your root chord. move your CofG forwards by this amount. this is the MOST! you can go rearwards, in real terms i use 8% to be safe
how do i work out where the normal CofG should be?
i draw a line 1/3 of the tip to 1/3 of the root.
i then take a line 1/3 of that line and join that to 1/3 on the other side. 1/3rd meaning if you start from root and work down towards the tip.
it depends on how much taper i have wether i stick to this or move forwards a bit, but its always somewhere near the CofG if you where just dealing with the root, just behind it.
i cant be bothered to get out a calculator but i've never been far off the money so far

DICKEYBIRD

Try this site guys: http://ourworld.compuserve.com/homep...le/page17.html

rsieminski

Thanks, I'll try it and post back as to how it flew/crashed.