FT Mini Arrow CG question

[Obi-Wan B.O.B.]

Hello all,
So I’ve been building a Mini Arrow with the idea of sloping with it. I‘ve found that setting the CG using the usual start method of putting a finger on each mark to be really finicky. One time it will tilt forward, one time backward, one time hold still. My other SOP is to do a toss glider test. This is my first wing design so I would like to know: Does the toss glider test work? The fingertip test shows it to be pretty good (I think) but the toss ends up with a gradual downward decent for a few feet and then down on it’s nose.

Thanks in advance for any tips and tricks!

 

[Merv]

...Thanks in advance for any tips and tricks!...

You really need to be using some kind of balance stand. The finger method is just not accurate enough. It's far to easy to cheat and roll you fingers to make it stay put. Flying wings are very sensitive to CG, if you get it right, they are a pleasure to fly.

I drill one hole in 2 small pieces of scrap lumber and insert a dowel or BBQ skewers in each hole. Make the balance stands 3-4 inches tall and Balance you plane on these stands. A mirror can be useful to get the stands on your CG marks. I use 2 other pieces of scrap lumber to limit the plane from falling off the stands, one in front and one at the rear of the plane. Make your your balance stands slightly taller than your supports. I move things around until the plane will stay on the balance stands unsupported.

 

[Obi-Wan B.O.B.]

You really need to be using some kind of balance stand. The finger method is just not accurate enough. It's far to easy to cheat and roll you fingers to make it stay put. Flying wings are very sensitive to CG, if you get it right, they are a pleasure to fly.

I drill one hole in 2 small pieces of scrap lumber and insert a dowel or BBQ skewers in each hole. Make the balance stands 3-4 inches tall and Balance you plane on these stands. A mirror can be useful to get the stands on your CG marks. I use 2 other pieces of scrap lumber to limit the plane from falling off the stands, one in front and one at the rear of the plane. Make your your balance stands slightly taller than your supports. I move things around until the plane will stay on the balance stands unsupported.

Thanks for the suggestion. When I got off work today, I whipped out a quick stand using some 3/4” plywood and 1/4” dowel that I had laying around. Standard gear was as follows:

1. No motor or firewall/power pod
2. 20A ESC
3. Spektrum 410 receiver tucked into one of the wing spars
4. 3S 850 battery tucked up into the nose as far forward as possible

With that arrangement, I ended up hot glueing two 3/8” flat washers under each of the underwing gear flaps. I wrapped them in painter’s tape so hopefully I can take them out fairly easily should I ever decide to motorize it.

I took out into the back yard and gave it a toss. With just a tiny bit of up elevator, it had a nice glide before running out of forward energy.