Hi I have a Tek Sumo where I used online tool to calculate CG which is 7 inches behind nose. You can see from video it is way off balance (with 1 amp battery, motor, components in place). I would have to add 8+ ounces to front to get true balance. Is this an issue? If so what would you do to fix? Don't want to add a lot of weight to front.

Delta Wing 1 (0 min 33 sec)

Without adding more weight, the only solution is to move your existing weight forward, or lighten the gear, moving the CG forward. The motor aft the trailing edge adds to the problem, and the servos could be moved forward.

Otherwise, more weight forward, such as a larger (heavier) battery.

Thanks, it's possible to move the motor forward but it requires alteration. I'll try to fly it and see how it does. Seems like it's not well designed; it only takes a certain size battery. Lots of surgery involved here.

This may be more than you're willing or want to do but here's a suggestion:
Cut another cavity behind the battery and move your ESC/Rx into it. If you have another piece of foam you can then cut a block the size of the rear cavity and fill it back in. You can move the esc/rx there before cutting a new cavity just to check it. This way, if you do have to add weight, it will be less than you would be adding as it stands now.
Also, is there a spar in there somewhere? Seems like the esc/rx cavity would create a weak point for bending and flexing.

This is based off an observation at 0:08 into the video.

Also, not sure if this would help either, but maybe turn your battery 90* and move it between what looks to be like two little "spars"(?).

If you're feeling crafty, cut a new section up front to hold the battery (maybe you could install it on it's side for this application) AND the esc/rx, side by side, and fill in the back cavity altogether.

A simple solution that might work and leaves the current structure intact:
Add a plywood tongue that extends forward of the nose about 8 inches and mount your battery there. More than 8 inches might be pushing it. You can test this all out before you actually secure the tongue in place. I've done this on several planes and it worked out just fine.

Put the motor on the front !!!

^^^^^...that works, too....but waaay too easy.

J/K, of course.

Still might require some modification though.

Originally Posted by gpw

Put the motor on the front !!!

I do that on my Komet-style planes and that allows the battery (of any weight) go right on the proper CG.

As a last resort for wings, I've done what nuteman suggests also - it looks crazy but it doesn't add any weight, save for the extension itself.

I tried flying tek sumo today, crashed like a rock. Not surprised.

The best suggestion is the plywood tongue. However, this should not be needed. If the wing was designed right, should balance without this. Seen a million videos of wings w/o a tongue.

But thanks for the suggestions, everyone.

I think the solution is to make my own wing with a more obtuse (wider) angle between the halves. This would put less weight behind the center of gravity. And possibly putting two batteries in the front.

No, gpw, that's where the camera will go. Hmm, camera is 70 grams, that would help balance this.

OK, Camera will also work !!! Did you do any test gliding over tall grass... ?

Is that a 900mm wingspan? If so I think it's the same plane as my PopWing and the CG is spec'ed at 200 to 212mm. I set mine at the fwd limit and it took 2 oz of weight, to be replaced soon with a bigger battery (mine is currently 1300mah). I can't imagine why yours would require 8.

BTW, at 200mm CG and about 3/16" initial reflex, maiden launch was totally un-dramatic. Don't even have to throw it -- just pulls away from my hand. Love it.

gpw, there's no tall grass in northern Virginia, just lawns. But yeah, if you can find it, that's a good way to test.

hard line, is that right? 1300 mah would make a difference. Doesn't matter, my sumo is so broken after today I trashed it. I'll try with my wire-cut foam wing and let you know. BTW my CG was 7 inches or about 175 mm, 1000 mah battery.