I thought it was time to start a thread with a new name so we don't sound so negative about the Impact. Mine is electric and I am at the critical step, making the battery mount. The question is where do we really want the cg to end up? The suggested spot is at the back edge of the wing tube. Have any of you folks who have flown these got a better suggestion?

Jim O

Jim I have been flying mine at the front edge of the wingtube. When trimming it I was in a lot of wind and felt like this made it track a little better. When I started I was aft of the wing tube which was ok in calm air. The only difference I could tell by moving it forward was it tracked better, didnt seem to change much else.


Brian

Thanks Brian. I was afraid of that. That means I'll need to put the battery pack right behind the motor which means it'll be very difficult to install/remove through the cockpit. I've been thinking about mounting it in the chin cowl after seeing Jerry Budd's Abbra. That's where he has it, very far forward and low. I seem to remember Tony F saying that lowering the cg helped the upline so maybe that is the way to go. I hate to think about ripping out my beautiful baffle system but it might be the best solution.

Jim O

Jim,

I seem to be the odd-ball with reference to Impact CG. I started at about 1/8th inch behind the wing tube and wasn't happy until moving it about 3/8" behind the wing tube. For me it just was too nose heavy otherwise. It didn't roll well, wouldn't hold the angle well when in a climing 45 degree and rolling inverted, it required too much down to hold level inverted, etc.

I've wondered if this has something to do with my stab incidence because I'm clearly in the minority on this one, but I'll say this, I was never happy with the plane until moving to the current 3/8" back CG.

BTW, I moved all sorts of weight to the front of the plane (including some lead) to get to where others seems to like the CG, just to need to remove it.

Keith B

I ran some calculations on an aero design computer program today and it says for aerobatics the cg should be 0.5 to 1.25 inches behind the wing tube so it sounds like you are going in the right direction Kieth. The same program yields 0.75 to 1.5 inches in front of the tube for trainer type stability. That tells me there is a wide operating range and I should design a mount that allows me to move the packs quite a distance. By the way it looks like the wing tube center line is just slightly forward of the mean aerodynamic quarter chord of the wing. The aero center of the whole plane is aft of there so the calculations sound reasonable.
Thanks for the inputs guys.

Jim O

Jim --

Kudos for starting a more positvely named Impact thread!

CG: In the original extremely long Impact build thread there was some discussion of CG location during the course of which some discrepencies of wing tube location were discovered. I don't remeber numbers off the top but we started refering to the location as X" back from the LE of the wing at the root -- seemed to make comparisons more valid. The discussion was about 2/3 of the way through pages, I believe.

You said you used Rustoleum paints for the trim -- any particular type to look for? Are they fuel proof or do they require clear coating? From the photo in your post they looked great.

I am also looking at touching up some seams -- did you order the white touch up paint through Composite-Arf's web site or do you have a alternate source? If from their website, how long did it take?

Thanks,
Tom

Keith, I had the CG as much as .625 behind the wing tube on the plane also. I had done a layout of the wing to find MAC as Jim did with a similar result. The plane does hold 45's requiring some stick pressure to hold inverted, which is what im used to.

When you say it didnt roll right what was it doing that bugged you?