Figuring CG on a staggerwing?
 

Been reading around, and determined that I need 23% of MAC as well as percentage of chord.

http://www.rcuniverse.com/forum/aero...g-biplane.html

What I have is a lower wing forward Stagger wing Bipe Cub. Its a regular Cub with the bottom wing forward of the top wing and its the clipped wing on bottom, full wing on top.

So haw to I figure 23% MAC and percentage of stagger? Since its the SIG 1/5th Cub kit, I have the wing areas of both wings known. I just don't know how to calculate the rest. Bottom wing is full, no ailerons, top standard ailerons, if that matters.

I assume that both wings have a constant chord. If that is the case, the Mean Aerodynamic Chord is the chord. Calculate the 30% point from the leading edge of each wing. Place the CG of the airplane at the midpoint of those two points. That is what I did for this bipe and it flies great. Dan.


http://www.rcuniverse.com/forum/atta...mentid=2163414

OK, well following what I have read here, 30% of the MAC comes out to 4.425", roughly 4 3/8' or a little more than that. Splitting the difference between leading edges places it at, guess where, 3 1/2", which also happens to be the actual balance point for a normal Cub. This one came out a little tail heavy compared to my other Cub, both are SIG 1/5th kits, so the wood in the tail may have been heavier, or I used more dope(which wouldn't surprise me with all the coats needed to make it look yellow. There are at least 8 or more coats, 2 nitrate, 2 clear, 2 white, and 2 yellow.

I have it all put together now, tomorrow is its maiden flight. If all goes well, then I will finish the details on it with the decals. This time I made darn sure the dummy engine will stay on the cowl. My other one looks silly with an outline of where the dummy engine used to be. First flight on that one it came off. Thats what I get for not gluing it on before painting. I had scraped the paint away from where it glued, but that wasn't enough.

Good luck with that maiden. I'm going to expect a FULL report (as are a lot of other guys you know).

Good luck!!

Well..... I was almost ready to maiden. Weather outlook was good. Loaded up and headed out. Got there, started setting up and the winds started gusting. Damned weather channel got it all wrong, those were not 9 MPH winds. I got the Cub all assembled, she looks good in the sun. Got the engine running, its a used 100 Saito, and it is well tuned, but needs bearings, I can hear them at idle and there is some shaft play now that its been run. Any way, I had it on the run up stand, got the engine adjusted, figured out the cut off settings, and the engine would not stop running. I swear it was idling at 400 RPM. I could see the blades of the prop it was going so slow. I finally stuck my finger in the cowl and pressed the fuel line closed which finally got it to stop running. My other 100 is just like that. So I walk back to my trailer with my field box and radio, and then walk back to the run up stand, and find the Cub hanging off the side of the stand. Thankfully it didn't get full wind or it may have wound up in the pond behind the field.

Checked it out, and no damage was done, WHEW, close call. SO I got it back to my trailer, and contemplated flying it, but wanted to check the winds up high, got my Somethin Extra out, and flew it. Winds weren't too bad up aove, but landing was hairy, mainly due to the fact there are still large semi trailers at one end of the field, which in this case is the approach side, and the winds were unpredictable, W, NNW, WNW, and gusting up to 25 MPH. It was pushing the SSE towards the trailers on every approach. I finally got it lined up just right and almost greased it in, but a wind gust slowed it enough to drop the nose, and I bounced it. :( Was almost a perfect landing.

I then thought, well I know how my other Cub flies, so let me try it. I got it off the rack, checked the battery and they were low, so put it on the charger. 35 minutes later the winds were getting worse, so I packed it up. No sense ruining a year and a half of work to rush it.

It was so windy that the sides of my friends trailer were booming. It was whistling through mine, and as I held a Pepsi bottle it was singing a tune. When its like that, not worth the risk. If they were steady and in one direction, I would have had no problem flying it, but with the way it was swinging around from the north to the south out of the west, I felt it be better to wait a little longer. If the winds were out of the east I may have tried it though, its those semi trailers on the east end of the run way that had me concerned, hit one of those on landing and its all over. Hopefully they will have the containers moved onto the pads and the semi trailers unloaded and removed soon. It really is impacting our runway.