Could someone help me find the CG for my scale x-29 project? Thanks
Nick

but that plane "is so unstable that it needs a computer to control it"

wouldn't it just be the same as a regular canard?


dave

Well... those canards are not just regular canards... they are "close-coupled" canards... meaning that they actually modify flow over the main wing to a significant degree. Notice that there is a "back porch" as well.

Cautrell05, did you try looking through the NASA research papers on the airplane? You would have to modify the CG location from there because the X-29 itself is statically unstable.

Make a small balsa chuck glider of the same scale dimnsions with a profile fuse and add weight to the nose till it gives a long flat glide. If you have a side profile, just ahead or the main gear struts is a good place to start. Did the Viggen, among others, this way.

I looked at a lot of sites and even bought a book by Bill Gunston about the X-29. Found a lot of good pics and learned some things but in all the pics I never found any that indicated where the CG was. I know the full scale X had some stability issues, but that challenge makes it more fun.

The first one will be a pusher for simplicity, with either a 400 or 540 size motor depending on how big I make it. The canards will be functional but main pitch control will be from the strake flaps near the exhaust cone. The strake flaps will have alot of travel but the canards will will be adjusted for alot less travel. That should help a little with pitch stability. I also thought about adding a micro gyro on the elevator servo.
What would happen if the canard was mounted slightly higher?

Nick

for the most part, just more knife edge coupling. there was a canard calculator thingy around here somewhere which would give you the cg for any given wing shape with any given canard shape at any given distance. do a search

I would do this as well, but the long flat glide is not your critical condition. WHat you want to do is make the canard adjustable - use a straw or dowel as an axle. The critical aspect on a plane like this is uncontrollable pitch-up. When you get the elevator/canard control past a certain point, the plane will continue pitching up until it is inverted, if the CG is too far aft. It would either flip over at takeoff and slide down the runway tail first, or pull-off a figure 9 when on approach.

The problem is, it will fly just fine when trimmed for level flight. So, you need to check the CG for slow flight characteristics. Set the canard for 20 deg pitch up. Adjust the CG so that when you gently toss it the nose hangs up high while the glider flies slowly but maybe not so efficiently. THis will ensure that the plane will remain controllable at low speed.

As for using the rear fuselage strakes for control, the shape of the surface will not allow very much control power at all. You should keep it simple and use the canard for pitch control.

What do you mean by knife edge coupling?
Nick

Anyone?

when you are in knife edge, sometimes you get pitch or roll coupling. the plane may nose up or down, or roll one way or another. that is knife edge coupling