I've been making my own airplanes. They are are cross between SPAD and the Sturdy Birdy. I use coroplast to make the wings and PVC for the fuselage. I copied the 3/4 inch Aluminum channel coming out of the fuselage from the sturdy birdy. Great planes "Durapane" also uses this Aluminum Channel in their design. The result is a plane that is easy to construct, has a place to mount the electronics, and can survive rough treatment. I have built 3 so far and they all fly extremely well with one exception. They want to climb. I have to add a lot of down elevator so that they will fly straight. The planes are balanced. I've even made one nose heavy, but still it wants to climb.

I have noticed in the design of the sturdy Birdy II that they angle the engine down. My guess is they have the same problem and have solved it by making the engine pull down on the front of the plane. This design has to result in a loss of efficiency. I don't want to angle my engine down and I don't want to keep adding weight to the front of the airplane. My wing is as far back as I can go.

What is causing my planes to climb? Is there anything else I can do to keep this plane from climbing?

What is the wing incidence set at??? Also, almost all aircraft have thier powerplants set at an angle to off set the affects of powerplant on the airframe. They will almost always either be angled down & right or at least to the right due to the way the props pulls thru the air. If you don't do that, you will never have a straight flying airframe. Even turbines are angled in most airframes to some degree.[8D]

Incidence is the angle of the wings and tail to the thrust line. In your case in line with the crankshaft of the engine. Robart and Great Planes have them. I have a Robart myself. Check to see if the wing and tail have the same incidence. If they do try putting a few washers under the top of the motor mount-to-firewall screws. This will add down thrust. If it clears it up then you are done. If not try shimming the back of the wing up a little at a time until the tendancy to climb is gone.

Flat bottom wing trainers do have a tendancy to climb under full power. This is normal due to the wings producing so much lift. Try shimming things and I feel you will do just fine. A combination may work best. This is an area for experimentation, so have at it. God luck.

Mark Shuman

I'm am not an experience builder. I just kind of copied some other designs. I assume that the wing incidence is the angle a which the wing sets on the fuselage. I have not checked this and I'm not sure how. But, I think you're on to something. The SPAD plans call for a wing that is flat on the bottom and sets flat on the fuselage, but my first two planes I did not make them flat and the front bottom of the wing is angled up off the fuselage. I bet this is the problem. Tell me what you think. What can I do? Do I have to make another wing or can I use the one I have?

I would try the tests that PHREAD59 sugguested. First what type of powerplant are you running? It must be set to the correct angles or it will pull the plane in all the wrong directions. Second make sure that you have the wing set at the same angle as the tail plus about 1 degree of up at the L.E. and have a little washout (turn down) at the wind tips. 1 degree of up at the Leading edge of the wing gives it a nice flight angle and the washout keeps tip stalls at a minimum. [8D]

The basic problem is that the airplanes are nose heavy. The more forward the cg, the more stable in pitch so the more they will pitch up with addition of power. As the cg is moved rearward they will become more "groovy" tending to go where they are pointed without pitching up. Move the cg a little at a time, and when it flys like you want it stop. Too far rearward and it can become unstable and hard to control. A little downthrust will help control the pitch up tendency if you leave the cg a little forward.

My Powerplants are O.S. LA 40 and a LA 46. Two of the palnes have 40s and one that has the 46.

I cannot move my wing back any more to adjust CG. I could (but don't want to) add angle down. This might be the easiest.

Don't move the wing just add a little lead to the tail and try it. Buy the way it sounds like you built it moving components is not an easy thing so just add a little lead for the tests. When you are happy with the CG then try to move the battery or receiver to keep it lighter and still get the CG you want. All the CG changes in the world will not help if the flight surfaces are not set right and thrust issues are too far off.[8D]

I have SPAD 3D and it likes to fly nose high no matter what, I can't complain much since I built it to learn hovering and harriers. Which hovers stupid easy.

The madien flight was nerve braking for me as I too had to put a lot of down elevator to fly it level but then it was easy to fly.

Try adjusting the ailerons natural position if you lover them they will act as flaps and plane will climb so you should rise them till you are satisfied but in my case SPAD 3D it does not fly like balsa plane but they are okay and some people like them a lot.


Note: these are my opinons, I don't want to trash spads or say something like the spad is the best.

You will get better and faster response in Spad forum in RCU,

RE: Plane Continues to Climb? (in reply to GarMan) Report This Post | (Post No. 8)


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I cannot move my wing back any more to adjust CG. I could (but don't want to) add angle down. This might be the easiest.

ok,,,,wait....you dont move the wing to get the CG right..you have to balance the model ON the CG.....if its a constant wing...(no sweep)...put a mark on the wing 25% of the chord...if the wing is 12 inches put a mark 4 inches back from the leading edge...and theres your balance...you dont move the wing bud....hope this helps....min. setting balance is 25% max is 33%,,,but the 33% is for real touch'y feel of the elevator...please dont do this right away...as you might not be able to handle it...good luck bud...Rod

So the CG is 25% from the front of the wing. This will help me in the future. When I move the wing back, am I not moving the CG back? I'm confused. I moved the wing back as far as I could so that the plane would balance. It would be the same as moving the rest of the plane forward. If I move the rest of the plane forward the CG stays still. I think I know what you're talking about, but I can'nt expain it very well. I think we are still talking about the same thing, just in different ways.

Garman,

I have a SPAD Debonair with a flat bottom wing - that climbed liked crazy.

I tried reflexing the ailerons up which sometimes works. Make sure your ailerons are level with the fuse or slightly raised above level of the fuse. This works for some planes, didn't work for mine.

I also tried another trick that has worked for some guys. Tape a piece of yardstick under the TE of your wing. Be sure and relevel your ailerons with the fuse before you fly, however. This also didn't work for my plane.

I added 2-3 degrees of down thrust to my engine. Problem solved. My plane now flies very well. The crazy climbing is gone.

You answered your own question. Too much positive incidence. Incidence is the angle of the flying surfaces relative to a neutral reference line. If you have a symmetrical airfoil laid down flat on the trailing edge, it will be too much positive. The advice to get an incidence meter is good. In fact, get two if you're going to keep scratch building. Work on the wing mount (build it up?) until the wing, tail and engine are all at 0-0-0 degrees. Test fly. You should be able to trim the plane to fly level at medium throttle, climb at full throttle, and glide gently at idle. If it climbs under power, add engine downthrust 1-3 degrees as needed. If it dives in the glide, you may need to shim the leading edge of the wing up 1-2 degrees. That ought to get you in the ballpark, assuning the balance point is about right. Try about 25% of the wing chord to start.

Follow phread and kdheath's advice and you'll solve your problem.