rdjohnston

I've just completed a A1 Skyraider from an old Heritage kit. Its equipped with an OS 70 4 stroke that sits sideways. I put a 3 blad prop on it. Now here's the issue: When I throttle it up, with the elevator in up position), the tail rises up. If I don't hold the tail down, I'm sure it will nose down completely. I've added a small washer tobottom two screws on the engine mount, thinking the engine was pitched down. This didn't help. I lowered the incident angle on the horizontal stabilizer (plans say .7 degrees, but I think I had it way too high), but this had no effect. I put as much up in the elevator as possible but no effect. I checked the balance and she is right on.

The model does have a bit of a stubby fuselage, so there is little in the way of tail length.

Do I add more weight to the tail, even though it may become more tail heavy? Do I add more washers to the engin mount to increase up angle of the engine?

Frankly, this is my 10th model I've built and never had this issue before. My scratch built planes never give me this problem. I wonder if there is a design flaw.

Help !!!!

rdjohnston

N1EDM

My Feedback: (2)

If you give it up-elevator, yeah, it should hold the tail down. I agree. I wonder if the wing is blanking the elevators so that they can't reallly see a lot of prop wash??

Just grasping at straws....

Bob

Laird SS

I would assume that when you are running the engine, the plane is sitting on its wheels. This puts the thrust line of the engine above the pivot point of the aircraft, the contact patch of the wheels. Having the thrust line above the contact point will create a healthy rotary moment acting through the contact area of the tires. This would cause the tail to rise. Maybe that's the cause of your problem. Could also be that the blanking of the elevators makes the problem worse.

rdjohnston

Yes, the plane is sitting on its landing gear. Is there a solution to the blanking of the elevator or the rotary movement? I'm wondering is this motion will go away as its taxiing down the run way. I'm afraid to try flying it.

N1EDM

My Feedback: (2)

If you don't mind a 'square one' comment, how about doing a re-check of the CG using something more than the ol' fingertip method, i.e., put it up on a real CG stand. It almost sounds like the CG is too close to the mains.

Just my $.02

Bob

rdjohnston

I do appreciate your 2 cents, but I have a balance stand; don't use the finger tip method.

Any thoughts on whether its safe to fly it as is?

TFF

What can be a problem is the landing gear not raked far enough forward. Wheels too close to the CG and the plane wants to tip up. Spitfires are tearable with this. If it has no retracts, bend the gear forward if you think the CG is good.

rdjohnston

Yes it does have retracts. I put the new electric one on it. It was designed for simple mechanical ones. So that may be where the design issue is; I changed the design . I will experiment with the gear. Thanks for the tips.

rdjohnston

I want to thank you all who helped me on this problem. I added 1/8 inch to the back of the landing gear; pushing them forward and ten I increased the up angle on the elevator. The combination of the two resolved the tendency this aircraft had for rotating nose down when running full throttle in a static position.

I learned a lot on this little problem