multicasting

I built the Hooker designed by Chuck Cunningham. It seems to have gone together very well. The problem I am running into is that I have to put in about 15 degrees of up elevator when running at higher speeds for level flight. Yet, at lower speeds, it seems to require less. I have increased the wing incidence by about 2 degrees with little effect. I removed the STOL wingtips (Custom design on a hooker from the 1970s I once flew) and replaced them with flat tips. I have tried adding up thrust until until I reached 10 degrees which only did wierd things when I gassed the engine. The horizontal stab has a balsa stick running the length to provide an airfoil effect. Perhaps something is set up wrong on this, I really don't know. Any ideas?

Bob

multicasting

Any Ideas?

Tall Paul

Where's the c.g.?
The "stick" on the horizontal.. top side only?

saramos

I would think that the problem is with the balsa stick on the horizontal stabilizer. Most stabs use a symmetrical airfoil. I would try removing the balsa stick and use just a flat stab.

Scott

DT56

My Feedback: (18)

If the horizontal stab needs the balsa stick for strength, glue one on the bottom side of the stab to form a symmetrical airfoil.


DT56

dicknadine

the photo shows very loose -unequal covering on the hortizontal surfaces, try tightening it up and check all the rest of the covering, also looks loose. dick

beepee

Chuck's designs only used the stick in the stab for aerodynamics. The instructions in the design I built called that stick optional.

Good luck,

Bedford

da Rock

Does the elevator horn come out on the bottom? Pushrod flex sometimes just shows up at higher speeds.

Does the airplane take what seems like an extra amount of elevator throw at faster speeds when it's inverted? Pushrod flex doesn't happen when the rod is pulling.

Ed_Moorman

My Feedback: (1)

The stick on your stab is giving you a flat bottom, lifting airfoil on the tail. As you airspeed increases, the stab lifts causing the nose to point down. You have added up elevator trim to compensate. As your speed decreases, your need for up trim decreases.

You need to remove the stick airfoil or put a second one on the bottom, making a symmetrical airfoil.

On most RC models, the CG is ahead of the center of lift causing the plane to want to pitch forward, nose down, so the stab provides a countering, downward force. Your airfoil, upward lifting stab has countered this causing the nose down force.

Certain planes, the Telemaster comes to mind, use a lifting stab to compensate for a flat bottom or lifting airfoil at high speed. The idea is as speed increases, the airfoil wants to cause the plane to climb. We have all noticed this in using full power on a trainer. It wants to nose up. Adding a positive lifting stab can compensate. As speed increases, the stab gets more lift, raising the tail, countering the tendency of the nose to climb. The plane does fly around in a nose down attitude at speed, however.

A lifting stab should not be needed on a plane with a symmetrical airfoil.

multicasting

There is a stick on the top and bottom of the stab. The covering has been tightened. The pushrod is very well re-enforced. CG is as according to plans. I think that I will remove both sticks and see if that helps. The higher the speed, the more up trim that is needed. In my previous experience, Up trim is needed more at lower speeds. So, perhaps the tail is generating too much lift as speed builds.

I have a lot of time in this thing. I would really like to get it working correctly. I really worry about flying at higher speeds with this much trim. It has to be causing some stress somewhere.

Ed_Moorman

My Feedback: (1)

If you have sticks on both sides of the stab, you may have one or more of the incidences incorrect. You really need to check all the incidences of the plane. This is easy if you have an incidence meter. The Hooker probably should be at 0-0-0 for wings, stab and engine. Since I have been flying ARFs, I haven't used my incidence meter very much, but when I built my own, especially original designs, I found they flew 100% better after I started using an incidence meter to line everything up.

If you don't have an incidence meter, after you get the sticks off the stab, get a small level and prop the tail up so the stab is level. Measure from the table up to the center of the leading edge and the center of the trailing edge. They should be the same. Sit a square up against the firewall to make sure it is square.

Another thing, check the position of the ailerons. They both should be straight out from the TE of the wing. If both are down or up you can get pitching of the plane at speed.

multicasting

Ed, Thanks for all the help.

I actually went and bought an incidence meter just for this aircraft when I realized there was a problem. Here are the numbers from the plan. I have matched these numbers. Wing is at +1, stab is at 0, engine is 5 down, 2 right.

I have to tell you, I think I still have a bit to learn about how surface adjustments affects flight. I understand the principles of each surface. However, I assume that placing a negative incidence on the stab would cause the nose to rise. A positive incidence on the wing will cause the tail to rise. Is this correct? I have inboard flaps on this model. Should I experiment with these in a slight spoiler condition? To remove the stab at this point would be very difficult since it is epoxied on. Can you suggest any other mods I can try?

DT56

My Feedback: (18)

Does this design have a symmetrical wing airfoil? If not, try removing the stick from the top of stab only to make an inverted airfoil that will increase the download on the tail. It's the lifting stab idea in reverse. Since your problem increases with speed, it suggests an increased pitching force common to unsymmetrical wing airfoils.

Does the wing have tip washout?

Good luck and Merry Christmas!

DT56