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This might be a balance question or problem

Old 10-10-2003, 12:00 PM
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Flyboy1958
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Default This might be a balance question or problem

I have a Spectra sailplane and everything works just fine. I am new to flying sailplanes so I'm not sure if mine is reacting the way it should be. For one thing it tends to turn left a lot easier than turning right, even with the motor shut off. Could this maybe be a slight warp in the wing I didn't detect yet? The thing I'm really not used to is the fact that I can't get a good climb going without it pitching up and wanting to stall dipping to the left all the time. Seems to fly 20 feet, pitch up, stall, over and over. If I keep a little right stick and am very gental with the controls, I can get some decent altitude out of it, but maybe I am just used to flying my glow powered airplanes and seeing better performance. The sailplane only has rudder and elevator along with throttle. Could this be a balance problem? I have it balanced right at 3-1/8" from the leading edge as it recommends with the correct throws.
Old 10-11-2003, 11:08 AM
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crewchief_432
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Default RE: This might be a balance question or problem

did you try lateral balancing the plane?
Old 10-11-2003, 02:32 PM
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Dr Kiwi
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Default RE: This might be a balance question or problem

Sounds as if your left wing is heavier than the right, or one is (or both are) warped. The pitching up suggests you are tail heavy. Add a bit of weight to the nose and see if it makes a difference.

Cheers, Phil
Old 10-13-2003, 07:48 AM
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Matt Kirsch
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Default RE: This might be a balance question or problem

I know enough about flying sailplanes to know that it's a whole different ball of wax compared to flying glow planes.

Power planes are trimmed to fly straight and level with the power on. When you reduce power, the plane pitches down.

A sailplane is trimmed to fly straight and level with the power off. When you add power, it does the opposite, and pitches up.

Flat-bottom airfoils are the worst offenders for this pitch-up phenomenon. That's why most trainers have lots of down thrust built into the firewall.

IMHO, you have several possible solutions:
1. Simplest: Adjust the linkages so your elevator trim tab is centered when the plane's trimmed out to fly straight and level. Move the trim tab ahead for launch so the plane takes off with a bunch of down trim to hold it level. If you have a computer radio, you could program it with some down elevator on a switch, and have a "takeoff mode." I think this is a common practice for gliders.
2. Next simplest: Shim the motor to give 2 degrees of downthrust. Adjust as necessary.
3. Might help: Move the CG forward; make the plane slightly nose heavy.
4. A long shot: Check the incedence of the wings. Make sure they're close to specifications. A wing with too much positive incedence will cause the plane to fly.
5. More power: Put a ~3:1 gearbox and 12x8 folding prop on the nose. This simple mod will triple the amount of thrust the plane has so it can maintain a steeper climb angle. They make planetary gearboxes (3.33:1) that'll bolt right in between the motor and firewall if space is tight.

...and by all means, check the wings for obvious warps and twists. They have to be pretty significant to affect the way the plane flies, though.
Old 10-15-2003, 08:25 PM
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Jim Finn
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Default RE: This might be a balance question or problem

In my skimmer 400 sailplane I had to put in more than 5 degrees downthrust to stop it from doing just what you have discribed. Check to see if you have the same amount of washout in each wing to try to correct the not flying streight.
Old 10-16-2003, 12:02 AM
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sierra gold
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Default RE: This might be a balance question or problem

One thought for you to check - are you getting the same amount of movement on the rudder for both right and left? Sometimes hinging or movement of the push rod tube will limit one or the other.

I fly a Hangar 9 EP Aspire which has similar characteristics to the Spirit/Spectra. I find I have to put in about 2-4 clicks of down elevator on launching and then take it out once I cut the motor. If doing that eliminates the stall on launch, then you can change the down thrust of the motor or use my routine.

Sierra Gold
Old 10-16-2003, 05:57 AM
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Jim Finn
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Default RE: This might be a balance question or problem

Adjusting the trim to correct this will work fine. I set up my transmitter to put in downthrust at full throttle. I did it with the skimmer at first but the problem I ran into was that as the battery wore down the motor ran slower at high throttle settings and landings required a little more up elevator.

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