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Issues with a Sig Riser 78

Old 02-23-2013, 08:10 PM
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cwick1989
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Default Issues with a Sig Riser 78

Ok so I got my Dad a Sig riser from our local hobby shop. Put the servos in it loaded it up grabbed a hi start and went to the local flying field. Our sailplane expert was there so we let him do the 1st launch. Needless to say he even said it was a hand full. I got on the sticks next and I even noticed it flew worse than any sailplane I've had. The wing isn't warped very straight and well built. WHen we give it full rudder (when I say full I mean full) it doesnt turn. Needless to say it has been put up for the time being. The CG is 1/4-1/2in behind the spar. I'm at a loss for words Ive always heard theyre great planes. Any advice?
Old 02-24-2013, 03:44 AM
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hattend
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Default RE: Issues with a Sig Riser 78

How much throw is "full" rudder?

I have never had a 2 channel sailplane that doesn't turn. You did put in the correct polyhedral, right? Or is this an ARF? Never had a Riser but it should be in the Spirit/Gentle Lady class of 2 channel sailplane.

Try to get as much throw in the rudder as possible. If you have a sloppy pushrod, firm it up. Air pressure could be pushing the rudder back to neutral (although this is unlikely)

If you have a large gap in the hingeline, seal it up.

If all else fails, make the rudder surface bigger.

Don
Old 02-24-2013, 05:17 AM
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cwick1989
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Default RE: Issues with a Sig Riser 78

As much throw as I can get without contacting the elevator. When we come in for a close landing we can see full rudder and the plane flying in a straight line. It was a prebuilt plane. As far as I know the polyhedral is right. I guess I'm just going to upsize the rudder. Its the only logical thing I can think of.
Old 02-24-2013, 05:35 AM
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soarrich
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Default RE: Issues with a Sig Riser 78


ORIGINAL: cwick1989

. I guess I'm just going to upsize the rudder. Its the only logical thing I can think of.
I don't think that will work, there's something else wrong. A picture would be very helpful.
Old 02-24-2013, 07:57 AM
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da Rock
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Default RE: Issues with a Sig Riser 78

It could be a weak rudder servo. Of course you said the rudder deflection was obvious so it shouldn't be that.

Look around for anything that would affect the rudder's ability to turn the plane. Hinge gap for example.

The Risers I've seen all turned with no drama at all.

How much trim did it take to fly straight. How much rudder deflection is present? 1/2"?

How wide are the hinge gaps? Is either the elevator or rudder more than 1/16"?
Old 02-24-2013, 08:20 AM
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denoferth
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Default RE: Issues with a Sig Riser 78

Had the same problem with an original design I built at Hanscom Field in 1968. It had an under cambered, polyhedral, Hershey bar, D-tube wing of about 12 foot span and an air foiled stabilizer and rudder, (about 12%). Before I gave up on it the vertical stabilizer had been cut down to about 1/4th of the stab area and the rudder size increased to ½ the total size of the stab with almost a third of that as balance area ahead of the hinge line. It would fly wings level and as straight and stable as a rock and with full rubber in either direction would slip about 15 degrees again with the wings dead level. I suspected the spar wasn’t stiff enough and the wing was twisting but I never did figure it out and a military move relegated it to the dumpster as it was way too big for the SAAB 99 I had at the time. As my wife and I drove off I watched a kid pulling it from the dumpster. I hope it didn’t sour him on model flying forever.
Old 02-24-2013, 08:40 AM
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Antares100
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Default RE: Issues with a Sig Riser 78

I had a Riser back in the '80's for my first plane. It was a great flyer.You said it was pre-built, I am wondering if it uses nyrods (plastic tubes) for pushrods. If so, and they weren't glued in well, they may be moving (bending)when you use the servos. The movement of the tubes(sidewaysin the fuselage) along with the air pressure against the rudder may restrict rudder movement while in the air. When you check them on the ground, there is no pressure against the rudder, so the rudder moves. Hold the rudder (gently) and try to move the rudder, Do you hear the servo straining against your hand or is there little or no pressure? Do you hear anything moving in the fuselage (nyrod coming loose)?
Old 02-24-2013, 11:30 AM
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cwick1989
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Default RE: Issues with a Sig Riser 78

It doesn't take any trim at all. It flies straight into the wind. you cant turn it from the wind but it points its self into the wing darn good[>:]. The pushrods are good the 1st thing I checked. Even with me putting pressure on it they still pushed my hand. Could the wing torque while in flight?
Old 02-24-2013, 02:15 PM
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soarrich
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Default RE: Issues with a Sig Riser 78


ORIGINAL: cwick1989

Could the wing torque while in flight?
There nothing really to torque it.

You said it doesn't turn, but yet you got two flights out of it.

Years ago I built my daughter a stock OLY II, when I test flew it I thought I had radio failure it turned so poorly. I put more polyhedral in the tips, (like 10"extra), she went on to win the 100" and Unlimited Jr classes at the '85 Nats with that plane.

I never had a Riser, but from your symptoms I would say the wing is too flat. If it has a metal wing rod, bend it to give you more dihedral. If it's like the OLY II, which stock turned like a pig, this will solve your problem.
Old 03-17-2013, 04:35 PM
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snuts
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Default RE: Issues with a Sig Riser 78

Are the tips squared off? Cut the tips up at a 45*. I've seen beginers miss this important aerodynamic detail. Yah, promotes roll.
Hope this helps,
-Snuts-
Old 03-22-2013, 06:17 AM
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Kiowa Guy
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Default RE: Issues with a Sig Riser 78

Bet if you move the CG forward to a least the spar or better yet ahead of the spar about an 1/8 inch you will find a real nice flying bird.
Good luck
Old 03-22-2013, 07:46 PM
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speedracerntrixie
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Default RE: Issues with a Sig Riser 78

Sounds like you just have it trimmed to fly too slowly. As previously mentioned a picture would help. I did look up a few pics and they all do seem to be a bit shallow on the poly. I would suggest adding more.





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