Sig Riser 2m weight Q - RC Groups
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Jan 21, 2002, 02:58 PM
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Steve Fehr's Avatar

Sig Riser 2m weight Q

I'm just finishing up building a 2m Sig Riser, and have some questions about the weight and hi-start hook... This is my first glider. (I've flown a friend's Gentle Lady a few times before, so I know sorta what to expect off an up-start)

For starters, my weight came out to be appx 23oz which seems awfully low to me when compared to other 2m gliders. (20oz + 3oz lead). Is this normal? I used HS-81 servos and other lightweight electonics, and built the plane almost entirely with probond II, which probably helped greatly. But 7oz seems to be a big difference; I should probably point out that I don't have a scale, and used a calibrated rubber band & exponential interpolation but it's so simple, I trust it to be accurate within an oz. Well, that is, if the hardware store didn't short-change me on the 1oz sinkers I used for ballast and calibration, lol

After I have it balanced, where should I mount the tow hook? I was going to do the ole' hang upside-down at 10 and drill, but the instructions say to add nose weight on first flights and when it's windy, and I'm worried that will push the CG forward of the hook for those flights and cause me big problems on launch. But if I move the hook forward to compensate, it'll be too tail-heavy on calmer days... The hook will be epoxyed in if I follow the plans, so I want to make sure it's right.
Last edited by Steve Fehr; Jan 21, 2002 at 03:02 PM.
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Jan 21, 2002, 03:24 PM
Faded away
The plane is light enough that you should be able to give it a test ride on the ground before putting it up on a hi-start. You want to get a flat straight glide that takes a minimum of stick movement. Adjust you CG and trim to achieve that. I have always been able to do that with my 2M ships.

Maybe, for the first flights up the hi-start, you might want to add in a little extra nose weight to move the CG up a little from what looked correct in the hand toss. In flight the speeds will be much higher than in the hand toss and the nose will have a tendency to rise if you have a rearward CG.

If you do this you should have your CG close enough that your towhook positioning should be correct the first time. There are on-line shops that sell adjustable towhooks, too.

Jan 21, 2002, 04:06 PM
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Steve Fehr's Avatar
Thanks! I just did a bunch of glide tests- I guess I can pat myself on the back for making it true, because with the CG as per the drawings, rudder and elevator trimmed out perfectly in line with the stabs It pitches forward in a stall, but, unfortunately, it does seem to pitch up when I throw it harder. I started out with an extra ounce of lead in the nose, but it was clearly too nose-heavy and flew much better when I took it out. I'll see if I can find about 1/4-1/2oz of ballast and try again before the rain starts back up.

Ah, apparently, CG was slightly aft; I must have velcros the lead a little further back than where I sat it earlier for balancing. A bicycle brake shoe did the trick and brought it level more or less where it was in the drawings, trying to err on the side of nose-heavy. I then trimmed it out neutral- so now, with a hard launch, it goes straight with no pitch-up tendancies. With a soft launch, it goes straight, but slowly starts to dip nose-down, and has to be corrected with about 3/4 up trim. It's cool- I can fly it with my thumb on the trim lever Is this the right place to trim it, or should I trim it for hands-off gliding? Or trim it neutral in the linkages, and adjust the servo trim in flight?

I can't believe how far it glides- my FMA Razor 400 has roughly the same wing loading, and will go about 200' on a hard throw, but tossing this sailplane with less effort I can not only meet that 200', but turn around and land at my feet! One time I was too high even for that and ended up doing a 360 hehe... The field I glide test in beside my house is only 200' by 100', with overhead power lines, btw. So being able to fly a 2m glider around kinda blows my mind!
Last edited by Steve Fehr; Jan 21, 2002 at 05:13 PM.
Jan 22, 2002, 05:43 PM
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Thanks dave- it flies great All the good advice worked! Did about a dozen up-start launches this afternoon, and all went well. I was unable to launch directly into the wind at times (due to a large puddle) which lead to a lot of yaw, but I learned to correct after a few launches and actually got a few really nice flights outa it. Managed not to crash, but did drag the wingtip a couple times. Left the field with naught but a small gash in the middle of my wing (damned if I know what tore it, must've been a rogue stalk!) Just gotta take a crowbar along next time to help "persuade" the stake in & out

On an unrelated note, smack in the middle of the football field, I also found a gunther prop that fell off my Razor about 3 months ago that I'd given up for lost... Of course, it looks like the lawnmower found it first
Jan 23, 2002, 08:48 AM
Mr Mootsie
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If the weather clears in the next few days, I'll meet you at Hugo Owens to work with you on your Riser. I have more than a few hours of flight time on it!