Cause of launch spiral?

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Rktman

Eric Noguchi
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Hoping the glider pros here can diagnose why my scratch-built slide pod did a 360° spiral on the way up? It wasn't a tight spiral, but more like a quick loop before settling into a normal glide at ejection.
Confirmed that nothing is misaligned (although I purposely made one wing 1/8" lower to get the glider to circle) and there was no rod-whip, it only did the loop about mid way up.
 
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BABAR

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Gremlins. Gotta be Gremlins.
 

Charles_McG

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Hoping the glider pros here can diagnose why my scratch-built slide pod did a 360° spiral on the way up? It wasn't a tight spiral, but more like a quick loop before settling into a normal glide at ejection.
Confirmed that nothing is misaligned (although I purposely made one wing 1/8" lower to get the glider to circle) and there was no rod-whip, it only did the loop about mid way up.
So you intentionally made a differential in angle of attach in order to have a little roll so the glider turns. And what happened at high airspeed during boost?
 

Rktman

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So you intentionally made a differential in angle of attach in order to have a little roll so the glider turns. And what happened at high airspeed during boost?
It did a single 360° spiral, more of a loose corkscrewing loop actually. Could it be related to insufficient dihedral, or maybe the intentional difference in dihedral of each wing?
 

Charles_McG

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I don’t know enough to say - but you did clarify the angles. You essentially set the body at a small angle on its side. I don’t know what that would do, if anything.

Flat sheet, or did you sand an aerofoil?
 

Nytrunner

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And if you still cant figure it out, you at least have a rocket that does a cool trick!
 

Rktman

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I don’t know enough to say - but you did clarify the angles. You essentially set the body at a small angle on its side. I don’t know what that would do, if anything.

Flat sheet, or did you sand an aerofoil?
Airfoil.
 

burkefj

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I'm confused, loop and spiral/corkscrew are completely different, did it do a loop, ie in pitch do a complete 360 degree loop, or did it simply corkscrew/roll around the long axis and make a full roll before deployment?
 

Rktman

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I'm confused, loop and spiral/corkscrew are completely different, did it do a loop, ie in pitch do a complete 360 degree loop, or did it simply corkscrew/roll around the long axis and make a full roll before deployment?
It corkscrewed around the long axis once before transitioning into a normal looking glide.
 

Rktman

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I have a glider that rolls left - I’m pretty sure the airfoil isn’t the same on both sides.
When launched or when gliding?
In almost every case, one wing will weigh more than the other, even when they're cut out as one piece from the same sheet of balsa. Normally I don't mind since it causes the plane to circle when gliding, but I've never had it or the airfoil cause the glider to spiral on the way up. That was a totally unexpected and unintentional bit of weirdness.
 

Charles_McG

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Hand tossed. It hang tests level, but does a hard roll left when tossed.

It's an upscale Tercel that I haven't launched yet. Haven't had the opportunity to do it without witnesses.
 

Rktman

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Hand tossed. It hang tests level, but does a hard roll left when tossed.

It's an upscale Tercel that I haven't launched yet. Haven't had the opportunity to do it without witnesses.
Ugh, hate when they do that. First glider I ever scratch built as a BAR insisted on taking a hard right downward. Took a close squint at it and realized the intense summer humidity here had warped the rudder, stab and fuselage just enough to make it impossible to fly straight. Tried steam and heat to straighten things but it didn't work, so now it sits on my shelf as a reminder to humidity-proof all my glider builds (but that's a whole other story).
 

burkefj

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Another reason i like foam, i can fly in the rain and the only time they spiral is if i push on the sticks as others commented could be thrust axis, rudder, wing warp or airfoil..
 
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Rktman

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I think I may finally I have discovered the reason for the spiraling at launch: too much play in the slide box. I had the same problem with my Apogee Cirrus Breeze, only it was a slide wing and therefore a much more severe situation because the slide box was even looser, causing it to get into a death spiral once it transitioned to glide mode.

Apparently having the pod's slide box loose enough to rock a few degrees on the way up is enough to cause a bit of spiralling (in itself not a bad thing) but it's definitely not something you'd want once it transitions to glide. I've since managed to tighten things up, but due to the pandemic thing, won't be able to test fly it till later.
 
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Matt Danison

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Eric, I live in East Central Florida (high humidity) and am curious how you "humidity-proof" your glider builds. I have already spray painted three Red Barons and am currently constructing three Mega Barons. Thank you in advance.
 

Rktman

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Eric, I live in East Central Florida (high humidity) and am curious how you "humidity-proof" your glider builds. I have already spray painted three Red Barons and am currently constructing three Mega Barons. Thank you in advance.
2 - 3 coats of thinned dope (50/50) to really penetrate the balsa, followed by a final coat of unthinned dope. Doesn't add as much weight as paint and I've never had any warping problems even though we have extremely humid summer conditions here as well.
 

o1d_dude

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More lift Is being generated by the wing that is skewed.

Build your glider wings “straight“ and that should cure the high power spiral.

“Breathe” in a little turn to the vertical tail and maybe a little clay ballast on the outboard wingtip to adjust the glide circle.

Hand launch gliders (HLG or Discus Launched Glider) are thrown at an angle and banked to counter the glide circle which is obviously not possible with a boost glider. In hand launch we generally use “warps” to trim out a glider rather than building the wings at different angles of attack. The warps can “deflect” under launch and resume their adjustment once the velocity slows to normal glide speed...kind of a primitive auto-surface.

Welcome to rocket-assisted Free Flight.
 

Rktman

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More lift Is being generated by the wing that is skewed.

Build your glider wings “straight“ and that should cure the high power spiral.

“Breathe” in a little turn to the vertical tail and maybe a little clay ballast on the outboard wingtip to adjust the glide circle.

Hand launch gliders (HLG or Discus Launched Glider) are thrown at an angle and banked to counter the glide circle which is obviously not possible with a boost glider. In hand launch we generally use “warps” to trim out a glider rather than building the wings at different angles of attack. The warps can “deflect” under launch and resume their adjustment once the velocity slows to normal glide speed...kind of a primitive auto-surface.

Welcome to rocket-assisted Free Flight.
My bad, didn't word it clearly enough. My scratch built is a slide pod glider and not a slide wing. The motor pod's pylon functions as a slide box and there was enough unintentional looseness that it could rock from side to side longitudinally a degree or so.
Guess I shouldn't have mentioned the Cirrus Breeze because it's a slide wing, but it had the same kind of behavior (actually worse, as it would go into a deatg spiral at apogee) because its slidebox was too loose fitting. Tightened it and the problem went away. That clued me in that the culprit is probably the same with my scratch-built : my motor pod's slide box.
 

BABAR

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Can you post picture of your slide box glider, that’s not one I am familiar with (although it probably has plenty of company!)
Thanks
 

Rktman

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Can you post picture of your slide box glider, that’s not one I am familiar with (although it probably has plenty of company!)
Thanks
1st pic is glider overall, 2nd pic is motor pod launch position, 3rd pic is pod glide position.
Slipstream A1 RG.JPG
Slipstream A1 pod launch position.JPG
Slipstream A1 pod glide position.JPG
 

Ez2cDave

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Eric,

You are talking about spiraling during Boost, right ?

A few years ago, I had a D R/G do the same thing. It was due to the fact that I had built in some Rudder deflection. Once I re-aligned the Rudder and used Stab Tilt, instead, to induce a turn, the problem went away.

Dave F.
 

Rktman

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Eric,

You are talking about spiraling during Boost, right ?

A few years ago, I had a D R/G do the same thing. It was due to the fact that I had built in some Rudder deflection. Once I re-aligned the Rudder and used Stab Tilt, instead, to induce a turn, the problem went away.

Dave F.
I suspected something like that at first so I re-examined all the flight surfaces to confirm they we're all aligned correctly. Everything straight and true and no warping, which left me stumped until I noticed that my slide wing glider was exhibiting the same wonky kind of behavior. The only thing "off" with that one was that the wing's slide box fit was sloppy enough to allow the wings to wobble a degree or two in the roll axis. I used thick CA to "fatten up" the fuse till it fit snugly and the problem went away. That's what got me to thinking that there's too much play in the fit of my slide pod, and that's the reason for the launch spiral. Snugged it up, but I guess I won't know for sure till I can fly it again.
 
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Ez2cDave

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Another possibility might be that the Tail Boom is flexing during Boost.

Hopefully, tightening up the Pod cures the problem.

Dave F.
 
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