Why a Video Rocket might spin, or might not.

I have had rockets spin with video on them, and rockets that stay very
straight, like on rails.
Besides the LOC Bruiser I flew straight as an arrow, in my last video post,
I have a LOC I-Roc that stays straight in flight as well.
click on the link below and click on the video for:
JMRC MIS Speedway GearCam
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By the way, the video preloader on this one starts out with a ground based
liftoff shot of the rocket while the video buffers load.
It will not spin in this video either. This was done with the low power
Mini-GearCam
in a Hitch Hiker on the side of the rocket. See:
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So, we have a I-Roc with launch lugs, and rail buttons both.
It has a Hitch Hiker on it, and all that stuff sticking out in the wind.
yet flies very well with no spin, but did move just a twitch or two in the
wind.
I also have a LOC Mini Magg that I saw video taken from the ground and it
flew straight as well.
It has colors on each fin and you could see a color change if it did spin.
I open the discussion up on why these three rockets might not spin.
Or what is the same about them.
Art Upton
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Reply to
ArtU
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Fin Alignment... nothing more. You want to win an altitude contest... make your fins straight. Want no spin in "down looking video"... make your fins straight.
Doug
Reply to
Rocketweb
Hi Doug:
Of course fin alignment is the most obvious and most important factor in achieving spin-free boosts.
But apparently, it is not the only factor. I'm sure you've seen the down-looking videos that spin first in one direction, then the other. I don't think this phenomenon can be explained by fin alignment alone. I believe wind shear effects play a complex secondary role.
Reply to
Andy Schecter
I have also noticed that in many videos, the spinning stops at propellant burnout. I have been wondering if there is some spinning of the gasses inside the combustion chamber, not coming out exactly in an axial fashion, but more like water going down a drain. This would cause the airframe to want to rotate in the opposite direction.
Just a hypothesis...
Bill the Geek
Reply to
Bill VanRemmen
uneven nozzle erosion perhaps? shockie B)
Reply to
shockwaveriderz
The mirror shroud also needs to be as straight as possible.
Reply to
RayDunakin
In the case of the I-roc, the rocket has this hitch hiker on the side.
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no mirror or shroud.
In the Brusier, the camera is just out their in the wind, bolted on the side of the payload bay, looking down at a slight angle. the shroud was left off, as the rocket would not be going super sonic. On a K660, the cam did not even move on it's axis mount.
I had it angled slightly out from stright down., to avoid seeing the payload coupler after apogee, like in pervious Videos I had done.
I posted a small picture of it on a.b.m.r.
so those two things are different between both the rockets.
Reply to
ArtU
Acceleration decreases very rapidly after MECO.
I have been wondering if there is some spinning of the gasses
Reply to
ArtU
Cool. I just made up a "hitchhiker" like that to put a PerfectFlight mini-alt onto my smallest camera rockets. I can easily swap it from one rocket to another as needed. I made it out of an aluminum cigar case and an old balsa nosecone.
Reply to
RayDunakin
3099. the A8-3 Flight test
Next comes an L800 for the B6-4 milk run.
Probably wont be till aug till a field around here opens up for that.
Around October, I hope to put the new CTI M560 long burn in it for the C6-7 it's gone flight.
Reply to
ArtU
Grain geometry has a lot to do with spin. I suspect you'll see quite a bit of spin with a bit of corkscrew with the M560 since it is either a c-slot or moonburner....can't remember which.
Mike Fisher
Reply to
Mfreptiles
Good point. Yes.
I have a great photo shot of a Big Brute on a F20 c-clot that really shows the flame offset.
It will be an interesting test.
The rocket is only 24lbs sans motor.
Reply to
ArtU
Well, there's dumb luck, fin alignment and ** how many fins you are using **.
In a 3-fin rocket, there is coupling between angular momentum about the long axis and that purpendicular to it. Thus, as the fins correct the rocket's path, they turn the rocket about its axis.
In a 4-fin rocket, there is no such coupling - at least not through fin corrections. That doesn't mean the rocket won't spin, but it should not turn because of stability corrections.
Regards, -Larry Curcio
Reply to
Larry Curcio
Interesting. so far, the rockets I've used are 3FNC.
I do understand the ideal of the four fin units since you mention it, and will have to look further into setting up a 4FNC unit to test.
Reply to
ArtU

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