How to reduce: roll during boost

"shockwaveriderz" wrote: I'm looking for suggestions, ideas, recommendations on how to design anti-roll/spin into a typical model rocket. Is it possible to design a rocket such that it will not roll on boost and coast?

Do a Google search on "rollerons".

Relatively large diameter Relatively high surface fins Very even airfoiling and fin placement. That's about it. maybe piston launch it too to increase initial speed.

Jerry

anti-roll/spin into a typical model rocket.

An Idea I had in Evansville just came to mind Shockie.

Use old R/C helicopter mechanical gyro's. their cheap in the flee markets and Ebay. I got two and you can't turn them when they are on.

the new Peizo gyro's have made the mechanical spinning gyroscopes obsolete.

put two at cross angles to keep the rocket straight or one to keep it from rolling., or all three. run's on 4.8 volts at BTW.

would make a real great NAR R&D project my Wave Rider Friend.

ArtU

anti-roll/spin into a typical model rocket.

You can build in roll damping, but any true anti-roll/spin design would not be "a typical model rocket".

Alan

alan: what design features would built-in roll damping involve? shockie B)

anti-roll/spin into a typical model rocket.=20

"shockwaveriderz" wrote: alan: what design features would built-in roll damping involve? shockie B)

Rollerons?

You might be on to something. I have a video of mid powered rocket in the UK that flew with out fins. Even when the motor cut out the rock was still pointing up. Weird and erie at the same time.

Ted Novak TRA#5512

bb: I looked up rollerons as they are used on the fin tips of the sidewinder = missile..... for the model rocket I have in mind they would only be 1/4" to 1/2" = square, and it appears to me that the rotating wheel is enclosed in a = box that can swivel freely......?

and how does this rolleron increase roll stability?

shockie B)

anti-roll/spin into a typical model rocket.

What kind of mission are you trying to perform? What are the size/weight constraints you are working with?? Rollerons would be too heavy for a 'typical' model rocket, whatever that is anymore.

Regards,

Bob Bernatchez

NAR 29996

I'm trying to design a camera/video rocket that will not roll on boost = and coast ... DEFG powered=20 shockie B)

anti-roll/spin into a typical model rocket.=20

The little spinning wheel acts like a gyroscope... if the rocket is rolling, the gyroscopic action wants to twist the movable part of the fin so it acts like an aileron trying to roll the rocket the other way.

-dave w

"shockwaveriderz" wrote in news: snipped-for-privacy@comcast.com:

Yeah, align the fins properly. Very few of my models exhibit any significant roll during bosst or coast.

len.

and it appears to me that the rotating wheel is enclosed in a > box that can swivel freely......?

If you're only talking about a small rocket, then go with a 4-fin design. Fins should be small, symmetrically airfoiled (i.e. flat, with rounded leading and trailing edges), long root chord, and short span. Align carefully with the long axis of the rocket. Place the launch lug between 2 fins, not in a fin-BT joint.

I indicate my fin slots within .001" using an indexing head on a Bridgeport mill . My rockets don't exhibit any spin, either. Fin alignment is probably the most important thing in preventing spin. Dave ~~~~~~~~~~~~~~~~~~~~~ Dave Griffith NAR 14156 The R.A.T.T.-works Monterey Machine Products

1504-A Industrial Park Street Covina, CA 91722 U.S.A.

coast ... DEFG powered

That is what I suspected. Fins, particularly those with large spans, have natural roll damping. If you remember the old Estes Camroc Carrier(?), it had canted fins on the booster stage to help ensure straight flights, and large uncanted upper stage fins that quickly damp out the spin imparted by the booster fins.

Rollerons also provide roll damping. However, they are not practical for your application and are best used for R&D.

At the FG level you could certainly go active and use a HH gyro system to hold a fixed roll angle over your short flight duration.

I also built a high performance Cineroc carrier for the cross Mississippi project. The fins were 3 1x2x1/16" plywood elliptical fins. I would strongly recommend much larger fins for high pitch yaw damping on video rockets. I built adjustable spin tabs into the fins, so that any roll could be trimmed out over a series of flights. Of course we never got a series that exceded 1 flight on each rocket. The fins were cut from the trailing edge root to about the tip. Build up a couple layers of Titebond on the edges and then glue together with Tightbond. Finish and build as usual. The roll trim tabs can be adjusted by heating and bending.

Alan

I don't agree. Hemisphere airfoils encourage vortex drag at the tips which is a contributing factor to low spin rates.

I would have said the opposite about rooot and span since a higher aspect ratio fin (sticking out more) has more damping action as to spin. Assuming it is straight to begin with.

I refer the reader to my prior post on the matter.

I invite BB to go away. While this was a tech post and probably wrong, many of his posts are simple trolls or outright personal attacks.

Jerry

anti-roll/spin into a typical model rocket.

4 relatively long span fins, carefully aligned and shaped, and a symmetric airframe; undamped, unbalanced forces are your enemy.

Symmetry and detail will minimize the tendency to roll making the job of any active anti-roll devices either easier, or unnecessary.

Perfect fin alignment is probably the most important factor, period. It goes without saying that a properly built fin alignment jig will go a long way in preventing roll.

I wonder if offsetting the launch lug drag by having a second, oppositely placed launch lug would delay pitchover substantially? Thereby prolonging the time the camera would point downwards? Then again, shots of the horizon as the rocket arcs over near apogee might be desireable.

]> I wonder if offsetting the launch lug drag by having a second, oppositely

Very.

Jerry