Coning

[MarkStull]

I was concerned about coning with moon burner motors for our project. I asked the Waco HotRocs about coning:

What is coning? Is that a type of corkscrewing? Some say off center mass is no problem, as long as the rocket is spinning a few RPS.

"That's pretty much what it is. Imagine taping a quarter to the edge of a frisbee. The rocket is rolling and yawing/pitching at the same time. The rocket is essentially moving laterally as well as vertically. Since coning is the rocket spinning around an off-center axis, I don't know if increasing the spin rate would help."

A coning rocket sounds pretty inefficient. And picturing the quarter taped to the frisbee, spinning faster shouldn't help. It also follows that an off center mass, near either end of a rocket, would make it yaw. But an off center mass, near the CG of the rocket wouldn't. The rocket would stay vertical, and just vibrate... circularly. So... my sloping core idea shouldn't cause much yawing, since the off center part of the motor is near the top.

I'm attaching a drawing of my sloping core idea. It would yeild a strong boost, followed by a moderate sustain that gradually tails off... which sounds perfect for getting high altitudes in bad weather.

Mark E. Stull

 

[Rocketjunkie]

Originally posted by MarkStull
I was concerned about coning with moon burner motors for our project. I asked the Waco HotRocs about coning:

What is coning? Is that a type of corkscrewing? Some say off center mass is no problem, as long as the rocket is spinning a few RPS.

Coning is a result of roll coupled instability. When the roll rate matches the natural frequency of the fin's corrective force, the rocket will corkscrew. Usually, the corkscrewing gets worse until either the motor burns out or the rocket shreds. The grain configuration of the motor has no effect on this instability. I've flown large moon burners in small rockets with good straight flights. If the roll rate is well away (faster or slower) than the natural frequency of correction, the rocket will fly straight.

 

[teflonrocketry1]

Also, if there is no corrective force along the axis of the roll, you will get a rocket that corkscrews but flies stable. My one finned design exploits this feature! Imagine a ring-finned rocket where the ring is directly connected to the airframe, i.e. an asymmetric design with no support struts or fins.

Bruce S. Levison, NAR #69055

 

[MarkABrown]

Originally posted by teflonrocketry1
Also, if there is no corrective force along the axis of the roll, you will get a rocket that corkscrews but flies stable. My one finned design exploits this feature! Imagine a ring-finned rocket where the ring is directly connected to the airframe, i.e. an asymmetric design with no support struts or fins.

Bruce S. Levison, NAR #69055

Wow Bruce. That sounds really interesting. Have you got any photos of this rocket or launch/flight pics?

 

[teflonrocketry1]

Attached is picture of my one finned rocket called CorkScrew2. Its has been flown many times on B6-4's C6-3's and C6-5's, that's why it has so many battle scars.

Bruce S. Levison, NAR #69055

 

[wyldbill]

heh heh heh ... I GOTTA try that.....

 

[RoyAtl]

I'm resurrecting this thread almost sixteen years later to describe an intentionally coning version of the Big Bertha. This rocket was flown at some of our launches in the mid 2000's by someone named Ashley Robinson. He took one fin of a Big Bertha, glued it on about, oh, 8" forward, while the other three were in their normal places. He called it "Bad Bertha". The flights made by this rocket were ever widening circles, but they were "stable".