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other than fin stabilization?

I'm glad to see someone in this discussion finally mention Krushnik. (Man, wasn't The Point cool? Everybody should download the plans and build one!)

But as for no fin, cylindrical rockets, a number of years ago at LDRS in Argonia, there were several no fin, high power rockets flown. Motors weren't in the front but there was enough nose weight added to create the correct CG/CP relationship. First of all, this created a very heavy rocket. So in spite of flying on a high power motor, these moderately sized rockets attained very little altitude. Secondly, I was hard pressed to consider it a stable flight. Yes, overall they did fly upwards and successfully prove that the CP/CG relationship makes a rocket fly. But a large AOA was required before they would start swinging the nose back upwards. They flew with a heavy oscillation about the vertical for a terribly ungraceful flight. This also helped rob altitude from the vehicle. Watching an HPR motor wallow up to a couple of hundred feet to be able to fly something without fins seemed like a waste to me.

Lastly, "pulling instead of pushing" has been tried numerous times. Yes Goddard's first rockets were designed based on this theory. Goddard's first rockets also were unstable and crashed. It's a fine theory until you realize that the aerodynamic effects of CP/CG are the dominant forces acting on rocket stability.

Dave

Reply to
David Bacque
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Those "side bars" were the LOX and gasoline feeds to the combustion chamber at the top of the rocket.

As others have pointed out, Goddard's 1926 rockets were not stable, as the LOX and gasoline plus tanks at the bottom were a lot heavier than the combustion chamber at the top.

However, the shape of Goddard's rocket is not necessarily unstable. Make the LOX and gasoline "tanks" very light and the thing flies straight and true:

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The escape towers on the Mercury and Apollo (Gemini had no escape tower) did indeed "tractor pull" the capsule, but the system was stable because of the shape of the capsule. The stack would have flown if the escape rocket had been in the heat shield.

CG ahead of CP = stable, CG behind CP = unstable, regardless of where the motor is.

Reply to
Steve Humphrey

Speaking of Goddard's first liquid-fuel rocket, that makes me think...maybe a scale-like scratch build...with standard composite engine power, of course. Might be a neat project.

Reply to
bob352

Forgive my ignorance but what is the Krushnik effect?

thanks for the info, KT

Reply to
kimballt

The Russians put the escape engines fwd of the capsule without a tower. They canted 4 engines outward at 20 degrees. to keep them close to the capsule thus saving them from having to make a tower. Nasa is thinking about doing the same in future manned flight (same as Russians). The shuttle will be replaced with a capsuled vehicle with such a device. I am currently designing a test stand for a prototype of this at the place I work.

KT

Reply to
kimballt

A (partial) vacuum created at or inside the base of a rocket. Particularly pronounced on rockets whose motors are positioned inside the base plane of the model.

Such placement creates a drag suction which saps thrust from the motor.

Jerry

Reply to
Jerry Irvine

Extreme turbulence in the exhaust that results in an almost total loss of thrust. Named for the guy who discovered it in the early days of the hobby. The rule of thumb is do not recess a motor more than one body diameter from the base of the rocket. The old Estes Phoenix was just under that limit. Move the motor mount farther forward, and it wouldn't work.

Something similar to cavitation in a propeller.

I'm sure it's explained better in Stine's "Handbook"

Reply to
Bob Kaplow

Unless you specifically want it to be cool, and loud.

Reply to
Jerry Irvine

Thanks for the explanation.

KT

Reply to
kimballt

Thanks for explaining,

KT

Reply to
kimballt

How about a finless rocket with flat sides? Maybe a tri/rectangular body or body section aft?

The coning of a finless payloader makes sense due to the low lift of a tube and the relatively large moment of a payload.

Would some flat airftame surfaces back aft generate more restoring lift?

Reply to
Gary

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