How much spin must a spin bird spin

[DynaSoar]

so as not to somersault around the field and scare the neighbors?

I want to build a particular design of spin stabilized bird, but have no clue how much spin it would need to stabilize it. Spin vanes would be just that, not fins. It'll have an outer shell hanging below the internal engine tube, but probably not enough to add any stability.

Luckily I do have a tower, so I can get it spun up before it goes free flight, but I can't figure out how spun it needs to be.

 

[edwardw]

I have only seen canted fin rockets for spin inducement. And then they only cant them 1-3 degrees depending on how fast they are flying.

Back on your topic though, you are using motor exhause to spin some vanes to stabilize, if I read correctly, and I'd like to think that I am...

I would say a good 5x a second or 300 rpm. That's going pretty fast. And if they should create a moment that doesn't get cancelled then you could quickly have a mishap on your hands....

Edward

 

[Silverleaf]

Luckily I do have a tower, so I can get it spun up before it goes free flight, but I can't figure out how spun it needs to be.

Um, I may be missing this key point, but if shes attached to the pad, or even to a rail system, how will you be able to get her to spin before she leaves the safety of the rail?

Doesn't a rail system use a triangulation, or even 4 rails to support the rocket on all sides ?

If I'm missing the point, please forgive me..*blush*

 

[Stymye]

by spin vanes do you mean a screw -like shape,rather than fins
so the rocket would basically screw out of the tower?

seems like the rocket could sustain a higher rate of spin than a typical model,,interesting

the trick would be keeping the rocket from wedging inside the tower or wasting it's thrust as it makes it's way thru the tower

neat idea,but sounds very tricky

 

[DynaSoar]

Originally posted by stymye
by spin vanes do you mean a screw -like shape,rather than fins
so the rocket would basically screw out of the tower?

seems like the rocket could sustain a higher rate of spin than a typical model,,interesting

the trick would be keeping the rocket from wedging inside the tower or wasting it's thrust as it makes it's way thru the tower

neat idea,but sounds very tricky

Some explanation is in order, since pictures aren't ready.

It looks like a jet turbine engine. The outer body is only that -- a smooth 1.6" tube about a foot long. Inside is a minimum diamater 18mm bird. Instead of fins, it has turbine vanes holding it in the middle of the outer tube. It contains recovery gear of course. The outer tube covers everything except the very tip of the nose poking out. Up it goes and the whole thing spins.

I've given it six vanes near the top and six near the bottom. With nothing outside but round tube, it'll be free to rotate while still in the tower. The rails are 4 foot tall. 3 foot is usually enough for a fee fall bird to get going, so I'm betting within 4 this thing should be getting its fair share of aerodynamic action. Could probably even be tube launched.

The vanes are canted at about 10 degrees. Also, they're beveled on opposite edges to increase the cant a bit. Just guessing, I'd say it's going to get a lot more than 300 RPM. The aft of the engine is recessed an inch inside the outer tube, to bring the CG forward a little. Between that and the spin this should sound pretty impressive. If it works out I'll try an MPR bird, canting the aft vanes more than the front, to increase the air flow, and try an intake and nozzle arrangement on the outer tube. If I can get it to pull air and use that to add some altitude, it'd help overcome the atrocious drag of the thing. I might could add some weight around the outer tube to give it some momentum.

But not until after I'm confident this thing won't just drill core.

 

[shrox]

I have done similar and it worked. Let's say your's will too.

shrox

 

[solrules]

Originally posted by stymye
by spin vanes do you mean a screw -like shape,rather than fins
so the rocket would basically screw out of the tower?

seems like the rocket could sustain a higher rate of spin than a typical model,,interesting

the trick would be keeping the rocket from wedging inside the tower or wasting it's thrust as it makes it's way thru the tower

neat idea,but sounds very tricky

Sounds exactly like the Super Loki Dart. It uses 1.5 twists in about 7-10 feet. This provides some stability, but the booster as well as the dart still have uncanted fins.

 

[DynaSoar]

Originally posted by shrox
I have done similar and it worked. Let's say your's will too.

shrox

Thanks. Nothing to do but test it then. At 34 grams pre-engine I don't suppose a failure could do much damage.