Spool Rocket Stability

[Zeroignite]

Hiya,

I'm new to the non-kit scene, and am just wondering... how in the hells are spool rockets stable?

Seems to me that CP would be right on top of CG unless you stuck a lump of lead on top, and that drag stabilization wouldn't help you either since the top and bottom disks are the same diameter.

 

[H_Rocket]

Part of it (as explained to me) is the fact that as the spool tips to one side air spills over the edge causing it to self correct by the other side pushing down. Essentially it oscillates on the way up.

 

[rstaff3]

I always thought it was largely the same mechanism that makes a saucer work...base drag. I've flown a spool with only a top plate and I think I've seen them with only a bottom.

 

[Mightyrocketman]

The stagnation pressure of the flat disk causes enough drag to move the dynamic center of pressure below the center of gravity and the thrust of the motor to move the center of gravity forward thus making it stable. The turbulent boundary layer of the top disk causes the smaller exposed surface area of the bottom disk to be somewhat ineffective.

 

[Winston]

www.apogeerockets.com/downloads/Newsletter154.pdf

"Various aerodynamic texts confirm the fact that the dynamic Center-of-Pressure (CP) of flat plate lying perpendicular to a flow, lies behind the plate along its central axis, due to a base vortex that forms when the air begins flowing over its surface. Published data shows the CP for a flat plate in a perpendicular flow is about 2.2 diameters behind the plate along the axis perpendicular to the face of the plate through its center."

Also very useful info when designing fat and short rockets which is primarily what that Apogee newsletter article is about. I've read of people putting a lot of weight in the nose of a Big Daddy when used with higher power motors because of CP/CG issues indicated by Rocksim. I had the same simulation result until I applied the simple base drag compensation mentioned in that newsletter. When applied, the method indicated that a Big Daddy previously indicated as marginally stable was very stable when base drag was taken into consideration. The actual rocket flew great without any nose weight.

 

[Rich Holmes]

I'm building one of these; reports are that (with some nose weight added) it's quite stable:

View attachment 152650
Same principle?

 

[Zeroignite]

Excellent, thanks folks

 

[chris m]

I'm building one of these; reports are that (with some nose weight added) it's quite stable:

View attachment 152650
Same principle?

Very cool . What bt are you using ? What is the diameters of the fins

 

[Rich Holmes]

BT50 and 5055, 5060, 5070, 5080. Build thread here: https://www.rocketryforum.com/showthread.php?59954-Building-a-Bohica-s-Dead-Ringer

 

[chris m]

Very cool with the CR's

 

[rdbones]

I'm building one of these; reports are that (with some nose weight added) it's quite stable:

View attachment 152650
Same principle?

The screams Up Scale !!!

 

[rdbones]

The Arizona Rocketry Team flew this



At Spring Fest in Jean, NV last weekend

I will tell you that it needed nose weight.

The rocket was about 125 on the pad and about half of that was the nose.

 

[Zeroignite]

Is that a AT Redline or CTI Red Lightning?

 

[les]

I'm building one of these; reports are that (with some nose weight added) it's quite stable:

View attachment 152650

I saw your build thread and loved it so I'm building two (one will be donated). I used 5060, 5070, 5080, and 50100

 

[rdbones]

Is that a AT Redline or CTI Red Lightning?

AT M2000R :grin:

 

[kramer714]

drag is a great help for stability. I have done many saucer and spool rockets on motors from A to K. The center of pressure under power is actually behind the rocket making it pretty easy to get the center of gravity in front of the center of pressure.

Spools are stable as long as they are under power once they start to coast they slow down and become unstable, a rocket with a base plate can stay stable during coast and will remain stable during the arc, the Bottle Rocket and ketchup/Mustard stay stable.

Spools and the Shroom fly straight until the motor burns out and then starts to tumble. The Pizza rocket (the spool had a 14 inch pizza on the top, table cloth from Italian restaurant on the bottom plate) was on a K skyripper. wobbled a bit but stayed stable until the motor burned out, the Skyripper burns for a long time so it was a great motor to use for it.

One other way to create base drag is with the Mop Rocket, the mop adds drag to the aft portion of the rocket, there is a bit of nose weight in that one since the motor is mounted up top.

base