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Why do spools fly?

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THier

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OK,,

What is the theory behind spools?

They will fly as spools,, if you remove the top plate they won't fly,,, if you remove the base plate they will fly. Can't be base drag,

Tom
 

rokitflite

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No matter how many times I see one fly, I still hide behind something when the countdown starts.
 

rstaff3

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I thought a spool without the top plate would fly. Why should this be much different that an Art Applewhite Delta saucer with really long motor installed (hanging out the front)?

Spools rocket be the safest rocket of this type I've seen. The only unstable ones I've witnesses spun end over end and still went it an upwards direction. By 'this type' I mean saucers, pyramids, cones, etc.
 

les

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Why do spools fly?

Because someone stuck an engine and igniter in them...:p
 

The EGE

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Circular plates, IIRC will put the CP 2.2 plate diameters behind the plate. So short spools *may* fly with only the front plate.

They'll almost definitely fly with only the aft plate; as Dick Stafford pointed out, it's just like a saucer with an extended forward tube.

It is base drag.

I still do a double-take when I see one fly. But they fly incredibly stable. Just watch out for wind gusts, they can push the flight over. They don't weathercock.
 

rstaff3

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I've seen the front plate only work but have never witnessed the bottom only. I thought Lance Alligood had successfully flown both. But the base drag business makes sense for either. A few years ago someone was selling a wind tunnel report on spools. I think the link is on by blog (the big stability post).
 

rstaff3

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Good point,,, smarty pants,,, (keeping it "G" rated)

Tom
That answer didn't even make sense. I've put motors in plenty of stuff that didn't fly. Well, at least as expected. :y:
 

THier

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That answer didn't even make sense. I've put motors in plenty of stuff that didn't fly. Well, at least as expected. :y:

Good point Dick,,, How true,, I remember someone burning up a good portion of the field,, and launch equipment,, and an engine is a mechanical thing,, we use motors,,, but that is being too picky.

Tom
 

Scotty Dog

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I saw a cow jump over the moon .A chicken cross the road. And a spool fly. My life is complete. :D Scotty Dog
 
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MarkII

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The spool on the hill sees the sun going down...

Mark K.
 

powderburner

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Why do spools fly?

Because someone stuck an engine and igniter in them...:p
(I am only angry because you beat me to this obvious answer)

From what I have seen of the spools I have launched, they are stable (sorta....they still wobble around a bit) when the motor is firing but immediately go unstable at burnout.

It is my theory that what we are seeing (under powered flight) is a strong jet-pumped ring vortex that attaches to the aft face of the lower plate. (Think of it as a donut-shaped swirl of air with the motor exhausting through the donut hole.) Airflow passing the edge/perimeter of the aft plate tries to turn the corner toward the center, and is also pulled inward as the motor exhaust tries to entrain ambient air. The resulting ring vortex is stuck to the bottom of the plate by local air pressure, and the outer "face" of that same vortex effectively forms a cylindrical surface that acts as an aft stabilizing fin. When the propellant burns out and the high-velocity exhaust is no longer there to pump and maintain the vortex, the vortex dissipates and the spool is no longer stable. (Someone else may have already thought of this reasoning.)
 

Micromeister

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They fly because they have burning BP or AP thrusting behind them LOL!!

and Yes they'll fly without a forward plate also. Like the thumb-tack. but note the distance the motor hangs from the rear. more like a forward plate to me...

MM 312p1e-sm_MM 3X ThumbTack Odd-roc 4pic pg 96dpi_08-14-05.jpg
 

H_Rocket

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Well, you can do HPR on a spool

Here is the Armageddojn Industries Spool o'Doom on a Loki I110 Moon Burner at Red Glare.
 

powderburner

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Apogee shares lots of useful info, but in this case Apogee/Levison may have missed the mark a bit.

Their description of the phenomenon ("...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") reflects a mistake that is easy to make. Think of it this way: if the stability was due to the described airflow, the spool would be stable all the way up....and all the way back down.

If you watch a spool configuration in flight you will see it begin to tumble when the thrust quits. This occurs whether you use a booster motor or a motor with a delay charge and ejection charge. This clearly indicates that spool stability is due to an aerodynamic effect caused by the thrust. I can't see any way around that.

Stability can only be imparted to a spool configuration (which has no "normal" or conventional fin area on the aft end) if there is something else attached to the spool body which acts the same as side-facing fin area. It is my guess that there is a ring vortex behind the aft spool plate, strengthened by the motor thrust which jets through the center of the vortex. I would expect (intuitively) that the vortex would extend 0.5 to 1.0 diameters behind the aft plate, not 2.2 diameters. The vortex remains "attached" to the plate due to a low-pressure zone on the aft face; the low pressure is created by the circulation of the vortex itself. I am not sure that the imparted stability has anything at all to do with airflow ahead of the aft plate, or moving around the outside edge of the aft plate (traditional subsonic aerodynamics would suggest that airflow attempting to turn the sharp corner of the outer edge of the plate would stall and separate)

When the motor quits, the vortex weakens and quickly dissipates, and the spool becomes unstable again.
 

MarkII

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The POF article doesn't actually deal with spools. In addition to their wide base, the types of rockets described in the article have other design features that keep them in stable trajectories after the motor stops thrusting. The process that makes spools stable is somewhat comparable to the base drag vortex phenomenon, but is more complex due to the spool's shape (an extreme hourglass).

I suspect that rockets using base vortex-induced stability need to have a velocity about some critical threshold for the vortex to form, but unlike spools, they don't need the additional contribution of the motor's exhaust jet to maintain the vacuum behind the base. They maintain stability as long as their forward velocity is above that critical limit. I see something that appears to be this process quite often when I launch my Art Applewhite saucers and cubes. During the thrust and the brief coast time they move fast enough to be stabilized by base drag. At apogee, when the their air speed suddenly drops to zero, they tumble or "flip over." (Unlike traditional rocket designs, these polygon shapes don't slow down in a gradual coast, but instead slam to a stop in mid-air as soon as the forward momentum drops below a critical speed.) As the larger, heavier polygons descend, they quickly regain the needed velocity for the base vortex to form again, and they "aerobrake" or drop in a stable manner with the air flowing over the top surface. Although fast enough to impart stability, the descent is still slow enough to constitute a safe recovery due to the high drag of the design. The smaller, lighter versions of his rockets often do not drop at a high enough speed to regain this stability; instead, they tumble as they descend, continuously flipping end over end in much the same manner as a tree leaf falling from a branch. In the process, they maintain a very low descent rate that is equal to or often even slower than that of rockets returning on parachutes.

MK
 

ScrapDaddy

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I just built a rocket out off an unused toilet paper roll 2 centering rings and a MMT, will it fly since it is basically a spool? :confused:
 

cjl

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I just built a rocket out off an unused toilet paper roll 2 centering rings and a MMT, will it fly since it is basically a spool? :confused:
With no endplates you mean? No, it won't. You need at least one of the endplates for a spool to work.
 

ScrapDaddy

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With no endplates you mean? No, it won't. You need at least one of the endplates for a spool to work.
[YOUTUBE]_lW8p8-y1K0[/YOUTUBE] I beg to differ, and i just entered it in the SNF competition :D
 

troj

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Someone actually wrote an article, with lots of math and other items guaranteed to give you a headache...

Going from memory, it has to do with the pressure differences on the face of the plate due to changed angle of attack. As the "rocket" (very loose use of the term, just like saucers) tilts, pressure increases on the upper side and decreases on the lower side, causing it to tilt back into alignment. This is what causes the wobble you often seen in spool and saucer flights.

I might remember who wrote it; I'll check with him, and if so, try to get it posted.

-Kevin
 

rocketman

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Someone actually wrote an article, with lots of math and other items guaranteed to give you a headache...
Remember we're on a rocketry forum here, and thus are rocket scientists, so maths shouldn't be a problem :p

Tom
 
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MarkII

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Remember we're on a rocketry forum here, and thus are rocket scientists, so maths shouldn't be a problem :p

Tom
Riiiiiiiiggggghhhhtttt. I keep forgetting that whenever I resort to pulling out my abacus.
 
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