Boundary Layer Aerodynamics

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Hospital_Rocket

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Has there been any papers written by hobbyists on controlling boundary layer
airflow?

I was painting a rocket with Kilz and was wondering if it would make sense,
instead of sanding it smooth, to leave the rough finish to break up the
airflow.

Sort of like a golfball.
 

Stymye

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Micromister did such a study.. he found a rough surface decreased altitude ,, he has a thread somewhere
 

Elapid

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use such a system to reduce drag...
i can't imagine that rockets flying through the air is much different...


of course, they don't use random roughness...
 

rstaff3

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The answer may be reliant on the medium involved (air vs. water) and the velocities involved. Maybe model rockets don't go fast enough to take advantage of this. ???
 

Elapid

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but i wish i had an extra 200 bux to buy one of those suits so i could cut it up and make a tube from it...
;)

and how about a teflon nose cone?
might it help?
 

Stymye

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I'm guessing the dimples of a golf ball are more to reduce spin by breaking up the boundry layer.. hence a straighter flight..
.....except in my case
 

Stymye

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I found 2 tubes at a flea market reciently, they are Kraft tubes coated with 80 grit
I need to make a cone for them than I can compare it with a slick finished version
 

Hospital_Rocket

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I'm hoping Illini kicks in because, I think, fluid dynamics is one of his areas of expertise...
 

Chuck Rudy

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Originally posted by stymye
I'm guessing the dimples of a golf ball are more to reduce spin by breaking up the boundry layer.. hence a straighter flight..
.....except in my case
Since all golf balls backspin the dimples create lift on the layer of air, much like the threads on a base ball help it curve. To create a golf ball which flies straight simply fill in three rows of dimples completely around one circumference. This allows the backspin to force the ball into a straight trajectory regardless of how it's hit. Much like the idea of how a spool manages the air to make a straight flight.

Back to the original question. I'm guessing the biggest help to rocketry would be if vortex generators were utilized with the chord line of a fin, then smaller fins would be necessary to fly, or it could help eliminate coning at slower speeds.
 

DynaSoar

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Originally posted by Hospital_Rocket
Has there been any papers written by hobbyists on controlling boundary layer
airflow?

I was painting a rocket with Kilz and was wondering if it would make sense,
instead of sanding it smooth, to leave the rough finish to break up the
airflow.

Sort of like a golfball.
Anything that causes the laminar surface flow to break up into chaotic turbulence increases drag. We did lots and lots of tests on turbulence at Santa Fe Institute since it's a manifestation of chaos. Anything that preserves the laminar flow is good.

The dimples on a golf ball don't reduce drag, they increase it, but selectively according to the spin, to cause the ball to rise and/or curve. Not surpising that they increase drag, after all, wings on an airplane increase drag. But they produce enough lift to overcome the drag they create.

Here's a thought: a dolphin's shape can't account for its speed and efficiency. Fact is, they exude little gel-like hairs from their skin that preserve the laminar flow, and they ablate, that is, after they get so long and start to get curly or bent (that would increase turbulence) they break/wash off and float away taking the turbulence with them.

Two words: fur rocket.

Or maybe feathers. I have a packet of feathers from a turkey around somewhere if you want to try it.
 

Hospital_Rocket

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Dynasoar, you are the one who makes flying furniture....

I expect a faux fur rocket at the next launch. ;)


Actually, I am now thinking about buying one of those 12 packs of rockets just for a little pseudoscientific fun.

A
 

powderburner

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If you build your rocket with smooth surfaces and finish with a little wax, you can easily get laminar flow over the full length of many models.

The biggest problem most rockets have is a sloppy joint at the base of the NC. By sloppy I mean: if you can feel it with your fingernail, it's too big. You need to fit the NC well to the front of the BT. You need to use sealer/filler to eliminate any surface discontinuity. You need to make the joint just about invisible.

Thus the advantage of mid-ejection models in many competitions. It's a lot easier to get a well-finished joint at the NC/BT interface if this is a permanent assembly. A working joint at a location farther aft along the BT causes less drag penalty.
 

Hospital_Rocket

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I double posted this thread

It's also on RMR

Thre are 24 responses and not one flaming whiny post

I think that may be a record.

;)
 

DynaSoar

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Originally posted by Hospital_Rocket
Actually, I am now thinking about buying one of those 12 packs of rockets just for a little pseudoscientific fun.

A
HAIR!

Get the cuttings from a barbershop.
Chop them up small with scissors.
Spray the bird with spray adhesive.
Set it in front of a fan, nose towards the airflow.
Drop hair in front of bird.
Continue until fuzzy.

Sure, it sounds messy and might not work, but as Ford Prefect says "It's a wonderful way to relax."
 

Hospital_Rocket

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Originally posted by DynaSoar
Sure, it sounds messy and might not work, but as Ford Prefect says "It's a wonderful way to relax."
You definitely need a hobby
 

DynaSoar

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Originally posted by Hospital_Rocket
You definitely need a hobby
I've got one, using epoxy to pull dried CyA off my fingers.

Of course it doesn't work worth a darn. Wouldn't be much of a hobby if it were so easy.
 

Stymye

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If you build your rocket with smooth surfaces and finish with a little wax, you can easily get laminar flow over the full length of many models.
If you have a joint at the cone to body area..it will trip the flow no matter how smooth you make it... I suspect you would have to have a darn near completly solid surface with a perfect finish down to the micron..without a lug or fins, to have a completly laminar flow !

now Powder...I've just started learning more about it ,so I'm not 100% sure of this.
 
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