Kushnerik Effect

Kushnerik Effect

Post by Kevin Crawfor » Thu, 23 May 2002 12:26:02



Can anyone point me to a good site that might help enlighten me on this
phenomenon?

Thanx
Kevin C
CAR S569 L2

 
 
 

Kushnerik Effect

Post by paul_poc » Thu, 23 May 2002 12:39:21


Kev,

What is it?

Paul


Quote:
> Can anyone point me to a good site that might help enlighten me on this
> phenomenon?

> Thanx
> Kevin C
> CAR S569 L2


 
 
 

Kushnerik Effect

Post by Fred Shecte » Thu, 23 May 2002 12:41:08


Spell it correct and use search to find:

http://www.home.mpinet.net/sruud/Glossary.htm#K

-Fred Shecter NAR 20117


Quote:
> Can anyone point me to a good site that might help enlighten me on this
> phenomenon?

> Thanx
> Kevin C
> CAR S569 L2

 
 
 

Kushnerik Effect

Post by nojun » Thu, 23 May 2002 12:46:22


Quote:

> Can anyone point me to a good site that might help enlighten me on this
> phenomenon?

It's the Krushnik Effect.  Using that spelling in web searches may find
you a little more <g>.

www.esteseducator.com/Pdf_files/1948mrst.pdf
www.esteseducator.com/Pdf_files/Projects.pdf

Basically has one sentence...essentially, it's the loss of thrust that
you get when the motor is recessed more than one BT diameter into the
body tube.

I remember seeing another document floating around that had more of the
actual science involved, but can't for the life of me find it now.

--
Mike    KD7PVT
NAR #70953 - Sr/HPR Level-1 ~ SeaNAR - The Seattle NAR Section #568
NO Junk Email, please! Real email to: amphoto [at] blarg [dot] net.
<Vegetables aren't food; vegetables are what the food eats!>

 
 
 

Kushnerik Effect

Post by BJames » Thu, 23 May 2002 14:07:19


Krushnik Effect:

when the engine nozzle is recessed into the airframe it results in a loss of
thrust.

Over 30 years ago I did a science fair project on this.  I built a test stand
that would generate motor thrust:time curves.  It had a rotating drum wrapped
in paper, and a shaft that the engine carriage could slide on operating against
springs.  It would generate curves much like what you see in catalogs.  The
data that I gathered showed the loss of thrust at various positions of the
engine in the body tube.

I never found a scientific explanation for the effect.  It seems to me that the
exhaust gas velocity must be reduced by some kind of flow effect within the
tube.  That's my guess anyway.

 
 
 

Kushnerik Effect

Post by James Padfiel » Thu, 23 May 2002 19:43:30


From Dave Hall's website
(http://www.ridgenet.net/~thehalls/Rockets/Gunlaunch/gunpro.html):

The Kushnik Effect is nothing more than the formation of a vacuum via
venturi effects inside a body tube with a recessed motor. The result is a
large pressure imbalance on the rocket body that, technically speaking,
causes a huge (speaking from experience there!) drag increase that is more
commonly viewed as a thrust decrease.

In order to beat Mr. Kushnik, you must break the vacuum. I reasoned that
some holes drilled into the body tube just behind the nozzle exit plane
should allow external air into the body tube to replace air "sucked out" by
the exhaust plume's venturi effects (see sketch).

The holes worked! I launched two rockets of this design. Both flew like a
bat out of hell, never to be seen again.

 
 
 

Kushnerik Effect

Post by Leonard Fehsken » Thu, 23 May 2002 23:42:07




Quote:
> The Kushnik Effect is nothing more than the formation of a vacuum via
> venturi effects inside a body tube with a recessed motor. The result is
> a large pressure imbalance on the rocket body that, technically
> speaking, causes a huge (speaking from experience there!) drag increase
> that is more commonly viewed as a thrust decrease.

Then why is the Krushnik effect observed in static tests when there's no
movement and no drag?

len.

 
 
 

Kushnerik Effect

Post by Jerry Irvin » Fri, 24 May 2002 00:29:27




Quote:


> > The Kushnik Effect is nothing more than the formation of a vacuum via
> > venturi effects inside a body tube with a recessed motor. The result is
> > a large pressure imbalance on the rocket body that, technically
> > speaking, causes a huge (speaking from experience there!) drag increase
> > that is more commonly viewed as a thrust decrease.

> Then why is the Krushnik effect observed in static tests when there's no
> movement and no drag?

The momentum of the ejecta forms a boundry layer and it is formed by the
Bernoilli effect among others.

Quote:

> len.

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA

Please bring common sense back to rocketry administration.
Produce then publish.
 
 
 

Kushnerik Effect

Post by Jonathan Sivie » Fri, 24 May 2002 01:01:16


Quote:

>Krushnik Effect:
>I never found a scientific explanation for the effect.  It seems to me that the
>exhaust gas velocity must be reduced by some kind of flow effect within the
>tube.  That's my guess anyway.

   My quasi-educated guess would be that the bodytube below the motor would
behave as an extension to the nozzle.  The effect would be the same if you
made a extra large nozzle for the motor.  The exhaust gasses become over
expanded and thus their velocity drops, reducing thrust.

Jonathan

"Remember to always keep the pointy end up."
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Kushnerik Effect

Post by Roger Smit » Fri, 24 May 2002 00:58:58


Quote:
> when the engine nozzle is recessed into the airframe it results in a loss
of
> thrust.

> Over 30 years ago I did a science fair project on this.  I built a test
stand
> that would generate motor thrust:time curves.  It had a rotating drum
wrapped
> in paper, and a shaft that the engine carriage could slide on operating
against
> springs.  It would generate curves much like what you see in catalogs.
The
> data that I gathered showed the loss of thrust at various positions of the
> engine in the body tube.

> I never found a scientific explanation for the effect.  It seems to me
that the
> exhaust gas velocity must be reduced by some kind of flow effect within
the
> tube.  That's my guess anyway.

I used it as the basis for a science fair project, too.  I hypothesized that
the effect was due to the body tube acting as an extension of the nozzle.  I
calculated the thrust for an engine with its regular nozzle and the thrust
for it if it had a larger nozzle based on recessing the engine various
depths into the body tube.  Then I did static tests with engine not recessed
and recessed the same amounts I had used in the calculations.  The results
matched pretty well.

-- Roger
http://www.payloadbay.com/

 
 
 

Kushnerik Effect

Post by David Erbas-Whit » Fri, 24 May 2002 01:24:34


This raises an interesting question for me.  With the Estes Saturn V,
the engine is recessed quite a bit up into the base.  As is, the rocket
BARELY flies with a D12-3.  Has anyone done any experimentation to see
if drilling holes would work better with the Saturn V?  I understand
that due to CG/CP problems one wouldn't want to move the engine back any
farther, but I'm wondering if there are any programs (a la Rocksim) that
would calculate the 'Kushnik effect' on a model rocket, or that would
determine the optimum placement/size/number of holes for alleviating
this problem? I have to admit (sheepishly) this is the first time I've
heard of this effect.

David Erbas-White

Quote:

> From Dave Hall's website
> (http://www.ridgenet.net/~thehalls/Rockets/Gunlaunch/gunpro.html):

> The Kushnik Effect is nothing more than the formation of a vacuum via
> venturi effects inside a body tube with a recessed motor. The result is a
> large pressure imbalance on the rocket body that, technically speaking,
> causes a huge (speaking from experience there!) drag increase that is more
> commonly viewed as a thrust decrease.

> In order to beat Mr. Kushnik, you must break the vacuum. I reasoned that
> some holes drilled into the body tube just behind the nozzle exit plane
> should allow external air into the body tube to replace air "sucked out" by
> the exhaust plume's venturi effects (see sketch).

> The holes worked! I launched two rockets of this design. Both flew like a
> bat out of hell, never to be seen again.