I'm designing a rocket that will have an avionics bay just forward of
the fins. Due to some packaging considerations, the static port will
be in line with a fin, or just slightly offset from the fin. How far
forward of the fin's leading edge should the static port be placed so
as to avoid turbulence issues created by the fin?
Thanks,
Bob Chmara
In article <20030903180641.17992.00000344@mb-m25.aol.com>,
ggoldy@aol.comnichspam (GGoldy) wrote:
>>> >I would say 1/3 finchord.
>
>>
>> Jerry, could you explain why? Or point us toward why? Nothing too technical.
>> Laymans terms. I'm not real smart, but I hang around some pretty smart people.
>>
>>
>> da rmr plumber
>> Gary R Goldenbaum
>> NAR #73669 L1
>> Northwest Florida
>> remove 'nichspam' to reply
Pardon in advance the tech post.
You are taking a reading of an aerodynamic flow from the "leading edge"
of a flowfield (ala interference generator).
You want that reading to be in freeflow.
If I am wrong so far, ignore this post.
The points of turbulance aqround a fin or wing or fin/body joint or
wing/body joint varies with shape and velocity. I am assuming basic and
somewhat aerodynamic shapes.
I am further assuming you have a body/fin type arrangement generally.
The 1/3 of the chord figure comes from wing studies that show that field
turbulance (perturbances) happen well in front of the wing in the form
of wake or a shock wave. A shock wave is thinner but more powerful and
an aero-flow turbulance or wake is thicker and less energetic.
Therefore if you want to take readings from say zero velocity to M0.5
then you should assume turbulant thick flowfields and stick your sensor
pretty far out in the wind. If you note pitot tubes on research
aircraft, they are 4-8 FEET out in front.
One of the disadvantages to a 1/3 chord distance on a model rocket is it
constitutes a major portion of the overall aerodynamics and a similar
shape object on the other side as well would be adviseable.
Just Jerry
Jerry Irvine
Box 1242, Claremont, California 91711 USA
Opinion, the whole thing.
Please bring common sense back to rocketry administration. Produce then publish.
http://www.usrockets.com