Wind Tunnels
Gene Ambacher
Where could I find information on building my own wind tunnel?
Bob Fortune
Where could I find information on building my own wind tunnel?
bob dahlquist, tripoli central california, had his tunnel written up in HPR in march.
he's quite the genius type, check out his other stuff, too. lot's of great things.
bob fortune
James L. Ball
Gene Ambacher wrote:
> Where could I find information on building my own wind tunnel?
A really effective wind tunnel is probably beyond the scope of most
rocketeers.
If you had access to an old 4-cyl Lycoming aircraft engine, or maybe an
ultralight Rotax engine and propeller--you might be able to come up with
something effective and powerful enough to static test stability, CG/CP
relationships and maybe do some rough drag analysis..
A homeade supersonic wind tunnel is not realistic IMHO.
I remember in the mid-60's, Estes produced a Technical Bulletin on
building a wind tunnel for model rockets. It even had a smoke generator
for doing drag studies!
A copy of that bulletin is probably available from one of the Estes
O.O.P. collectors that frequent this newsgroup.
I think if some of the engineers and tech-types frequenting this
newsgroup could come up with an effective and reasonable wind tunnel
design suitable for construction and operation by a club or group, it
would be a great service to this hobby.
Any takers?
Jim Ball
Ted Cochran
In article <359C3E2E...@fament.com>, "James L. Ball"
<jim...@fament.com> wrote:
[snip good stuff]
>
>I think if some of the engineers and tech-types frequenting this
>newsgroup could come up with an effective and reasonable wind tunnel
>design suitable for construction and operation by a club or group, it
>would be a great service to this hobby.
>
Well, it turns out you don't really need to get into generating high wind
speeds unless you need to test transonic stuff. Aerodynamic effects
scale over velocity pretty well, through the subsonic range, so if you can
get to 40 mph you are probably in reasonable shape.
You do need to worry about scaling for size, (which is why NASA has such
frigging big wind tunnels scattered around the country), but we're
building pretty small vehicles to begin with, so no sweat.
Building a tunnel is straightforward, but time consuming (A buddy and I
built one in high school in about 1000 person hours, but we
over-engineered it quite a bit and learned to use a bunch of woodworking
tools as we went. He still has nightmares about the joiner). THe
instrumentation is the PITA, but cheap strain gauges have made things much
easier.
THe basic open tunnel has a bell shaped front end (45 degree angles will
do) that is four to six times larger at its opening than is the test
chamber behind it. THen there is a long, gradually expanding diffuser
section, after which comes the fan. That's the easiest way to do it. THe
closed tunnel is more efficient, but you have to worry about heat, the
size gets enormous, and you need to make smooth curves or you lose all the
advantages of efficiency you started out with.
40-60 mph can be had in a 12 x 12 x 12 inch test section with a 3' exhaust
fan (like for an attic) in a cowl, driven by a hefty electric motor with
some speed reduction via belts or chains. Be careful that the fan is rated
for the RPMs you will be driving it at! THe diffuser between this motor
and the test section should be something like 6 feet long, the longer the
better. THe bell on the other end is wide--4 x 4 feet or so, but short.
You can stick some flow laminizers in the narrow end; fluorescent light
grills with 1/2 x 1/2 inch squares are fine. THe idea is to move a lot of
air with the fan and let the narrow throat of the test chamber do the work
of accelerating the flow.
The sides need to be stiff or they'll start to flutter. Use something
like 1/2" marine plywood, and brace it around the outside at the edges
with 2 by 3s. Use bolts not nails. Build it so that the 2 x 3s on the
edges of each panel can be bolted together like a flange.
Someone with an engineering background can work out the details about how
big a motor to move how much air (you might want to use a 220v hookup) and
what ratio of test chamber size to fan size works best.
FWIW,
--tc
My opinions only.
Craig Utley
A search at amazon.com revealed this book and 23 others...
Low-Speed Wind Tunnel Testing ~ Ships in 2-3 days
William H. Rae, Alan Lamont Pope / Paperback / Published 1984
Our Price: $125.00
--
Remove NOSPAM to reply via e-mail.
Gene Ambacher wrote in message <359BF3F9...@wang.com>...
Des Bromilow
Gene Ambacher wrote:
>
> Where could I find information on building my own wind tunnel?
Don't know but I have seen one homemade one that looked to work OK and
one commercial one. First the homemade one...
They (a youth group) had got an exhaust fan and ducted it's output into
the end of the tunnel. (the fan was located under the tunnel)
once at the end of the tunnel the air (wind) had to pass through a
device which broke up the turbulence and tried to get a laminar flow
going for the tunnel.
The device used consisted of a set of square tubes all stacked together
to create a grid (when veiwed from the end) which filled the end of the
tunnel and was around 12-14" (300- 350 mm) long. the rest of the tunnel
was around 24" (500mm) long and the whole tunnel was only approx 12"
(300mm) by 12" (300mm) in area.
There was various hatches to get access to whatever model was in the
tunnel and to allow a windspeed measuring tool to be inserted. Windspeed
was controlled by a speed adjustment on the fan motor.
The University I went too also had a wind tunnel with an open testing
area of approx 2' by 2' and the fan was located at one end approx 6'
away from the testing area. I can't tell you how the turbulence was
removed from the flow, but I know it took all of the 6' to achieve it.
The fan on the end was approx 4' in diameter and was of a turbofan type
design and had huge cowlings around it to try and increase the air
sucked into it.
Speed on this tunnel was also controlled by means of motor speed
control.
From memory BOTH tunnels had NO provision for the outputted air to be
ducted back in again for reuse. This would have required two things...
the first would have been more ducting which may cause some back
pressure in the air stream,
the second would be if the recycled air would require cooling since it
had to pass around the motor in each design and may heat up (aside from
frictional heating) which after a while may cause problems for your
motor and influence your results.(air density is related to temperature)
I hope this helps
Des Bromilow
QRA
Brisbane
Australia
IBPYRONSKI
>
>I remember in the mid-60's, Estes produced a Technical Bulletin on
>building a wind tunnel for model rockets. It even had a smoke generator
>for doing drag studies!
>
>
yes Estes put out a TB and as I recall it used a cage type blower and a grid of
short lenghts of body tubes glued together as a flow straightener.The box was
to be made of plywood with a clear sheet plastic window.
Tom
Michael Toelle
James L. Ball wrote:
<snip irrelevant stuff>
> I remember in the mid-60's, Estes produced a Technical Bulletin on
> building a wind tunnel for model rockets. It even had a smoke generator
> for doing drag studies!
>
<snip irrelevant stuff>
That bulletin is in the "Classic Collection" book of old technical reports
from Estes.
Mike Toelle
NAR 31692
TRA 3562 L1
Darren J. Longhorn
There was an article in Scientific American either late last year or early this
year, i'll dig it out and email you the exact issue.
--
Darren J. Longhorn
Unorthodox Engineer
darrenl...@geocities.com
http://www.geocities.com/CapeCanaveral/Hangar/8238/
Gene Ambacher <gene.a...@wang.com> wrote in article
<359BF3F9...@wang.com>...
Bob Kaplow
In article <359BF3F9...@wang.com>, Gene Ambacher <gene.a...@wang.com> writes:
> Where could I find information on building my own wind tunnel?
You might also check with Kevin McKiou of Vector Aero (Cuda RCRG kit maker).
He's built one in his basement. But don't expect to hear from him for the
next month or so, as he's getting ready to go to the world championships and
win a gold medal!
Bob Kaplow NAR # 18L TRA # "Ctrl-Alt-Del"
Kaplow Klips: http://members.aol.com/myhprcato/KaplowKlips.html
NIRA: http://www.nira.chicago.il.us
PnmaFloyd
If you're interested in the old Estes plans mentioned earlier, look for the
tech report TR-5. Unlike most Estes things, I never built that one...
-"Panama" Floyd