Drag reduction question
Drag reduction question
(OP)
What effect on drag would this test have?
If the highest pressure surface area was perforated with thousands of small holes, say 1/32", that discharged air or some gas from an onboard supply, at high velocity, into the oncoming air stream. Would this increase drag or decrease drag. If done correctly, the oncoming air stream would not touch the surface of the vehical. I can build a test unit but before doing so I would like some feedback on this therory.
Thank you
Jeff LeDoux
If the highest pressure surface area was perforated with thousands of small holes, say 1/32", that discharged air or some gas from an onboard supply, at high velocity, into the oncoming air stream. Would this increase drag or decrease drag. If done correctly, the oncoming air stream would not touch the surface of the vehical. I can build a test unit but before doing so I would like some feedback on this therory.
Thank you
Jeff LeDoux





RE: Drag reduction question
RE: Drag reduction question
RE: Drag reduction question
i think the idea is to create a blanket of air (or "gas") around the vehicle. if this is the case i think the gas you're pushing out into the flow will "mess" in a severe way with the airflow round the vehicle, creating a huge turbluent "mess". for airplanes, boundary layer suction has been used in the past (refer Buccanneer (sp?) in-service with the RAF '60s - '80s).
maybe if you contained the gas within an elastic membrane, it'd prevent mixing with the airflow ??
RE: Drag reduction question
http://en.wikipedia.org/wiki/Supercavitation
However, it may be exceedingly difficult to do that in air.
As for the OP, the amount of air, and the velocity of the air generated must be powered by your fuel source, so, you won't be able devote as much power to propulsion, leading to a lower speed, anyway.
One would thinkg that running air at high speeds through those little holes probably burns a bunch of power as well.
TTFN
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RE: Drag reduction question
RE: Drag reduction question
You nailed it, thats exactly what Im trying to achieve only through air not water.
RE: Drag reduction question
I googled Boundry layer Energization and that looks interesting as well. Now I just need to see how it pertains to our project. It would be interesting to talk to some of the people who did the experiment.
Thank you
RE: Drag reduction question
Do this: try and do a better job of rounding the corners near the front, if at all possible. I see what look like square corners there. Chuck some bondo onto your thermoforming mold, and blend some fillets over those corners, and suck it again.
Also, before you get too wrapped up in the concept, do a simple spreadsheet calculation, and calculate what improvement in time you will get for a reduction in Cd from 1.0 (roughly what that bluff-ended fairing does) to 0.3 (like you might get from a more completely enclosed cockpit). Study bobsled designs, those get a lot of wind tunnel time.
RE: Drag reduction question
RE: Drag reduction question
I think you may have missed RB1957 point on the dirt. It's not just the air passing through the holes that generate dirt. Mud, spray, bugs etc in the air through which the vehicle is passing will tend to impact on the surface and potentially clog the holes.
As several mention the idea of suction on a wing or potentially fuselage/nassle has been experimented with off & on for some time. This is to remove the sluggish boundary layer and retain laminar flow and prevent the airflow going turbulent which increases drag.
As regards the Blackburn Buccaneer, were you thinking of the flaps RB? These were blown flaps more about increasing thrust than decreasing drag. http://en.wikipedia.org/wiki/Blown_flap
KENAT,
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RE: Drag reduction question
KENAT,
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RE: Drag reduction question
thrust from flaps, indeed ! lift is more like it !!
RE: Drag reduction question
Nice summary Thanks for helping with my tunnel vision!
RB1957,
If this concept actually could be made to work, I was only going to apply it during the period of highest pressure,The last 3 seconds of the run, thinking it would help the most at that period and help make the idea more practical. Im just trying to think outside the box.Traction issues are pretty straight forward. Tryng to make everything as effiecent as possible. Cant really get much lighter and at this point Im not sure more power will help, could actually hurt. I think a trip to a wind tunnel is in our future.
Thanks for ALL input
Jeff LeDoux
RE: Drag reduction question
good luck
RE: Drag reduction question
RE: Drag reduction question
I thought the American equivalent was a pi$$ ant but I may be getting my metric/Imperial/US customary units mixed up.
KENAT,
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RE: Drag reduction question