C10CoryM
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| posted on 12/4/09 at 06:42 PM |
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Real world aero measuremnts
Couple posts recently about aerodynamics of the locost shape. Has no one ever had some fun with a manometer on their locost?
Meaning go for a drive at the same speed with a manometer taped in different locations to find out where, and how strong the high/low pressure areas
are. Then adjust accordingly with some taped on panels etc to see how to reduce the drag and lift.
I have a few ideas of how to reduce the aero drag, and intend mine to be a bit of a test-bed. It's about a year off though so just wondering if
anyone else has an interest.
You can buy a low pressure transducer for about $60 to plug into a scanner or digital multimeter, or a mechanical manometer for a bit less (can make
your own too).
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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SPYDER
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| posted on 12/4/09 at 08:17 PM |
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In a similar vein I remember taping dozens of short lengths of wool all over the front of our TR7V8 circuit racer. We took photographs from a chase
car at various speeds. The results were interesting in so much as in various spots the airflow was at right angles to what you might expect and even
180 degrees out in a few spots.
We were chiefly interested in the flow patterns around the radiator opening and across the top of the bonnet.
Your manometer idea sounds interesting though. I've often wondered what pressure exists under the bonnet of a fast moving car, in particular
around the engine intakes.
I suspect that in many cases that air is flowing in the wrong direction down carefully placed cold air trunking. I might be wrong. ( I'll ask
my wife)
Geoff.
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smart51
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| posted on 12/4/09 at 08:35 PM |
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I've found that when the car crosses 70 MPH without the bonnet fastened down, it just lifts off the car. I'm guessing there's low
pressure over the bonnet then. Luckily the track had a grassed area at the side. I'm still fixing the crazed gelcoat though.
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A1
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| posted on 12/4/09 at 11:24 PM |
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it would be quite interesting to book a windtunnel for the day...anyone up for a group buy?
i want to see if my new vents and wind deflector are doing what i want...
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Staple balls
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| posted on 12/4/09 at 11:36 PM |
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quote:
Originally posted by A1
it would be quite interesting to book a windtunnel for the day...anyone up for a group buy?
i want to see if my new vents and wind deflector are doing what i want...
Might be better off with a small scale windtunnel, (should be easy enough to build) and a few locost models?
I expect it'd work out a fair bit cheaper than renting a wind tunnel for a few hours, and you'd have time to play with different
designs/ideas.
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nstrug
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| posted on 13/4/09 at 09:01 AM |
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See this post for a quick and dirty way of calculating your car's CdA:
http://www.locostbuilders.co.uk/viewthread.php?tid=103265&page=&contribmessage=none
Everything I have read suggests that the Cd of a 7 is very high, however as the A (cross-sectional area) is quite low (especially if you don't
have a windscreen), I would have though that the CdA is not too bad.
Painting the car with dyed paraffin and going for a high speed run is a good way of looking for high/low pressure spots and skin airflows.
Nick
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greggors84
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| posted on 13/4/09 at 12:27 PM |
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Have done a bit of CFD analysis work before. If I could find a locost way of getting the software then it wouldnt be hard to knock up a basic Locost
shape and do some simple calculations and adjustments and see what happens.
Back when I did it home PCs and Laptops didnt have the power to do the calculations but they have come on quite far now.
Will look into it.
Chris
The Magnificent 7!
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C10CoryM
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| posted on 13/4/09 at 02:35 PM |
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I'm not sure how much good an model air tunnel would do. You would have to go quite large in order to see what was happening, and you would
need accurate scales under each wheel to measure lift etc. It also wouldn't help much in reducing the drag at the rear panel which I think is
one of the major factors (that you can do something about). I think knowing the pressures would be far more usefull.
I tried a CFD program before (30day trial) but my PC wasn't smart enough to handle it. Maybe someone with a better PC can give it a go.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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