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Originally Posted by b3lha
It would certainly be impressive if you could improve upon the work of Subaru's wind tunnel engineers. Even if you can't, it would be a learning experience. You could use this site to document the project, so we can see how you are progressing.
Phil.
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In theory, and almost certainly in practice too, liberating another 40 horsepower by reducing aerodynamic drag should be a doddle
The problem is
proving that you have done it!
Let me explain, one horsepower is 550 foot-pounds/second, a velocity of 150 m.p.h. is 220 feet per second; so the force required to expend one horsepower at such speeds is a mere 550/220 pounds, that's
2.5 pounds
If we are looking to liberate another 40 horsepower then we would need to reduce the aerodynamic drag by a mere 40 x 2.5 pounds,
only 100 lbs.
I maintain that getting an aerodynamic drag reduction of that order of magnitude should be an easy task - if you don't believe me, try sticking your hand out of the window when driving along at a high velocity and see just how much drag even a small obstacle to smooth airflow generates.
Now look underneath the car. Does it look like anybody spent any time at all worrying about airflow management?
What is all that ironmongery doing under there? You'd be very upset if the upper side of the body design was as lumpy and bumpy as that.
Late model Subarus have had some attention paid to this area, and have an undertray, whose purpose is not merely to annoy people at every oil change!
Unfortunately the changes that we are looking for are so small that attempting to discover whether the drag has actually gone up or gone down by a few pounds is pretty much impossible without access to a wind tunnel. In the example that I quote, of looking for a reduction of 100 lbs in drag, it is less than 3% of the weight of the car. How could we possibly measure that?
One possibility is to wind the car up to maximum speed, slip it into neutral (possibly buggering the gearbox in the process) and measure the decelleration of the car due to the aerodynamic drag.
Could we repeatably measure this?
How accurate would our measurements actually be, could we even get the same measurements repeatably within 3%?
Just a small variation in initial and final velocities, or the windspeed, temperature, relative humidity, etc. may totally invalidate any results.
Put the car in a windtunnel, tethered via a strain-gauge to measure the forces, and such experiments become much more feasible.
I've no doubt that I could cobble something together that might
look right, but as I implied earlier, aerodynamics has little to do with aesthetics, and what looks right may
actually be worse.
So, has anybody got access to a windtunnel?