an@hou2h.UUCP (A.NGUYEN) (03/02/84)
. A Cd of say .35 means the vehicle has 35% of the aerodynamic resistance of a barndoor of the same frontal area. Notice that low Cd alone does not mean less drag. A Mercedes with a .35 Cd would still have more drag than a Civic CRX of the same Cd, because of the former's larger frontal area. Streamlining isn't just making a swoopy shape (see Porsche 928.) The object is to smooth the airflow around the vehicle. Details are important (see Mercedes Benz.) Competitive swimmers shave their body. Aircrafts use paints that present a smoother surface to the air rushing by. Aerodynamic effects increase with velocity squared. Double the speed and air resistance is quadrupled. Aerodynamic resistance is the major power consumer above 30-40 mph approx. Because of this, streamlining is the most sensible way to improve performance (gas mileage, acceleration from higher speeds, top speed, etc, see Honda Civic CRX.) Less power used to punch a hole in the air means more power left to accelerate you from 50 to 70 mph for that quick pass (left lane hogs take notice!) Au Nguyen
sr@u1100a.UUCP (Steven Radtke) (03/04/84)
The comments about special drag-reducing paint on aircraft in Nguyen's article reminded me of a comment that has been a bug in my ear for years. When I drove a motorcycle, I used to take one day every 2-3 weeks to clean and polish it. My friend would often clean his at the same time. My impetus to polish came from the fact that I hated to drive a $4000 bike that looked all ratty. My frieand always said somewhere towards the end of one of these exercises that a clean bike goes faster, and I'm afraid he said it to me often enough that I began to believe it, rationalizing about drag coefficients. I'd like to hear what others think.
ralph@inuxc.UUCP (Ralph Keyser) (03/07/84)
I think it is a reasonably well accepted fact that clean vehicles are in fact "faster". How much faster is the real question, and that has to do with how fast the vehicle goes since aerodynamic drag is an exponential kinda function. For a light aircraft (cruise at 150 mph), a clean one is about 2-3 mph faster than a dirty one (with dead bugs along the leading edges), so a car isn't likely to see as much of a gain. So you can say that a clean car is faster, but in truth, the reason for washing your car is more for better looks than more speed. Ralph Keyser ...!ihnp4!inuxc!ralph
scw@cepu.UUCP (03/08/84)
<>
The comments about special drag-reducing paint on aircraft
[...] towards the end of one of these exercises that a clean bike
goes faster, and I'm afraid he said it to me often enough that I
began to believe it, rationalizing about drag coefficients. I'd
like to hear what others think.
Well yes, a very clean and waxed bike will have a lower coefficient of
drag that a dirty bike. Unfortunatly the primary component of aerodynamic
drag on a motorcycle is parasitic drag (rider, handle bars, engine,&tc.).
I suspect that washing and waxing a bike makes no detectable difference.
--
Stephen C. Woods (VA Wadsworth Med Ctr./UCLA Dept. of Neurology)
uucp: { {ihnp4, uiucdcs}!bradley, hao, trwrb, sdcsvax!bmcg}!cepu!scw
ARPA: cepu!scw@ucla-locus
location: N 34 06'37" W 118 25'43"dmmartindale@watcgl.UUCP (Dave Martindale) (03/09/84)
A clean bike would go (marginally) faster if you were going at the maximum speed allowed by engine power. Light airplanes are flown this way all the time - the power output is set to some specific target, and then you see what airspeed you get. And it is known that the usual accumulation of bugs, dirt, and bird droppings on the plane's surface will reduce its speed by several knots over that of a plane with a clean, waxed skin.