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Wheel Covers used in Time Trials
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Wheel Covers used in Time Trials
Shock wrote:
drag than all those spokes whipping up the air. There has even been some wind tunnel data to suggest that disc wheels and wheel covers may even provide some small amount of propulsion in certain crosswind situations... Which is evidently nonsensical - the wheel is symmetrical fore-aft. -- David Damerell Distortion Field! |
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Wheel Covers used in Time Trials
David Damerell wrote in message ...
Shock wrote: drag than all those spokes whipping up the air. There has even been some wind tunnel data to suggest that disc wheels and wheel covers may even provide some small amount of propulsion in certain crosswind situations... Which is evidently nonsensical - the wheel is symmetrical fore-aft. No, he's correct. It's similar to a sailboat getting propulsion from a sidewind or even quartering headwind. Haven't you ever seen a sailboat tack into the wind? Jeff |
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Wheel Covers used in Time Trials
Shock wrote:
drag than all those spokes whipping up the air. There has even been some wind tunnel data to suggest that disc wheels and wheel covers may even provide some small amount of propulsion in certain crosswind situations... "David Damerell" wrote in message ... Which is evidently nonsensical - the wheel is symmetrical fore-aft. Couldn't it if the wind was from one side and behind ? Unlikely but not nonsensical. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971 |
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Wheel Covers used in Time Trials
On Tue, 22 Jul 2003, Dave Lehnen wrote: David Damerell wrote: Shock wrote: drag than all those spokes whipping up the air. There has even been some wind tunnel data to suggest that disc wheels and wheel covers may even provide some small amount of propulsion in certain crosswind situations... Which is evidently nonsensical - the wheel is symmetrical fore-aft. It may be counter-intuitive but it's not nonsensical. Disc wheels, and some other wheels such as the tri-spoke wheels with airfoil spokes and deep section rims, can generate some forward thrust in a crosswind. This has been measured in wind tunnels and does not contradict theory. The thrust is not nearly enough to overcome drag of the rider and the rest of the bike, but it is enough to make a difference. FWIW, vertical-axis wind turbines typically use symmetrical airfoils, with the airfoil's plane of symmetry tangent to its circle of rotation. They won't self-start, but generate power after being started by external power. Snip of the rest of a nice post For a practical example of a symmetric airfoil (essentially no camber) making thrust, see one of my hpv's he http://www.interq.or.jp/cool/yutakai...aero4/main.htm As with the windmills you note above, it has to be pedaled up to some speed first, then the wind takes over. With a steady crosswind this bike sails quite nicely. I've done many miles without pedaling, on the flat, at 15-20 mph. Of course with that much side area, gusty winds or high speed traffic (opposing trucks are the worst) can be scary--small boat warnings apply(!) Wind tunnel tests also confirm these results--the x-force (force along the centerline of the bike) becomes thrust at some yaw angle (angle of the relative wind). -- Doug Milliken www.millikenresearch.com |
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Wheel Covers used in Time Trials
David Damerell wrote:
snip I am not convinced by the sail analogy; a sail produces thrust perpendicular to the plane of the sail (yes, yes, it's curved) and matters can be arranged such that vector points fowards; but perpendicular to the plane of a disc wheel will always be directly sideways. While this seems intuitively reasonable, it's not true. You may need to look at airfoil test results to convince yourself of this. What is true is that the resultant force (vector sum of lift and drag) can never be at an angle of 90 degrees or less to the apparent wind, otherwise perpetual motion would be possible; sailboats and wind turbines would work in a dead calm. Dave Lehnen |
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