Quote:
Originally Posted by
uberthumper
<post 27 - sniped cos it's quite long!
|
One thing I absolutaly agree with you, it's easier with a whiteborad, and being in the same room!
------
I have infront of me a number of crude sketches depicting various windflows over a symetrical (assuming the bike is symetrical - which it isn't, well not perfectly anyway), and I'm still happy that the OP is correct, regarding the flow of air over the bike.
What has perplexed and vexed me over the weekend is the relationship of the headwind to the sidewind, given that the headwind isn't actually a moving force, it's just the realionship to the bike that has the effect of an oncoming wind. I can safely say it gave me a headache just thinking about it!
At some point, where a sidewind exceeds the 'power' of the headwind then things are going to go wrong, so this might as well be ignored for now. Lets concentrat on a relatively small sidewind force of 9 meters per second (about 20mph) , against say a 27 meters per second (about 60mph). To further simplify this, I'm going to take a sidewind at 90 degrees to the bike, the results change as the asngle of incidence becomes smaller than 90 degress and greater than 90 degrees.
You'll have to forgive the rough drawings.
Under normal (no sidewind) riding the bike would part the oncoming air (headwind) in a nice equal pattern
Assuming the bike is stationary, the sidewind would part something like this.
But when both are present, the sidewind, having less velocity than the headwind would not be able to pass around the motorcycle in the same way due to the velocity of the headwind being greater than the sidewind, as airflow is easily defelcted, the result would be that the sidewinfd flow would pass to the rear of the bike, this is what would cause the lower pressure on the widward side of the bike
Therefore you get higher windflow down the side of the bike on the windward side, thus lower atmospheric pressure.
I've looked at the possibility that the power of the sidewind is somehow expelled as energy, but there is no other energy that is being shown, the scrub off the tyres isn't really evident (you don't get black line down the road) and the bikes dont move in the direction of the wind anyway, there is no noise (but that is difficult to demonstrate or prove due the the windnoise being created around your helmet), no heat is being created, so I can't see any evidence of the winds power being converted to energy. Therefore I can only conclude that the wind is still there and being deflected. Of course a bike isn't a 2 dimensional object, so wind can deflect over and under the machine, I haven't even thought about the complications a 3d view would give.
Another thing that strikes me, this topic is 4 or 5 pages long and other than the OP there has been no other attempt to describe why a bike moves in the way it does when in a sidewind....... lots of disagreements, but no alternative theory.