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Originally Posted by sendler
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Incorrect Lift Theory
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Again Ken Fry comes through with an important concept we have been missing. I have been imagining the streamliner going 60 mph down the road as a steady state with a side wind blowing on it being a new and completely separate force pushing straight on the side area of the bike. As he said, this is not the case when the bike is moving forward fast. The side wind will seem to combine with the 60 mph head wind to make a new wind that is at an angle just off the straight ahead direction. Giving the symmetrical airfoil of your streamliner an angle of attack.
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I found a computer simulator at Nasa.gov that lets you play with an airfoil's angle of attack and probe the pressure and velocity at any point on the screen. And observe the movement of all of the air particles. There is also a guided experiment to show how the "equal transit" theory of air flow over a wing that we have all been brought up with has been proven wrong. The air particles that are next to each other before splitting up to go over and under the wing do not speed up and slow down to meet at the back. And Pluto is not a planet. But anyway. The speed IS different at the top and bottom but the pairs don't have to meet. Interesting but not what I was getting at.
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A symmetrical airfoil with an angle of attack creates lift. Or in our case, side. You can see from the simulator that there is a pressure difference between each side of the airfoil which is greatest in the area of the fat part of the wing. This is why Craig Vetter discovered from actual road tests that his streamliner was much better in sidewinds without the "door" covering the entire right side even though the left side was open. By leaving the entire streamline open in front of his legs and chest he has completely vented the majority of the pressure differential right at the fat part of the wing.
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This also explains why, contrary to my intuition, he has found from road tests that the full, cd improving tail is no problem in sidewinds. It is only really a side wind on the tail when the bike is parked. Great work Craig and Ken. |
That is just the bit of information I was looking for ...thanks !