Motorcycle aerodynamics, a slippery and windy, slope?

[PeterS]

I think square is sufficient but concave might be better ! I have no idea !

As I'm planning to use the Kamm tail as storage square will do me .

[sendler]

A bike company gas developed a new tube profile with better aerodynamics than an airfoil with 5 times the length. Trek has used a classic Kamm pictured 2nd from the right in the gray photo but the new ovoid shape on the far right would seem to have the much better cd of an impractically long complete airfoil.

[PeterS]

Yep, that's the shape ..... but unfortunately our real world side lift doesn't allow it !

[Grant-53]

Use the 5:1 airfoil and a 25% kamm cut as the beltline (X-Z plane). Curve to the top and bottom using ellipsoids. Use the 3D graph option on a spreadsheet to match your bike dimensions. Max width between the the handle bars and the shoulders. The rounded shapes will reduce wind loading and could generate a bit of down force if the minor axis of the lower part is greater than the top part. If max width is 24 inches then overall length is 90 inches.

[Kincurd]

I'm back to some scooter/motorcycle sketching.

I love the idea of a Scooter like Allert's, with a canopy, extended seating area (and longer-overall chassis) to sit lower, and slightly longer tail. If it's shaped right, more like a tapered diamond instead of a sail, I'm pretty sure the wind won't affect it too harshly. I'm also thinking that the openings for my legs and feet should be made with brush and/or neoprene with slits, to cut down on the parachute effect.

[sendler]

Here's an interesting photo showing how a bike automatically leans into a 50 mph side wind blast coming out of the fans at the left.
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[PeterS]

Originally Posted by Grant-53

Use the 5:1 airfoil and a 25% kamm cut as the beltline (X-Z plane). Curve to the top and bottom using ellipsoids. Use the 3D graph option on a spreadsheet to match your bike dimensions. Max width between the the handle bars and the shoulders. The rounded shapes will reduce wind loading and could generate a bit of down force if the minor axis of the lower part is greater than the top part. If max width is 24 inches then overall length is 90 inches.

Grant, do you reckon you could do a drawing of what you mean then post it? I'm finding that hard to follow .

[PeterS]

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 !

[Varn]

I have seen streamliners get pushed to the side almost 30 feet.

We were at Casa Grande at the Nissan test track in 2007 with our bicycle streamliner the Varna2. Rob the rider was circulating the track at 50 mph in the one hour competition and encountered a 30+ mph cross wind.

The gust pushed him sideways. He had the luxury of using the entire width of the 3 lane track to keep upright. Something that would not be available on a normal roadway. Our rider had a lot of miles riding the Varna 2.

Had he been going faster he would have had to move further to stay upright.

There is a youtube video which shows this even occurring.

Seeing the stills of the bike passing a fan is not the same thing as having mother natures wind.

[redyaris]

Varn
It is important to differentiate between a 220 lb bicycle & rider steamliner and a 660 lb motorcycle & rider steamliner. The additional mass alone will make the motorcycle move less and move slower in a side wind. Although most of what is learned in reducing side wind effects on bicycles is transferable to motorcyles, as you suggest.