Motorcycle Aerobody Research

[Jyden]

This fabulous 2-cylinder, 250cc, Rennmax NSU out 36hp @ 11000rpm dominated the sport in 1954. Werner Haas of Augsburg defended his world championship in superior style, by decisively winning the first four World Championship races on the silver Dolphin. The bike could go 131.4 mph, an astonishing feat for such small displacement. NSU had a 6-speed transmission, and weighed in at only 117 kg complete with fairing. NSU only built six of these bikes and were not-for-sale factory racers.

[godscountry]

If I'm correct,Authur Wagner,Peraves,designer and builder of the Ecomobile had built gliders before building his enclosed MC.I have always said,glider cockpits ,fuselages make for a great start in building a low drag enclosed Motorcycle.Thanks for the post.

[ElectricRider66]

Originally Posted by sendler

The Delta 11 has an inherent design disadvantage in cross winds of an ultra low CG from the batteries. But he still seems to manage. The important thing to keep in mind is that the lift (side) of a fast moving vehicle in side winds is nowhere near where you think it is by looking at the static side CoP. And having it centered on the steering head may be better than having it further back, like an arrow, until you get up to salt flat speeds where the tires are barely contributing to the direction control.
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Is a big streamliner easier to blow off the stand? Yes. Is it worse in side winds on the road? Not necessarily.

On the Delta-11, it actually doesn't have a low Center of Gravity due to low battery weight. Two of the battery packs, the external ones, are mounted high (they weigh 100 lbs total). These external packs are about the same as having an extra rider on the bike. I believe this helps stability in gusts. The bike now has 8,500 miles on it and I'm very happy with the handling under wind speeds of 25mph. When the wind gets stronger than that, it's unnerving and I worry about safety when I am crossing a local metal grated bridge - I always wonder if I'll have enough traction for the wheels to not slide sideways from under me. Here is a link showing the location of the external battery packs.

The bike self corrects for wind gusts when the wind velocity is less than 25mph. Above that, I have to admit that I'm a bit of a chicken about seeing what will happen, having the nagging memory of how I was pushed across the centerline into oncoming traffic on a 600cc Ninja in high gusting winds...a few years back.

What's tricky is not riding on straight roads during gusting, the bike does a great job of self correcting and I just sit there and let it lean itself correctly. What's tricky is leaning into a high speed corner in traffic and then getting hit with gusting winds. You need to lean to steer through a corner, and then the lean is being affected by a gust, the question of how to compensate the lean is urgent. Will the gust intensify or diminish? It doesn't happen regularly or with predictability so it's hard to study - but it does cause my heart to skip a beat or three when it happens.


http://www.schultzengineering.us/june4a.jpg

[sendler]

Originally Posted by ElectricRider66

On the Delta-11, it actually doesn't have a low Center of Gravity due to low battery weight. Two of the battery packs, the external ones, are mounted high http://www.schultzengineering.us/june4a.jpg

My mistake. You have had so many different versions of your electric streamliner it is hard to keep track. I was thinking of one of your drawings which showed a stack of lead batteries along the bottom, under your legs.

[sendler]

Here is a good page on cross winds.
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Delta Bike USA - Forge Design Competition A - Cross Wind Stability
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[orange4boy]

To my mind the main issue with streamlining is lift from crosswinds and how to kill it. (I an using lift in the sense of a force generated by an airfoil with a positive angle of attack not as in vertical lift.) I imagine front mounted spoilers in the same region where vortex generators are placed on wings They could be either passive or active. This would reduce side lift dramatically. As we all know, streamlining reduces the force transmitted by the wind to the vehicle except when lift is an issue.

As an example, I know that nascar vehicles have strakes on the roof, parallel to normal flow which act as spoilers to kill lift if the car goes sideways. I have also seen this in Hucho somewhere in relation to sidewinds on cars or trucks

An active system could use air pressure differences to activate spoilers on the lift side in gusts although moving parts are less attractive than passive spoliers.

This narrow focus on C of P could be why there is so much discussion around tails and why weight and center of pressure fixes did not work. Don't move the lift or the C of G, Kill the lift! If there is still lift generated at the front of the bike it does not matter much how long the tail is, it will still cause a large side force near the front of the bike.

My $.02

[sendler]

Originally Posted by orange4boy

To my mind the main issue with streamlining is lift from crosswinds and how to kill it.

The lift (side) from yaw winds creating an angle of attack to the symmetrical airfoil of a streamlined motorcycle can be minimized by venting the resulting pressure differential across the rider's legs and lap. Which must be open for egress and holding the bike up at stops anyway.

[orange4boy]

That's why most modern faired motorcycles are OK in crosswinds.

I was addressing enclosed bikes, although there would still be lift created on the section in front of the rider gap which might still benefit from a yaw spoiler.

[Grant-53]

The cross section of the body and the ground clearance go a long way in determining side lift and drag. The fairing I built for a city bike is essentially two cones, two feet from the ground. It is barely affected by cross wind. Generating down force instead of lift is key to stability along with reducing drag.
The dustbin fairing Kraig is using generates lift. The cross section is close to being a circle. A tail section helps turn the body into the wind. The Morelli/Aptera body has an horizontal oval shape for lower side drag. The shape looks to be a symmetric air foil with the center line bent in a shallow S curve.
The stability versus response balance is often a rider's preference. A low nose and a higher tail box seems to be a good balance to reduce lift and drag. Angled strakes at the nose can generate down force at the price of more drag.

[godscountry]

Originally Posted by sendler

The lift (side) from yaw winds creating an angle of attack to the symmetrical airfoil of a streamlined motorcycle can be minimized by venting the resulting pressure differential across the rider's legs and lap. Which must be open for egress and holding the bike up at stops anyway.

The Monotracer,fully enclosed,has no real problems with side winds.Long wheelbase,with lots of surface area behind the center of gravity,kind of like a arrow with feathers.The Monotracer turns into the wind,people who have been in it says its does the opposite of what you would expect.I really think ,looking at sales of high mileage[Toyota] vehicles,people will embrace the technology.I think a body like the BMW Simple concept packaged on a tilting chassis or 2 wheel motorcycle platform would work,safe,comfortable,incredible range with it 0.16 cd ?no matter what the propulsion.Lit Motors ,generated a lot of interest,whether or not they can deliver is to be seen.they are going to control the lean via the gyros.I always thought ,the best is the natural physics,no mechanical assist,but it is very complicated process and I'm not a expert on the physics of the steering input,lean etc internal,external forces etc.Learn math, guys and gals,at least you can come up with some numbers to work off of.