Inertia
I am working on a vehicle guidance problem now, and thought about the Husaberg engine configuration. The real advantage just came to me.
If you think about a motorcycle, when you corner, you are rotating roughly around the rear axle if you aren't slipping the rear wheel too much (and if you are slipping the rear wheel, the yaw axis moves forward, closer to the vertical axis of the rider). By moving the crankshaft REARWARD, you really are reducing the motorcycle's inertial moment in yaw (and the effect is a function of the SQUARE of the distance from the yaw center). Less yaw inertia increases the responsiveness of the motorcycle in yaw.
In a conventional design, the crank (and its rotating mass) is considerably further ahead, which will increase the motorcycle's rotational inertia in the yaw axis when compared to the Husaberg design.
Same with the fuel. Moving the fuel closer to the yaw center of the motorcycle will reduce its inertia in yaw, allowing the motorcycle to rotate in yaw with less effort.
Because of the distance squared effect, this should have a huge effect on how it turns. I am a crappy rider, so i may not be able to take full advantage of it, but my guess is that this wouldn't be too hard to feel.
Now that I've thought about it, it seems to be a quite brilliant move. Don't think mass, think about mass distribution and inertia. Moving the crank up DOES affect inertia in roll, but if you think distance squared, the distance they've moved the crank up isn't very much compared to a conventional design. (And possibly offset by the near horizontal cylinder configuration because that mass rides, on average, lower).
It all makes sense to me now. It is certainly a good idea from a vehicle dynamics point of view. It is not a gimmick, but a well reasoned approach to high performance motorcycle design. My hat is off to Husaberg! Good work.
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