Motorcycle aerodynamics, a slippery and windy, slope?

[Kincurd]

Scooters get to be pretty light. That one Dutch Honda we all know and love was originally intended only for non-windy use, but IIRC, he did fine in the wind. Probably due in no small part to the fact that he used steel and thick fiberglass for the streamlining. Had it been aluminum and thin carbon fiber, it may have been a no-go.

[fefrie]

Originally Posted by 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.

The other thing to remember is that a motorcycle will travel much faster than a bicycle, so that most side winds won't interact with a motorcycle at a perpendicular angle, but rather at an angle more akin to a headwind.

[PeterS]

Originally Posted by fefrie

The other thing to remember is that a motorcycle will travel much faster than a bicycle, so that most side winds won't interact with a motorcycle at a perpendicular angle, but rather at an angle more akin to a headwind.

Not quite , were the winds from ahead all would be well, it's the 15 degrees off the nose that is the problem, they generate unequal side loadings. Craig Vetter seems to have the solution, a substantial gap at the apex of the curve so that pressures can equalise across the fairing .

[Varn]

Our bike has only been used for racing and is ridden by professional riders. It has been 66 mph in a straight line with good wind conditions and 50 mph for an hour in some bad wind.

What has been your experience fefrie and redyaris? You both make points in opposition to what I said so please share your actual experience before you take down my statement of fact. Do you race a Bonneville in the wind?

I don't think I would be fun to be riding a fully enclosed motorcycle on a windy day. You guys be careful in the wind

Originally Posted by fefrie

The other thing to remember is that a motorcycle will travel much faster than a bicycle, so that most side winds won't interact with a motorcycle at a perpendicular angle, but rather at an angle more akin to a headwind.

[PeterS]

This a rough of what I hope to build, based on a diesel engined Royal Enfield, the only type of bike my local registration authority will let me fit a diesel into. A diesel will give me 50% more engine efficiency and i can run it on biodiesel .

I have no idea of the drag coefficient of this fairing but it should be quite similar to Craig Vetter's machine ... perhaps .55?

[Varn]

One aspect of streamlining is that the noise that develops inside is incredible. Even in our pedal powered liners the noise level gets pretty high. The bodies tend to resonate over the road like a transducer.

I am guessing that if you add a clattery air cooled diesel even if the engine is isolated by a firewall, you won't hear the traffic around you.

Perhaps someone who has built or ridden one can add. Might make a good case for having the engine water cooled and somewhat isolated from the rider.

[PeterS]

Air cooled diesels are noisy but there is plenty of sound dampening material around, 50mm or 2 layers of that and a fibre glass shell around the engine is the plan .I'd prefer a light weight water cooled diesel but apart from being very bulky and hard to come by they are heavy and expensive !

As an aside it is possible make a diesel quite quiet, comparable to a petrol engine by injecting propane into the airbox. it has the effect of lengthening the moment of combustion.... the reason for the diesel 'clatter '... you might note how quiet modern common rail diesels with their multitude of tiny injections of fuel through the combustion period are. Direct injection diesel have a very rapid burn, it's quite efficient but give the characteristic loud "crack".

Do NOT spray propane into the airbox until the engine is started .

[renault_megane_dci]

Convert you air cooled diesel to water cooled with a suitably formed sheet of alloy and solder it with tin ?
My plan, anyway ...

[PeterS]

Originally Posted by renault_megane_dci

Convert you air cooled diesel to water cooled with a suitably formed sheet of alloy and solder it with tin ?
My plan, anyway ...

The aim is just quietening ? Sound dampening might be a lot simpler.

[renault_megane_dci]

My aim is relocate the cooling interface (it is much simpler to locate a radiator than to build proper (efficient) air ducting for the engine)