RE: Motorcycle Aerodynamics - 2

Zitat von Clifton im Beitrag #15

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It's not like pushing a rounded lump compared to a plate through the air because the "rounded lump" is actually a shape that's made from a whole conglomerate of bowls, flats, cubes, angles, etc. which each make their own vortices which contributes to more turbulence. A car's shape is more like your rounded lump analogy.

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Motorcycles have absolutely horrible aerodynamics.






........It’s not just the sticking out bits like elbows, head, feet and knees that break up the lamina air flow, it’s the sudden disappearance of a smooth guided path. Once air crosses the trailing edge of a motorcycle’s fairing into the open space between the fairing and rider, laminar flow disintegrates. The air pocket behind the wind screen is roiling mess of eddies and currents that are highly turbulent. Slow moving, but full of odd and unpredictable pressures, they slam into the high-speed, laminar flow rushing past. That collision creates a vacuum effect, sucking the turbulent air into the laminar flow, agitating the collision still more


The resulting turbulence then squeaks out in pulses wherever it can: under an armpit, over a shoulder, along a an invisible vortex of high-speed air trailing dozens of meters behind the motorcycle, like the foamy currents of a fast-moving river after a large rock.

Behind the rider air is in pure chaos. The rear wheel is churning up air like a blender, sucking it in on one side and blowing it out another, while the hot exhaust gasses are blasted out backwards, adding much heat energy to the random mix. No matter what shapes exist behind the rider’s back, the air has been chopped up and spit out like a felled tree through a wood chipper.......

Hans Muth seemed to have had some ability to handle the challenge.
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Zitat von Mr. 36654 im Beitrag #18

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Hans Muth seemed to have had some ability to handle the challenge.

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Zitat von Freddyfruitbat im Beitrag #19

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Zitat von Mr. 36654 im Beitrag #18

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Hans Muth seemed to have had some ability to handle the challenge.

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I know that bike had a legendary fairing (never ridden one myself) but was it really as effective as that photo with the drawn-in raindrops suggests?

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Back in the mid-70's a man, who turned out to be a very good, life long friend, Bertrand Cadart, started a motorcycle fairing business. Cadart, a Frenchman, came to Oz after de-mobbing from the French Army in the South Pacific, and ultimately started the La Parisienne fairing business. If any of the forum members saw the original Mad Max, the "bikie" in the one piece brown leathers ("Clunk") was Bertrand as well. He had the actual script, which he lent to me some decades ago (and he got it back). It was great fun to see the actor's script for an iconic movie.
Anyhow well before Japan Inc. adopted fairings (and the period when Graeme Crosby entered the Bol d'Or on Russ Hannon's naked superbike Kawasaki) he began to make fairings. Bikini fairings (like the smaller on the R90S or the Z1-R Kawasaki, larger "steering mounted" ones (but not as big as the Vetter "Windjammer") and frame mounted full fairings.
Engineering for the mounting system was amazing. Engineering for the fairing was "by eye and by logic", nil science.
What came out of some years of making these things was Bertrand's fixing on the need to "vent" the "vacuum" created behind the screen, and the approach he used is actually found on our RS bikes, the vent in the high pressure point at the bottom of the screen.
When BMW made the original Muth RS, it sealed the bike as fully as possible, even the fork leg / fairing opening was covered by a full rubber diaphragm. I don't know of any bike since that has made as much effort to seal off the back of the fairing, and it certainly has not been a feature of road racing bikes. (to be fair those things have all sorts of need for as much air as possible).
My guess on the advertising photo? Pure Madison Avenue. However one of my mates had the RS at the time, and its weather protection for the rider was first rate as long as you were moving. I think there may be been an oddity (and my memory on this is poor) about the back of the jacket getting the rain / spray more than the front.

Below is a photo of my XS 750 E with the La Parisienne fairing.

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IIRC, both the airhead RS and RT fairings included fork gaiters to block the flow from under the nose.

Zitat von Clifton im Beitrag #17

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Motorcycles have absolutely horrible aerodynamics.

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Zitat von Mr. 36654 im Beitrag #23

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1978 BMW Ad copy...…………..Sometimes, it's just a newer analysis tool, instead of increased knowledge.

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The Canadian website story contained a lot of verbiage and some nice pictures, but not much substance. The dustbins and Hans Muth's fairings were pretty much the best efforts of their day. Today, drag isn't an issue, excluding some concerns relative to buffeting in the separated flows.

How can that be? Well, you answered the my question with your question about the GSA. It's a barn door driving thru the air at 70-80 mph, much like the 4WD, 3/4-ton crew-cab pick-up, two lanes over. At the current prices for fuel, we don't care about these things.

I kind of expected someone to mention the 1990-1991 BMW K1. Kind of an ugly beast and it didn't seem to sell very well - which may give you an indication why we don't see more technical (as against visual) streamlining on production motorcycles.