Aerodynamics-101

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OB_Animal

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As promised, shortened (?) report of very extensive article in German Motorrad mag about their windtunnel test of some fine specimen of this years sport bikes.

They used the Volkswagen windtunnel located in Wolfsburg Germany and decided on the following bikes to represent the most important sports classes:
- MV Agusta F4 750S and Suzuki GSX-R 750
- Honda CBR900RR Fireblade and Yamaha YZF-R1
- Kawasaki ZX-12R and our beloved Hayabusa.

Measurements (calculations) were done of the following:
- Frontal area, bike only, rider prone, rider sitting-up
- Aerodynamic drag coefficient, rider prone, rider sitting-up
- Resulting Aerodynamic drag from multiplying above 2 values for prone/sitting-up
- HP needed to reach certain speeds prone/sitting-up
- Front wheel lift at 125 mph prone/sitting-up
- Rear wheel downforce at 125 mph prone/sitting-up.

As you can probably understand it's waaaaaaaaaaaaay too much data to put it all in here, but I'll mention some of the "highlights" according to my perception.

Frontal areas: Busa and ZX12 were of course biggest here but it's also very clear that protection comes into play here and that the percentual increase of the frontal area with rider added versus just the bike itself was a lot lower on these 2 compared to the others. Numbers in square meters with rider prone/sitting-up were .691 and .780 for Busa and .700 and .800 for ZX12 respectively.

Aerodynamic drag coefficient (how "slippery" are they) rider prone was .477 for Busa, .486 for GSXR750 and .510 for ZX12 and MV Agusta both.
With rider sitting-up the order changed to .540 for ZX12, .545 for Busa and .565 for both 750's.

Resulting aerodynamic drag rider prone was .326 for the MV750, .327 for GSXR750, .330 for Busa and .357 for ZX12, so Busa around 8% better than ZX12.
Same with rider sitting-up was .406 for MV750, .425 for Busa, .428 for GSXR750 and .432 for ZX12, so Busa around 1.5% better than ZX12.

The darn good values for both 750's explain why both of them reach such high topspeeds on relatively little HP, like in both of them only needing just under 90 RWHP for reaching 250 kph (say 156 mph) whereas ZX12 needs 97.6 RWHP for that same speed.

Looking at the ongoing Busa versus ZX12 topspeed wars it's interesting to know that to reach 300 kph (say 187 mph) Busa needs "only" 156.3 RWHP versus the 169.1 that the ZX12 needs to accomplish that.

And from averaging the stock RWHP numbers I've seen both privately as well as in a multitude of bike mags from at least 5 countries around the world for Busa versus ZX12 this confirms the fact that normally, all things being equal, the Busa will be faster on top-speed (not that this matters one iota to me personally).

Final interesting tidbits were the lift and downforce figures.
ZX12 had the most lift at the front wheel, especially very high with rider sitting-up, Busa was one but lowest rider prone and average sitting-up.
Busa was ridiculously low on rear wheel downforce with rider prone, ZX12 highest and with rider sitting-up this changed to Busa just below average but ZX12 still highest.

Motorrad concluded for Busa versus ZX12 that Busa was clearly darn good with aerodynamics but a little low on wind protection and the ZX12 disappointing in the aerodynamics but clearly offering better protection.
 
I suspected this. I figured the only way the 12 could be slower than the 'Busa even though it has more power -- is the aerodynamics. When Kawasaki introduced the 12, the most touted feature was the new aerodynamics, little wings and all. Even after a year of catch-up work, Kawasaki seems like they couldn't match the 'Busas slippery bodywork.

So, if it the big green thing isn't that shape for aerodynamic reasons (GSXR750 is more aerodynamic), why is it so butt ugly. For those who don't like the looks of the Hayabusa, at least it has an excuse --a .477 drag coefficient.

Thanks, good reading.
 
Boneman, I'm sorry but the average Busa has nothing like 163 at the rear, the average is c.155. We know it's putting out 175 at the crank compared to the 12's 181, so whether it's 155, 158, on average, it's six or so down on a 12. Christ, some 12's have dyno'd at 171 at the rear but it'd be ludicrous to claim that as meaningful.

I don't think anyone can argue with an average of 6hp difference.

Kawasaki claim 13hp for the ram air. Some other tuners evaluated it and estimated 12, which is the figure i used.

The Busa's ram air was estimated at 5hp when i had mine. I've seen another at 6 but many have said 3 or 4 at best. I used the highest figure for the Busa - 6hp.

This leaves us with 173 hp at full whack compared to 161 of the Busa. We can argue all day about specifics but the power difference is not going to be far off 12hp.

Is 12hp enough to offset the difference in drag when the busa has a proned rider and it's hump? Maybe, maybe not, but it's got to be close.

It also seems that the speed simulated was not anything like 200mph. At those speeds, I understand tiny differences and variations can result in significant changes in air flow. We know not of the benefits of the mirrors and flow separators at those speeds, so to look at this as the be all and end all is wrong.

My point in all of this is that those who used this to say because the Busa's more sleek with the rider proned this, in isolation, proves the Busa's faster. No mention was made of the power difference etc. If nothing more, this thread has proved just how close it is.

Fearsome.



[This message has been edited by FearsomeKawasaki (edited 10 August 2000).]
 
was the test done with the mirrors in place?

if the kaw makes more horse power than the bus (which most agree it does), does this conclude that the kaw may out accelerate the bus while the coeff. is not a limiting factor?

Certainly the bus will out tourque the kaw off the line but when in the upper ranges of hp the kaw should out accel the bus until the coeff. begins to limit this.

hats off to Suzie and Kaw for creating the most excitement in this class in a loooonnng while (and to the forum members for creating interesting drama/reading on a daily basis).
 
"...My 99 Busa dynoed at 162.8 horsepower today.We dynoed 4 different Busas today. By the way,my bike is totally stock..."



I think I can safely round up to 163.

Another quote..."We know not of the benefits of the mirrors and flow separators at those speeds, so to look at this as the be all and end all is wrong."....Yes we do, I don't recall him saying that those were removed when the Drag, area etc were calculated (they didn't perform a drag buildup, they tested the full vehicle). I'm sure the vg's have benefit just as the hump does. All things said the busa has a lower Cd. Fact.

What's your point, peak hp, or top speed, fit and finish, bang for the buck, smile factor? I'd say some of that is relative (some of us have lower standards than others and are willing to pay more for it.) but others are unquestionable. Personally I think the busa's motor has way more potential output, its not near as tweaked as the 12. CC's rule.
 
Guys, guys, sorry I left out some details.

That windtunnel can "blow" up to 180 kmh (112.5 mph) and that's the speed at which the Cw was measured/calculated.

Everything was in place on all the bikes (mirrors ... hump on Busa) and the same full size European (Germans don't come that small LOL) fully dressed in proper leather gear was on board, only thing removed from the bikes was the rear brake that was in the way on all of them because of how they were clamped down.

Hope that satisfies some of you guys' remarks?
 
Close but no cigar - the story of your life FK.

Blown out of the water again.

Kawasaki claims 12 [TWELVE] hp for their ramair - not 13. That is unverified so far. Get it right for a change.

Bad enough you leave piles of BS all over Lab.org - now you have to stink up the clean house too!

Thanks for posting the test results Animal. We knew what the results would be but undisputable scientific proof is always best.

[This message has been edited by Todd (edited 10 August 2000).]
 
Maybe this will finally lay to rest the myth about the ZX12 being slower than the Hayabusa because it is restricted (which its not)

It is as I've said from day 1, its because it simply isn't as aerodynamic
 
FUNDAMENTAL FLAW!

Take out the obtrusive nozzle at the front of the 12 and the bike is MUCH sleeker. The drag co's etc are close and without the nozzle at that critical area of the bike, the balance would swing the other way.

The ram-air duct is there for a reason, deliberately interupting the airflow AS FAR AS POSSIBLE. Kawasaki have identified that the power gains with ram-air more than offset the aerodynamic losses of the nozzle protruding like that!!!!!

Let's re-do that calculation:

To be fair on the busa, average 12 has just 6hp advantage at the rear end -161hp v's 155. Add to this the 12 hp gain from the ram - air estimated by independant testers (Kawasaki claim 13), you have total rwhp at top of 173.

Busa average of 155 at the rear (6hp down on the 12) plus estimated ram air gain of 5, no say 6 for the sake of fairness, although many estimate the gain to be no more than 3 or 4 hp (if you want your bike to be sleek, not much air can be afforded to be forced into the face of the bike afterall). That makes a total rwhp figure at top end of 161hp.

173 v's 161 means the 12 is pulling 7.45% on the Busa at top end. The article claims Drag Co of Busa (prone) v's 12 (prone) is 6.9% better.

So there you have it. Proof that:

a) The 12 in stock form has the same if not better top end potential than the Busa.

b) We know from the pictures in the silver book issued to 12 owners that the "pre-Feb agreement" 12R has had is timing retarded and that the stock engine, free of noise regulations, puts out 210hp at the crank still meeting all emmissions requirements (noise is a Euro problem so hell knows why you lot over in the states do not have 12's with more horses).

So thanks for that, we now know that kawasaki were right to go with the ram-air as the overall gain of power more than offsets the losses in aero efficiency.

Fearsome.
 
Fearsome,
If you are going to use power to drag ratio, use Effective area (.330 vs .357), not coefficient of drag. There the Busa wins by 8%, slightly more than offsetting the power difference. Also, yes more pressure in the ram air tube makes better ram air and more drag, but the ram air area of the front of the bike is a small part of the overall picture. One of the most important areas of being slick, is reducing a pressure drop behind the bike that sucks the bike backwards. The busa deals with that with the hump. That does not affect ram air efficiency. I think the 12 makes better ram air power because Kawasaki is just plain good at making ram air systems. They've proved it over and over again. Look at the idiot air box design on the Suzuki, how do you pressurize that?


End result, ZX12 loses, if they made a trade off of drag for power, they may have made a bad choice judging from the results.
 
Ya daft *******'* from ******stan, 112 mph!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Ha! what does this tell us, most of the aero features on the 12 don't even come into play at this speed.

This means the findings here are as relevant as Rottenegg's first run against my 12 at York!

As the guru said, "nuff said".

fearsome.
 
FS, Air resistance is squared against speed, 8% less drag at the kind of speeds we are talking about is worth a heck of a lot more than 8% more power.
 
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