Aerodynamics-101

[OB_boneman]

The number is a valid point, and for the most part we never crunched any numbers with the exception of you FK. With a few more values that don't necessarily have to be at top speed you can pretty safely extrapolate beyond the top end. And you've done a splended job of being arrogant and touting like you know everything guru. Well done.

I still want to see some more data at both ends, it would be interesting.

 

[DaveO]

Animal,

Good info!!!!


Dave

 

[OB_BusaGeek]

Well actually the speed part is squared. The bike stop accelerating when the drag force equals the force provided by the engine. At a given speed, the busa's drag will be 8% less than the 12, at peak power, the force provided by the engine will be 7.45% less. That means that at any speed (at peak power), the busa will have .55% times the drag force more power to use to accelerate.
At top speed the drag force is equal to the engine force (minus losses). So, when the 12 stop running, the busa has about 1HP of power left to push it faster.
Animal, the squared thing means that the busa will not necessarily go .55% faster, just at the same speed have that much of an advantage.

Drag Force = Cd * Ea * Velocity^2

Cd=Drag Coefficient
Ea=Effective area

Above is from Engineering Mechanics book.

Note, These number are all derived from one test on one sample of each bike and FearsomeK's estimations. Take them with a HUGE grain of salt. The numbers may change, but the analysis is the same. This also matches most empirical tests (Magazine test rider drives really fast toward radar gun).

 

[OB_boneman]

Being an aerodynamacist myself those Cd's you quote, what "flight conditions" (if you will) were they taken at? Is that an average over a speed range, or the coefficient at top speed? I'd be interested in seeing a plot of Cd vs MPH and Cl vs MPH for each bike. Cl being the lift coefficient.

BTW - these are massive Drag Coefficients, fighter aircraft typically run 0.03 ish level flight at 0.6 mach. Cars are inbetween the two but still a good order of magnitude different than aircraft. Bikes are the dogs in this arena. But the plus side is the power to weight, we can outrun any fighter 0-120, after that they're airborne and gone.

 

[OB_BusaGeek]

To put this in perspective, a Hayabusa with a tucked rider is a little more aerodynamic than a 3-foot beach ball.


Really, motorcycles are that bad aerodynamically. Good thing we have the power to weight thing going for us.

 

[OB_boneman]

Once again FK shows his true lack of brain power and his need to prove his machismo.

And I quote, "Take out the obtrusive nozzle at the front of the 12 and the bike is MUCH sleeker."

Based on what analysis? Your intuition...doesn't hold water dude. Just because it looks good doesn't neccesarily mean that it performs well.

"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."

Again, based on what data, you have none. The only thing you got right was the placement of the duct in that location. It's there to capture the least "disturbed" airflow and gain the highest Cp while minimizing the losses that may occur if it were located farther back. At any rate, to get it right you'd need to have a diverter and/or stick that thing out past the front wheel for max performance. They would have never sold the bike had it looked like that though. But neither you nor I have seen a Pressure Coefficient profile to say either way.

"...Kawasaki have identified that the power gains with ram-air more than offset the aerodynamic losses of the nozzle protruding like that!!!!!"

Again based on what data? I contend that the increases in drag (if any) created by the snout are so insignificant compared to that of the scheme of things, i.e. the rider position etc, it doesn't matter, the Cd goes up almost a full tenth with the rider up, position is everything (that's huge). Same goes for the gains created by the ram air. I think Suzuki has that black art down pretty well since the gixxer750 top ended the R-1, ZX9r, and 929. (Motorcyclist). So don't go touting Kawi's prowess in that arena.

"Let's re-do that calculation:" Lets not, what a waste of bandwidth. Poor assumptions and incorrect assesments. I've seen the busa's read 163 at the rear wheel in stock form, I've seen them read 155. Same goes for the 12. You amaze me, it's almost as if you built the bike yourself and are defending your engineering feat.

"The 12 in stock form has the same if not better top end potential than the Busa" Gosh potential, well I'll step back and hold my breath.

Don't get me wrong, I like both bikes quite a bit, who wouldn't want either of them at 160ish at the rear wheel. Rock on! But frankly it comes down to personal taste. No way in god's green earth would you ever reach the potential of either bike. It's just braggin rights and you seem to be tied up in knots about. If we talk potential, lets say the 1300 was tuned to the 12.1 compression and reworked cams etc. put on 92+ octane fuel, I have no doubt it has the potential to kick arse, but why do that when it already does on an engine slightly detuned and more civilized.

Sorry 'bout that but I'm tired of FK's rants.
Wish UBB had individual kill lists.

 

[Guest]

Generally, an excellent thread......

The ZX12 is within 1 or 2 mph of the Busa in best top speeds....192-194...

To compensate for its less aerodynamic shape, it must be making significantly more power at its terminal velocity than the Busa....

Anyone care to figure out how much hp was needed to generate Muzzy's piped 199.1 mph run....192 stock I believe....

Anyway, I enjoyed this thread...Minimal bs and lots of technical analysis....

What two awesome machines we have to play with....and only for $10k +/-

 

[OB_BusaGeek]

I just ran accross a formula for that.


Needed HP=0.000069 * MPH^3 * Cd * Frontal Area

Using this formula, the 12 needs 197HP to reach 200MPH, the busa needs 182. I don't know how accurate the formulas are, but it sounds close.

As boneman brings up, maybe those Cd numbers weren't taken at top speed, data not given. It did mention 125MPH in one place. Cds are not constant in many real life cases.

 

[OB_Animal]

Sorry Boneman, that Volkswagen windtunnel's TOP air speed from the giant jet fan is 180 kilometers per hour so that's all they did (going lower no use of course) and apparently this is enough for them although they also have cars easily beating that????

 

[OB_FearsomeKawasaki]

112mph is no place to test the aero's of hyperbikes. This may be why the sportsbikes looked so good next to the 12 and the busa.

Both the shape of the busa and the 12 are sculpted for 170mph+ wind, where small eddy's at 112 can cause serious airflow problems at 190.

The mirrors and flow separators on the 12 will have negligable beneficial effect at 112. This speed is no test of the attributes of a Hyperbike, where they are wanting least resistance at 180+.

Those winglets on formula 1 cars have no beneficial effect whatsoever until 150+, which is why they are not used in some races where mph is not the priority. Same goes here.

So as a test of real world aero-efficiency and protection, the results are worthwhile.

As a test of the aero characteristics at hyperbike speeds, it's meaningless, as the features of the 12, and the Busa, will not result in any benefit until well in excess of 112mph.

So to say this proves the Busa has greater top end potential is logically unsound.

FK

 

[OB_Animal]

Tone and arguments are starting to sound very reasonable, FK, keep it up!

Not knowledgable in that field myself so I just absorb ALL info and draw my own conclusions based on what I see/read combined with some common sense.

 

[OB_THE MOTORHEAD]

HOW ACCURATE IS A WIND TUNNEL?SINCE THE OBJECT IS STATIONARY INSTEAD OF MOVING AND THE FAN CREATES A NON REALISTIC TURBULANT AIR?SHOULD'NT THE FAN ACTUALLY BE MOUNTED BEHIND AND SUCK THE AIR TOWARD THE MACHINE?SEEMS LIKE THE WHOLE THING IS BACKWARDS TO ME.

 

[OB_DangerMouse]

If Kawasaki paid so much attention to aerodynamics why did they go and stick standard indicators on the fairing? (which disrupt airflow) as for the winglets, I thought they were a stability aid no more.

 

[OB_Animal]

TMH, get into wind tunnel design a bit and you'll find out that they thought of this too!

It's really not just a big fan a couple of yards in front of the object tested but a huge complex/building with non-turbulent air in the passage where objects are mounted.

It's a specialized high-tech field of expertise that probably started from the airplane manufacturers but is now very common-ground for all modern car manufacturers since many years (don't know about US brands with their relative gas-guzzling and low fuel prices).

Can send you some scanned pics from the article that show more details about that windtunnel to give you some idea?

 

[OB_BusaGeek]

Motorhead,
I understand that is a real issue with high speed vehicles. Somewhere in France there is a 200MPH wind tunnel with a rolling floor. They use it to test trains. With a rolling floor, it pretty accurately simulates a vehicle moving relative to the ground and the associated drag and air disturbances. It also moves the wheels, the positive pressure at the top of the front tire from it rolling forward must have some detrimental effect. Stationary wind tunnels are for designed for aircraft.

 

[OB_ZX9RAY]

Well obviously the air intake on the zx12 works well otherwise why would Eureka vacuum cleaners have used them for so many years?? My contribution to science guys.

 

[OB_boneman]

Since you asked...

Motorhead, yes you are correct in your assumption about the tunnel(s). Some are what's called a blowdown tunnel, these have a big high pressure bottle of air blowing down the circuit, the test section (area where the model sits) is optimized to get the least turbulent flow possible. The amount of turbulence a test section sees is controlled by screens, vanes and the shape of the diffuser,etc.. NASA ames has a bunch of these in varying sizes. From tiny high mach blowdowns to massive low speed open/closed circuit tunnels where you can fit full size aircraft in them. A lot of cars and the like have been tested at these facilities. The closed circuit tunnels where they are actually on a "circuit", where air is flowed around large tubes like a racetrack (open circuit just pulls the air through a straight pipe, if you will). One side is the test section, the other a set of turbines. These are often pressurized and can simulate altitudes, AEDC (Arnold Engineering Development Center) which is where I worked quite a bit, has two massive ones, 16T and 16S, 16 meaning 16'x16' test section and the T meaning transonic M=0-1.5 and S meaning supersonic M=0-3.0ish, they haven't tested at that speed in a while, in fact X-33 was the last test I know about (and worked on) at 16S. You can visit their website for pics of tests they've done etc.
(their site looks down right now) http://www.arnold.af.mil/

Those tunnels have a lot of unique features, the main one being it's set up for jet-effects testing, where you can actually place a missle with a live engine in it "FFFire" as Beavis would say. Most tunnels aren't setup to do this. Models of aircraft will use high pressure air to simulate plume fields. This is how you accurately predict performance for vehicles. At any rate, the NASA Ames site is very informative, lots a great pics and information about the tunnels.... http://windtunnels.arc.nasa.gov/windtunnels/index.html

The Euro tunnels and scandanavian countries have facilities that are quite modern and nice to work at, most of ours were built 50 yrs ago, so they've been through the ringer.

Well I'm getting off track here...
Hope that helps a bit, let me know if you have any more questions, it's pretty fun work sometimes, othertimes it's pretty boring. Testing is always cool though.