[MadMax]

How about the older hurricane (1987~1989)? Not quite as rounded as the Kat but overall body flow is similar.

[FloridaKat]

So let's look at a different model of the physics....

There are really two types of drag happening to the Katana (or all vehicles for that matter). Induced and parasitic drag. Ok folks, let me explain.

Parasitic drag is the resultant of all the frictional forces created by the surface area (i.e. what can the air hang on to as it passes by). The larger the surface area......yep....you guessed it, the more parasitic drag. Induced drag is a result of flow over a shape. An airfoil (or as some call it a "rain drop") has been proven to be a highly effective aerodynamic shape. Since the sum of these two forces is factored into the drag coefficient, or Cd, you would likely want to minimize both. So, an airfoil shape with minimal frontal area and consistent vortex generators creating low pressure areas, strategically placed, is the optimum design.

Think of a modern day IndyCar. These cars generate sufficient downforce via the undertrays that the 1550 lb. car can stick to ceiling doing 80 mph. Magic? Hardly. Further, they angle their exhaust outlets to point toward the rear wings. This increases downforce on the back of the car, without the penalty of aerodynamic obstruction(s).

My own design thoughts? I would start with a less rigid fairing design that would proportionally shrink with speed. You'll reduce the induced drag. You'll also change the CG of the bike which may take some getting used to. The skins of our modern day F16 Falcons have a flex skin that does the same thing, thus allowing for tighter turns than conventional, rigid airframes.

[mod4]

Don't forget - the less drag an object produces the more lift it will develop - it's a linear relationship. When you are dealing with almost anything with wheels going fast, lift is a bad thing unless carefully controlled.

Just like Indy /F1 cars that have huge amounts of drag (cg's in the 50's) because that "drag" is actually downforce. You have to understand where the tradeoff occurs.

Take a look at a World Of Outlaw dirt SprintCar. they don't care a bit about drag.

BTW - this also is why Salt Flat vehicles aren't teardrop shaped - they have to keep the powered wheels on the ground.

[FloridaKat]

Don't forget - the less drag an object produces the more lift it will develop - it's a linear relationship.

If we we're exclusively talking about airfoils, I would agree. However, less drag on a vehicle does not necessarily equate to more lift. I could lower drag, but with some fancy moving of parts/weights and shift the CG, I could lower the drag without increasing lift.

[smileyman]

Bikes don't have to worry too much about lift since they are narrow and it is difficult to get air underneath.

Using airfoils to cut Induced drag is the ticket. Golf ball type dimples (ever wonder why they fly so far?)or NACA duct air managment even simple body contours or ridges. If you look closely at the '06 ZX14 they are everywhere. Front fender, mirror stalks, huge NACA ram air opening, side flairs, ect.


As for the bending shape to cut wind resistance or shrinking to reduce area, the Air Force doesn't have a monopoly anymore. NASCAR teams (I know bad word) discovered this in wind tunnel testing and "tune" the body for the aero properties they need. Ever watch a Monte Carlo or Taurus hood deflect and bend at 200 mph? Of course F1 has been at the front of all this in motorsports application, using it to aid downforce and cornering speed. Even to the point of on the fly aero adjustments (now illegal).

Bike makers and racers have played with it for years too. Honda teams have used golf ball dimples as early as with the CBR900 in '93 I believe, but more recently they were using clear adhesive strips with golf ball dimples at Daytona and Phillip Island to manage air properties...

[smileyman]

Oh and remember the Rhino fender used by some GP racers? Designed to streamline the nose and cut air out of the opening between the front fender and fairing nose.

Here is a pic I found of the ZX14 as example... The 'Busa also has ugly styling cues that aid aero...

[smileyman]

Here is a better veiw of those slim mirror stalks...You can also see how slim the profile is and how everything is tucked away

[mod4]

no offense - but the hoods on NASCARs aren't bending from air touching them - they are bending from the low pressure area produced by the nose underneith the hood. The air flow is several inches above the hood until it stacks at the bottom of the windshield. And the low pressure generated there (base of the windshield) is used to feed the motors air.

And, while I am being desagreeable .... back to an earlier post .... air flow over an item creates either downforce OR lift .... in the real world there is no neutral flow. So if you're not producing downforce, you are producing lift. From what I can find, most bikes produce less then 20lbs of lift at 100+ mph. Most of it seems to come from the rider, actually.
So in the real world (not Salt Flats) it's a non issue.

When you talk about Jets, it's useless to us. Sub-sonic and super sonic air characteristics are completely different. What we do, we need to learn from the DC-9, not the F-16. Once you go hypersonic, you deal with compressable flow, something no motorcycle will ever encounter.

Please don't take my tone as smart alec, I am learning from y'all, but this subject I've worked with a bit. Air does NOT act like you think it would
as far as adhearance and direction without a LOT of help.

[The CyberPoet]

I'm enjoying this thread (wheee!)...

Now to add more insult to injury:

Drag coefficients I stated above for motorcycles were, um, well, frankly understated.
Here are some concrete numbers (source: Cycle Canada magazine - Blown Away (wind tunnel testing) issue, Oct 2000 ):
Hayabusa - 0.561 Cd
Kawasaki ZX-12R - 0.603 Cd
'96 Honda RS125 GP Bike - 0.644 Cd
For comparison, a circular cylinder has a drag co-efficient of 1.2 (1.2 Cd).

The '98 GSX-R750 falls between the Hayabusa and ZX-12R in terms of total drag (not Cd, but CdA - the drag coefficient times the frontal area), inspite having substancially slimmer dimensions than either.
(source: http://www.qsl.net/n5mya/aero.html )

And Suzuki (at least as of '98/'99) claimed the hayabusa was the most aerodynamically efficient motorcycle on the mass market (in terms of absolute Cd), but also stated in their press releases that the primary reason for this wasn't specifically in how it opened the air envelope, but primarily how smoothly it closed the envelope, reducing the size and intensity of low-pressure area that forms behind most bikes/vehicles at speed (that low-pressure area acts as an anchor, producing rearward pull on the bike & rider).
Here's an image from their marketing materials of the time:


I'm curious what the total Cd will be for the ZX-14...

And now for the grin of the day:


Cheers,
=-= The CyberPoet

[smileyman]

Not offended but I do not believe I stated that NASCAR hood deflect from frontal air pressure. They are being sucked in from underneath but the laminar airflow over the deflected hood allows for better aero effect for the cars. There is a benefit, otherwise they would brace them accordingly.

And yes bikes (or bike/ rider) produce lift but not near to the effect as with a car. Less than 20 lbs lift for a bike/rider is not an issue compared to a car that is creating enough lift to have only approx. (can't find my old figures and stats) 40 lbs of downforce at each corner at 100 mph.

But as was stated earlier, we ain't at Bonneville.

I suppose the issue for those of us without windtunnel access is how many of us are willing to put up with ugly styling cues for the promise of better ultra hi speed aerodynamics? Styling is subjective and I don't think any of the above mentioned are really ugly (to me ugly is a full dress Harely or 'Wing).

Speaking of sonic and sub sonic flight, a little trivia...Can anyone guess which aircraft design was the first to come to grips with the air compressability problem? Hint Hint WW2? I will post back later with the answer.

[The CyberPoet]

But as was stated earlier, we ain't at Bonneville.

But drag factors into acceleration, gas mileage, and rider comfort (ever ride a bike that tugs you rearwards at highway speeds? if not, count yourself lucky)...

Speaking of sonic and sub sonic flight, a little trivia...Can anyone guess which aircraft design was the first to come to grips with the air compressability problem? Hint Hint WW2? I will post back later with the answer.

Which air compressability problem -- are we talking about the wing issue or the engine-feed issues for various engines?
For wings, I'm guessing your talking about the Messerschmitt (ME262) swept wing design, which actually originates in the earlier Pfeilfluegel II.
On the engine end, there are a host of aircraft that qualify, some dating to prior to WW2 as well (and the V1 buzz bomb with it's pulse-jet also plays games with air compressibility).

Cheers,
=-= The CyberPoet

[tzortn]

Bikes don't have to worry too much about lift since they are narrow and it is difficult to get air underneath.

Is this true? I would argue that when leaned over, especially at race speeds, lift becomes a major issue. That is why I make the comment earlier about drag not being the only measure of aerodynamic efficiency. Motorcycle land speed racers work great in a straight line. I would bet that making a turn is a whole other ball game.

[FloridaKat]

And, while I am being desagreeable .... back to an earlier post .... air flow over an item creates either downforce OR lift .... in the real world there is no neutral flow.

Uhmmmm...nope. I have added split deflectors to models in which you CAN add DRAG (not downforce) without compromising the lift vectors. I, too, have spent quite a bit of time studying flow dynamics (Floworks). Here's a real world example you can try. While in a car, put you arm out the window with your palms parallel to the ground. Now, twist your wrist 90 degrees so that your palm is now perpendicular to the ground. Feel the resistance? The lift component vector (in terms of magnitude) hasn't changed, but the drag has increased. If my palm was at any other angle but 90, then lift is directly proportional to the drag.

Hope I'm not trying to sound arguementative either.

Oh....Indycars and Champcars generate most of their downforce from the undertrays, not wings. They produce concentrated, low-pressure vortices flowing through the tunnels and exit at the rear of the vehicle. The dimensions are regulated and, as such, chassis manufacturers are constantly playing with the tunnel flow dynamics. The cars are literally "sucked" to the ground (not pushed by the air). Same premise as the hood deflection on a stock car.

[FloridaKat]

Speaking of sonic and sub sonic flight, a little trivia...Can anyone guess which aircraft design was the first to come to grips with the air compressability problem? Hint Hint WW2? I will post back later with the answer.

I know that some WWI planes had issues with the propellers not being tuned correctly and would cause excessive "pops" on each revolution. Does this qualify as an air compressibility problem?

[mod4]

I stand corrected

Great responses.

FloridaKat, you've clearly got more knowledge on this subject. I've messed with planes ( a little ) and racecars (a ****load) Formula 2000, Winged Sprints and pavement Late Models. But everything you have said rings true. So I'll hush and learn !

My race engines are built in Ocala, we need to hook up for a ride down there sometime, y'all have some great back roads there !