Motorcycle aero question

[gowing]

The snow has started falling here in the Colorado Mountains and that has pushed me into working inside the shop for the next few months.
So I've been tinkering with the race bike.

Since the bike is mechanically ready to race (I was all set to run this year, but... stupid rain),
 I started looking at the aero - AGAIN.

I know that my bike can legally run a lot more bodywork than it currently has, so I picked up a Gen1 Busa body to possibly put on it.
Looking things over, the hayabusa fairing has a huge frontal area compared to what I currently have and that has me concerned.

My question is:
will the increase in the FA be offset by the reduction in side drag?

Here's my bike:



I have done a few things already ,
different levers, different wheels , moved the footpegs down and back a bit , modified the seat to get my ass up a little higher to flatten out my back.

Is a full body ALWAYS the fastest?

[Frank06]

The Gen 1 Hayabusa has an excellent fairing but I think it's impact is more measurable at higher speeds.  In 2006 Sport Rider magazine did a comparison between the ZX-12R and 'Busa and showed it's superior aerodynamics were mostly responsible for it's higher speed.  I strongly suspect a motorcycle with X amount of power would be faster with the 'Busa fairing than without, or with only a small handlebar fairing.  Especially if it would cover the cylinders and your forearms better.

[jacksoni]

The Gen 1 Hayabusa has an excellent fairing but I think it's impact is more measurable at higher speeds.  In 2006 Sport Rider magazine did a comparison between the ZX-12R and 'Busa and showed it's superior aerodynamics were mostly responsible for it's higher speed.  I strongly suspect a motorcycle with X amount of power would be faster with the 'Busa fairing than without, or with only a small handlebar fairing.  Especially if it would cover the cylinders and your forearms better.

The first sentence here is of course true for all circumstances as aero drag is proportional to V^2. As far as the rest of this  basic question, the only real way to tell, (particularly as there may be many small differences  (or large ones) between a given fairing on one bike and rider vs a different bike and rider,) is to test. Though I am a car guy I have talked a lot with a professional aerodynamacist about these sorts of situations and it always comes back to the same thing. You can't tell, you have to test it. And modeling this case for CFD I would consider mostly impossible. So Wind tunnel it is. (Or I guess down your lonely stretch of highway LOL) An example. I perceive generally with a car at LSR speeds most people think some rake is better. I guess it comes down to less lift in the rear perhaps which may be better in traction limited situations, vs the possibility or likelihood of increased overall drag. Which is better? Depends. And only way to tell is test it. My car had less drag level.

[Stainless1]

The answer is as Jack suggested.... unknown
However let's get a little more info... did you buy stock plastic fairing pieces or an aftermarket glass fairing... I ask because you may want to modify to fit your situation. 
Case pix below... all same bike, basically same tune, but the stock gsxr fairing went 184, the first modified 191 and the last modified 197.  Yes the modified bikes got a pipe and tune for that as well as lost the stock rear fender... but the point being the more you take advantage of the rules the faster you might go.  BTW as an A bike with a better front fender, a few more holes plugged and a little better tune it went 209... that's before long covered tails were allowed.

[RansomT]

One way to test that you can't do well with a car is listen (assuming the exhaust isn't terribly loud) .  With a given fairing and driver's position, how much wind sound do you hear?? ... adjust body position, now how much do you hear? ...change fairing and listen again.  A few seconds at 100 or so MPH is all you need.
A Gen 1 Busa with a cut tank and OEM fairing, can get really quite with the proper position.  An aftermarket fairing designed for LSR can get even more quite. Sealing up all the holes in the bottom of the OEM fairing helps, too.   Once you get the wind noise reduced, then work on the tail.. should be a smooth connected arc line down your back to the tip of the tail ... and be as long as allowed.

[TheBaron]

Hi Gowing,

I applaud your efforts so far, and I remember the 4-cyl 1000cc Gold wing quite well. It was crazy fast in its day.

I'm about to give you THE speed secret of motorcycle fairings ( that is almost never mentioned or understood).

Are you ready?

THE PURPOSE OF A RACING FAIRING IS TO STREAMLINE THE RIDER !!!! THE MAIN PURPOSE OF THE FAIRING SHAPE ON MODERN SUPERBIKES IS TO LOOK FAST!!

The best CD numbers I've seen on modern street superbikes is .561 for the Suzuki Hayabusa.

Our Race bike has a CD in the .410 to .418 range (without any tail aero)

Take a Marker Pen and trace your outline on the head-on photo and let that be your Fairing Outline at your location station.

Hints: turn the handle bars down (75-80 degrees) to get them inside the profile, and make tear drop blisters for the Cylinder heads as they should protrude outside the profile in order to minimize frontal area...

Testing: Determine the top speed "Naked" then with the fairing and you should be 15 mph faster (minimum).. If not, you have more work to do. We see 108 mph Naked and 124- 126 mph faired.

Check out our team site . It has Aero info in two different section that might prove useful.

Smitty

https://red-baron-racing.com/engineering/aerodynamics/

[Stainless1]

OK, now scroll back up and look at your head on again... it only looks like there is a small frontal area, it may be, but there are all those parts sticking out creating turbulence and drag... stopping air, not letting it go smoothly by.
Keep as much air as possible that was parted by the front wheel from swirling back under the bike and creating bad air for the rear wheel to go through.  Close as many vents and holes in the front as you can and still be able to keep the motor from overheating.   
Just my opinion... not necessarily that of the staff and management   

[gowing]

The replies are awesome, thank you gentlemen.

Logically I know that some slick full body fairing like a charlie toy is probably the best way to go for any LSR bike,
but then I see this motorcycle and think....
Hold on a second!


It's apparent to me that he concentrated his aero efforts on the problem areas and it obviously worked out well on this bike.

* there's a poster of this bike hanging out in the shop, I look at it quite a bit *
.

[Beairsto Racing]

This is a great discussion...
I love the Britten, but we are now comparing apples and oranges.
A road race bike needs to be light weight, start & stop quickly, change direction with little effort etc.
An LSR bike has only one purpose...to go fast and straight.

There's a reason why you see Harleys with Busa fairings...because it works.
But it's kind of boring, when you see yet another Hayabusa on the salt...and I mean no offense by that, I ran a couple of them for many years.
Part of the appeal of Bonneville, is the variety and ingenuity.

A look through Air Tech's LSR offerings and a chat with Kent, will put you on your own path...he supports our sport.

-Scott

[gowing]

There's a reason why you see Harleys with Busa fairings...because it works.
But it's kind of boring, when you see yet another Hayabusa on the salt...and I mean no offense by that, I ran a couple of them for many years.
Part of the appeal of Bonneville, is the variety and ingenuity.

Amen!

Stainless' post showing the evolution of aero on his Suzuki confirms it.

As probably most here, I've experimented with some of my own aerodynamic ideas in the past.
Only to find out that it's a lot more complicated than it looks.

Moving forward, the plan is to fab some mounts and get the busa body hanging on the bike.
Then evaluate and modify as needed.

[Stainless1]

You can turn this into your aero diary...  Keep us posted...