Motorcycle CFD Reduction Tips

[interested bystander]

    What it boils down too is:

    Penetration is ONLY good in the bedroom, right?


      (That OK, SSS?)

 

[donpearsall]

Ok Kent. Thank you. However I don't have the 2009 SCTA rulebook, just the 2008. That book's 7.G.11 bold print just specifies the visibility of the rider. So that does not apply do what we are talking about. What does the 2009 have to say about rear streamlining? Has it changed from 2008?

BTW, for those who don't know, there is a big difference in AMA vs SCTA rules. SCTA allows 8" of rear seat streamlining past the rear tire. However AMA does not allow ANYTHING past the rear tire. And I was there watching while some weeping riders were sawing off their tail sections in tech. inspection.

Don

[joea]

Don......you need a NEW rule book.......if interested
in SCTA rules.........which allow much more innovation
than AMA....and FIM........

hopefully ama /fim will again adopt SCTA rules so that
bikes prepared for one can easily run in the other.....

[jl222]

donpearsall:
"I think the reason for this is that the radiator is more drag than just the flat plate surface area of it. The air slows down quite a bit going through the fins, and then gets stagnant right behind the radiator."
---
Agreed. At high speed you would want a smaller inlet and use a shroud contoured to slow the air and recover air pressure. After the radiator you would want to split the air and contour an after-shroud to use pressure and heat to speed the air back up before dumping it out and back. Search through NACA engine cowlings and items like the P-51 oil radiator.

Once the air is fully turbulent the structure following is just added wetted area. The trick is delaying and reducing turbulence to keep the tail still somewhat usefull at reducing overall drag.

  We still can learn a lot from WWII tech. I believe it was the P-51s that got a net thrust from the airflow exit thru the various radiators.

   JL222

[interested bystander]

Re P-51s rads-

Colin Chapman reversed it with the successful Lotus 75 (?) M Andretti, driver.

DOWNFORCE w/ (some) thrust.

[Larry Forstall]

What can be done.This picture was taken after the record return run of 229 MPH on motor by Mark DeLuca. You can't see it but fiberglass panels enclose the front of the engine entirely (all the way up to the steering head). No radiator, the bike has a water tank over the swingarm. Ten MPH faster than factory bodywork. Oh, and the four men pictured have a combined speed on bikes of 960 MPH. If you eliminate me the slow N/A rider the average would be over 250 MPH.    Larry

[donpearsall]

More photos Larry!
Thanks for sharing
Don

[slopoke]

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[slopoke]

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[Seldom Seen Slim]

Back a few posts:

IB, why limit ourselves to the bedroom?

[WhizzbangK.C.]

Under AMA/BUB rules MPS (modified partial streamlined) bikes may not have rear streamlining extending past rear edge of rear tire.

 The rules for APS (special construction partial streamlining) are different.

 "Streamlining must not extend beyond the rear edge of the rear tire more than 8 inches. No streamlining beyond the rear axle is permitted to be lower than the top rim of the rear wheel."

Just trying to keep things straight between the rule books. There's a lot of misinformation around that seems cause confusion, at least for me  , when folks start talking rules between sanctioning bodies. 

[joea]

.......and they DIFFER GREATLY even more now with
respect to SCTA special contruction rules........

[narider]

What can be done.This picture was taken after the record return run of 229 MPH on motor by Mark DeLuca.

Larry, very nice of you to share that info. Thank you!
Todd

[Seldom Seen Slim]

Todd:

Take the hint and run with it, hey?

Jussi

[WhizzbangK.C.]

This is what we at Speed Team Doo have come up with for our XR500 racer. The engine is stock for now, with the exception of carb and exhaust.

We'd like to get some feedback from the aero folks here about how you think it'll work, since it's all based on SWAG at the moment. The only wind tunnel we have access to is the hot air blowing out the garage door during our bench racing sessions. 

So let us have it, good, bad, or indifferent, we're open for critique. 







We also have the option of installing the lower fairing seen here in mockup. We're not really sold on it being any improvement though, without side fairings running back to the rider's legs it just seems like an added layer of turbulence. The engine is not really any wider than the forks so adding the lower fairing may just add drag??