Minimizing drag at 140mph+

[gumby79]

5.2.12 No streamlining may be attached to the rider.

..... this makes my prvious tail/butt fairing useable, unless it is attached to the tail of the bike.

5.2.12.A. All fairings must be made of plastic, fiberglass or carbon fiber.

.... Theas are the materials you can use for your mods. Except parts associated with drake cooling and wind deflectors.

5.2.11 Fairings must be mounted in at least three locations. The front wheel
must be clearly visible from both sides except for the portion covered by the fender. The rider must be visible from the side and above, while in a normal riding position, and transparent material may not be used to allow for such visibility.

....I read this to mean the entire front wheel/tire can be covered by a 1pice finnder

5.2.4.C. Aftermarket brake cooling ducts or wind deflectors may be made of metal providing the design does not pose a safety risk to any competitor.
Final approval of unit rests with the Tech Inspector. (each and evry race)

A 1 pice finnder would combine both 5.2.11 and 5.2.4.c

5.2.10 Rear fender or seat must extend to the rear of a line drawn vertically at
the rear axle.

They state a minimum... no maximum. Added length is a compromise between reduced aerodynamic drag and increased Rolling Resistance coefficients. Use Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com to figure out how far you can go and see a benefit.
Gumby Stay Flexible.

[seifrob]

Originally Posted by jakehammer2000

Is this one available as a transparent overlay? I am only finding the side view

In tool "aerodynamic template overlay" select "Template #2" in point 4 of upper table. You should see it.

[Michael Moore]

Harley XR750 long-track fairing with custom large/shallow taper seat:







The HD and Norton JPN fairing are the main "classic" RR fairings that I know of that were wind tunnel tested instead of styled. The HD was done by the Wixom brothers in the CalTech tunnel and I think the Norton at MIRA.



A 13" wide seat like that on the red bike (shown is a 15" seat) added 500 RPM in top gear to a pretty stock CB125 Honda engined bike and was good with tuft testing at freeway speeds. That bike had about 7-8 hp. Most rider's butts are 15+" wide and the seat should match the rider and fill in behind the legs to give a smoother outer surface.

Here's a photo of the last version of my Laverda F750 racer with HD fairing and big seat (not the same as the "big butt" HD seat):



The back of the bike is more important than the front, and remember that the bodywork is there to streamline the rider NOT the bike. Unless you've got a CBX or a Boss Hoss the rider is the wide part of the combo.

Most rule books I've seen exempt the hands and forearms from the "rider must be visible from the side/top" rule.

If you look in this folder on my website

Index of /graphics/aero

you'll find a scan of an article (Free Speed) comparing 1970s RR fairings, including the Norton and HD.

Try to find a copy (used only available at this time) of John Bradley's "The Racing Motorcycle, Vol 1" as it has a lot of good info on RR streamlining including the wind tunnel runs on the Can Am LSR bike.

The trend in modern bikes seems to be to lower the top of the tank to make the rider's back more horizontal. Of course, that can make it difficult for the rider to see where they are going if they can't tilt their head back far enough.

cheers,
Michael

[California98Civic]

Those are good Michael Moore!

[Frank]

Typical land speed front fender, supposedly good for 2-3 mph:

[seifrob]

Can you relocate your exhaust above rear wheel to fill the wake?

[Grant-53]

Good stuff. Some organizations limit the height of the tail box so you might want to check into that. If your back is horizontal with a slight curve, be sure there is no gap between you and the tail. A top view should look like a teardrop to minimize air flow separation. One trick we use on our pedal bikes is to streamline the spokes on the front wheel and use smooth disk wheel covers on the rear.

[Frank]

Something else to consider is whether or not you can get adequate leverage on the bars/clip-ons if you move them inboard. You might have to move the master cylinder inboard of the clamp or something similar, but that mod allows you to get your elbows out of the windstream some more. Also, consider running some duct tape around the top of your boots.

[Michael Moore]

On my 216cc Honda vintage racer I made the bars very steep and narrow to encourage me to stay on the tank (the only time they were comfortable) as much as possible.







It ended up with a fairing that was sort of a 7/8 scale version of the HD long track part. A long Seeley aluminum fender never got installed on the bike before I moved on to other projects:

[CoClimber]

I did a bit of research and some fluid dynamic work when I was building my land speed racing moped. It is my belief that you want to do as much as you can to reattach the air behind you to minimize the vacuum. The attached photo isn't the final result but you get the idea. I was not able to get any wind tunnel testing but the bike holds the record for being the fastest 50cc motorcycle to run at the Ohio Mile. It is a 1977 Puch single speed moped so I suspect the aero had to help. The rear section starts out as the width of my butt and tapers as much as possible without the air separating then is chopped flat as per the rules pertaining to how far back the aero may extend.