engineering my second recumbent motorbike

[redyaris]

Grant-53 The moment you mentioned using down force on the front wheel i thought that sounds like a good idea why didn't I think of that? so thanks I will look into that idea some more.

[Grant-53]

It helps to live within 50 miles of the National Soaring Museum, the Glenn Curtiss Museum, and the International Motorsport Library at Watkins Glen, NY...
As for the long tail vs Kamm back, the surface drag of a long tail is more than offset by the reduction in drag induced by turbulence and separation. There are lots of good books and articles available that explain this in detail. I use my old college text on fluid mechanics and Dr. Joseph Katz's book "Race Car Aerodynamics: Designing for Speed".
The interactions with side wind and the lean angle of a faired recumbent will take a good bit of thought and testing to optimize. Some air will go under and some will spill over the top. Reduce side drag and try to minimize lift, again rounder on the bottom and flatter on top. My boys want a home made wind tunnel for a science project and I have some models to test. My fairings on an upright bike come only to the knee and are round cones at present. Cross winds have had little effect.

[Bicycle Bob]

Thanks, Grant. The VW 1L is truncated for compactness, not drag.

Another way to reduce side force is to just arrange for vent flaps to open, defeating any pressure differential. It is unfortunate, but as long as the air stays attached, you can get an actual boost from a side wind, but if you have to spill it to reduce side force, even the drag goes up.

[redyaris]

AMDparts In looking at your yellow recumbent bike I see one area you have neglected and that is the underside of the bike beween the wheels. What I have done on my bikes; and recomend you do is to install a underbody that goes from close behind the front wheel to the centerstand then cover the underside of the centerstand. this may improve FE by 5%. I use 2mm aluminium for my street bikes and 3mm aluminium for my duelsport bikes.

[Bicycle Bob]

Originally Posted by redyaris

Grant-53 The moment you mentioned using down force on the front wheel i thought that sounds like a good idea why didn't I think of that? so thanks I will look into that idea some more.

The trouble with wings on a tilting vehicle is that they wind up pushing you to the outside of a turn. Downforce affects traction, but won't help with basic directional stability.

[AMDparts]

hi redyaris, i've done that this week. the bottomside of the frame is covered with 1.8mm PMMA plating. a cheap way of cover and with some heat you can form it the way you want it.

the bottom of the nose has had a cover also , and the sides of the nose too. those forms i'm making better at the moment. i think it's working quit well, my fuel-log wil show it soon...........

[redyaris]

Originally Posted by Bicycle Bob

The trouble with wings on a tilting vehicle is that they wind up pushing you to the outside of a turn. Downforce affects traction, but won't help with basic directional stability.

I do agree that wings are a problem for single track vehicles, however BMW does add down force on the front wheel of the 1988 - 1993 K1 to counter-act the pitch moment that reduces the down force on the front wheel of most motorcycle as speed goes up. The fairing of the K1 is designed to add a messured amont of down force on the front wheel. The K1 fairing is one of the few that was developed with aerodynamics in mind, and in fact it has one of the lowest drag coefficiants of any production bike [see chapter 10 of Hucho]. If I am not mistaken Hucho also mentions that some down force on the front wheel can in fact help basic directional stability. Motorcycle aerodynamic design is alway problematic in that ...some may be good but more may not be better..., I suspect that this is the case with downforce on the front wheel. Although some work has been done to generate downforce on the wheels of a racing motorcycle, to incrrease traction and cornering speed, the systems proved to be overly complex and no one has ever gone beyond the prototype stage.