Welcome to the club
Hi Teri, welcome to a very small club – people actively trying to understand the aerodynamics of full bodied motorcycles. My own research has shown there to be very little genuine high-quality study in this area and your last comment - “ I wish I had a streamliner to test the theory out on” may prove to be the only way to really know.
I doubt that there is any company or academic institution worldwide currently undertaking serious research on the fundamentals of motorcycle stability through aerodynamics. This is primarily because there are no true full-body motorcycles currently in production other than the monotracer.
Think of all the superscooters and cruisers, which sport significant portions of bodywork and the manufacturers of those products, you would think aero research would be a well-trodden path.
The reasons that it is not are many and varied, but put simply; those people most interested in the subject are blessed with the least resources. Conversely, companies blessed with adequate resources, like the big-four Japanese manufacturers seem oblivious to the opportunities for enclosed motorcycles.
I have evaluated the options (for research), just as you have, and my thoughts are: that the time and expense of building a small scale wind tunnel would not be justified as the accuracy of results are unlikely to provide clear answers. So realistically it means testing at full scale and real-world conditions, ie build one and play.
Of course this testing method is not without hazards, as explained by Roger Dunkley in his aerobike blog.
AeroBike Enclosed Motorcycle
Those brave souls who have tried this method are fewer even than the bike builders. When I recall pictures of Craig Vetter and his tuft testing, I think this represents the most scientific published information. Despite Royce Creasey’s writing and theory I have yet to see similar basic testing methods employed.
It occurs to me while writing this, that tuft testing of a superscooter (with tufts on rider and rear of machine) would advance our knowledge greatly. The ideal test would involve images taken at high degree of lean and during strong sidewinds (maybe simultaneously) as well as the more traditional straight-ahead shots.
Anyway, back to your original question about forms of separation device. I’m a few months away from my own road testing and would be happy to try some of these ideas on your behalf. However, I feel that quantifying the effect of a device is the biggest obstacle, after all the “feel” of a vehicle is a highly subjective subject.
Just like you, I hope a well-informed discussion of this topic results from your opening post.