Quote:
Originally Posted by sendler
The goal is 100 mpgUS lifetime and 100 mph air speed capable.
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Well. I could get 60+ mpg on a unmodified 700cc street ride, but only at about 45 mph in top gear. The trick was to ride as slow as possible in top gear, without lugging the engine. So I think 100 mpg on a smaller displacement bike is achievable without a lot of modification, if that is your only goal. I don't normally ride like that, but I have on couple of occasions done it at night when I was low on fuel in rather remote and desolate places, far from any open gas station.
You would probably want narrow, very hard, high-pressure tires to minimize rolling resistance - maybe racing slicks (no tread.) Maybe even solid rubber tires. So you might want to look only at bikes that have the same wheel size as available racing slick tire. And you might want to fill them with nitrogen instead of air. If you do that, don't ride in the rain.
Reaching 100 mph on a small engine will require a very efficient fairing, and likely wind tunnel testing, as aerodynamic drag force increases as the square of the velocity. This might be much harder to achieve than getting 100mpg at slower speeds. The honest sustainable top speed on my un-faired 700cc ride was only about 95mph. Of course, I could go faster than that down hill, or with a strong wind at my back.
I think you might want an aerodynamic consultant like Burt Rutan, or at least look at his work, and maybe write him for ideas. A few decades or so ago, when I was still an active airplane pilot, He designed and built a 20 hp airplane that could fly a single person at 100 mph and get around 100 mpg. Burt Rutan is a genius, and I don't know that anyone has duplicated that, so it is not such an easy thing to do. Somebody may still sell his kit, If you could get one of his fuselages without any wings, maybe you could stuff a small motorcycle inside it
If you are designing your own, I'd go for the ultra-reclined position to minimize frontal area. For a long ride, that would be far more comfortable that the tucked-in, crouched position motorcycle racers use.
If you are going to design and build your own fairing, you might also want to consider "dimpling" the surface, as on a golf ball, rather than a smooth surface. I think Mythbusters (on TV) did some half-assed testing on that concept.
Sounds like an interesting project for a group of aeronautical engineering students.