Russ writes – “For many years now, I have tinkered with all kinds of interesting projects, and have found a lot of fun in the realm of DIY gas turbine engines. These engines are based around turbochargers, but are in every sense real jets. They produce considerable thrust, and can even be used with afterburners. While I have been tinkering with one of these with a friend of mine, we debated on what kind of vehicle to put it on for testing. He suggested a small boat or a go cart. My theory was that if you really wanted to test out the speed of one of these, you would need a good long stretch of road. That being the case I thought it best to put the engine into a street legal frame. This is where the YSR came into my head. Firstly, a motorcycle would be perfect, as it is street legal, easily registered, and also has very little friction from the tires and wind drag.” Link.
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Quote: Firstly, a motorcycle would be perfect, as it … has very little friction from the tires and wind drag.
Friction has both advantages and disadvantages. While we are in motion, friction tries to slow us down. But, it also allows us to grip the surface, so that we can start moving and increase our speed. Because motorcylces have low friction, they are not able to grip the road properly. This means that the motorcycle will not be able to use the full power of jet engine. In fact, in a test between an F1 car and a motorcycle shown on Top Gear, the motorcycle lost despite its initial lead. Thats because, it was unable to grip the road and use its power to the fullest. Also, because of low friction, the motorcycle did an involuntary wheelie.
Actually, motorcycles have about the same traction as high performance cars, where traction is a function of vehicle weight, contact patch, tire stickiness, etc. Motorcycles tend to accelerate as fast or faster than the fastest cars, but can’t reach the same speeds because their high speed aerodynamics suck compared to cars. The bike will jump ahead coming out of turns, but on any long straight, the car will catch up and pass him.
As for the wheelie, that has nothing to do with inadequate traction. If anything, you could argue that the rear tire has a little too much traction (but you need that traction at high speeds, so you really wouldn’t). The rear tire has enough traction to apply enough torque to the whole frame of the bike to lift the front of the bike (and the rider) off the ground instead of spinning out. That’s a LOT of traction.
As to friction (and energy losses to friction), you’re really only paying attention to two kinds: wheel to pavement and wind resistance. The motorcycle always has less wheel to pavement friction than a car. The wind resistance will start much lower, but at high speeds, a well-designed motorcycle will have more wind reistance than a well-designed car. The exact speed of the inflection point depends on the aerodynamic coefficients and front cross section of the two vehicles, but would probably be in the range 120-150mph for an F1 to R1 comparison.
To the guy who commented on friction. Tire to ground friction means NOTHING in a thrust powered application. It requires ZERO traction to move, as the power for motion is through the air, not the wheels. The friction described in the article is talking about the rolling friction of the wheels and bearings that would need to be overcome.
Wheelies are a result of torque at the rear wheel only. Because there is ZERO torque applied to the wheels, this would NEVER happen.
Now, of this was a turboSHAFT application, where a shaft is attached to the turbine to drive the wheels (like in a helicopter, not an airplane) THEN we would need to discuss the friction between the ground and wheels.
Either way, a motorcycle is a bit cheaper than an F1, and would be your best anyways, for portability, easy of adaption, and cost. Try registering an F1 for street use…