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Rocket Science on Two Wheels
dstone writes "Tim Pickens, president of Orion Propulsion, the rocket design firm behind SpaceShipOne, has designed a bicycle-mounted 200-pound-thrust rocket engine that will allow a bicycle to accelerate from 0 to 60 mph in 5 seconds. From the article: 'The rocket bike employs the same hybrid rocket technology as the suborbital rocket plane SpaceShipOne, whose propulsion system Pickens helped design. [...] The engineer's next project is to build a company car: a pickup truck with a removable 2,000-pound-thrust rocket strapped into the bed.'"
How long does the fuel last for? 5 seconds? You couldn't carry a long time's worth of rocket fuel on a bike.
How good do you want your brakes? There's no point having brakes better than required to lock a wheel or lift the backend, and mid-price bicycle brakes are already plenty good enough to do that. The prerequisite for improving the stopping power of a bicycle is lower the centre of mass or to put more weight on it, especially at the back. After that, you can get disk brakes if you need them - these are commonly used on recumbents, particularly recumbentstrikes, and sometimes on tandems.
rockets are pretty poor at starting an object from a standstill, which is why motorbikes can easily beat this thing even though they are several times heavier. I thought up an allegory after reading a description of how a wider, slower flow helps low speed acceleration rather than an intense high powered flow - think of the difference between getting pushed (wider surface area) to getting stabbed (lower surface area which cuts straight through without much resistance). The rocket is better when the object is actually moving.
"Let me make it quite clear that a pulsejet is not the ideal means of powering a flying platform -- the effective conversion of thrust to horsepower at low speeds with a pulsejet is abysmal. What's needed to create a hovering/flying platform is a wide column of fairly slow moving air -- pulsejets create a very narrow column of extremely fast-moving air." "You can think of this as being like a car stuck in top gear -- very efficient when you're moving fast but not at all good for moving at low speeds or pulling away from a standing start" http://aardvark.co.nz/pjet/xplatform.shtml
I know that that article refers to vertical rather than horizontal thrust, but I think the same applies - if that rocket was being used to spin a turbine connected to some gears you could probably get a lot better acceleration from standstill..
which is totally what she said