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Thread: I'm going to put a jet engine on a bicycle.

  1. #11
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    Would need a few of those for liftoff!!

    Anyone for cold thrusters on their non-Tesla car??

  2. #12
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    Quote Originally Posted by Dicknose View Post
    Jets + rockets are measured in thrust. They are generally constant force engines. You get the same acceleration at all speeds!!! 0-100, 100-200, 200-300 all the same. Ok the aero drag increases to offset this.
    The power then depends on the speed, the faster you go the more powerful.

    Internal combustion is best modelled as constant power (assume the average power thru the rev range that the gears allow).
    But this means that acceleration drops as speed increases.


    love the way we can count on GTXF to have a good concise explanation of things that would be a ten-page argument on lesser forums.

    I did a quick calc, I think 36lbs is 16kg which is approx 160N of thrust.
    If I'm right, it appears that you'll have about 1hp at 10mph, increasing proportionally with speed so 2hp at 20mph, up to 10hp at 100mph if you went that fast.

    Top speed will be whatever speed you have 160N of drag force at.

  3. #13
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    Quote Originally Posted by samoht View Post


    love the way we can count on GTXF to have a good concise explanation of things that would be a ten-page argument on lesser forums.

    I did a quick calc, I think 36lbs is 16kg which is approx 160N of thrust.
    If I'm right, it appears that you'll have about 1hp at 10mph, increasing proportionally with speed so 2hp at 20mph, up to 10hp at 100mph if you went that fast.

    Top speed will be whatever speed you have 160N of drag force at.
    Yeah it is 160Nm of thrust, hence why the engine is called the Cheetah 160. How much force is 160Nm of drag? This is all so puzzling.

  4. #14
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    Quote Originally Posted by Sad, little man View Post
    Yeah it is 160Nm of thrust, hence why the engine is called the Cheetah 160. How much force is 160Nm of drag? This is all so puzzling.
    https://www.exploratorium.edu/cyclin...dynamics1.html

    Putting in 78mph and zeros for the velocity and zeros for the other inputs, that outputs a drag of 159.9N.

    That's probably a lower-drag bicycle than yours, and doesn't account for rolling resistance. At a total guess, I'd say you should be able to get over 50mph, based on this. Probably worth pedalling it up to 20mph to get it going, then see what the jet can do.
    Suggest wearing motorbiking protective clothing if you're getting towards those sort of speeds.

  5. #15
    反重力 Rikadyn's Avatar
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    You should do two of them for balance...

  6. #16
    Corvette Enthusiast Kchrpm's Avatar
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    Quote Originally Posted by samoht View Post
    Suggest wearing motorbiking protective clothing if you're getting towards those sort of speeds.
    Definitely agree with this.
    Get that weak shit off my track

  7. #17
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    Yeah I will definitely wear more protective gear whenever I really wind it out. Only challenge is what do I do with it all when I want to go back to riding it as a bike, because no way am I going to pedal a bike in hot stuffy motorcycle gear.

  8. #18
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    Quote Originally Posted by Rikadyn View Post
    You should do two of them for balance...
    My bank account says no.

  9. #19
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    Drag numbers are hard to do without some experimentation.
    As long as you have an approx number, test it and get terminal speed and work backwards.

  10. #20
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    Quote Originally Posted by Sad, little man View Post
    Yeah it is 160Nm of thrust, hence why the engine is called the Cheetah 160. How much force is 160Nm of drag? This is all so puzzling.
    Being pedantic - in case you are doing calc or posting elsewhere...

    Thrust (force) should be in Newtons (N).
    Nm is a torque. Thats a force at a distance. Rotating stuff (like car engine) have torque. As do levers. When its applied via wheels it ends up back as a force.

    And just to be even more confusing, that dimensionally torque and energy are the same - Force * distance. But you should never use Joules as the unit!
    Force and distance are both vectors (have a direction). Energy is when the force and distance are in the same direction (or opposite direction).
    Torque is when the distance is at right angles to the force.

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