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

  1. #21
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    Quote Originally Posted by Dicknose View Post
    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.
    Yeah. Best experiment I could think of would be a coast-down test, pedal it up to a certain speed, stop pedalling and see what the speed each second thereafter. A phone app w/ GPS might possibly be accurate enough to do this and log it. Do it in both directions and you could potentially account for gradient and wind, assuming the latter remains fairly constant. A phone app connected to a sensor counting a magnet on the wheel would be more accurate tho.

    (Since the jet is yet to be attached).

    But yeah, super-hard to work out a theoretical calc for the pictured bicycle with you on it. I guess that racing bicycles are relatively well-modelled and thus reasonably representative figures are known, but this thing is a lot different from one of those

  2. #22
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    Quote Originally Posted by Dicknose View Post
    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.
    You know, that had never occurred to me. I'm totally doing my wheelnuts up to 50 kJ now!

  3. #23
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  4. #24
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    Just a little update. I was having trouble getting the little telemetry box to connect to the jet engine. The company sent me some replacement parts, and it turns out the fuel pump/electronics module was bad. So now I have the engine electronically up and running. I have not actually plumbed all the fuel lines into it and fired it up, but that will be next.

    The biggest technical hurdle in all of this was how I was going to control the throttle on the engine. Since it's designed for a radio controlled airplane, the fuel pump module is looking for a throttle signal from a radio control receiver. It's the same signal that an RC car uses for the throttle and steering servos if anyone is familiar with those. But luckily, there is a library for the Arduino that is specifically made to control servos. So I was able to use that to send the proper throttle signals to the electronics on the jet.

    I also managed to connect an e-bike throttle to the Arduino as an input. So ultimately, I'm going to have a standard twist grip throttle on my handlebars to control the jet engine, which I think is pretty cool. I have seen other people put jet engines on bikes before on YouTube, but they are all really hacked together installs with weird little knobs (servo testers) to control the jet. I didn't think it seemed very practical or safe to be fiddling around with a little knob while you're riding a jet bike. So I'm looking forward to having a nice clean install, and a twist grip throttle.

  5. #25
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    You're going to be famous/infamous.

  6. #26
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    Yes, we are witnessing the birth of Iron Little Man.

  7. #27
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    I spent a lot of the winter traveling, so I haven't had a ton of time to work on the jet engine. I did get it running on a little test stand I made for it, but shockingly it had some kind of problem, and seized up. I talked to the company and they were really good about it, despite both of us having no idea what happened, and they hooked me up with a new engine, so that's amazing.

    Ran the new engine on a test stand with no issues. While I was in Arizona over the winter a friend let me strap it onto the back of his late '70s Yamaha that had a blown engine. I pulled out the motorcycle engine and trans to lose some weight, and put the jet onto the luggage rack on the back. The weight of the motorcycle, even without the engine and trans, was a pretty formidable match for the little jet. However it did still move. The jet had a few fuel errors and kept shutting itself down, so I never really got to let it rip for a prolonged run on the motorcycle. I'm back home now and over the next few weeks I'm going to work towards putting it on my bike and hopefully figuring out the fuel issues. It uses a lot of fuel, so I think the problems may have been related to some restrictions in fuel flow somewhere.

  8. #28
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    I look forward to further updates.

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    Assuming more than expected fuel consumption means its burning too fuel rich, then maybe air not flow properly is the problem?

    Anyway, hope you can get it working because I'm sure we're all dying to see...

  10. #30
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    Jet engines control the throttle by just adding or removing fuel. I thought a lot about whether or not a jet engine can actually run "rich" or "lean" because effectively if you add fuel you are also adding air, because more combustion will make the turbine wheel spin faster, which is on the same shaft as the compressor that pulls air in, thereby adding more air. This was kind of a mind bender and it just made my head hurt. But now I think the potential for a jet to run rich or lean probably comes more from the overall design of the engine rather than how much fuel you're delivering. If it's designed right, I would think the compressor would be sized right and spin the right speed based on however much fuel is being burned.

    Anyway, here is the one video I took of the jet when I had it strapped onto an engine-less Yamaha in Arizona. I was really hoping for more speed since I really wanted to blast across the desert on a jet engine. I think I could have gotten some decent speed going if I could have kept it running longer. On this run, the ECU threw an error that it wasn't able to reach the desired RPM properly. You can hear I let off the throttle a few seconds before it died. I think I accelerated back up to full thrust too fast and it didn't like that. It's kinda weird to me how this thing is made to go in R/C planes and it seems like the default for any issue that it senses is to just totally shut down the engine. But, oh well.

    Also I was tucking my head down because I was watching the little telemetry screen that I stuck onto the fuel tank.

    You can also get a sense of how godawful loud this thing is. It really is shocking how much noise comes out of something this small.

    https://youtu.be/fhCEMEM__mo

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