Jet Bicycle

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simwalsh
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Joined: Sun Nov 02, 2008 1:10 pm

Jet Bicycle

Post by simwalsh » Sun Nov 02, 2008 1:26 pm

Hi Guys,

I'm new here.

I'd like some advice from you about adding a jet to a bicycle. what kind of thrust would i need and can i run it on petrol (gasoline)? is there a specific type of engine that would suit the bicycle application best?
what kind of starting options do i have? would i need to bring around a air pump?

Thanks in Advance

Sim

larry cottrill
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Re: Jet Bicycle

Post by larry cottrill » Tue Nov 04, 2008 2:14 pm

Sim -

What you want is doable. It is also fraught with problems. I'll attach a white paper you can download; don't be put off by the fact that it's specifically written for model vehicles -- most of the problems covered will be applicable to what you want to do. In general, this kind of effort is interesting but will probably be disappointing in terms of performance. Such a vehicle WILL amaze your friends -- but probably just because of the heat and noise generated.

Practically speaking, you will probably need to carry a spark source and an air pump. However, if your engine is well designed and built, the air supply requirement will be minimal -- once you're used to starting your engine, you'll probably find that an ordinary bike tire pump will do what you need. I would not get rid of the petals and sprocket set, since there is always the chance that you will not be able to re-start an engine that has stopped.

You should mount your engine as low as possible while still providing reasonable ground clearance, and you should get it tucked in as close to the bike centerline as you can, or you will have balancing and control problems. Remember that pulsejets are lightweight, BUT they are bulky! To be practical, the minimum size would be around 20 lb thrust, and that is a pretty good size engine, possibly a meter or more in length, depending on the design. Of course, I like valveless engines, but a valved engine will be less bulky for the power obtained. Also, even with an engine this size, hill climbing will be ridiculous to impossible, AND fast acceleration from a standing start will not be achieved. (These are not a matter of design, they are limitations imposed by the laws of physics.) Note that the close-in engine mounting requirement means you will need GOOD heat shielding (sheet aluminum is perfect) to prevent melting through tire sidewalls and singing pantlegs, etc.

If you use propane fuel, one more thing needs to be mentioned: You MUST have an instant-shutoff valve for safety (like a "dead man throttle"), not just in case of the rider losing hold of the bike, but also because of the possibility for full-power flameout, which leaves you with a HUGE flow of burning propane that billows uncontrollably from the engine rear end AND intake. This can get very dangerous very quickly, especially if there is a breeze from behind you, and you need a good way of shutting down fuel flow completely and instantaneously when (not if) this occurs.

Another problem to consider is this: Starting and running your pulsejet takes practice; it isn't like a piston mill that you just turn the key to start up and it runs reliably every time down the chute. Starting technique especially can be affected by changes in air temperature and humidity. Some experimentation required.

L Cottrill
Attachments
Pulsejet_Model_Vehicle.pdf
Pulsejet Model Vehicle white paper Copyright 2008 Larry Cottrill
(276.81 KiB) Downloaded 461 times

TigerToothBikes.com
Posts: 1
Joined: Fri Apr 03, 2009 3:56 pm

Re: Jet Bicycle

Post by TigerToothBikes.com » Fri Apr 03, 2009 4:44 pm

Hi,

We are attempting exactly that, here's a preliminary CAD design. The end result will undoubtably differ from that shown....

Image
Attachments
Jet Promo.jpg

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