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jet packs Answered

Does anyone have any experience making a small jet pack, one which would power a skateboard?

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Goodhart (author)2008-04-17

"Starting it" may be the biggest challenge: not having it push the skateboard out from under you, for instance.....

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killerjackalope (author)Goodhart2008-04-17

Not really, ou could either lean forward or it the propulsion is controllable just go up in power slowly, honestly once I get my money and pipes I'll be able to tell you exactly how hard the jet amagigs are to control. Also if you jump with a wheeled object that has a from of rocket or jet propulsion does it seem reasonable that it would just fly for some distance? This is a safety question for my sake, it's my one worry, that and the fact that as of yet I havn't made an effective killswitch yet...

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thejrb (author)killerjackalope2008-04-20

Kind of like a grenade theres a pin in the engine you hold on to a string attached to the pin when you yank the string pin pops out engine stops.

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killerjackalope (author)thejrb2008-04-20

Yeah, a rocket however would be hard to stop...

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thejrb (author)killerjackalope2008-04-22

Where did I mention a rocket?

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killerjackalope (author)thejrb2008-04-22

my mistake kiteman did...

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user

. I think the problem would lay in modulating the power of a DIY rocket. They tend to be all or nothing without sophisticated (ie, expensive) controls. . . hmmmm I don't think you will "fly," but it will add to the distance. If your shoes lose traction on the board, it's liable to start traveling faster than you are. . A normally-closed (NC) solenoid-operated valve (SOV) should make a great kill "switch."

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user

My project is a different one, by fly I mean continue to accerate in the air... Hmm maybe I'll just have a nice steel flip toggle operating a solenoid operated valve, I just don't have one, my other option is a simple valve mounted on the controls that cuts off all fuel, of course the engine design means I could have a couple of valves on the engine that open to break the jet cycle and cause the engine to quit... really I want simple, I'm thinking of just using an electric fuel pump and have a master switch for that... Also my project should be quite green, in the sense that it'll burn clean fuel thoroughly and not much fuel being used, on the other hand it may gobble fuel like pacman gobbles pills on a saturday night...

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user

> continue to accerate in the air
. If the thrust is greater than your air resistance, you will accelerate. If you were accelerating when you hit the ramp (air resistance + wheel friction), you'll probably be accelerating in the air. Come to think of it, the board's acceleration in air will be greater (loss of wheel friction) so it may try to jump out from under you.
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> flip toggle
. I'd go with a fail-safe/dead-man setup: NO pushbutton and NC valve (or a pump). If you let go of the button, it dies. In case you get knocked out and don't want to do high-speed break dancing.
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> valve mounted on the controls
. To lessen the amount of fuel that has to be burnt away, mount the valve as close to the engine as possible. Same with a pump.
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> Also my project should be quite green
. Running a lean mixture will help reduce unburned hydrocarbons, but boosts NOx production and may cause excessive chamber temperature. The only way I know to reduce emissions is by "scrubbing" the exhaust (eg, catalytic converter) - probably not a viable solution.

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user

Ermm you didn't pay attention to the first bit, I have no intentions of making a board object, I just had a little cause for concern were I to leave the ground... My plan was a master on for the pump and a safety peg like you have on running machines, if you fall off the bracelet pull the peg out and cuts power.... I can run a very lean mixture once I get the big engines built up and finished, that and the chamber temperatures are not a big worry... then engine doens't run hot enough to damage itself, except over time but it's enevitable either way... I'm not sure how well it'll fare in terms of fuel economy after some thought, it really depends on what full power turns out to be, if it's good then I'll use less fuel being able to run lower throttle... If I was a very good boy I could always have a set of platinum screens throughout the exhaust, just to be enviro happy...

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user

. Well, if you have enough thrust to get off the ground at all, you will accelerate until you throttle back, or atmospheric O2 limits your power output, or you run out of fuel.

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Now I meant more due to terrain changes and whatnot, though with enough thrust and perfect balancing it could be possible to do something similar to gliding based on forward momentum being greater than gravity, so you lose height slow and whatnot, I'm away to find a cliff...

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. Since you'll only be able to carry a few seconds worth of fuel, I don't think terrain changes are going to be a problem. . Think of lift and travel as perpendicular vectors. If you are hovering (zero travel) and want to travel, you angle your thrust. Since some of the thrust is going to travel, you'll have to apply more throttle to maintain height. Basic physics.

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I know that, it's more the idea that greater heights could be come from... For the last time I'm not using a rocket or a board nacho... I will be carrying more than a few seconds of fuel, more like around five minutes or more, Granted I don't plan on leaving the ground I'd just like to have en idea what happens if I do...

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user

. Well then, what ARE you doing? You ask for help/opinions, yet you beat around the bush when it comes to details.

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my projects shrouded in mystery for a reason... I didn't start the thread, just commented on it then it occured to me I may have to worry about something and asked, you answered and I helped but you kept coming back to the board which isn't my plan... Thanks for answering my questions, sorry about the strange things, I refues to unveil it until it works...

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Goodhart (author)killerjackalope2008-04-17

It will have to be either limited in power (or else leaning forward will be like spitting into the wind :-), or as you said, you will have to have quite a gradual control on it (and you will STILL have to lean forward ;-)

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killerjackalope (author)Goodhart2008-04-17

Or you could sit down, which would probably increase the thrils being that close to the ground is fun at speed...

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Goodhart (author)killerjackalope2008-04-17

Yep, that is what Sledding was all about on really long steep hills :-) Still, I would want a wider wheel base if I were riding at any speed

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mburton (author)2008-04-17

This project is for a school science fair. It will be an unmanned craft, and will not (I think) leave the ground. Seems like tha main problems are the start mechanism, the kill switch and the catalyst. Anyone have any ideas? Thanks...

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killerjackalope (author)2008-04-16

Working on it right now, after pocket jet engine, I and a few others have been building mini jet engines, well I'm working on bigger ones, a skateboard would go fast with one of these on it, I have different plans...

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mburton (author)killerjackalope2008-04-17

Thanks for the reply. Do you have any specifics on materials? Looking for small-scale items, 1 tank for liquid nitrogen, 1 tank for hydrogen peroxide. How does the catalyst work? Any help would be great....

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killerjackalope (author)mburton2008-04-17

Ok I was talking about a jet engine, I didn't realise you wanted to make a rocket board, that sounds damn cool, I can't remember catalysts off the top of my head but will have a check. I think pound for pound the rocket would have more thrust but the jet engine would have longer running time and would probably be more durable...

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Kiteman (author)killerjackalope2008-04-17

The usual catalyst for H2O2 rockets is hot (600oC) silver.

It has to be pre-heated before use, but the decomposition reaction is exothermic and maintains the temperature after that.

For a small rocket pack, that's all you need (apart from pressurisation tanks and valves and what-not). When peroxide was (is?) used for large-scale rocketry (the old British space-programme was designed around peroxide motors), they sometimes injected additional fuel (into the motor after the catalyst. The fuel reacted with the oxygen in the rocket plume to produce extra thrust.

This site seems quite knowledgeable on the subject.

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Kiteman (author)Kiteman2008-04-17

Oh, be very careful with concentrated peroxide - any contamination (especially organic matter) can kick off the reaction leading to a violent, potentially explosive chain reaction.

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killerjackalope (author)Kiteman2008-04-17

I still think a jet engine is a better bet, both get hot anyway but it has way less chance of blowing up, especially if it's running on liquid fuels, bog standard petrol is flammable but not explosive in liquid form, it can be made in to gas by the engine's properties saving you the worry of massive explosisions caused by peeing in the peroxide bucket by accident... Organic matter and whatnot, better hope it wasn't twosies... also a bucket of hydrogen peroxide seems like an ominous prospect aswell...

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