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propane as fuel?

I am designing a top-secret device. However, i need to know whether i can use propane as its fuel source. i need enough thrust to lift a 120-pound weight (54.5 kg) about 3-5 in (roughly 6-11 cm) off the ground for a long time, until i turn it off or run out of fuel. I am wondering if propane is the best option for somebody who can not afford to spend a lot of money on expensive fuels. Also, can it work without any extra propellants, just air?

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gun4877 years ago
 The amount of propane needed to generate forces to hover something (120 lbs at that) would be large. the engine itself would be large also.  both propane and an engine weigh a lot so you must compensate and engineer a engine that could deliver more thrust while using less fuel, and is smaller. This is what all engineers do. More powerful, Less upkeep, And smaller. Difficult but not impossible you could Tell us what your building and people could help you with tips. Don't worry, we wont tell your mom.
I don't get it.  Can't you use like a stack of phone books, or a dictionary or something?  Maybe a cinder block? No fuel required.  It shouldn't take any work to just hold a weight some distance above the ground.
jeff-o7 years ago
Sounds cool.  I suppose propane could do it, if it were used to power a jet turbine.  It'll get mighty hot under that device though!  Be careful!
thegeniusdude (author)  jeff-o7 years ago
well, i don't mean it like that. my device is WAY too small for any jet turbines. i mean the direct force from a controlled propane explosion. i read on Wikipedia that when properly combusted, propane produces about 50 Megajoules/kilogram of energy.  would the combined force of four simultaneous controlled explosions be enough? and I will most likely use titanium as a heat shield, due to its low thermal conductivity.

I will trust you with a bit more information on my product. it is actually two separate but identical things which each have two combustion chambers. each explosion would have to lift a quarter of the weight.
.  Controlling and synchronizing individual explosions is probably going to be way beyond the resources you have available.
.  You might be able use four small rockets, but, once again, controlling/synching them is probably going to be prohibitively difficult for you.
.  I'd go with some type of ducted fan hovercraft design.
.  If you must use an explosive fuel, go with something with a lower vapor pressure (eg, gasoline or diesel).
You're not going to strap these to your hands and feet, are you?  If so, I'd like to nominate you for a Darwin award right now.

Have you done your calculations using f=ma and work(in J) = Newtons / meter?

(at least I think those are the ones you need).  There will probably be a fairly large inefficiency factor to include there as well, due to a lot of energy lost to heat.
It is theoretically possible that a device could be built using propane to generate the kind of thrust you need, but whether it's practically possible depends entirely on your design. Since it's top-secret, I'm afraid that theory is the best you're going to get.

So, here's a theory: Using a few gasoline-powered leaf blowers or lawn mower engines converted to propane, you could make a hovercraft that would lift 120 pounds a few inches. That would meet the criteria as you laid them out.