HELP!

Jets that defy normal classification

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jtj12358
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HELP!

Post by jtj12358 » Tue Mar 10, 2009 7:19 am

im not sure exactly what i am looking for, but i'm trying to research information on building jet engine's, which do not use fuel. im interested in an engine that run's off of electricity probably using a motor instead of a propellant, the design will most likely be, between a ram jet and / or turbo jet. im not sure the best way to go about designing such a jet. but what id like to do with this is to make a model, and use solar power to power the jet., and see if its possible to create any usable lift with it, i understand that the energy required to generate the rpms necessary is ridiculous but if its possible in theory it would be an engine that would never need to refuel , i think a prop. engine is simpler to design but. jet engines are more efficient any help or direction in finding information on this would be greatly appreciated

larry cottrill
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Re: HELP!

Post by larry cottrill » Tue Mar 10, 2009 12:47 pm

jtj -

I have been interested for some time is ramjets that get their heat externally. This is difficult in terms of what is called "thermal efficiency" because it's so hard to get enough heat to cause enough expansion to drive the jet action. Be aware that a jet powerplant is only "more efficient" at relatively high propulsion speeds -- this is in line with laws of physics, NOT the features of this or that particular design.

In order to achieve the gas expansion needed, extremely high heat input is required. Remember that the expanded gas (air) leaves the engine in a hurry, and has to be replaced with incoming cold air that in turn has to be rapidly heated.

To make a ramjet that runs on the ground, you apply a ducted fan to the front end, ending up with what is called a "motor jet"; so that's really what I'm referring to from here on. Obviously, you could come up with a motorized fan that is solar powered, so that part is theoretically taken care of. Now, there is one way I know of to get the kind of heating you need in the expansion chamber (the "combustion chamber" in a fueled jet) -- a BIG paraboloidal reflector that concentrates the sun's heat right where you need it. Of course, this could just as easily be an array of flat mirrors adjusted to aim their reflected beams into the chamber. Your expansion chamber could be fused quartz, to let in the heat/light and still survive the thermal gradients at the mounting points. There could be a very black panel inside the chamber (say, lining the "back side" opposite where the heat comes in) to quickly convert solar energy to heat for expansion.

This setup, while not mobile (in fact, not even PORTABLE!), would be enough to get you started experimenting. HOWEVER, note that even in this case, there will be considerable energy losses at several points in the process. For jet propulsion, it is going to be VERY hard to match having internal combustion (i.e. rapid release of chemical energy)in the chamber! However, skeptics should remember that there are lots of uses for jets besides propelling a lightweight vehicle -- especially where a simple air mover delivering hot, dry air is the basic requirement.

L Cottrill

fastnova
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Re: HELP!

Post by fastnova » Tue Mar 10, 2009 9:37 pm

The kind of quality and quantity of mirrors or lenses required for such an engine would be both huge in cost and size, and very dependent on weather (no so dependable here in England!)
Perhaps a more practical and portable solution would be a laser, ok so its not free energy, but it does suggest a kind of fly by wire. You could keep the laser on the ground and use some kind of GPS tracking device to keep it on the target.

Or even have all the mirrors on the ground and focus them in much the same way as you would the laser, except you cant create a constant strait beam like you can with a laser so the tracking device would have to be much more complex so that it focuses the light to a point on the target at all times. I wouldn’t like to be the one to figure that out, but an interesting idea all the same.
Imagine the payloads and distances planes could fly if they didn’t have to carry any fuel!
I don’t see problems, only opportunities.

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Re: HELP!

Post by Mike Everman » Tue Mar 10, 2009 11:29 pm

Do a google search for work done by Leif Myrabo. He's done this in a big way.
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jtj12358
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Re: HELP!

Post by jtj12358 » Wed Mar 11, 2009 5:43 am

thank you guys so much , i actually live only a few miles from where Leif Myrabo works, i think his idea's might be to complex for me to understand at the moment and to use on the scale model i wish to build. it seems like his idea's lead to hyper drives and warp drives and explains a lot of U.F.O. incidents.

Bruno Ogorelec
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Re: HELP!

Post by Bruno Ogorelec » Thu Mar 12, 2009 7:44 am

You might consider a transparent zeppelin, with wall panels functioning as lenses to concentrate sunlight onto a tubular central backbone. The central tube, which might also act as a structural member, would function as a ramjet. Air enters the central tube at the nose, gets heated in the tube and blasts out at the tail, creating thrust. Give it internal corrugations like a Tesla gas conduit, so that it only blows the hot air backwards.

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Re: HELP!

Post by larry cottrill » Thu Mar 12, 2009 12:24 pm

Bruno Ogorelec wrote:You might consider a transparent zeppelin, with wall panels functioning as lenses to concentrate sunlight onto a tubular central backbone. The central tube, which might also act as a structural member, would function as a ramjet. Air enters the central tube at the nose, gets heated in the tube and blasts out at the tail, creating thrust. Give it internal corrugations like a Tesla gas conduit, so that it only blows the hot air backwards.
jtj -

The above is an excellent beginning, but I would modify as follows:

Forget "lenses" -- make the lower half of the Zeppelin envelope reflective (an aluminum interioir coating would be ideal) and the top half transparent. The bottom half will act as a concave relfector, concentrating heat on the central core, while the top half will act as a "greenhouse" type canopy to hold in re-radiated heat. The entire envelope contents (air) will become quite hot with this approach, and the concentration of heat from the reflective lower part will be quite intense (depending on the overall surface area, naturally). It would be beneficial for the Zeppelin to take the form of a long cylinder with rounded ends (like the Americam helium Zeppelin conversions of the 1930s) for the best optical performance of the reflector.

I would still "motorize" it with a ducted fan at the front end of the tube; remember, you are not going to get much ram air speed from something with this much external drag. The Graf Zeppelin and the Hindenburg managed about 60 MPH, and each had FOUR 1100HP Mercedes diesels for power. (Of course, they were 800 ft, or 40 metres, long -- probably a little bigger than what you might want for a first build. ;-)

Do not assume that Bruno or I are being whimsical here; this is probably as close to a reasonable approach as you are likely to get, if you really are after vehicle propulsion. To get propulsive power from solar heat will take a LOT of surface area; there's no way around that.

L Cottrill

Bruno Ogorelec
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Re: HELP!

Post by Bruno Ogorelec » Thu Mar 12, 2009 7:39 pm

Larry, you are right. I posted off the top of my head, what occurred to me as I was reading the question. Lower-half mirror is of course the way to go.

As I write this, what occurs to me is an alternative -- a closed-loop helium system in which the central tube is a gas heater and the shielded area below the reflector is the radiator that cools the gas. The big temperature difference generates a gas flow, which turns a turbine, which drives propellers.

The relatively low temperatures involved would allow lightweight carbon-fiber machinery parts to be used, rather than metal.

jtj12358
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Re: HELP!

Post by jtj12358 » Fri Mar 13, 2009 7:43 am

thanks again, i had not considered using lenses to focus heat, but that is a very elective way to heat something up im also not looking for any thing to go fast, i'm actually just looking to use it to make a plat form hover like the helium in a zeppelin would, would it be possible to make the housing for the engine its self act like a zeppelin using helium then i could use the thrust form the engine to move the plat form. . would that work?. if i made the whole plat form the housing and made the engine it's self span the distance and used solar power to, power the fans in the engine, and heat up the air as it exits i cant imagine it generating any notable thrust, keep in mind my goal is a to make something self sufficient and green, even if i couldn't make the plat form its self hover a few "engines" could probably do so.

i have not done any significant design work on the plat form or the engine its self yet i'm still not sure how i want to do it, i know i don't want to use any fuel if necessary and id like to use solar power as best i can, so that what i make would be able to stay in the air in theory endlessly expect for repairs etc. i'm also only looking to make a model about 1ft-2ft a max how do i attach images?

paul fellows
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Re: HELP!

Post by paul fellows » Fri Apr 02, 2010 8:09 pm

i firly new to this and have not fully gotten to grips with PJs yet
but
if what you want is to heat a smallish volume of air to high tempritures quickly? why not an electric discharge?
or as some bright spark already tryed this :lol:
two test tickles

paul fellows
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Re: HELP!

Post by paul fellows » Fri Apr 02, 2010 9:41 pm

a further quick thought

if you split the induction coil that is genorating the spark and mount it top and bottem and pass the spark horizontaly through the magnetic field, you will get a bit of a MHD push. a bit of delay line will help get the spark into the strongest part of the magnetic field.
two test tickles

paul fellows
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Re: HELP!

Post by paul fellows » Mon Apr 05, 2010 12:59 pm

question :?:
if i put the zepplin above on the scale and it weighs nothing what dose that do for its power to weight ratio?
if it becomes positivly bouant (negitive weight ) what dose a negitive power to weight ratio mean?
two test tickles

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