Sciencemadness Discussion Board - How does a jet pack sound?

How does a jet pack sound?

BromicAcid - 9-7-2004 at 16:54

Rocket Man's Web Page

The technical info for the rocket pack, one of only two in the world. Only flys for 30 seconds but sounds very cool, videos and such. The pilot was on the local radio the other day so I got some specifics not on the site. Such as the propellant is pressurized slowly into the fuel canister. The site states that the propellant is hydrogen peroxide, the pilot stated that some of the propellant dripped out into the back of his shoe and started a substantial fire where his tendons were scorched black, giving an indication of concentration.

How about someone build one

I've just always liked the possibility of personal flight.

Another 'Jet Pack' I put Jet Pack in brackets because this one actually uses two giant fans to produce the lift. Still very interesting, they say it is totally for real and if it is, it gives substantially better results, being able to stay in the air an hour. They also sell plans to build the device but the motors are very expensive.

The point of this post. Personal flight jet packs are very interesting and pose many technological challenges. But it is indeed mad science to build such a thing, the perfect thing for the army of the future

So what do you think of these jet packs, how feasible is an at home jet pack?

And you say AP is dangerous?

IvX - 10-7-2004 at 03:06

The idea's nothing new(hell there was some guy who tried that almost 20 years ago- did'nt live to tell about it).But the problem of safety is prety much the same since effectivly were using almost the same things as we did 30/40 years ago.

OTOH are you familier with magnetic 'hydro drives'? Theyre basically large coils that run on 10-50(or more)Kv's so the water breaks so the water is carried on the field.

With modern baterys,fuell cell's,etc you could have something like that.That is ofcourse ignoring the obvious problems of the extremely high voltage

BromicAcid - 10-7-2004 at 19:42

I'm not really up on the technological aspects of what you're brining up IvX, however it does sound interesting.

One thing I was wondering about though, the page for the rocket pack says that steam is the lifting mechanism. However it says hydrogen peroxide is the fuel, so it's just going to spew out a large trail of highly concentrated oxygen gas without taking advantage of any of it, and wouldn't that create a fire hazard?

Organikum - 10-7-2004 at 23:55

I guess there will be a second compound to the H2O2...
.... the first use of such a energy source known to me was in the german "Walter" submarines at end of WWII. They used H2O2 and tetralin to generate steam for a steam-turbine, some catalyst was involved too if I remember right.

The jet-packs are not new, thats true. I remember one in an old James Bond movie, it was a real existing model from the US-Army. These gadgets existed but had some severe problems which got never completely solved: To loud, didnt have enough fuel for a flight of more than some 20 minutes perhaps and most important - they were hard to fly even for trained persons.
As always in aviation there is one comfort, they always come down....

There are some physical principles which speak against such a thing soon to become reality: The energy needed for VTOL machines is exeptional high and the space available on a "rucksack to fly with" is limited as weight is. Steering is hard to do with a vertical stick - and thats a human basically.

Nearest to the idea come those motorized parachutes which go as ultra-ultralights. A few meters for start and landing and able to stay in air for hours. The main point of critics is for me the noise. It should be a "silent running" I feel or somethings not right.

DDTea - 11-7-2004 at 06:43

Quote:

To loud, didnt have enough fuel for a flight of more than some 20 minutes perhaps and most important - they were hard to fly even for trained persons.

Actually, the greatest inconvenience of the jetpack was its flight time--measured in seconds not minutes. If I recall correctly, it could only fly for 30-40 seconds or so... I imagine it would take a lot of H2O2 to keep an average weight man + the jetpack in the air for extended periods of time.

Instead of H2O2 though, why not investigate alternative fuels??? As always, fuel is the limiting resource. Why not something like a liquid fueled rocket engine, of course with some kind of heat shield for the person wearing it? To me that sounds a lot more feasible than high concentration H2O2.

Cyrus - 11-7-2004 at 13:23

BromicAcid, I was always bugged by the fact that some H2O2 powered rockets wasted the oxygen produced, but wouldn't the water vapor present hinder combustion?

Jet packs do sound fun, next we need to equip ourselves with lots of electric gizmos, thermites and HEs, and take out something...

(With James Bond music playing in the background of course.)

I think an electromagnetic pulse gun would come in handy.

Chemicaly powered jet packs are about useless IMHO, and I am not about to strap 20kg of rocket fuel to my back. The superconducting levitator disk being "developed" by Smalley and Li Ning? sp? might work, or maybe the whole thing is a hoax. I think pop. mech. did an article on that several years ago.
Does anyone know how the progress is going? I think that the theory could be valid, but there is no way to get all of the atoms to line up, yet.

If mad scientists could get this problem solved...

Geomancer - 11-7-2004 at 17:42

H2O2 monopropellant strikes me as a decent choice for this application, at least for demonstration purposes. A monoprop rocket is very simple, therefore reliable. H2O2 "burns" somewhat cold, so you don't need fragile refractories and can reuse the device many times. The only other widely used liquid monopropellant is hydrazine, but you really don't want to be carrying that on your back (H2O2 is dangerous, but not very by the standard of rocket propellants). I wouldn't think the fire hazard is any greater than having a full temperature bipropellant flame jetting out of the thing.

H2O2 is also great in bipropellant mixtures, being somewhat storable, relatively non-toxic, and dense, while retaining decent specific impulse capability. You can also use it to run your turbopumps, and it can be hypergolic with special fuels. Many amatuers would sell thier souls for a good cheap source, but last I heard, none was available.

BromicAcid - 11-7-2004 at 18:08

The rocket man jet pack is the same jet pack designed by the army and used in the James Bond film. The original one ran for 22 seconds or so, the only modifications to the one used by the rocket man is a larger fuel capacity and more of it is made from fiber glass.

The pilot stated that when he wanted to lift off he maxed out the throttle and kept it that way till just before touch down so control is not too major, maybe a solid rocket propellant

However that would increase the temperature of the exit gasses, the pilot stated that they come out at 900 degrees, weather it was Celsius or ferenheit was not stated. Another technical aspect is that the fuel lines are 3x the diameter of the fuel lines in a motor vehicle, and the pack has extreme control, the pilot can take off and land anywhere within the distance the pack can travel to within a half meter or so.

Good idea Geomancer, I was thinking of hydrazine for a monopropellent just a bit ago for such a thing. It would be the same principle, just pressurize and run though some decomposition catalyst, e.g., hot platinum screen, copper covered asbestos and you're good to go.

Still though, I don't think air time would be substantially increased.... However I haven't done any calculations. The other jet pack that I mentioned shows more promise, if it really works, a fifty mile radius is incredible for such a thing, although the fans are quite bulky and it would be expensive as I've said before. How about a pulse jet?

Geomancer - 12-7-2004 at 08:17

I suspect that flight time, to a first approximation, scales linearly with specific impulse. I haven't been into rocketry for a while, so I don't have any good references around, but I suspect you won't do any better than a factor of two improvement. Solids have some good properties, but are a non-starter in this application for anyone without x-rays and ultrasound to examine the grain for defects.

FrankRizzo - 12-7-2004 at 13:59

Cyrus,

Here's that PopSci article that you were talking about :

http://popularmechanics.com/science/research/1999/10/taming_...

Sorry for the delay

IvX - 12-7-2004 at 23:16

I tried looking for the orignal patent of mag drive I was talking about but no luck.

Anyways how about small solid fuell 'tablets' put end to end with some sort of barrier that acts as an igniter(like having a small explosive inside high temp ceramic or something like that).

Or perhaps some sort of loading sort of loading system for the tablets.

JC - 1-8-2004 at 13:36

For something like this, you need to consider the specific impulse of the fuel, yes, but it is mainly the specific impulse of the whole system that matters.

A higher impulse fuel that meant wearing rather heavy asbestos trousers would be a false economy, as it were.

Control problems could be solved with a good fly-by-wire control system, as seen on the Harrier "carefree handling" upgrades, and the Eurofighter, which flies worse than a brick without 100's of tweaks to the control surfaces every second. Even something as simple as the "Flying bedsteads" would be capable as troop transporters with one of these systems, which would let them get out of ground effect, and into the air.

[Edited on 1-8-2004 by JC]

franklyn - 19-10-2006 at 03:15

The reason rocket propulsion for hovering, in flights that can
exceed a minute in duration, can never be acheived, appears in the
specifications given for one of these machines. It must generate
750 horsepower equivalent. This power more efficiently lifts the
4 1/2 ton combined weight of a fueled helicopter and its payload.
This is better than a 20 to one efficiency over the less than 400
pound combined weight of a pilot with rocket belt. There are far
more elegant means for personal levitation, as I posted here

http://www.sciencemadness.org/talk/viewthread.php?tid=6730

.

a_bab - 21-10-2006 at 12:19

Bromic acid, the second link for buying "plans" is pure crap. There was a myth busters show where they actually bought and build the thing. Guess what? It didn't work.

The site alse sells NI3 making plans for 10 dollars, and they say that "If dilluted and formed into balls, it makes a great substitute ammo for paint ball guns".

I'd never buy anything from them.