Glenn (and Popular Mechanics) confuse the terms. As is pointed out in the article, rocket packs aren't "jet" packs.

Remember the rules? If you want to cruise in the atmosphere, use an air breather. A rocket belt sounds cool, but it really makes no sense for this application. Rockets are for accelerating, and getting out of the atmosphere as soon as possible (or for traveling in space, if you've already done that). They're not for tooling around near the ground, or for atmospheric transportation (rocket races being an exception, because it helps push the technology, and sounds cool). A true jet pack, though, would be actually cool, as opposed to merely sounding (and looking, when you see a pro do it at a show, for a minute or so) cool.

I believe this device was originally called the "Bell jet belt."

"Jet" most commonly refers to a turbojet or ramjet, but remember the original meaning of jet was "a stream of fluid or particles." Thus, the term is also used things like aquatic "jet thrusters."

Rockets are propelled by jets of hot gas, and in other times were often called "jets." Even Rhysling the blind singer of the spaceways called them "jets."

A true jet pack, though, would be actually cool

That was tried, back in the 60's or 70's, but the weight of jet engines at the time made the pack too heavy to be practical. Imagine landing with a couple hundred pounts on your back. Rocket engines were a lot lighter, but the poor Isp of monopropellant H2O2 made the flight time very short, and higher Isp engines have higher flame temperatures which would be quite dangerous for the wearer. Juggling all tradeoffs while keeping the unit small enough to wear on the back proved to be very dangerous, so they ultimately went to jet platforms instead. Higher T/W jet engines might help, but I suspect the same evolution will happen again if development continues.

I remember something 7 or 8 years ago about a ducted fan flight pack.

There's this guy with a jet engine and small wing that he wears on his back, using his body as fuselage. Not enough thrust to hover though .. and too much wing loading to use his built-in undercarriage!

http://youtube.com/watch?v=bEXxkWXncuo

All the more reason to get on with the development of robot exoskeletons already. The synthetic muscle actuators can support the weight of the powerplant and fuel. The exoskeletal frame can withstand the rigors of flight to protect the operator. And the plasma cannons can melt all those who stand in your way.

Betraying my own lack of knowledge: I take it, then, that these "jet packs" are actually rockets?

Has anyone tried to build a genuine air-breathing jet pack lately? What's the smallest feasible jet engine nowadays?

This one has 6kg of thrust. Probably too small for a jetpack, unless you're planning on fitting it to a small dog.

http://www.artesjet.com/prod04.htm

Ed - Thanks for remembering Rhysling's usage...and therefore that of Heinlein and the first era of spaceflight enthusiasts. The common usage may have shifted with time, but the a rocket still creates thrust by producing a jet... as do those things that gulp their oxydizer from the atmosphere.

The other problem is that running out of fuel or having an engine failure at any altitude between about ten feet and minimum parachute altitude is fatal.

Heh, one finnish Skydiver Visa Parviainen actually flew in a skydiving birdman costume, with two model jets on his legs. thats a real jet-man.

the story with prictures and video is here:
http://www.dropzone.com/content/Detailed/613.html

And of course youtube has Visa Parviainen too:

http://youtube.com/watch?v=OVxeZYdVRLM

It's hard to tell, but either he has very little fuel, or else he doesn't have enough thrust to maintain altitude.

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off topic but interesting...

NASA seems close to adopt MY "underside-LAS" ... :) :) :)

in an effort to increase the Orion's SAFETY and REDUCE its (now oversized) mass (of about 1000 lbs.) NASA seems close to adopt an "Alternate Launch Abort System" (ALAS) as explained in this document:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070018751_2007018905.pdf

the ALAS works EXACTLY like MY (February 10, 2007) "underside-LAS" published FIVE months ago in this article:

http://www.gaetanomarano.it/articles/020newLAS.html

as you can see from the pictures in the NASA document, the ALAS has a big FARING that forces the abort motor's thrust from the top of the LAS to the bottom of the Orion's Service Module, so, in both (ALAS and underside-LAS) systems, the Orion capsule (on abort) is NOT "dragged" from the top, but "pushed" from the bottom (like happen with rockets)

the ALAS has two different designs, one with the LAS' flux canalized on the external side of the fairing (ALAS-1) and one with the flux canalized on the internal side of the fairing (ALAS-2 and ALAS-3)

unfortunately, the NASA design (in the ALAS-2 and ALAS-3 versions) looks VERY DANGEROUS since (on abort) the LAS motor's (very hot and powerful) thurst flux "travels" between the fairing and the capsule with the astronauts!!!!!!

also, the ALAS seems NOT able to reduce the Orion's weight (as claimed) since it needs a big (and heavy) fairing and nearly TWICE the LAS motor's power/mass/dimensions/price to push (on abort) the GIANT Orion+LAS+fairing+Service Module mass!!!

so... why NASA doesn't adopt MY (ways simpler, safer, cheaper and lighter) "underside-LAS" ??? :)

This would seem to be a possible application for the air-turborocket concept I came up with a few years ago. At t/w of 25, the engine would mass 15-20 pounds. With Isp ~1,000 a few minute flight seems feasible.

Just send me a few million and I'll see what I can do. :-)

What is the point of a jet pack, even if fuel were no object? Rocketeer helmet or not, you aren't going to be getting much horizontal speed, and every inch of distance would cost dearly compared to ground transportation. There might be applications for skyscraper rescue, but passive escape systems would seem a lot more practical.

Don't be too hard on them, considering that JPL is the Jet Propulsion Laboratory, when their initial work was in rockets.

::It's hard to tell, but either he has very little fuel,

He had his fuel packed in plastic bags around the body, and he claims to have maintained level flight for about 30 seconds. IIRC, he has done this for a couple of times by now.

This source has some info on jet powered flying belts. Personally, I like the WASP better. Since your legs aren't the landing gear, you aren't as limited in fuel capacity or engine power.

Initial flight tests of the one and two man WASP (Williams Aerial Systems Platform), a turbine powered flying platform developed by William Research Corporation of Walled Lake, Michigan. Powered by the world's smallest fanjet engine, the WASP is designed to take off vertically, accelerate rapidly, move forward, backward, sideways, hover, rotate and enable one or two men to fly for 30 minutes at speeds of 60 miles per hour. Flown here on a safely tether line used during early trails tests - by test pilot Robert Courter (left photo) and with passenger Jack Benson (right), the WASP was built and demonstrated under a U.S. Marine Corps research and development program STAMP (Small Tactical Aerial Mobility Platform).

There was also the Williams X-Jet. That looks like fun.

Which would get you more distance with current technology and a 50kg weight limit:

1) A carbon wing for gliding after rocketing to altitude

2) A wing and a (air breathing) jet

3) a copter pack

Which would get you the most height? Would a chute help with distance or height?

Which would get you the most height? Would a chute help with distance or height?

Powered parachutes can stay aloft for hours, so you could potentially cover a hundred miles or so. I suspect you could reach a considerable altitude, too, but I don't know if anyone's attempted that. The main point of the sport seems to be to fly low and slow.

I only call turbojets (either the engines or the vehicles) "jets", but I suppose any reaction engine could be called jet propulsion.

A jet pack would be great (with suitable ear protection) but I think there's an unexplored niche between model turbines (~15 lbf thrust) and "real" engines (~1000 lbf).

Since the movie ROCKETEER sported an air intake, his pack was technically a jet pack. Current torbogans are down to about 300 lbs. A small turbofan could be built by making the fans part of a single cast part.

The AMT Netherlands (www.amtjets.com)Olympus 2 turbojet delivers 51.7 lbf of thrust and weighs 6.5 lb and has a fuel flow of 640 grams/minute at that thrust at sea level standard day. Six of them would support a person for vertical takeoff with enough fuel for maybe 10 - 15 minutes of flight.

I got to run one last December when I visited a drone manufacturer and inspected disassembled engines also. Two of them with a little tweaking will fly my sailplane nicely. Soon, I hope.