Jet pack

https://en.wikipedia.org/wiki/Jet_pack

A jet pack, rocket belt or rocket pack is a device, usually worn on the back,
which uses jets of gas (or in some cases liquid) to propel the wearer through
the air.

The concept emerged from science fiction in the 1960s and became popular as the
technology became a reality. The most common use of the jet pack has been in
extra-vehicular activities for astronauts. Despite decades of advancement in the
technology, many obstacles remain in the way of use of the jetpack in the
military or as a means of personal transport, including the challenges of
Earth's atmosphere, Earth's gravity, low energy density of available fuels, and
the human body not being naturally adapted to fly. To compensate for the
limitations of the human body, the jet pack must accommodate for all factors of
flight such as lift and stabilization.

Andreyev: oxygen-and-methane, with wings

The first jet pack was developed in 1919 by the Russian inventor Aleksandr
Fyodorovich Andreyev. The project was well regarded by Nikolai Rynin and
technology historians Yu. V. Biryukov and S. V. Golotyuk. Later it was issued a
patent but apparently was not built or tested. It was oxygen-and-methane-powered
(likeliest a rocket) with wings each roughly 1 m (3 feet) long.

Hydrogen peroxide-powered rocket packs

A hydrogen peroxide-powered engine is based on the decomposition reaction of
hydrogen peroxide. Nearly pure (90% in the Bell Rocket Belt) hydrogen peroxide
is used. Pure hydrogen peroxide is relatively stable, but in contact with a
catalyst (for example, silver) it decomposes into a mixture of superheated steam
and oxygen in less than 1/10 millisecond, increasing in volume 5,000 times: 2
H2O2 ? 2 H2O + O2. The reaction is exothermic, i.e., accompanied by the
liberation of much heat (about 2,500 kJ/kg [5,800 BTU/lb]), forming in this case
a steam-gas mixture at 740 °C [1,360 °F]. This hot gas is used exclusively as
the reaction mass and is fed directly to one or more jet nozzles.

The great disadvantage is the limited operating time. The jet of steam and
oxygen can provide significant thrust from fairly lightweight rockets, but the
jet has a relatively low exhaust velocity and hence a poor specific impulse.
Currently, such rocket belts can only fly for about 30 seconds (because of the
limited amount of fuel the user can carry unassisted).

A more conventional bipropellant could more than double the specific impulse.
However, although the exhaust gases from the peroxide-based engine are very hot,
they are still significantly cooler than those generated by alternative
propellants. Using a peroxide-based propellant greatly reduces the risk of a
fire/explosion which would cause severe injury to the operator.

In contrast to, for example, turbojet engines which mainly expel atmospheric air
to produce thrust, rocket packs are far simpler to build than devices using
turbojets. The classical rocket pack construction of Wendell Moore can be made
under workshop conditions, given good engineering training and a high level of
tool-making craftsmanship.

Current technology

At the TechCrunch Disrupt conference in 2014, Astro Teller, head of Google X
(Google's research laboratory), said they investigated jetpacks but found them
too inefficient to be practical, with fuel consumption as high as 940 L/100 km
(1/4 mpg-US), and were as loud as a motorcycle, so they decided not to pursue
developing them.

In recent years, the rocket pack has become popular among enthusiasts, and some
have built them for themselves. The pack's basic construction is rather simple,
but its flying capability depends on two key parts: the gas generator, and the
thrust control valve. The rocket packs being built today are largely based on
the research and inventions of Wendell Moore at Bell Helicopter.

One of the largest stumbling blocks that would-be rocket pack builders have
faced is the difficulty of obtaining concentrated hydrogen peroxide, which is no
longer produced by many chemical companies. The few companies that produce
high-concentration hydrogen peroxide only sell to large corporations or
governments, forcing some amateurs and professionals to set up their own
hydrogen peroxide distillation installations. High-concentration hydrogen
peroxide for rocket belts was produced by Peroxide Propulsion (Gothenburg,
Sweden) from 2004 to 2010, but after a serious accident Peroxide Propulsion
stopped making it.

Yves Rossy's jet wingpack

Swiss ex-military and commercial pilot Yves Rossy developed and built a winged
pack with rigid aeroplane-type carbon-fiber wings spanning about 2.4 m (8 ft)
and four small kerosene-burning Jetcat P400 jet engines underneath; these
engines are large versions of a type designed for model aeroplanes.[19] He wears
a heat-resistant suit similar to that of a firefighter or racing driver to
protect him from the hot jet exhaust.[20][21] Similarly, to further protect the
wearer, the engines are modified by adding a carbon fibre heat shield extending
the jet nozzle around the exhaust tail.

Rossy claims to be "the first person to gain altitude and maintain a stable
horizontal flight thanks to aerodynamic carbon foldable wings", which are folded
by hinges at their midpoint. After being lifted to altitude by a plane, he
ignites the engines just before he exits the plane with the wings folded. The
wings unfold while in free-fall, and he then can fly horizontally for several
minutes, landing with the help of a parachute.[22] He achieves true controlled
flight using his body and a hand throttle to maneuver; jet wingsuits use small
turbojets, but differ from other aircraft in that the fuselage and flight
control surfaces consist of a human.

On 26 September 2008, Yves successfully flew across the English Channel from
Calais, France to Dover, England in 9 minutes, 7 seconds. His speed reached 300
km/h (190 mph) during the crossing,[34] and was 200 km/h (120 mph) when he
deployed the parachute. Since then he has—in several flights—managed to fly in a
formation with three military jets and cross the Grand Canyon, but he failed to
fly across the Strait of Gibraltar—he made an emergency landing in the water.





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