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Jet pack

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File:Bell Rocket Belt in flight.gif
The Bell Rocket Belt in flight.

A jet pack or rocket pack or rocket belt etc is a device, usually worn on the back, that uses jets of escaping gases to allow the user to fly. The name is also a byword for numerous other devices with differing designs but the same function. The concept of this device evolved from the 1920s when Buck Rogers, science fiction comic strip hero, used one for future travel.

Types

Strictly, a jetpack contains a turbojet engine, and a rocketpack contains a rocket. The rocket can be an ordinary solid-fuelled or liquid-fuelled rocket, or a hydrogen peroxide powered rocket, or powered by compressed gas (usually nitrogen) escaping from a gas cylinder.

See also Backpack helicopter.

Hydrogen peroxide powered rocket

A hydrogen peroxide powered motor is based on the decomposition reaction of hydrogen peroxide. Nearly pure (90% in the Bell Rocket Belt) hydrogen peroxide is used: it is a colorless liquid with a density of 1,35 g/cc. Pure hydrogen peroxide is relatively stable, but in contact with the catalyst (for example, silver) it decomposes into a mixture of superheated steam and oxygen in less than 1/10 millisecond increasing in volume 5000 times: 2 H2O2 = 2 H2O + O2. The reaction is exothermic, i.e. with liberation of much heat (~2500 kJ/kg), forming in this case a steam-gas mixture at 740°C.

This hot gas is led to one or more jet nozzles. The great disadvantage is the limited amount of fuel that can be carried. Because the jet of steam is what provides the thrust, the engine has a low specific impulse. The rocket belt not only uses the peroxide as fuel, but also as reaction mass - in contrast to, for example, jet engines which mainly expel atmospheric air to produce thrust. A man's carrying capacity sets an upper bound on weight, and so currently such rocket belts can only fly for about 30 seconds.

(Hydrogen peroxide motors have been used elsewhere also: in World War II Germany widely used them in torpedoes and submarines and aircraft and rockets, and in the fighter-interceptor Me-163. The Me-163 had a speed up to 960 km/h, and it could rise to height 12,000 meters in 3 minutes, with flight duration up to 8 minutes. Hydrogen peroxide also adapted in the V-2 rockets, but as the auxiliary fuel - on it worked the turbine pumps, which fed fuel and oxidizer into the combustion chamber of the main rocket engine.)

Rocket packs are very simple in construction; therefore they won acceptance. The classical rocket pack of the construction of Wendell Moore can be prepared in workshop conditions but needs good engineering training and high level of tool-making craftsmanship. A main fault in the rocket pack is short duration of flight (to 30 seconds) and the high expense of scarce fuel (hydrogen peroxide). These circumstances limit the sphere of the application of rocket packs to very spectacular public demonstration flights. Rocket pack flights always seize the attention of spectators and enjoy great success. For example, a flight was arranged in the course of the opening ceremony of the summer Olympic Games 1984 in Los Angeles, USA.

Rockets using ordinary rocket fuel

Before or during WWII Germany made crude early experiments of strapping large firework-type rockets to a man's back: this did not work, and risked the man's life.

Devices have been made using rockets intended for missiles, but they are extremely dangerous and difficult to control and have never been flown. The heat from the rockets also tends to be too great.

The fictional device used by The Rocketeer was a rocket pack that was technically unique (at least in the film adaptation) because it was designed to remain cool.

Turbojets

Packs with the turbojet engine work on the traditional kerosene. They have higher efficiency, greater height and duration of flight, but they are complex in construction and very expensive. To make this sort of pack under primitive conditions is impossible. Only one working model of this pack was made; it underwent flight tests in the 1960's and at present it no longer flies.

Current real usefulness

While jetpacks may appear appealing, current real jetpacks have little practical value. The United States military, which conducted most jetpack research, has declared that helicopters are far more practical. Many others have worked on devising a functional jet pack, but with limited success. Currently the most advanced designs are more similar to helicopters than jets. Because of the current impracticality of long-term use of jet or rocket packs, they have found more use in contemporary fiction or more futuristic science fiction.

Thomas Moore's "jet vest" (hydrogen peroxide powered)

(IMAGE: Thomas Moore's "jet vest", worn by one of his colleagues)

After the end of WWII German rocket technologies arrived in the USA together with the famous designer Werner von Braun. One of the American engineers who worked with him was Thomas Moore, who devised a small lift device, which he named "Jet Vest", which worked on hydrogen peroxide. In 1952 Moore knew how to get a grant of $25,000 from the US Army to make and test his device. A "jet vest" prepared and during the bench tests could raise the pilot above the earth for several seconds.

But Moore's "waistcoat" had an extremely inconvenient control system. On the pilot's chest was placed a box, from which went cables to the thrust regulator and the pack's two controlled nozzles. To the right and to the left box had handwheels: the right handwheel governed thrust, and the two left coaxial handwheels governed the left and right nozzles. Each nozzle could be slanted forward or back. To turn to the side, the pilot revolved one of the handwheels, slanting one nozzle. To fly forward or back, the pilot revolved both handwheels at once. So this appeared in theory. Thomas Moore's "jet vest" could not complete a solo flight, the army ended financing, and the work was wound up.

The Jump Belt (mostly compressed gas powered)

(IMAGE: "jump belt" in action.)
In 1958 Garry Burdett and Alexander Bohr, engineers of Thiokol Corporation created the "Jump Belt", which they named Project Grasshopper. Thrust was created by high-pressure compressed nitrogen. On the "belt" were fixed two small nozzles, directed vertically downward. The "belt"'s wearer could open a valve, letting out from the nitrogen gas cylinder through the nozzles, in this case it was tossed upward to the height to 7 meters. After leaning forward, it was possible with the aid of the "jump belt"'s thrust to run at 45 to 50 km/h. Then Burdett and Bohr tested a hydrogen peroxide powered version. The "jump belt" was demonstrated by a serviceman in action, but there was no financing, and the matter again did not go to further tests.

But American servicemen did not lose interest in this type of flight vehicle. Control of transport studies of the US Army (U.S. Army Transportation Research Command, TRECOM) assumed that personal jet apparatuses could find the most diverse uses: for reconnaissance, crossing rivers, amphibious landing, access to steep mountain slopes, overcoming minefields, tactical maneuvering, etc. The concept was named Small Rocket Lift Device, SRLD.

Within the framework of this concept the administration in 1959 concluded with the company Aerojet- General a contract to research on the possibility of designing an SRLD, suitable for army purposes. Aerojet came to the conclusion that the version with the engine running on hydrogen peroxide was most suitable. However, it became soon military known that engineer Wendell Moore of the company Bell Aerosystems already for several years had carried out experiments to make a personal jet device. After becoming acquainted with his work, servicemen during August 1960 decided to send a order for Bell Aerosystems to develop an SLRD. Wendell Moore was appointed as the chief project engineer.

Bell Textron Rocket Belt (hydrogen peroxide powered)

This is the best known type of jetpack or rocketpack. See Bell Rocket Belt.

RB2000 Rocket Belt (hydrogen peroxide powered)

This is a successor to the Bell Rocket Belt. See Bell Rocket Belt#RB2000 Rocket Belt.

Turbojet pack (Bell Jet Flying Belt)

In 1965 "Bell Aerosystems" concluded a new contract with the military agency ARPA to develop a jetpack pack with a turbojet engine. This project was named "Jet Flying Belt", or simply "Jet Belt". Wendell Moore, and John K Hulbert (a specialist in gas turbines), worked to design anew turbojet pack. To Bell's order the new pack company "Williams Research Corporation" designed and prepared the turbojet engine Wr-19, with thrust 195 kg and weight 31 kg. This new pack was made in 1969.

On 7 April, 1969, on the Niagara Falls airfield took place the first free flight of the turbojet pack "Jet Belt". Pilot Robert Courter flew about 100 meter in a circle at height 7 meters, reaching a speed of 45 km/h. The following flights were longer, to 5 minutes. Theoretically this new pack could fly for 25 minutes and develop speed to 135 km/h.

In spite of successful tests, the US Army did not again appear interested. The pack was complex to maintain and too heavy. The pilot landing with this load on his arms was unsafe. Furthermore, if the engine was damaged the turbine blades could fly away at high speed, threatening the pilot's life.

Thus the "Bell Jet Flying Belt" remained an experimental model. On 29 May 1969 Wendell Moore died of disease, and work on the turbojet pack was wound up. Bell sold to the Williams company the sole version of the "Bell pack" together with the patents and the technical documentation. This pack at present is in the Williams Research Corporation's museum.

Special features of the turbojet pack

(IMAGE: Turbojet pack "Bell Jet Flying Belt". Pilot Robert Courter. 1969.)

The "Jet Belt" has a Wr-19 turbojet engine, which weighs 31 kg, thrust 195 kg, diameter 30 cm. The engine is fixed vertically, with its air duct downward (1). Air intake is compressed by turbine and is divided into two flows. One flow goes into the combustion chamber. The second flow goers between the double walls of the engine, then it is mixed with the flow of the outgoing hot gases, cooling them and protecting the pilot from the high temperature. In the upper part of the engine the mixed flow is divided and enters two pipes, which lead to jet nozzles (2). The construction of the nozzles makes it possible to move the jet to any side. Fuel kerosene is in tanks (3) beside the engine. Control of turbojet pack is similar to control of rocket pack, but the pilot no longer can incline entire engine. Maneuvering is carried out only by deflecting the controlled nozzles. Inclining levers, pilot can move the jets of both nozzles forward, back, or sideways. The pilot rotates by the turning the left handle. The right handle, as usual, governs the engine thrust. The jet engine is started with the aid of a powder cartridge. While testing this starter, a mobile starter on a special cart was used. There are instruments to control the power of the engine, and a portable radio to connect and transmit telemetry data to ground-based engineers. On top on the pack is a parachute (4) (a standard landing auxiliary chute);. it is effective only when opened higher than 20 meters.

Real space use

Rocket packs can be useful in space, where much less thrust is needed, because the weightlessness of space removes the need to continually fight against gravity.

NASA's Manned Maneuvering Unit (MMU) (compressed gas powered)

In the 1980s, NASA demonstrated the Manned Maneuvering Unit (MMU), a rocket pack that allowed an astronaut to function as his/her own spacecraft, but the system was retired before the decade was gone. The MMU is the only jetpack of practical importance. Its operational area is the universe, where it can operate from the space shuttle out and with it an astronaut can limitedly move independently. The MMU's propulsion was produced by high-pressure nitrogen gas discharged through nozzles (which the MMU has 24 of). The MMU was used since 1984 in three Space Shuttle missions (STS-41-B, STS-41-C and STS-51-A).

NASA's SAFER

Recently, NASA has introduced the SAFER, a smaller simpler version of the MMU meant to be used in case of accidental separation from spacecraft or station. With only small amounts of thrust needed, safety and temperature are much more manageable than in Earth gravity in the atmosphere.

Artist's depiction of a jetpack with folding wings

The future?

Jetpacks and rocketpacks would likely have much better flight time on a tankful of fuel if they had wings. There have been occasional real cases of a man gliding horizontally long distances with his body horizontal and no flying aid except airplane-type wings strapped directly to his body, but never with a motor added as far as is known.

Rocket pack in show business

In the 60's the "Bell Rocket Belt" was on the peak of popularity. Bell arranged demonstration flights in THE USA and other countries, each time causing the public enthusiasm.

In 1965 on the screens came the James Bond movie Thunderball. Bond (played by Sean Connery) penetrates a enclosed factory, where is concealed an agent of the mysterious organization "SPECTRE". Bond liquidates the enemy, then flees to the roof and flies away using the previously hidden rocket pack.

In the filming two packs were used. One is a non-functional prop: it can be seen on Sean Connery in the large-scale planning scenes. The second was a genuine "Bell Rocket Belt" and it genuinely flew. The Bell Company pilots Bill Suitor and Gordon Yaeger flew it. The scenes with Sean Connery and the pack had to be shot twice, because the first time they photographed it his head was uncovered, and in the flying shots Bill Suitor flatly refused to take off without a crash helmet.

In the film's sound track the real shrill roar of the engine of pack was replaced with the hiss of a fire extinguisher - "to seem more realistic".

(IMAGE: Olympiad of 1984. Pilot Bill Suitor. pack belongs to Nelson Tayler.)

One additional famous appearance of a pack occurred on the opening of the summer Olympic Games in Los Angeles in 1984. The pack was piloted by Bill Suitor, a legendary personality (in all calculation more than 1200 flights - more than in any other pilot to this day). Bill took off from platforms, flew above many spectators, who from the unexpected contingency covered their heads with their hands, and landed opposite the presidential platform, where sat Ronald Reagan. This flight was seen by 100,000 spectators on the platforms and about 2.5 billion television viewers (besides the USSR, which boycotted that Olympiad).

The company Powerhouse Productions Incorporated offers Rocketbelt performances around the world under the character name, "Rocketman".

In 2001 the pilot Eric Scott stated that he had flown the jetpack to 152 feet height. However, confirmation did not follow this record.

Making a rocket pack at home using plans from the internet

See Episode 32 in MythBusters episodes. There is an urban myth that a jetpack or rocketpack can be built from plans purchased off the internet and limited funds. The jetpack produced by the Mythbusters was not powerful enough to lift itself off the ground. The sum of its parts cost too much to let the average person to build it on a budget. The plans did not have enough details to give builders a clear example of what to build.

Rocket pack in our time

In recent years the rocket pack has become popular among enthusiasts, who by their efforts have made some. The pack's construction is sufficiently simple, but suitabiity for flying depends on two key parts: the gas generator, and the thrust regulator valve. Specifically, they were led to the mind of Wendell Moore in the course of long tests.

The multiplication of packs is held in control by the scarcity of concentrated hydrogen peroxide, which is no longer produced by important chemical companies. Missileman-amateurs have made their own installations to make concentrated hydrogen peroxide by electrolysis.

In the world are not now more than 5 successfully flying rocket packs. For forty and more years from the day of the first flight of Harold Graham only eleven people (including him) have flown one, due to the lethal factor on the pack in free-air conditions (without the safety leash). Most known of them, as has already been mentioned, is Bill Suitor, who once lived near Wendell Moore and asked if he could fly with the pack, which Moore brought home in a baggage carrier.

Fictional use

Jetpacks or rocketpacks have been used in some movies and have long been a staple of science fiction, e.g. in:-

See also

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