Jet Pack



"Rocket belt", "rocket pack", "jet pack", and similar names, are various types of device, usually worn on the back, that uses jets of escaping gases to allow the user to fly. The concept of these devices evolved from the 1920s when Buck Rogers, science fiction comic strip hero, used a rocket pack for future travel.

The backpack harness (like a parachute harness), should have a strap between the legs so that the pilot does not fall out of the harness during flight.

The names containing "jet-" and the names containing "rocket-" are often used with each others' meanings, but there is a difference between them. 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.

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/cm³. 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 (about 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 typically 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.

During WWII, Germany made late-war experiments of strapping two wearable shortened Schmidt pulse jet tubes of low thrust to the body of a pilot. The working principle was the the same as the Schmidt-Argus pulse jet that powered the Fieseler Fi 103 flying bomb whereas the size was much smaller.

The device was called "Himmelstürmer" (Skystormer) and operated as follows: when the flier ignited both engines simultaneously the tubes began to pulse modulate. The angled rear tube strapped to the flier's back provided both lift and forward thrust while the chest mounted deflector tube of lower thrust maintained a constant upward thrust. This lifted the flier up and forward. By opening the throttle to the rear tube, calculated "jumps" could be made of up to 60 meter (180 ft) at low altitude (under 50 ft, 15 m). The tubes consumed very little fuel but not much could be carried either.

The intended use for this device was for German pioneers to cross minefields, barbed wire obstacles, and bridgeless waters. The device was never intended for troop use, despite a crude depiction of it in that role in the comic book and film The Rocketeer (which was a prop bearing no resemblance to the real device).

At the end of the war this device was handed over to Bell which tested it on a tether out of fear of harm as no test flier was willing to risk his life with the German machine. What became of the device is not known but Bell later came up with its famous "Rocketbelt" design that Wendel Moore claimed was his own. Although of different configuration and operation, it is suspected that Moore had knowledge of the German machine - hardly an "original" idea.

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. The Himmelsturmer, by comparison, never operated long enough to get extremely hot and both tubes were angled away from the body of the flier. In operation the thrust difference between pulse tubes acted as a push/pull/lift system. Flight time for jumps was in seconds with no lengthy descent time as altitude was minimal. As soon as the throttle was disengaged the device was shut off, a very simple operation and no report of any casualties.

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 1960s and at present it no longer flies.

While jetpacks may appear appealing, current real jetpacks have little practical value. The United States military, which conducted most jet pack 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.

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.

In 1959 Aerojet General Corporation won a U.S. Army contract to make a jetpack or rocketpack. At the start of 1960 Richard Peoples made his first tethered flight with his Aeropack.

But American servicemen did not lose interest in this type of flight vehicle. Control of transport studies of the 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 became known to the military that engineer Wendell Moore of the company Bell Aerosystems had for several years been carrying out experiments to make a personal jet device. After becoming acquainted with his work, servicemen during August 1960 decided to send an order for Bell Aerosystems to develop an SLRD. Wendell Moore was appointed as the chief project engineer.

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 kgf (1,910 newtons) 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 meters 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 go up to 135 km/h.

In spite of successful tests, the U.S. 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 complications from a heart attack he had had six months earlier, and work on the turbojet pack was wound up. Bell sold to Williams Research Corporation in Walled Lake, Michigan 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.

The "Jet Belt" has a Wr-19 turbojet engine, which weighs 31 kg, thrust 195 kgf (1,910 N), diameter 30 cm. The engine is fixed vertically, with its air duct downward. Air intake is compressed by turbine and is divided into two flows. One flow goes into the combustion chamber. The second flow goes 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. The construction of the nozzles makes it possible to move the jet to any side. Fuel kerosene is in tanks beside the engine. Control of turbojet pack is similar to control of rocket pack, but the pilot no can no longer incline the entire engine. Maneuvering is carried out only by deflecting the controlled nozzles. By inclining levers, the 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 (a standard landing auxiliary chute);. it is effective only when opened higher than 20 meters.

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

Rocket packs were tested during mission STS-64. Mission Specialists Carl Meade and Mark Lee tested the SAFER Rocket Pack while Hammond remained inside the Orbiter.

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).

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.

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 or clothing, wingsuits are a good example. On October 25th of 2005 in Lahti in Finland, Visa Parviainen jumped from a hot air balloon in a wingsuit with two small jet engines attach to his feet. The turbojets used provided approximately 16 kg (35 lbs) of thrust each and ran on Kerosene (JET A-1) fuel. Visa apparently achieved approximately 30 seconds of horizontal flight with no noticeable loss of altitude.

In the 1960s the "Bell Rocket Belt" was on the peak of popularity. Bell arranged demonstration flights in the U.S. 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 an 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 rocket pack's engine was replaced with the hiss of a fire extinguisher - "to seem more realistic".

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 jet pack to 152 feet (46 m) height. However, confirmation did not follow this record.

There is an urban legend that a jetpack or rocketpack can be built from plans purchased off the Internet and limited funds. The jet pack 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 build it on a budget. The plans did not have enough details to give builders a clear example of what to build.

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 suitability 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 now no 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.

Jet packs or rocket packs have been used in some movies, such as the 1965 James Bond movie Thunderball, and have long been a staple of science fiction. They have appeared in many comics: for example, in one set in a 20th-century-type Earth city a detective easily recognised that an upper floor windowsill had been "burnt by the exhaust of an army jetpack", as if in that story's world jet packs were routinely used.Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts.
Virtual Magic is a human knowledge database blog. Text Based On Information From Wikipedia, Under The GNU Free Documentation License. Copyright (c) 2007 Virtual Magic. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

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