Where is my damn jetpack? I mean seriously! Itâ€™s 2007! Werenâ€™t we all supposed to be flying around in these in the future, as predicted in the 1950â€™s and 1960â€™s? Technology has progressed by leaps and bounds in the past few decades and still NO JETPACK!
Sure there are other personal flying devices like ultralights and powered paragliders, but I want a jetpack!
The whole idea of a jetpack is like the Zen of flying machines. A manageably-sized, easy to fly, light-weight, safe pack which you can strap on and go off for a flight to the supermarket or to work or for just a bit of sightseeing. You land your jetpack where you want and then simply walk inside and leave the pack next to your desk.
When the days out, you strap it on and head outside. You might pick up a newspaper, which you stick in the jetpacks side pocket, and then extend the controller arms, grab the stick, step politely away from anyone who might get disheveled by the jetwash and then fire it up and take off for home.
Why donâ€™t we have those? Well, there are some reasons. Jetpacks have been built and are not totally fictional. They do work, but getting one with adequate range and size is a tough nut to crack.
To be a true, usable, practical â€œjet pack , like is seen in the movies the device must meet some basic criteria: Be of manageable weight, no more than a couple hundred pounds at the very most, and ideally much less. Have good endurance of approximately 35-45 minutes, at the very least. Be able to product enough thrust to lift itself, its pilot and still have enough left over to maneuver. Be relatively safe and easy to use.
Can it be done? Maybe. To understand, lets take a look at the history of backpack flight.
In the beginning
The Bell Corporation began developing the concept of a jetpack, or as it was called, a â€œflying belt as early as the late 1950′s. Although earlier attempts had been made, this was the first serious effort at a wearable flying device. With funding from the military, the project produced its first workable prototypes in the 1961.
The first successful â€œflying belt, was the Bell Rocketbelt, a relatively simple, strap-on flying backpack powered by hydrogen-peroxide rockets. It was relatively easy to fly, had plenty of power for lifting and maneuvering, good controls and was reasonably sized with manageable weight. It seemed like the perfect starting point and proof of concept. However, it also only could fly for about 22 seconds before the fuel tanks ran dry.
Additionally, the fact that it ran on 90% concentration hydrogen peroxide could be a bit of a concern. The system decomposed hydrogen peroxide on a catalytic grid to make high pressure steam for thrust, and although this was a simple and effective means of propulsion, the peroxide could eat human flesh down to the bone if it were accidentally spilled or the tanks ruptured. Due to these limitations, the army was rather disappointed and saw little potential for the rocketbelt, with the project ending in 1969.
This type of device is actually still around today, and newer versions have pushed the flight time up to 30 seconds (by enlarging the fuel tanks). The rocket belt is commonly used for exhibitions and movie and television stunts. With good editing and camera changes, its 30 seconds of flight time can be made to look like much more, but practical uses beyond entertainment are limited by the very short flight time. One of the most notable appearances was in the 1984 Olympic Gamesâ€™ opening ceremony.
Enter the jet engine
The limitations of a rocket-based system were apparent from the beginning. Although the rocket engines provided a small, controllable and high power means of thrust, rocket engines are hardly fuel-efficient. Rocket engines are most efficient for uses which require very high speed and relatively short durations of use. For a device like a flying belt or pack, they are not a very good solution.
Thus focus at
The Jet Belt did achieve itâ€™s goal of better endurance, with flight times ranging from about 25 minutes all the way up to 40 minutes, depending on fuel load and how much maneuvering was done. However, it did have some shortcomings. For one thing, the pack weighed a good 300-400 pounds, depending on how much fuel was carried. This hardly made it a practical â€œwearable pack that one could walk around with and necessitated an external stand to bare the weight when the pilot strapped it on.
The performance was decent, but left much to be desired. Although it did have enough power to fly, it was still somewhat underpowered, making it sluggish in climbing and maneuvering when compared to the rocket-based systems. To achieve stability and control, the jet engine was mounted with the intake facing downward and the thrust channeled through two U-shaped ducts which did not help efficiency and made an already loud jet engine even louder.
Additionally, major safety concerns existed. Aside from having scorching hot jet exhaust blowing just a foot and a half from the pilots head, the single jet engine was less than 100% reliable and unlike aircraft, which have some glide ability or helicopters, which can use the inertia of their spinning blades and the principal of autorotation to make an emergency landing, if the engine were to seize up or flame out, the jet pack and pilot would drop like a stone. A rapid-deployable parachute was therefore an important part of the system, but at altitudes of less than 180-200 feet, it would be of little use. Pilots reported that flying in close quarters with obstructions, such as wires was extremely dicey, as wires were very difficult to see when flying at a high rate of speed.
Despite showing some promising results for a feasible jetpack, the project died as funding dried up in the 1970â€™s.
The Williams X-Jet: Williams International, a company well known for pioneering work in microjet engines and the maker of the engine that powered the Jetbelt took the concept a bit further with the experimental X-Jet. Dispensing with the backpack design and adding greater fuel capacity and a slightly larger engine, the prototype was dubbed the â€œFlying pulpit and could fly for a solid 45 minutes with good maneuverability and speed. However, the X-Jet never went into production, as it was seen as having little commercial potential, given the competition from conventional helicopters. But it still looks like a lot of fun.
Ducted Fans: In theory, a ducted fan based system could achieve much greater efficiency and therefore endurance than a jet engine. The reason is that large diameter fans more a greater volume of air but do so at a lower velocity. Compared to a jet engine, which moves less air, but does so at a much higher pressure and velocity, the approach is considerably more efficient for low-speed and lift applications.
Although a few concept designs have been made, and the principal has been shown workable on full-sized aircraft, there are no known successful ducted fan packs which are airworthy. However, internet sites do sell plans for a ducted fan based flying pack. But when investigated by the Mythbusters, the design failed to do much more than shake and rattle.
Of course, if a ducted fan pack were created, the size of the fans would make it a far cry from the dreams of a â€œtrue jetpack
Helicopter Packs: Another approach has been to use a helicopter-based backpack as a means of creating a personal flying device. Small one-man helicopters have been built and the concept of strapping such a machine to one’s back is not beyond the realm of possibility, but only limited success has been achieved in creating a stable and safe system based on this arrangement. It seems that the jetpack design offers few advantages over a more conventional layout.
Winged Jetpacks:Adding wings to a jetpack would, in theory, improve efficiency for horizontal flight. The addition of wings would generate some aerodynamic lift, reducing the need for jet thrust alone to maintain flight. However, this does have a major problem: jet packs do not fly like superman. They fly relatively vertically, because a prone position would lead to the pilot’s legs hanging down haphazardly. Only at very high speeds would there be enough air velocity to keep the legs elevated. Just try holding up your legs while your upper body is supported by a bed or table. Also, the addition of wings would increase size.
The only successful uses of winged jetpacks have been by skydivers, where the wings act mostly as a glider, helping to achieve control and gliding while falling from an aircraft. The small jets allow for greater velocity and maneuvering, but do not actually make the setup capable of sustained flight.
While the development of jetpacks has been relatively dead since the 1970â€™s, technology in applicable fields has progressed rapidly. Is it possible that a true usable, reliable, workable jetpack could be in the future? Maybe. Possibly.
What a new jetpack might be like:
(Pure speculation, but based on current technology)
With weight such a constant concern, a modern jetpack would most certainly be built out of composite materials, with a thin shell made out of carbon fiber or something similar and a frame made out of similar composites or possibly tubular titanium alloy. The basic frame and shell would weigh as little as a few pounds.
The inefficiencies and complications of the ducting system could possibly be alleviated by an active control system, which would keep the platform stable and adjust the thrust and thrust vectoring by using sensors such as piezoelectric gyroscopes. The Segway has shown that
active stabilizing systems are feasible for small platforms. Modern use of fly by wire systems have proven them to be robust and reliable. For such a critical system, there would need to be built in redundancy, with uninterrupted power, multiple gyroscopic sensors and simple failsafe logic systems which could take over in a system failure. With modern electronics, this could easily fit on a small circuit board.
Navigation and Collision Avoidance:
The dangers of wires or other obstacles can likewise be addressed by easily available electronics. GPS and a stored database could help store known hazards and wires can be detected by optical sensors, LIDAR or simple radar rangefinders, like those used in police radar guns. A helmet-mounted or goggle display can give such warnings and, if necessary, the electronic control system could force the unit to slow down or climb if it is headed toward a collision.
The benefits of such technology goes beyond avoiding wires or other hazards, however. Modern electronics would allow pilots to fly at low levels safely and without needing to devote all their attention to avoiding hazards. Communications and navigation systems could allow for enhanced safety and prevent becoming lost or disoriented.
Safety if the engine fails:
Modern ballistic parachutes are effective even at low altitudes.
If the altitude is so low that a parachute may not be effective, yet high enough to cause serious injury, ejection seat technology may be useful. Modern ejection seats can function even if the aircraft is very near the ground, by employing small short-burn solid fueled rockets to achieve the necessary altitude and to clear the aircraft. Such technology could be added to the jetpack.
Additionally, if it were possible to add a second engine unit, this may allow for enough thrust for a safe landing. Although it would be lopsided electronic thrust vectoring could help counteract the inherent stability issues.
Since the time of the Bell Jetbelt, microjet technology has progressed greatly. The latest incarnation of the technology is the Williams International EJ22, which is currently in development and which has, unfortunately, been postponed from commercial deployment due to production delays and loss of a contract with Eclipse Aviation.
The prototype of the EJ22 weighs only 85 pounds but can produce 750 pounds of thrust! It reportedly is also one of the most efficient small engines ever developed. It may be possible to scale this engine down even further or to optimize itâ€™s efficiency for lower thrust needs.
The most efficient modern jet engines for low to medium speed use are high bypass turbofan engines. Such engines achieve high efficiency by using the jet turbine to turn an outer fan turbine, which essentially works as a ducted fan. By doing this, the engines are able to move a larger volume of air, and therefore do not need move the air at as high a rate of compression or velocity as a turbojet would. And by mixing the air, the air coming out is not necessarily as scorchingly hot. Modern jets are also quieter
Using dual turbofan engines, made up of large fan compressors and relatively small combustion chambers may be able to achieve higher efficiency than other means. This also offers possible safety benefits as mentioned above.
With adequate funding and development, a safe and practical jet pack may be in the future. But then again, that has been said many times before
Williams International – Makers of microturbofan engines.
Peroxide Propulsion – Sells hydrogen peroxide and modern rocketbelt units.
Jetpack International – Sells rocketbelt units and claims to have a turbojet engine under development.
Roketbelt Technologies – Yet another manufacturer of a modern derivative of the original rocketbelt system.
Rocketman – A guy who does exhibitions using with rocketbelt system.
Flying Contraptions – Info on the rocketbelt, jetbelt and other aircraft.
Popular Mechanics Article – Info on recent rocketbelt shows and developments.
Bell Rocket Belt Info – Historical info on the Bell Rocketbelt.
The Rocketbelt Caper- Information about a strange incident where some guys built some rocketbelts and then one got murdered.
Unread Aircraft – More info on the Jetbelt.
The RB 2000 – An updated Rocketbelt design that has larger tanks and can get a few seconds more flight.
Imperfect Ideas – Much good info on the development of the original rocketbelt and the jetbelt.
The Most Comprehensive Website on Rocket and Jet Belts – The name pretty much says it all…
Skywalker Jet – An article about a guy who strapped a bunch of large model-aircraft jet engines together to make a pack of sorts. I have spoken with some amateur jet engine builders and engineers who referred to the guy as a complete idiot. Not surprisingly, the official website is now down.
Also, info from Wikipedia is available via the links embedded in the post…
This entry was posted on Monday, September 10th, 2007 at 2:22 pm and is filed under Culture, Good Science, History. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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