“I produce almost all of the hardware in my own workshop - turning, milling, fabrication, welding etc. My wife tells me I spend an unhealthy amount of time in there!” A sentiment surely heard across the world, but the projects that come out of British engineer Richard Brown’s workshop are rather more unusual. His latest creation is his most ambitious; it’s nothing short of a real functioning jet pack. He’s already carrying out tethered hovering tests and with any luck this persistent dream of science fiction should be lifting off, somewhere near High Wycombe, next year.
Personal flying devices have been frustratingly limited; the Rocket Belt concept first developed in the 50’s is still around and used for publicity purposes is lightweight, simple and can accelerate pilots rapidly up to 60mph, but only for 30 seconds. Then it runs out of highly volatile 90% proof hydrogen peroxide and drops like a stone if you haven’t already landed. Brown’s however is jet powered, uses ordinary kerosene and offers the potential of much longer flights, so are we on the verge of a revolution in personal travel?
Brown has worked on an impressive list of propulsion related projects; including liquid and hybrid rocket engines and a gas turbine motorbike. In 1999 he made a successful attempt to attain the 2 wheeled land speed record. The vehicle he and fellow engineer Andy Scott created for the attempt was a 10 metre long, streamlined 2 wheeler, powered by up to three 772kg thrust hybrid rocket engines. The engines, which were also developed in-house by Brown, burnt solid polyethylene fuel with hydrogen peroxide oxidiser.
During initial trials at Pendine sands in Wales all the technology performed well but Brown discovered how difficult the bike was to drive. Returning to High Wycombe he and Scott built a piston powered training bike, nicknamed Muttley’s Liner, and spent many hours driving up and down a local airfield to get the hang of it. In 1998 all the practice paid off when he successfully achieved a British record of 264mph at Elvington in Yorkshire, on just one engine. The following year it was off to Bonneville Salt Flats in Utah for the growing project team. Their target speed had to be reduced as damp conditions made the salt softer than usual and prevented them using all metal wheels. The best available tyres were rated at 300mph, just below the existing record at 322mph! During 2 weeks at Bonneville they made seven powered runs and achieved the world’s fastest one way speed, now surpassed, of 365mph; surviving a deflation of the rear tyre when it expanded off the wheel rim due to the speed.
After this he endeavoured to use the hybrid engine technology to launch the first privately funded rocket into space, FARIspace. Despite completing the rocket he was unfortunately delayed by bureaucracy to such a degree that the sponsors pulled out ending the project. He had initially hoped to fly from the MOD range at Benbecula in the Hebrides, but after completing all the required documentation the MOD decided not to allow the launch, suggesting that he spend the £50,000 launch fee somewhere else! Brown then tried Woomera in Australia, but was again stymied by legislation, before obtaining approval to fly from the Denel range in South Africa. The launch date was set for March the 12th 2003 and the launch team set about preparations. The one additional requirement the range had was for a certified “flight termination receiver”, to cut thrust if the rocket veered off course. The sole supplier was a company called L3 communications; who, after Brown had succeeded in obtaining all the necessary export permissions, forgot to process the order… The rocket couldn’t fly without the receiver, the sponsors couldn’t support the project past the given launch date and the whole programme collapsed. Scaled Composites went on to make the first wholly private space launch with SpaceShip 1 in 2004.
“As the receiver had to meet certain certification requirements to satisfy the range insurance, L3 Communications had a world monopoly on the item, so powerless to stop events I watched the 3 year project collapse like a pack of cards.”
With the disappointment of FARIspace Brown decided to concentrate on a project less dependent upon factors beyond his control; he’d always been interested in the stalled potential of personal flight and decided to do some design studies.
Jet or rocket packs first appeared in the cinema serials of the 30’s; a number of heroes appeared with back packs of some kind, one rather inconveniently controlled by dials on the breastplate including one labelled Up/Down! These serials went on to inspire the Joe Johnston movie “The Rocketeer”, which featured a nicely thought out, if magically lightweight, pack.
Real wearable flying devices had to wait until the late 50’s, when Wendell Moore created the Bell Rocket belt. This employed a hydrogen peroxide rocket system, where hydrogen peroxide is decomposed into steam and oxygen, rather than burning with a separate fuel, by passing it through a silver mesh. This technology was based on thrusters used for attitude control in Bell’s research aircraft. Peroxide was forced out of pressurised tanks on the pilots back, through a single silver mesh catalyst unit behind the head; and the resulting hot gases split into two downwards facing tubes that protruded from the pack. At the end of each tube was a steerable nozzle that the pilot could use to control the flight.
The rocket belt is light and effective but with one major flaw; it can only carry enough peroxide for a maximum of 30 seconds flight; otherwise it gets too heavy to use and needs even more peroxide to lift the extra peroxide! Despite the issues the US military was impressed by the idea and Moore was funded to develop a jet powered version. Because jet engines burn a small amount of fuel to accelerate a large amount of air, rather than expelling a fixed quantity of propellant like a rocket, they can run for much longer, but do tend to be heavier engines.
The Jet Belt was created in cooperation with small jet engine specialists the Williams Research Corporation; it used a small cruise missile engine and potentially promised 10 minutes flight time. But the project faltered when Moore died and, despite the Jet Belt making it into the air in 1969, was cancelled. The final chapter of the development came when Williams took on the idea and tried to tackle perhaps the biggest problem with the Jet Belt, trying to land with a heavy jet engine on your back. They took one of their small engines and mounted it in a platform on which a pilot stood, a fairing extended up to handrail height and the pilot stabilised and controlled the vehicle by shifting their weight around the platform. The project was finally ruled out by the military in the mid eighties, 30 minutes endurance was just too limited and all these craft are far too noisy for any kind of covert operation; The only application where they might offer an advantage over straight forward helicopters.
In recent years a number of people have built rocket belts for their own interest and for publicity work. British airline pilot Stuart Ross has been working on one since 2003 and is due to fly free very soon. But no one has tried to make a real jet pack since Wendell Moore.
Like many people Brown first saw the rocket belt on the TV coverage of the Olympic opening ceremony from Los Angeles in 1984; he maintained a general interest in personal flight and eventually reached the point where he had the opportunity and skill to have ago himself.
“I went into this knowing it would be my most challenging project yet, but I still underestimated just how difficult it would become.”
Brown began work on his Mark 1 jetpack in late 2002 as FARIspace foundered.
“I spent a vast amount of time considering many different conceptual designs. Most were focused on solving the challenging and almost unique combination of engine requirements - Minimal Gyroscopic energy, minimum torque reaction, excellent power to weight ratio, good fuel efficiency, compact layout small enough for a man's back, preferably upward facing air intake & high positioned thrust outlets and above all "Helicopter like" reliability. Needless to say no "off the shelf" engine meets all this criteria, so after several attempts I have now developed my own purpose designed and built contra-rotating medium bypass turbo fan engine and associated Jetpack components.”
Brown set out to build as much of the pack as he could while using proven off the shelf parts for the most highly stressed components. A jet engine consists of a compressor system, these are the fans seen on the front of a jet engine and force air into the engine; A combustion chamber were fuel, typically kerosene, is burnt with the air coming from the compressor, and the turbine system, hot gas exhausting from the combustion chamber escapes through the turbines, which in turn power the compressors, before exhausting from the engine.
“I decided very early in the design that I was prepared to manufacture everything except the turbine rotors, I also wanted to avoid scratch building the compressor, fan rotors and combustor. These parts, particularly the turbines are highly stressed components. To produce rotors with the required level of performance and integrity & subject them to the 'type testing' normally associated with man rated flight would be prohibitively expensive and beyond my budget. I therefore chose to source these parts from existing, preferably man-rated engines that could be secured as military surplus. However identifying & then matching suitable parts from different engines & conceiving a design to bring them all together proved very difficult, just this part of the design process took 4-5 months!”
The Mark 1 proved to be the most complex and compact of his designs, he spent two years building and testing this unit but performance fell short. The “swallowing capacity” of the turbine, its capacity to accept the hot gas from the combustion chamber, was 15 to 20% less than expected, limiting the maximum thrust. It became clear that mark 1 wasn’t going to provide enough thrust and he had to revise the design.
Mark 2 was designed to use a larger front fan driven by a simpler existing small jet engine. In all of Brown’s designs cold air ducted from the front fan provides the thrust, with the hot gas exhaust providing power for the fan, not thrust. He spent a year testing mark 2 but again performance was still below what he needed. Also the jet engine used in the pack was designed as a high performing, limited life engine for unmanned vehicles. It had to be de-rated to a lower power to ensure longer term reliability and was going to need extensive work to make it capable of running vertically.
Brown started the final design, Mark 3 in mid 2005; it is approximately 85kg all up weight (including 23kg of fuel). This is quite a lot to have on your back but the weight will be offset by the idle thrust setting, so whenever someone is wearing the pack it will essentially weigh nothing. It’s intended to carry pilots up to 95kg so the 195 kg thrust leaves about 15 kg spare capacity. Given the fuel consumption measured under ground test, the pack should be capable of up to ten minutes flight time. That may not sound much, but it’s twenty times the endurance of the best Rocket Belt and will seem long enough when you’re hovering around in a harness!
The pack consists of a jet engine mounted high on the back pack so the engine intake is above the pilots head. The engine is a turbofan, where some of the air sucked in by the front fan bypasses the combustion chamber where the fuel is burnt. In this case cold air from the fan is diverted into the lift ducts that stick out level with the pilots shoulders. These are what actually provide the lift thrust and have steerable nozzles, moved by a joystick, to control the flight. The hot gas from the combustion chamber first drives a turbine that powers the intake fans and then exhausts at the base of the pack; carefully directed away from the pilots legs!
Brown began ground testing of the Mk3 pack in 2006, initially he found excessive losses in the lift ducts and has refined their shape with the aid of CFD, computational fluid dynamics, and has now progressed to flight testing.
“Almost all of the unit has been custom designed & built by me for this one project with only the turbine rotors, part of the combustor, part of the compressor and fan rotor originating from several different other man rated engines. This very difficult development has now taken the project to 6 years of constant effort but I am at the exciting stage of beginning to add and test the flight controls.”
In the interests of safety he is beginning by attaching the pack to a movable arm. This is counter balanced like an angle poise lamp, so that it doesn’t add or remove any weight from the pack, and allows it to rotate freely while still keeping a safe hold of it. The arm can also be locked up to restrict movement in any axis; enabling Brown to gradually learn the flight control technique in stages.
If the restrained tests go as planned Brown hopes to make the first free flight some time next year. Once he is confident in free flight he plans to exhibit it at air shows and events. As to future applications of the technology he has no plans. “I’m doing this for my own interest. If the technology had a practical application then it would already exist, I’m often asked if the military will be interested but it’s much too bulky to run around with and it’s so loud you’d hear anyone coming a mile away.”
There is of course another approach to jet packs, that being developed by Swiss pilot Yves Rossy. His work focuses on powered personal horizontal flight, using a pack consisting of folding carbon fibre wings and a number of small jet engines. His pack is flown from an aeroplane already in the air and can’t take off or hover; but could the two technologies be brought together? “It’s an interesting idea and I’ve tremendous admiration for what Yves has achieved but we’ve simply not come into contact as yet. Maybe it’s something for the future.” He won’t be drawn either on what he intends to work on next, the completed FARIspace rocket still sits in his workshops so might we yet see a new independent space shot?
“The hardware exists and on a personal level I would love to see the rocket fly, but it’s not a priority for me. At the time we’d have launched there had been no privately funded space launches and of course that’s all changing very quickly.”
We may not be about to see jet packs for sale but we should see more of Brown’s project. Who knows, one of the enduring images of the 1984 Los Angeles Olympics was Bill Suitor flying the Bell Rocket Belt into the stadium. Maybe Browns Jet Belt might be able to put in a much more accomplished display for London 2012 and inspire another generation of engineers…
Personal rotorcraft and the Martin Jet pack
Accelerating a large mass of air a small amount, like a rotor or propeller, is much more energy efficient than accelerating a small mass of air to a high speed, like a turbojet. In light of this some people have sought to increase the effectiveness of the jet pack concept by trying to create personal helicopters or vehicles lifted by fans. One such effort, Solotrek of California, progressed to the stage of flight testing under a safety tether; but a problem with the tether system in 2002 led to the loss of the prototype, the pilot survived unharmed, but the company collapsed.
Another new project that attracted significant attention, and indeed bile from a number of established US rocket belters, is the Martin Jet Pack from New Zealand. It has been under development by Glen Martin for 27 years and consists of a V4 piston engine driving two ducted fans. These are mounted either side the pilot at shoulder level. It is controlled by directing the airflow from the fans and is equipped with a parachute in the event of engine failure. It’s too heavy to walk around with and has been classified as an experimental ultralight aircraft by the US Federal Aviation Administration. It should be capable of 60mph for 30 minutes and Martin hopes to start selling the first production Martin Jet Packs for $100,000 in 2009.