Accelerating a Jetpack with 3D Design Software
Jetpacks have long been a staple of science fiction. Since the 1950s, British comic book hero Dan Dare (“Pilot of the Future”) would use one in battle with his nemesis, the green-headed Mekon. More recently, there was Boba Fett in the Star Wars saga.
For various reasons of safety and practicality, they have stayed relegated to fiction . . . until now.
Enter the Martin Jetpack, the first commercially available practical jetpack from the Martin Aircraft Company, based in New Zealand. More accurately, it is a ducted-fan pack, but we can ignore semantics here because jetpack just sounds more awesome.
So what makes the Martin Jetpack so practical where so many others have failed?
Generally speaking, there have been two main hurdles in developing a practical jetpack: safety and flight time.
The most commonly known jetpack was the Bell Rocket Belt. First demonstrated in 1961, this device used high-grade hydrogen peroxide as a fuel. The nitrogen-pressurized H2O2 would be blasted through a catalyst bed (typically silver or platinum) resulting in a rapid exothermic decomposition of the H2O2 into high-pressure water (steam) and oxygen, which would eject through the nozzle resulting in an upward motion (in accordance with Newton’s third law). This was a true rocket (or jet) pack in every sense of the word.
This use of H2O2 leads to one problem in particular—it results in high specific impulse, but very low flight time (around 30 seconds at most). This means that these types of rocket packs tend to be useful for all but the briefest of demonstrations (Super Bowl halftime shows, etc.). And because of the 30-second flight time (15 seconds to climb, 15 seconds to safely descend) it means that the operator never reaches the minimum safe altitude for a parachute to work.
Fast forward over 50 years, and Glenn Martin, founder of the Martin Jetpack, claims to have addressed these issues, thanks largely to the advances in composite materials, embedded computer systems (for stability and control) and also CAD and simulation software.
In terms of actual flight hardware, Martin did away with fuel-hungry H2O2 engines and replaced the propulsion system with two lightweight ducted fans powered by a 2 liter V4 gasoline engine capable of a respectable 200 horsepower. This system allows the jetpack to maintain 30 minutes of flight time and a load of 260 lb (120 kg), including a full tank of fuel. So there’s no problem reaching a safe parachute altitude there. As a little safety bonus, Martin included a ballistic parachute within the system itself, as a backup in case things go badly. Having only two rotors allows no redundancy. There is no auto-rotate option as is found in helicopters. The explosively deployed parachute is, therefore, completely necessary.
The control surfaces allow control and stability via usual aerodynamic principals. Aerodynamic slats positioned within the ducted airflow allow translation around the pitch, yaw and roll axes, all of which are regulated and governed by the onboard embedded flight control system.
In the early days of development, Martin relied on AutoCAD and other 2D CAD packages. Apparently the project moved at a fairly slow pace until they invested in SOLIDWORKS in 2008. This switch gave the engineers a much-needed shot of design adrenaline. In addition, the development process and, in particular, the prototyping cycle time was accelerated significantly.
Given the use of expensive composites (aramid fiber, carbon fiber) in the Martin Jetpack, especially in the ductwork design, it was fundamental to ensure that accurate CAD models and robust simulations were in place before committing to building prototypes. Proper model surfacing and simulations enabled models to be constructed quickly and the fluid flow to be analyzed before blowing wads of cash on molds for the ductwork.
One thing of vital importance requiring high-dimensional accuracy is the blade tip clearance in between the rotors and the ducting inner walls. Any deviation from these tolerances can result in either a blade/duct collision or reduced efficiency of the propulsion system. Therefore, modeling the mechanical aspects as well as the fluid dynamic elements was made vastly more effective by using the solutions provided by SOLIDWORKS.
The Flow Simulation analysis also allows easy visualization of not just the flow trajectory (alleviating areas of potential stagnation) but also allowed Martin to color the flow elements according to the speed and/or pressure of the flow. And as any aerospace engineer (and Monsieur Bernoulli himself) will tell you, fluid speed and pressure are fairly important in the world of aerodynamics.
The flow simulation (see Figure 1) shows air being sucked into the ducts, forced through the ducts via the fans and ejected at high pressure (depicted as red and yellow lines).
Figure 1. Flow simulation.
Additionally, the assembly feature (see Figure 2) was used to determine how the unit fit together and was also used to create kinematic motion studies as well as animations for marketing purposes. Examples of both the Flow Simulation visualization and the animated assembly can be seen within the Martin Jetpack App (available on Android and IOS).
Figure 2. Assembly animation.
For marketing and promotional purposes, Martin also made extensive usage of the PhotoView 360 rendering tool (see Figure 3). Undoubtedly, Martin has made a mechanically awesome product here. But finding the right aesthetic is also a key element for marketing and for the end user. Utilizing the PhotoView 360 renderer enabled Martin to create photorealistic renders from the early stage, which helped keep the aesthetics front and center during the design process. And, as most design engineers and product designers will agree, a realistic renderer can be beneficial from a visual and creative viewpoint.
Figure 3. Rendering from PhotoView 360.
According to Martin, “We’re using the renderings in our brochures and pamphlets. When I’m traveling overseas, I use these renderings and eDrawings files to show how the jetpack works in as much detail as necessary. SOLIDWORKS solutions are integral to every facet of the jetpack’s development.”
Will we all have our very own jetpacks? What about the price?
According to the Martin Jetpack website, the company is aiming for the sub-USD$150,000 bracket for the recreational version. It is the cost of a luxury car, but you will have your own flying machine and beat the traffic jams.
Start saving. The Martin Jetpack will be on sale to the public later in 2016.
Check out the Martin Jetpack test flight.
About the Author
Phillip Keane is currently studying his PhD at the School of Mechanical and Aerospace Engineering at Nanyang Technological University, Singapore. His background is in aerospace engineering, and his current studies are focused on the use of 3D-printed components in spaceflight. He previously worked at Rolls-Royce and Airbus Military and served as an intern for Made In Space and the European Southern Observatory.