Agent 007 James Bond has nothing on German engineering
student Mario Böhme, who developed a portable jetpack as a fun project.
A rocket drive buckled to the back of a pilot provides
thrust for a lift off-at least in theory.
What's particularly interesting about his design is the use
of plastic bearings in the overall construction, including in the control
handles and in the system that bears the pilot's weight.
"I considered other materials, but the plastic bearings had
the lowest weight and will show less failure based on corrosion processes,"
says Böhme. The propulsion reaction generates corrosive gases that are more
damaging to metal than the specially developed plastic compound used in the bearings.
A plastic rod end bearing holds the whole rocket assembly
together and covers the pilot's weight. "If this bearing fails, the rocket
assembly will separate from the pilot - the pilot will fall down," says Böhme.
"So it must be proven that the bearing can cover the stress during the flight.
For safety reasons the bearing will be replaced after a couple of flights."
The temperature for the bearings in the jetpack will not
exceed 40C (104F), according to Böhme.
"The whole project was planned, designed and built by just
one person - me," says Böhme. "Some parts were bought as off the shelf parts,
but this was just a handful. The other parts were designed and calculated by
myself with the latest CAD technology I could use at my university."
Böhme worked on the project for more than five years without
any sponsors. "Now I'm looking for sponsors to get enough money to get the
jetpack into the sky and improve my personal handling of the flying system. The
fuel is the most expensive part at this stage," says Böhme.
The project was recognized as part of the manus 2011 awards program
held by igus GmbH.
Igus developed the manus program to showcase innovative uses of plastic
Igus develops tribologically optimized material compounds
designed for low wear and long life. They are widely used as bearings and cable
All of the igus technology is in house and very proprietary -
even the identity of base polymers and particularly the compounds and
compounding methods. It is known from company literature that polymer families
used include polyamide 6, 66 and PEEK (polyetheretherketone). Reinforcements
include glass and carbon fiber, as well as a newly developed nanomaterial.
A 2011 winner
in the Design News Golden Mousetrap
competition is an advanced tribological polymer from igus using nano-sized
particles. Use of nanotechnology improves the lifetime of its high-performance
plastic plain bearing predecessors by a factor of six, according to igus.
The company manufactures its own tooling and operates several
hundred molding machines at its home base in Cologne, Germany. These molding
machines make parts used for products assembled in Germany, East Providence, RI
and elsewhere and are shipped globally.
"The biggest battle we still have is convincing engineers that
plastics can do a better job than steel as bearings," bearings unit manager Tom
Miller commented in an interview with Design
News at the company's Rhode Island location. "One thing we run into is an
engineer who says ‘We tried plastics 10 years ago and it didn't do the job.'"
As in all technical applications - and particularly for
bearings - it's critical to make sure you have the right plastic formulation
and that the parts are stress-free and made to the correct tolerances. Miller
says that a lot of molders are selling plastic bearings that aren't up to
One of the big benefits of igus plastic bearings is that
they run dry - no external lubricants are required. That makes them good
candidates for machinery used to process food or pharmaceuticals. Also,
according to Miller, no maintenance is required. They also operate much quieter
than metal bearings. And as Mario Böhme found, they are much lighter than metal
bearings and the right compounds offer good chemical resistance.
Bearings made from PEEK compounds can take thermal
conditions up to 600C (482F).
Miller says, however, that plastic bearings are not
recommended for continuous heat, including applications such as fans.
I'd like to learn about the design as well. However, I like it when young engineers or in this case a student start to think outside the box and look at ideas that may be overlooked by others. It's a good opportunity for us "others" to take a second look at something like plastic ball bearings. I've had a little experience with plastic bearings at lower temps. My experience was positive because of the chemical resistance of the plastic.
Another idea may be to use plastic slides rather than bearings in some instances. In some designs a roller bearing type system may be a little overkill.
That something has always been done that way is the worst reason for not changing it ! Congrats to most people for trying new ways, just evaluate the risks, the failures and be careful. Far too many fail and don't put much effort into finding out why.
They all jumped on one error but missed the part about the bearings not being in the high temperature area. So, although there is a serious error, it is in a different area..
If the bearings are replaced every few flights, it would be very interesting to know why, since I don't do any applications where service that often would be accepted. In fact, A lot more information about the jetpack would be interesting. I don't think that the location of the jets was obvious, in fact, I did not see anything that looked like a jet any place above the wearers cg. and so I would really like to know how it is made to be stable. It does seem to be quite different from the other jetpacks that I have seen. So more information on that part would be good.
I do wonder more than a little about the durability of the IGUS bearings if they must be replaced that often, how about a description of why?
Welcome to the world of flight. For the pilot's safety and longevity, a bearing that keeps him secured to his craft is an important component. The aviation authorities probably thinks so as well. This old guy would rather see an established material used with a robust configuration (AKA overkill) on this critical component until the loading parameters are better defined and the plastic bearing can be tested and confirmed to a much higher reliability. Why do you think aircraft cost so much?
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