Vehicle: Bicycle: Frame
Compressed Air Bike Frame   (+7)  [vote for, against]
Safe AND light frame for velomobile

I have an 8 mile commute and like many people, drive it alone in a 3000lb vehicle burning more gas than really necessary, so I should just ride my bike to work. The reason I don't is threefold: safety, lack of carrying capacity and cleanliness/weather. I have to think there are a lot of people who are in similar situations or who could use a vehicle like this for basic transportation.

The basic solution I usually come to is the velomobile (link). It solves two of the three issues, but fails due to cost and safety. The small amount of safety afforded a bicyclist is in their ability to avoid danger, i.e. hopping to a sidewalk, keeping out of normal traffic, etc. These options are not available to a velomobile and due to weight restraints most velomobiles would probably fair badly if even tapped by a small car. Also cost. You can easily purchase a small car or motorcycle cheaper than getting any velomobile. This situation certainly adds to the cost as no one has the volume to reach economies of scale which would lower prices.

So my idea is for a scalable frame design which incorporates safety, scalable carrying capacity and options for enclosability to keep occupants insulated from road dirt and weather. Add to that the option for a small auxiliary power source like gas/electric hybrid or electric and batteries and I think this could be the solution for lots of people’s transportation needs. To do that we need to create a spot for the driver inside a strong cage that can then be wrapped with an aerodynamic external shell and because people are weak, as the average human being can only produce about .1 HP continuously (link), the whole structure needs to be light and suffer from as little drag as possible. Normal trikes are built on steel or aluminum frames. Velomobiles have been made with aluminum and steel subframes, aluminum monocoque, fiberglass over foam and even carbon fiber monocoque in the case of the Go-One (link).

The core concept of this frame design can be easily visualized by anyone who has held a plastic bottle of carbonated soda. The bottle alone is very weak, but when pressurized it can support large loads. Now imagine a long tube with the diameter of a 2 liter PET soda bottle wrapped by fiberglass and pressured to a multiple of the normal soda bottle pressure and you get the idea. To protect the driver and provide a basically aerodynamic form the PET tube will not be straight, but formed in a tear drop shape though tapered and open (like a U bent to almost touch) at the pointy end. This will then get wrapped by alternate layers of rosin soaked fiberglass tapes running axially then radially. The radial wraps will eventually resist hoop stress caused by the air pressure and the axial tapes will resist both longitudinal stress from the air pressure and torsional stresses imposed externally on the frame. This frame member will be placed at bumper height as the central spine of the vehicle. To it will be attached two similarly constructed secondary rib members of about half the diameter tapered at the back where they are bound to the main member and with spherical ends at the front where they all attach to the main member. They each run from the front down to the floor level at each side and then connect to the main member at the back. There is one similarly constructed circular tube, located just behind the driver and inside all the longitudinal ribs. The structure is then enclosed in shrinkwrap plastic and windows added where desirable. Each tube is connected to a central system for inflation and monitoring, but also has an overpressure blow out valve vented to a muffler in the back.

Into this cage arrangement a standard mesh recumbent style seat and petals are installed, plus twin external front wheels and single rear wheel that attaches to and rides between the tips of the main drop shaped member. The whole structure should be light and very stiff. In an accident the tubes would become overpressurized at which point the gas would be vented to absorb the energy. The rollcage would protect the driver though would probably be destroyed in the crash though the driver and the expensive drive chain would be preserved to be moved to a new vehicle. The PET liners could then be recycled to make new PET liners.

When I want to ride my bike, I always have to check the air pressure in the tires, in this case I'd have to check the air pressure in the tires AND the frame. I'd have to get a large volume foot pump and then just pump it till the overpressure valves squeaked.

My greatest worry is having a structural blowout near my ear and loosing hearing, so maybe having a thin shell around the drivers head or on driver facing surfaces might be a nice add-on, but not necessary as long as quality control and necessary extra material is used to far exceed design stresses are used.

I think these could be HUGE sellers in China. Add in a stand for the front or a hook in the back and you could store them vertically to save space when not in use.
-- MisterQED, Sep 14 2010

Velomobile http://www.bentride...velomobileguide.htm
[MisterQED, Sep 14 2010]

Go One 3
[MisterQED, Sep 14 2010]

Strength of glass http://www.roymech....s/Matter/Glass.html
[MisterQED, Sep 14 2010]

Human HP
[MisterQED, Sep 14 2010]

I never imagined this being used as a bicycle frame, but I have imagined it being used in serious structural applications.

(Don't fret, I'm only a designer/programmer - I can't make that call, but I still have ideas).

My thought was to put a liquid under pressure in a cylindrical member.

I think it would work - thus my + vote! Bravo!

I do know that high strength grout in steel tubes tensioned by cables produces incredible strengths.

Field test for the unimpressed:

Roll up your garden hose under pressure. Then drain it & roll it up.
-- Zimmy, Sep 15 2010

Put a regulator on the head-stock and you could use it for SCUBA diving [+]
-- coprocephalous, Sep 15 2010

With regard to the safety aspect: Any light vehicle has a fundamental problem in a collision with a heavier vehicle. The light vehicle will experience greater acceleration (in inverse proportion to it's mass). It is the acceleration which causes injuries, particularly to the brain and internal organs when they collide with the inside of the skull, rib cage etc.

I very much support the idea of light vehicles, but while consumers base their perception of safety on crash performance, heavy vehicles will win every time.

The challenge is to swing consumers perception of safety.

In the meantime, a pressurised thin wall tube is a nice idea, so bun for that!
-- Twizz, Sep 15 2010

[Zimmy] If you go with liquids, it is a short step to using sand which was used by the Egyptians. I'm suggesting compressed air for which I have only read one reference which was ~25 years ago I read about someone trying to build a human powered heleicopter and was using compressed air in the rotors for stiffness. It is an interesting idea that I have kicked around try to find a correct application. It works, it has to. It's advantage is only when the pressurization exceeds the compression strength of standard foam cores and then only by it's light weight. It's most common use is in Zodiacs, though the skin there is very heavy and the air pressure is low, ~3 psi in mine. I have a 13 footer.

[Twizz] Yes, physics is against light vehicles, which is why I made energy dissipation so integral in the design. Is it perfect, no, but it's WAY better than a motorcycle or even some small cars. The good news is it won't have enough power to drive on the highway so those heavy vehicles will be going slower. I also see this in places like China and India where most things are lighter and slower and where it's inexpensive construction would be most appreciated.
-- MisterQED, Sep 15 2010

The energy absorbtion element is meaningless without any distance over which to absorb that energy or mass to react against.

I don't agree that it's safer than a motorcycle. I've survived a collision by jumping clear while my motorcycle hit an oncoming car on the wrong side of the road. I wouldn't be able to do that if I was in a cage.

It's also worse than any small car, simply because it's lighter and smaller and the laws of physics apply. Higher accelerations and shorter distances over which to absorb energy will always result in more injury. Keeping the occupant in the impact zone doesn't help.

The emphasis should be on active safety - don't crash!

How does the velomobile's lack of power make heavy vehicles move more slowly? Are you suggesting it could only be used in 30mph speed limit areas?
-- Twizz, Sep 16 2010

So essentially, a crash cage surrounded by airbags? [+]
-- BunsenHoneydew, Sep 26 2010

random, halfbakery