Proposed Twin FWE-boosted Recumbent Trike

[larry cottrill]

Well, here's a drawing I've been putting together in my spere time for the past few days. This idea was triggered by the photos of Chris's sidecar-style trike, although this is almost nothing like it. The drawing is just a basic layout - anyone who would build such a beast can easily work out the details on their own, anyway. Probably, "real" bike builders will find a lot to criticize about it.

I like the recumbent plan because it keeps the CG low on the machine with rider in place. I decided that two wheels in front is better than two in back, for good turning, so there is a tie rod reaching across. The tie rod arms also provide for the "inside" wheel being turned sharper than the "outside" wheel in the turn. Also, the side-by-side front wheels mean that the pedal crank can actually be ahead of the front axle, to keep the wheelbase reasonably short even with the fuel tank behind the headrest and in front of the driving wheel. Sprockets and derailleurs are standard ten-speed mountain gearing, with controls on the handlebars in the usual manner. The jet throttle could also be handlebar mounted, or could be an aircraft style throttle at the side of the cockpit area. I show a second tie rod, rather than chain and sprockets, to connect the handlebar to the center turning hub for the front wheels. One obvious criticism will be the narrow stance of the front wheels, but I felt this was adequate considering the low center of mass achieved.

Engines are twin giant FWE III [Fo Mi Chin II intake style], scaled up to 1420mm overall length and 128mm tailpipe diameter, with sheet aluminum heat shields inboard. Propane shown for fueling, although a liquid fuel scheme could theoretically be used. The drawing suggests a lightweight plastic speed shell as a nice option, shown as a thin outline around the bike.

Just something thrown out for fun. All comments / criticisms welcomed.

EDIT: Alas, I have discovered a serious mis-scaling on the drawing: I made the pedal crank location so far forward that the fully extended pedal is almost SIX FEET from the lower edge of the seat back! You would need to be built like Charles Lindbergh, and even a bit taller yet, to use the machine as pictured. All that would be needed to correct it would be to move the pedal axis rearward as needed. My apologies to short people [such as myself] everywhere ...

L Cottrill

[El-Kablooey]

Very cool!! I like it!

[mk]

I'd like the version with a cogwheel cascade instead of the ultra-long chain.
Hehehe...

Looks neat.

[hinote]

A) Put the drive wheels in the front and make the single rear wheel the steering one.

Mike:

I believe rear-wheel steering is inherently unstable. Can anybody confirm?

Bill H.
Acousctic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

[Mike Kirney]

I have two small criticisms:

A) Put the drive wheels in the front and make the single rear wheel the steering one. You will avoid many mechanical problems and save a lot of weight this way. Ultra-long drive chains are very inefficient and wear out very quickly, especially on a bicycle where even the slightest mechanical inefficiency is very noticeable.

B) The rider's posterior is too close to the ground. You should have at least 20 cm of clearance between your buttocks and the road surface, lest you get something lodged between them (like a broken bottle or a dead racoon) while travelling at high speed. Front wheels will kick up stones and other road trash so you want the rider's face to be well above the top of the front wheels. Of course fenders will largely solve this problem.

The overall concept is very promising. It looks amazingly similar to an HPV I have been meaning to build for years now. I like the cambered front wheels. The 'tadpole' trike with cambered wheels will be hard to steer but almost impossible to roll over or upset. Remember to include a seat you can adjust forward and back to account for different rider leg lengths. Full cowlings are not practical on road-going designs because they are heavy and trap heat and moisture around the rider's body. They are also usually fragile and liable to get trashed very quickly in everyday use. I think it would be better to go with a partial cowling/windscreen and streamlined fenders or something. Cycling is no fun without the wind in your face anyway :-) .

[hinote]

I like the recumbent plan because it keeps the CG low on the machine with rider in place. I decided that two wheels in front is better than two in back, for good turning, so there is a tie rod reaching across. The tie rod arms also provide for the "inside" wheel being turned sharper than the "outside" wheel in the turn. Also, the side-by-side front wheels mean that the pedal crank can actually be ahead of the front axle, to keep the wheelbase reasonably short even with the fuel tank behind the headrest and in front of the driving wheel.

See the attached photo. Wheels-front trikes are quite numerous--so the concept obviously works.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

[Mike Kirney]

Rear-wheel steering on a tricycle such as this requires more attention from the driver but does not affect actual vehcile stability at all. Buckminster Fuller designed an 3-wheeled automobile with rear wheel steering and it was said to be able to catch phenomenal air off of various obstacles and land with perfect safety. It was practically impossible to roll over. Accidental spin-outs are a danger and rear-steered vehicles can be very difficult to control in a cross-wind, but from a mechanical prototype point of view they make much more sense than having to articulate two wheels and transfer power down the entire length of the vehicle. The dead simplest version of a FWD 'tadpole' trike would have pedals attached directly to a cranked front axle and a tiller attached to the rear wheel suspension or forks. No chains, struts, tie rods or other anything required.

[Mike Kirney]

You can overcome high speed instability by giving your trike a longer wheelbase. Commerically available trikes like the one pictured have wheelbases as short as possible to make for snappy handling and easy storage and transport.

[Mike Everman]

Hey, Tundra. Good to see you posting again. Cheers.

[larry cottrill]

I believe rear-wheel steering is inherently unstable. Can anybody confirm?

On a bicycle, this is quite true. There was an experiment done years ago with a bike set up for rear wheel turning, and NO ONE could successfully ride it. This was reported in an old issue of American Wheelman magazine. What's really strange is that no one seemed to have an explanation as to why this was impossible, yet the physical explanation is actually extremely simple:

When you turn the front wheel of a normally arranged bicycle, the front of the spinning wheel is pushed into the turn, with the wheel spinning counterclockwise as seen from the left. This is the correct action for the gyroscopic precession of the wheel to cause the bike and rider to "lean into" the turn, i.e. establish a proper banked turn even on level ground. By putting the steerable wheel in the back, the turn is made by pushing the front of the wheel to the OUTSIDE - since the wheel rotation is still the same, the precession of this gyroscope tries to flop the bike and rider to the OUTSIDE of the turn! You would have to be very big and be a prime athlete with a perfect sense of timing to overcome such a force.

So yes, it has been proven by actual experiment. This was probably reported sometime back in the 1970s.

L Cottrill

[JetSet]

I believe Thrust SSC had rear wheel steering :)

[Bruno Ogorelec]

When you turn the front wheel of a normally arranged bicycle, the front of the spinning wheel is pushed into the turn, with the wheel spinning counterclockwise as seen from the left. This is the correct action for the gyroscopic precession of the wheel to cause the bike and rider to "lean into" the turn, i.e. establish a proper banked turn even on level ground. By putting the steerable wheel in the back, the turn is made by pushing the front of the wheel to the OUTSIDE - since the wheel rotation is still the same, the precession of this gyroscope tries to flop the bike and rider to the OUTSIDE of the turn! You would have to be very big and be a prime athlete with a perfect sense of timing to overcome such a force.

Interesting. Years and years ago -- also in the 1970s I think -- there was an article in (I think) Scientific American saying that gyroscopic forces on a bicycle wheel were so small to be insignificant for the purposes of keeping your balance. In addition, people found riding bicycles with very small wheels almost equalyl easy as those with big wheels, further indicating that teh gyroscopic effect played little (if any) role.

I think the consensus is that the bicycle balance is almost entirely due to the rider's sense of balance and unthinking corrections. The gyroscopic effect starts being felt only when a bike is pushed along without a rider. The small forces then become big enough (compared to the mass of the bike) to be felt, but even then do not help all that much.

[Mike Everman]

There's a wierd bicycle building contest somewhere and I was reading a write-up that basically said that it's not possible to design a bike that a human can't figure out how to ride; square wheels, rear steering, whatever, we can master anything with practice.

[Mike Kirney]

Thanks, Mike! I think another reason rear-wheel steering is more difficult to control is because you are indirectly 'aiming' the front of the bike into the path you want it to take. With front-wheel steering, you point the front wheel where you want it to go, and that's where it goes. With rear-wheel steering, there is a microsecond of delay between your turning the wheel and the response of the front end of the bike and it becomes much easier to make a minute error that has catastrophic results (like an accidental spin-out).

[Mark]

Here's a link on this topic.
Mark
http://wannee.nl/hpv/abt/e-index.htm