I’ve got a great idea, but I can’t tell you about it…

Do you think you have a new idea that will revolutionize the Human Powered world and make you a million dollars? In the quest for speed, many things have been tried. Some work better than others. Just remember, that some very smart people have been trying to optimize the bicycle for over 100 years. Don't design in a vacuum!  If a certain type of propulsion or body position is not being used, there’s probably a good reason for it. Here are some of the things that have been tried that don’t work so well, and the reasons why they are less than desirable.

Rear Steering
Having the steering in the back of the vehicle solves a host of issues. It makes the front of the bike much less complex, and in a faired vehicle, much cleaner aerodynamically. Unfortunately, rear steering in both bikes and trikes causes odd turning at low speeds, and crashes at high speeds. Rear steer recumbent bikes are generally unrideable.  Some success has been had with streamlined trikes designed for straight line only. These trikes have extremely limited turning. Also some success has been had with center steered bikes.

Linear Drivetrain
This is the one that crops up most often. A linear drive when you push the pedals straight out can be more aero than a normal round pedal stroke. You can bench press a lot of weight right? Unfortunately, most linear drive systems only use the “push” power stroke, and then they have a spring or cable to return the pedals to the next power stroke. Even ones that optimize this movement, allow a pull as well as a push stroke, and use cables to return the non power side suffer from power losses when the legs have to stop and change direction at the end of each stroke. In addition they suffer losses converting the straight line motion to the circular motion of the gears/drivewheel. Linear drivetrains do work, they are just not as efficient as a circular  drive.

Prone Bikes

A prone bike is one where the rider is laying on his stomach, as opposed to the traditional supine recumbent position where the rider lays on his back. Some success has been had with prone bikes as the position is very good for sprinting. It’s also a good position aerodynamically as you can cram your head and shoulders into a narrower package than your legs and pedals. The position is bad ergonomically though, as the rider has to strain his head backwards, and the cradle required to support the body in that position restricts the lungs. This means that the rider suffers in any long races or rides.

Head First Recumbent

A head first recumbent requires you to lie on your back and look into a mirror to see what’s in front of you. This means that everything is reversed. As with prone bikes, this position puts the human body into a very compact position. It is actually possible to ride in this position, in a straight line, after a lot of practice. One rider/vehicle in particular has done very well with this position, aside from the crashes and cracked neck vertebrae.

Hand/Foot Power
You can build a drivetrain that uses both hands and feet to power a bike. More muscles mean faster speeds, right? Some success has been had with non-faired hand/foot powered bikes. They work well for sprinting, but not so well for longer distance races/rides. The issue is that the human legs are more than able to use all of the cardiovascular output that a body can generate. Once you get past the sprint, it’s more efficient to just use the legs. Also in a faired vehicle, hand power is a packaging problem.

The Big Fairing
So you want to build a fairing so you can go real fast with human power, but you don't want to be constricted, so you figure you can build in some room to move around a little. Well, here's how it works, you can make a fairing fast, or you can make it comfy. You can't have it both ways. For a fairing to be really fast, it needs to fit the rider like a glove. If you just want to go halffast you can build one a bit bigger. If you add a couple inches to your total shoulder width, that's going to be slow.

Laminar Flow
A faired body can potentially have extremely low drag if the airflow remains laminar over the entire fairing. This term means that the layer of air that flows over the surface of the fairing stays attached without any eddies, backflow, or other arcane airflow terms to create drag. Unfortunately, even if you really know what your are doing, have good design, perfect surfaces, perfect manufacturing and perfect weather conditions, designing for laminar flow might actually increase the drag of the vehicle. This is because any time you take this vehicle out on the road, minute road vibrations, slight side winds, and bugs smashed on the nose of your perfect fairing will delaminate the air.

I'm going to go 100 MPH at Bonneville.
Go for it dude. While the Bonneville salt flats are great for cars with big tires and bigger horsepower, faired bikes with puny humans for engines and skinny tires don't fair as well. The issue is that the salt surface isn't as hard as asphalt. Bike wheels will sink a bit in it. The Easy Racers team did try it once, but didn't go as fast as they expected, and filled up their fairing with salt.

More riders = faster speed
More riders means more horsepower, and we can put them all in a line, so the frontal area of the fairing stays the same. This will do 100MPH for sure, right? Two person back to back lowracer tandems seem to be the fastest multirider configuration. In a stock configuration, with strong riders, this configuration is hard to beat. Unfortunately because of issues with drivetrain complexity, packaging, the skin friction of a longer vehicle and weight, historically faired vehicles with more riders have always been slower than single rider vehicles.

Electric Transmission
Yes, you can crank a generator to power a motor that drives the wheels instead of using a bike chain. This idea may work well in a human/electric hybrid vehicle where routing the chain is an issue, and the human power is not the primary means of powering the vehicle. The problem is that generators and motors are heavy, and that the power transfer efficiency is much less than that of a bike chain, which is about 97% efficient. Using AC generators to power motors motors in conjunction with storage batteries and the required management electronics can be up to 80% efficient. Typically the average person is able to run about 25% efficiency. This means that for every Watt produced by a bike generator, the person doing the pedaling is putting out 4 Watts.