Velomobile Frame Design

I have been coming up with different ideas on the design of the velomobile frame. I have decided that including some sort of impact protection would be a good idea so the above idea has 'side impact bars' which also double as handles to aid getting in and out of the velomobile.
I also want this frame to be stiff in torsion as well as bending forces as a stiff chassis makes for a better handling vehicle. I have chosen aluminium as the material for the frame as it is a material that when used with large diameter and thin walls both stiff and lightweight.
The seat is formed from plywood and will have a little adjustment fore and aft with the bottom bracket providing most of the adjustment for different size riders

Velomobile tyres

There is lots of debate about the pros & cons of various wheel sizes. I do not wish to add to this discussion but speak from my experiences.

I have used both 406 ERTO & 349 ERTO size wheels/tyres for my early velomobiles. I have found there is no noticeable difference between the two sizes in everyday riding.

Being a smaller rider I prefer the 349 size as it makes for a more compact trike/velomobile as well as being slightly lighter. I have noticed that tyre pressure has more influence on the ride & speed of the tyre than anything else.
A lot of the roads in my area are coarse chip and I have found that running tyres at a lower pressure is better on these surfaces. High pressures lead to more 'road buzz' and a very hard ride. Lower pressures (50-60psi) reduced the road buzz and made the ride and handing much nicer. However on smooth asphalt roads higher pressures are the best. It is all about finding what works for the particular vehicle and the rider.

Here is a little movie I made of the virtual wind tunnel with Veloci Velo in it. This is a slightly different body with more of a "swoop" in the side on profile. Part of the reason is purely cosmetic and also helps bring down the drag co-efficient.

Suspension for Velomobiles

Because Velomobiles are capable of higher average speed than conventional bicycles the need for suspension on all three wheels is a requirement. Suspension is not just needed for rider comfort but also to allow the wheels to keep in contact with the road surface and allow the tyres maximum grip when changing direction. Because Velomobiles are low mass vehicles there are some  considerations when designing suspension -

1. Keep unsprung weight to a minimum.
2. A torsionally rigid frame/chassis.
3. Keep the center of gravity as low as possible.
4. Use of a fully independent suspension.
5. The roll centre should be as low as possible for a low mass vehicle.
6. Roll stiffness is essential for a low mass vehicles especially so with a three wheeler as the single rear wheels provides no roll resistance.

There are many different geometries for suspension and the design of suspension systems is a complicated process AutoSpeed has this excellent article on the basics of geometry of different suspensions. My design for Velocivelo will follow the above 6 steps to arrive at the design.

The suspension I think that is suitable for velomobiles is the swing axle as it has a low unsprung weight, is fully independent and can be arranged to have a low roll centre. Disadvantages are "jacking" and lack of roll stiffness, but theses are negated to a certain extent because of the low mass of a velomobile.

One design of front suspension that is already out there is the ICE - Road Response Suspension. If there was a trike chassis to base a lightweight velomobile on it would be the ICE SPRINT with Road Response Suspension.