Velomobile Frontal area

I finally have measured the frontal area of the new shape and the result has been good as the frontal area for this new shape is 0.36m2.

Calculating the CdA is now 0.36 x 0.21 (Cd) = 0.0756 CdA.
I can calculate using this excellent calculator power outputs and speeds for Veloci-velomobile. The graph below shows that for a modest 150W of power  a speed of  approx. 46 km/hr can be attained. I used 150W because this is what a untrained but fit cyclist could acheive for any length of time.

I also found that smoothing my final shape did not make any real difference to the Cd factor, at the most  it would have changed it by 0.1 so it is best to leave it as is. Now to build the models and then the real thing!

Velomobile aerodynamics final design

After re-drawing the bodyshell to fit the exact dimensions required I have found that the CdA figure has dropped to 0.081 Here is a few images of latest and final renderings before I make a full size working prototype.

This is a great result as I had thought that anything 0.10 or less would be adequate. My goals for the design have been reached with the low drag co-efficient, the low weight due to the construction in coroplast/corflute and I think I have achieved a a good looking design which is important for consumer acceptance.

I have been reading a lot about vehicle & chassis design and one thing really stood out to me was the way the automobile industry goes about designing a new vehicle as they take a very different approach.
Their most important criteria is asthetics. This is a basic overview of the design process...

1. Draw-up concepts
2. Choose a concept
3. Refine the concept
4. Larger scale concept produced concept adjusted to fit people and parts
5. Adjustments made to fit chassis platform and suspension
6. Body changes for aerodynamics
7. Prototypes built andtested, changes made
8. Production readying

Again the auto industry starts by defining the design by its appearance, designing a velomobile in such a way would lead to a vehicle that would not perform as expected. The design process for a velomobile and indeed Veloci-velomobile has been...

1. Application definition - lightweight, aerodynamic, single occupant, human powered vehicle
2. Chassis and suspension design - lightweight, stiff, independent suspension
3. Aerodynamically designed to envelop rider and chassis - again lightweight
4. Development of the entire design to make it user friendly and asthetically pleasing

So the design process is quite the opposite to the auto industry approach, I think I have achieved my goals in this design. Please feel free to comment.

Measurements

Using the 'mule' I have been fine-tuning the dimensions of Veloci Velomobile. I have changed the design of the frame to have a perimeter upper frame to provide extra impact protection and added torsional strength. At the moment I have been setting up the 'mule' to check seating position and clearances for wheels, steering bits and of course the rider to bodyshell interferences. I have found by doing this that I can make the Veloci-velo even a little bit smaller than I had planned with the entire bodyshell being able to envelop me the rider as close as possible.

The 'mule' test rig for Veloci-velo

This was one of my goals in building this velomobile and that was for it to be a scalable design instead of a "one size fits all" policy. In a production version the rider would supply the essential measurements and the bodyshell would be custom designed to fit his body / seating position. The chassis would be basically the same for every rider but the shell would specific to the rider.

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.