New Renderings - Detail changes

Since my last design renderings I have further developed the design to improve the aerodynamics and the interior packaging. This has made it a little harder to construct but I think the overall look of of veloci-velo is quite unique to the velomobile world.

Unwrap that body!

I have been busy with finalising the body and chassis details and construction methods. Using 3D software allows me to 'unwrap' my veloci-velo model so I can cut it out into its various parts. Rendering below is a of the 5 parts that make up the bodyshell. Minimising the part count leads to savings in weight and cost so I am very conscious of keeping the design of this velomobile very simple.

Veloci-velomobile, showing major bodyparts

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.

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.