Aero Revelations

I have recently read an article on Mercedes-Benz modelling a car on a animal called the Box Fish. This fish has a remarkable ability to swim in very turbulent currents. Mercedes-Benz then took the basic shape of a Box Fish and built a car which then has a Cd of 0.19 which is very impressive for such a boxy looking vehicle.

I thought I would give this a try on the model on Veloci-velo with startling results.

The previous best cDA figure I achieved was 0.081

Re-modelled "Box Fish" shape cDA= 0.027 !!!

I could not believe it so I ran three separate tests and all tests came back with the same result!

This is quite a reduction in drag and would make Veloci-Velo and very fast velomobile.

I am conducting more tests and calibrating with objects of known Cd factors, More to come on this!

Continued Development update

Its has been a while since my last post. Chassis design still in progress. I really want to incorporate crash protection into the velomobile. Semi-monocoque with the seat being part of the load bearing structure seems logical. Other velomobiles (apart from the Rotovelo) have separate seats which offer no strength to the structure but are only used for the rider to sit on. When you consider that the seat weighs about 1kg it makes perfect sense for the seat to be integrated into the chassis or in fact become the chassis with suspension members hanging off it. There will be a rendering/picture to follow in the next few days.

Trisled RotoVelo

Crash Protection

There have been quite a few cyclists lately been run over and killed or seriously injured over the Christmas break. This was after the cyclists had gone to great length to make themselves visible and they were all experienced riders. Cyclists are vulnerable and it seems some drivers are not being careful enough.

How can we make bicycles safer? I don't think bikes are unsafe - it is more that other road users are careless and not considerate enough. Still it has made me think again about how to make Veloci-velo safer to use and I am exploring ways to make this velomobile a safe transport option. This could include crumple zones and / or airbags to help protect the rider.

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.