Cuda-W Cd Analysis

Cuda-W Cd Analysis

Wayne Shook has created an application "HPV Shell Designer" for Windows that allows you to create streamliner fairings based on a human model and frame that you can easily build and size.  The application also allows you to export the 3D mesh file to a Cd (coefficient of drag) Analysis tool.

You can download Wayne's app here:
Shell Designer Installer.msi
Setup.exe

Here's the Cuda-W in it's current configuration.

(click on the images for a bigger view)

Here's the model I created in Wayne's application. It's a pretty close approximation of my existing Cuda-W. Wayne's app allows you to see the size of the shell after you have created it.

Length: 113.6 inches
Width: 18.5 inches
Height:30.5 inches
Frontal Area: 140 sq inches
Here's the modeled shell pasted onto the actual bike. The front 2/3 of the bike are very similar to the Cuda-W, the back and canopy are a bit different.
Wayne imported the model into AutoDesk Flow Design and ran some simulations. The analysis runs he performed came up with CdA values between .21 and .16. This one shows the average Cd as 0.16

CdA = Cd * frontal area (in meters)
Frontal Area = 410 sq in = 0.264516 sq M
CdA = 0.16 * 0.0903224 = 0.042
CdA = 0.21 * 0.0903224 = 0.055

These numbers are higher than the CdA I had estimated which was 0.03. This is probably due to the canopy which is not well optimized in this version of the HPV Shell Designer, and the lack of wheel fairings.

The HPV Simulator shows that the bike above would go about 36 MPH under ideal conditions on a flat course at sea level with a consistent 200 watts to push it. That's a almost exactly what I average on the 1/2 mile oval tracks or smaller I race on, but I am not generating 200 watts for the entire race. With a slight downhill slope like at Battle Mountain, and at 4500 feet, the simulator shows it would take about 600 watts to go 64 MPH, which corresponds to my performances at the event fairly well but I know I did not generate 600 watts for the entire speed run.

After several analysis runs with some varying of the shell the following because clear:
* Tilting the front down makes it slower
* Raising the nose makes it slower
* Raising the height of the fairing makes it faster.
* Removing the canopy makes the bike faster.

This agrees with my observations. The Cuda-W was about 1 MPH faster the first time I raced it at Battle Mountain, and that time it was about 2 inches higher than the second time I raced it there.

What this all means is that if I want to go back to Battle Mountain and try to improve my top speed, I will need to make some changes to the bike
 

Wayne's HPV Shell Designer software and simulations show that with my existing shell and drivetrain I can:

- Change the 700C rear wheel to 20 inch.
- Change the seat back to lean it back more
- Raise the bike an inch or two
- Remove the canopy and use a camera for navigation.

This Simulation run shows a CD of .17, but the drag force is less than the version with a canopy because of the lower frontal area.

This run with the bike raised shows a Cd of .13.
This design has a frontal area of 406 sq in = 0.261935 sq M.
CdA = 0.13 * 0.261935 = .034

According to these simulations this would improve my speed at Battle Mountain to 69 MPH. I am thinking that this design plus fairing the wheels would allow me to break 70 MPH at Battle Mountain.

   
   

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