Team Racing Calculator Spreadsheet 

What's hot and what's not in Team Racing? -- From a physics and aerodynamics viewpoint.

Updated August, 2009

The key to success in T/R while keeping a livelihood is to concentrate on the things that really matter and leave all other stuff to a later date. Such a practice will take you to the starting line with some decent equipment, in time.

To sort out these things at the engineering stage rather than at the field, I have designed this Excel application, that gives an overview of the physics and aerodynamics influencing a Team Racing model in flight.
Here I display a non-interactive web version of the spreadsheet. The actual Excel file allows the user to change things and see how the changes affect performance.
Metric units are used throughout. In a few cases, inch and BHP conversions have been added.
You can download the Excel files, see below.

An example spreadsheet:


Commas used as decimal points instead of dots in the Swedish setup of Excel.


Download: Spreadsheet V7 for Excel (2009 version for 0.35 mm lines) (111 kb)

The spreadsheet is in constant occasional development, so look out for updates.
The spreadsheet has macros for certain operations. When you open it you get a box cautioning you. You should select "Enable Macros".

Hints for Using the Spreadsheet

The YELLOW fields are user input data. (Shaded in older versions.) All other fields are calculated. There are comments attached to many fields, marked by red triangles. Just move the cursor over the field, and the comment is displayed.

For the handle position, some prefer giving this as a radius from the centre of rotation to the handle plus the angle from the straight line between the model and this centre. In the way I give it, see the comments, the numbers .2 m and -.3 m correspond to a radius of .3605 m and an angle of -56.3 deg.

The "Speed" field, found in upper left corner, is used to calculate most things. However, the normal input you have is a time for ten laps. This you could enter in the "Target Time" field. If the "Time for 10 laps" field says something else, you use a macro to adjust the speed so this value becomes equal to your "Target Time". First, however, change all the other yellow fields to match your setup.
You reach the macros by pressing Alt-F8.
Click on the row "SetSpeedForGivenTime" and press run. Now the speed is changed so that the "Time for 10 laps" corresponds to your "Target Time".
After you have set up everything, and want to use this as a reference case to compare everything to, also run the macros SetTargetEfficiency and SetTargetPower.

Now you are setup and ready to change something and see how it affects performance.

Example:

You would like to see how a .01 mm change in line diameter affects the speed.

Find the line diameter field and change the value by .01 (from .296 to .306 in the above example)! A lot of values will change. For instance, the Power is no longer equal to the Target Power, but has increased by around 9 watts. As the available power hasn't changed, you want to see the effect on the speed. This you do by running the macro SetSpeedForGivenPower. The new speed and time for 10 laps will be calculated. It turns out you will go around .09 seconds slower for 10 laps.
This, however, assumes that you can keep the engine power. As the speed has gone down a bit, flying your range (of 33 powered laps) will take a little more time, and therefore you have to reduce the engine power to keep the range. You probably will be reducing the venturi diameter or something similar. In the spreadsheet you can, instead of assuming constant engine Power, say that the Engine Efficiency is kept. Then you run the macro SetSpeedForGivenEfficiency. After this you see that you will go around .13 seconds slower for 10 laps.
In Reality the result will probably be something else, but the calculated result would be valid if everything else were adjusted to the new situation.

Be aware that the spreadsheet is based on things that range from Scientific Truth through estimates and guesstimates to mere guesses. It would take me too much space to tell you what's what. You have better make yourself familiar with the calculations in detail by studying the formulas before you base far-ranging conclusions from any figures.

I'm aware that these hints don't amount to anything near complete instructions. Don't hesitate to e-mail me if you have questions as well as ideas for improvement.

The Propeller Data part is merely for orientation. To make a propeller design, check Martin Hepperle's site. You can take the input parameters from the spreadsheet!

Well, then, what can be learned from all this?

The most important things are HANDLE POSITION, HANDLE POSITION, and HANDLE POSITION!
The values in the example, 2 decimeters outside and 3 decimeters to the right of the centre of rotation, probably represent the best you can do while flying legally three-up. If you are forced into a position where your handle is 6 decimeters to the right, it's the same as the model dragging almost an extra wing!

Another comparison: Let's say you spend a lot of effort making a retracting landing gear. This gives you the same advantage as moving the handle FOUR CENTIMETERS to the left! Maybe the effort is better spent refining pilot technique?!

Good luck,

Göran Olsson

  I'm indebted to Pete Soule for pointing to errors and for general discussions.