Frequently Asked Questions


  1. Why did my email get rejected, and how then can I contact you?

  2. How do I get the software?

  3. Can I run the software offline?
  4. Why do I need to install JRE 1.4 and Java Web Start before getting the Club Cycom software?

  5. How do I join or subscribe?

  6. I am poor or especially useful to you or involved in a good cause. Can I negotiate the price?

  7. Can I become a member over the phone?

  8. Can I use the software on more than one PC?

  9. Can I become a member for ever?

  10. I have printed my invoice. How do I continue?

  11. I type in a URL but it is not found. What is wrong?
  12. Why does not the "Mean power (Pm)" calculated result change when I vary the "Power coeff. (Cp)"?

  13. How does one know for sure that it is the optimum design?

  14. Why bother to twist and taper the blade?

  15. Why are airfoils often asymmetric?
  16. How do I choose a turbine rotor diameter?

  17. How do I choose the number of blades?
  18. How do I choose a practical chordwidth limit?

  19. How do I choose a Tip Speed Ratio (TSR)?
  20. What is the angle of attack?

  21. What are Lift and Drag coefficients?
  22. How do I use Radius of Station parameter?

  23. How does windspeed affect my rotor design?
  24. How does Altitude, Temperature and air Density and Viscosity affect my rotor design?

  25. What are "Center X and Center Y (fraction of chord width)"?
  26. Where can I get a hot-wire polystyrene foam cutter?

  27. The software fails and says "Unable to launch Club Cycom ...". What is wrong?

  28. The software shows the "Welcome" panel but fails later. What is wrong?

  29. When I access the startURL http://www.cycom.co.uk/club/login.jnlp java web start says "Checking for updates" and never seems to finish. Why?
  30. How accurate is the wing section profile near the blade root?

  31. What effect does downwash and wing tip vortex have on the angle-of-attack?

Q. Why did my email get rejected, and how then can I contact you?

A. Cycom uses anti-spam mail filters. This can unfairly reject mail from the mail server that you now use and we know it is not your fault so please do not be offended!. Please use the web form to tell us about it. This web form will allow you to send a message to us which will not be rejected.

Q. How do I get the software?

A. Point your web browser at the start URL link at the top of the page at http://club.cycom.co.uk/startURL.html. Download, installation, updating and running will all be automatic.

Q. Can I run the software offline?

A. Yes. After the first time, you will be able to start the software offline (when you are disconnected from the Internet) by starting Java Web Start Application Manager from the normal shortcuts or menus on your computer desktop. You will be able to see the "Club Cycom" application listed as a downloaded application (Choose "View" menu, then menu option "Downloaded applications"). Start the "Club Cycom" application by double-clicking it.

Q. Why do I need to install JRE 1.5 and Java Web Start before getting the Club Cycom software?

A. The Club Cycom software will run on Macintosh, Unix (Solaris, Linux) and Microsoft platforms. The Java Web Start layer is required to hide the peculiarities of specific operating systems from the portable Club Cycom software. In an ideal world, the operating system vendors will have already installed the Java Web Start layer for you and new Apple Macs with OS-X will soon do this. Until then, you have to do it yourself, but only once! The benefits are that you can choose to change computers or operating systems and know that you will still have access to your Club Cycom software and any other Java based software. You are not obliged to buy Microsoft. We are protecting you and ourselves from possible anti-competitive actions by a vendor with a virtual monopoly and also giving that vendor a motivation to improve the openness, security and reliability of its products.

Q. How do I join or subscribe?

A. Download, install and run the software. The software itself has the screen to enter your email and  licence key. You should check that you are able to run the software before you subscribe. From the software's welcome screen, press the "License management" button. This will bring up the license management screen. Type in your email address into the field labelled "Your email address".
Use your web browser to navigate to "http://club.cycom.co.uk/#subscribe" and you will see on that page a "Buy Now" button. Press the "Buy Now" button. You will be directed to a secure PayPal site which will take your credit card details and payment for the service which should show as a "1 year non recurring subscription to club cycom". When you have finished paying for the subscription you should see a button labelled "Back to Merchant". Press the "Back to Merchant" button. Your browser will now show your final invoice which will include your email address and new license key. Print this page or make a note of your license key (it will also have been emailed to you). Copy the license key number into the field labelled "New license key" on the "License management" screen (which will still be on your screen somewhere but probably hidden underneath the browser window). Ensure that there are no surplus space characters at the end of any of the fields, especially if you have uses cut and paste to paste the licence key. Press the button labelled "Set new license key and email" which is on the right-hand side of the "License management" screen. Now you can close the license management screen by pressing the "Close" button. From the welcome screen you should see your license key listed and a number of days of validity remaining in brackets. Don't worry about the expiry date of the software since this not the expiry date of your license!. It just means that I will update the software to be newer and better before then. You can now press the "Aerodynamics" button to use the wind turbine design tool or press any other button to use the corresponding application.

Q. I am poor or especially useful to you or involved in a good cause. Can I negotiate the price?

A. Yes!

Q. Can I become a member over the phone?

A. You must have a computer with an internet connection to become a member. We can take credit card details by phone if needed although the online processing is perfectly secured.

Q. Can I use the software on more than one PC?

A. Yes. Just re-enter your existing licence number and email address on the license manager screen. If you do this to more than 10 computers we might ask why!

Q. Can I become a member for ever?

A. No. The longest license duration is 2 years. You need to resubscribe after the licence expires. The software itself is regularly upgraded and you will need to visit the web site at least once a year to refresh it. There is no charge for upgrades. Both software expiry and licence expiry are shown on the welcome screen so you will always know how long you have left. I will issue an unlimited duration version to you all if we ever decide to close the business. Cycom Limited was incorporated in 1983.

Q. I have printed my invoice. How do I continue?

A. Return to the "License Management" screen of the software itself. It will still be there underneath your browser window but just restart it if not. Enter the license key and email address in the appropriate fields and press the "Set new license key and email" button which is located towards the right edge of the panel (do not use the "Close" button!). If successful, you will see the new license key be listed in gray at the top of the panel followed by a number of days remaining in brackets. Now you can close the "License Management" screen and the welcome screen buttons should now start your desired application (previously they kept redirecting you to the "License Management" screen. The button for the wind turbine module is labeled "Aerodynamics".

Q. I type in a URL but it is not found. What is wrong?

A. A URL stands for Uniform Resource Locator. It is the full address of some information anywhere on the web. It has several components. E.g. "http://club.cycom.co.uk/" or "http://club.cycom.co.uk/faq.html" specifies http (hypertext transfer protocol) to computer "club.cycom.co.uk" and the default index file or file "faq.html" (frequently asked questions, hypertext markup language). You must type the full URL (including the "http://" prefix and a "/" suffix for hostnames, directories or default index files) into your browsers "location" field ensuring that the letter case is exactly right and that you do not confuse a number 1 with the letter l (lower case L). If a URL is not exactly right or has any components missing, then it is likely that your browser will send the location to some search engine such as MSN which will try to guess the correct URL by prefixing "http://www." or searching its indexes. This guessing strategy can easily fail for technical sites that do not have "www" as the hostname and use case sensitive operating systems such as Unix for the web servers. Also you may not want Microsoft to learn about every URL you access.

Q. What is the "Power coeff. (Cp)"?

A. This is an empirical (evidence based) estimate of the overall efficiency in turning wind energy into electrical energy. It is typically 0.15. The software allows you to use this to compute empirical power but also directly calculates integrated theoretical power based purely on aeodynamic theory and your actual turbine design (i.e. not using Cp). This theoretical mechanical power assumes no electrical losses and assumes the load is such that the actual TSR is at the the design point. It is up to you whether you use the empirical or theoretical powers in choosing a rotor diameter to match your generator. The theoretical powers often correspond to a Cp of 0.4 which is more than twice the empirical value suggested by Hugh Piggott.

Q. Why does not the "Mean power (Pm)" calculated result change when I vary the "Power coeff. (Cp)"?

A. Mean power is an empirical formula (based on in-service measurement on many real existing turbines). Since Cp varies with windspeed it cannot easily be used in the formula (but is probably assumed to be around 0.15 mean) . Also the distribution of windspeed around the mean affects power as the cube of the instantaneous speed! This long term mean power is what other people have actually achieved and you can't change that result by making your own turbine more efficient. This is your target to beat!

Q. How does one know for sure that it is the optimum design?

A. According to a theory by Betz, it is optimum if slows the wind down to 1/3 of its original speed eventually. Half of the decelaration occurs before the rotor and half after the rotor. So wind speed at rotor is 2/3 of original wind speed. My software always computes for this optimum. My software then calculates the mechanical power available at the shaft so you can see what you get and you can try alternatives if you think you can get more or get a better match to your generator. You could measure the windspeed at the rotor to check that it is 2/3 of the original free windspeed. Note also that you will need to present an electrical load that will maintain the rotor speed at the design tip speed ratio if you really want optimum energy capture.

Q. Why bother to twist and taper the blade?

A. The twisted tapered blade produces an even pressure distribution over the whole rotor disc area to minimise vortex formation and maximise power extraction. Also the tapered blade is stronger and lighter. Also a non-twisted blade will be stalled near the root. An optimum blade will probably produce twice as much power as a simpler blade.

Q. Why are airfoils often asymmetric?

A. The lift and drag of an asymmetric airoil are better than a symmetric airfoil. However symmetric airfoils have an advantage that then do not suffer a pitching moment (tendency to twist under load) if balanced at the 25% chord point.

Q. How do I choose a turbine rotor diameter?

A. Try various diameters and look at the computed results of integrated power, rpm, and integrated thrust at various windspeeds. Pick a diameter that best matches your generator characteristics and power requirements and tower strength.

Q. How do I choose the number of blades?

A. 3 blades is normally best (smoothest thrust). 2 blades are more bumpy but can run faster and lighter. 1 blade is very unbalanced but can be even faster. Less blades means more chordwidth per blade and better reynolds numbers and strength.

Q. How do I  choose a practical chordwidth limit?

A. Near to the blade root the optimum chordwidths go to extremes. If you do not intend actually carving your blade to large chordwidths near the root then choose a practical chordwidth limit to suit your mechanical limits. This can be larger that the A4 paper sizes and you can use the mouse to drag and move the airfoil outline before printing to print the parts you want. Later you can join the paper plots together (with sissors and glue) using the plotted alignment marks to reconstruct a plot up to 1 meter chordwidth.

Q. How do I choose a Tip Speed Ratio (TSR)?

A. Just try some values between 3 and 10 and look at the size of the airfoil section for a station radius equal to the tip radius. You will find that your blades become impractically large or small if you have an unsuitable ratio. Also consider the rpm match to the generator and consider if your rotor will be able to start from standstill (when blades are stalled) given the friction, cogging etc. Also look at the computed reynolds numbers to see if your airfoil is efficient at those numbers.

Q. What is the angle of attack?

A. This is the angle between the airfoil chordline and the oncoming relative wind direction. This angle affects the performance (lift and drag)  of the airfoil and there is usually some optimum value between 4 and 7 degrees. Lift coefficient will rise by 0.1 for each 1 degree increase in angle of attack but drag will also increase. Since the relative wind is a resultant vector of the real wind through the rotor and the headwind caused by blade motion (which itself varies with station radius and TSR) then the blade must be twisted from root to tip in order to maintain a constant angle of attack.

Q. What are Lift and Drag coefficients?

A. The Lift is the force at right-angles to the airflow. The Drag is the force parallel to the airflow. Both parameters depend on airfoil shape, and reynolds number and angle of attack. You need windtunnel test results to assess the best point on the curves to choose for your design angle of attack, lift and drag. The list chooser for airfoil will suggest an optimum value to use for angle of attack and lift. Drag will often be around 0.002. You want to maximise Cl cubed divided by Cd squared.

Q. How do I use Radius of Station parameter?

A. This does not affect your whole rotor design at all, it merely tells the computer which station radius on the blade you are interested in computing and displaying results for at this moment. A whole blade is a complex twisting 3 dimensional object and so we want to look at simpler 2 dimensional cross sections when we are manufacturing it.  For any  given design with diameter D you will typically display results for 5 station radii ( say 0.1*D, 0.2*D, 0.3*D, 0.4*D and 0.5*D or tip radius) so you can see the angles and chordwidths at each station along the blade and the forces acting at this station.

Q.  How does windspeed affect my rotor design?

A. Your rotor is optimised for a particular tip speed ratio. As long the ratio is maintained, your same physical rotor will still be optimum at any windspeed. The matching to your generator however will vary with windspeed and so you may want to adjust diameter and TSR and number of blades to best suit your generator at a particular windspeed which you expect to be the norm.
Also windspeed affects the reynolds numbers which then affect lift and drag which might then prompt you to revise the rotor design (particularly at low reynolds numbers below 100000).

Q. How does Altitude, Temperature and air Density and Viscosity affect my rotor design?

A. As the previous question, your rotor is optimised for a particular tip speed ratio. As long the ratio is maintained, your same physical rotor will still be optimum at any air density. Air density and windspeed both affect power and so affect the matching to your generator. Altitude (ASL is Altitude above Sea Level) and Temperature merely affect air density and are provided as a shortcut to compute air density. Air viscosity is only used in computing reynolds numbers. The default values for air density amd viscosity will be good enough for all practical design purposes so no changes need be made to these parameters.

Q. What are "Center X and Center Y (fraction of chord width)"?

A. It is where the cross-hairs intersect on the profile section.  Supposed to be the center of lift or center of weight or center of torsion. You don't need to change this as the default is reasonably centered. All the sections should align on this center.(Drill a hole to ensure this). The purpose of choosing and aligning the centers is to minimise distortion of the blade under load conditions (centrifugal or aerodynamic) or to know where to add a balancing weight. It might even be adjusted to give sweepback and deliberate aerodynamic twist under load.

Q. Where can I get a hot-wire polystyrene foam cutter?

A. You can easily make your own hot-wire cutter. See how I made my hot-wire cutter.


Known Bugs

Q. The software fails and says "Unable to launch Club Cycom ...". What is wrong?

A. There is a Java bug that affects the Turkish locale. Set your PC locale to another region (such as US) before starting Java Web Start. If that doesn't fix it, email me on cwturner@cycom.co.uk with as many details as possible (see next question for how to enable logging).

Q. The software shows the "Welcome" panel but fails later. What is wrong?

A. There is some bug. I will need some more diagnostic information to fix it. Please enable logging and send me any error message details. To enable logging in Java Web Start choose menu "file/preferences" then tab "Advanced" and enable the checkbox "Log Output". Type "cycomlog.log" into the field labeled "Log File Name". Click the "OK" button, then close Java Web Start and Club Cycom (if still running) and restart Club Cycom and provoke the buggy behaviour. Then email me the file named "cycomlog.log". It will be in your default home directory somewhere. Search for it by name if you don't know where this is. There will be a reward for any bugs found.

Q. When I access the startURL http://www.cycom.co.uk/club/login.jnlp java web start says "Checking for updates" and never seems to finish. Why?

A. There is a bug in Java Web Start that can delay this check for updates for more than 30 minutes. It will eventually finish so please just be patient, don't cancel, but do something else on the internet in another window while leaving it running. Hopefully it will finish within a 30 minutes or so and will be instant startup on subsequent occaisions.

Q. How accurate is the wing section profile near the blade root?

A. For wide chords near the blade root (first 20% of radius) the relative airflow will follow a significantly curved circular arc rather than a straight line from wing leading edge to trailing edge. The wing section plots should therefore ideally be curved in this same arc before being used to cut a wing segment which is clearly difficult with flat sheet polystyrene. A later version of the software is planned to compensate for this distortion so allowing flat sheet to be used all the way to the root. Both the drag and power contributions of this first 20% of blade are relatively small so in practice the current inaccuracy is not very significant.

Q. What effect does downwash and wing tip vortex have on the angle-of-attack?

A. The wing tip vortex changes the downwash and therefore angle-of-attack along the blade. Aircraft wings use an elliptical planform to minimise the variation in angle-of-attack due to downwash. The turbine blade design should make similar computations to optimise efficiency. The extra induced drag caused by downwash is currently computed by the program but not yet the chord width or angle changes needed to compensate for it.