# Coordinate System in FAST **URL:** \ **Category:** Computer-Aided Engineering Software Tools\ **Created:** [January 24, 2013, 4:41pm UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632 "2013-01-24T16:41:35Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![Arnold.Ramsland](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@Arnold.Ramsland](https://forums.nlr.gov/u/Arnold.Ramsland)\ **Post date:** [April 2, 2018, 10:41pm UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632/41 "2018-04-02T22:41:57Z")
Hello, I’d like to follow up on a post dated June 27, 2016 to René where it was stated that ''c1" and “b1” refer to the orientation, not the origin, of the coordinate system by requesting a further clarification of the shaft (xs, ys, zs) and azimuth (xa, ya and za) coordinate systems. According to the FAST Users Guide, the shaft and azimuth coordinate systems are located at the origin, which is defined as the intersection of the yn-/zn-plane and the rotor axis. According to the diagrams shown, this intersection occurs at the yaw axis at the top of the tower. Many of the output variables indicate rotations about the ys, zs, ya and za axes. Examples include: TeetVya: Rotor teeter angular velocity about the ya-axis TeetAya: Rotor teeter angular acceleration about the ya-axis LSSTipMya: Rotating LSS bending moment at the shaft tip (teeter pin for two-bladed turbines, apex of rotationfor three-bladed turbines) About the ya-axis LSSTipMza: Rotating LSS bending moment at the shaft tip(teeter pin for two-bladed turbines, apex of rotation for three-bladed turbines) About the za-axis LSSTipMys: Nonrotating LSS bending moment at the shaft tip (teeter pin for two-bladed turbines, apex of rotation for three-bladed turbines) About the ys-axis LSSTipMzs: Nonrotating LSS bending moment at the shaft tip (teeter pin for two-bladed turbines, apex of rotation for three-bladed turbines) About the zs-axis LSSGagMys: Nonrotating LSS bending moment at the shaft’s strain gage (shaft strain gage located by input ShftGagL) About the ys-axis LSSGagMzs Nonrotating LSS bending moment at the shaft’s strain gage (shaft strain gage located by input ShftGagL) About the zs-axis I have always assumed that the origin of the ys, zs, ya, and za axes would move along the xs axis to the designated position, e.g, shaft tip, teeter pin, strain gauge location, however I cannot find that stated in the FAST Users Guide and would appreciate your clarification. This interpretation would be consistent with the earlier post regarding “C1” and “b1” where the ys, zs, ya and za axes in the output variables listed above refer to the orientation, rather than the origin of the coordinate systems. Sincerely, Arnold Ramsland ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [April 2, 2018, 11:12pm UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632/42 "2018-04-02T23:12:54Z")
Dear Arnold, Yes, I agree with your understanding that the origin of the ys, zs, ya, and za axes would move along the xa / xs axis to the designated position, e.g, shaft tip, teeter pin, strain gauge location depending on the output parameter of interest. Best regards, ---
**Author:** ![Arnold.Ramsland](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@Arnold.Ramsland](https://forums.nlr.gov/u/Arnold.Ramsland)\ **Post date:** [April 4, 2018, 12:45am UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632/43 "2018-04-04T00:45:48Z")
Thank you, Arnold ---
**Author:** ![Yingyi.Liu](https://avatars.discourse-cdn.com/v4/letter/y/278dde/32.png) [@Yingyi.Liu](https://forums.nlr.gov/u/Yingyi.Liu)\ **Post date:** [November 19, 2018, 5:13pm UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632/44 "2018-11-19T17:13:28Z")
> [@Jason.Jonkman](#): > > Dear Attila, > > Yes, the blade coordinate system is unchanged by the upwind or downwind configuration. For the upwind case, the rotor in Figure 9 is unchanged, but the nacelle and tower are downwind of the tower instead of upwind. > > Yes, I agree with the updated signs of your forces. Aerodynamic thrust will act along positive x, aerodynamic lift that drives rotation will have a component acting along negative y, and centrifugal forces due to rotation will act along positive z. The blade-root loads output by FAST can be thought of as the loads applied to the hub transmitted by the blade. This convention is consistent throughout the turbine–e.g., the tower-top loads output by FAST are the loads applied to the tower transmitted by the nacelle. > > Best regards, Dear Jason, Can I confirm the following points again for an upwind wind turbine? (check it together with the blade system in the following picture): (1) NREL-5MW baseline wind turbine is an upwind wind turbine, and its blade rotation direction is clockwise. (2) The aerodynamic lift that drives rotation has a component acting along negative y, which is opposite to the rotation tangential direction. (3) Aerodynamic thrust acts along negative x. Are the above statements correct? If they are correct, I can’t understand why the aerodynamic lift force points opposite to the blade rotation direction, could you explain the reason? Thanks. Best regards, Yingyi Liu ![Blade system.jpg](https://europe1.discourse-cdn.com/nrel/original/2X/4/45fa1cf7861397ce207daf0e68379407e5e397a1.jpeg) ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [November 19, 2018, 5:26pm UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632/45 "2018-11-19T17:26:24Z")
Dear Yingyi.Lin, I agree with points (1) and (2), but point (3) and your picture are not correct. Regarding (3), the thrust for an upwind wind turbine should be directed along positive x. Regarding your picture, it would be correct if you rotate each blade 180 degrees around its z axis, such that x points downwind and the rotor spins clockswise (when looking downwind) opposite to the direction of y. Best regards, ---
**Author:** ![Yingyi.Liu](https://avatars.discourse-cdn.com/v4/letter/y/278dde/32.png) [@Yingyi.Liu](https://forums.nlr.gov/u/Yingyi.Liu)\ **Post date:** [November 19, 2018, 6:37pm UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632/46 "2018-11-19T18:37:34Z")
> [@Jason.Jonkman](#): > > Dear Yingyi.Lin, > > I agree with points (1) and (2), but point (3) and your picture are not correct. Regarding (3), the thrust for an upwind wind turbine should be directed along positive x. Regarding your picture, it would be correct if you rotate each blade 180 degrees around its z axis, such that x points downwind and the rotor spins clockswise (when looking downwind) opposite to the direction of y. > > Best regards, Dear Jason, Thanks. So does it mean that a wind turbine always spins clockwise (looking downwind), no matter it is an upwind or a downwind turbine? Is this understanding correct? Best regards, Yingyi Liu ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [November 19, 2018, 8:21pm UTC](https://forums.nlr.gov/t/coordinate-system-in-fast/632/47 "2018-11-19T20:21:14Z")
Dear Yingyi.Lin, Yes, in FAST, both upwind and downwind wind turbines spin clockwise when looking downwind. Best regards, [Previous page](https://forums.nlr.gov/t/coordinate-system-in-fast/632.md?page=2)