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Thread: Winds aloft

  1. #1

    Winds aloft

    Yesterday we were flying on a long cross country. My friends plane is RV-8 mine is an RV-6 both Hartzell CS with Lyc. 360's. Manifold pressure 22.1 RPM's 2450. We were .3 miles apart same altitude. (8500' on a heading of 192) My winds aloft were showing 355 at 37, his were 020 at 41. Both units are 4500's and we had exactly the same GPS ground speed of 212.

    Trevor or Rob is this a calibration issue or static error in my plane? We flew exactly the same course on auto pilot, we were never more than .4 miles apart for a 2 hour trip. The ground speeds never varied from one another, but the indicated winds direction and speed were never the same.
    I checked the winds aloft on XM weather but the arrows are not degree specific.
    I know my IAS is about 10 knots high, so my TAS is also 10 out. Is there a settings adjustment for this in the EFIS?
    Thank you for your help.

  2. #2
    Winds aloft uses GPS data as well as IAS/TAS. If your IAS is off, it will significantly affect the winds aloft calculation. There is an adjustment for airspeed, but we caution using that feature as it is for calibration during a VFR/IFR certification. Have you gotten a VFR/IFR cert yet (pitot/static check)?
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  3. #3
    Yes I got an IFR pitot static check after my annual. The sticker says altimeter, transponder, and static system tests as required FAR 91.411 an 91.413 and comply FAR 43 Appendix E and F ...etc. I do not think they adjusted anything.
    Doug

  4. #4
    What indication do you have that it is 10kts off? If it passed a p/s check, you should be golden.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  5. #5
    The other item that differ from the RV-8 to mine was his outside air temperature was reading 2-3 degrees warmer than mine. It is rare when a RV-6 is reading the same ground speed as an RV-8. When it does, I would think all the numbers should read the same.

  6. #6
    Unless the Outside Air Temp.; Indicated Airspeed and compass are nuts on, there will be an error, the more any of these are out of parameter, the greater the error. I would suggest first, calibrate the compass again; second, use a good manometer to calibrate your airspeed, you can build one quite simply suing a clear plexi hose and water to measure inches of water calibrated to indicated airspeed; third, check your OAT against a known value. Then give it a try, it is, after all, a computer, garbage in, garbage out! ( I also has to do with AL-GOREythm's)

  7. #7
    There are a number of factors like OAT, IAS, and heading that will greatly affect the trigonometry required to calculate winds aloft. If your heading is a degree or two different, OAT a few degrees different, or IAS a few knots off, it will change the winds greatly. Ensure the OAT is accurate, ensure IAS is accurate, and ensure your magnetometer is properly aligned.
    ---
    Trevor Conroy
    Technical Support
    Advanced Flight Systems
    Support@Advanced-Flight-Systems.com

  8. #8
    Trevor and Sharpdoug,
    Your indicated airspeed as checked during an ifr cert does not take into account static system errors other than leaks. If you have flush ports or any other mounting issues both your altitude and airspeed will be off by anywhere from a few to possibly as much as 20 k and 1500 ft. The best way to check this is to fly a gps four leg course and maintain altitude and airspeed within 50 ft 2 k. compare with your ground speed from the gps. Do this flight very early in as close to zero wind as possible. You may need to do a static port ramp adjustment.

  9. #9
    i am planning to redo magnetometers calibration, as far as OAT I plan on moving the sensors at my annual in March. Currently in the probes are inside the wing root fairing and will move them out into the inspection panels. I will go back to Avionics Unlimited and see about IAS calibration, I did pay $300 for the test. As far as the static ports I used the ones on the Cessna's from ACS. Flat aluminum plate with the hole in the center. I have heard a lot of talk about those not working on a RV, changing them now would be a lot of work. So if I could change the IAS in the AFS instead that would be easier.

  10. #10
    I installed flush ports and the fix was not that difficult. I removed the screw on connection, drilled out the port to allow the Van's pop rivet to be installed. Drove out the mandrel and cleaned all chips out and re-installed the static line. That was it. Only took about an hour.

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