RasAeroII Negative Wind Speed

Discussion in 'Rocketry Electronics and Software' started by Wulfram, Sep 15, 2019.

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  1. Sep 15, 2019 #1

    Wulfram

    Wulfram

    Wulfram

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    I'm trying to determine how launching in the direction of the wind might affect apogee. In RasAeroII, you can input a launch angle (only positive) and a wind speed (positive or negative). From what I've determined, inputting a positive windspeed works basically as expected, with the rail starting pointing into the wind and the rocket turning more into the wind.

    It should be optimal to launch with the wind, such that as the rocket turns into the wind, it actually becomes more vertical with respect to the ground. I suspected that this was the purpose of a negative wind speed for the RasAero launch conditions. However, when I give a negative wind speed (for any rocket -- pick a random example one that comes with the program and try it) -- the rocket becomes unstable almost immediately upon leaving the rail.

    Could someone tell me either how I'm misusing this feature/what it is meant for, or how I might successfully model this?
     
  2. Sep 15, 2019 #2

    mikec

    mikec

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    Manual says: Wind speed (mph). Positive wind speed is a headwind, which the rocket will weathercock into, and which will blow the rocket on a parachute back towards the launch pad. Negative wind speed is a tailwind, which will blow the rocket on a parachute away from the launch pad.

    I don't know if the behavior you describe is a bug or what. I don't usually use RASAero to look at wind stability, I use Openrocket for that.
     
  3. Sep 15, 2019 #3

    Wulfram

    Wulfram

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    I also saw that in the manual. There's also only one wind-speed value to input, so it doesn't appear to be a separate feature just for descent under parachute. It could be a bug, but I wasn't sure if someone else may have something to add.
     
  4. Sep 25, 2019 #4

    Chuck Rogers

    Chuck Rogers

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    Wulfram:

    I checked it out, it's a bug in the software.

    So unfortunately until we fix this bug, you can only enter a positive wind speed in RASAero II.

    I checked out the current release version of RASAero II with a positive wind speed, everything is fine, the trajectory output numbers check out. It's just when you enter a negative wind speed that you get the bug in the software.

    RASAero II only has one wind speed entry (ground wind speed) for doing studies of launch dynamics off the rail, studies of wind stability, and studying weathercocking effects. The same ground wind speed is used for all altitudes for parachute drift. Multiple wind speed entries at multiple altitudes weren't added as that requires balloon data, or daily wind profiles from web sites which most users don't enter. But it's likely something we'll be adding at a later date.

    We'll have to fix this negative wind speed bug in the next release of the RASAero II software.


    Charles E. (Chuck) Rogers
    Rogers Aeroscience
     
    timbucktoo likes this.
  5. Sep 25, 2019 #5

    Wulfram

    Wulfram

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    Got it, thanks Chuck. I appreciate all your work, looking forward to the next release.
     

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