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Homework Help: Groundspeed/Airspeed of insect

  1. Mar 12, 2007 #1
    Hi all,

    I am involved in a project to fly small moths down a wind tunnel to measure their flight patterns.
    the moths fly a total of 1.15m into a headwind of 1m/s. i am currently using velocity=distance/time to calculate an average speed but am unsure if this would be a called a groundspeed or airspeed?? most moths take about 6 seconds to fly this distance.
    does anyone have any ideas? other thoughts about how to calculate these velocities?


  2. jcsd
  3. Mar 12, 2007 #2
    That is the ground speed. You are measuring it relative to a fixed ground frame.
  4. Mar 12, 2007 #3


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    Airspeed is the speed relative to the air. Groundspeed is relative to the ground. The 1.15/6 m/s is the ground speed. The airspeed is 1.15+1 m/s.

    Airspeed is used for performance calculations like max lift, etc... Groundspeed is used to calculate time of flight.
  5. Mar 12, 2007 #4
    surely airspeed would be groundspeed-windspeed (which in this case would be negative 1m/s due to it being a headwind)?
  6. Mar 12, 2007 #5


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    It is negative if it is a tailwind, not a headwind.
  7. Mar 12, 2007 #6


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    And any angle between forward and backward results in intermediate values. Despite my total lack of math ability, I could work out wind-vector triangles like a demon. (Gotta love that Cessna flight computer. :biggrin: )
    What I really want to know is how you convince a moth to fly upwind rather than down. :uhh:
  8. Mar 13, 2007 #7
    surely that can't be right - the insects fly into a headwind so the windspeed must be a negative number (see http://www.aerospaceweb.org/question/instruments/q0210.shtml)
    using a positive number gives an airspeed of -0.8m/s!!

    moths and most other animals fly into head winds for tracking purposes
  9. Mar 13, 2007 #8
    I suppose it depends on convention--I would thing Sg=Sa+Sw surely if we were talking velocies, this is the case. So the airspeed=2.15m/s as fred suggested. In fact if we were to raise the windspeed to this value, I believe :

    Sg=0. Sw=-2.15 and the Sa=2.15
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