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Question about stall warning system

  1. Mar 14, 2015 #1
    My question is how precise is the stall warning vane in detecting the stagnation point on the wing?

    The lift transducer is an LVDT so electrically speaking it is a continuous signal. But when approaching a stall, could the vane be held in between center and full deflection for a few seconds? (The vane is spring loaded to center, not sure of the exact force required to move but feels very light to touch).

    Or maybe a better question: If the airflow at the stagnation point is 0 (vane center), does the airflow around the stagnation point slowly increase (vane in between center and full deflection) or is it pretty much full speed (vane instantly deflects to full position)?

    The aircraft is of the 707 variant.
     
  2. jcsd
  3. Mar 19, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
     
  4. Mar 19, 2015 #3
    From talking with various different people it seems as though the vane is precise enough to detect the exact stagnation point for a stall and that it is calibrated to go off somewhere between center and full forward (different positions depending on flap position signal). So the system would need to be calibrated to that exact position.
     
  5. Mar 20, 2015 #4
    Stall warning is a safety feature, thus it is designed to trigger before the wing actually reaches stall, so that the pilot has sufficient time to react.

    If I remember correctly they usually start sounding 2-3 degrees before the critical angle. But the critical angle depends heavily on flap position and wing contamination. The former can be taken into account when designing the control circuitry/program for the stall warning system, but the letter can be an issue, thus some aircraft may start giving the stall warning around 5 degrees prior to the critical aoa. What are actual current offset values, for these systems, I don’t know.

    Historically there have been quite a few different designs, some worked like on/off switches, others were incremental or continuous. As far as I know only the letter are in use today and they give the pilot an incremental feedback (sound and stick shaking) on how near stall they are.
     
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