Displacement during snap rolls

[Ken Velez]

 I have to agree with you Dean. A stall is caused by the separation of airflow from the wing upper surface resulting in a rapid decrease in lift regardless of airspeed , flight attitude or weight. The problem we face is what happends when from a staight flight 0, 1 or 2 deg. for given airplane or airspeed to critical 17, 18+ deg. Climbs or displaces thru the time that it takes to go thru 2,3,4 to 15 deg.
Later.

Ken Velez
  ----- Original Message ----- 
  From: Dean Pappas 
  To: discussion at nsrca.org 
  Sent: Wednesday, December 29, 2004 10:19 AM
  Subject: RE: Displacement during snap rolls


  Hi Archie,
  That just isn't true. A stall is not an on/off switch deal. It progresses over a range of angles of attack,
  and the autorotative tendency of the plane both comes and goes as the plane increases angle of attack.
  Stalled does not mean zero lift! The center of gravity will and must wobble some in a snap. 
  Because the plane does not go from flying to stalled  instantaneously, there will be a displacement of the
  CG both to the top of the plane, and to the side being snapped, assuming a positive snap.
  We need to write a standard for what is acceptable. I remember 1/2 wingspan in an old IAC judges' guide,
  but I need to look it up, as the last time I saw one of those was nearly 20 years ago.

  I was one of those FAI judges at the NATs, and we were not looking for a "VERY clean break", to quote you ... we were just looking and hoping to see one, at all !
  You have to see a change in pitch. If you don't see one, or if the pilot treats you to a change in yaw before, the rolling starts,
  then you have been presented with what I like to call a twinkle roll. That's not a snap.  
  Things are busy here, at work today, so this is a short note, about a long subject, but I feel the need to throw my two cents in.
  Later,
      Dean

  Dean Pappas 
  Sr. Design Engineer 
  Kodeos Communications 
  111 Corporate Blvd. 
  South Plainfield, N.J. 07080 
  (908) 222-7817 phone 
  (908) 222-2392 fax 
  d.pappas at kodeos.com 

    -----Original Message-----
    From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On Behalf Of Archie Stafford
    Sent: Wednesday, December 29, 2004 9:57 AM
    To: discussion at nsrca.org
    Subject: RE: Displacement during snap rolls (was Why is it so quiet?)


    Last year at the NATS the biggest thing they were looking for was the break.  You really had to show a VERY clean break.  The rule book doesn't specify how much break, but it was obvious last year that you really had to show a VERY clean break, even on the avalanches, which is very tough to do at the top of a loop and give a good break, or in FAI the snap at the bottom of the loop.  I talked to Andrew Jesky as well and he said the FAI judges were being the same way, the you really had to show a very definite break.

     

    I think the key to the displacement is how much rudder is in the snap.  From my experience if you have too much rudder the plane will displace from one side or the other.  You can take out some of the rudder and still have a truly stalled maneuver.  You use the elevator to stall the aircraft.

     

    I do have a question though.  How can an aircraft be "semi-stalled?"  Either the aircraft is stalled or it isn't. 

     

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