F3A - snap roll query

[Del Rykert]

Don.
     Thanks for tackling and giving what I consider a very accurate description and analysis.
 
     Del K. Rykert
     AMA - 8928 
     NSRCA - 473
     Kb2joi - General 


  ----- Original Message ----- 
  From: Don Ramsey 
  To: discussion at nsrca.org 
  Sent: Wednesday, November 05, 2003 12:10 PM
  Subject: Re: F3A - snap roll query


  Here's what I wrote for the KFactor about this subject.



  Snaps!  Now there's a maneuver that causes some heated discussion.  Van
  Putte was asked at the NATS Pilot's Meeting if a snap should be downgraded
  if it displaces from the line.  He took that question in stride and promptly
  handed it off to me.  I tried to pass it back to him and to Earl Haury but
  no one would answer.  Well my answer was, "It should not displace
  significantly from the flight path for maximum points."  I caught a lot of
  flack for that answer but I believe it is correct.  How did I come to
  believe this?  Here's what the Competition Regulations say about snaps.



  Snaps - A Snap is a simultaneous, rapid autorotation in the pitch, yaw and
  roll axis of flight in a stalled wing attitude.  The following criteria
  apply:

    1.. Since the maneuver is defined as a stall maneuver (initiated by a
  rapid stall of the wing induced by a change in pitch attitude), the nose of
  the fuselage should show a definite break from the flight path in the
  direction of the snap (positive or negative) while the track closely
  maintains the flight path. The track visualized as the path of the Center of
  Gravity (CG) should ideally follow the geometric flight path of the maneuver
  while the nose and tail autorotate through opposite helical arcs around the
  flight path. A snap that does not show a break and stall to initiate the
  snap, but does enter a stalled attitude during the maneuver is severely
  downgraded.
    2.. If the stall does not occur and the model barrel- rolls around, the
  maneuver is  zeroed. A barrel roll can be identified when the CG, the nose
  and tail scribe the same helical path through the required rotation of the
  maneuver.
    3.. Snap rolls have the same judging criteria as axial rolls as far as
  start and stop of rotation, constant flight path through the maneuver, and
  rate are concerned.
    4.. Snap rolls may be either positive or negative.
    5.. If the model returns to an unstalled condition during the maneuver,
  such that the autorotation is not visible and the model rolls to complete
  the maneuver, it would be severely downgraded.
    6.. Airspeed is not criteria which should be used to judge this maneuver.
  As the wing of the model is stalled during this maneuver a significant
  decrease in speed may occur and is not a cause for downgrade.
  There are several things to notice about snaps.  From #1 above, "the nose of
  the fuselage should show a definite break from the flight path in the
  direction of the snap." You make the call here.  If you don't see the break,
  maybe it didn't happen.  The last sentence in #1 says, "A snap that does not
  show a break and stall to initiate the snap, but does enter a stalled
  attitude during the maneuver is severely downgraded."



  How about displacing from the line?  Again in #1, ". while the track closely
  maintains the flight path. The track visualized as the path of the Center of
  Gravity (CG) should ideally follow the geometric flight path of the maneuver
  while the nose and tail autorotate through opposite helical arcs around the
  flight path."  And, from #3, ".constant flight path through the maneuver
   ..."   That's where I got the answer, "It should not displace significantly
  from the flight path for maximum points."



  So, my answer would be, there would be a downgrade depending on the severity
  of the displacement but NOT a zero.



  Don Ramsey

  NSRCA Judging Committee Chairman





  ----- Original Message ----- 
  From: "PENNISI Peter" <Peter.Pennisi at publicworks.qld.gov.au>
  To: <discussion at nsrca.org>
  Sent: Tuesday, November 04, 2003 7:58 PM
  Subject: F3A - snap roll query



  Hi Guys,

  I recently read that any snap roll which finishes higher than where it
  started should be zeroed automatically even if the jump is slight. I am
  referring in particular to the 1-1/2

  How is this ruling being interpreted in your country. If this is the case I
  will need to perform these snaps at very low speeds.

  Given the stability of our modern aircraft and the relatively long tail
  moments this is not an easy accomplishment.

  Peter

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