Displacement during snap rolls (was Why is it so quiet?)

[J.Oddino]

Hi Dean,
I haven't kept up with rules in pattern but it is not clear where this "break" in pitch prior to the snap came from.  If the airplane snaps it must have reached a high angle of attack meaning it pitched.  Why must the pitch lead the yaw?  In fact it sounds like everyone likes the opposite yaw prior to the pitch.  Something doesn't add up.
Jim
  ----- Original Message ----- 
  From: Dean Pappas 
  To: discussion at nsrca.org 
  Sent: Thursday, December 30, 2004 11:19 AM
  Subject: RE: Displacement during snap rolls (was Why is it so quiet?)


  Harrumph, Bob!
  There will and must be a high G spike in an unloaded snap to get the stall to occur. Once the stall develops, the G loading is limited, but not necessarily to 1G.
  If the entry speed is higher than the 1G stall speed, then the G loading during the first half turn or so is going to be a function of the higher speed. 
  Then the energy bleeds off rather quickly.
  That's almost a good functional definition of a high-energy snap.
  I've ridden through a great many snaps in a Decathlon, and because they were always entered at moderate (sub maneuvering) speed, they weren't all that violent.

  Happy New Year ...

  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 Bob Richards
    Sent: Thursday, December 30, 2004 10:26 AM
    To: discussion at nsrca.org
    Subject: Re: Displacement during snap rolls (was Why is it so quiet?)


    A stalled wing is still producing lift. Just look at the 3D fliers.

    If you look at a lift curve (angle-of-attack vs lift), the lift keeps increasing linearly until the wing begins to stall. Even after a portion of the wing has begun to stall, the lift will still increase, just not linearly. At some point (a very deep stall) the lift will decrease, but never go to zero.

    JMHO.

    You are correct that a stall can occur at any airspeed or attitude. Also, the plane does not have to be stalled just because it is below the "stall speed".

    Someone mentioned in this discussion about it being impossible to break a wing doing a snap roll, if they do then they did not do a proper snap roll. It is possible to break a wing, from the mere fact that the angle-of-attack can't possibly increase from a normal to a stalled condition instantaneously -- it must go through a range of AOA that will include the maximum lift AOA. Technically, the "snap" did not break the wing, the entry into the snap DID.

    In full-scale planes, there is something called "maneuvering speed".  Over that speed, it is possible that full control surface deflection can cause the G forces to exceed the design limits of the airframe.  I'll bet that the number of full-scale pilots that have succesfully performed snap-rolls under the "maneuvering speed" far exceeds those that have done snaps over that speed. :-)


    Bob R.

     
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