Snaps

[RC Steve Sterling]

Whoa Whoa-- I just got out my book and looked. NOWHERE does it use the word
"before" or "prior". It says
"Snap Roll is the simultaneous, rapid autorotation in the pitch, yaw and
roll axes of flight...."

I'll grant that it then goes on to talk about an "initiating break", I don't
think that precludes that break in pitch occuring simultaneously with rudder
induced yaw and roll. Especially since the opening definition uses the word
simultaneous.

Just because the nose breaks up doesn't mean the airplane is stalling
either. I don't think my Focus will stall if I just pull back hard on the
elevator, it just does a tight loop. But kick full elevator and rudder, it
certainly does stall (and snap) then!
  -----Original Message-----
  From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On
Behalf Of David Lockhart
  Sent: Tuesday, April 13, 2004 1:20 PM
  To: discussion at nsrca.org
  Subject: Snaps


  Interesting discussion RE snaps.

  The way the snaps are currently defined (correctly I think) requires the
aircraft to be stalled in pitch prior to any rotation in yaw and roll.  The
break is a required element of the maneuver (not unlike other maneuvers).
As with any maneuver, I believe it is the pilots responsibility to clearly
show/demonstrate all elements of a maneuver.  If a stall is not demonstrated
at the point of entry into a spin, the maneuver should be scored zero.  If a
snap does not have a break on the entry, it should also be scored zero.

  It is not likely that a good break and snap entry will occur using a snap
switch/button - unless the elevator servo is much faster than the other
servos.  What helps define the break on the entry of the snaps is very fast
application of the elevator input and a very fast elevator servo - lots of
throw also helps (I have used as much as 30 degrees of throw on some planes
for some snaps).  The result is a very rapid change in the pitch attitude of
the plane (like the definition says) with very little displacement in track.
If the airplane is truly stalled at the time of rudder (and aileron)
application, the change in track in yaw will be minimal, if any.  It is not
easy to get a modern day pattern plane to perform a nice snap - as has been
noted, they are very stable in pitch, generally have fairly small elevators,
very light wing loadings, and generally have control throw setups that lack
the authority to initiate a clean break.  Most pattern planes I see on the
flightline quite simply won't break cleanly because they lack the elevator
throw to do so.

  If the plane displaces from the entry track during the break and then
resumes a parallel track after the snap, that is ok (and actually required
depending on ones interpretation of the FAI book).  If the track of the
plane does change slightly during either the break or after the snap, this
can be downgraded - and the downgrade could be minimal to the point of not
reducing the maneuver score due solely to the change in track.  A "10" is
not a flawless maneuver, it is a maneuver which is perfect or contains flaws
that are not substantial enough to warrant downgrading to a 9.5 (or 9 in
FAI).

  The rotation rate of the plane during the snap depends on many factors -
including design parameters of the plane (wingspan being a biggy) and the
pilot technique.  In general, the greater the break (deeper the stall), the
slower the rotation of the plane will be.  If the left/right wings are
stalled equally at the break, the rotation rate is largely determined by the
amount of rudder applied (which accelerates one wing panel forward and the
other aft resulting in asymmetric lift which causes the rotation about the
roll axis).  The same airplane that does not break cleanly in pitch (reduced
throw, poor technique) will likely break in yaw - meaning the wing panel
accelerated forward by application of the rudder never does actually stall,
and the wing panel accelerated aft does stall and the asymmetry in lift
again results in rotation about the roll axis.  The difference between these
two scenarios is that the first contains the element of the break and is a
scorable snap.  The second scenario does not contain the element of the
break and should be scored zero.

  What is interesting to note (and I've many witnesses to this at the
practice field), is that the difference in the rotation rate of the snap is
not effected noticeably by the amount of aileron used - 10 degrees or 15
degrees of aileron throw result in the same rotation rate - IF the snap was
entered from a stalled condition.  If I substantially reduce the elevator
throw (and the break becomes very, ahem, questionable), the amount of
aileron used has a dramatic effect on the rotation rate.

  The entry speed of the plane is not a judging criteria.  With proper setup
and technique, the airplane can be made to break in pitch at virtually any
airspeed (with commensurate increases in stress at higher speeds) - but the
break is usually slower and easier to judge at lower speeds.

  For several years at the US NATs, I received comments from both pilots and
judges regarding the crispness of my snap entries and the easily visible
cone of the nose/tail during the snap.  Many of the pilots suggested I
should "back off" the snaps and exaggerate the break less to make them
easier to do (even tho I rarely missed an exit).  In general, my scores on
maneuvers containing snaps were not very good (relative to other maneuvers
in the flight).  Since that time, I have "toned" down the snap entry and the
snap itself - the break is now much less defined and harder to see, and the
snap itself is much more axial, and the rotation rate is faster (and after
adapting, I miss the same number of exits - none on a good day <G>).  My
scores have generally increased - my conclusion is that very few judges are
either capable of seeing the break, looking for the break, understand the
break, or have the confidence to downgrade (to zero) a snap which does not
demonstrate a break.  I believe both styles of snaps I flew are within the
rulebook definition - but one scores better than the other - I guess I'll
continue to fly the style that scores better, even tho I think it is the
style that is harder to judge.

  And, if I've offended any of the aerodynamic purists out there with my
oversimplification of the dynamics of a snap, my apologies - I didn't think
additional detail about the aerodynamics were of help in this discussion.

  Regards,

  Dave Lockhart
  DaveL322 at comcast.net




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