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<DIV><FONT face=sans-serif size=2>Interesting discussion RE snaps.</FONT></DIV>
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<DIV><FONT face=Arial size=2>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.</FONT></DIV>
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<DIV><FONT face=Arial size=2>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.</FONT></DIV>
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<DIV><FONT face=Arial size=2>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).</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>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.</FONT></DIV>
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<DIV><FONT face=Arial size=2>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. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>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.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>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.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>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.</FONT></DIV>
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<DIV><FONT face=Arial size=2>Regards,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Dave Lockhart</FONT></DIV>
<DIV><FONT face=Arial size=2><A
href="mailto:DaveL322@comcast.net">DaveL322@comcast.net</A></FONT></DIV>
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