F3A - snap roll query

[Don Ramsey]

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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