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<DIV><FONT face=Arial size=2>Earl,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Been following this thread for a while now and felt
compelled to offer my two cents worth. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I have a little problem with your auto analogy. In
the case of an abrupt steering input in a fast moving car, the forces trying
to change the car's path are due to the traction of the tire against the
pavement; the force trying to keep the car going in its original
direction is due to the momentum of the vehicle, according to some guy
named Newton. Even the smallest lateral force will produce some correspondingly
small change in direction. In the real world, a lot of factors come into play:
sidewall flex causing tire slip angle, suspension response, roll stiffness
and so on. If traction were lost immediately, as might be the case when driving
on a sheet of ice, turning the wheel sharply produces no change in direction -
momentum keeps the car going straight ahead. Only after some traction is
regained will the car turn.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Now let me switch gears a bit and talk about snaps
and spins. I'm not an aerodynamicist so I don't pretend to understand all the
aerodynamic events that take place in a snap. But I do have quite a bit of
experience in full scale aerobatics in a variety of aircraft ranging from Cessna
Aerobats, Pitts bipes, Giles 200&202 to the Sukhoi 26. I have
also been flying pattern since the '70's (with a few breaks here and there) and
recently, IMAC, so I appreciate that aspect as well. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The judging criteria for snap rolls is basically
the same in all three venues; particularly with respect to the pitch break. I
have received zeros in all three venues when that was not clearly observed ( I
can't recall any 10's even when the break was obvious). That does not mean
the airplane did not snap (auto-rotation); I just didn't do it according to the
prevailing judging criteria. When you're in the aircraft, its quite
obvious when auto-rotation occurs. Some aircraft, particularly the Giles
200, can roll so fast (about 540 deg/sec) that its nearly impossible from the
ground to tell a full deflection aileron roll, with a little rudder thrown in,
from a true snap. And you do not need the pitch break to get a true snap - just
jerk the stick toward the right (or left) rear corner and kick hard right
(or left) rudder simultaneously, and I guarantee you'll experience a
violent snap with true auto-rotation. The G-200 is the closest thing you can
imagine to a model; you can fly it with two fingers and it responds about the
same as an IMAC plane.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The other extreme is the Su-26. Its like flying a
John Deere. Two hands on a stick that resembles a baseball bat. If you try the
same control inputs for the snap as the Giles, it just mushes around. Here, the
pitch break to load the wing seems more of a necessity. And (in a positive snap)
you only pull the stick back partially,but smartly, maybe a third of the
way, then shove it quickly toward the right forward corner to unload the
elevator and bring in the aileron. Full right rudder applied just as the nose
pitches up. Despite the significant mass, and relatively high polar moments, the
plane auto-rotates with surprising speed - not like the Giles, but pretty darn
quick. To stop on heading, you need hard left rudder and some left aileron. You
may stop on heading (with practice) but you will have moved to the right of your
original flight path - that can be readily observed in a snap on the
vertical up line.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Why the Sukhoi and the Giles behave so differently
is due to a lot of factors. I suspect one major factor is the gyroscopic
effect of the extremely large prop on the Sukhoi; the gyro effects are much more
noticeable - that's why it does a Lomcevak so well. The wing loading of the
Sukhoi is much higher than the Giles, and so are the moments of inertia. Of
course, the wing airfoil is different too. Many other differences (including
fuel consumption).</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Regarding spins, hardly any full scale pilot does a
true spin in competition. The entry is usually done in the classic way; stick
full back to the stall break, nursing it with subtle aileron and rudder input to
get it to drop off on the side you want, then as soon as the nose falls through,
push the stick forward to break the stall and keep the rotation going with
aileron and rudder. You're really in a tight aileron turn, both wings are
flying, but it looks like a spin. Most important, you can stop on heading very
accurately. The downside is that you probably lose a little more altitude. You
could just hold the stick back, full rudder deflection and neutral aileron, then
stop the spin with opposite rudder and stick forward but the stop is
unpredictable.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>How does all this relate to models? Not sure, but I
thought a different perspective might be interesting. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>It might also be interesting to know the that the
same topics - spins, snaps, judging competence, etc - receive about the same
amount of gripes in each venue. No surprise there.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Jack</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>----- Original Message ----- </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=ejhaury@comcast.net href="mailto:ejhaury@comcast.net">Earl Haury</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">Discussion List, NSRCA</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, October 23, 2007 5:26
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [NSRCA-discussion] Judging Snaps
& spins II</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial>
<DIV><FONT face=Arial>Posted this as a reply yesterday but it got snagged as
too long with the ongoing thread attached - started a new thread.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Jim</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Don't think that'll work very well. Let's take the
analogy of a car moving in a straight line slowly - turn the steering quickly
and the car will turn - changing "track". Do the same thing at high speed and
the car will skid - track stays mostly the same and only attitude changes.
Entering a snap is similar - establish a "skid". In both cases there will be a
minimal departure from the original line until "traction" is lost and the skid
occurs. </FONT><FONT face=Arial>Consider that the faster the pitch input
the less AOA increase will be needed before rudder application. This is where
we get into trouble trying to define a "break" into a snap, some visualize
this as needing to be huge while, in reality, it may only be a few degrees.
</FONT></DIV>
<DIV> </DIV>
<DIV>Also - with regard to the departure from track before the "skid". F3A
rules require a "separation from the flight path" and AMA rules allow it
"track closely maintains the flight path". Numerous things will define the
amount of "separation" including rapidity of pitch / yaw, mass of
airplane, wing loading, etc. The separation may be a few inches to a couple of
feet and is not to be downgraded as long as the aircraft "closely maintains"
track. So - if the snap (skid) progresses more or less parallel to but
slightly offset (maybe in both pitch & yaw) it's not only OK, but a pretty
good indicator that the snap isn't an axial roll.</DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Use the description to think through set-up and control
inputs. Recognize that a properly done snap entry takes only a fraction of a
second (if you have time to see exactly what's going on you'll be getting
downgrades for track changes). With the proper set-up and practice a snap
entry can be perfect almost every time - that just leaves the exit to deal
with. Finish wings level and enjoy the 10!</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Earl</FONT></DIV></FONT></DIV>
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