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<DIV><FONT face=Arial>Jack</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>No problem - I agree with your assessment of the auto
skid. It's just something that more folks may relate to and seems to
have helped some with the "break while nearly retaining track"
notion.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Relating your considerable full scale aerobatic
experience and the relationship to both pattern and IMAC is great! It sure
reinforces the point that different designs behave differently in snaps. (Also
confirms my observations of the Giles.) </FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Of course, as you're aware, model pilots don't have
the sensory input of full scale pilots when entering a spin. Interesting that
the full scale guys manage a spin as you describe. Model guys really just need
to be patient during entry and give the airplane time to slow enough, then tweak
the rudder to get the "stall" into the spin. Usually, relaxing the elevator a
little will still result in a true spin that's easy to stop. Again, model set-up
is key - enough control to get the job done, but not too much.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>This list benefits from folks with your experience
providing factual info, thanks again. </FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Earl</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<BLOCKQUOTE
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=jtkeiser@comcast.net href="mailto:jtkeiser@comcast.net">Jack
Keiser</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">NSRCA Mailing List</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, October 23, 2007 10:41
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Judging
Snaps & spins II</DIV>
<DIV><BR></DIV>
<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
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<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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