[NSRCA-discussion] Snap entry in FAI
george w. kennie
geobet at gis.net
Mon Jun 16 13:53:21 AKDT 2008
John,
We often think that the wing is producing zero effect when we go K.E., but the AOA of the wing is still positive to the datum line and as long as we have forward movement of the airframe a force will be generated away from the gear. That's why you have down elevator mixed to rudder in order to nullify this effect. I hear many people state that in K.E. the wing is not producing any lift, but it sure is reacting to the airflow and decalage.
For the K.E. Snap the airframe still needs to be in a stalled condition and it's still elevator that's necessary to produce the effect of the stall. Due to the visual perspective the increased AOA required to stall the wing will be undectable to the pilot as well as the judges because in K.E. the pitch-up will take place horizontally instead of vertically.
But then this is just my understanding and I'm sure there are others who will straighten me out.
G.
----- Original Message -----
From: John Pavlick
To: General pattern discussion
Sent: Monday, June 16, 2008 4:57 PM
Subject: Re: [NSRCA-discussion] Snap entry in FAI
Which axis do you need to show a "break" in for a knife edge snap? The wing isn't really "lifting", the fuse is.
John Pavlick
"george w. kennie" <geobet at gis.net> wrote:

My lip is becoming too painful from biting it, so I think I'm going to stick my nose in here somewhere.
I think I'm with Jon on this one.
My logic, however flawed, tells me that if I am flying my plane straight and level and I input rudder, no matter how much, there is no way that this input will induce a stall to the airframe. Therefore, it seems to me, that the necessary force required to stall the main lifting surface must come from the elevator. It would further seem to me that this input must, by it's very nature produce a pitching attitude to the fuselage whether positive or negative. So I would have to conclude that the attitude "break" referenced by the rule can only refer to a "pitch" break and would be impossible to confuse with an attitude change induced by the rudder seeing that the required result is to stall the main wing.
And yes Jon, I agree that it would be necessary to lead with the elevator in order to bring about this attitude change before rotation is started, however miniscule the interval might be.
Of course I'm still open to hearing other interpretations and their validations as these observations are strictly opinions.
G.
----- Original Message -----
From: Jon Lowe
To: nsrca-discussion at lists.nsrca.org
Sent: Monday, June 16, 2008 2:10 PM
Subject: Re: [NSRCA-discussion] Snap entry in FAI
Jim,
I have no clue how you think all three axes can be initiated at the same time. You keep forgetting the part of the RULE, quoted verbatim below, that says the "fuselage break and separation from the flight path" must happen "BEFORE THE ROTATION IS STARTED". I'm NOT equating fueselage break to pitch break, it could break in pitch and/or yaw, if it doesn't start rotation at the same time. If you initiate all three axis at the same time, rotation WILL start at the same instant, and that is specifically NOT permitted. READ THE RULE! The judge MUST determine if the fuselage broke and separated from the flight path first, BEFORE the rotation started. If it didn't, he MUST severely downgrade.
Jon Lowe
-----Original Message-----
From: Woodward, Jim (US SSA) <jim.woodward at baesystems.com>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Mon, 16 Jun 2008 12:37 pm
Subject: Re: [NSRCA-discussion] Snap entry in FAI
Jon,
Iâ?Tm shocked - you are totally wrong here. Do not equate â?ofuselageâ? to â?opitchâ? in the reading of this definition. As a judge you should NOT apply a â?opitch-assessmentâ? pass/fail criteria to judging FAI snap rolls. It is completely rejected. The plane and therefore â?ofuselageâ? must autorotate about the flight axis, which means that the nose and tail of the plane will move in a conical fashion. The pilot can initiate with all 3 axis at one time.
It is the responsibility of the judge to determine if autorotation occurred, and not determine how or in what order the pilot did it.
Thanks,
Jim
--------------------------------------------------------------------------
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Jon Lowe
Sent: Monday, June 16, 2008 1:21 PM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] Snap entry in FAI
You are correct, as long as there is no roll induced at the same instant. I overlooked that possibility. Not sure how rudder alone will induce the "supposed to be in a stalled condition" though!! There are many attitudes (e.g. 45 down on center) where a judge could not likely see a rudder departure alone first, and thus conclude that departure did not occur before the roll departure started. And a judge might also not see a pitch departure first on a end box upline snap, but he could see rudder first. It is VERY clear that simultaneous roll with either or both of the other axes departures is NOT allowed as others have tried to state here. I did say that pitch and yaw departure could happen simutaneously, in my original post, as long as roll doesn't occur at the same time.
Jon Lowe
-----Original Message-----
From: JShulman <jshulman at cfl.rr.com>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Mon, 16 Jun 2008 11:22 am
Subject: Re: [NSRCA-discussion] Snap entry in FAI
Jon,
I don't see where it says pitch break? Rudder first will show attitude break and separation from the flight path. So if one uses rudder and elevator first this is also correct.
Regards,
Jason
www.jasonshulman.com
www.shulmanaviation.com
www.composite-arf.com
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Jon Lowe
Sent: Monday, June 16, 2008 12:11 PM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] Snap entry in FAI
I suggest people re-read the definition ofsnap-rolls from the FAI sporting code. I did a few minutes ago. Here it is:
"5B.7.5. SNAP-ROLLS
A snap-roll (or flick roll/rudder roll) is a rapid autorotative roll where the model aircraft is in a stalled
attitude, with a continuous high angle of attack
Snap-rolls have the same judging criteria as axial rolls as far as start and stop of the rotation, and
constant flight path through the manoeuvre is concerned.
At the start of a snap-roll, the fuselage attitude must show a definite break and separation from the
flight path, before the rotation is started, since the model aircraft is supposed to be in a stalled
condition throughout the manoeuvre, If the stall/break does not occur and the model aircraft barrelrolls
around, the manoeuvre must be severely downgraded (more than 5 points). Similarly, axial
rolls disguised as snap-rolls must be severely downgraded (more than 5 points).
Snap-rolls can be flown both positive and negative, and the same criteria apply. The attitude
(positive or negative) is at the competitorâ?Ts discretion. If the model aircraft returns to an unstalled
condition during the snap-roll, the manoeuvre is severely downgraded using the 1 point/15 degree
rule."
Note that "the fuselage attitude must show a definite break and separation from the flight path, before the rotation is started..." That means that simultaneous pitch and rotation is specifically NOT permitted. I would interpret it as meaning that pitch and yaw could theoretically happen simultaneously, as long as no roll is involved. Sorry Matt, the rules as written do NOT allow actuation in all three axes simultaneously. The rule also states that a constant flight path has to be maintained.
Let's face it, the only way to prevent severe downgrading from EVERY judge, not just some judges, is to have a pitch break first. Takes any question away.
Jon Lowe
-----Original Message-----
From: rcmaster199 at aol.com
To: nsrca-discussion at lists.nsrca.org
Sent: Mon, 16 Jun 2008 10:46 am
Subject: Re: [NSRCA-discussion] Snap entry in FAI
A "Flick" and a "Snap" roll are the same roll in full scale aerobatics parlance and reference material.
Do these mean the same thing in model aerobatics? In my view, they do
The latest FAI regs allow actuation of the three main axes simultaneously...that is, the regs don't specifically differentiate "Pitch Break" from other deviations. I don't think they specifically require that the model must rotate about it's flight path either, I don't believe (.....plane must rotate in a conical fashion about the fight axis....). The model would probably present the best if that's done, so pilots may want to consider that when executing the maneuver.
In my take, a rapid Pitch is desired to preload the wing. Contrary to popular belief, both panels dot not have to stall for a snap to occur. Quite the opposite. Upon rudder deflection, the port panel will practically stall (lift much much less than the other panel) but the starboard panel must be lifting to create the autorotation. If both panels stall, the model will fall out of the sky for a distance and a snap would not occur at the correct moment in time
MattK
-----Original Message-----
From: Woodward, Jim (US SSA) <jim.woodward at baesystems.com>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Mon, 16 Jun 2008 8:47 am
Subject: Re: [NSRCA-discussion] Snap entry in FAI
Guys,
I thought the FAI changes explicitly allowed flick rolls? The rule
reads, "... fuselage attitude must show a definite break and separation
from the flight path."
It does not say, "MUST SHOW PITCH BREAK." Please DO NOT ERROUNIOUSLY
APPLY A PASS/FAIL MAJOR DEDUCTION initial assessment to the snap roll.
Watch the whole maneuver then render your score.
A break and separation from the flight path simply means that the nose
and tail of the plane must rotate in a conical fashion about the fight
axis. Yaw, roll, and pitch can all break at the same moment if that is
how the pilot does it.
Hey :) some really handsome smart guy wrote some stuff at this link
below about snap rolls to help clarify how they are done in IMAC.
http://www.mini-iac.com/DesktopDefault.aspx?tabid=77
thanks,
Jim
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