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Ahhh. angle of attack is not the same as the aircraft attitude.Websters
defines angle of attack as "the acute angle between the chord of an
airfoil and the line of relative air flow". The relative wind flows
parallel and opposite the direction of the wing's movement through the
air.The wing's attitude as we see it from the ground is NOT the same as
angle of attack. If you are in a vertical climb is the wing stalled?
After all it is 90 degrees ATTUIUDE from your perspective on the
ground, right? But the wing is not stalled because the relative wind is
coming parallel and opposite the direction of flight. You can be in a
nose low descent and stall a wing. Now take a straight and level pass
and give it an instantaneous large amount of up elevator. What happens?
First, the plane continues in the direction it was going (straight
ahead) for a short time, but what is important is that the angle
between the relative wind (straight ahead) and the wing which is now
pivoting up increases until it reaches the critical angle of attack and
it stalls. Without knowing the specifics of that wing design, we can't
know when exactly this will occur, but it can be extremely fast and at
a relatively low ATTITUDE in relation to the ground. Hence, you do not
need a high nose ATTITUDE in order to have a high angle of attack.
There are too many variables for one to say that they need to see a
nose high attitude in order to define a high angle of attack and thus a
stall. Remember also, that different wings have a different critical
angle of attack where a wing will stall. How does anyone know where
that angle is without a wind tunnel and testing? and who am I to say it
did not pitch up enough to stall therefore I giveth the pilot a 5 or
zero even though I cannot possibly know the particulars of the wing
that I am watching.<br>
My comment of the 1-2 degrees was to say that we do not know how
closely any particular wing is flying from it's critical angle of
attack. If it is in fact close, a change of only 1-2 degrees can cause
a stall. We are trying to be aerodynamic engineers from the ground and
deciding for ourselves what the angle "should" look like and
downgrading accordingly. Now throw in the conceptual difference
between angle of attack and aircraft attitude, and it is easy to come
to the wrong conclusion about stall or no stall. Are we fling only 1-2
degrees from the critical angle most of the time, no but the point it
that there is absolutely no aerodynamic requirement for a very nose
high ATTITUDE to be a requirement in order to get a high angle of
attack on the wing.<br>
<br>
Chris<br>
<br>
<br>
Vicente "Vince" Bortone wrote:
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<p>Chris,</p>
<p> </p>
<p>I am copying from the first sentence FAI rule book: "<font size="2">
</font>A snap-roll (or flick roll/rudder roll) is a rapid
autorotative roll where the model aircraft is in a stalled attitude, <strong>with
a continuous high angle of attack</strong>" The question: Is 1-2
degrees consider a good amount to define a high angle of attack? </p>
<p> </p>
<p>Vicente "Vince" Bortone<br>
<br>
----- Original Message -----<br>
From: "Chris Moon" <a class="moz-txt-link-rfc2396E" href="mailto:cjm767driver@hotmail.com"><cjm767driver@hotmail.com></a><br>
To: "General pattern discussion"
<a class="moz-txt-link-rfc2396E" href="mailto:nsrca-discussion@lists.nsrca.org"><nsrca-discussion@lists.nsrca.org></a><br>
Sent: Tuesday, October 13, 2009 3:07:01 PM GMT -06:00 US/Canada Central<br>
Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)<br>
<br>
I think what this goes back to is the erroneous belief that you need to
see an exaggerated pitch departure or it should be severely
downgraded. Keep reading the maneuver description. It needs "A" pitch
break, and depending on the current aoa (angle of attack) that can be a
difference of just a degree or 2 if you are near the critical aoa.
Please don't tell me guys, you are looking for MORE than a simple
exceeding of the critical aoa and resulting stall. An exaggerated
pitch break just to prove to naysayers that you make a break is wrong,
wrong, wrong. It says it needs "A" break. Please keep re-reading it.
Same for spin entry. It needs to stall, not go 30 degrees nose up to
"prove" a stall. We are getting wound up over a misunderstanding of
the mechanics of a stalled condition. As Don and Verne are alluding
to, it really is not that complicated.<br>
<br>
Chris<br>
<br>
<a moz-do-not-send="true" class="moz-txt-link-abbreviated"
href="mailto:verne@twmi.rr.com" target="_blank">verne@twmi.rr.com</a>
wrote: </p>
<blockquote
cite="mid:20091013195050.5HLQG.283850.root@hrndva-web08-z01">
<pre>Or you could just write in "DNO".... I always seem to see the break as in, nose up, tail down, and my 56 year old eyes are lousy. Verne ---- "Vicente "Vince" Bortone" <a
moz-do-not-send="true" class="moz-txt-link-rfc2396E"
href="mailto:vicenterc@comcast.net" target="_blank"><vicenterc@comcast.net></a> wrote:
</pre>
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<pre>Verne, Following AMA description: if we don't see the break is 5 points downgrade. That is 1/2 of the snap roll maneuver. Therefore, if we see the snap roll but don't see the break the judge has the right to write down 5 points score assuming that all other components are perfect. Therefore, base on the rule book the snap roll without a break has a value of 5 points. Vicente "Vince" Bortone ----- Original Message ----- From: verne @ twmi . rr .com To: "General pattern discussion" < nsrca -discussion@lists. nsrca .org> Cc: "Don Ramsey" <don. ramsey @ suddenlink .net> Sent: Tuesday, October 13, 2009 2:14:02 PM GMT -06:00 US/Canada Central Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC) Is there anybody involved in this discussion that honestly can't recognize a snap when they see one? I'm just asking..... Verne ---- Don Ramsey <don. ramsey @ suddenlink .net> wrote:
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<pre>Vince, What about the next sentence in the FAI definition, “If the stall/break does not occur and the model aircraft barrel rolls around, the manoeuvre must be severely downgraded (more than 5 points).” How about if the break does not show and the model does NOT barrel roll around. Do you still downgrade by 5 or more points? I don’t know what the intent of the rule was but I can tell you for a fact that the judges that only score FAI in Europe do not downgrade it by 5 or more points. I believe they use the “If it’s not a barrel and not an axial roll then it’s probably a snap, so judge it that way” because they have been instructed in the past to do it that way. Don rom: nsrca -discussion-bounces@lists. nsrca .org [mailto: nsrca -discussion-bounces@lists. nsrca .org] On Behalf Of Vicente "Vince" Bortone Sent: Tuesday, October 13, 2009 12:10 PM To: General pattern discussion Subject: Re: [NSRCA-discussion] How I became an expe
rt Snap Judge (TIC) Matt, I am copying the snap description from the current FAI and AMA manuals. I don't see the AND you mention in the FAI rule book. See the important portion in bold. I see that the AMA description is better in this respect. You are correct in regard the downgrade in FAI . 5 or more points if you don't see the break and the model barrel rolls. Therefore, what is the downgrade in FAI if the judge does not see the break and there is autorotation? I will say 5 points since it says 5 or more points if the model barrel rolls. Again, it appears that AMA down grad descriptions are better. FAI : 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 competitor’s 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. AMA: Snaps: A Snap roll is a simultaneous, rapid autorotation in the pitch, yaw and roll axes of flight in a stalled wing attitude. The following criteria apply: 1. Since the maneuver is defined as a stalled maneuver, initiat
ed by a stall of the wing induced by a rapid change in pitch attitude, the nose of the fuselage must show a definite break in pitch attitude from the flight path in the direction of the snap (positive or negative) while the track closely maintains the flight path. The lack of a discernable pitch break is downgraded by 5 points. Large deviations from the flight path, indicative of a delayed stall, are to be downgraded using the 1 point per 15-degree rule for each axis of the excursion before stall. For example, it the model pitches 15 degrees nose up and the wings rotate 15 degrees before the stall, the maneuver should be downgraded 1 point for pitch and 1 point for roll. 2. The track visualized as the path of the Center of Gravity (CG) should closely follow the geometric flight path of the maneuver while the nose and tail auto rotate through opposite helical arcs around the flight path. Lack of these helical arcs (or coning) is indicative of an axial roll and is scored zero.
3. If a stall does not occur and the model barrel rolls, the score is zero. A barrel roll can be identified when the CG, the nose, and tails scribe the same helical path through the required rotation of the maneuver 4. 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 centering on lines. 5. If the model returns to an unstalled condition during the maneuver, such that the autorotation is not visible and the model rolls or barrel rolls to complete the maneuver, it would be downgraded using the 1 point per 15 degree rule. 6. Airspeed is not a criteria which should be used to judge this maneuver. The wing of the model is stalled during this maneuver; therefore a significant decrease in speed may occur and is not a cause for downgrade. Vicente "Vince" Bortone ----- Original Message ----- From: "Matthew Frederick" <a
moz-do-not-send="true" class="moz-txt-link-rfc2396E"
href="mailto:mjfrederick@cox.net" target="_blank"><mjfrederick@cox.net></a>
To: "General pattern discussion" < nsrca -discussion@lists. nsrca .org> Sent: Tuesday, October 13, 2009 9:47:30 AM GMT -06:00 US/Canada Central Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC) ? While speaking with Don Ramsey about the nuances of judging snaps at a recent contest I found that he agreed with my interpretation of the FAI snap rule. The severe downgrade should only be applied if there is no break AND there is no autorotation (this is exactly what the rule says). Basically, lack of a break is not substantial grounds for the severe downgrade in FAI . If the break is not seen and autorotation still occurs at some point during the roll the one point per 15 degree rule applies. Since the snaps happen so fast, for me it's usually not more than 1 or 2 points unless it was blatantly obvious that the plane rotated a while before the snap truly began. It's the same as if you stop the snap before completing the rotation and do an axial roll to
finish. This nonsense of people being so quick to apply a severe downgrade has gone too far. One element of a maneuver (because I can't think of any sequence that has just a snap roll) should not ruin a whole flight, or eve n that one maneuver unless it just wasn't a snap. I like the idea of "if it's not a barrell roll and not an axial roll, it's probably a snap." Matt ----- Original Message ----- From: Vicente <a
moz-do-not-send="true" class="moz-txt-link-rfc2396E"
href="mailto:vicenterc@comcast.net" target="_blank"><mailto:vicenterc@comcast.net></a> "Vince" Bortone To: General pattern discussion <mailto: nsrca -discussion@lists. nsrca .org> Sent: Monday, October 12, 2009 5:12 PM Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC) I believe that the current downgrade is severe. AMA 5 points. FAI 5 or more points if my memory is correct. In local contest I have been using 3 points downgrade. I know that is wrong but it has been my best way for me to take into account the break issue. It used to be zero and it was changed to 5 points (IMAC still a 10 points downgrade or nada). Therefore, Ron is correct. Probably makes sense to go 2-3 points downgrade if the judge can not see the break before rotation. Vicente "Vince" Bortone ----- Original Message ----- From: "John Fuqua" <a
moz-do-not-send="true" class="moz-txt-link-rfc2396E"
href="mailto:johnfuqua@embarqmail.com" target="_blank"><johnfuqua@embarqmail.com></a>
To: "General pattern discussion" < nsrca -discussion@lists. nsrca .org> Sent: Monday, October 12, 2009 1:51:00 PM GMT -06:00 US/Canada Central Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC) Ron makes valid observation which I came to many years ago at the TOC when Mr. Bill graciously funded for full scale pilots like Patty Wagstaff do demo flights to entertain us. The one thing that I came away with in comparing full scale to our airplanes is the speed of the snap/rotation. In the full size aerobatics types that I observed there was plenty of time to see the nose pitch and then after somewhat of a hesitation yaw and rotate. In our pattern planes, especially when using a snap switch, it all gets to be a blur due to sheer speed. I have no solution to this issue but to MAKE the pilots show a break by having severe downgrades. Otherwise the concept of a snap will be ignored. Yes it's hard to see which makes it incumbent on the pilot to
present it to the judges. -----Original Message----- From: nsrca -discussion-bounces@lists. nsrca .org [mailto: nsrca -discussion-bounces@lists. nsrca .org] On Behalf Of
<a moz-do-not-send="true" class="moz-txt-link-abbreviated"
href="mailto:ronlock@comcast.net" target="_blank">ronlock@comcast.net</a>
Sent: Monday, October 12, 2009 1:26 PM To: General pattern discussion Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC) Here is a description that shows technically correct snap execution, and valid, consistent judging is possible. (Half of the District One guy need not read this, they have already heard it) <G> At a small airport airshow, one of demos was an in-trail formation of four full scale AT-6 Texans. As each plane got to stage center, it did a single positive snap roll. Spectators saw four snap rolls in a row, about 5 seconds apart. The flight of four went around, and repeated the maneuver. Some spectators are getting bored - even a pattern guy could get bored with a string of 8 nearly identical maneuvers. And then, they did it yet again!! What's in this for us? The snap maneuver by each AT-6 appeared to take a second or so, from initiation to completion. By the time the fourth plane did a snap, you could start s
eeing.... - there is a nose pitch up, - then a yaw, - then plane rolled in direction of yaw, - plane returned to straight and level flight. By the time the flight came around for another four snaps, you could see more details.. - there is a nose pitch up, (somewhat sudden, at least sudden for an AT-6) - then a large amount of yaw, - then rapid roll in direction of yaw, (rolling faster than it could with ailerons) - plane returned to fairly close straight and level, nose slightly high. By the time the flight positioned for yet another four snaps, (Yawn, spectators headed for cotton candy) the four distinct elements of the snap roll maneuver were easy to see, and there was time to evaluate (judge) each element. 1. there is a nose pitch up, (somewhat sudden, at least sudden for an AT-6, with little rise in altitude) 2. then large amount of yaw, (the yaw proceeds the upcoming roll) 3. then autorotation at rate faster than it could do an ail
eron roll) 4. plane returns to level flight track, with nose lowering to level flight attitude. We can all be expert Snap Roll Judges! Ahhh, at least for AT-6 snaps. What I take from all of this- The problem is not snap descriptions. It's the application of them; observation, discrimination and judging of elements in the split second observation time we have. Is the task beyond reasonable expectations of most of us as a judging community? I suppose we will continue work started over 10 years ago to improve in these areas. In the meantime, shall we reduce the impact of inconsistent judging of snaps by limiting the downgrade of the snap portion of a maneuver to say..two points2? Ron Lockhart _______________________________________________ NSRCA-discussion mailing list NSRCA-discussion@lists. nsrca .org
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