<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Arial; font-size: 12pt; color: #000000'>Ive not lost interest here, but will be off line till Monday, heading to<br>Keystone Indoor Electric Fly near Willamsport PA,<br><br>Later Ron Lockhart<br>----- Original Message -----<br>From: "Vicente \"Vince\" Bortone" <vicenterc@comcast.net><br>To: "General pattern discussion" <nsrca-discussion@lists.nsrca.org><br>Sent: Thursday, October 15, 2009 3:27:10 PM (GMT-0500) Auto-Detected<br>Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)<br><br><style>p { margin: 0; }</style><div style="font-family: Arial; font-size: 12pt; color: rgb(0, 0, 0);"><div style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Arial;">
<p>Yes, you deleted many post without reading. I erased most but kept one because I need more time to read it and digest it. This is by Jerry Budd. </p>
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<p>Here is a copy. Happy reading:</p>
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<p class="MsoNormal" style="margin: 0in 0in 0pt;"><span style="color: black; font-family: 'Arial','sans-serif';">>Angle of attack, alpha or AOA, for the<br>> aircraft is the difference<br>> between the flight path angle, gamma, and the aircraft<br>> attitude, theta<br>> (assuming the airfoil zero lift angle is essentially<br>> aligned with the aircraft<br>> reference datum, which for all practical purposes on our<br>> designs, it is).<br>> Reference: </span><span id="OBJ_PREFIX_DWT544"><span class="object2"><span style="font-family: 'Arial','sans-serif';"><a href="http://www.aerospaceweb.org/question/aerodynamics/q0165.shtml" target="_blank">http://www.aerospaceweb.org/question/aerodynamics/q0165.shtml</a></span></span></span><span style="color: black; font-family: 'Arial','sans-serif';">.<br>> Flight path angle is the aircraft trajectory, or in<br>> pattern speak,<br>> "track" but along the pitch axis, i.e. climbing<br>> or descending.<br>> In level, steady state flight (~1-g), the flight path<br>> angle is zero.<br>> Which means that the angle of attack is equal to the<br>> aircraft pitch<br>> attitude. If you run the numbers using a reasonable<br>> airfoil lift curve<br>> slope at a representative level flight speed for our planes<br>> you'll find that<br>> our planes trim out around ~ 0.5 degrees alpha (Lift =<br>> Weight = CL * Qbar * S<br>> where CL is the lift coefficient, Qbar is the dynamic<br>> pressure, and S is the<br>> reference wing area). This is because of our<br>> extremely low wing loading,<br>> it simply doesn't take a lot of angle of attack to<br>> generate 1-g of lift when<br>> your airplane only weighs 10 or 11 lbs. Here's<br>> the other part: with the<br>> exception of velocity (or airspeed), the equation is<br>> linear, which means that<br>> if you double the aircraft weight, for the same flight<br>> speed, you get twice the</span></p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"><span style="color: black; font-family: 'Arial','sans-serif';">alpha (again, for 1-g trim). Or if you kept the<br>> weight at say 10 lbs, but<br>> cut the wing area in half, the angle of attack would then<br>> double to ~ 1 degree<br>> (again, for level, steady, 1-g flight). Velocity is a<br>> little trickier to<br>> account for because it's a non-linear second order<br>> function in the lift<br>> equation (remember Qbar? Reference: </span><span id="OBJ_PREFIX_DWT545"><span class="object2"><span style="font-family: 'Arial','sans-serif';"><a href="http://en.wikipedia.org/wiki/Dynamic_pressure" target="_blank"><font color="#00008b">http://en.wikipedia.org/wiki/Dynamic_pressure</font></a></span></span></span><span style="color: black; font-family: 'Arial','sans-serif';">,<br>> Qbar = 1/2 * rho * V**2) where rho is air density and V is<br>> the velocity).<br>> Essentially, the lift doubles every time we increase<br>> Qbar by 2, or<br>> velocity by the square root of 2 (or 1.414). So if<br>> you're flying along in<br>> level flight at 60 mph (88 feet per second), and you speed<br>> up to 85 mph mph<br>> (124.45 feet per second), you've doubled your dynamic<br>> pressure (Qbar) and to<br>> stay at level 1-g flight, you'd have to retrim your<br>> plane in pitch to 1/2 of<br>> what your AOA was before (or you'll start climbing).<br>> In this case the AOA<br>> would be ~ 0.25 degrees (as would the pitch attitude).<br>> One last bit of<br>> info for the point I'm about to make is that the lift<br>> curve slope for our<br>> airfoils at the Reynolds Numbers we are operating at is<br>> linear out to around<br>> ~15-16 degrees alpha, with separation of lift occurring<br>> above that, closer to<br>> 18-20 degrees alpha (Reference: </span><span id="OBJ_PREFIX_DWT546"><span class="object2"><span style="font-family: 'Arial','sans-serif';"><a href="http://www.aerospaceweb.org/question/aerodynamics/q0136.shtml" target="_blank"><font color="#00008b">http://www.aerospaceweb.org/question/aerodynamics/q0136.shtml</font></a></span></span></span><span style="color: black; font-family: 'Arial','sans-serif';">).<br>> Note that the onset of separation is independent of<br>> airspeed, it's purely<br>> a flow angle phenomenon, i.e. you can stall an airfoil at<br>> any airspeed, or</span></p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"><span style="color: black; font-family: 'Arial','sans-serif';">attitude (if you can get to a high enough angle of<br>> attack). That's<br>> essentially what Chris is saying below. <br>>So what does this all mean? <br>> <br>> If you look at the numbers, for our<br>> planes, you can't get to<br>> stall from steady level flight (at any reasonable cruise<br>> speed) without<br>> inducing a significant G-loading on the aircraft (which<br>> will cause a<br>> noticeable, and very observable, change in the flight path<br>> angle), BEFORE the<br>> airfoil stalls. <br>> > Here's some more numbers to help<br>> you connect the dots:<br>> from level 1-g trim flight at 1/2 degree AOA,</span></p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"><span style="color: black; font-family: 'Arial','sans-serif';">for our models), you<br>> have to generate nearly 5-6 g's to reach stall (think<br>> you'd notice that?).<br>> Don't believe me? OK answer this: Have you<br>> ever quickly but<br>> smoothly from level upright 1-g flight at a normal cruise<br>> speed input full aft<br>> stick for a second or two and then release it but no<br>> lateral input? What<br>> happens? Unless something is grossly wrong with your<br>> airplane you're<br>> likely to see a rapid pitch up and a corresponding change<br>> in flight path angle,<br>> probably to something approaching a near vertical attitude,<br>> but not much else.<br>> Why? Our planes are so lightly loaded that only<br>> at spin entry and<br>> landing speeds can we induce enough angle of attack to<br>> approach stall on the<br>> airfoil on the plane without inducing significant g's<br>> and grossly altering the<br>> flight path angle (and flight path angle is what we really<br>> see when we're<br>> flying at cruise speeds BTW, not so much the pitch attitude<br>> until we're at much<br>> lower speeds. That's because we mentally<br>> integrate the velocity vector in<br>> our minds but that's a topic for another time/day).<br>> Full scale aerobatic<br>> planes (and to a lessor degree IMAC planes) don't<br>> suffer this problem nearly so<br>> badly since their wing loadings and inertia's are much<br>> higher (dynamic stability</span></p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"><span style="color: black; font-family: 'Arial','sans-serif';">is somewhat more complex than static stability so I'm<br>> not going to go much<br>> further than this on this topic). The bottom line is<br>> this: we're<br>> not stalling the wing when we do our snaps, not even a<br>> portion of it (unless<br>> you're VERY low on airspeed at entry such as a spin).<br>> We're too lightly<br>> loaded to get to stall at any reasonable airspeed, the<br>> airplane will respond<br>> too quickly in the pitch axis resulting in a rapid change<br>> in flight path<br>> angle, effectively unloading the AOA during the<br>> response. <br>> So what are we doing to make the plane<br>> present what appears<br>> to be a snap roll when we can't actually be stalling<br>> the wing asymmetrically to<br>> induce autorotation like many claim? Lots of control<br>> power in pitch and<br>> roll coupled with additional rolling moment induced by<br>> dihedral effect<br>> (sideslip driven by rudder input). Pretty much<br>> everyone knows that at<br>> higher AOA you can command/control roll with rudder, well</span></p>
<p class="MsoNormal" style="margin: 0in 0in 0pt;"><span style="color: black; font-family: 'Arial','sans-serif';">that's due to<br>> dihedral effect (roll with rudder), it gets more powerful<br>> with a little AOA.<br>> That's where you get the part of the dynamic that<br>> visually emulates a<br>> full scale snap roll but physically is quite different (you<br>> can make it look<br>> like a full-scale snap, but it really isn't). <br>> <br>> So the bigger question is should<br>> emulating a full-scale snap<br>> roll be a pattern judging criterion or do we even care? (we<br>> know what the<br>> answer is for full scale aerobatics and probably IMAC too<br>> but we are neither of<br>> these). Until we decide the answer to THAT question,<br>> we're really just<br>> debating "how many angels can dance on the head of a<br>> pin"... <br>></span></p>
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<p><br><br>Vicente "Vince" Bortone<br><br>----- Original Message -----<br>From: "J Shu" <jshulman@cfl.rr.com><br>To: "General pattern discussion" <nsrca-discussion@lists.nsrca.org><br>Sent: Thursday, October 15, 2009 1:46:52 PM GMT -06:00 US/Canada Central<br>Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)<br><br>
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<div><font color="#000080" face="Arial">But they left NO doubt about pitch break... isn't that what everyone needs to see, or did I delete too many posts without reading them?</font></div>
<div><br>Regards,<br>Jason<br><a href="http://www.shulmanaviation.com/" target="_blank">www.shulmanaviation.com</a><br><a href="http://www.composite-arf.com/" target="_blank">www.composite-arf.com</a><br></div>
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<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;">----- Original Message ----- </div>
<div style="background: rgb(228, 228, 228) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>From:</b> <a title="vicenterc@comcast.net" href="mailto:vicenterc@comcast.net" target="_blank">Vicente "Vince" Bortone</a> </div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>To:</b> <a title="nsrca-discussion@lists.nsrca.org" href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank">General pattern discussion</a> </div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>Sent:</b> Thursday, October 15, 2009 2:42 PM</div>
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<div style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Arial;">and SEBANDREW SNAP for the not normal one.<br><br>Vicente "Vince" Bortone<br><br>----- Original Message -----<br>From: "Vicente \"Vince\" Bortone" <<a href="mailto:vicenterc@comcast.net" target="_blank">vicenterc@comcast.net</a>><br>To: "General pattern discussion" <<a href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank">nsrca-discussion@lists.nsrca.org</a>><br>Sent: Thursday, October 15, 2009 1:40:03 PM GMT -06:00 US/Canada Central<br>Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)<br><br>
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<div style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Arial;">Let's called NORMAL SNAP. <br><br>Vicente "Vince" Bortone<br><br>----- Original Message -----<br>From: "J Shu" <jshulman@cfl.rr.com><br>To: "General pattern discussion" <nsrca-discussion@lists.nsrca.org><br>Sent: Thursday, October 15, 2009 11:45:13 AM GMT -06:00 US/Canada Central<br>Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)<br><br>
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<div><font color="#000080" face="Arial">I don't remember anyone saying they received a 0 at the Worlds. Andrew and Seba had the 'IMAC' pitch break, most of the the rest of us had the 'normal' snap.</font></div>
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<div><font color="#000080" face="Arial">One thing I found funny was some of the other pilots that would 'show pitch break' would actually do mostly a roll afterwards. I guess if you 'show pitch break' the plane 'must be stalled' right...lol.</font></div>
<div><br>Regards,<br>Jason<br><a href="http://www.shulmanaviation.com/" target="_blank">www.shulmanaviation.com</a><br><a href="http://www.composite-arf.com/" target="_blank">www.composite-arf.com</a><br></div>
<blockquote style="border-left: 2px solid rgb(0, 0, 128); padding-right: 0px; padding-left: 5px; margin-left: 5px; margin-right: 0px;">
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;">----- Original Message ----- </div>
<div style="background: rgb(228, 228, 228) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>From:</b> <a title="vicenterc@comcast.net" href="mailto:vicenterc@comcast.net" target="_blank">Vicente "Vince" Bortone</a> </div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>To:</b> <a title="nsrca-discussion@lists.nsrca.org" href="mailto:nsrca-discussion@lists.nsrca.org" target="_blank">General pattern discussion</a> </div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>Sent:</b> Thursday, October 15, 2009 12:35 PM</div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal; -x-system-font: none;"><b>Subject:</b> Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)</div>
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<p>Jason,</p>
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<p>It will be interesting to know at the WC in Portugal. I never got one in local contests this year. I don't think at local contest we are zeroing even when there is not a clear snap. At the Nats I zeroed some years ago. I never got a complain. I have been downgrading 3 points for not presenting the break in pitch trying to use the current snap description. <br><br>Vicente "Vince" Bortone<br><br>----- Original Message -----<br>From: "J Shu" <jshulman@cfl.rr.com><br>To: "General pattern discussion" <nsrca-discussion@lists.nsrca.org><br>Sent: Thursday, October 15, 2009 11:17:46 AM GMT -06:00 US/Canada Central<br>Subject: Re: [NSRCA-discussion] How I became an expert Snap Judge (TIC)<br><br>
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<div><font color="#000080" face="Arial">Just curious... how many are getting zero'd for doing snaps?</font></div>
<div><br>Regards,<br>Jason<br><a href="http://www.shulmanaviation.com/" target="_blank">www.shulmanaviation.com</a><br><a href="http://www.composite-arf.com/" target="_blank">www.composite-arf.com</a></div><br>_______________________________________________ NSRCA-discussion mailing list NSRCA-discussion@lists.nsrca.org http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</div></div>
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