Posted by tl3
Posted on 1/14/2018
What Is and What Isn’t…
I hope everyone out there in Scale Aerobatics land, had spectacular holidays! Believe it or not, we are already in 2018, and as the calendar flipped, the ball dropped, and the fireworks ushered in the Year of the Dog (though not technically until 2/16), we roll into a new IRPS Series and a World Championships year. For all the CDs and scorekeepers out there, there are some updates and changes to the Score software, so watch for training sessions coming to a screen near you and make sure you have the most recent version of Score. Hopefully people are also looking at and planning to attend one or more of the upcoming judging schools during the “offseason.”
The last issue of RR covered rolls integrated into loops. Now, it’s time we delve a little deeper into some of those particular rolls and have a candid snap chat (ha, see what I did there? ;-) Snap rolls generate more, eh, discussion than probably most other maneuvers combined; much of it needlessly so. Admittedly, they can at times be challenging to judge, but from a criterion based standpoint, snap rolls are no more complex than any other figure. Since any rules or judging discussion should be based on the rule in question, please refer to SCA 55 of your Scale Aerobatics rulebook for the specific snap roll standards.
Before we jump in to the specific criteria, let’s mosey through the aerodynamic workings of the critters. Snap rolls, or Flick rolls as they also known, are complex stalled or partially stalled rolls in which the aircraft departs straight flight in all three axes: pitch, yaw, and roll. This happens very quickly, especially with lightly wing-loaded model aircraft. The sequence in which these events occur is important and must begin with either a pitch, or a simultaneous pitch and yaw, input. The pitch input rapidly changes the wing’s angle of attack, which when coupled with yaw creates a lift imbalance between the left and right wings. In full scale aircraft, these two inputs alone are often enough to create a full or partial stall. The pitch input causes the wing to exceed its critical angle-of-attack (the point where the wing begins to stall, or lose lift), while the yaw input causes the receding wing to lose lift while the advancing wing retains it, resulting in autorotation (where one wing flies around the other wing). In other words the aircraft rolls around a point somewhere close to the cg while the nose and tail are displaced in both the pitch and yaw axes. Due to a few major dissimilarities, model aircraft snaps are performed a little differently and present differently than their full-scale counter parts. Model aircraft have a very low wing-loading factor compared to full-scale aerobatic aircraft. What does this mean? Well, if we look by square inch at how much lift is required of the wing to enable the plane to fly, our model’s wings are doing much less lifting work than their full-scale brethren. This results in a much larger speed and angle-of-attack envelope in which the model’s wing will fly before it stalls. There are also significant mass and inertia differences between models and full-scale. A 1000lb full-scale plane travelling at 180 mph wants to continue moving in the established line of flight (inertia), which means it’s easier to induce a stalled or partially stalled condition because the aircraft is more resistant to establishing a new flight path with rapid control inputs. By comparison, a 40lb model travelling at 90 mph has much less inertia, and with its lightly loaded wing is more likely to continue flying and establish a new flight path, even with rapid control inputs. Given these factors, it is common practice for model aircraft snaps to include a fair amount of aileron input to assist in generating the required rotation component. Interestingly, though, a close examination of many of the top full-scale competitors reveals a very similar snap methodology there as well. One of the reasons is that the raised aileron on the inside wing (the one towards the direction of rotation) helps to stall, or maintain the stalled condition of that wing.
Now that we’ve covered a bit of the snap roll’s aerodynamic minutia, let’s jump feet first into a few of the judging challenges that tend to arise on the flight-line by addressing some of the most common questions heard regarding snap judging.
- What is, and what is not a snap? Well, that’s simpler than it seems at times. Snaps are a pass or fail, yay or nay, it did or it didn’t proposition, there is no gradient. As a judge, you either see the requirements or you don’t. If you see them, then you continue judging the figure by the remainder of the criteria. If you don’t see them, the figure earns a zero, and you move on. A snap that has pitch departure (in the correct direction) and autorotation passes that litmus test and should continue to be graded. A snap that is missing either or both of those criteria, well, is not a snap.
- What is “pitch departure” and how much do I need to see for the snap to be scored? Pitch departure is the rapid change in the aircraft’s pitch attitude (nose pitches towards the canopy or away from it) initiated by elevator input. There is no gradient for pitch departure, you see it or you don’t. So the quick answer is: If you can see it, it’s enough. If you don’t see any pitch departure, it’s a zero!
- What does autorotation mean? For our purposes, autorotation simply means the aircraft has departed straight line flight - horizontal, vertical, 45 degree, or loop radius - in all three axes. In other words, as a judge you must see a pitch departure, a yaw departure, and a simultaneous roll. It is also acceptable for the pitch to occur first, and then the yaw and roll are introduced, but the aircraft must not establish a new flight path with the initial pitch input.
- How many types of snaps are there? There are only two types of snaps: positive or negative. Any other designation or descriptor is simply a way of defining something a judge saw, usually in place of an actual snap. You can call it whatever you like if it helps you understand what may or may not have happened in the air, but the judging criteria consists only of positive and negative snaps.
- How long do pilots have to reestablish their line after the snap is complete? The track, or flight path, must be corrected immediately upon completion of the snap. Often times a snap will result in the aircraft having a slight pitch or yaw (or both) heading correction that needs to be made in order for the proper flight path to be re-assumed. There is no deduction for these corrections. However, if they are not made quickly enough and the aircraft establish a new flight path that is not parallel to that which it should be on, there must be a deduction for the flight path error.
- A lot of pilots snap very fast, at what point does a snap get zeroed simply because it rotates too quickly? Many pilots do snap very fast, be that as it may, speed of rotation is not a judging criterion. Just as line length is not a criterion in hammerheads, or diameter is not a loop criterion, the rate at which a snap rotates is not a determining factor in whether or not the figure should or should not be scored. The judge must focus on the actual criteria: was there pitch departure, and was there autorotation? Remember, it is not possible to test the presence, or lack of, these criteria in replay or video review, as a judge you only operate with what was presented in real time, in the sky.
- What if it looks like a snap, but I’m not really sure if it actually snapped? As a judge you have two tools at your disposal: The criteria in the rulebook, and your eyes. If what you saw looked like a snap and met the criteria established in the rulebook, you have to score it. You must give the pilot the benefit of the doubt.
- What is a shoulder snap, or shoulder roll? This is what happens as a result of a pilot inputting wrong rudder with a snap. For example, a positive snap to the right, but the pilot mistakenly inputs left rudder. These “snaps” are actually closer to a tumble and must receive a zero if you’re certain that is what you saw.
- How is a snap different than a “barrel roll”? Snaps and barrel rolls can at times appear similar, but there is a distinct and fundamental difference. A barrel roll consists of the aircraft flying a cylindrical flight path. In other words, both wings fully retain lift and transcribe something that resembles a barrel, whereas in a snap one wing is at least partially stalled, and the lifting wing flies “around” the stalled wing.
Snaps, due to many aspects, can be challenging to judge accurately. Among other factors, pilot technique, proficiency, aircraft attitude, and aircraft type all play key roles in how snaps present. From a judging perspective, all of those elements are irrelevant. The judge’s responsibility is to issue a score based solely on the defined criteria and whether or not the aircraft fulfilled said criteria. Much like flying them, the best way to become proficient at judging them is to get on the line and practice. And if you’re uncertain of the specific criteria for judging snaps, or any other maneuver for that matter, well, luckily we’re in the midst of school season. With that said, thank you for taking the time to exercise our craft, and hopefully we can all recognize the value in devoting them same type of energy to our judging skills as we do our flying skills. I also want to extend a big thanks to Earle Andrews, 1988 IAC Championships Unlimited Champion and current IMAC advanced protagonist, for his contributions to this article.
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Upcoming Judging Schools by Region
North East: TBD
South East: Florida Judging School #1 - 1/27/2018, Bradenton, FL
Clover Creek Judging School - 3/10/2018, Toone, TN
North Carolina Are Judging School - 3/24/2018, Welcome, NC
North Central: 2018 North Central Judging School - 4/21/2018, Muncie, IN
South Central: TBD
North West: Northwest Judging School - 3/3/2018 - Richland, WA
South West: Colorado Judging School - 5/19/2018 - Northglenn, CO
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