[NSRCA-discussion] IMAC and snap roll rules

[mike mueller]

 This is long but clear to me. I'd like to see our snap discrption follow this one so we could clear up the unclear situation we have now. Here it is. Thanks, Mike Mueller
 

by Bruce Hanley, IMAC Rules Committee Chair ---  

WLW-PilotsJudgesCornerAerobaticTurns_E6D7-Bruce_thumbThe first issue you must decide when judging snaps is that he did or did not do the type of snap called for by the Aresti. Snaps can be positive (pitch to the canopy)   or negative (pitch to the wheels). If he does the wrong type, he gets a zero for the maneuver - the whole maneuver. If he gets this part right, you go on to judge the rest of the maneuver.

“Is it a snap” is the second decision you, as a judge, must wrestle with. This is a binary choice. There is no gray area. You must decide if he did or did not snap. If the answer is no, you zero the maneuver - the whole maneuver. If the answer is yes, then you proceed to judge the applicable downgrades for the snap and apply them to the maneuver.

So lets deal with “Is it a snap”. To be a snap there must be a stall and there must be autorotation. That is what the F&JG tells us. The stall is a high speed stall induced by the pilot with a rapid pitch movement that increases the angle of attack sufficiently to stall a wing. The lift on the wing that is still flying will force rapid rotation about the roll axis and also, combined with rudder deflection, will produce a yaw in the direction of the roll. So everything is moving here. A judge-able snap will have movement on all three axis - pitch, roll and yaw.

When must the pilot get these three motions all moving? Unlike the spin where the stall and wing drop are supposed to occur simultaneously, the snap may have the pitch (stall) and the autorotation begin simultaneously OR sequentially in that order (pitch then autorotation). No downgrade applies if he starts the pitch and autorotation together. No downgrade applies if he pitches and then immediately starts auto-rotating. If, however, he initiates the rotation first without a pitch you ding him .5 for each 5 degrees he rotates before he shows you the pitch. If he gets to 90 degrees without a pitch, you zero the maneuver. Note that many pilots intentionally and legitimately delay the start of autorotation momentarily to be sure to clearly show the pitch/stall before the start of autorotation in order to minimize the risk of getting a zero.

So, how do you, the judge, know that all this is happening as it should? Its hard since it all happens so quickly but you can clearly identify the pitch that starts it all. Without a pitch there will be no stall. No stall equals no snap and results in a zero. Just don’t ding the guy if the autorotation starts at the same time as the pitch/stall. At the point of the break (stall) into the snap you have a couple of indicators that you can use to make the “Is it a snap” decision. If he did snap:

    - There will be displacement of the plane’s pitch axis relative to the entry line, i.e., entering the snap the plane should not be on the same exact line as it was prior to the snap. If he stalled, he went either to the canopy or the wheels and he shouldn’t be on the identical line.

    - There will be yaw displacement. The rudder deflection and stall of the wing will yaw the plane in the direction of rotation. So on entering the snap the plane will be pointed at some angle (it may be small) to the line he was on before the snap.

Note that these are only indicators. They are not of themselves judging criteria.

But, to look at it another way, if he remains on exactly the same line during his snap he did an aileron roll. If he spirals around his entry line, he is doing a barrel roll. Neither case qualifies as a judge-able snap and each should be zeroed.

Before we talk about downgrades for judge-able snaps, lets consider what the pilot must do after the snap. What he must do is immediately get the plane back on the required flight path in the appropriate attitude. So, given the discussion above, since he has pitched and yawed from his original track, he will likely have to make a pitch and a yaw correction to resume the correct flight path. If the snap is being done on a line, the post snap line should be parallel to the pre-snap line but not identical to it since it will be displaced by some distance from the pre-snap line. This may be a very small distance. If the snap is being done on an arc, he may or may not need to realign in order to continue along the radius he is flying. The critical point is that you should not downgrade the guy for realignment movements done immediately after the snap. These movements may not be perceptible but if they are he is allowed to “straighten” the plane without
 downgrade. He must do this immedia
tely after completion of the snap. If the realignment is necessary and he delays it he will be showing you a misaligned line or arc that is inconsistent with the Aresti and you should downgrade that line or arc.

OK - he did a snap, it was the correct type of snap and you did not zero it. What are the downgrades that may apply. For the snap element itself, the only downgrade is under or over rotation. Once autorotation is initiated in the snap the pilot must maintain autorotation to exactly the stopping point called for by the Aresti. If he stops early, you downgrade .5 for every 5 degrees that he under rotated. Same if he over rotates. Note that it is common to see a pilot come out of autorotation early and aileron to the finish - and some pilots do it very skillfully. This gets a downgrade and is treated as the under rotation just covered, i.e., you ding him .5 for 5 for however much he is aileron-ing to the finish. The indicator that you look for to identify that this is happening is a change in the rate of rotation. Rotation rate is not in itself a judging criteria within snaps, but the rate of rotation within an autorotation will be pretty constant and any
 change will be gradual as the
plane loses energy in the snap. So, a perceptible and perhaps abrupt change of roll rate toward the end of the snap is a clue that the pilot is not auto-rotating to the finish but, rather, is completing his snap with ailerons. It can be a tough call.

Beyond the snap element itself you must, in judging a snap, be alert to the following:

- Line centering:  If the snap is done on a line, it must be centered on the line. If it is not the following downgrade applies based on the two line segments either side of the snap:

    - line segments vary but the difference is less that 2 to 1 - deduct 1 pt

    - line segments differ by 2 to 1 but less than 3 to 1 - deduct 2pt

    - line segments differ by 3 to 1 or more - deduct 3 pt max

    - omits one line segment - deduct 4 pt

    - omits both line segments - deduct 2 pt

- Exit of a part loop: If the snap is done when exiting a part loop such as at the exit of an Immelman it must be done exactly at the completion of the part loop. If not the following downgrades apply:

    - If done early before the completion of the part loop ding him .5 for each 5 degrees that he is early

    - If done late and he shows you a line after completion of the part loop and before the snap, it is a t least a two point deduction - more if the line is extended. The F&JG doesn’t help us with applying a deduction of more than two points. Also, at some point the line can get so long that the maneuver should be zero’d. Again the F&JG doesn’t help us here. It is up to you to set some personal standard for these cases. Just be consistent.

- Entry to a part loop: If the snap is done when entering a part loop such as at the beginning of an Split S, the arc of the part loop must begin immediately after completion of the snap.

    - If he shows you a line after the snap and before starting the arc, it is again the same “at least two points” deduction just discussed above. Again, you have to personally come up with a scheme for handling the “more if extended”.

    - If he is late and starts the arc (establishes a radius...) and then does the snap we again are left on our own. If he only impinges a little on the arc and does the snap I would ding him .5 for 5 for being late. If he is very noticeably late I would zero the maneuver. What is a “little” and what is “noticeably late” again requires that you set a personal standard that you can apply consistently.

- Arc centering: If the snap is done on an arc (loop or part loop) it must be centered on that arc. If it is not centered the following downgrade applies:

    - .5 for each 5 degrees that he misses the center

- Follow the arc:  If the snap is being done on an arc (loop or part loop) it must follow the radius of that arc during the time that it is being executed. The alternative is to flatten out the radius and do the snap on a line. In general, adding a line where you shouldn’t have one is a 2 pt deduction. So, if he does not follow the arc during the snap and instead does it on a line, or shows you well defined lines before and/or after the snap, the following downgrades apply:

    - 2 pt if he flattens out and does the snap on a line

    - 2 pt per line if he shows you a defined line (no radius) before the snap is initiated or after the snap is completed. What is the length that makes it a “defined line” is up to you.

Note that the snap may be done as part of a combination of optional elements. For example: a line that has a snap followed by an opposite half roll. If so, then the downgrades discussed above (centering, follow the arc, etc...) always apply to the total combination. The exception to this is the spin. The spin is an optional element which ends with a down line. Another optional element such as a snap after the spin may be required on that down line and if so there is no centering requirement imposed upon it.

So that is pretty much it. The difficulty in judging the snap lies with the speed of the maneuver and how quickly it all happens. You really have to be paying attention and anticipating the snap so you are concentrating on what the pilot actually shows you. As with all judging it is critical to know the sequence to avoid looking away from the plane - and, as always, the pilot gets the benefit of the doubt.


      
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