Snap rolls (long) - the ins and outs...

[Keith Black]

This is a great thread on the anatomy of a snap! 

What I'd like to hear are techniques for executing good positive and negative snaps. I'm interested in things like what's the best direction to snap (left?), what are the necessary stick movements for positive and negative snaps, timing of stick movements, what should be done differently on down-line vs. horizontal vs. up-line snap, etc. 

I've heard that the top fliers don't just jam the sticks at the same time but they break the snap into multiple components to keep it true and on heading. This is a complete mystery to me and I'd love to understand it more.

Also, of great interest to me is how much throw is necessary for good snaps and how to fly smoothly with that much throw. Obviously each plane will vary but I'm looking for some basic guidelines on throws, maybe with specific planes just as a idea. And how do the top level fliers deal with having enough throw to execute snaps AND keep their other maneuvers from being jerky? Dual rates, huge expo, snap switch, or just REALLY steady fingers? 

This weekend at the Nederland, TX contest FAI flew F03 in the sixth round. All of us mortals sat around in amazement watching snap after snap in every conceivable attitude and direction. And Earl you're correct, these snaps looked nothing like a lot of snaps in the other classes. They were extremely crisp, quick and solid. 

So please, someone share your secrets so we can improve on those mediocre snaps that everyone keeps referring to! :-)

Thanks,
Keith Black

  ----- Original Message ----- 
  From: EHaury at aol.com 
  To: discussion at nsrca.org 
  Sent: Monday, June 23, 2003 10:03 AM
  Subject: Snap rolls (long)


  With the Nats fast approaching I thought it might be useful to review / discuss the snap roll and its proper judging. My observation is that there is a lack of quality demonstrated by many snaps. There seems to be some tendency for folks that fly the maneuver poorly to judge it leniently, or worse yet, judge well executed snaps harshly because they look unfamiliar. No other maneuver is executed so quickly, making it even more demanding to judge.

  Please refer to page 78 of the rulebook under "Snaps." Consider Item 1 carefully. 
  "the nose should show a definite break" and "while the track closely maintains the flight path" are key criteria for judging the entrance to the snap. A rapid pitch attitude change, simultaneously or closely followed by a yaw attitude change will create a stalled wing in the direction of the snap and rapid autorotation rotation generated by the opposite wing. The track will "closely" follow that established before the snap.

  I ask that you consider the often seen snap entrance. The aircraft pitches, yaws, and rolls quite a bit off track before the stall occurs. The aircraft then stalls and maintains that track, finishing with considerable offset from the initial track. In my opinion, the rules require the change in track during the snap iniation to be downgraded. Typically the changes are 15 to 30 degrees in the vertical and horizontal plane, so 1 or 2 points for each plane. At the same time, due to concurrent application of aileron, some 15 to 30 degrees of roll occurs before the stall. Another point or 2 off for lack of proper snap rotational angle at the entrance. At the same time, please realize that there will be some small change of track as enough attitude change occurs to initiate stall. This is recognized in the rules i.e. "track closely follows." Certainly this is another one of the approximation words that shouldn't be in rules. I believe, however, that "closely" better defines 5 degrees or so of track change and certainly does not allow 15 to 30.

  Observe also that some pilots will change the track horizontally (yaw) opposite the snap to accommodate the poor entry and facilitate exit on the desired track. This change of entry track should also be downgraded at 1 point / 15 degrees.

  Item 2 describes a barrel roll (zero). If the events described in the discussion of Item 1 occur without an eventual stall, the maneuver is a barrel roll. It may be fairly tight and still be a barrel. This is tough to call, I've video taped a number of snaps that appeared fine but were clearly barrels when viewed in slo-mo. The trick in judging this is to look for the CG to stay on the original track, as stated in the rules. In my opinion, so many snaps are barrels that this look may be becoming the standard, with true snaps on track are being judged as axial rolls.

  Item 3 deals with wing position at start and stop and seems well understood.

  Item 4 mentions that snaps may be either positive or negative. Look for the proper horizontal break direction.

  Item 5 "If model returns to an unstalled condition" "such that autorotation is not visible" "model rolls to complete" indicates that rolling to finish a snap must be severely downgraded. I suggest that 1 point / 15 degrees is appropriate, as most of these rolled finishes will be 45 to 90 degrees which results in a 3 to 6 point downgrade. As per Item 1 there should also be a severe downgrade for unstalling early. 

  Item 6 discusses airspeed as not being a criteria.

  OK, recognize that there is a lot going on in a snap in very short period of time. Look for all the elements to be there, clean break, with the nose and tail autorotating in an attitude different from the track, and a unstalling and rotation stop at the proper point. Please be aware that there are many details to be considered beyond "it is or isn't" and "the wings finish in proper plane." Also recognize that well performed clean snaps may look a bit different depending on technique and aircraft. 

  These interpretations are my own and outside of any official capacity. I welcome discussion, addition, and disagreement.

  Good flying

  Earl 
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