7/25/2019 Snap Rolls.doc

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ACRO II FLYERS REPORT:

Snap Rolling The Acro-Sport IIBy Don Baker

I finally got back to learning the snap roll in my Acro II.The good news is you can snap the ACRO with no

changes to the wings or airframe. the bad news is that ittakes some work to perfect it. After unsuccessfulattempts last fall, I talked with various aerobatic pilotsand read much material pertaining to snap rolls. Out ofall this came a common line of reasoning: too deep astall will kill the snap roll. That is exactly what theproblem turned out to be. ou cannot pull full upelevator, then kick rudder and get theA!"O II to snaproll. Instead, you will be left hanging upside down byyour belts after only half a snap is complete wonderinghow anyone can screw up such a simple maneuver.

The theory is relatively simple. #art of the problem isthat the A!"O has enough tail surface area to createan excessive angle of attack when high speed stalled

with full stick. The rest of the problem, I believe, is dueto the straight wing on the A!"O II. A snap roll is anautorotation maneuver. It is essentially a high speedspin. It is necessary to get one wing stalled and theother one still lifting to produce the desiredautorotation. $hen an airplane is yawed, one wing willadvance and one will recede long as the yaw persists.In a swept %aft& wing airplane. 'oth wing halves % rightleft& intersect the same amount of air during straightflight. 'ut during yaw, the advancing wing willcut throughthe air relative wind more s(uare to the leading edgethan the receding wing. )ince the yaw inducedadvancing wing is exposed to more air, its wing loadingdecreases whereas the receding wing sees less airand its loading increases. It this airplane is near stalland then yawed with rudder, the receding wing is

assured of stalling long before the advancing wing.This is a nice setup for a snap roll. *ot only does theswept wing have the desired geometry for snap rollentry, but is also more or less insures that one sidewill remain stalled and the other unstalled throughoutthe maneuver provided yaw is maintained with rudder.

A good line of demarcation %stalled vs. unstalled& isinherently provided at the sweep back +unction of thewing. Too much elevator and I am sure that you couldalso mess up a snap roll in a swept wing airplane,however, it should be (uite tolerant of elevatormisapplication because of the sweep back effect.

or a straight winged airplane %A!"O II& the situationis different. $hen yawed, both halves of the wing see

the same relative wind so both halves intersect thesame amount of air, remain e(ually loaded, and tendto stall at the same time. Thus an inherent stall line ofdemarcation between halves of the wing does notexist as in the swept wing design. It is up to the pilot toput it and hold it where it belongs during themaneuver. This re(uires the pilot to feel the airplanethroughout the snap roll and ad+ust the controls on thefly %pun intended&.

After well over - snap rolls %of varying (uality&, Ithink that I have found how to do them in the A!"O/)#O"T II. The airplane stalls far too deeply to allowfull elevator for snaps. )nap rolls to the left are to beavoided because as we all know, left yawing causespropeller gyroscopic forces in the nose0up direction

which will increase angle of attack, deepen the stalland worsen the problem. The line of demarcation%stalled vs. unstalled& can be affected by either rudderor elevator so control of both is important. *either canbe fully applied or kicked. 'oth must be applied (uicklyand steadily until rotation starts, and then moved asnecessary to complete the snap roll.

1ere is what works for me. irst ac(uire entry speed ofslightly below. I use 23 mph indicated for an entry speedwhich is about 43to - mph actual. I still have not foundthe source of error in my airspeed system. 'ut that sanother story *ext advance the throttle to well abovecruise power, full power is O5. $hen the speed reachesentry speed, begin pulling elevator first followed almostimmediately with right rudder. 6ove both togetherbutkeep the elevator slightly ahead the rudder. 7o not +erkeither elevator or rudder or you will lose the feel. Atabout 8 to 9 degrees nose up attitude, the lift willbreak and the snap roll begins. 7o not advance therudder beyond this point, otherwise the snap will mush

out, hold the rudder position. Also, do not pull theelevator further or the stall will worsen and the snap willmush out. Instead, play; the elevator %forward& andyou will feel the roll rate increase dramatically. The trickis to maximi