Snaps/Spins

[Bill Glaze]

Gentlemen:
I can assure you that your discussions find more than a few very
interested ears.
Thanks.
Bill Glaze
Capt. United Airlines, (ret'd.)

Ron Van Putte wrote:

> For a non- aeronautical engineer, Earl has a great explanation about
> what happens during a snap roll.  I tried to find fault and couldn't.
> Nice job Earl.
>
> Ron Van Putte
> aeronautical engineer
>
>
> EHaury at aol.com wrote:
>
>> Ron
>>
>> Very good points. The rotational rate changes during snap initiation
>> and stopping should not be downgraded. My point is that major track
>> changes during initiation should be downgraded, as well as returning
>> to an unstalled condition and rolling to finish. The latter is not a
>> zero, but a severe downgrade!
>>
>> You're the AE, take a look at my view of the snap. First the wing
>> must be quickly (to maintain track) loaded to stall or very near
>> stall. The mechanism is pitch input in the positive or negative
>> direction. The pitch angle needed will vary with the stall
>> characteristics of the wing, the existing load (level, 45, vertical)
>> and speed. Fast pitch change is definitely better!
>>
>> Just as the wing reaches stall a yaw input In the desired direction
>> of rotation retracts one wing and advances the other. The retracting
>> wing now has less relative airspeed and stalls (or stalls more
>> deeply) than the advancing (higher airspeed) wing and rotation
>> occurs as though a wing fell off. Again fast rudder input is good.
>>
>> The accelerations and decels of the rotation of snaps done this way
>> will be very dependent upon the roll axis inertial characteristics
>> of the aircraft. The lighter the wings the better, with heavy wings
>> making the snap unmanageable.
>>
>> Enter ailerons. The ailerons contribute in a couple of ways. The
>> upward traveling aileron on the retracting wing, that we wish to
>> stall more deeply, helps the stall while the downward traveling
>> aileron on the other lowers stall speed of this wing somewhat like a
>> flap. Therefore less pitch and yaw to stall / rotate. The big
>> benefit is that the aileron application helps overcome the roll
>> inertia involved at the start and stop, making both more
>> controllable. (Yes, the full scale folks use ailerons in snaps to
>> help manage inertia also.)
>>
>> Back to the elevator. The amount of pitch needed to initiate a snap
>> is more than required to maintain it (likewise yaw). If maintained
>> at high angles throughout the snap the aircraft will retain some
>> pitch and yaw upon snap exit. (General term is "buried snap.") If
>> the pitch and yaw inputs are reduced after snap initiation to levels
>> just sufficient to maintain the snap, the snap will be tighter and
>> exits cleaner. Unfortunately, some who have the skills to achieve
>> this level of control are mistakenly accused of performing an axial
>> roll.
>>
>> Another spin control that can be used to advantage is the throttle,
>> remember that the faster the wing is moving the more pitch angle is
>> needed to effect stall and the more likely the track will change
>> before stall occurs. While idle will get the quickest stall, the
>> drag created during the snap will render the airplane a dead duck on
>> exit. Some middle ground exists for each airplane design, be it
>> faster entry or powering up during the snap to offset drag.
>>
>> I agree that the snap is probably more difficult to judge than
>> execute. However, it seems that it's here to stay (and it's a fun
>> maneuver). I started this discussion to stimulate thought and
>> encourage folks to think about appropriate judging of the maneuver.
>> "Sticks in the corner" doesn't necessarily result in a good snap and
>> the very skilled folks, who have developed techniques to make the
>> snap a joy to watch, haven't all figured out a way get something
>> that isn't a snap judged as such.
>>
>> Earl
>
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