Split Topic: Snap Roll vs "autorotation"

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Ryan Smith
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Re: NTSB Final Report: Bruce and Kathy Rymes accident

Post by Ryan Smith »

Aryana wrote:George, most of my friends just left KHAF for the IAC38 competition in Coalinga this weekend and the topic of a snap roll vs horizontal spin came up for discussion before they left. They were adamant that a proper snap roll is not a horizontal spin, but instead an induced autorotation of the airplane, which if done correctly is identifiable by the fact that the airplane autorotates faster than the regular roll rate of the aircraft during an aileron roll.

Can you shed some light on what they might have been trying to differentiate between an autorotation and a horizontal spin? Some of these guys are long time aerobatic guys flying unlimited class Edge 540s and Yak 55s, but weren't able to articulate why a horizontal autorotation ("snap roll") was not considered a horizontal spin or how they were different. I have a hunch that the perfect scoring aerobatic snap roll may be different than the elementary definition that may be applicable to the rest of us that aren't trying to score points. Have you heard of anything like this before?

I hope this is ok for me to ask here in this thread as I just hope to learn something and appreciate the ability to tap into the years of flying talent and knowledge from the folks in the group. Feel free to move it if you think that's appropriate.
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GAHorn
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Re: Split Topic: Snap Roll vs "autorotation"

Post by GAHorn »

Aryana wrote:George, ...

Can you shed some light on what they might have been trying to differentiate between an autorotation and a horizontal spin? ....
In a nutshell... No.

If they ...(who are using these terms to describe their own maneuvers)... cannot differentiate what they mean... I certainly can not, especially not being in that conversation... but I'll make a "stab" at it (pardon the pun.) :wink:

The term "horizontal spin" has been used for decades to describe snap rolls because that term seems to "fit" the aeronautical reasons for duplicating the maneuver. If competition aerobatic pilots have some other vocabulary to describe some fine-tweaking or minor difference of how they believe their maneuver is different from that historical description... then to be honest, that's new to me.

I am not a competition/aerobatic pilot. I am not even "current" in the hobby. I studied under Gene Soucy and his instructors when he ran a school north of Dallas in the early '80s, earning both his Basic and Advanced Aerobatics certificates,... and his method of teaching snap-rolls was to use the nomenclature of "horizontal spin".
I do not know if he has since changed that description, but that's the way his school taught it.

Yes, the airplane will roll faster in a snap roll than it will in an aileron roll, and it does so for the simple reason that one wing is stalled (or nearly so) while the other is not. If you spin your 150 or 170 or... whatever... it will also rotate faster than it will by ailerons alone....maybe not for the first rotation (because if you performed the maneuver correctly you were at/near stalling speed)...but the subsequent ones certainly will as the speed builds toward the speed at which snap rolls are performed in airplanes approved for them. In order for a common spin to occur, the airplane wing must experience a stall, with either one wing subsequently re-acquiring a flight AOA, or by only one wing being stalled due to the application of yaw.
If the stall does not occur then the airplane does not spin...it spirals.

If the airplane does not rotate while attempting to perform the (snap roll) maneuver....then the pilot failed to produce the accelerated stall of one wing (usually by timid elevator/rudder application, insufficient entry-speed, or by premature application of rudder.) If the airplane does not snap... it spirals. (Perhaps that is what is meant by an "autorotation"?)

WARNING: NONE of the Standard/Utility category Cessnas are approved for snap-rolls. DO NOT ATTEMPT snap rolls in these Cessnas...not even below maneuvering speed (Va) as it very likely will result in airframe damage or failure.

(Personally, I do not spin my 60+ year old 170-B despite it's full-restoration 20+ years ago because I don't think that's "kind" to it and I want to preserve it for my grandkids and I want to live long enough to see them fly it the way bluEldr tells 'em.) If I wanted to fly aerobatics I'd go rent a proper airplane and parachute for the purpose.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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