Displacement during snap rolls (was Why is it so quiet?)

[Dean Pappas]

Hi All,
before I crawl back to the lab ... and see what's on the slab ...
 
While I agree that some displacement is inevitable, I wouldn't want to see a rule that says that if you don't see any, then it's not a snap.
The very best high energy snaps will displace so little that it will be really hard to say that it's there.
 
1) My guess would be that most really good snaps probably displace about 1/2 wingspan, both up and to the side.
Gravity will possibly kill any evidence of the UP part. Try doing an inside snap from inverted, or try a snap from knife edge. You'll see the UP displacement! 
2) As the elevator throw is reduced, from that needed to do a good snap, the airplane displaces worse and worse, as it takes longer for the plane to stall deeply enough, to make little enough lift to continue changing the airplane's course appreciably.
3) If the elevator throw is further reduced, the displacement goes away! Hmm.
4) Leading the elevator reduces the necessary amount of throw, for a good snap. 
 
Here's the aesthetic question behind the argument:
Do we all agree that when you see a snap with an "in your face" break that it really is a thing of beauty?
Or do some of us think it's untidy, and not"on a line"? I had a judge ask me (back in '91) "What's with the twitch before the snap?"
 
I'm as confused as anybody. I guess that's as good a way to start the new year as any.
 

Dean Pappas 
Sr. Design Engineer 
Kodeos Communications 
111 Corporate Blvd. 
South Plainfield, N.J. 07080 
(908) 222-7817 phone 
(908) 222-2392 fax 
d.pappas at kodeos.com 

-----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On Behalf Of Rcmaster199 at aol.com
Sent: Wednesday, December 29, 2004 11:48 AM
To: discussion at nsrca.org
Subject: Re: Displacement during snap rolls (was Why is it so quiet?)



Thanks Chris, thats what I saw also. No real help there. 
 
Six months ago when we last had SNAP conversations on these pages, it was implied by one pilot who also flies Scale Aerobatic planes, that if sideways displacement does not occur in SA routines on the order of a wing span or two, (some SA models have 10 foot wing spans) it isn't a snap and is zeroed. I wished to see that commentary in print. I hope to see Fred Johnson in March in Ocala and I will try to get an answer.
 
In Pattern, about the only time we will see the plane displace one wing span or more, is when it is led with rudder. I saw a couple like these in the F3A Final last summer and zeroed these maneuvers. But the biggest factor that was the total lack of break in attitude  prior to the snap. (I agree with Dean and Dave, that's what I saw also) Judging from the number of zero scores pilots received on snapping maneuvers, Finals Judges in general saw things similarly. It is the pilot's responsibility to make the break obvious and eliminate the guesswork on the judge's part. If the pilot decides to displace first by first applying rudder, so be it. 
 
Personally, when the model enters the snap in accordance to the rules and then displaces (pitch or yaw or both), I will downgrade proportionately to the degree of displacement I see. One to four points for each type. To me, it isn't "1 pt per 15 deg" rule that applies in these cases, but the smoothness and gracefulness rule. (Its a judgement call, that's why we call it Judging, duh!!) 
 
Many Pattern models set-up properly, are capable of displacing very small amounts, almost nil really, in both pitch and yaw and still perform real Snap Rolls. Yet, I agree with Bob that a very small amount of displacement is unavoidable due to finite amount of time it takes to move the surfaces, and in that time span, the model is in transition, moving to a stalled condition. 
 
Happy New Year everybody
 
MattK
 

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