Displacement during snap rolls (was Why is it so quiet?)
George Kennie
geobet at gis.net
Wed Dec 29 14:20:58 AKST 2004
I have to confess that I'm having some problems here. There is
nothing "smooth or graceful" about a snap executed in the manner
required to satisfy the powers that be who have expressed their
judging standards on this forum. I would submit that if you were to
perform a snap that met their criteria for "smooth and graceful",
you would probably earn a reward of zero ( claiming it didn't snap).
A snap is, by nature, a violent maneuver and the lines approaching
and exiting same are just lines and may be considered precise, but I
would have difficulty classifying a line as graceful, after all it's
only a line. Smooth,..........maybe.
As far as the C.G. staying on track,......that's what the AMA video
portrays, but it's a physical impossibility. Just by virtue of the
pitch break the C.G. will be wrenched from the flight path and when
the rudder kicks in the lateral displacement will be added. By
skillful manipulation the pitch line can be restored, but the
lateral displacement is a much tougher correction to master even
when utilizing leading opposite rudder.
Remember that you can't increase the AOA without also increasing
lift, which will in turn break the flight path vertically.The same
is true when the rudder enters the equation and you can't correct
for it's lateral displacement by inputting opposite rudder without
screwing up your heading.
Like somebody said, it's a subjective thing and we're never going to
get everyone on the same page on this one.
IMHO, if there's a pitch break and the nose and tail cones are
visible "IT'S A SNAP" and you can pretty much disregard the lateral
displacement (unless somebody wants to make the effort to get it
inserted in the book).
I do seem to remember that there were a couple of guys in the finals
at the Nats that were able to get that center up-line snap to come
back to the vertical track consistantly so I would have to guess
that there is something significantly aerodynamically different
going on when the wing is unloaded............Hmmmmm.
Georgie
Dean Pappas wrote:
> Jerry,I have no problem with a dead slow snap, as long as all
> the elements are there.An outside snap at the top of an inside
> loop may be very slow, if the plane is decellerated to near the
> level flight stall speed, at the top.If you do a snap at just
> above landing speed, how fast is the rotation? Relatively slow,
> I'll bet.Not zeroed, but downgraded. 1 point per 15 for the extra
> yaw, and a downgrade for loss of smoothness/gracefulness.The snap
> itself may be violent, but the approach and departure should be
> graceful.Regards, 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 Jerry
> Voth
> Sent: Wednesday, December 29, 2004 4:21 PM
> To: discussion at nsrca.org
> Subject: Re: Displacement during snap rolls (was Why is
> it so quiet?)
> How would you judge a snap that meets all the criteria
> that has been mentioned in this thread that constitutes
> a good snap but takes almost a full second to
> complete? I also was at the T.O.C. when the guy that won
> used opposite rudder just prior to his vertical snaps-as
> I recall it was a very quick move. Wouldn't they be
> zeroed using the current thinking because the initial
> break was sideways before the up break? kJerry
>
> ----- Original Message -----
> From: Dean Pappas
> To: discussion at nsrca.org
> Sent: Wednesday, December 29, 2004 3:10 PM
> Subject: RE: Displacement during snap rolls
> (was Why is it so quiet?)
> After re-reading the post, it occurred to me
> I should clarify:I was writing about what I
> thought a good standard might be.For right
> now, the book is it, and as Bob pointed out,
> there is no specific track downgrade.Anyone
> have an IAC judges' guide handy? I'm
> curious.By the way, the full scale guys do
> horrible things to snaps, including completely
> unstalling the plane (particularly during
> consecutive snaps).That don't make it
> right!Archie has a good point, not only does
> the standard need to be better nailed down,
> but some people may never be trained to "see
> fast". Add in some "tired from 4 hours in the
> chair" and you have mush.This is a good
> discussion! 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 Dean Pappas
> Sent: Wednesday, December 29, 2004
> 1:15 PM
> To: discussion at nsrca.org
> Subject: RE: Displacement during
> snap rolls (was Why is it so quiet?)
> 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
>
>
>
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