[NSRCA-discussion] 747 Snap Entry?

Tue Jul 1 14:42:41 AKDT 2008

During initial training I was told stories about pilots that would extend
the flaps to 2 degrees at altitude to increase fuel efficiency, but to do
that you have to pull a couple circuit breakers to disable the leading edge
devices (LED's) which are limited by Boeing from being extended above 20,000
feet.  When you do this stunt, you are risking air pressure getting up under
the spoilers and causing them to float - thus negating what you're trying to
accomplish.  Also, the elevator trim is controlled by the autopilot at
altitude . . . if you try to trim the nose up the autopilot will kick itself
off.  I could see where an unbriefed pilot resetting the LED circuit
breakers at altitude could cause really hideous problems. . . but I highly
doubt the Split-S (with 2 of 4??) maneuver . . . more likely a 7.5 on their
Straight Flight Out followed by a Zero'd flight due to the LED's departing
the aircraft.

Besides, the flaps and trim have no effect on the CG of the airplane. . . it
is a function of how the plane is loaded and the current fuel load - which
by the way moves the CG forward during flight unless your S/O does something
really, really wrong on the fuel panel.   My company is currently trying to
load the airplanes with an aft CG for fuel efficiency.

Now, back to the original subject. . . will a swept wing commercial
transport aircraft perform a proper snap roll? . . . . My vote is "only
once". . .

On Tue, Jul 1, 2008 at 6:03 PM, Gerald Gallagher <ggall at bellsouth.net>
wrote:

> I was a pilot with TWA & knew the captain that is accused of this, also a
> TWA Pilot. To this day he denies this ever happened & so do the 2 other
> crew
> members that were flying that 727. The loss of altitude was, according to
> the three crewmembers aboard was clear air turbulence. I believe the pilot,
> but I am prejudice.
>
> Jerry Gallagher
>
>
>
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of
> rcmaster199 at aol.com
> Sent: Tuesday, July 01, 2008 5:47 PM
> To: nsrca-discussion at lists.nsrca.org
> Subject: Re: [NSRCA-discussion] 747 Snap Entry?
>
>
> A few of us were discussing just such an occurence recently which
> apparently happened by accident and darned near crashed the plane. Dean
> remembered the details which went something like this:
>
> The pilot of the 727 about 20 years ago had the plane trimmed as far
> aft as possible and had inputed a bit of flap to use fuel most
> efficiently. The co-pilot, soon after returning from a visit to the
> loo, saw the trimmed flap and flipped the switch to return the flap to
> neutral. This action immediately made the plane too tail heavy which
> made the plane do a pretty violent half snap to inverted. The pilot
> lost close to 25k feet pulling the plane out of the dive, which he did
> successfully but not before deploying the gear to slow the crate down.
> That had to be some kind of experience
>
> Legend has it that the pilot then went straight to loo himself to
> change his britches (G)
>
> Matt
>
> -----Original Message-----
> From: Koenig, Tom <Tom.Koenig at actewagl.com.au>
> To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
> Sent: Mon, 30 Jun 2008 10:25 pm
> Subject: Re: [NSRCA-discussion] 747 Snap Entry?
>
>  Hey John,
>
> Out of interest.....has anyone ever attempted a snap in an airliner???
>
> I have heard of a captain doing a slow roll in a 747....but a snap? Is it
> possible?? What does a simulator do when pushed to such limits ( I know a
> simulator cant snap BTW...well, I assume any way LOL!!)
>
> Tom
>
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of John Gayer
> Sent: Tuesday, 1 July 2008 11:42 AM
> To: General pattern discussion
> Subject: Re: [NSRCA-discussion] Snap Entry
>
> Actually a snap can occur without any aileron input...but I challenge
> anyone
> to show a pattern ship doing a snap roll on a 45 degree downline without
> ailerons.
>
> The approach snap can occur with only the use of elevator and it involves
> one wing panel stalling before the other. Try an approach with crossed
> controls(aileron/rudder with some power. pull the nose up gradually and see
> which wing drops. It will be the wing with the aileron trailing edge down.
> This is contrary to what we see in a pattern snap roll which always snaps
> in
> the direction of the aileron deflection thus indicating the lack of any
> stalled condition
>
> John
>
> seefo at san.rr.com wrote:
>
> >Just to stir the pot a little further..
> >
> >I'm not sure a contemporary pattern plane can generate enough pitch
> rate to reach critical angle of attack and properly perform a snap roll. I
> think it's far more likely that we're seeing nothing but a heavily yawed
> aileron roll, with the pitch break only being shown to judges to convince
> them there is actually a stall happening, when in fact there is not.
> >
> >If a snap cannot occur using ONLY elevator and rudder, then the wing is
> not stalling. Aileron inputs into a snap actually inhibit flow separation,
> as the inboard wing angle of attack is drastically reduced, and the
> outboard
> wing AoA is drastically increased.
> >
> >But since there is no way to actually determine what is happening
> aerodynamically on an F3A airplane, the best a pilot can do is fly the
> airplane to what the judges expect to see based upon the rules. It really
> doesn't matter what the control inputs are if the airplane LOOKS like it's
> doing the right maneuver.
> >_______________________________________________
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> >
> >
> >
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-- 

Keith Hoard
Collierville, TN
khoard at gmail.com
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