|
> Not in an actual spin,
where one wing is stalled, no. If the instrument is
> on the left
side of the panel the ball will deflect to the left in a spin,
> no
matter which direction you are spinning. If the instrument is on the
> right the ball will always deflect to the right.
>
> Tom
Gourley
Hmmm... Tom, what airplanes are
we talking about? C152s? If it had two needle-ball isntruments, one on the
left and one of the rightpanel, would they show the plane was yawing both ways
at once?. This is strange.
I was recalling experience from
unusual attitude recovery training in SNJs 50 years ago... the needle and ball
was in the middle of the panel.
Step on the ball -- was
the procedure to recover from any unusual attitude ... the instructor had you
under the 'bag' so you couldn't see outside, and then put the plane through some
crazy gyrations, and finally said 'You've got it." You might be upside down, or
going straight up, or whatever. A little game for fun. Anyway, you had to recover.
Then I'd just do the procedure, and it worked quickly, every time. Step on the
ball to stop the yaw and the turn, then apply or reduce power depending on if
the altimeter was going up or down, while applying elevator , up or down, to
stop altitude changing up or down.
But I don't know it any one of
those unusual attitudes was a spin. So my suggestion to 'step on the
ball' for spin recovery might be wrong. Sorry about that.
But your info that the ball is
useless or ambiguous for seeing yaw in a spin is puzzing. So I did some refresher reading about
spins.
Back when I was designing
experimentals i did a lot of reading about spins and characteristics of planes
that are good or bad for recovery. In 1960 NASA did TR R-57 "Status of
Spin Research"; and in 1977 NASA Tech Paper 1009 "Spin Tnnel Investigation
of Spinning Characteristics of Typical Single-Engine GenAv Airplane Designs -- I
- Low Wing Model A: Effect of Tail Configurations."
Langley's been spin-tunnel
testing since about 1940, and by now have certainly tested about 1000 dirrerent configurations with
good correlation between the mdels and the airpalnes.
An interesting addition to NASA
spin info I found was NASA TT GF-442, which is "Flight Testing of
Aircraft" by M.G. Kotik et al, USSR aeronautical engineers prepared for students
at their aviation colleges, a translation with ten pages of descriptions of both
normal and inverted spins, and of each of those, stable or unstable, and of the
three types of stable, and three types of unstable. Also given are the
four types of recovery. All four could be used for normal spins, and
three for inverted spins, and it noted which is appropriate for which type
of spin. The types were 1. Rudder, elevator and ailerons neutral; 2.
Rudder agaisnt, elev neutral after 2-4 seconds, and ail neutral. 3.
Rud against, and after 3-6 sec., elev against full down, ail neutral; 4. Same as
3., but simulatneously with rudder, the ailerons are deflected with the
spin. ... pretty much what we do.
The report describes the
normal spin as occuring at "medium to low altitudes, with extended
duration, at high angles of attack, at very high rates of magnitude of rate of
rotation with very slight oscillations."
It defines
(on p. 284) "The spin axis is the axis of the spiral-like trajectory of motion
of the aircraft's center of gravity in the spin, and the spin radius is the
radius of the spiral along which the aircraft's center of gravity moves in
the steady state spin regime." That is, the aircraft does not spin around it's
own CG, but it and its CG whips around outward on a radius from the spin
axis. So there's a radial accelleration there ... which will move a
slip-ball, depending on how the slip instrument is aligned. The ball has
to show an accelleration ... that's what it does. I don't see how it could
show opposite accellerations depending on which side of the panel it's on, U
NLESS the spin axis of the plane you're describing is right through the middle
of the plane... but then how could the plane spin?... with one wing going
backwards?
Then the ball wouldn't
deflect at all if it was in the middle of the panel, or would show accelleration
left or right if you moved the ball to the left or right of the axis.
But how can any plane spin
about it's own CG? Is one of your wings going backward?
One wing has to be stalled, and
the other unstalled to provide energy for autorotation.
I guess what's really
important for spin recovery IFC is seeing the direction of rotation ... and
that should be the DG's needle.
Would that be right? If
you're turning right, then step on the opposite rudder?
Maybe this rumination will
help us understand what's going on.
Terrence O'Neill
|