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Posted for "terrence o'neill" <troneill@charter.net>:
John,
Talking about the situation of finding one's self in a spin IFR, with
only partial panel, --
Doesn't the DG's ball always indicate slip/yaw away from the direction of
rotation?
So, step on the ball, we were taught, and it works, stopping the turn.
Then reduce the AOA... (down elevator).
The DG's needle indicates direction of turn, for levelling out after the
wing's unstalled.
The Navy "Aerodynamics For Naval Aviators' (p. 291,2,3 and 309-312)text
simply observes that the rudder is the primary control for spin rcovery. ..
for most conventikonal aircraft. Also gives illustrations, and other data for
less conventional ones)
Of course, since spin AOAs run from about 20 -25 degrees for normal, to
about 4or more degrees for flat spins, the effectiveness of the rudder
depends on things like a swept-back hingeline (so that the airfl.ow goes up
the hingeline and rudder insead of perpendicular to it, and has little effect.
And that's compounded by the location of the horizontal tail.. whether
it traps airflow and forces it to flow over the rudder even if swept... or
most unfavorably, the h-tail may be located so that it stalls (a little after
the wing stalls) and then the h-tail wake blankets the rudder, rendering it
useless to stop rotation. .. and also cutting it's 'unstall power' in half.
The Lancair (235/320/360 h-tail feeds trapped and useful airflow to about
25% rudder , but it looks like its stalled wake probably would blanket part of
the top of the rudder.
Then there's the contribution of the fuselage to the pitching moment at
high AOAs. I don't know of any pitching moment measurements of the
configuration, but it looks like the engine cowling at high AOAs would tend to
keep the nose up and tend ot hold the wing at high AOA, while the small aft
fuselage wouldn't help reduce the high AOA. (If so, aft strakes woujld be one
remedy). It would be nice and useful to see some wind-tunnel pitching moment
measurements like NASA did on the VariEZ and the Dragonfly, and the Piper
canard., for AOAs from zero to 90 deg.
Talking about what airspeeds the L235 etc. Lancair stalls at might be a
little misleading, sinve the pilot's stick forces for pitch are pretty small,
and a little exuberance might easily produce a surprise 2G stall, or a
secondary stall on a pullout, if the pilot had no AOA to assure him that he
was n ot pulling his wing up past its stall AOA again.
Just some related comments on the post, that might be food for thought..
Terrence
L235/320 N211AL
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