wrote:
On Sep 6, 3:27 pm, Dudley Henriques wrote:
DR wrote:
Fred the Red Shirt wrote:
Here deep stall is defined as a condition in which the
main wing is stalled and the stabilizer is enveloped
in the turbulent wake of the stalled wing so that
the pilot has lost pitch control and thus cannot lower
the nose to recover. For certain airframe geometries,
(such as the illustration above) that condition can
occur even if the aircraft is within the proper CG limits.
Err, that's not how I see it,
The aircraft can/will still pitch down after stall for 2 reasons: First,
the center of wing lift moves aft once the wing is stalled which will
drop the nose. Second, the tail is pushing the nose up to increase angle
of attack so that once blanketed the nose drops.
As far as I understand it, all certificated aircraft must be able to
recover from a basic stall.
My 2c
Cheers
Not so for the F16. Deep stall is an issue for the Viper at specific
angles of attack and cg configurations, especially if the airplane is
out of fuel balance. The result of deep stall in the Viper is a flat
extremely fast ROD either with occiliation or without.
The ONLY way to break deep stall in the Viper is to INCREASE the aoa,
then quickly input forward stick to induce a high nose rate down through
the deep stall region into a recovery.
Make no mistake, if the aoa is not increased before this fast nose down
pitch rate, the Viper will stay in deep stall and can be completely
unrecoverable.
There is no "automatic" nose down pitch rate in deep stall in the F16.



The F16 elevator is in not a high configuration is it? So, how does it
get blanketed in the way the thread is discussing?


Deep stall isn't restricted to T tails. It just happens that T tails are
especially susceptible to deep stall.
Blanketing of the tail can occur in any aircraft if the design and
weight and balance scenario couples just right.
The reason you don't see deep stall in your vanilla GA airplane is
because regulations dictate specific design parameters that insure
specific stall behavior in these airplanes.

This discussion on deep stall brings up a point that I have been making
for years in the flight instruction community.
When you learn to fly, there is a natural tendency for flight
instructors to teach people to fly based on the aerodynamics involved
with the specific airplane in use for the training.
There is a whole world of aerodynamics that isn't covered when training
is accomplished in general aviation. Some students go through entire
careers as pilots not knowing how aerodynamics are affected as design
changes and airplanes fly at greater gross weights and airspeeds.

One poster correctly suggested that a pitch down moment was to be
expected in stall recovery behavior. This is correct for a Cessna or a
Piper light GA airplane manufactured in the normal or utility categories.
Just keep in mind that the design considerations for these airplanes
that handle the aerodynamics found at stall won't necessarily hold true
for the next airplane you fly.
As for the Viper; it will enter deep stall when aoa stabilizes at a high
positive or negative value outside the pitch limiter. In this stall
configuration, the Viper doesn't have full pitch authority on the
horizontal tails and won't reduce aoa enough to break the stall.
In the case of the Viper, fuel imbalance, external stores location, and
other factors that cause a rearward cg condition can cause deep stall.

The main point to make in this discussion is that the stall conditions
you learn for your Cessna 172 in training for your PPL apply to that
general category of airplane. Pilots are well advised to extend their
knowledge WELL beyond that accepted for the certificate and to delve
deeply into the new environment in which they have chosen to operate.
Learning about deep stall is a good start along that path.

--
Dudley Henriques