Approaching Deep Stall

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?

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

On Thu, 06 Sep 2007 12:31:39 -0400, Dudley Henriques
wrote:

snip

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.

Which reminds me... I've let many pilots fly the Deb. A few years back
one of the locals was interested in getting a Deb or F-33 and wanted
to see how they flew. He and his wife had been flying a Cherokee 140
or 160. I think he really liked the control harmony and response as
well as the take off and landing performance, but he was used to a
very docile airplane that would let him used the ailerons in a stall.
Do that in the Deb and it'll roll over and bite you and I do mean
roll. Which ever wing you try to raise will drop *abruptly*. You can
learn to feel the stall coming in through the yoke and the stall
warning horn and light give ample warning, but there is very little
buffet with a rather abrupt break and a *strong* tendency to roll left
if you don't stop it "with the rudder". You can put it into a stall
and bring the yoke all the way back while keeping the nose pointed up
with the rudder "with practice", but it's much like balancing on a
tight rope.

I demonstrated departure, approach, and accelerated stalls and the
ease of recovery keeping everything in the proper attitude, but after
just two tries he decided he was going to stick with something like
the Cherokee and maybe upgrade to a 180 or Archer. Stall recovery is
not difficult to learn, but it is different. He didn't like the idea
of carrying power down final either. One other thing is you can't fly
it using the VSI which is poor form in any plane, but the Deb and
F-33s are so quick, using the VSI for anything other than a trend
instrument "which is its intended purpose" will put the pilot into a
PIO of 2Gs out of the bottom and zero over the top. That's typical of
both Piper and Cessna pilots the first time they fly it. There are
exceptions though.

As you say, each plane has its characteristics and they aren't
necessarily those of what we fly as trainers. These characteristics
are not unique to the Deb although it does have some of its own. With
only a few exceptions it's characteristics are common to most high
performance retracts. If flown properly it is an outstanding short
field airplane. Surprisingly although it shouldn't be, not many pilots
land the Deb and F-33s according to the POH. "Flying by the numbers"
puts them in a flight realm they learned to avoid as students and
could avoid in most of the planes they have flown. Unfortunately that
means landing these planes much faster than necessary. The Deb and
F-33 have about twice the glide ratio of a 172, but it's in the
neighborhood of 120 MPH.

I've mentioned it before, but at the Bo specific training, you should
have heard the complaining and exclamations when they told the group
the instructors would be blocking the yoke so they wouldn't be able to
use the ailerons when doing stalls.

roger (K8RI)

On Sep 6, 9:31 am, Dudley Henriques wrote:

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.

I don't think I agree with your statement but I will say that any
pilot transitioning from the C-172 to the F-16 should ensure they get
a complete checkout.

-Robert, CFII

Robert M. Gary wrote:
On Sep 6, 9:31 am, Dudley Henriques wrote:

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.

I don't think I agree with your statement but I will say that any
pilot transitioning from the C-172 to the F-16 should ensure they get
a complete checkout.

-Robert, CFII

It's helpful if instead of simply saying you disagree with something
that you go on to state exactly WHY you disagree with it. In that way
you maximize any educational value your post might have for a new pilot.

I seriously doubt that we have to worry about anyone transitioning from
a 172 to the Viper. The F16 deep stall scenario was simply used to
emphasize the fact that deep stall is not restricted to T tails which
should have been obvious.


--
Dudley Henriques