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?

Recently, Dudley Henriques posted:

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.

Thank you for this explanation! One of my favorite past-times is playing
Falcon 4.0 (F-16 sim), and there have been times when I've gotten into
deep stall and have not found a way to recover. Perhaps the game is not
sophisticated enough to execute the manouver as you've described, but at
least I understand better what's happening.

More on-topic, my basic training was in a Tomahawk, and can say that the
liklihood of deep stalls in that plane are rather slim unless there is
some significant weight in the baggage area.

Neil

On Wed, 5 Sep 2007 at 21:18:53 in message
, Airbus wrote:
In article . com,
says...


On Sep 5, 11:29 am, Fred the Red Shirt
wrote:
For a while I have been wondering why there seem to be no
airplanes with a low wing and a high tail.

Duchess and Seminole come to mind.


Not to mention the DC-9 and MDxx variants
or the KingAir200

The deep stall first got real attention in the crash of the BAC1-11
during test flying. The full official report is included in Brian
Trubshaw's book Test Pilot. The configuration of the BAC 1-11 and the
DC-9 were very similar. The 1-11 descended almost flat with little
forward velocity until it struck the ground during a stall test flight.
All the crew were killed.

For test flying after the crash a tail parachute was installed. Part of
the trouble was the use of servo-tab elevators which at High AoA became
almost useless.

Both aircraft went on to fly safely for many years.
--
David CL Francis

In article .com,
says...


On Sep 6, 4:18 am, Airbus wrote:
In article . com,
says...



On Sep 5, 11:29 am, Fred the Red Shirt
wrote:
For a while I have been wondering why there seem to be no
airplanes with a low wing and a high tail.

Duchess and Seminole come to mind.

Not to mention the DC-9 and MDxx variants
or the KingAir200

All of those have T-tails.

Are you guys not familiar with the Zodiac 701?

It does not have a T-tail.



Yet the BAC 111 (http://www.airliners.net/open.file/1255880/M/) was
famous for its deep-stall capability - or at least one high-profile
accident is attributed to this.

In article , says...



Yet the BAC 111 (http://www.airliners.net/open.file/1255880/M/) was
famous for its deep-stall capability - or at least one high-profile
accident is attributed to this.


And the caravelle (http://www.airliners.net/open.file/1258343/M/) to the
best of my knowledge was not particularly associated with this trait ..

Fred the Red Shirt wrote:
On Sep 6, 12:37 am, wrote:
On Wed, 05 Sep 2007 12:06:01 -0700, cjcampbell

wrote:
On Sep 5, 11:29 am, Fred the Red Shirt
wrote:
For a while I have been wondering why there seem to be no
airplanes with a low wing and a high tail.

Duchess and Seminole come to mind.

doesn't have to be a "high tail". ever heard of the Cheyenne II's
stability augmentation system? didn't really do a whole lot for
controllability, primarily made it feel like there was airflow over
the elevator when there wasn't much...

one has to be exploring the edges of the envelope, but other PA31's
are able to place the tail into "bad" air also.


This is the sort of Zodiac-like high tail I was thinking of:

http://www.icfn.net/bluesky/air1/N70...%20PIPER%20PA-
31T%20CHEYENNE%20II%20(OFEK).jpg

and this is not:

http://www.dc3d.co.nz/tutorials/OFP/...enne.lllSm.GIF

Both are what I's call a "high" tail in the sense that the horizontal
stabilizer flies at a higher altitude than does the main wing, and
hence both would seem to have the same vulnerability to
deep stall.

FF

If that is your definition of "high" tail you don't have to leave the Zenith
line to find a low wing that fits that description take a close look at the
601XL. Not as high as the 701 but the bottom of the horz. stabilizer is
higher than the top of the wing.

On Thu, 6 Sep 2007 06:18:24 -0500, "Neil Gould"
wrote:

Recently, Dudley Henriques posted:

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.

Thank you for this explanation! One of my favorite past-times is playing
Falcon 4.0 (F-16 sim), and there have been times when I've gotten into
deep stall and have not found a way to recover. Perhaps the game is not

The explanation as to what is happening and how to recover is in the
Falcon 4 manual.

Roger (K8RI)

sophisticated enough to execute the manouver as you've described, but at
least I understand better what's happening.

More on-topic, my basic training was in a Tomahawk, and can say that the
liklihood of deep stalls in that plane are rather slim unless there is
some significant weight in the baggage area.

Neil

In article , 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.


An additional definition of "deep stall" occurs in some twins (Twin
Comanche and Baron come to mind) is when the nacelles develop their own
positive pitching moment (up) at very high angles of attack. The result
is that the elevator has insufficient control authority to effect
recovery.

These planes have conventional mounting of the stabilizer.

The phenomenon in the F-16 described by another poster appears to be a
similar phenomenon, where the forward fuselage develops a high pitching
moment that the elevator cannot handle.

EridanMan wrote:
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.

Your Aeronautical point is valid, but for most of us flying spam cans,
wing loadings alone dictate that the Aerodynamic forces on the
aircraft will overpower the aircrafts momentum to eventually break
free of a deep stall, as long as the aircraft is designed such that
the cL always remains behind the cG.

My comment was in response to a general statement that deep stall
results in a nose down pitch moment. This is not always the case.
Notice as well that the Viper is NOT a T tail aircraft.

--
Dudley Henriques

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