Approaching Deep Stall

On Sep 6, 3:16 am, 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.

The conditions that DEFINE Deep Stall cause a loss
of lift at tail as well, though the tail is not necessarily
stalled in the same sense as the main wing.


As far as I understand it, all certificated aircraft must be able to
recover from a basic stall.

My 2c


Deep Stall is not a basic stall. See the description
above, or the previously referenced webpage.

--

FF

On Sep 6, 12:58 pm, Airbus wrote:
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.

http://www.airliners.net/open.file/1255880/M/

Looks like A T-tail, not a cruciform tail like the Zodiac-701.

But assuming that Deep Stall is the same for a 'high' cruciform
tail as for a T-tail, how about addressing the second part,
how the aircraft gets into that condition in the first place,
and would it be avoided if stall were delayed until after the
horizonatl stabilizer passed through the wake of the main wing
during increasing AOA?

--

FF

On Sep 5, 6:39 pm, "El Maximo" wrote:
"Fred the Red Shirt" wrote in ooglegroups.com...

For a while I have been wondering why there seem to be no
airplanes with a low wing and a high tail.

Like This?

http://www.kesnat.com/DSC06717.JPG


Perhaps your point is that if the designer wants to put the
horizontal stabilizer higher than the main wind, a T-tail is
more aerodynamically efficient than using a cruciform tail
which would put the rubber REALLY high.

--

FF

On Sep 5, 6:42 pm, Dave Doe wrote:
In article .com,
says...





For a while I have been wondering why there seem to be no
airplanes with a low wing and a high tail. Say for instance
with a fuselage and epenage like the Zodiac 701, but with
a low wing instead of the high wing. Then I read about deep
stall, as illustrated he

http://www.answers.com/topic/deep-stall-png

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.

My question regards the orientation that immediately
precedes the deep stall. If the angle of attack at stall
is exactly the same as the angle that puts the stabilizer
in the shadow of the wing, that will precipitate a deep
stall, right?

What if the wing stalls at a lower AOA? Would the
stabilizer then drop into the wake?

ISTM that if the AOA that stalls the wing is higher than
the AOA that puts the stabilizer in the wake of the wing
then that aircraft is immune to this sort of deep stall,
so long as it is flying within the CG limits, right?

Only Robert's mentioned the Traumahawk - which surely remains one of the
most popular/common training aircraft today.

I did all my ab-initio training in a Tomahawk, it's a great plane to
learn stalls and spins in, with it's sharp wing drop characteristics.

I've provided primary training in the Tomahawk and never found any
disturbing charactersitics. Stalls were nice and straight ahead thanks
to an AD that mandated stall strips be added. Sadly I could never spin
it because the owner wouldn't allow it but I have a friend who owns
one and he spins it all the time. However, we're both a bit "gurthy"
so I can't ride along while he does the spins.

-Robert, CFII

Recently, Roger (K8RI) posted:

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

Thanks, Roger. After looking it over, I think I was doing everything right
except hitting the MPO switch.

Neil

Recently, Nomen Nescio posted:

-----BEGIN PGP SIGNED MESSAGE-----

From: "Neil Gould"

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.

Engage the Manual Pitch Override by pressing the "O" button. Then
increase
the amplitude of the pitch oscillations by rocking the nose with the
joystick. Two or three oscillations will get the nose down enough to
get you flying, again.

Thanks, Nomen. After Roger's suggestion to read up on it in the manual, I
"discovered" the MPO switch. Coming from Falcon 3, I apparently didn't
read the Falcon 4 manual as thoroughly as I should.

BTW, the first snowfall in New England
signals the beginning of "F 4.0 dogfight season" in our house. If
you'd be interested in a little online combat, let me know. And if
you've got a friend with Falcon 4.0 and would like some 2 on 2
action, my wife can also be a rather formidable adversary (and the
best damned "wingman" I could ever ask for).

I would be interested in trying some online combat, and would need some
guidance to connect up via the internet. Perhaps that's in the manual, too
(although I don't see it in the index)? ;-)

Neil

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 Thu, 06 Sep 2007 20:49:08 -0400, john smith wrote:

That's the result of poor initial flight training.

Roger (K8RI) wrote:
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.

Yup and only 3 out of 60 pilots had done full stalls in a Bo, only two
had done accelerated stalls, and one still continued to practice them.
Only about 6 had current charts. According to the instructor I drew,
most of them were also flying final about 10 to 20 knots too fast and
of those most would be near the higher speed.

When I was first checked out in the Deb (which has tip tanks) on the
first stall it tried to roll. After that the instructor, who also
happened to fly a Deb would no longer do full stalls. So after he
signed me off to make the insurance company happy, I went out to the
practice area and spent over an hour doing nothing but stalls. (with a
little unusual attitude recover thrown in early ong)


Roger (K8RI)

In article ,
says...

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.


Deep stall got further attention with the crash of the H-S Trident near
Heathrow. This is a "high" T-tail, precursor of the Boeing 727.

From Danny Deger:
The space shuttle could not be certified by the FAA. It pitches up when
stalled. Due to span wise flow, the outboard portions of the wings stall
first. Because it is a delta wing the outboard wings are also aft, so the
center of lift moves forward.

The dreaded Pitch Divergence!


~ CT