Thinking about stalls

On Fri, 14 Mar 2008 16:58:35 +0000 (UTC), Bertie the Bunyip
wrote:

wrote in
:

On Mar 14, 11:37*am, Bertie the Bunyip wrote:
TakeFlight wrote in
news:935d6394-8224-482e-9428-
:

Put me in the "not enough info" column.

Plane #2 could be in fact _in_ a stall (or spin), "descending fast
with 50% power" or _more_. *Think Delta Flight 191, for example.

That was something else entirely. That was a microburst. The rules
pretty much go out the window with one of those.
not to say the laws of physics are suspended, but it's a scenario
that is so different from what we learn as pilots that drastic
retraining was * introduced right across the board after it. Flight
guidance systems were modified to account for the new methods, so
it's not really relevant.

Just to give you some idea of what I mean, I'll give you a scenario.
You'v
e
just aken off and yoou're climibing away at best rate. Suddenly, your
airspeed increases by a fairly large lump. 15-20 knots, say. you
increase your pitcha bit to absorb it and your speed bleeds back a
tad. Still plent
y
in hand, though. all the sudden the pitch you have is dragging your
speed back and it's beginning to decrease as the wind that delivered
that extra speed vanishes. You're still OK and back to your orignal
pitch and have a couple of knots more than you had at the beginning.
All the sudden, the bottom falls out of your airplane. Your climb
stops and then a second late
r *
you begin to sink, and fast. another second or two and your speed
washes off even further and now you're sinkng and your stall warning
is starting to squeak.

you gotta do something and right now. you still have some altitude,
say 40
0
feet. what do you do?

Bertie

Alt-Ctl-Del

No, wait, change my underwear.

Yoke forward, nose down and max power?

That's what the Delta guys did. And that 727 in New Orleans. A different
approach was needed and what they came up with was full power. and in a
jet that means firewall and overboost to your little heart's contenet,
and nose up as much as you can. The stall warnign should be ringing off

Bertie, this brings up an incident I had in the Cherokee 180 many
years ago. It resulted in quite a discussion with many asserting I
didn't do the right things and quite possibly I didn't but I'd like
your input.

I was on final for 06 at our airport. It was a gusty day so I was
carrying a good 90 on final when at 300 feet the ASI basically and
abruptly went to zip and I was on the express elevator down. I'd never
seen the ASI drop to the peg like that. I knew two things. What
nature takes away in gusts she eventually gives back. The other was at
300 feet and essentially zero for IAS I'd become a lawn dart if I
shoved the nose down as I was not going to accelerate enough get
flying speed and enough energy to flare in that distance unless the
wind changed. It would have been different if the ASI had been a
little low or at least had some indication.

Of course at the first instance of sink I instinctively went full
power. The only thing I could think of at that point was to put the
plane in the best attitude for survival on impact if it didn't start
flying. The one thing I didn't want was to hit nose low. The
airspeed came back as I was entering ground effect and at that point I
was able to ease the nose down and pick up a enough speed that I made
a normal landing. Actually the landing was a good one if you didn't
count the last few hundred feet of final. :-))



the wall ( we have stick shakers, but same thing) and you keep this up
til you fly out the other side of the mess. It goes against everything
we've learned but that's what they tell us to do. There's generally some
guidance form the flight director as well. On some it's a set of yellow
"antlers" that give you best pitch and on others the pitch bar on the
flight director just gives you all the pitch info you need ( you just
put the airplane wings on a magenta bar, no brains required)
note this is for a sustained and powerful microburst and not for
recovery form a tiny bit of wind shear in a 20 knot wind.

Bertie
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Roger wrote in
:
Bertie, this brings up an incident I had in the Cherokee 180 many
years ago. It resulted in quite a discussion with many asserting I
didn't do the right things and quite possibly I didn't but I'd like
your input.

I was on final for 06 at our airport. It was a gusty day so I was
carrying a good 90 on final when at 300 feet the ASI basically and
abruptly went to zip and I was on the express elevator down. I'd never
seen the ASI drop to the peg like that. I knew two things. What
nature takes away in gusts she eventually gives back. The other was at
300 feet and essentially zero for IAS I'd become a lawn dart if I
shoved the nose down as I was not going to accelerate enough get
flying speed and enough energy to flare in that distance unless the
wind changed. It would have been different if the ASI had been a
little low or at least had some indication.

Of course at the first instance of sink I instinctively went full
power. The only thing I could think of at that point was to put the
plane in the best attitude for survival on impact if it didn't start
flying. The one thing I didn't want was to hit nose low. The
airspeed came back as I was entering ground effect and at that point I
was able to ease the nose down and pick up a enough speed that I made
a normal landing. Actually the landing was a good one if you didn't
count the last few hundred feet of final. :-))

Yow! Sounds like you did the right thing to me, alright. Proof is in the
pudding of course and you got away with it, but I have to agree with you,
putting the nose down would have been disasterous. I had a similar
experience to your's in a glider which ended up with us landing short of
the field but no damage. Difficut to train for things lke this though.
Familiarity with the feel of the the airplane at and beyond the edge
obviously paid off for you, I'd say!

Bertie

WingFlaps wrote:
Hi All,

Imagine a plane in 2 conditions.

1) Climbing with full power
2) Descending fast with 50% power.

Both have constant rates of ascent and descent.

Question A: Which wing is closer to stall?
Question B: A big updraft occurs, which is more likely to stall?

If you vote first it _may_ lead to some good discussion later...

Cheers


Is the "full power" climb with or without afterburner?? :-)

You haven't provided enough information.

1) Climbing with full power

What Speed? The pilot selects the AOA when he chooses to either climb
out at Vx, Vy, or a Cruise Climb. Of these, Vx is the closest to the
stall, so lets pick that one for the sake of your question.

2) Descending fast with 50% power.

Again, what type of descent? Straight forward and clean? Emergency
Dirty? Because Of lack of specificity, I am going to assume you mean
straight forward and clean, and as such, I'm assuming you mean a high-
speed (cruise) descent.

Both have constant rates of ascent and descent.

So to clarify, your assuming that all 'zooming' energy has been
expended and the aircraft are in a state of equilibrium?

Also, given that you have not specified a particular aircraft, I am
going to use my own personal Bird's speed's as a reference for all
further questions (PA-28-140).

Question A: Which wing is closer to stall?

In state 1, the ship is operating at 74mph, on the low side of L/D max
operating in the region of reversed control authority.
In state 2, the ship is operating at its parasitic-Drag-Limited
descent-rate. Lets assume that the pilot is descending at 500fpm
(glide rate, power off). Obviously the pilot is going to be doing a
lot faster than the 80mph Vg, since the plane can do that power off,
and in this case the pilot will be suppling a substantial amount of
energy from the mill... in my bird, 50% power on a cruise descent
gives me ~140mph, but in any case you'll be substantially faster than
the best glide speed.

That said, the answer is trivial, of course the 74tas aircraft is
closer to stall than the 80+tas aircraft.

Granted, there is an odd case, its possible that the pilot is
operating at 50% power, but right ahead of the stall regime in the
region of reversed command authority. In that case, if he is
requiring 50% of his power to maintain a 500fpm descent, he's probably
pretty damn close to the wing's stall threshold... But that would just
be poor judgement on the pilot's part.

Question B: A big updraft occurs, which is more likely to stall?

I'm not sure Updrafts are your problem so much as tail-winds, but in
any case, obviously the ship that is operating closer to Stall will
have less margin for variances an ambient wind direction.

If you vote first it _may_ lead to some good discussion later...