Thinking about stalls

On Mar 13, 1:37 pm, WingFlaps wrote:

Nope, if the airspeed is constant, the lift from the two wings is not
the same. This is thought provoking discussion I was hoping to start!
Can you see why lift does not equal weight in both cases?

Common misconception: that a climbing wing is generating more
lift than a descending wing. If the flight paths are both straight
lines, whether climbing or descending, the lift is the same in both
cases. As Jim said, only a change in the direction of flight will
change the lift/weight ratio. A G-meter (such as in our Citabrias)
will prove it.
If the airspeeds are the same and the flight paths are both
straight, the AOAs are both the same, too. But change the speeds while
leaving the flight paths alone, and the AOA will change. It's why the
airplane has a nose-high attitude in level slow flight as opposed to a
lower nose attitude in level cruise.

Dan

On Mar 14, 9:59*am, Jim Logajan wrote:
WingFlaps wrote:
On Mar 14, 9:33*am, Jim Logajan wrote:
WingFlaps wrote:
On Mar 14, 9:11*am, Brian wrote:
As for your question above, given that the airplanes are ascending
or decending at constant rates then the lift is equal to the
wieght of the airplane in both cases. If the aircraft are the same
wieght then the lift generated will be the same.

That is not correct.

Hmmm. Brian's statement appears essentially correct - and you are
correct too. The "gotcha" is that the vertical component of the lift
force exceeds

the weight only during the transition from level flight to constant
ascending flight. And the lift force is less than the weight during
the transition from level flight to constant descending flight.

But once the vertical speed becomes constant (whether up or down) the
vertical component of lift has to equal the downward force of
gravity. If it didn't, then the aircraft would begin _accelerating_
up or down, depending on the difference.

Nope, if the airspeed is constant, the lift from the two wings is not
the same. This is thought provoking discussion I was hoping to start!
Can you see why lift does not equal weight in both cases?

I don't wish to be confrontational since you are looking for thought
provoking discussion, but I am pretty sure there is a fair amount of
imprecision, and therefore ambiguity, in your statements. This tends to
make it difficult to get very far in these discussions.

Would it help any if I presented the 2-D equations of force involved?
And perhaps you could do the same?- Hide quoted text -


Sure here you go:
D=drag
L=lift
W=weight
T=thrust
alpha=angle of thrust

For no acceleration in any plane:

W=Tsin(alpha) + L
D=Tcos(alpha)

What you and many other texts have missed is that the thrust angle
changes...
What this means is that when you make a plane climb at constant speed
you are deliberately reducing lift from from the wing and supplanting
it with engine thrust! To extend this idea further, it is not the
climb per se that may be the problem but a decaying airspeed... The
above equations can be extended to the AOA and airspeed but the
conclusion remains the same.

Now, what about that tricky updraft? Is this thought provoking :-)

Cheers

On Mar 14, 1:00*pm, wrote:
On Mar 13, 1:37 pm, WingFlaps wrote:

Nope, if the airspeed is constant, the lift from the two wings is not
the same. This is thought provoking discussion I was hoping to start!
Can you see why lift does not equal weight in both cases?

* * * Common misconception: that a climbing wing is generating more
lift than a descending wing. If the flight paths are both straight
lines, whether *climbing or descending, the lift is the same in both
cases. As Jim said, only a change in the direction of flight will
change the lift/weight ratio. A G-meter (such as in our Citabrias)
will prove it.
* * * If the airspeeds are the same and the flight paths are both
straight, the AOAs are both the same, too. But change the speeds while
leaving the flight paths alone, and the AOA will change. It's why the
airplane has a nose-high attitude in level slow flight as opposed to a
lower nose attitude in level cruise.


Hi Dan see my rely to Jim. In fact, lift is reduced in a steady climb.

Cheers

On Mar 13, 8:50 pm, WingFlaps wrote:
On Mar 14, 1:00 pm, wrote:



On Mar 13, 1:37 pm, WingFlaps wrote:

Nope, if the airspeed is constant, the lift from the two wings is not
the same. This is thought provoking discussion I was hoping to start!
Can you see why lift does not equal weight in both cases?

Common misconception: that a climbing wing is generating more
lift than a descending wing. If the flight paths are both straight
lines, whether climbing or descending, the lift is the same in both
cases. As Jim said, only a change in the direction of flight will
change the lift/weight ratio. A G-meter (such as in our Citabrias)
will prove it.
If the airspeeds are the same and the flight paths are both
straight, the AOAs are both the same, too. But change the speeds while
leaving the flight paths alone, and the AOA will change. It's why the
airplane has a nose-high attitude in level slow flight as opposed to a
lower nose attitude in level cruise.

Hi Dan see my rely to Jim. In fact, lift is reduced in a steady climb.

Cheers

The trust vector is added to the lift vector in a climb, as the drag
is added to weight.

Dan Mc

On Mar 14, 2:46*pm, Dan wrote:
On Mar 13, 8:50 pm, WingFlaps wrote:





On Mar 14, 1:00 pm, wrote:

On Mar 13, 1:37 pm, WingFlaps wrote:

Nope, if the airspeed is constant, the lift from the two wings is not
the same. This is thought provoking discussion I was hoping to start!
Can you see why lift does not equal weight in both cases?

* * * Common misconception: that a climbing wing is generating more
lift than a descending wing. If the flight paths are both straight
lines, whether *climbing or descending, the lift is the same in both
cases. As Jim said, only a change in the direction of flight will
change the lift/weight ratio. A G-meter (such as in our Citabrias)
will prove it.
* * * If the airspeeds are the same and the flight paths are both
straight, the AOAs are both the same, too. But change the speeds while
leaving the flight paths alone, and the AOA will change. It's why the
airplane has a nose-high attitude in level slow flight as opposed to a
lower nose attitude in level cruise.

Hi Dan see my rely to Jim. In fact, lift is reduced in a steady climb.

Cheers

The trust vector is added to the lift vector in a climb, as the drag
is added to weight.


Are you saying that wing lift does not change with attitude in a non-
accelerating frame?

Cheers

On Mar 13, 9:57 pm, WingFlaps wrote:
On Mar 14, 2:46 pm, Dan wrote:



On Mar 13, 8:50 pm, WingFlaps wrote:

On Mar 14, 1:00 pm, wrote:

On Mar 13, 1:37 pm, WingFlaps wrote:

Nope, if the airspeed is constant, the lift from the two wings is not
the same. This is thought provoking discussion I was hoping to start!
Can you see why lift does not equal weight in both cases?

Common misconception: that a climbing wing is generating more
lift than a descending wing. If the flight paths are both straight
lines, whether climbing or descending, the lift is the same in both
cases. As Jim said, only a change in the direction of flight will
change the lift/weight ratio. A G-meter (such as in our Citabrias)
will prove it.
If the airspeeds are the same and the flight paths are both
straight, the AOAs are both the same, too. But change the speeds while
leaving the flight paths alone, and the AOA will change. It's why the
airplane has a nose-high attitude in level slow flight as opposed to a
lower nose attitude in level cruise.

Hi Dan see my rely to Jim. In fact, lift is reduced in a steady climb.

Cheers

The trust vector is added to the lift vector in a climb, as the drag
is added to weight.

Are you saying that wing lift does not change with attitude in a non-
accelerating frame?

Cheers

Of course it does.

However -- In a climb thrust acts contrary to drag some component of
weight (depending on the angle of climb). Thus the angle of attack is
not *necessarily* equal to the angle of climb.


Dan Mc

On Mar 15, 12:08 am, Dan wrote:
On Mar 13, 9:57 pm, WingFlaps wrote:





On Mar 14, 2:46 pm, Dan wrote:

On Mar 13, 8:50 pm, WingFlaps wrote:

On Mar 14, 1:00 pm, wrote:

On Mar 13, 1:37 pm, WingFlaps wrote:

Nope, if the airspeed is constant, the lift from the two wings is not
the same. This is thought provoking discussion I was hoping to start!
Can you see why lift does not equal weight in both cases?

Common misconception: that a climbing wing is generating more
lift than a descending wing. If the flight paths are both straight
lines, whether climbing or descending, the lift is the same in both
cases. As Jim said, only a change in the direction of flight will
change the lift/weight ratio. A G-meter (such as in our Citabrias)
will prove it.
If the airspeeds are the same and the flight paths are both
straight, the AOAs are both the same, too. But change the speeds while
leaving the flight paths alone, and the AOA will change. It's why the
airplane has a nose-high attitude in level slow flight as opposed to a
lower nose attitude in level cruise.

Hi Dan see my rely to Jim. In fact, lift is reduced in a steady climb.

Cheers

The trust vector is added to the lift vector in a climb, as the drag
is added to weight.

Are you saying that wing lift does not change with attitude in a non-
accelerating frame?

Cheers

Of course it does.

However -- In a climb thrust acts contrary to drag some component of
weight (depending on the angle of climb). Thus the angle of attack is
not *necessarily* equal to the angle of climb.

I'm sorry but I'm having trouble understanding where you are coming
from. In my equations above I wrote that D=Tcos(alpha) and this is
based on the idea that W,D and L are 3 orthogonal forces. Of course
you can rewrite them non orthogonally if you please but my expression
makes good sense (to me anyway). This is why: Imagine a jet in a
steady vertical climb (alpha=90 degrees). My equation says D=0 so how
can that be? The answer is that this simplified (wing + engine) model
is really only considering induced drag and that the thrust line is
close to 0 AOA (not bad approximations IMHO). For induced drag to be
zero, wing LIFT _must_ be zero and so we see that Weight =Tsin(90) + L
- W=T -exactly as it should be for a vertical climb! The pilot has
reduced AOA to zero, the wing produces NO lift and the plane climbs
vertically. Again, I say L should be dropped to zero for a true steady
vertical climb and L=W only in straight and level flight or if the
plane is gliding (T=0). In all steady climbs LW and all descents LW.

I was a bit surprised when I realized that to be in a steady climb
the pilot must be operating the plane in a condition where wing lift
and AOA are actually lower than in straight and level -all thanks to
a component of thrust adding to lift !!! Although the effect may not
be large for low power planes (TW) , if what I'm saying makes sense,
one may see some advantages in this approach -e.g. why increasing
power leads to a nice steady climb or cutting power causes the nose to
drop and a descent to begin...

Cheers

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've
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 plenty
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 later
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 400
feet. what do you do?



Bertie

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've
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 plenty
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 later *
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 400
feet. what do you do?

Bertie

Alt-Ctl-Del

No, wait, change my underwear.

Yoke forward, nose down and max power?

Richard

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
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