spins from coordinated flight

The answer to the ball question is no. It won't spin. A ball centered airplane in a climbing turn is compensated by rudder and is considered coordinated (in the classic sense).

Ok, now I'm confused again. If "stall plus yaw" is all that's necessary, and all (normal) turns involve yaw, then why won't it spin? Do I have the wrong definition of "yaw"?

Jose
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Jose wrote:
The answer to the ball question is no. It won't spin. A ball centered
airplane in a climbing turn is compensated by rudder and is considered
coordinated (in the classic sense).

Ok, now I'm confused again. If "stall plus yaw" is all that's
necessary, and all (normal) turns involve yaw, then why won't it spin?
Do I have the wrong definition of "yaw"?

Jose

A "normal" turn is accomplished by splitting the lift vector, NOT by
holding in yaw. Yaw should only be present in the turn dynamic during
the entry into the turn and exit from the turn. Once stabilized in the
turn, there should be no yaw present. There could be however if the turn
was a slipping turn or a skidding turn.


--
Dudley Henriques

A "normal" turn is accomplished by splitting the lift vector, NOT by holding in yaw. Yaw should only be present in the turn dynamic during the entry into the turn and exit from the turn.

Ok, then what exactly is "yaw"? My understanding is that it is a change of direction of the longitudinal axis of the aircraft in the plane that is roughly coplanar with the wings.

Splitting the lift vector serves to change the direction of flight, but not to change the heading. To do that you need what I was calling yaw, and if you want to stay in a coordinated turn, you need to continually change the heading as you continually change the direction of flight. You would have a steady change in heading (which will include a steady yaw) with no acceleration in the yaw direction.

You seem to be defining yaw as a rotational =acceleration= of the longitudinal axis of the aircraft in the plane that is roughly coplanar with the wings.

Do I have that right?

Jose
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Jose wrote:
A "normal" turn is accomplished by splitting the lift vector, NOT by
holding in yaw. Yaw should only be present in the turn dynamic during
the entry into the turn and exit from the turn.

Ok, then what exactly is "yaw"? My understanding is that it is a change
of direction of the longitudinal axis of the aircraft in the plane that
is roughly coplanar with the wings.

Yaw, as we define the term in flight test as it relates to directional
stability is defined as moments about the VERTICAL axis, not the
longitudinal axis. These moments also relate to Yaw Angle, Yaw Rate, and
Sideslip Angle.


--
Dudley Henriques

Ok, then what exactly is "yaw"? My understanding is that it is a change of direction of the longitudinal axis of the aircraft in the plane that is roughly coplanar with the wings.

Yaw, as we define the term in flight test as it relates to directional stability is defined as moments about the VERTICAL axis, not the longitudinal axis.

Yes, that is pretty much what I said. Change in direction =of= the longitudinal axis, =in= the plane (of the wings), [(therefore) =about= the vertical axis.] I am however using "vertical" and "horizontal" as referenced to the aircraft, not the earth, thus when the aircraft pitches up, the yaw axis (as I understand it defined) would change.

Jose
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Dudley Henriques schrieb:

Yaw should only be present in the turn dynamic during
the entry into the turn and exit from the turn. Once stabilized in the
turn, there should be no yaw present.

I don't agree. A coordinated turn is *always* a turn around all three
axes. (The only exception is a turn with a 90 degrees bank.) You can
easily demonstrate this by "hand-flying" a toy airplane.

Stefan wrote:
Dudley Henriques schrieb:

Yaw should only be present in the turn dynamic during the entry into
the turn and exit from the turn. Once stabilized in the turn, there
should be no yaw present.

I don't agree. A coordinated turn is *always* a turn around all three
axes. (The only exception is a turn with a 90 degrees bank.) You can
easily demonstrate this by "hand-flying" a toy airplane.


Axis isn't really used in this way. You will notice if you move your toy
airplane that the axis system remains in place and moves with the
aircraft centered on the aircraft's cg.

To define turn using axis reference is not the best way to explain turn
since once established in a stable turn there should be no movement on
the airplane's axis system. The axis system references the lines
crossing through the aircraft's Cg and are used to define movement and
moment on each axis. The axis system moves in place with the aircraft
and never deviates from it's center point through the cg.
There is movement on the longitudinal axis in roll as the airplane is
rolled into and out of the turn, and movement as well on the lateral
axis in pitch as angle of attack is increased to compensate for the
split in the lift vector. There is movement on the Vertical axis as
rudder is used to compensate for adverse yaw both during and exiting the
turn, but once established in a coordinated turn, (I'm using medium
banked turn here for easy reference as under bank and over bank in
shallow and steep turns cause in turn axis changes complicating the
situation a bit) all movement on the aircraft's axis should be stable.

The proper way to define turn as relates to change in direction is to
define the change in the velocity vector as relates to heading change
not as a change on or around the axis of the aircraft.


--
Dudley Henriques

To define turn using axis reference is not the best way to explain turn since once established in a stable turn there should be no movement on the airplane's axis system.

I am not sure I'm getting this.

We'll ignore translation (straight line motion).

The axis system is (as I have been using it) fixed to the aircraft, and the axis system moves whenever the aircraft rotates (around any point). It has nothing to do with the actual earth's horizon.

Then, as I understand it, rotation of the aircraft involves a rotation around one or more of the axes. Yaw involves rotation (=of= the longitudinal axis, and thus the airplane) =about= the (airplane) vertical axis, =in= the plane (roughly described by the wing tips and tail) of the (airplane) horizontal axes.

In a turn, slipping, skidding, or coordinated, the nose of the airplane (dragging the longitudinal axis with it) is changing its direction. The airplane is changing heading. If this happens at a constant rate (say, 3 degrees per second), I would say the aircraft is yawing at a steady angular velocity, and undergoing no acceleration in yaw. To =enter= or =leave= this state would require an =acceleration= of yaw in one direction or another.

Where do our understandings and vocabulary diverge?

Jose
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You can choose whom to befriend, but you cannot choose whom to love.
for Email, make the obvious change in the address.

Jose wrote:
To define turn using axis reference is not the best way to explain
turn since once established in a stable turn there should be no
movement on the airplane's axis system.

I am not sure I'm getting this.

We'll ignore translation (straight line motion).

The axis system is (as I have been using it) fixed to the aircraft, and
the axis system moves whenever the aircraft rotates (around any point).
It has nothing to do with the actual earth's horizon.
Then, as I understand it, rotation of the aircraft involves a rotation
around one or more of the axes. Yaw involves rotation (=of= the
longitudinal axis, and thus the airplane) =about= the (airplane)
vertical axis, =in= the plane (roughly described by the wing tips and
tail) of the (airplane) horizontal axes.

In a turn, slipping, skidding, or coordinated, the nose of the airplane
(dragging the longitudinal axis with it) is changing its direction. The
airplane is changing heading. If this happens at a constant rate (say,
3 degrees per second), I would say the aircraft is yawing at a steady
angular velocity, and undergoing no acceleration in yaw. To =enter= or
=leave= this state would require an =acceleration= of yaw in one
direction or another.

Where do our understandings and vocabulary diverge?

Jose
Jose;
Do some research on the aircraft axis system and what each axis
represents, then research forces in turns. It should become clearer then.
Thank you


--
Dudley Henriques