spins from coordinated flight

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

99% of the pilots will never have the ball centered all the way to a stall
break, it might look good 1/4 of a second before the break, but most pilots
stop actively flying when they start to feel the onset of the buffet. The
skilled pilot never stops making control adjustments.

I'll cite a comment made by a DPE after he had passed a student I sent him
for the private pilot practical test...
"That airplane is out of rig, everybody spins it doing accelerated stalls,
but your student didn't."



"Kyle Boatright" wrote in message
. ..
|
My thought is that we're splitting hairs in this thread. If the airplane is
in coordinated flight and stalls straight ahead (no wing drop), a spin can't
happen. But on most aircraft, one wing will drop first even if the ball is
centered. This wing drop creates a yaw, opening up the possibility for a
spin.

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

Dudley Henriques schrieb:

When someone asks what causes a spin, ... the correct answer is
that stall and yaw rate must be present to produce a spin
....
If you then ask a student to explain the aerodynamics in play as a spin
develops, it's THEN you want the auto rotational aerodynamics.

Different approach. You, as a military pilot (as I think to have
understood), believe in the behavioristic approach. Me, as a scientist
(and amateur pilot) follow the cognitive approach. Your approach yields
pilots who exactly know what to do in this or that situation, but
probably without really understanding the deeper reasons. My approach
tries to understand the underlying physics and to deduct the needed
pilot action from there. Not nessecairy for a pilot, but it's my style,
I think it's interesting and it's the prerequisite if you want to go on
your own feet beyond the tought stuff.

Now if only that fog around here would go away so I could go and rent
that Cap 10 and do some spins...

clarification edit inserted
"Jim Macklin" wrote in message
...
| In my experience, a stall break while straight and level or in a 60 degree
| bank if perfectly coordinated will drop the nose straight down.
[edit--relative to the pilot, not the horizon]
| The kicker is that 98% of the pilots have lazy feet and don't really keep
| the aircraft coordinated. If power is ON, the aircraft will need more
| rudder to control yaw and that amount of rudder will increase as speed is
| decreased approaching the stall. Some airplanes may not have enough
rudder
| to stay coordinated to the stall, most pilots will not use the rudder that
| is available.
| Some airplanes will not spin, even wit yaw supplied by maximum rudder
input
| at the stall in a pro-spin direction. The Beech Skipper [BE77] requires
| that the stall be entered, just before the stall, full pro-spin rudder is
| applied to induce a roll. At a 90 degree bank angle, sudden and full
| aileron in the opposite direction as the rudder is necessary to stall the
| wing crisply at the outer half. That will cause the airplane to roll
| rapidly and enter a spin. If not timed or done correctly, the aircraft
will
| enter a spiral.
|
| In the accidental spin, the pilot is likely to do exactly the same thing,
| just not with thought and skill. The plane is stalled while yawing
| [uncoordinated] and when the break happens, the poorly trained and
| non-current pilot's reaction will often be to try to pick-up the wing that
| is falling and the nose with aileron and up elevator. The natural
reaction,
| which training and experience correct, is to "fight" the falling nose, the
| falling wing, with normal control input.
|
| IF the aircraft is coordinated perfectly, the difference in lift vector is
| due slightly to the radial airspeed difference between the L&R wings, but
| more my the dihedral built in the airplane. The problem is that flight is
| very dynamic, control forces are changing, humans have reaction times, and
| the control authority created by the aerodynamic surfaces rapidly falls
with
| a small decrease in airspeed [lift equation] and the other forces, such as
| P-factor and engine torque involve inertia and mass.
|
|
|
| "Todd W. Deckard" wrote in message
| ...
||
|| "Dudley Henriques" wrote in message
|| ...
|| There is only one thing you have to know about spins. To enter one you
|| need 2 things to be present; stall and a yaw rate.
||
|| So to corner your answer to my question: you cannot? spin from
| coordinated
|| flight.
|| The airplane must be yawed during the stall break (thus the inclinometer
|| ball slips or skids
|| to one side).
||
|| My question is not to seek out practical advice in spins, or recoveries.
| It
|| is to explore two
|| academic debates: Can a certificated airplane depart if the ball is
|| precisely in the middle
|| and is there something telling in the emphasis from the foreign sources
|| cited that exposes a
|| gap in our US training practices and material.
||
|| Thank you for your response.
||
|| I'll be making a new years resolution to try it out in the neighboorhood
|| Decathalon (with an appropriate
|| chaperone) but as it is cold and snowy I thought I would put it to the
|| uunet.
||
|| Best regards,
|| Todd
||
||
|
|

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

I don't know of any autopilot that could be programmed to fly an aerobatic
maneuver based on predicted actions. Yet an autopilot can be designed to
observe and respond to the observed dynamic actions of the airplane.



"Stefan" wrote in message
...
| Dudley Henriques schrieb:
|
| When someone asks what causes a spin, ... the correct answer is
| that stall and yaw rate must be present to produce a spin
| ...
| If you then ask a student to explain the aerodynamics in play as a spin
| develops, it's THEN you want the auto rotational aerodynamics.
|
| Different approach. You, as a military pilot (as I think to have
| understood), believe in the behavioristic approach. Me, as a scientist
| (and amateur pilot) follow the cognitive approach. Your approach yields
| pilots who exactly know what to do in this or that situation, but
| probably without really understanding the deeper reasons. My approach
| tries to understand the underlying physics and to deduct the needed
| pilot action from there. Not nessecairy for a pilot, but it's my style,
| I think it's interesting and it's the prerequisite if you want to go on
| your own feet beyond the tought stuff.
|
| Now if only that fog around here would go away so I could go and rent
| that Cap 10 and do some spins...

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.

Jim Macklin schrieb:

I don't know of any autopilot that could be programmed to fly an aerobatic
maneuver based on predicted actions. Yet an autopilot can be designed to
observe and respond to the observed dynamic actions of the airplane.

I don't know of any autopilot that could be programmed to perform
rolling circles, either. But where's the relevance?

Recently, Bertie the Bunyip posted:

BTW, stalls in a climbing turn are pretty much standard standard stuff
even for Private pilots.

Standard, and _required_ for the practical. I had to do both climbing and
descending turning stalls for my checkride. Possibly because I chose to do
my checkride in the middle of winter with an 18 kt. breeze and the
examiner didn't want to die... ;-)

Neil