spins from coordinated flight

Stefan wrote:
Dudley Henriques schrieb:

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. All the rest is
simply stating different ways to make these two things happen.

While I agree that this is a correct and simple recipe and therefore
quite useful in practice, I don't agree that it helps to *understand*
the situation, because *reason* for the spin is not the yaw rate. The
reason for the spin is an asymmetric angle of attack, i.e. one wing is
more stalled than the other. Of course this situation can only occur if
there is some yaw, which leads us to the recipe given above.

Recipe: As there is always some yaw in a coordinated turn (otherwise it
wouldn't be coordinated), you can perfectly enter a spin from a
coordinated turn. Aerodynamic reason: The inner wing has a higher angle
of attack than the outer, so it stalls first or, if both wings stall, it
is more stalled. Asymmetric stall condition - spin.


You can argue this until the cows come home but the answer is always the
same. To spin an airplane you need stall and a yaw rate...period! All
the rest of it, the difference in aoa, the dynamics of autorotation, the
whole magilla, is nothing but explaining in aerodynamic terms what
happens AFTER the stall and yaw rate are introduced.

As you say, understanding these things is essential, but they are the
EFFECT of what causes spin.
Look at it this way. Without stall and without a yaw rate being
introduced, you will have none of the things happening that you have
mentioned. None will be present until stall occurs and a yaw rate
introduced.

They are relevant of course, but not the single answer a pilot needs to
know when addressing the subject of spins.

When I ask a student what causes a spin, I don't want that student to
tell me what happens to each wing of the airplane as the spin is
developing. If I get that answer I'm immediately going to ask that
student how the airplane was placed in a position to cause these effects
to happen.

When someone asks what causes a spin, or whether or not an airplane can
be spun from this flight position or that one, the correct answer is
that stall and yaw rate must be present to produce a spin; and that spin
can be entered from ANY flight condition.
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.

--
Dudley Henriques