ASW 20 SPIN CHARACTERISTICS

Jack wrote in message

They unflex because the load is removed. In order to stall they would
have to unflex faster than the load is removed. If the pilot is pushing,
the stall speed can go _way_ down. It's when he starts to load the wings
again that his technique, or failure to track his loss of airspeed in
the pull/push, can bring about the stall.


Jack

Isn't it also true that lift will be reduced if a highly flexed wing
increases its angle attack beyond the critical angle of attack. If
the wing is producing less lift it cannot maintain the flex that
existed before the critical angle of attack was exceeded. As the wing
unflexes the tip angle of attack increases.

Which of those assumptions is invalid?

Andy

On 16 Jul 2004 07:03:55 -0700, (Andy Durbin)
wrote:


Isn't it also true that lift will be reduced if a highly flexed wing
increases its angle attack beyond the critical angle of attack. If
the wing is producing less lift it cannot maintain the flex that
existed before the critical angle of attack was exceeded. As the wing
unflexes the tip angle of attack increases.

Which of those assumptions is invalid?

All of threse assumptions are valid.
But if the tip is already stalled it doesn't matter a lot if it has
exceeded its maximum AoA by 2 degrees or 6 - the resulting stall is
the same.

But to stall a 20 with sufficient g-load to get significant wing flex,
you need a lot of speed and a nearly fully pulled-back stick.

I havent's flown a 20 for a couple of years now - maybe one of the
current 20 drivers could check this out, but I doubt that at 4g the
wing flex is more than three ft compared to level flight. The
resulting AoA change as the wing reflexes will be less than 1.5
degrees then.... neglectable.

Bye
Andreas

In article ,
Andreas Maurer wrote:

But if the tip is already stalled it doesn't matter a lot if it has
exceeded its maximum AoA by 2 degrees or 6 - the resulting stall is
the same.

No it's not. There isn't a "maximum angle of attack". There is only an
"angle of attack for maximum lift". As you approach that angle of
attack the rate of lift increase gets smaller and smaller, then you get
the same amount of lift at slightly increasing angles of attack, and
then with still more angle of attack you get less lift. The more you
take the angle of attack past the point of maximum lift the less lift
you get.

So, yes, it does matter whether you are 2 degrees or 6 degrees past the
angle of attack for maximum lift.

-- Bruce

On Sat, 17 Jul 2004 12:18:58 +1200, Bruce Hoult
wrote:

No it's not. There isn't a "maximum angle of attack". There is only an
"angle of attack for maximum lift". As you approach that angle of
attack the rate of lift increase gets smaller and smaller, then you get
the same amount of lift at slightly increasing angles of attack, and
then with still more angle of attack you get less lift. The more you
take the angle of attack past the point of maximum lift the less lift
you get.

So, yes, it does matter whether you are 2 degrees or 6 degrees past the
angle of attack for maximum lift.

Of course you are correct as ever, Bruce.

I used the term "maximum angle of attack" to define the point where
the airflow separates close to the leading edge, creating a massive
and sudden loss of lift (this situation being usually defined as "the
stall"). Is there a better technical term in English for this?

In scientific terms maximum AoA would be Pi (or 180 degrees) of
course, e.g. in a tailslide.



Bye
Andreas

Andy Durbin wrote:

Jack wrote in message

They unflex because the load is removed.

Isn't it also true that lift will be reduced if a highly flexed wing
increases its angle attack beyond the critical angle of attack. If
the wing is producing less lift it cannot maintain the flex that
existed before the critical angle of attack was exceeded. As the wing
unflexes the tip angle of attack increases.

I see nothing in your comments which is invalid. If the wing unflexes
due to stall and resultant loss of lift, the further increase in the
angle of attack during the unflex may be of little consequence.


--
Jack