ASW 20 SPIN CHARACTERISTICS

Martin Gregorie wrote:


I've not played with calibrated AoA indicators. If you have, what AoA
was reached at the stall? I'm curious.

I haven't used calibrated ones either, so I don't know.


I think our modern airfoils have very little separation at minimum sink,
and certainly far aft of the 60% point. Instead of "separation", perhaps
you mean the transition from laminar flow to turbulent flow? That does
occur somewhere around the 60% point (maybe 70% or so) on modern airfoils.


Depends on the surface texture and Re number: the turbulent transition
is just behind the hi-point with a paper covered surface and Re =
50,000. I'd guess the separation point was about at the aileron hinge
line on a Discus 1 - otherwise why put the turbulator there? Its job
is to increase the boundary layer energy by forcing a transition from
laminar to turbulent and hence causing separation to be delayed.
Without measuring the wing, that must be in the 80% ballpark.

I was talking about the separation on the top surface at high AOA
during a "stall situation". I now realize you were talking about laminar
flow separation on the bottom surface, which isn't related to the stall
situation.

For the modern laminar airfoils, the transition (from laminar flow to
turbulent flow on the bottom of the airfoil) is at least 80% or more. On
my ASH 26 E, the turbulators are on the flaps and ailerons at about 95%.

The transition from laminar flow to turbulent flow on the top of the
airfoil is sooner, perhaps in the 60%-80% range. There is rarely a
laminar flow separation, though the Speed Astir is a well-known example.

--
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Eric Greenwell
Washington State
USA

Any particular reason you picked a right turn? Mine tends to drop the
left wing in a stall.

Your suggestion sounds like a good exercise to try: normally I don't
go below 50 kts at the top of a fast pull-up. Maybe Monday or
Tuesday....

Dear Martin, No particular reason...just describing the manuever. It
will work either way. Rudy

On Sun, 18 Jul 2004 12:45:02 -0700, Eric Greenwell
wrote:

I was talking about the separation on the top surface at high AOA
during a "stall situation". I now realize you were talking about laminar
flow separation on the bottom surface, which isn't related to the stall
situation.

Actually, I was talking about upper surface separation at low speed -
thermalling regime. Our oldest club Discus has zigzag turbs just ahead
of the aileron hinges and those were the turbs I was thinking about.
I'm not sure how common there are, come to think of it, because the
other club ship (Czech-bult with tiplets) doesn't have them.

I forgot about the lower surface turbs, but I think their placement is
due to airfoil shape rather than anything else. I've only seen them in
front of the narrow undercambered area under the TE and assumed they
were to stop separation in the undercamber dish at the top end of the
speed range.

I hope I didn't cause too much confusion there.

For the modern laminar airfoils, the transition (from laminar flow to
turbulent flow on the bottom of the airfoil) is at least 80% or more. On
my ASH 26 E, the turbulators are on the flaps and ailerons at about 95%.

Interesting - I've never seen a 26E close enough to know what its
airfoil looks like. Does it also have a somewhat hooked trailing edge?

The transition from laminar flow to turbulent flow on the top of the
airfoil is sooner, perhaps in the 60%-80% range. There is rarely a
laminar flow separation, though the Speed Astir is a well-known example.

Could it have been more of a problem on the early glass? I've read
Will Schueman's article about the development of his triple break
leading edge a couple of times. The separation bubble on his ASW-12
seems to have been huge and thick. His analysis of the problem and the
way he went about developing the fix is a classic.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

On 18 Jul 2004 12:57:10 -0700, (Rudy Allemann)
wrote:

Any particular reason you picked a right turn? Mine tends to drop the
left wing in a stall.

Your suggestion sounds like a good exercise to try: normally I don't
go below 50 kts at the top of a fast pull-up. Maybe Monday or
Tuesday....

Dear Martin, No particular reason...just describing the manuever. It
will work either way. Rudy

Thanks for the clarification. I'll report back once we've had good
enough soaring weather to try it at a reasonable height.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

On Sun, 18 Jul 2004 15:14:37 +1200, Bruce Hoult
wrote:

Presumably you've seen aircraft such as the F/A-18 demonstrate a slow
pass at very high and stalled angle of attack? They are getting some of
their support from the downward component of the engine thrust, of
course, but with an AoA of, say, around 30 degrees it would need a
thrust:weight ratio of around 2 in order for thrust to be enough to
support the entire aircraft weight.

Great example! But don't forget that the F-18 (as well as any other
fighter) uses a couple of tricks, notably the strakes - the vortices
produced by the strakes produce a large percentage of the lift while
the outer wings are completely stalled and produce only very little
lift.

These fighters and delta winged aircraft don't play fair concerning
lift creation.

Bye
Andreas

Martin Gregorie wrote:

On Sun, 18 Jul 2004 12:45:02 -0700, Eric Greenwell
wrote:


I was talking about the separation on the top surface at high AOA
during a "stall situation". I now realize you were talking about laminar
flow separation on the bottom surface, which isn't related to the stall
situation.


Actually, I was talking about upper surface separation at low speed -
thermalling regime. Our oldest club Discus has zigzag turbs just ahead
of the aileron hinges and those were the turbs I was thinking about.
I'm not sure how common there are, come to think of it, because the
other club ship (Czech-bult with tiplets) doesn't have them.

Turbulators on the top of the wing are uncommon. Except for a Speed
Astir, I haven't seen any, not even on Discus(es?). Generally, I believe
the separation that occurs while thermalling is not laminar flow
separation (which would start around 60% or so on the airfoil), but
turbulent flow separation starting at/near the trailing edge at the
onset of stall (flying too slowly).

I forgot about the lower surface turbs, but I think their placement is
due to airfoil shape rather than anything else. I've only seen them in
front of the narrow undercambered area under the TE and assumed they
were to stop separation in the undercamber dish at the top end of the
speed range.

I hope I didn't cause too much confusion there.


For the modern laminar airfoils, the transition (from laminar flow to
turbulent flow on the bottom of the airfoil) is at least 80% or more. On
my ASH 26 E, the turbulators are on the flaps and ailerons at about 95%.


Interesting - I've never seen a 26E close enough to know what its
airfoil looks like. Does it also have a somewhat hooked trailing edge?

Well, it is a flapped ship, so the trailing edge can deflected down 10
degrees or so. The flap and aileron seem to have a slight concavity on
the top side. The ASW 27 is essentially identical, and they both use
blow turbulators, like the ASW 20 models.


The transition from laminar flow to turbulent flow on the top of the
airfoil is sooner, perhaps in the 60%-80% range. There is rarely a
laminar flow separation, though the Speed Astir is a well-known example.


Could it have been more of a problem on the early glass?

I haven't heard that it was. I think it was eventually found on the
Astir because it performed so far below expectations, that much effort
went into discovering the cause.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

I have never tried to spin my ASW20 in this way but I have done the =
exercise in a K13 at low level too. The results were a very fast stall =
and wingdrop, which is what I expected and is how I would I expect most =
gliders to behave. I what way does the ASW20 behave differently?? =
Bearing in mind that in a accidental spin flaps have to be moved to =
negative as well as the usual recovery, the glider will pick up speed =
that much faster any spin at 500ft is going to be irrecoverable.
Pulling up into a thermal, and slowing down as you turn attention must =
be paid to air speed as the load comes back onto the wings.
This is explained in the flight manual at .5G and 0 flap minimum speed =
is 30kts at 1g it is 42kts at 2g it is 68kts and add 5 kts to all those =
with ballast. Based on those speeds when thermaling in turbulent air =
lack of control response will be felt easily and either more speed or =
less bank will be needed. In 3 years I have found that my ASW20 gives =
plenty of warning that speed is too low or indeed that speed is too high =
for the flap setting selected.
A pilot with 100+hours solo that has read and understood the manual =
should have no problems, it is not a novice glider. It can be flown =
level or in gentle turns at less than 40 kts but do not try it in rough =
conditions the airflow will break away unpredictably.

David Smith

"David Smith" wrote...
I have never tried to spin my ASW20 in this way but I have done the =
exercise in a K13 at low level too. The results were a very fast stall =
and wingdrop, which is what I expected and is how I would I expect most =
gliders to behave. I what way does the ASW20 behave differently?? =

The ASW20s I've flown will do both normal spin entries (inner wing drops)
and over the top spin entries (outer wing drops) from a turn, depending on
how the glider is handled. Spin entry is also more abrupt than the typical
training glider. Those who have trained in something other than a K13 or a
Puchacz will not have experienced this type of spin behavior.

A pilot with 100+hours solo that has read and understood the manual =
should have no problems, it is not a novice glider. It can be flown =
level or in gentle turns at less than 40 kts but do not try it in rough =
conditions the airflow will break away unpredictably.

100+ hour pilots vary greatly in level of training and experience. I've
know 100 hour pilots who could safely fly just about any glider. I've also
known 1000 hour pilots who barely survive flying Grob Twins...

Marc

Nicely written, Todd. I liked that explanation...

Todd Pattist wrote:
That increase in AOA occurs because the airplane begins to
descend as lift drops below the aircraft weight and the
additional descent vector acts to increase AOA.
etc.....


--

------------+
Mark Boyd
Avenal, California, USA

Marc
Do any other single seaters spin over the top in the same way and just =
how do deliberately make the glider do it. I certainly have done a left =
hand spin off a right hand turn in a Puchacz but I think you are =
describing different behavior.

David Smith