Are 'Single 180 Turn From Downwind to Final' and 'Stall-spin on Turnfrom Base to Final' mutually exclusive?

On Wed, 23 Nov 2016 08:36:45 -0800 (PST), Tango Whisky
wrote:

Bob, I've flown about 40 different types of gliders, and did voluntary spins with about half of them, wingspans ranging from 10 m to 26 m.

And the ASW20C was stunning in this respect - pulling from cruise into thermal a bit sharply, and the sky turns green although the glider just felt perfectly normal. In Germany in the mid-eighties, this behaviour did kill a couple of ASW20C pilots. Moving the CoG forward changes the behaviour to "normal".
The only other glider I came across having this behaviour was a Fox - but then, this one is designed to do exactly that.

So, there ARE gliders out there that bite without barking first.


Hi Bert,

the ASW-20 is a nice example of how little airfoil differences can
make huge differences.

I've flown two different ASW-20's.

The first was a 20L with slightly modiefied leading edge radius.
Performance-wise it was probably the best ASW-20 ever, and, stalled
with flaps 4, it had that sudden departure into a spin that you
descibe.

The other one was an ASW-20C. As docile as it gets - it was even
possible to thermal it with flaps 4 and less than 80 kp/h without the
slightest sign of a stall, not to mention that it didn't even drop a
wing if stalled.
CG a little bit more forward than in the 20L, though. This pilot got
heavier over the years.


And then there are those open class ships. I was quite surprised how
smoothly the Nimbus 3D went into a spin when I was checking out its
low-speed thermalling manners...



Viele Gruesse aus der Pfalz
Andreas

On Saturday, November 19, 2016 at 8:05:44 PM UTC-8, SoaringXCellence wrote:
Tom,

Is the Artificial Horizon really an AoA Indicator? If you hold a true nose-on-the-horizon in a glider, it will slow down and begin a descent, which means the AoA is increasing, but the nose still shows a 0 degree reference to the horizon. I've been teaching and flying instruments for 22 years and even in a power plane the Artificial Horizon almost never shows the Angle of attack.

Mike

You're right: it is not a true AOA indicator, but it will suffice when you fly normal pattern speeds. As I wrote, I don't use it and prefer instantaneous winds and ground speed instead. Wind shear can be a real killer, even if you think you're doing everything right.

Tom

On Wednesday, July 27, 2016 at 4:33:48 PM UTC-7, son_of_flubber wrote:
The 'Single 180 Turn From Downwind to Final' (aka 'military style pattern') and 'Stall-spin on Turn from Base to Final' are both well discussed as independent topics on RAS. But I've not seen anything about how these pieces fit together.

Having recently tried the 'Single 180 Turn...' and LIKED it, I'm wondering if there is any good reason why I should not fly this approach at an uncontrolled airport with mostly glider traffic. What about at a controlled airport with mostly GA power traffic?

And I'm wondering if anyone has ever stall-spinned from a 'Single 180 Turn...' pattern and whether there are subtle 'gotchas' associated with that pattern shape that I should know about.

What is the military's track record wrt 'Stall-spin in the pattern'? Does it happen just as often with the 'Single 180 Turn...'?

Bob Whelan wrote on 11/22/2016 9:06 PM:
True, before the wing "let go" there was (almost always) an absence of
aerodynamic burble felt through the stick or one's butt or merely
"drummed" through the metal fuselage, but by the time the wing did let
go, "all the other usual suspects" had put in their appearances: low
wind noise; nose noticeably high; controls (especially stick) getting
sloppy; etc. Subsequent to checking out in the ship, I found it
"intellectual fun" to mess around with it in slow flight "trying to find
the burble." Abrupt departure from controlled flight - yes, indeed! "No
warning?" - not by a long shot.

The nose was not noticeably high in either glider (20 C or 26E); the
wind noise was subdued, but both gliders were very quiet, and the change
in noise was very small; there was no burble or "butt feel"; the
controls were light but not unusually so; and the wing "departure" was
not abrupt - I simply ran out aileron, and the wing would start
downward. I'm guessing the inside wing tip doesn't stall, but can't be
sure about that.

But that scenario is with a shallow turn - 20 degree bank? - and at
30-40 degrees bank, it was harder to provoke the incipient spin. Much
harder, as I recall.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

On Saturday, November 26, 2016 at 6:50:46 AM UTC+3, Eric Greenwell wrote:
Bob Whelan wrote on 11/22/2016 9:06 PM:
True, before the wing "let go" there was (almost always) an absence of
aerodynamic burble felt through the stick or one's butt or merely
"drummed" through the metal fuselage, but by the time the wing did let
go, "all the other usual suspects" had put in their appearances: low
wind noise; nose noticeably high; controls (especially stick) getting
sloppy; etc. Subsequent to checking out in the ship, I found it
"intellectual fun" to mess around with it in slow flight "trying to find
the burble." Abrupt departure from controlled flight - yes, indeed! "No
warning?" - not by a long shot.

The nose was not noticeably high in either glider (20 C or 26E); the
wind noise was subdued, but both gliders were very quiet, and the change
in noise was very small; there was no burble or "butt feel"; the
controls were light but not unusually so; and the wing "departure" was
not abrupt - I simply ran out aileron, and the wing would start
downward. I'm guessing the inside wing tip doesn't stall, but can't be
sure about that.

Stick quickly a little bit forward restored aileron authority?

Bruce Hoult wrote on 11/26/2016 12:40 AM:
On Saturday, November 26, 2016 at 6:50:46 AM UTC+3, Eric Greenwell wrote:
Bob Whelan wrote on 11/22/2016 9:06 PM:
True, before the wing "let go" there was (almost always) an absence of
aerodynamic burble felt through the stick or one's butt or merely
"drummed" through the metal fuselage, but by the time the wing did let
go, "all the other usual suspects" had put in their appearances: low
wind noise; nose noticeably high; controls (especially stick) getting
sloppy; etc. Subsequent to checking out in the ship, I found it
"intellectual fun" to mess around with it in slow flight "trying to find
the burble." Abrupt departure from controlled flight - yes, indeed! "No
warning?" - not by a long shot.

The nose was not noticeably high in either glider (20 C or 26E); the
wind noise was subdued, but both gliders were very quiet, and the change
in noise was very small; there was no burble or "butt feel"; the
controls were light but not unusually so; and the wing "departure" was
not abrupt - I simply ran out aileron, and the wing would start
downward. I'm guessing the inside wing tip doesn't stall, but can't be
sure about that.

Stick quickly a little bit forward restored aileron authority?

The normal spin recovery works fine; even quicker was moving the flap
lever forward to the first negative flap position. I don't recall if
only stick forward was enough.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

On Sat, 26 Nov 2016 21:16:47 -0800, Eric Greenwell wrote:

Bruce Hoult wrote on 11/26/2016 12:40 AM:
On Saturday, November 26, 2016 at 6:50:46 AM UTC+3, Eric Greenwell
wrote:
Bob Whelan wrote on 11/22/2016 9:06 PM:
True, before the wing "let go" there was (almost always) an absence
of aerodynamic burble felt through the stick or one's butt or merely
"drummed" through the metal fuselage, but by the time the wing did
let go, "all the other usual suspects" had put in their appearances:
low wind noise; nose noticeably high; controls (especially stick)
getting sloppy; etc. Subsequent to checking out in the ship, I found
it "intellectual fun" to mess around with it in slow flight "trying
to find the burble." Abrupt departure from controlled flight - yes,
indeed! "No warning?" - not by a long shot.

The nose was not noticeably high in either glider (20 C or 26E); the
wind noise was subdued, but both gliders were very quiet, and the
change in noise was very small; there was no burble or "butt feel";
the controls were light but not unusually so; and the wing "departure"
was not abrupt - I simply ran out aileron, and the wing would start
downward. I'm guessing the inside wing tip doesn't stall, but can't be
sure about that.

Stick quickly a little bit forward restored aileron authority?

The normal spin recovery works fine; even quicker was moving the flap
lever forward to the first negative flap position. I don't recall if
only stick forward was enough.

The ASW 20 manual says applying full negative flap should be the first
spin recovery action and will often be sufficient for recovery. IME that
worked well and since, also IME, immediate recovery from an incipient
could cost 300 ft and add 40kts, full negative flap is always a good idea
since that also gives you the greatest Vne.

In case you're wondering, mine departed twice from a thermal turn with no
warning I could detect. Both times I was thermalling at a bit over 45 kts
in flap 3 (zero flap) in a well-banked turn. It was something I couldn't
replicate intentionally: I wonder if it could be connected with
microturbulence in the thermal.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

I had a Nimbus 4 depart with no warning. Was flying dry and being how slow it would thermal. A wing dropped and a quarter turn before recovery. I remember thinking there was no sign of impending stall had full roll control up to departure.

On Sunday, November 27, 2016 at 4:32:32 AM UTC-8, Martin Gregorie wrote:
On Sat, 26 Nov 2016 21:16:47 -0800, Eric Greenwell wrote:

Bruce Hoult wrote on 11/26/2016 12:40 AM:
On Saturday, November 26, 2016 at 6:50:46 AM UTC+3, Eric Greenwell
wrote:
Bob Whelan wrote on 11/22/2016 9:06 PM:
True, before the wing "let go" there was (almost always) an absence
of aerodynamic burble felt through the stick or one's butt or merely
"drummed" through the metal fuselage, but by the time the wing did
let go, "all the other usual suspects" had put in their appearances:
low wind noise; nose noticeably high; controls (especially stick)
getting sloppy; etc. Subsequent to checking out in the ship, I found
it "intellectual fun" to mess around with it in slow flight "trying
to find the burble." Abrupt departure from controlled flight - yes,
indeed! "No warning?" - not by a long shot.

The nose was not noticeably high in either glider (20 C or 26E); the
wind noise was subdued, but both gliders were very quiet, and the
change in noise was very small; there was no burble or "butt feel";
the controls were light but not unusually so; and the wing "departure"
was not abrupt - I simply ran out aileron, and the wing would start
downward. I'm guessing the inside wing tip doesn't stall, but can't be
sure about that.

Stick quickly a little bit forward restored aileron authority?

The normal spin recovery works fine; even quicker was moving the flap
lever forward to the first negative flap position. I don't recall if
only stick forward was enough.

The ASW 20 manual says applying full negative flap should be the first
spin recovery action and will often be sufficient for recovery. IME that
worked well and since, also IME, immediate recovery from an incipient
could cost 300 ft and add 40kts, full negative flap is always a good idea
since that also gives you the greatest Vne.

In case you're wondering, mine departed twice from a thermal turn with no
warning I could detect. Both times I was thermalling at a bit over 45 kts
in flap 3 (zero flap) in a well-banked turn. It was something I couldn't
replicate intentionally: I wonder if it could be connected with
microturbulence in the thermal.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

This question has generated a long string of notes about the landing pattern & few about the stall.
One important factor is speed: As we all know, aircraft fall if a wing or a large part of it goes too slow.
Why would an intelligent, thoughtful pilot like us go too slow when close to the ground (turn to final)?
Because of the vection (false motion) illusion.
At 1000ft/300 meters, the ground passes by slowly. At 200ft/60 meters, the ground passes more swiftly and *it feels as though we have sped up*!
Only with frequent glances at the ASI can we be confident of not having to respond to one of Tom Knauf's six signs of the stall. The seventh of which is the ground rushing up and the controls being all floppy.
This is independent of the shape of the circuit pattern...

One important factor is speed: As we all know, aircraft fall if a wing or a large part of it goes too slow.

The glider does not stall because you fly too slow, it stalls because the wing reaches a critical angle of attack. That is why when you deflect an aileron you can stall a good chunk of a wing.