one more for low tow

On aerotow in Oz in a Libelle std ( with ballast) behind
a Pawnee, the airspeed decayed to a value uncomfortably
close to stall; full back stick failed to hold the
the low tow position and I sank low enough ( with my hand on the (release)
that the rope contributed enough nose up to stabilise
the position using rudder and not ailerons to stay level.

It was later explained that the Pawnee ASI was kaput.
JMF

In article , johnfirth0
@gmail.com, John Firth says...

On aerotow in Oz in a Libelle std ( with ballast) behind
a Pawnee, the airspeed decayed to a value uncomfortably
close to stall; full back stick failed to hold the
the low tow position and I sank low enough ( with my hand on the (release)
that the rope contributed enough nose up to stabilise
the position using rudder and not ailerons to stay level.

It was later explained that the Pawnee ASI was kaput.
JMF

Interesting - what's the tow pilot got to say? One would have thought,
"it doesn't feel right, it feels slow, it sounds slow..." ???

--
Duncan.

I know a Libelle is light on tow, especially for a Pawnee.
But as a Pawnee tow pilot, I fly pitch attitude, keep the eyes outside, the ASI is for reference!

We did have a similar incident here many years ago, not our operation.
Tow pilot got slow on climbout, brand new DG300 stalled on tow below 150ft AGL, glider released and hard landing destroyed the glider.
Pilot walked away, slightly sore.

BillT.

On Sunday, February 23, 2014 9:40:18 PM UTC-5, Bill T wrote:

Tow pilot got slow on climbout, brand new DG300 stalled on tow below 150ft AGL, glider released and hard landing destroyed the glider.

There's something important here that I don't understand.

I understand that irrespective of air speed, wing stall happens when the wing exceeds critical angle of attack. I assume that the DG300 is in high tow position (aka level tow) and that the glider and the Pawnee are therefore both in level flight. (Or is a glider on tow not "in level flight" and therefore capable of stalling at a higher airspeed than off-tow-stall-speed?)

Is the stall speed of the Pawnee lower than the DG300 or is there something else going on here?

Tangentially related, what happens to the tow plane if the glider stalls while the glider is in low tow position?

On Sunday, February 23, 2014 10:28:21 PM UTC-5, son_of_flubber wrote:
There's something important here that I don't understand.

For sure, see postings from Andreas Maurer, myself, etc...


Is the stall speed of the Pawnee lower than the DG300 or is
there something else going on here?

Glider controllable speed and stall speed are much higher
on tow than in free air, especially behind a Pawnee.

On Sunday, February 23, 2014 10:32:59 PM UTC-5, Dave Nadler wrote:
On Sunday, February 23, 2014 10:28:21 PM UTC-5, son_of_flubber wrote:

There's something important here that I don't understand.

For sure, see postings from Andreas Maurer, myself, etc...

I did a search and found a whole lot of posts.

Glider controllable speed and stall speed are much higher
on tow than in free air, especially behind a Pawnee.

Thanks for the tip.

On Sunday, February 23, 2014 10:28:21 PM UTC-5, son_of_flubber wrote:
On Sunday, February 23, 2014 9:40:18 PM UTC-5, Bill T wrote:



Tow pilot got slow on climbout, brand new DG300 stalled on tow below 150ft AGL, glider released and hard landing destroyed the glider.

There's something important here that I don't understand.

Okay. I think I got it.

At the speed determined by the tow plane and with the glider wing at less than the critical angle of attack, the glider does not generate enough lift to increase altitude at the same rate as the tow plane. This is possible even if tow plane (and glider) are flying above the level flight stall speed of the glider.

So falling below tow position, glider pilot increases AOA to increase lift, and in doing so achieves the critical angle of attack, at which point the glider wing stalls, and the glider goes nose down. Glider pilot pulls release.

So if the glider does not release immediately after stalling on tow, the tow rope pulls the tail of the tow plane down, puts the wing of the tow plane above critical angle of attack, and stalls the tow plane?

At 02:16 24 February 2014, Dave Doe wrote:
In article , johnfirth0
, John Firth says...

On aerotow in Oz in a Libelle std ( with ballast) behind
a Pawnee, the airspeed decayed to a value uncomfortably
close to stall; full back stick failed to hold the
the low tow position and I sank low enough ( with my hand on the
(release)
that the rope contributed enough nose up to stabilise
the position using rudder and not ailerons to stay level.

It was later explained that the Pawnee ASI was kaput.
JMF

Interesting - what's the tow pilot got to say? One would have thought,
"it doesn't feel right, it feels slow, it sounds slow..." ???

--
Duncan.

Most of those towpilots at that contest were crop sprayers
moonlighting for extra cash.
JMF

On Monday, February 24, 2014 3:08:07 PM UTC-5, son_of_flubber wrote:
On Sunday, February 23, 2014 10:28:21 PM UTC-5, son_of_flubber wrote: On Sunday, February 23, 2014 9:40:18 PM UTC-5, Bill T wrote: Tow pilot got slow on climbout, brand new DG300 stalled on tow below 150ft AGL, glider released and hard landing destroyed the glider. There's something important here that I don't understand. Okay. I think I got it. At the speed determined by the tow plane and with the glider wing at less than the critical angle of attack, the glider does not generate enough lift to increase altitude at the same rate as the tow plane. This is possible even if tow plane (and glider) are flying above the level flight stall speed of the glider. So falling below tow position, glider pilot increases AOA to increase lift, and in doing so achieves the critical angle of attack, at which point the glider wing stalls, and the glider goes nose down. Glider pilot pulls release. So if the glider does not release immediately after stalling on tow, the tow rope pulls the tail of the tow plane down, puts the wing of the tow plane above critical angle of attack, and stalls the tow plane?

The scenario you describe of the glider yanking the tail of the tow plane down and stalling the tow plane is one that I have never heard of happening.
I would find it impossible to believe a glider pilot would not release, as the DG300 pilot did.
Now, I'll anticipate the next goofy scenario which is glider release failure.
Let's not carry all of this too far.
UH

At 22:43 24 February 2014, wrote:

Now, I'll anticipate the next goofy scenario which is glider release
failur=
e.
Let's not carry all of this too far.=20
UH

Not so far into the past at the RAFGSA centre, Bicester UK budding
instructors on courses were required to simulate a fail to release at both
ends and land behind the tug. I **** you not!