one more for low tow

[John Firth[_4_]]

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

[Dave Doe]

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.

[Bill T]

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.

[son_of_flubber]

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?

[Dave Nadler]

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.

[son_of_flubber]

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.

[son_of_flubber]

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?

[John Firth[_4_]]

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

[[email protected]]

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

[Don Johnstone[_4_]]

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!

[SF]

One of my most memorable contest tow radio call between a ballasted glider and the tow plane:

Glider: "Five more knots <color & Type tow plane>"
Tow plane: "If I speed up any more we are not going to climb"
Glider: "If you don't speed up, we are both going to die"

The second call from the glider had a good bit of heat behind it. If it don't feel right ask for more speed. Speed and Altitude are your true friends, the rest can't be counted on when the going gets tough.

[[email protected]]

On Monday, February 24, 2014 8:00:25 PM UTC-5, Don Johnstone wrote:
> 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!

Yep- we used to it too, but more for the fun of it.
The point I was trying to make is that the probability of being too low AND having the release fail is so low as to not be worth bringing up. I was mostly just getting ahead of the "what if?" guys.
UH

[son_of_flubber]

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.

Totally goofy, but plausible.

On Monday, February 24, 2014 5:43:53 PM UTC-5, wrote:

> Now, I'll anticipate the next goofy scenario which is glider release failure.
> Let's not carry all of this too far.

Totally goofy, but implausible. We need to draw a line somewhere. I take your point.

The guy that would fail to promptly pull the release when his glider stalled on tow would be the guy who was surprised to suddenly learn that it was possible to stall a glider on tow at 60 knots, and that guy was the tug pilot in Bill T's anecdote. Best to learn these lessons on the ground.

[Chris Rollings[_2_]]

At 01:00 25 February 2014, Don Johnstone wrote:
>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!
>
>
Back in the 70's we did a few trials, at Booke, of landing with the glider
still on tow (one of the times you do use low tow) and concluded that
regularly practicing that was far more likely to cause an accident than the
very rare event (don't actually recall ever hearing of one) of release
failure at both ends. Safer and easier to deliberately break the weak
link.

[Andreas Maurer]

On Mon, 24 Feb 2014 18:43:42 -0800 (PST), son_of_flubber
> wrote:


>> Now, I'll anticipate the next goofy scenario which is glider release failure.
>> Let's not carry all of this too far.
>
>Totally goofy, but implausible. We need to draw a line somewhere. I take your point.
>
>The guy that would fail to promptly pull the release when his glider stalled on tow would be the guy who was surprised to suddenly learn that it was possible to stall a glider on tow at 60 knots, and that guy was the tug pilot in Bill T's anecdote. Best to learn these lessons on the ground.


Never say never.

Two years ago we had a freak accident in Germany where the glider
pilot was unable to release during a winch tow.

Unfortunately, the winch driver was also unable to cut the winch
cable.

With incredible skill (and some luck) the glider pilot was able to
fly most of a circle tethered to the winch, until finally the winch
cable got caught in some bushes and he crashed from only about 30 ft
of altitude.
ASW-19 badly damaged, pilot fortunately not hurt.


Andreas

[son_of_flubber]

On Tuesday, February 25, 2014 8:02:47 AM UTC-5, Andreas Maurer wrote:

> Never say never.
>
>
>
> Two years ago we had a freak accident in Germany where the glider
>
> pilot was unable to release during a winch tow.
>
>
>
> Unfortunately, the winch driver was also unable to cut the winch
>
> cable.
>
>
>
> With incredible skill (and some luck) the glider pilot was able to
>
> fly most of a circle tethered to the winch, until finally the winch
>
> cable got caught in some bushes and he crashed from only about 30 ft
>
> of altitude.
>
> ASW-19 badly damaged, pilot fortunately not hurt.

This is implausible and frankly unbelievable. I would have thought that a slack Spectra line could be cut with a sharp pocket knife.

[Don Johnstone[_4_]]

At 15:10 25 February 2014, son_of_flubber wrote:
>On Tuesday, February 25, 2014 8:02:47 AM UTC-5, Andreas Maurer wrote:
>
>> Never say never.
>>
>>
>>
>> Two years ago we had a freak accident in Germany where the glider
>>
>> pilot was unable to release during a winch tow.
>>
>>
>>
>> Unfortunately, the winch driver was also unable to cut the winch
>>
>> cable.
>>
>>
>>
>> With incredible skill (and some luck) the glider pilot was able to
>>
>> fly most of a circle tethered to the winch, until finally the winch
>>
>> cable got caught in some bushes and he crashed from only about 30 ft
>>
>> of altitude.
>>
>> ASW-19 badly damaged, pilot fortunately not hurt.
>
>This is implausible and frankly unbelievable. I would have thought that
a
>slack Spectra line could be cut with a sharp pocket knife.

It may surprise you to learn that not every one is using synthetic rope.
Wire rope is still used in many places today for various reasons.
>

[BruceGreeff]

Not that this has anything to do with low tow.

Regrettably, your incredulity needs to be stretched some more.
Flubber is quite good at that. ;-)

There was a similar incident in South Africa a few years ago.

Very experienced pilot, high drag trainer, on the second stall he worked
out the problem.
Wire was fouled on the winch so cutting at the guillotine would make no
difference.

Pilot executed a steep descending turn laying the cable down on the
ground in a wide loop around the winch.
Finished by tighetening turn to overfly the winch in a full airbrake
steep and slow final.

The cable stopped the fun about 10m after touchdown, but there was no
damage found on the glider. The "arrestor wire" was effectively lined up
behind the glider and broke at the weak link.

Couple of lessons, including
Use the correct weak link.
Use good condition OEM rings
Service your release hooks as per the manual
Have a working guillotine - and - Use it earlier rather than later (the
only thing these folk did not do)

And FINALLY - stuff still happens, so have a plan for eventualities.

On 2014/02/25 5:10 PM, son_of_flubber wrote:
> On Tuesday, February 25, 2014 8:02:47 AM UTC-5, Andreas Maurer wrote:
>
>> Never say never.
>>
>>
>>
>> Two years ago we had a freak accident in Germany where the glider
>>
>> pilot was unable to release during a winch tow.
>>
>>
>>
>> Unfortunately, the winch driver was also unable to cut the winch
>>
>> cable.
>>
>>
>>
>> With incredible skill (and some luck) the glider pilot was able to
>>
>> fly most of a circle tethered to the winch, until finally the winch
>>
>> cable got caught in some bushes and he crashed from only about 30 ft
>>
>> of altitude.
>>
>> ASW-19 badly damaged, pilot fortunately not hurt.
>
> This is implausible and frankly unbelievable. I would have thought that a slack Spectra line could be cut with a sharp pocket knife.
>

--
Bruce Greeff
T59D #1771

[Eric Munk]

>This is implausible and frankly unbelievable. I would have thought that
a
>slack Spectra line could be cut with a sharp pocket knife.

Yet, it is true.

Report here:
http://www.bfu-web.de/DE/Publikationen/Untersuchungsberichte/2012/Bericht_12_3X100_ASW19_Kirn.pdf?__blob=publication File

[Eric Munk]

For my tow license I had to demonstrate a tow down to the deck all the way
from 1500 feet, while behind tow.

'it'll never happen for real' -> some years later I watched a Blanik doing
a formation landing after the two rope got tangled around the bungee hook,
including the weaklink. No cutter on the towplane. All landed safely in
tight formation.