poor lateral control on a slow tow?

At 13:24 02 January 2011, wrote:
On Jan 2, 2:49=A0am, Doug Greenwell wrote:
At 03:11 02 January 2011, wrote:



On Jan 1, 10:34=3DA0am, Doug Greenwell =A0wrote:
At 15:09 01 January 2011, Derek C wrote:

On Jan 1, 11:15=3D3DA0am, Doug Greenwell =3DA0wrote:
At 20:23 31 December 2010, bildan wrote:

On Dec 31, 1:06=3D3D3DA0pm, Todd =3D3DA0wrote:
I too agree with the real or perceived tow handling
characteristics.

Looking at things =3D3D3DA0from and aerodynamics standpoint
(and=
I
am
abou=3D3D
t
as
far from and aerodynamicist as you can get) it should seem
that
part
of the empirical data would suggest an experiment where you
fly
a
glider equipped with and Angel of Attack meter at your
typical
tow
speeds and record the AoA at various speeds. =3D3D3DA0Then
fly
that
glider
on
tow at those same speeds and record the results.

Done that - and as nearly as I can see, there's no difference
in
AoA.

I've flown some pretty heavy high performance gliders behind
some
pretty bad tow pilots - one of them stalled the tug with me on
tow.
If I'm careful not to over-control the ailerons, there's no
problem
at
all.

Heavily ballasted gliders respond sluggishly in roll just due
to
the
extra roll inertia. =3D3DA0A pilot trying to hold a precise
positi=
on
behind
a tug needs and expects crisp aileron response. =3D3DA0When he
doesn't
get
it, he increases the amount and frequency of aileron with a
corresponding increase in adverse yaw. =3D3DA0If he's less
than
equally
crisp with rudder to oppose the adverse yaw, it gets wobbly.

Where did you mount the AoA meter?

It's not the angle of attack that's the problem, but the
change
in
local
incidence along the wing. =3D3DA0The overall lift may not change
by
very
much
when near to the tug wake, but its distribution along the wing
does,
with
increased lift at the tips and reduced lift at the root -
putting
the
aileron region close to the stall and hence reducing control
effectiveness.

I agree that increased roll inertia due to ballast is a factor,
but
since
the same factor applies to maintaining bank angle in a
thermalling
turn
I
don't see how it can account for a significant difference in
handling
between tow and thermalling?- Hide quoted text -

- Show quoted text -

What started the debate at Lasham was using a Rotax engined Falke
as
a
glider tug. This towed best at about 50 to 55 knots (c.f. 60+
knots
with a normal tug), but K13s with a stalling speed of 36 knots
felt
very unhappy behind it, especially two up. In a conventional
powered
aircraft you pull the nose up (to increase the angle of attack and
produce more lift) and increase power to climb, the extra power
being
used to prevent the aircraft from slowing down. I don't see why
gliders should behave any differently, except that the power is
coming
from an external source. As you try not to tow in the wake and
downwash from the tug, I can't see that this is particularly
significant,

Derek C

In a steady climb in any light aircraft the climb angles are so low
(
10deg) that the lift remains pretty well equal to weight. =3DA0For
examp=
le
=3D
a
10deg climb angle at 60 kts corresponds to an impressive climb rate
of
10.5kts - but that would only give Lift =3D3D Weight/cos(10deg)
=3D3D
=
1.02
x
Weight. =3DA0You don't need to increase lift to climb - you
increase
thrust
to overcome the aft component of the weight, and the stick comes
back
to
maintain speed ... at constant speed the increased power input
comes
out
as increasing potential energy =3D3D increasing height.

I think a lot of people confuse the actions needed to initiate a
climb
with what is actually happening in a steady climb. =3DA0

On your second point, if you are on tow anywhere sensible behind a
tug
yo=3D
u
are in its wake and are being affected by the wing downwash.
=3DA0Wake
is
n=3D
ot
really a good word, since it seems to get confused with the much
more
localised (and turbulent) propwash.

A (very) crude way of visualising the affected wake area is to
imagine
a
cylinder with a diameter equal to the tug wing span extending back
from
the tug - that's the downwash region, and then in addition
there's
an
upwash region extending perhaps another half-span out either side.-
Hide
=3D
quoted text -

- Show quoted text -

"aft component of weight??"

Not that this adds anything to the discussion, but.....weight acts in
a "downward" direction toward the center of the earth.

In a climb, on tow, the "aft" forces are drag (mostly) and a small
bit
of lift.

Anyway, interesting topic.......has been beat to death at our local
field...EVERY pilot seems to have had it happen, in all different
kinds of gliders......many explainations....not one all-encompassing
explaination yet.

Cookie

it depends on your reference frame - lift and drag are perpendicular
to
the direction of motion (relative to the air), which is inclined
upwards
=
-
so if you take 'aft' as relative to the glider flight path rather
than
the earth, then there is an aft component of weight.- Hide quoted text
-

- Show quoted text -

Lift is perpendicular.......drag is parallel........


... oh alright - I left a few words out :-)

At 15:06 02 January 2011, n7ly wrote:
..
=A0'Actually the only totally reliable sysmptom of being stalled is
that
the elevator will no longer raise the nose.'

HUH? =A0 Many cases possible where we could have full elevator and not
be stalled. =A0(I demonstrate this is 2-33 and grob 103 and ask-21.
All you need is heavy pilot (forward CG) and gentle stick back to the
stop. =A0Glider will mush, but not stall. =A0Elevator will not raise
the
nose........wing does not have angle to stall.

..
whoa - depends on who's defining "stall". The FAA definition is
indeed
that when the aircraft does not respond in the direction of the
control input that it's done. When you can no longer move the elevator
up, you're done. Nose doesn't respond in direction of aft stick
deflection, you're stalled. I don't remember exactly the way they
word it, but the result is that touch the elevator limit, that's it.
Slow entry rates result in higher stall speeds. Forward cg's give
higher stall speeds. Trim settings (on some configs) affect stall
speeds. Weight, etc., etc. The scene that seems the most insidious
is the slow entry rate. They sneak up on you, kind of like a slow tow.


Not necessarily - have the CG too far forward, and you'll run out of
elevator before you stall.

Admittedly that is still a stall according to FAR23/25 definitions
"a stall is produced, as shown by either:
(1) An uncontrollable downward
pitching motion of the airplane;
(2) A downward pitching motion of
the airplane that results from the activation
of a stall avoidance device (for
example, stick pusher); or
(3) The control reaching the stop."

At 15:06 02 January 2011, n7ly wrote:
..
=A0'Actually the only totally reliable sysmptom of being stalled is
that
the elevator will no longer raise the nose.'

HUH? =A0 Many cases possible where we could have full elevator and not
be stalled. =A0(I demonstrate this is 2-33 and grob 103 and ask-21.
All you need is heavy pilot (forward CG) and gentle stick back to the
stop. =A0Glider will mush, but not stall. =A0Elevator will not raise
the
nose........wing does not have angle to stall.

..
whoa - depends on who's defining "stall". The FAA definition is
indeed
that when the aircraft does not respond in the direction of the
control input that it's done. When you can no longer move the elevator
up, you're done. Nose doesn't respond in direction of aft stick
deflection, you're stalled. I don't remember exactly the way they
word it, but the result is that touch the elevator limit, that's it.
Slow entry rates result in higher stall speeds. Forward cg's give
higher stall speeds. Trim settings (on some configs) affect stall
speeds. Weight, etc., etc. The scene that seems the most insidious
is the slow entry rate. They sneak up on you, kind of like a slow tow.


Not necessarily - have the CG too far forward, and you'll run out of
elevator before you stall.

Admittedly that is still a stall according to FAR23/25 definitions
"a stall is produced, as shown by either:
(1) An uncontrollable downward
pitching motion of the airplane;
(2) A downward pitching motion of
the airplane that results from the activation
of a stall avoidance device (for
example, stick pusher); or
(3) The control reaching the stop."

On Jan 2, 1:20*pm, "
wrote:

*'Actually the only totally reliable sysmptom of being stalled is that

the elevator will no longer raise the nose.'

HUH? * Many cases possible where we could have full elevator and not
be stalled. *(I demonstrate this is 2-33 and grob 103 and ask-21.
All you need is heavy pilot (forward CG) and gentle stick back to the
stop. *Glider will mush, but not stall. *Elevator will not raise the
nose........wing does not have angle to stall.

On tow the only additional "weight component" would be a downward
component to the tow rope (thrust). *Since the tension on the tow rope
is fairly low........it should *not have a big effect, but there is
some effect.

But yeah, that extra 10 knots makes all the difference in the world.
(I remember occasionally getting a "slow tow" when flying a 2-32 with
three aboard..........what a handful!!!
Cookie

I know that you have some 'persons of size' out in the States, but I
have never flown a glider that could not stalled in straight flight
with a legal weight (less than 110kg, 242lbs) person in the front
seat. This includes the K21 and the G103. Sometimes you run out of
trim when circling in a thermal with such folk. I weigh about 190lbs
by the way.

Derek C

At 18:34 02 January 2011, kirk.stant wrote:
On Jan 1, 12:44=A0pm, Free Flight 107 wrote:
On Jan 1, 3:21=A0am, Doug Greenwell wrote: At 0=
6:24 01 January 2011, Anne wrote:

I've certainly sparked some interest here - considering it's New
Year
:-)- Hide quoted text -

And I mignt add this is a very fast moving discussion too! While I was
loging in 2 messages were posted..

Concerning the Tow Plane position while on tow, two of my CFIs have
said to position yourglider as if you were going to Machine Gun the
pilot of the Tow Plane. this is equivelent of aligning the horizontal
of the TP with a portion of his foweward fuslage, like the wheels on a
Pawnee.

Works great in all conditions I've come accross in 15 years flying 8
different types from 2-33 to Duo Discuss. Never been criticized for it
either in BFRs.

Wayne

Without a gunsight, how do you do that? ;^)

I don't understand why the high tow position is taught by reference to
the towplane or horizon, when what should be taught is how to find the
correct tow position (just above or below the wake, which is actually
the propwash). Simple - once safely airborne (usually before the
towplane), just ease down until you feel the towplanes turbulence,
then ease up a bit. THEN look at the towplane and pick whatever
convenient references you need to maintain this vertical alignment.
Any significant change in towplane speed will require a readjustment
of the tow position (normally only a factor if on an aerotow
retrieve).

Obviously, if you only tow behind the same towplane on every flight,
you will quickly learn where to position your glider. But if you have
a variety of towplanes, or are towing behind something different
(Agcat, Wilga, AN-2, whatever) for the first time, you can use this
process to find the correct position quickly.

Many US instructors seem to only teach HOW to do something without
going into WHY it is done. As a result, there are a lot of "shortcuts"
being taught, and a lot of poorly trained pilots, IMHO. A result of
not having a standardized curriculum, a la BGA, perhaps?

Kirk
66



This is what I was taught - once I'd done a few tows it seemed pretty
straightforward even for an inexperienced pilot like me.

I know that you have some 'persons of size' out in the States, but I
have never flown a glider that could not stalled in straight flight

Not that this adds to the main discussion, but...

160lb (normal sized) pilot here... my SZD-59 couldn't be stalled
straight ahead without 'tricking' it (ease nose up till *near stall
and yank the stick for the last bit of travel). No mods were done to
plane to cause this, and a reliable W&B with me in it determined C/G
to be at 37%, well within the limits (it's JAR22 cert'd...). This is
actually common with this ship as well as the Jantar Std3 from which
it's derived. I added 5.5lbs to the tail via a brass/lead tailwheel
and now fly it at 50%, where it flies much nicer, with an honest (and
predictable) stall and a more usable trim range. At some point I'm
going to make an externally visible, removable weight set (replacement
rudder hinge access panels milled out of brass or tungsten) to add up
to 3 more lbs, to get it to 65% for mid-late season flying but plan on
leaving it at 50% for early season.

-p

On Jan 3, 12:01*am, Derek C wrote:
Actually the only totally reliable sysmptom of being stalled is that
the elevator will no longer raise the nose.

But that is neither necessary nor sufficient!

If you put enough weight in the front cockpit then there are plenty of
gliders where you reach the back stop while they are still flying just
fine.

Conversely, there are also plenty of gliders with sufficiently
powerful elevators that the wing can be stalled and you're mushing at
500+ fpm but you still have perfect control over the attitude of the
nose and can raise or lower it at will. Not to mention other aircraft
such as the F/A-18 which can be flown in perfect control with the wing
stalled at huge angles of attack.

I see in another post the definition:

Admittedly that is still a stall according to FAR23/25 definitions "a stall is produced, as shown by either:
(1) An uncontrollable downward pitching motion of the airplane;
(2) A downward pitching motion of the airplane that results from the activation of a stall avoidance device (for example, stick pusher); or
(3) The control reaching the stop."

Without having that document in front of me I will hazard a guess that
this is not a definition of a stall, but rather a definition of the
standards for what a pilot should do in order to pass a practical
flight examination. They're not going to fail him when the aircraft
fails to actually stall because the elevator reaches its stop first,
so they explicitly allow that as a signal that the pilot is allowed to
terminate the "stall" attempt and commence the stall recovery
procedure.

The only true definition of a stall is when the wing is at an angle of
attack such that a further increase of AoA produces a decrease of
lift.

*Usually* this will be accompanied by a large increase in drag such
that the combination of lift and drag is easily capable of supporting
the aircraft against gravity at a low speed and steep nose up descent
angle, but that may not necessarily always be the case and some
aircraft might speed up while stalled (perhaps at high altitude?).

The discussion of forces surrounding a climb on high tow has been
interesting.
However, has anyone considered descent on tow?

A SGS 2-33 glider descending on tow behind a Cessna 182 has some
interesting lateral control issues.
* Descending behind a 182 with 10 degrees of flap at 65 mph in high
tow with full spoilers is reasonably stable.
* At 40 degrees of flap the 2-33 is almost uncontrollable. You need
full stick and some patience to recover from the frequent level flight
excursions.
The 182 high lift/high drag wake is the obvious difference.

Would anyone care to venture an analysis or opinion?

Cheers, John Chapman, 1DG

On Jan 2, 1:34*pm, "kirk.stant" wrote:
On Jan 1, 12:44*pm, Free Flight 107 wrote:





On Jan 1, 3:21*am, Doug Greenwell wrote: At 06:24 01 January 2011, Anne wrote:

I've certainly sparked some interest here - considering it's New Year
:-)- Hide quoted text -

And I mignt add this is a very fast moving discussion too! While I was
loging in 2 messages were posted..

Concerning the Tow Plane position while on tow, two of my CFIs have
said to position yourglider as if you were going to Machine Gun the
pilot of the Tow Plane. this is equivelent of aligning the horizontal
of the TP with a portion of his foweward fuslage, like the wheels on a
Pawnee.

Works great in all conditions I've come accross in 15 years flying 8
different types from 2-33 to Duo Discuss. Never been criticized for it
either in BFRs.

Wayne

Without a gunsight, how do you do that? ;^)

I don't understand why the high tow position is taught by reference to
the towplane or horizon, when what should be taught is how to find the
correct tow position (just above or below the wake, which is actually
the propwash). *Simple - once safely airborne (usually before the
towplane), just ease down until you feel the towplanes turbulence,
then ease up a bit. *THEN look at the towplane and pick whatever
convenient references you need to maintain this vertical alignment.
Any significant change in towplane speed will require a readjustment
of the tow position (normally only a factor if on an aerotow
retrieve).

Obviously, if you only tow behind the same towplane on every flight,
you will quickly learn where to position your glider. *But if you have
a variety of towplanes, or are towing behind something different
(Agcat, Wilga, AN-2, whatever) for the first time, you can use this
process to find the correct position quickly.

Many US instructors seem to only teach HOW to do something without
going into WHY it is done. As a result, there are a lot of "shortcuts"
being taught, and a lot of poorly trained pilots, IMHO. *A result of
not having a standardized curriculum, a la BGA, perhaps?

Kirk
66- Hide quoted text -

- Show quoted text -

This is one of my pet peeves.........I don't like to use the term
"high tow" because beginners seem to assume it means that the glider
is flying higher than the tow plane. I use the terms "normal tow"
and low tow. (because around here we noramlly tow above the wake.)

But I do take the time to explain to my students that "high" tow means
"high" compared to the wake(not campared to the tow plane), and you
need only to be above the wake a little, and low tow is "low" compared
to the wake, and you want ot be just barely below the wake. Also that
flying "too high" on tow is a "mortal sin", and extremely dangerous.
In rough air gliders seem more prone to "bounce up" than to "bounce
down" so if your already running toward the high side on tow, one or
two good bounces will make you too high. If you fly just above the
wake, you have room to "bounce up" once or twice, and have time to re-
position, before getting "too high" giving the tow pilot a hard time.

As far as visual reference....there are several....some pilots and
some instructors seem to prefer some or one more than others. I like
to use the tow plane compared to the horizion. Another is the
position of the tow plane in the glider's canopy...if the towplane
appears low in the canopy, like under the inst panel, the glider is
too high......if the tow plane appears way high above the inst panel,
the glider is too low. My least favorite visual is lining up stuff on
the tow plane itself, like top of fin to pilot's head, or stab to
strut or whatever.....every make and modlel of tow plane is different,
and tow pilot may change pitch attitude........The problem with the
horizon method is if in hilly or mountainous terrain, the horizon is
not always visible, students sometimes use the wrong reference
then...The best is to use a sort of combination of all the visual
references at once......not hard after the student has a few flight
under the belt.

On X-C retreive, I find that once the towplane levels out, that the
wake goes way high, and to fly above the wake makes the glider too
high.......I recommend, and usually go to low tow then...and since the
wake is way up there, the low tow is not very low at all. In fact
I've done low tow retreives that were higher than some high tows
behind a strong tow plane!


Cookie

On Jan 2, 3:13*pm, Derek C wrote:
On Jan 2, 1:20*pm, "
wrote:







*'Actually the only totally reliable sysmptom of being stalled is that

the elevator will no longer raise the nose.'

HUH? * Many cases possible where we could have full elevator and not
be stalled. *(I demonstrate this is 2-33 and grob 103 and ask-21.
All you need is heavy pilot (forward CG) and gentle stick back to the
stop. *Glider will mush, but not stall. *Elevator will not raise the
nose........wing does not have angle to stall.

On tow the only additional "weight component" would be a downward
component to the tow rope (thrust). *Since the tension on the tow rope
is fairly low........it should *not have a big effect, but there is
some effect.

But yeah, that extra 10 knots makes all the difference in the world.
(I remember occasionally getting a "slow tow" when flying a 2-32 with
three aboard..........what a handful!!!
Cookie

I know that you have some 'persons of size' out in the States, but I
have never flown a glider that could not stalled in straight flight
with a legal weight (less than 110kg, 242lbs) person in the front
seat. This includes the K21 and the G103. Sometimes you run out of
trim when circling in a thermal with such folk. I weigh about 190lbs
by the way.

Derek C- Hide quoted text -

- Show quoted text -

I didn't say you "can't" stall these gliders. What I did say was that
you "can" get the stick back to the rear stop, without stalling, if
you are gentle, and if the GC is forward.

But then again.....a couple of new (to me) definitions of "stall" have
come up. I just attended a FAA seminar on stalls, and nobody defined
stall as "stick all the way back and nose won't come up".

I still go by the definition of stall as "when the angle of attack of
the wing reaches or exceeds the critical angle. "

Cookie