poor lateral control on a slow tow?

At 12:27 06 January 2011, cernauta wrote:
On Wed, 05 Jan 2011 17:52:28 +0000, Doug Greenwell
wrote:


Did you notice any kind of change in elevator control force before you
hit
the stops?

i didn't notice, I was probably busy trying to keep altitude behind
the tug

Did you experience this effect with any specific type of tug? Derek
Copeland has decribed a similar loss of elevator authority when towed
by
a
motor glider.

Andreas says that it's much less likely to happen bihind a
motorglider, however.
In my case, I'm not sure, it may have been both times a Robin dr400.

I think the "descending airmass" theory by Andreas is the easiest to
understand and believe. It explains both the running out of elevator,
and the poor lateral control (when not perfectly centered behind the
tug, or because of the increased AoA at the tips)

aldo cernezzi
-
www.voloavela.it
the italian gliding magazine



Yes - it's really difficult to explain in words, but Andreas'
description is good without being too technical.

On Jan 5, 10:52*am, Doug Greenwell wrote:
At 17:25 05 January 2011, cernauta wrote:



On Fri, 31 Dec 2010 11:40:53 -0000, "Doug"
wrote:

Is poor handling at low speed on tow a common experience? *I'd
appreciate

any thoughts/comments/war stories ... particularly bad tug/glider/speed
combinations, incidents of wing drop during a tow etc etc?

Yes, it is common. I use to fly mainly at competitions, and among the
5-10 tow pilots, there's always at least one who, despite being
briefed by the towmaster, flies too slowly.

In my personal experience, it happened to me 3 times in a double
seater (Janus B and DuoDiscus). I don't remember any occurrence in my
single seater.
I can describe it as being unable to raise the nose. As the towplane
was flying below 100 km/h, I just couldn't match the climbing rate
with the glider, so I was more and more into the propwash. A gentle
pull up wouldn't work; pulling more hits the stop and the glider feels
like it's sinking.

I also cannot find an easy and believable explanation for this
phenomenon. I didn't recognize a lack of _lateral_ control, anyway.

aldo cernezzi

Interesting - most people are reporting problems with lateral control
(which seems to have a reasonably simple explanation), but running out of
nose-up pitch control also seems to occur ... and is harder to understand..

Did you notice any kind of change in elevator control force before you hit
the stops? *
Did you experience this effect with any specific type of tug? *Derek
Copeland has decribed a similar loss of elevator authority when towed by a
motor glider.

Doug

I have also experienced the reduced of elevator authority effect while
towing a ballasted ASW-28 on a CG hook behind a Pawnee. Each time I
found myself in the top of the tug wake with a very loose feel to the
elevator and needing close to full back stick to get out of the wake
and wondering if that was gong to be effective. I favor a normal tow
position just above the wake rather than the super high position that
seems to be more common in U.S. That may mean it's more likely I'll
see this effect on a slow tow than others that tow higher. In smooth
air at a reasonable tow speed the ASW-28 on the CG hook will tow stick
free and maintain normal tow position for 5-10 seconds.

Andy

At 13:31 06 January 2011, Andy wrote:
On Jan 5, 10:52=A0am, Doug Greenwell wrote:
At 17:25 05 January 2011, cernauta wrote:



On Fri, 31 Dec 2010 11:40:53 -0000, "Doug"
wrote:

Is poor handling at low speed on tow a common experience? =A0I'd
appreciate

any thoughts/comments/war stories ... particularly bad
tug/glider/speed
combinations, incidents of wing drop during a tow etc etc?

Yes, it is common. I use to fly mainly at competitions, and among the
5-10 tow pilots, there's always at least one who, despite being
briefed by the towmaster, flies too slowly.

In my personal experience, it happened to me 3 times in a double
seater (Janus B and DuoDiscus). I don't remember any occurrence in
my
single seater.
I can describe it as being unable to raise the nose. As the towplane
was flying below 100 km/h, I just couldn't match the climbing rate
with the glider, so I was more and more into the propwash. A gentle
pull up wouldn't work; pulling more hits the stop and the glider
feels
like it's sinking.

I also cannot find an easy and believable explanation for this
phenomenon. I didn't recognize a lack of _lateral_ control, anyway.

aldo cernezzi

Interesting - most people are reporting problems with lateral control
(which seems to have a reasonably simple explanation), but running out
of
nose-up pitch control also seems to occur ... and is harder to
understand=
..

Did you notice any kind of change in elevator control force before you
hi=
t
the stops? =A0
Did you experience this effect with any specific type of tug? =A0Derek
Copeland has decribed a similar loss of elevator authority when towed
by
=
a
motor glider.

Doug

I have also experienced the reduced of elevator authority effect while
towing a ballasted ASW-28 on a CG hook behind a Pawnee. Each time I
found myself in the top of the tug wake with a very loose feel to the
elevator and needing close to full back stick to get out of the wake
and wondering if that was gong to be effective. I favor a normal tow
position just above the wake rather than the super high position that
seems to be more common in U.S. That may mean it's more likely I'll
see this effect on a slow tow than others that tow higher. In smooth
air at a reasonable tow speed the ASW-28 on the CG hook will tow stick
free and maintain normal tow position for 5-10 seconds.

Andy


This is interesting, because with a reasonable airspeed (even at a very
slow 50kts) the elevator shouldn't feel 'loose', since there should
still be airflow over it. Possibilities I can think of at the moment are
that either the airflow over the elevator is being disrupted due to an
upstream separation (wing or fuselage flow) or that the tailplane has
stalled due to the increased downwash from the tug.