poor lateral control on a slow tow?

On Jan 1, 11:15*am, Doug Greenwell wrote:
At 20:23 31 December 2010, bildan wrote:





On Dec 31, 1:06=A0pm, Todd *wrote:
I too agree with the real or perceived tow handling characteristics.

Looking at things =A0from and aerodynamics standpoint (and I am about
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. =A0Then 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. *A pilot trying to hold a precise position behind
a tug needs and expects crisp aileron response. *When he doesn't get
it, he increases the amount and frequency of aileron with a
corresponding increase in adverse yaw. *If 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. *The 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