At 07:51 04 January 2011, Darryl Ramm wrote:
On Jan 3, 8:54=A0pm, Eric Greenwell wrote:
On 1/3/2011 8:10 PM, Darryl Ramm wrote:



On Jan 3, 5:23 pm, "
The rate of climb is strictly a factor of the power available. =A0
Mor=
e
powerful towplane =3D faster rate of climb......lift on the
glider's
wing, and the =A0towlane's wing stays practically constant,
therefore
the angle of attack is just about constant.

It is the climb angle (direction of flight) which changes with
power,
not the AoA.

Cookie

Ugh?

The glider is flying, the towplane is not dragging the glider up an
incline. If the combination is going up faster (=3Dsteeper climb
rate/
angle) then both aircraft wings are generating more lift and they
get
this this from some combination of increased AoA and airspeed. The
more powerful towplane may allow both aircraft to fly at an
increased
AoA and overcome the associated drag. The increased climb angle
comes
from the increased lift. Assuming a constant airspeed means all the
increase is coming from an increase in AoA and the more powerful
towplane thrust is offsetting the increased drag. I'd be interested
to
see an explanation of any other way of generating an increase in
climb
angle without increasing the lift of the glider and/pr towplane.

Actually, I do think the towplane is pulling the glider up an incline!
The flight path is inclined, and the towplane is the only one that can
provide the force. In fact, I think the lift required *decreases* with
increased climb rate during tow! How could that be? The tow rope
provides some of the force needed to hold the glider in the air.

Imagine an extreme tow, a 50 knot airspeed, but climbing at 35 knots
(45
degree angle). The tow rope is providing 70% of the force holding the
glider in the air, so the wing needs to supply only 30% of the force.

Or imagine a really extreme, vertical tow: all the force required to
keep the glider moving steadily through the air is provided by the
towrope/towplane, and none by the wing.

Let the games begin!

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us"
to
email me)

I think you are trying to push this argument up an incline with a
rope. :-) But I'll take your points into consideration next time I'm
vertically towing behind a helicopter.

---

I think Chris Reed well nailed the (somewhat bleeding obvious when you
think about it) issue here with AoA and handling on slow tow.

Darryl



That's the problem with aeroplanes of any sort - the bleeding obvious is
not always right. I mean, it's obvious that if I'm a bit low on
approach I can stretch the glide by pulling back a bit more ... and a bit
more ... and ....