On Jan 3, 11:10*pm, Darryl Ramm wrote:
On Jan 3, 5:23*pm, "
wrote:





On Jan 3, 6:30*pm, ProfChrisReed wrote:

It seems to me that increased AoA must be a very large part of the
cause.

Imagine you are flying free @55kt. You have a sink rate of, say,
1.5kt. Now you are on tow, again @55kt, but this time the combination
is climbing @5kt. Your wings are generating 6.5kt more lift than in
free flight, and must therefore be at a substantially higher AoA.

Additionally, the faster you are climbing (in still air) the greater
the AoA must be for you to keep station with the tug.

I fly an Open Cirrus, towing from the C of G hook without ballast, and
never experienced this at my previous club which had a Citabria tug.
My current club has a Pawnee, and I have from time to time felt the
tow was too slow because the controls felt mushy and the glider
wallowed about, feeling as if it was close to the stall. The Pawnee
climbs much faster than the Citabria.

If in addition the tug's slipstream imparts a downward flow to the
airmass, even more lift and higher AoA is required.

I also disagree with you statement that the AoA *must be greater if
you climb more rapidly......not so....

Assuming a constant airspeed....

The rate of climb is strictly a factor of the power available. * More
powerful towplane = faster rate of climb......lift on the glider's
wing, and the *towlane'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 (=steeper 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.

Darryl- Hide quoted text -

- Show quoted text -

Do some simple vector diagrams....lift, weight drag and thrust.....do
these for various climb, (and glide) angles)... you will soon see that
the greatest lift occurs at "level" flight......the steeper the climb,
or the steeper the descent, the less the lift.

You will see that to achieve steep climb 9with constant airspeed) , we
need only to increase the thrust vector.......more power required.

In level flight, power is required......lift = weight lift tapers
off to zero as we approach straight up flight, and / or straight down
flight. In descending flight (gliding) less and less power is
required as we steepen the descent, until we reach best L/D, when no
power at all is required.

What you are thinking about is trying to increase climb angle with a
fixed amount of power.......to do this we have to increase the angle
of attack, and of course fly slower........Vx....Vy.......come in to
play now.......best rate, best angle ....at fixed power, we vary speed
and AoA to achieve Vx or Vy or whaterver rate or angle we want.....


But if we have a very powerful towplane, we can climb fairly steeply,
at a normal towing speed, and the AoA will be fairly low, certainly
not near stall....


But remember the premise of this discussion.......towing at a speed at
which the glider performs nicely in gliding flight, yet had control
issues in towing flight.....but speed constant. A glider which will
"glide" nicely at say 50 MPH, may not tow nicely at 50
MPH.............vector diagrams will show that the lift is nearly the
same in both cases, therefore the AoA is about the same........so some
or all of the other factor discussed in this thread must come into
play.

But rapid climb rate = high AoA is a fallacy.

High climb rate = high power is correct.


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