Martin Gregorie wrote on 12/19/2020 6:52 PM:
On Sat, 19 Dec 2020 16:24:01 -0800, Eric Greenwell wrote:

As we all know, tow ropes do not break in steady flight! It's dynamic
loads from turbulence and piloting that put the peak loads on the rope;
nonetheless, the average load (say, over 1 minute) will be close to the
simple physics of lifting the weight of the glider at the rate of climb.
That number doesn't have much value in our operational choices, I think.

Yep. I only made an attempt at calculating it a while back because I was
curious about the tension in the tow rope under during normal operating
conditions.

I think there are other towing factors that are probably more important
to understand. For instance, the aerodynamics of towing our gliders with
our typical tow planes are quite different from those of the majority of
military glider tows because almost for virtually all military towing the
tow plane has a bigger wingspan than the glider. This was the case for
all British and US operations in WW2 and for most German towing too.

In fact, the only cases I've found where the military glider was bigger
span than the tug was the ME 321 Gigant (the Gigant was bigger than its
He-111Z towplane) and the DFS 230 when it was being towed by a BF-109 or
Bf-110.

Conversely the only civilian gliders I'm aware of that are smaller than
their towplane are Perlan 2 when the Grob G520 Egrett is towing it
and an SGS 1-26 behind a Piper Cub.

This can matter, because if the glider is smaller than its tug, its
entire wing is operating in the downwash from the tug's wing, while if
the glider is bigger than its tug, then, while the inner part of its wing
is in the downwash behind the tug's wing, the outer parts of its wing
project through the tug's tip turbulence and into the upwash created by
the outer parts of the tug's tip vortex and may well give an tendency for
the glider to tip stall if the tow speed is too slow.

Doesn't the majority of the wash or downflow from the wing pass under the glider if it tows at
the same altitude as the tug? For example, I used to demonstrate the ease of positioning behind
the towplane to students by banking to left until the glider was way off center line, and I
never noticed any significant difference in the airflow from center to far out to the left.
This was with a 200' long towrope; perhaps, with a much shorter rope, the experience would be a
lot different.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1