Aerotow ropes: short or long, breakable or unbreakable?

IF the glider is flown perfectly balanced in the perfect position behind
the tow
plane and NEVER gets out of station or forms slack in the rope.


Tom



At 00:22 14 November 2013, Bob Cook wrote:
yes, I underestimated....

Say a 800 lb glider at 40:1 L/D so the drag is about 20 lbs...but
the
tension component in the rope due to the climb angle (say 10:1) is going
to be 80lbs....so you've got 100 lb tension on the rope.

But a rope "in spec" would offer a safety factor of 6x up to 16x.

Some tow planes can climb better than that...so more tension...

Cookie







At 23:46 13 November 2013, Martin Gregorie wrote:
On Tue, 12 Nov 2013 18:43:41 -0800, Cookie wrote:

My rough calculations show that the "normal" tension on a tow rope in
smooth tow is very low...It is basically the drag on the glider, plus
a
tiny bit extra due to the climb vector...so maybe 60 lbs tension...

I think its a bit more than that, but not much. Some time ago I did a
fairly detailed spreadsheet calculation for my Libelle being towed at 60

kts in a 600 fpm climb and got a total rope tension of 37.62 kg, which
was more or less what I'd guestimated from a mental round number
calculation.

The makeup of the rope tension did surprise me though: like you I
thought

drag would be the major part of it, but the spread sheet gave the
glider's drag as 9.97 kg and the force needed to haul my 280 kg Libelle
up a 5.67 degree slope at 60kts as 27.65 kg.

Yeah, I know, I should have only kept 1 decimal point: 2 decimals is
spurious accuracy.

Of course, the other interesting number would be what fraction of the
total drag of a climbing tug+glider combination was due to the glider. I

suspect the glider is contributing less than Wg/Wt where Wg is the
glider

weight and Wt is the tow planes's weight. I'd expect the straight ratio
to over-estimate the glider's contribution because it is likely to fly
rather more efficiently than the tug.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
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