Winch Launch Stresses on Vintage Gliders

On Tue, 24 Jan 2006 01:04:44 UTC, "Brian" wrote:

: But as I recall the weak link is supposed break before it carries twice
: the gross weight of the glider.
: So during the launch the wings must lift at a maximum the weight of the
: glider plus up to 2 times weight of the glider through the weak link.
: So the maximum load you should be able to put on the glider is 3G's.

It would actually be much higher than that. In a normal 3G turn, only
3 times the weight of the fuselage and contents a gets transmitted
through the wing attachments - the extra load of the wings is absorbed
internally. If you add the extra 2G with a winch cable, the wing
fittings are taking 1 x the weight of the fuelage plus 2 x the weight
of the entire glider, which is twice the weight of the wings more than
in the 3G turn. Since the wings are typically half the mass of the
glider, that means that the wing root stresses in a 3G (weight plus
2G) launch are roughly the same as those in a 4G turn.

Hence the typical 1.4 x AUW weak link specification - that gives a
maximum load on the wing roots equivalent to just under 3.5G, which is
generally the maximum permitted loading in normal flight.

Ian
:


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On Sun, 29 Jan 2006 15:35:45 UTC, "Bill Daniels"
bildan@comcast-dot-net wrote:

: It would be easy to dip one end of the slotted links in, say, tan paint.
: Seeing a link assembly with two white dogbones but with one showing a tan
: end would indicate that the link had been assembled correctly.

I'm pretty sure that I have seen genuine Tost weak links in which the
slotted ones had a paint band round the middle. But that may have been
added by the club in question. It's a sensible thing to do.

Ian