On Tue, 17 Oct 2017 01:47:08 -0700 (PDT), wrote:

So, Andreas, do we conclude the the physics and maths of tow hook placements are wrong or that there is always someone who sometime can manage to do something especially stupid?

Well...
let me put it this way:

As you probably know, the test flights that proved that the nose-up
momentum of a CG hook have been made by a German Akaflieg (project
pilot was a friend of mine, btw). And of course these flight tests
(using a Ka-8) proved that using a CG hook indeed made a huge
difference.


But:
Based upon these flight tests Germany introduced a law that aerotows
on CG hooks were only allowed if the pilot had recent aerotow
experience (3 aerotows during the last 6 months), and of course new
gliders had to be equipped with a nose hook.

Many people assumed that these limitations would affect aerotow safety
in a positive way. But it turned out that there was no influence of
these new rules on aerotow safety, not was there ever a hard
statistical proof that gliders with a CG hook had a higher aerotow
incident rate than gliders with nose hook (the odd man out being some
notorious gliders with problematic geometry and CG hook, especially
the Ka-6).


So last year this law was removed.


My conclusion:
In theory and flight test the maths and physics are correct, but in
practics they are not related to incident numbers.



p.s.
I usually fly an open class double seater with only a CG hook, and my
club's ASK-21 and Duo Discus XL. When teaching upset aertow situations
in the ASK-21 I never noticed any useful stabilizing effect of the
nose hook, nor did Iever in the Duo Discus. The same goes for the
DG-300 with and without nose hook which I had many chances to compare.