At 03:57 06 January 2011, Derek C wrote:
On Jan 6, 2:20=A0am, Andreas Maurer wrote:
On Wed, 5 Jan 2011 15:09:39 -0800 (PST), Derek C

wrote:

Hi Derek,

The two most scary aerotows I have ever had we

1) 2 up in a K13 behind a Rotax engined Falke at about 50 knots
indicated airspeed

Well... 50 kts is pretty slow...

2) 2 up in a K13 behind a 150hp Piper Cub when we visited another
site. This tug wasn't very powerful anyway and its pilot seemed to
be
trying to demonstrate how slowly he could fly. Indicated airspeed
slightly under 50 knots.

Clear case: Low aspect ratio, wing loading twice of the ASK-13. How
much above the stall speed of the Cub? 10 kts at maximum? Scary...

I guess you had a word with the tow pilot afterwards.

In both cases the glider wallowed about and it seemed very difficult
to keep above the wake turbulence/prop wash.

Yes, the typical situation for a very slow aerotow.

I have not been towed by a Dimona or Katana, but they seem to be a
bit
faster than the above, so may not give the same problems. I think the
problem is more lack of airspeed than the type of the tug aircraft.

Well, I guess we both agree that this problem only manifests itself at
the low-speed area of the envelope, don't we?

The general consensus here in Germany (as well as my own experience)
is that an aerotow behind a motorglider is *much* easier to control
despite the fact that it takes place at 110-115 kph (60-63 kts)
instead of the 130-140 kph (70-75 kts) =A0that are typical for Morane
MS
893 and Robin Remorqeur.
Of course similar wing loadings result in similar reactions to gusts,
which helps to follow the tow plane.

Regards
Andreas

Yes, but 50 knots (93kph) should be OK for a K13 when its stalling
speed in free flight is only about 36 knots (67kph). But it clearly
isn't! Therefore either the wing loading or the angle of attack (or
both) must be greater during an aerotow than in free flight.

Cheers,
Derek C


... or the distribution of lift over the wing has changed ...