Just watched a tug and glider from Booker which did not seem to be climbing very well and wondered if anyone has designed a glider tug whose aerodynamic characteristics more closely approximate those of a glider, for instance high aspect ratio wings with a profile matching the glider L/D curve?
Grob 109B turbo with a constant speed prop. meets the above, and having water cooled cylinder heads and air-brakes gets down very quickly, but rate of climb when towing is less than Robin or Pawnee.
Perhaps the tug you watched had forgotten to raise flaps after t/o or had left carb. heat on... It may also have been 2-up if a tug pilot training flight - or any combination of the above!