The above suggests that a tug with a highly aerodynamic airframe could
use far less HP which is why 80HP motorglider tugs seem to work so
quietly.

A tug like this: http://www.sportaircraftworks.com/ot...dynamicnew.htm
According to John Roake, turnaround on a 600m launch with this plane
averaged 4-5 minutes (takeoff to landing) and it only took 100 Euros
worth of fuel for 8 of these planes to launch a field of 60 gliders
(no other stats provided unfortunately). With efficiency like that I
bet these planes don't make a lot of noise though...

-Paul