Second glider-towing attempt

RK 7

RK 6 

The first attempt did not go unnoticed and in three weeks, the Raab-Katzenstein company of Kassel built the RK 7 glider (top) and using the RK 6 towplane above (a copy of an WW1 LVG biplane) on April 13 1927, the first successful towed flight took place. 
The test flights were successful enough that the Italians, Russians and Americans took note and the rig was actually sold to American interests.