Aachen FVA-19 "Auslegung eines Schleppflugzeugs"
The FVA-19 was a study of the efficiency and design of an efficient towplane. With the following consideration: Scale is the generally accepted winch launch operation, economy would be better with aerotow if the total expenses are equal to or less at the same efficiency. Capturing all the factors that make up the term economy as a whole, was by evaluating all the statistical material possible.
Statistical considerations included a comparison of the cost of the tow plane towing to height, which incurred expenses such as overhauls, usual minor repairs. et al and depreciation are included.
After extensive calculations, it was clear that the power requirement of the optimum towing aircraft must be well above 175 hp. For a comparison, the costs and benefits achievable in the winch towing operation had to be known.For this purpose , the fixed costs of a glider per year were collected , as well as that of the wind, and from the Annual Report of the National Association of North Rhine-Westphalia DAeC the years 1959 - 1961 taken from the middle tee times . This was followed by a gliding hourly rate of 90, - DM at 60 hours per glider and year down to 70, - DM at 80 hours per glider and year. The last statement (80 h / year) seemed the performance of the winds to be exhausted. Assuming a flight time of 25 minutes per start a drag start at the same annual total flight time of 80h year and the same hour flight price could cost 4.75 DM . That was the cost of the winch to let the glider fly 25 minutes. For this purpose, on average just over two winch launches were necessary). With sufficient utilization of the towing aircraft such start-up costs are possible.
This can be reached by aerotow, with more than 80h / year per glider, so even higher towing rates may still be economical. The glider hour is the same price for both types of launch when the glider has reached 60hr per year by winch, and 95hr year by aerotow, and this with a towing price of 15 , - DM (again, for an average flight time per launch 25 minutes according to a towing height of n = 750m) .
A summary of this study was published in the trade press which great interest in gliding circles. Since the construction and flight testing of the " Crow " the FVA still aero-towed until the end of the 60s and in 1963, a Piper Super Cub was purchased as a tow plane.Construction of FVA-19 began in 1965, but acquisition of the Super Cub made construction superfluous.
With the help of some old masters of the FVA this study went to Bremen where it was constructed by the flight Scientific Working Group Bremen, This single-seat aircraft was equipped with a 180 hp engine, and with the type designation ESS 641 was first flown on September 17, 1971.