FVA 18 - New Engine for the Primitivkrähe

At the end of 1971, the situation arose that a crashed but functional Limbach engine was still left from the superstructure of the purchased Rf 5 break. After some weighing, measuring and sketching, it became clear that a transplantation of the powerplant was possible. In the winter of 1972/73, the rebuild was completed in about 600 hours of work.

After dismantling the old power plant, an engine mount was welded from ordinary steel tubing and the engine was pre-assembled with it. A good overview of the available space was now available and the construction of the exhaust system, the engine cowling and the controls could begin.

The two mufflers were “fitted” from 0.8 mm V2A sheet metal behind the cylinder heads and the tailpipes (VW 1500) were led out downwards to keep the exhaust gases away from the window even at high angles of attack.

For the engine cowling, an old Rf 5 engine cowling was spackled on, then a negative mold was removed and the new cowling, made of twill fabric and epoxy resin, was laminated into it. Bowden cables were used as controls for the throttle and air flap, and a cable for the electric starter. In March 1972, the final engine mount was assembled in a jig and gas-shielded welded.

After the individual parts were painted, the engine and the control elements were assembled. The cooling air plates were then fabricated and the engine cowling was fitted and fastened with quick release fasteners. The electrical system with the control instruments and the propeller still had to be assembled and so the first stationary runs could take place in April 1972 in front of the workshop.

In the meantime, the proofs (strength test, center of gravity, power calculation, etc.) were compiled and submitted to the LBA in accordance with the American CAR 3 Part E (engine installation) regulations.

The engine conversion was inspected, the airframe was rechecked and the Crow flew for the first time on 17.5.1972 without any problems as never before: Put it in, start it (electrically), fly off!

The conversion went so quickly that the authorities only later realized that this was no longer a minor change. The old certification expired, and the crow, now called FVA-18b, was given a provisional airworthiness certificate for testing. After a postcard-sized piece was cut out of the Molor cowling, the temperature conditions on the engine were also right, and the Crow could be presented.

With the engine rebuild, all the disadvantages of the old powerplant were overcome. Only the formerly phenomenal acceleration at takeoff and thus the short takeoff roll distance were omitted; about 80 - 100 meters were now necessary.

Overall, the following improvements or flight performances were achieved:

  • Electric starter - before hand scribing on the propeller
  • Electric on-board power supply 12 V, 240 W
  • Increased climb rate from 1.6 m/s to 2.3 m/s at 450 kp
  • Increased cruising speed from 108 km/h to 128 km/h
  • Less noise due to exhaust system
  • No gearbox, thus simplified maintenance and less noise and vibration
  • Spare parts available quickly
  • Greater ground clearance of the propeller

At an oldtimer meeting in Dortmund - Wickede the gliding characteristics of the Crow could be demonstrated. It will probably not be seen again so soon that a powered glider pilot switches off the engine at an altitude of 150m and then cranks up to 450m above the airfield.

From today’s perspective, it can be said that the FVA fully achieved the technical goal, albeit with an intermediate step. With the development of the two-seat powered glider and the acquisition of one for the FVA, there was no further need for a powered aircraft - the Krähe was sold to an OUV member.