Designed by Ron Beattie and Walt Fellers, two North American Engineers who came to work for the Northrop Division, the 1948 Acme Sierra (a.k.a. “Sierra Sue”) N12K was built by the Acme Aircraft Co. at the Torrance Airport in late 1948. It was built by Acme’s Crawford and Keeney.

Designed and flown by Ron Beattie and Walt Fellers, the first flight took place on 23 November 1953. It was built according to Goodyear Racing Plane specifications. Although it was never entered in any races, extensive data was obtained during its many flights.

It was built to investigate the advantages of a pusher propeller configuration. It has a “Y” shaped tail incorporating ruddervators on the upper fins, an unswept wing mounted midway up the fuselage, an engine mounted directly behind the cockpit, and large air scoops mounted in the forward end of both wing roots. The aircraft, now designated as the Sierradyne S-1, was used by Sierradyne Inc. in the 1960’s to test and promote Northrop’s and Dr Werner Pfenninger’s boundary layer control concepts. Northrop used it as a flying technology demonstrator for the Air Force’s AX close-support aircraft design competition in 1972, but despite its being re-labeled as the Northrop Turbo-Pusher, the plane was never officially considered a Northrop aircraft.

It is reported displayed at the Los Angeles Science Museum.

Engine: Continental C-85, 85hp
Wing span: 20′ 2″
Length: 18′ 0″
Max speed: 200 mph
Empty weight: 590 lb
Seats: 1

Made by, Keiiche Abe, a teacher in Hokkaido, Japan, in 1977, the Mini-gyro-sail-motorplane has Bensen parts, Abe airfoils and a Toyota engine. It cruises at 48 mph, takes off in 510 feet, and lands in 160 feet. It cost around $1000.

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.

At the end of the fifties the FVA wanted each aviation student, after completing his studies, to have also private pilot’s license. It was decided to develop an inexpensive powered airplane, easy to fly, for training.

American engines were too expensive, so a Pollmann flight engine that was developed from the VW and gave a continuous output of 30PS at 3200 rpm was obtained. By selection of the propeller, it was possible to bring the propeller efficiency to 0.78%. It was necessary to give the propeller a comparatively large diameter of 2.15m.

It was necessary to reduce the speed of the engine to 1100 rev min. This was to be done by a V-belt reduction provided by the Pollmann, but this proved to be unusable. A transmission was developed by the FVA, with a reduction of 2.85 : l delivered by a helical spur.

Construction of the FVA18 “Primitive Krähe” (Primitive Crow, later Silver Crow) began in 1960. In the conventionally designed steel tube fuselage and one-piece wing was an extreme lightweight construction. It had a 250 kg empty weight for a two-seater powered aircraft with a wingspan of 10.50 m and a length of 6.70 m. The power plant took the flying weight to 430 kg. The plan was to only 400 kg.

The wings stems were examined at the Institute for Building Research on buckling strength.

The fuselage width of the FVA-18 was only 0.67 m. It turned out later that with this hull width a passenger, in tandem behind the pilot came in contact with the rudder pedals.

Aileron and elevator loading tests and suspension drop tests completed the test series.

The FVA-18 was built to CAR Part 3 Normal category. First flown in 1965, the flight tests were conducted under the provisions of “Civil Aeronaurics Manual (CAM)” and after “Flight Test Report Guide”. Here, every attitude and flight situation were subjected clearly defined requirements.

The self-designed gear had to be disassembled at fixed intervals to determine wear or replace bearings and oil seals leaking.

It soon became apparent that the propeller pitch was set too low. A new propeller was added at Hoffmann.

The first flights were destined to determine the normal behavior of the FVA-18. After a few minutes of flight, the oil temperature rose above the permissible level. Moreover, it was splashed on the front panel through the vent of the transmission oil.

The transmission made loud noises was at engine speeds below 1,800 rev / min, which, as it turned out, were also due to engine misfire. Metal shavings were found in the oil thrown out and the gearbox was disassembled after 20 minutes of flight time. The helical involute gears were shifting by 4 mm and beat against each other on a spacer. A newly designed additional spacer ring then prevented migration of the gears against each other, and the transmission was much quieter. Additional baffles enhanced oil cooling for level flight at a constant temperature of 90°C.

With a weight of 380 kg following flight performance were flown:
Cruising speed:
100 km / h at 3200 rev / min
90 km / h at 3000 rev / min

Lift-off distance:
40 m

Take-off distance 15m:
approximately 120 m

Rate of climb:
2.10 m / s

Altitude reached:
2500 m

Fuel consumption:
9 l / h

Range:
380 km

The first spin tests at medium gravity position could be recovered by normal control deflections and discharged again. The FVA -18 turned 1/4 to 1/2 turn. The spin was hardly different from a steep circle with minimum speed.

Flight testing was Dr. Mr. Professor. AW Quick performed the framework of the thesis of Freddy Schliewa at the Institute of Aerospace.

In 1971, she was presented in flight at the meeting of the Oskar Ursinus Vereinigung (OUV) in Egelsbach. where a lot of attention:

“The next day the representatives of the FVA Aachen presented their” primitive crow. “- Before FVA-18 from the flight characteristics of this bird that bears his name because of its simple construction with a right to all interested parties were able to convince themselves by relying on the stick translated and with the Crow Conclusion went into the air the idea of the aircraft from Aachen:… Everybody talks about the club aircraft to reproduction – we are only interested in (still) not sure “
(556 from German Aerokurier, Issue 8 71, p report on OUV-Meeting)

In particular, the low minimum speed of 55 km h and the harmless stall characteristics impressed. The simple construction aroused the interest of amateur aircraft builder. In the following years, numerous requests were answered and ten sets of drawings were delivered to interested parties.

At the end of 1971, a crashed Rf 5 Limbach engine was left. After some weighing, measuring and sketching it became clear that a transplant of the power plant was possible. Then the reconstruction was done in around 600 working hours in winter 1972/73 by Max Schörner and Erhard Schneider. The engine system and propeller had the first run-ups in April 1972.

The Crow flew for the first time on 17 May 1972. The old authorization expired, and now FVA-18b called Crow got a provisional airworthiness certification for testing. Acceleration at the start improved and short take-off run was now around 80 – 100 yards.

The following improvements and flight performance were achieved :

• Electric start – before by hand
• Vehicle electrical system 12 V, 240 W
• Increased rate of climb of 1.6 m / s to 2.3 m / s at 450 kp
• Increase the cruising speed of 108 km / h to 128 km / h
• Less noise from the exhaust system
• No gearbox, thereby simplified maintenance and less noise and vibration
• Increased ground clearance of the propeller

The FVA fully met the technical target with an intermediate stage. Through the development of the two-seater motor glider and the procurement of one for the FVA saw no further need for a powered aircraft. The Crow was sold to an OUV member.