Arado Ar 66
Arado's chief designer Walter Rethel started design of a new two-seat trainer in 1931, with the design being developed by Walter Blume when Rethel transferred to Messerschmitt, with the first prototype, the Ar 66a flying in 1932.
The Ar 66 had an Argus As 10 air-cooled inverted V8 engine producing about 179 kW (240 hp), which drove a 2.5 m (8.2 ft) two-blade propeller. It carried 205 L (54 US gal) of fuel, and 17 L (4 US gal) of oil.
The fuselage had an oval cross-section and was made of welded steel tubes, covered with fabric. The double wings provided very high lift, even at low speeds. Both wings had the same span and an 8° sweep. Construction consisted of a double pine wing spar structure, with lime tree ribs, and fabric covering. There were ailerons in both upper and lower wings. The tail had a conventional design, with the horizontal stabilizer mounted on the fuselage upper edge. The rudder was placed behind the elevator. Both the rudder and the elevator were of steel tube covered in fabric, and had a bigger surface than the first version to correct balance problems. The steel tube undercarriage was attached to the fuselage in a "V" shape and used a high-pressure rubber suspension.
The crew consisted of two: instructor pilot and trainee, seated in open tandem cockpits equipped with dual controls. The aircraft was equipped with instrument flight systems with photographic cameras were mounted as optional equipment.
The Ar 66 entered service with the Luftwaffe in 1933, serving as a trainer until well into World War II.  In 1943, the Luftwaffe set up a number of night harassment groups to operate on the Russian front. The Ar 66, along with the Gotha Go 145, formed the main equipment of these groups.
Type
A Two seat trainer
B Two seat seaplane trainer
C Two seat trainer
D Two seat trainer
Engine
1 Argus As 10, 200 hp
1 Argus As 10C-2, 240 hp
Dimensions
Length 8,30 m, height 2,93 m, span 10,00 m, wingarea 29,63 m2, wingloading 44 kg/m2, powerloading 5,4 kg/hp
Weights
Empty 885 kg, load 420 kg, flying
weight 1305 kg
 
Empty 885 kg, load 420 kg, flying weight 1305 kg
Performance
Max.speed 200 km/h
 
Max.speed 210 km/h, climb to 1000 m 4,1 min., service ceiling 4500 m,
range 716 km
B : Seaplane trainer, only 10 built
C and D Improved version with more powerful engine. Redesigned landinggear with hydraulic shock absorbers. wheelbrakes and low pressure tires. Horn balanced rudder and elevator, mass balanced ailerons. Wings modified .
The trainer were used also as fighter-trainers, training for gunners, telegraphists, bomb-dropping, photo-reconnaissance training, aerobatics, blind flying and nightflying.
Could be equipped with skis. In the last years of the war they were used in the Nachtschlachtgruppen on the east front and as reconnaissanse planes in Norway