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Akaflieg Berlin B-12



The students at Akaflieg Berlin set out to improve the performance of modern gliders by reducing drag. Design work on the B 12 began in October 1973. To reduce costs the group utilised production wings from a Schemp-Hirth Janus B, shortened to 18.2m, allowing the students to concentrate their efforts and budget on improving the fuselage.

The shape and profiles of the new fuselage were developed at the Institut für Luftfahrzeugbau (Institute for aircraft industry) and a new two-seat fuselage constructed using GFRP (Glass-fibre Reinforced Plastic) techniques in a monocoque shell. The B12 uses monocoque construction, and the cockpit seats two in tandem under large plexiglas canopies with the instructors seat, in the rear, set at a higher level to improve the instructors view ahead.

The wings are standard 'Janus B' items built using identical construction methods. The wing has a sweep forward of 2° 18' on the leading edge with glassfibre monocoque ailerons, flaps and Schempp-Hirth air brakes on the upper surfaces. The tail unit was originally built as a cruciform unit using an extremely thin NACA 0009-64 aerofoil section formed with ' Rohacell'/GFRP sandwich supported by CFRP (Carbon-Fibre Reinforced Plastic) spars. After a trailer accident during road transport in 1986, which destroyed the rear fuselage and tail-unit, a T-tail was fitted during repairs. A specially developed Wortmann FX-71 L 150/30 profile was utilised for the fin and rudder.

The single retractable main undercarrriage wheel is supported on a tall leg assembly which was originally built with electric actuation, but after a field landing with a flat battery caused a wheels-up landing a manual system was fitted. A rubber tailskid, capped with hardened steel, under the rear fuselage completes the undercarriage. Pullup doors fair over the main undercarriage well when the gear is retracted. In the original fuselage a braking parachute, used for approach control, was housed at the extreme rear, but this feature was not carried through to the replacement rear fuselage during repairs.

After the first flight of the B12 on 27 July 1977, piloted by Jürgen Ehlers Thorbeck, the B12 was used for research, cross country and competition flying until the trailer accident in 1986, whilst being transported by road, destroyed the tail section and twisted the rear fuselage. Repairs were carried out and the B12 was flying again on 1 August 1987 at the IDAFLIEG ( Interessengemeinschaft deutscher akademischer Fliegergruppen e.V. - interest group for academic flying groups) summer camp at Aalen-Elchingen, sporting a T-tail identical to that of the Akaflieg Berlin B13. The B12 continues to fly but rarely emerges from the hangar unless the soaring weather is good.
The measured glide-ratio (Idaflieg-summer-meeting 1978) is 40.5.

Wingspan: 18.2 m (59 ft 8.5 in)
Length: 8.7 m (28 ft 6.5 in)
Wing area: 16.58 sq.m (178.5 sq.ft)
Aspect ratio: 19.97
Wing profile: Root - Wortmann FX-67-K-170, Tip - Wortmann FX 67 K 150 [3]
Height: 6 ft 6 in
Empty weight: 446 kg (983 lb)
Gross weight: 620 kg (1,367 lb)
Wing Load: 37.4 kg /sq.m
Maximum speed: 200 km/h (124 mph)
Max aero-tow speed: 93 mph
Maximum glide ratio: 40.5 @ 110km/h (68mph)
Rate of sink: @90km/h (56mph) 0.68 m/s (133.9 ft/min)
No. of Seats: 2
No. Built: 1
L/DMax: 40.5 @ 110 kph
MinSink: 0.68 m/s @ 90 kph
Structure: GFRP





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