Swiss Federal Institute of Technology Ka-Bi-VoHBV Diamant
The ideal of an all-glassfibre sailplane was achieved in several stages, the first being development of the fuselage and tail unit designed by Thomas Bircher and J von Voornveld at the Swiss Federal Institute of Technology in Zurich under the direction of Professor Rauscher. A prototype fuselage was built in 1962 and was flown with the plywood and fabric wings of a Schleicher Ka 6CR, the resulting aircraft being designated Ka-Bi-Vo.
The Diamant's development was now gradually taken over by Plug- und Fahrzeugwerke AG FFA, and the next stage was the HBV-Diamant 15 which used the 15m span Hutter H-30TS wings of the Glasflugel H 301 Libelle. This first flew on 5 September 1964 and 13 of this variant were subsequently built; the Libelle's wings being glassfibre balsa sandwich shells without ribs, featuring ailerons that gave partial downward movement when the flaps were lowered, and there were glassfibre dive brakes forward of the flaps.
The HBV-Diamant 15 was followed by the generally similar Diamant 16.5, with wings of increased span (16.5m) designed and built by FFA; a total of 41 of this variant were built. This was the first all glass fiber production sailplane, not using balsa or other wood sandwiched between the fiberglass layers.
The Diamant 18 is an 18 m development of the 16.5, first flying in February 1968, with extended inboard wing and flap sections and a new wingtip cap. like the Diamant 16.5, water ballast an be carried in the wing roots. The monocoque fuselage is an epoxy-glassfibre sandwich with foam inserts, and the tail unit is of the same construction, the allmoving one-piece tailplane being mounted on top of the fin. As well as a small tailwheel (a tailskid is optional) there is a manually-retractable monowheel with a brake, and another feature is a glassfibre ring spring shock absorber; the tow release retracts with the landing gear. The pilot sits in a semi-reclining position under a long forward sliding one-piece canopy, and there is provision for radio and oxygen.
At least one Diamant 18 was substantially modified by Dan Pierson of Los Angeles, CA to have a 19.0 m / 62.3 ft wing carrying 145 kg / 320 lb of water ballast bringing the gross weight up to 673 kg/ 1,480 lb.
The HBV Diamant and Diamant 16.5 are ATC, while the Diamant 18 is EXP.
A powered version of the Diamant 18 known as the EFF Prometheus 1 made its first flight on 21 June 1971, powered by a 176lb st Microturbo Eclair II turbojet mounted behind the cockpit. The Prometheus was developed by EFF – Entwicklungsgemeinschaft fur Flugzeugbau der Akademischen Fluggruppe, and it was later converted back to a standard Diamant 18.
EEF Prometheus 1
Wing span: 16.5m / 54.2ft
Wing area: 12.2sq.m / 143sq.ft
Empty Weight: 270kg / 595lb
Payload: 138kg / 305lb
Gross Weight: 408kg / 900lb
Wing Load: 30.91kg/sq.m / 6.29lb/sq.ft
Water Ballast: 0
No. of Seats: 1
No. Built: 43
L/DMax: 42 100 kph / 54 kt / 62 mph
MinSink: 0.55 m/s / 1.80 fps / 1.0 kt
Aspect ratio: 20.5
Airfoil: Wortmann FX-62-Z-153
Wing span: 18m / 59ft
Wing area: 14.28sq.m / 153sq.ft
Airfoil: Wotmann FX-62-Z-153
Length: 25 ft 4 in
Height: 4 ft 5 in
Empty Weight: 280kg / 617lb
Payload: 160kg / 353lb
Gross Weight: 440kg / 970lb
Wing Load: 30.8kg/sq.m / 6.34lb/sq.ft
Max speed: 149 mph
MinSink: 0.52 m/s / 1.80 fps / 1.01 kt at 45 mph
L/DMax: 45 at 100 kph /54 kt / 62 mph
Aspect ratio: 22.7
No. of Seats: 1