| Orao | |
|---|---|
 | |
| Orao IIC | |
| Role | Single seat competition sailplane |
| National origin | Yugoslavia |
| Designer | Boris Cijan and Stanko Obad |
| First flight | 1948 |
| Number built | at least 3 |
The Cijan-Obad Orao (English: Eagle) is a competition single seat sailplane designed in Yugoslavia just after World War II, one of the most advanced of its type at the time. It flew in three World Gliding Championships, having greatest success at its first in 1950 when it reached third place.
For a time soon after World War II Yugoslavia was a leader in gliding flight and glider design. Many interesting sailplanes were designed and built. Of these the Orao II is the best known, representing "a pinnacle of sailplane design when it first flew in 1948". [1]
The Orao II is a cantilever, shoulder wing monoplane chiefly built of wood with plywood and fabric covering but with a slightly forward swept light alloy spar. It is a gull wing, with dihedral only on the inboard section where the leading edge is parallel to the spar and the trailing edge tapers towards it. Over most of the wing the profile is Göttingen 549R, a revision of the much used Göttingen 549 airfoil, the R indicating a reflexed, camber reduced trailing edge. Outboard the leading edge also tapers towards the spar, giving it sweepback, ending in semi-elliptical tips. The composite construction of the wing around the spar was completely new to sailplane construction; wooden extensions of the spar were bonded to it; wing ribs were riveted to the spa via metal brackets. [1] According to Simons the wing and control surfaces were entirely plywood covered but Jane's All the World's Aircraft 1952-53 says that ply was only used ahead of the spar, with fabric covering aft. [1] [2]
The wing trailing edge is filled by control surfaces, with Fowler flaps on the inboard sections then ailerons divided into three sections, first plain, then Frise and a short tip region. There are Schempp-Hirth parallel ruler action airbrakes immediately behind the spar on the inner part of the outer panels. [1]
The fuselage is an early pod and boom design, with an oval section forward section formed by longerons and frames with ply covering. The pilot sits in a semi-reclined position, his head forward of and above the wings, under a two piece, removable canopy. Aft of the wings the fuselage is a monocoque, skinned with stringers and balsa filling sandwiched between two ply sheets over wooden hoops. The tailplane is conventional, the fin constructed as part of the fuselage and ply covered. The fabric covered rudder is broad and extends down to the bottom of the fuselage where there is a sprung tail skid. The tailplane is ply covered with a swept leading edge and carries fabric covered elevators with a wide cut-out for rudder movement. The Orao lands on a rubber sprung skid. [1] [2]
The Orao, originally without a type number, first flew in 1948. After the national championships it underwent some small modifications, chiefly the removal of dihedral from the tailplane, to become the Orao II. After the tailboom failed catastrophically during a demonstration flight in 1950, killing the pilot, the Orao was seriously redesigned into the Orao IIC. The wing plan was unaffected but the airfoil section of the outer panels was thinned from Göttingen 549 to 682. Longer span, shorter chord plain flaps replaced the Fowler flaps and the ailerons were simplified, retaining only the outer pair. There were two suspected causes of the tail failure; the effect of repeated landing shocks and possible tail flutter. The fuselage underside was reshaped to distribute landing loads better and the fin was increased in area with a shallow dorsal fillet. The horizontal tail was made narrower, with straight taper and all ply covered, placed far enough forward so no rudder cut out in the now horn balanced elevators was required. The canopy was lengthened and made as a single piece of better aerodynamic form. Twin shoulder release hooks, placed just behind the wing leading edge, were added for Y-end towlines. The modifications added about 50 kg (110 lb) to the empty Orao IIC; the improved aerodynamics raised the glide ratio from about 32:1 to 36:1. [1] [2]
In 1949 the Orao attended its first competition, the Yugoslavian National Championships, where Milan Borisek set a new Yugoslav distance record of almost 600 km (373 mi) from Subotica to Salonika in Greece. [1] [3] After being modified into the Orao II it went to the World Gliding Championships (WGC) held at Örebro in Sweden the following year. Despite the Orao's lack of refined finishing compared with the best Weihes present, with unsealed ailerons and flaps and a lack of surface polish, and despite the lack of experience of the pilot, whose first international competition it was, the Orao came third. Its appearance and performance attracted much attention and prompted supervised comparative tests, without the WGC, of the Orao with the Weihe of Paul MacCready. These showed the two aircraft performed similarly at low speed but that the Orao had the lower sink rate at higher speeds. [1] [4]
Borisek was killed in the 1950 accident. Two Oraos IICs flew in the 1954 WGC, held at Camphill in the UK, but their highest placing was ninth. One also competed at the next WGC, held at Saint-Yan, France in 1956 but without success, coming in twenty-third. [1] [5]
Data from Sailplanes 1945-1965 [1]
Data from Jane's All the World's Aircraft 1952-53 [2] The World's Sailplanes:Die Segelflugzeuge der Welt:Les Planeurs du Monde [6]
General characteristics
Performance
The Slingsby T.25 Gull 4 is a British glider designed and built by Slingsby that first flew in 1947.
The Slingsby Type 34 Sky is a high performance single seat competition sailplane built in the United Kingdom. It was successful in major events, particularly in the World Gliding Championships of 1952.
The Slingsby Type 45 Swallow was designed as a club sailplane of reasonable performance and price. One of the most successful of Slingsby's gliders in sales terms, over 100 had been built when production was ended by a 1968 factory fire.
The Slingsby T.50 Skylark 4 was a British single seat competition glider built by Slingsby Sailplanes in the early 1960s. It sold in numbers and had success at national, though not world level competition.
The DFS Weihe is a German single-seat, high-wing, 18 metre wingspan, high-performance glider that was designed by Hans Jacobs in 1937-38.
The Czerwiński Sparrow, sometimes known as the de Havilland Canada glider, was a single seat glider, designed and built by a group of de Haviiland engineers in Canada in 1942. It was intended to popularise gliding and be suitable for both basic training and thermal soaring.
The Ikarus Košava is a two-seat sailplane designed and built in Yugoslavia in the early 1950s. It won the 1954 World Gliding Championships in the two seat category and came second in the same event two years later.
The Ikarus Meteor is a long-span, all-metal sailplane designed and built in Yugoslavia in the 1950s. It competed in World Gliding Championships (WGC) between 1956 and 1968 and was placed fourth in 1956; it also set new triangular-course world speed records.
The Beatty-Johl BJ-2 Assegai was a single seat, high performance competition glider built in South Africa in the early 1960s. Only one was built; it was optimised for South African conditions and performed well there, winning two nationals and setting several records, but was less successful under European conditions at the 1965 World Gliding Championships.
The Lie-Fang 1, some sources Jeifang 1, was one of the first gliders designed and built in China, though with Polish design input. It is an all-wood, two seat, intermediate training aircraft which first flew in 1958.
The Lommatzsch FES-530 Lehrmeister is a two-seat trainer glider that was built in the German Democratic Republic in the 1950s. Over 300 were built, with a mixture of 17 m and 15 m spans.
The VTC Delfin is a competition single seat Standard class glider designed and built in Yugoslavia in the 1960s. It had some success in national competitions and went into small scale production.
The Ciani EC 38/56 Urendo, or SSVV EC 38/56 Urendo is an Italian tandem-seat training glider from the 1950s. Four were built, one winning the Italian National Championships in 1959. Another, restored, still flies.
The Ciani EC.37/53 Spillo or SSVV EC.37/53 Spillo was a single seat competition glider designed and built in Italy in the 1950s. It had the highest aspect ratio wing of any wooden glider. Only one was built.
The CVT2 Veltro was an Italian competition glider built in the mid-1950s. Its advanced design incorporated a laminar flow wing, T-tail, retracting undercarriage and a reclining seat to reduce parasitic drag.
The Bruni 3V-1 Eolo was a single seat Italian competition glider, first flown in 1955. It took part World Gliding Championships of 1956 but retired early after sustaining damage.
The IFIL-Reghin RG-5 Pescăruș or CIL Reghin RG-5 Pescăruș was a Romanian single seat sailplane built in the 1950s. Twenty six were constructed for gliding clubs.
The Oberlerchner Mg 19 Steinadler is an Erwin Musger designed two seat tandem trainer glider built in Austria and first flown in 1951. Several examples of this successful aircraft, which competed in the two seat class at two World Gliding Championships in the 1950s, were still flying in 2000.
The Weber-Landholf-Münch WLM-1 is a 1940s Swiss high performance sailplane designed to meet a Swiss Air Force (SAF) requirement for a training glider that could initiate potential fighter pilots. To this end it is fast, aerobatic and equipped with standard military instrumentation. Only three were built.
The Ilić Ilindenka was a series of Yugoslavian standard class sailplanes capable of aerobatics.
 | Wikimedia Commons has media related to Ikarus Orao . |
