The SZD-21 was a successor to the IS-4 Jastrząb. Development began in January 1958 as the SZD-21 Sokół, but due to problems with the flying surfaces and a wood metal sandwich, a construction of the design was restarted as the SZD-21 Kobuz (Eurasian hobby), than SZD-21-2 Kobuz. The new SZD-21-2 retained the overall shape of the original project, but was constructed with wood throughout, using multiple spars for the wings. Design team was headed by Jerzy Trzeciak, later joined by M. Gracz in Kobuz 3 constructing.
Flight testing of the SZD-21 Kobuz began on 3 June 1961 with Stanisław Skrzydlewski at the controls,[2] but the results were disappointing prompting a re-build as the SZD-21-2A, with a completely revised fuselage, landing gear, canopy and differential ailerons. Flight tests resumed on in May 1962, but serious problems with the pitch and roll stability at high speed as well as flutter in a certain speed range prompted a further round of modifications. The resulting SZD-21-2AZ (still registered as SP-1990) continued the test program until 20 April 1963, when the aircraft broke up in flight during flutter testing, killing the pilot Sławomir Makaruk.[1]
The final version, the SZD-21-2B Kobuz 3, which was of all wood construction with very stiff wings to resist bending and flutter, was produced in small numbers in Wrocław. It first flew on 10 December 1964.[2] It competed at the highest levels into the late 1980s. Unfortunately, the Kobuz 3 was not immune to accidents and one high-profile fatal accident, at the world glider aerobatic championships at Hockenheim in Germany, highlighted problems with condensation soaking highly stressed wooden parts causing structural failure. The pilot, Krzysztof Wyskiel, was carrying out his competition routine with high accuracy until the penultimate manoeuvre when the wings failed, clapping hands above the fuselage which shot straight down to the ground like an arrow, killing Krzysztof Wyskiel instantly. The three remaining Kobuz 3's in the competition were grounded and remained so until the aircraft were cleared for limited manoeuvres only, curtailing their aerobatic competition careers.
In 1991 the design of a new (composite build) aerobatic glider, S-1 Swift had been finished, based on the Kobuz 3 design (the wings of the first production series of the Swift glider had been manufactured using the wings of Kobus 3 as molds).[3]
Variants
SZD-21 Sokół – The original designation of the project as begun in 1958.
SZD-21-2 Kobuz – The initial prototype version, (reg'n SP-1990), which proved unsatisfactory, modified to Kobuz 2A.
SZD-21-2A Kobuz 2A – The second version of the prototype, (reg'n SP-1990), again disappointing, modified to SZD-21-2AZ
SZD-21-2AZ – The final modification state of the SZD-21 prototype, (reg'n SP-1990), which crashed on 20 April 1963
SZD-21-2B Kobuz 3 – The final version of the Kobuz, first flight 10 December 1964,[1] which proved acceptable and a small production batch were completed.
^ abcd(in Polish) Babiejczuk, Janusz and Grzegorzewski, Jerzy. Polski przemysł lotniczy 1945–1973 (Polish aerospace industry 1945-197). Warsaw: Wydawnictwo MON, 1974, p. 126
kobuz, single, seat, aerobatic, glider, designed, built, poland, szybowcowy, zakład, doświadczalny, glider, experimental, works, bielsko, biała, from, 1958, kobuz, polish, aviation, museumrole, glidernational, origin, polandmanufacturer, glider, works, wrocław. The SZD 21 Kobuz was a single seat aerobatic glider designed and built in Poland at Szybowcowy Zaklad Doswiadczalny Glider Experimental Works in Bielsko Biala from 1958 SZD 21 KobuzSZD 21 2B Kobuz 3 in the Polish Aviation MuseumRole GliderNational origin PolandManufacturer Glider Works in WroclawDesigner Jerzy Trzeciak Marian GraczFirst flight 3 June 1961 1 Number built 30 1 Contents 1 Development 2 Variants 3 Specifications SZD 21 Kobuz 3 4 See also 5 References 6 External linksDevelopment EditThe SZD 21 was a successor to the IS 4 Jastrzab Development began in January 1958 as the SZD 21 Sokol but due to problems with the flying surfaces and a wood metal sandwich a construction of the design was restarted as the SZD 21 Kobuz Eurasian hobby than SZD 21 2 Kobuz The new SZD 21 2 retained the overall shape of the original project but was constructed with wood throughout using multiple spars for the wings Design team was headed by Jerzy Trzeciak later joined by M Gracz in Kobuz 3 constructing Flight testing of the SZD 21 Kobuz began on 3 June 1961 with Stanislaw Skrzydlewski at the controls 2 but the results were disappointing prompting a re build as the SZD 21 2A with a completely revised fuselage landing gear canopy and differential ailerons Flight tests resumed on in May 1962 but serious problems with the pitch and roll stability at high speed as well as flutter in a certain speed range prompted a further round of modifications The resulting SZD 21 2AZ still registered as SP 1990 continued the test program until 20 April 1963 when the aircraft broke up in flight during flutter testing killing the pilot Slawomir Makaruk 1 The final version the SZD 21 2B Kobuz 3 which was of all wood construction with very stiff wings to resist bending and flutter was produced in small numbers in Wroclaw It first flew on 10 December 1964 2 It competed at the highest levels into the late 1980s Unfortunately the Kobuz 3 was not immune to accidents and one high profile fatal accident at the world glider aerobatic championships at Hockenheim in Germany highlighted problems with condensation soaking highly stressed wooden parts causing structural failure The pilot Krzysztof Wyskiel was carrying out his competition routine with high accuracy until the penultimate manoeuvre when the wings failed clapping hands above the fuselage which shot straight down to the ground like an arrow killing Krzysztof Wyskiel instantly The three remaining Kobuz 3 s in the competition were grounded and remained so until the aircraft were cleared for limited manoeuvres only curtailing their aerobatic competition careers In 1991 the design of a new composite build aerobatic glider S 1 Swift had been finished based on the Kobuz 3 design the wings of the first production series of the Swift glider had been manufactured using the wings of Kobus 3 as molds 3 Variants EditSZD 21 Sokol The original designation of the project as begun in 1958 SZD 21 2 Kobuz The initial prototype version reg n SP 1990 which proved unsatisfactory modified to Kobuz 2A SZD 21 2A Kobuz 2A The second version of the prototype reg n SP 1990 again disappointing modified to SZD 21 2AZ SZD 21 2AZ The final modification state of the SZD 21 prototype reg n SP 1990 which crashed on 20 April 1963 SZD 21 2B Kobuz 3 The final version of the Kobuz first flight 10 December 1964 1 which proved acceptable and a small production batch were completed Specifications SZD 21 Kobuz 3 EditData from http www piotrp de SZYBOWCE dszd212b htmGeneral characteristicsCrew 1 Length 7 25 m 23 ft 9 in Wingspan 14 m 45 ft 11 in Height 1 9 m 6 ft 2 8 in Wing area 13 5 m2 145 3 sq ft Aspect ratio 14 5 1 Airfoil NACA 641 412 Empty weight 311 kg 685 6 lb Gross weight 401 kg 884 lb Performance Maximum speed 250 km h 154 3 mph 189 kn Stall speed 73 km h 45 mph 39 kn g limits 7 5 as built 4 1 5 post 1989 Maximum glide ratio 30 1 19 1 inverted at 100 km h 54 kts 62 mph Rate of sink 0 90 m s 177 ft min at 100 km h 62 kn See also EditAircraft of comparable role configuration and era Vogt Lo 100 Swift S 1 MDM 1 Fox PZL Bielsko SZD 59References Edit a b c d in Polish Babiejczuk Janusz and Grzegorzewski Jerzy Polski przemysl lotniczy 1945 1973 Polish aerospace industry 1945 197 Warsaw Wydawnictwo MON 1974 p 126 a b Glass A 1965 p 124 126 Segel Kunstflugzeuge Swift S 1 Taylor J H ed 1989 Jane s Encyclopedia of Aviation Studio Editions London p 29 Glass Andrzej ed 1965 Konstrukcje lotnicze Polski Ludowej Aviation constructions of People s Poland WKiL Warsaw p 124 126 Polish External links Edit Wikimedia Commons has media related to SZD 21 Kobuz http www abpic co uk search php q PZL Bielsko 20SZD 21 20Kobuz 203 amp u type https web archive org web 20090916142935 http www szdjezow com pl ofirmie eng html http luftfahrtmuseum org htmi itf szd21 htm permanent dead link http www piotrp de SZYBOWCE dszd212b htm http www piotrp de SZYBOWCE dszd21 htm http www sagach ch Deutsch Flugzeuge Kobuz htm http www flightglobal com pdfarchive view 1962 1962 20 200016 html http www flightglobal com pdfarchive view 1962 1962 20 200017 html https www youtube com watch v DjwNOoqf0WM Retrieved from https en wikipedia org w index php title SZD 21 Kobuz amp oldid 1107279179, wikipedia, wiki, book, books, library,
