Saab 17

The Saab 17 is a Swedish single-engine monoplane reconnaissance dive-bomber aircraft of the 1940s originally developed by ASJA prior to its merger into Saab. It was the first all-metal stressed skin aircraft developed in Sweden.

Design and development

The project was initiated in response to a 1938 request from the '' Flygvapnet'' (Swedish Air Force) for a reconnaissance aircraft to replace the obsolete Fokker S 6 (C.Ve) sesquiplane. Design work began at the end of the 1930s as the L 10 by ASJA, but once accepted by the '' Flygvapnet'' it was assigned the designations B 17 and S 17 for the bomber and reconnaissance versions respectively, and it became better known as the Saab 17.

The design chosen was a conventional mid-wing cantilever monoplane with a long greenhouse canopy and a single radial engine in the nose. Control surfaces were covered in fabric but the remainder was stressed-skin duraluminum. It could be fitted with wheels or skiis, both of which retracted straight to the rear along the underside of the wing, leaving prominent fairings, and when fitted with wheels the undercarriage doors could be used as dive brakes.Karlström, 1988, p.52 A retractable tailwheel was provided. A floatplane version was built in small numbers for coastal reconnaissance to replace the obsolete Svenska Aero S 5, with massive fairings joining the floats to the wings where the wheels would have been. To maintain stability small vertical fins were added to the horizontal stabilizer. The wings were reinforced so that it could be used as a dive bomber. Bomb racks were provided under the wings, along with a small bomb bay below the cockpit, although some examples used a conventional rack on the centreline. On the bomber versions, a crutch was fitted to swing the bomb clear of the aircraft in vertical diving attacks, when the bomb could otherwise have passed through the propeller. The reconnaissance versions lacked the crutch. Split flaps broken into four segments were fitted to the underside trailing edge of the wing.

Two L 10 prototypes were ordered, the first being powered by a Bristol Mercury XII radial engine built by Nohab in Sweden, and the second with an imported Pratt & Whitney R-1830 Twin Wasp C radial.

Supplies of suitable engines remained a major problem, and resulted in the aircraft being built in three versions with different engines.
The definitive B 17A used the Swedish-built STWC-3 (Swedish Twin Wasp C-3), an unlicenced copy of the R-1830. The B 17B used a Bristol Mercury XXIV built by Svenska Flygmotor AB (SFA) in Sweden, and the B 17C used an imported Piaggio P.XI radial from Italy. The United States government denied a request to purchase a licence to build the Twin Wasp, so an unlicensed, reverse engineered copy was built instead as the STWC-3 (Swedish Twin Wasp C-3) to supplement and replace the lower powered Mercury radials already being built under licence.Annerfalk, 1999, p.84 Until production caught up with demand, the earliest aircraft being delivered were flown to their destinations, the engines were removed and shipped back, to be used on the next aircraft to be delivered.

Operational history

The first flight was on 18 May 1940 and first deliveries of dive bombers to the ''Flygvapnet'' began in March 1942, while deliveries of reconnaissance versions began in June 1942, and the type was operational by September 1942 when the first exercises were carried out. Problems immediately arose with wing failures, and additional modifications were needed before it could be cleared for dive bombing, which remained limited to shallow attacks thereafter. The final aircraft was delivered on 31 August 1944.

A B 17 was used to test the ejection seat Saab had developed for use in the Saab 21 pusher fighter, which was first successfully fired on 27 February 1944 with a dummy.Annerfalk, 1999, p.95

Stig Wennerström gained some fame in Sweden for successfully bailing out from a B 17 from low altitude, with his gunner, but would later become a spy for the Soviet Union.Annerfalk, 1999, p.144

For several months in late 1944 and early 1945 fifteen B 17As were operated by the Danish Brigade in Sweden (Danforce) a unit of 5000 men (including 50 airmen) in Sweden which had been formed to assist in liberating occupied Denmark from the Nazis, and preventing the retreating German soldiers from using civilians as human shields, and carrying out scorched earth tactics as they had done elsewhere. However, due to the German surrender on 7 May 1945, the aircraft were no longer needed and were returned to ''Flygvapnet'' control a couple of months later.Annerfalk, 1999, p.100

Rapid advances in aviation related to improved aerodynamics, higher engine power and finally the introduction of jet engines, resulted in it having a short career, and it was gradually withdrawn from frontline service between 1948 and 1950, while the last examples were retired from secondary roles by 1954. Over the next few years, examples would be sold off to various operators.

Due to the efforts of Carl Gustaf von Rosen, the Ethiopian Air Force bought 47 which were operated from 1947 until 1968.

From 1951, 19 B 17s were loaned to '' Svensk Flygtjanst AB'' and AVIA for use as target tugs and painted yellow with civilian markings. One of these, a B 17A SE-BYF was sold to the Austrian ''Österreichische Luftstreitkräfte'' in 1957, where it continued to be used as a target tug until retired in 1963. Two B 17As were also sold to the Finnish ''Ilmavoimat'' in 1959 and 1960, also as target tugs. Neither of the Finnish aircraft lasted long before being destroyed in accidents.

Variants

Company designations

;L 10
:internal ASJA/Saab designation; two produced

;L 10A
:internal ASJA/Saab designation for 17A, B, and C
;L 10BL
:internal ASJA/Saab designation for S17BL
;L 10BS
:internal ASJA/Saab designation for S17BS

Flygvapnet designations

;P 7
:L 10 development prototypes

;B 8
:Preliminary designation for bomber version of L 10, not used

;B 17A
:Bomber with Svenska Flygmotor Aktiebolaget (SFA)-built STWC-3 (Pratt & Whitney R-1830-S1C3G Twin Wasp) radial engine; 132 built
;B 17B
:Bomber with SFA-built Bristol Mercury XXIV radial engine; 55 built
;B 17C
:Bomber with Piaggio P.XIbis R.C.40D radial engine; 77 built

;S 15
:Preliminary designation for reconnaissance version of the L 10, not used
;S 17BL
:Reconnaissance version of B 17B with wheeled or ski landing gear; 21 built
;S 17BS
:Reconnaissance version of B 17B with floats, powered by a Bristol Mercury XXIV engine; 38 built

A total of 326 Saab 17 aircraft of all types were produced, and some bombers were converted into reconnaissance aircraft.

Operators

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* ''Österreichische Luftstreitkräfte'' (Austrian Air Force) - operated one target tug
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* ''Flyvevåbnet'' (Royal Danish Air Force) - operated 15 on loan while in exile with the ''Den Danske Brigade'' Danforce in 1945.
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* ''Ye Ithopya A yer Hayl'' (Imperial Ethiopian Air Force) - operated 47 examples
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* ''Ilmavoimat'' (Finnish Air Force) - operated two target tugs
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* ''Svenska Flygvapnet'' (Swedish Air Force)
** F 2 Hägernäs/Roslagen Air Corps Naval Support Wing ( Hägernäs, near Stockholm) - S 17BS floatplanes onlyAnnerfalk, 1999, p.59
** F 4 Frösön/Jämtland Wing (Frösön)
** F 6 Karlsborg/Västgöta Wing ( Karlsborg)
** F 7 Såtenäs/Skaraborg Wing (Såtenäs)
** F 12 Kalmar/Kalmar Wing (Kalmar)

Surviving aircraft

Five Saab 17s are known to be in existence today, three of which are on public display.

The Swedish Air Force Museum in Linköping has two aircraft in their collection, a S 17BL '5', serial 17005 which is on static display in the museum, and a B 17A '7', serial 17239, the latter being kept in airworthy condition and which is periodically flown.

Another B 17A 'E', serial 17320 which was donated by the Flygvapnet after having served as a target tug is on display at the Danish Museum of Science and Technology in Helsingør/Elsinore.

Two former Ethiopian B 17As were recovered in the 1990s and purchased by a South African collector as a part of a large batch of ex-Ethiopian aircraft. These were shipped to Lithuania but their current status and location is unknown following the collapse of the collector's business interests.

Specifications (B 17C)

See also

References

Citations

Bibliography

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Further reading

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{{Swedish military aircraft designations

17
1940s Swedish bomber aircraft
Single-engined tractor aircraft
Mid-wing aircraft
Aircraft first flown in 1940
Aircraft with retractable conventional landing gear
Single-engined piston aircraft