Saab 17

Saab

Company type	Aerospace and defense company
Industry	Aerospace, defense
Predecessor	ASJA
Fate	Integration of ASJA into Saab
Headquarters	Sweden (implied) , Sweden
Area served	Worldwide (implied by export and military use)
Products	Aircraft, including Saab 17

Template:Infobox aircraft The Saab 17 was a Swedish single-engine monoplane developed during the 1940s, designed primarily for reconnaissance and dive-bombing roles. Initially created by ASJA before its integration into Saab, it holds the distinction of being Sweden’s first all-metal stressed skin aircraft.

Design and development

File:Assembly-Halls-with-B17-planes-in-Trollhättan-142370502302.jpg

B 17 aircraft inside the Trollhättan assembly facility, 1944

In response to a 1938 requirement from the Flygvapnet (Swedish Air Force) for a new reconnaissance platform to replace the outdated Fokker S 6 (C.Ve) sesquiplane, development began on the L 10 project at ASJA towards the end of the 1930s. Following acceptance by the Flygvapnet, it was designated as B 17 for bomber configurations and S 17 for reconnaissance variants, though it became widely recognized as the Saab 17.

The aircraft featured a conventional mid-wing cantilever monoplane layout with a lengthy greenhouse-style canopy and a single radial engine mounted in the nose. While the control surfaces were fabric-covered, the rest of the airframe employed stressed-skin construction using duraluminum. The landing gear could be fitted with either wheels or skis, both retracting rearwards beneath the wings and leaving noticeable fairings; when equipped with wheels, the undercarriage doors also functioned as dive brakes. A retractable tailwheel was standard. A limited number of floatplane variants were produced for coastal reconnaissance duties to succeed the obsolete Svenska Aero S 5, featuring large fairings connecting floats to wing areas where wheels would normally be located. To ensure stability, small vertical fins were added to the horizontal stabilizer. The wings were structurally reinforced to handle dive-bombing stresses. Bomb racks were installed beneath the wings along with a small bomb bay under the cockpit, although some models utilized a conventional centreline bomb rack. Bombers were fitted with a crutch mechanism allowing bombs to swing clear during vertical dives to avoid striking the propeller; this feature was omitted on reconnaissance versions. The wing’s trailing edge underside incorporated four-segment split flaps.

Two prototypes of the L 10 were commissioned: one powered by an 880 hp (660 kW) Bristol Mercury XII radial engine produced domestically by Nohab, and another equipped with an imported 1,065 hp (794 kW) Pratt & Whitney R-1830 Twin Wasp C radial engine.

Engine availability posed ongoing challenges, leading to production of three distinct variants featuring different powerplants. The definitive B 17A model used the Swedish-built STWC-3 (Swedish Twin Wasp C-3), an unlicensed copy of the Pratt & Whitney R-1830. The B 17B variant was fitted with a locally manufactured Bristol Mercury XXIV engine from Svenska Flygmotor AB (SFA), while the B 17C employed an imported 1,060 hp (790 kW) Piaggio P.XI radial engine from Italy. When denied permission by the United States government to license-build the Twin Wasp, Sweden resorted to reverse engineering it to produce the STWC-3, supplementing and eventually replacing lower-powered Mercury radials built under licence. Early deliveries involved flying aircraft without engines to their destinations so that engines could be returned and reused on subsequent units until production met demand.

Operational history

File:Saab B 17B on ground.jpg

Saab B 17B displaying the bombing crutch beneath the fuselage, which was necessary to ensure the bomb cleared the propeller during dives, alongside the prominent undercarriage doors that functioned as dive brakes

File:Saab B17B in the air.jpg

Saab B 17B airborne

The maiden flight took place on 18 May 1940, with initial deliveries of dive bomber variants to the Flygvapnet commencing in March 1942. Reconnaissance models began arriving in June 1942, and by September of that year, the aircraft had entered operational status, participating in its first exercises. Early on, wing structural failures became apparent, necessitating further adjustments before dive bombing could be authorized. Even then, dive attacks were restricted to shallow angles. The final unit was delivered on 31 August 1944.

One B 17 served as a test platform for Saab’s ejection seat developed for the Saab 21 pusher fighter; this system was successfully tested with a dummy pilot on 27 February 1944.

Stig Wennerström gained notoriety in Sweden after safely ejecting from a B 17 at low altitude along with his gunner; he later became known as a Soviet spy.

Between late 1944 and early 1945, fifteen B 17As were operated by the Danish Brigade in Sweden (Danforce), a contingent of approximately 5,000 personnel including 50 airmen. This unit was established in Sweden with the objective of assisting in Denmark’s liberation from Nazi occupation and preventing German troops from employing civilians as human shields or executing scorched earth tactics. Following Germany’s surrender on 7 May 1945, these aircraft were no longer required and were returned to Flygvapnet control within a few months.

Technological progress in aerodynamics, engine performance, and especially the advent of jet propulsion led to a relatively brief service life for the B 17. It was progressively phased out of frontline duties between 1948 and 1950, with remaining units withdrawn from secondary roles by 1954. Subsequently, several aircraft were sold to various operators.

Thanks to Carl Gustaf von Rosen’s efforts, the Ethiopian Air Force acquired 47 B 17s, which remained in service from 1947 until 1968.

Starting in 1951, nineteen B 17s were loaned to Svensk Flygtjanst AB and AVIA for use as target tug aircraft; these were painted yellow and bore civilian registration markings. One such aircraft, a B 17A registered SE-BYF, was sold to the Austrian Österreichische Luftstreitkräfte in 1957 and continued target tug duties until its retirement in 1963. Additionally, two B 17As were sold to the Finnish Ilmavoimat in 1959 and 1960 for similar roles; however, both Finnish aircraft were lost due to accidents within a short period.

Manufacturer designations

L 10

ASJA/Saab internal code; two units completed

File:Saab S 17BS.jpg

Saab S 17BS equipped with floats

L 10A

ASJA/Saab internal code covering models 17A, B, and C

L 10BL

ASJA/Saab internal code for the S17BL variant

L 10BS

ASJA/Saab internal code for the S17BS version

Swedish Air Force designations

P 7

Development prototypes of the L 10 series

B 8

Initial designation for the bomber variant of L 10, never officially adopted

File:Saab B 17C.png

Saab B 17C in flight. The three principal variants can be identified by their intake and exhaust configurations. The 17A featured a single intake centered atop the cowling, the 17B had an offset intake to starboard with a prominent exhaust on the same side, and the 17C was equipped with dual intakes on either side of the upper cowling

B 17A

Bomber powered by a 1,065 hp (794 kW) radial engine STWC-3 (Pratt & Whitney R-1830-S1C3G Twin Wasp) manufactured by Svenska Flygmotor Aktiebolaget (SFA); total of 132 produced

B 17B

Bomber fitted with a 980 hp (730 kW) Bristol Mercury XXIV radial engine built by SFA; 55 units produced

B 17C

Bomber variant powered by a 1,060 hp (790 kW) Piaggio P.XIbis R.C.40D radial engine; 77 aircraft built

S 15

Initial designation intended for reconnaissance adaptation of L 10, unused

S 17BL

Reconnaissance model derived from B 17B, equipped with wheeled or ski landing gear; production count of 21

S 17BS

Reconnaissance floatplane version of B 17B with Bristol Mercury XXIV engine; total of 38 manufactured

Altogether, production reached 326 Saab 17 aircraft across all versions, with some bombers later converted to reconnaissance roles.

Operators

File:17320 Danmarks Tekniske Museum.jpg

Saab B 17A exhibited in Helsingør bearing Danish markings

Template:AUT

• Österreichische Luftstreitkräfte (Austrian Air Force) - operated a single target tug aircraft

Template:DEN

• Flyvevåbnet (Royal Danish Air Force) - utilized fifteen units on loan during exile with the Den Danske Brigade (Danforce) in 1945

Template:Country data Ethiopia

• Ye Ithopya A yer Hayl (Imperial Ethiopian Air Force) - operated a fleet of forty-seven Saab 17s

Template:FIN

• Ilmavoimat (Finnish Air Force) - employed two aircraft as target tugs

Template:SWE

• Svenska Flygvapnet (Swedish Air Force)
  • F 2 Hägernäs/Roslagen Air Corps Naval Support Wing (Hägernäs, near Stockholm) - exclusively operated S 17BS floatplanes
  • 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

File:Saab B17A Fv17239 1.jpg

Saab B 17A preserved by the Swedish Air Force Museum. Another B 17 is also exhibited at the museum.

Currently, five Saab 17 aircraft are confirmed to survive, with three accessible to the public.

The Swedish Air Force Museum located in Linköping holds two examples: an S 17BL '5', serial number 17005 displayed statically within the museum, and a B 17A '7', serial number 17239 maintained in flying condition and occasionally flown.

Another B 17A 'E', serial number 17320, donated by the Flygvapnet after serving as a target tug, is exhibited at the Danish Museum of Science and Technology in Helsingør.

Two former Ethiopian B 17As were recovered during the 1990s and acquired by a South African collector as part of a large group of ex-Ethiopian aircraft. These were transported to Lithuania, but following the collapse of the collector's enterprise, their present location and status remain unknown.