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Saab B17A

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.

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. A retractable tailwheel was provided. A floatplane version was built in small numbers for coastal reconnaissance to replace the obsolete Svenska 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 and 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, while 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 an 880 hp (660 kW) Bristol Mercury XII radial engine built by Nohab in Sweden, and the second with an imported 1,065 hp (794 kW) 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 unlicensed 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 1,060 hp (790 kW) 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. Until production caught up to 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.

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