Saab 17

Sweden (1942)
Dive Bomber – 323 Built

The Saab B 17 is the product of Sweden’s need to procure assets to defend its sovereignty and neutrality in the light of a gradually complicated international and regional context, to the point that it was prioritized over the equally capable and versatile Saab B 18. This aircraft was a milestone for the main company in the Swedish aerospace industry, as it was the very first airplane produced and delivered by this company following its acquisition and merge with ASJA, the aircraft branch of the Swedish Railroad Workshops company. It was also the application of the lessons and experience provided by the licensed-manufacturing of the Northrop 8-A1 bomber by AJSA/Saab. AJSA was already commissioned by the Defence Material Administration to develop and build a single-engine and light fighter-bomber, so Saab took over the design and development process in 1939 after both companies merged, evolving into the final light bomber, dive bomber and reconnaissance aircraft. Designated as the L 10 by ASJA, the design became the Saab 17, incorporating a good number of innovations and becoming a very versatile and adaptable airframe. Yet its time of service with the Flygvapnet was rather brief, as it was de-commissioned by the late 40’s. This was due to new and more powerful powerplant technologies such as jet propulsion. Instead, it served for a long period of time in Ethiopia until 1968.

The Saab B 17 is a light bomber/dive bomber and reconnaissance plane with two seats, a single engine and a single tail, whose design bears a close resemblance with the Mitsubishi Ki-30 “Ann”, the Mitsubishi Ki-15, the Vought OS2U, and the Curtiss SB2C Helldiver, especially with the elongated shape of the main airframe and equally elongated windscreen of the cabin (as well as the same cockpit), which occupies most of the superior area of the airframe and it is fully incorporated in the fuselage. The wing is a mid-wing (cantilever) of trapezoid shape with a remarkable characteristic: where the retractable landing gear, which was covered with streamlined fairings, was placed, the rear part of the wing was divided. From the fuselage to the place of the landing gears, it was straight; from the landing gears area to the wingtip, it was angled. The forward area of the wing was straight, and the wingtips were rounded. The wing, from a frontal perspective, was slightly angled upwards from the landing gear area to the wingtip. It was also a reinforced wing to allow it to deal with the high stress by dive bombing missions.

The Saab B 17 was powered by different powerplants during its career, as many versions had their own powerplants. The two prototypes (L 10) were powered by a licensed-built Bristol Mercury XII of 880hp by NOHAB (Nydqvist & Holm AB) and by a Pratt & Whitney R-1830 Twin Wasp of 1065hp each. The first production version (B 17A) was powered by the same Pratt & Whitney R-1830 (S1G3C) of 1050hp, while the B 17B (and also the B 17BL and B 17BS) was powered by a licensed-built Bristol Mercury XXIV of 980hp, with the B 17C powered by a Piaggio P.XIbis R.C.40D of 1040hp. Consequently, speed tended to vary from version to version as well. For instance, the B 17A could reach speeds of up to 435 Km/h (270 mph); the B 17B could reach speeds of up to 395 Km/h (245 mph), the B 17BL and B 17BS could reach speed of up to 330 Km/h (205 mph); and the B 17C could reach speed of up to 435 Km/h (270 mph). The landing gear was also varied from version to version, as it could have the classic set of two wheels at the wings and a small tailwheel, skies as replacement for the wheels, and even special twin floats permanently attached. This gave the B 17 considerable versatility, as it could take off and land in normal runways to snow-covered terrain, and also in water surfaces.

The armament had no modifications, comprising of two 8mm Ksp m/22F machineguns placed at the forward section of the wings and after the landing gear area, a single and moveable 8 mm Ksp m/22R machine gun firing backwards for the observer/navigator/radio operator, and a payload of up to a 500-kg (1,102 lb) bomb or 700-kg (1,500 lb) bomb. Interestingly, the dive bomber version had an under-fuselage trapeze to accommodate a 500 Kg bomb, along the wing weapons stations. And it had state-of the art avionics for bombers by the time, like the bomb-sight BT2 (also known as m/42) that increased precision, mostly the late versions. In addition, it had two radios, an FR-2 and FRP-2. The reconnaissance version had a camera placed at the bottom of the fuselage.

The initial roles of the airplane were reconnaissance and artillery spotting, roles that were, however, already filled by other air assets such as the Fieseler Storch and the Hawker Hart. As a result, the new airplane was required to be a light dive-bomber as well. Nevertheless, the final model retained all of the two missions through its variants, as well as receiving a level light-bomber and dive-bomber role. It would also be used for target towing later in its career. The Saab B 17, like the B 18, had an American ‘soul’ as well, thanks to the 40-50 American engineers that were part of ASJA and contributed with the design and construction of the airplane, hence the abovementioned similarity with the American airplanes. And it needed to receive some structural modifications, especially for the dive-bombing missions, such as the reinforcing of the wings and the landing gear folding system. This could be retracted backwards and used as an airbrake, taking advantage of the fairing.

Development of the B 17 began in 1937 when ASJA began works on its L 10; as Saab merged with ASJA that same year, it continued with the development of the given aircraft, which would be an all metal airframe – something that was a novelty as airplanes back then used to have wood and other materials part of the fuselage. Two prototypes were built, each one having a different powerplant and flying for the first time in May 1940. The test pilot, Claes Smith, assessed the design as a good one, despite the fact the cockpit wheel came loose and fell prior landing. During development, it was realized that some modifications were needed, like changing the carburetor air intake from the top of the engine cowling to the starboard side of the cowling. This was done to prevent the engine from stopping. A spin fin was also added. By the end of 1940, the first 8 B 17s were produced, entering in service with the Flygvapnet in 1942. Some issues delayed the production programme, however. Nonetheless, 324 airframes were produced between 1942 and 1944, with three main versions: the B 17A light bomber and later target towing aircraft, the B 18B – and its sub-variants B 17B I, B 17B II, B 17BL and B 17BS – light bomber and reconnaissance versions (this version was the one that received most of structural the modifications), and the B 17C bomber version.

The B 17 had one of the shortest service period with the Flygvapnet, as it was retired 7 years after it was introduced; yet it remained in service in Austria, Finland, and Ethiopia until 1968. In Sweden, they remained in service with civilian operators and in very small numbers until 1959, where they received new avionics.

5 airframes remain, one of them airworthy and still operating today in airshows. Two are museum pieces in Linköping and one in Helsingør, Denmark. Two airframes are reportedly located in Lithuania.

Design

The design of the B 17 is similar to other aircraft used in WWII by other countries, meaning it has the typical ‘WWII style’. But instead of being the average WWII design, the B 17 has some remarkable and particular characteristics. The airplane is an all-metal airframe, with the bow having a cylinder shape thanks to the radial engine and the stern is topped off with the tail, and the overall airframe being elongated with a sort of conical shape. The airplane is also a semi-straight leading-edge wing airplane, but the wings also have a particular characteristic. In fact, the wings have a ‘divided’ shape, with the area of the landing gear being the dividing point. First, from the fuselage to the landing gear, the leading-edge is straight while the rear-edge is also straight, having two ‘dog-teeth’ that mark where the rear area of the fairings are located. Second, from the landing gears to the tip of the wings, the leading-edge of the wings are straight as well, but the rear-edges are angled, making this area of trapezoid shape. The tips are rounded. The wings also have a divided shape from a frontal perspective, with the landing gear being also the dividing area. From the fuselage to the landing gear area, the wing is straight. However, from the landing gear to the tip of the wings, it is angled upwards, similar to the Ju-87 Stuka or the Douglas SBD ‘Dauntless’, only that the angle is not as wide. The wing, furthermore, is installed in the middle of the fuselage (cantilever), also being reinforced. Such reinforcement can be seen through its thickness. The horizontal stabilizers are also of trapezoid shape, with the control surfaces per se having an inwards angle at the tip of the surface. The tail has a similar shape with the rudder occupying most of the surface and having also an inwards angle near the tip. Both horizontal and vertical stabilizers have an equally rounded shape.

The canopy is another remarkable characteristic of the B 17, as it is very elongated, occupying almost 40% of the superior area of the fuselage and making an impression that the B 17 has a crew of three, rather than the actual crew of 2: the pilot and the radio operator/navigator/observer. As a result, the cockpit had a lot of space, which allowed the second crewman to slide the seat back and forwards between the two different workstations. Beneath the forward area of the cockpit was where the bombs bay was located. A long antenna was placed above the canopy, right after the pilot’s seat, with a long cable connecting it with the tail. The landing gear was of classic configuration, with two (extended) wheels placed beneath the wings and a third wheel placed beneath the tail. The two forward wheels have a particular trait that gave the B 17 another distinctive characteristic either in land or when in flight: the forward landing gears were covered with an aerodynamic fairing as it folded backwards, into the wing. The purpose was to use such fairing as an airbrake, yet it was not entirely functional as the hydraulic system wasn’t powerful. The fairings were met by a ‘hood’ of sorts at the wing; when the landing gear folded, it gave the landing gears cover a cylinder shape, making the B 17 to have two cylindrical structures at the wings while in flight, making easy its recognition while in flight. The B 17 went through a series of modifications, especially the reconnaissance versions, as they received floats – with the purpose of operating from water – along with small endplates (placed right before the wing tips) and aerodynamic struts. The landing gear, in turn, could be replaced with skis instead of wheels, an ideal device for winter or Arctic operations.

The B 17 received three different type of powerplants. The first two prototypes were powered by a NOHAB-built Bristol Mercury XII and a Swedish-made Pratt & Whitney R-1830 Twin Wasp engines. The production versions had the following powerplants: a Swedish-made Pratt & Whitney R-1830 Twin Wasp (B 17A); a Swedish-made (by SFA) Bristol Mercury XXIV (B 17B and the different sub-variants); and the Piaggio P.XIbis R.C.40D (B 17C). All the engines were radial and air-cooled, with 9 or 14 cylinders. The propeller was a three-bladed Piaggio P.1001 variable pitch propeller. The engines yielded different speeds. The B 17A could reach speeds of up to 435 Km/h (270 mph), the B 17B could reach speed of up to 395 Km/h (205 mph), and the B 17C could reach also speeds of up to 435 Km/h (270 mph).

The B 17 had a standard armament with no variation from model to model, except for those with reconnaissance tasks. It consisted of two 8mm Ksp m/22F mounted at the wings and firing forwards, and one 8mm Ksp m/22R mounted at the stern of the cockpit, which was moveable and could fire backwards. A 500 Kg (1,102 lb) (B 17A) or a 700 kg (1,500 lb) (B 17B andC) could also be carried. Some units of the B 17A were modified to carry air-to-ground rockets. The reconnaissance versions were fitted with a camera type N2. An advanced bomb sight named the ‘m/42’ was introduced to enhance bombing efficiency, especially at dive-bombing, reducing the angle of bombing.

The B 17 was the very first plane produced by Saab, and incorporated many of the lessons and experiences acquired with the licensed-manufacturing of the Northrop 8-A1 bomber by ASJA and then Saab itself, being also the first then modern all-metal light bomber produced by Sweden during WWII. As the m/42 bomb-sight was developed and introduced for this aircraft, it was reportedly exported to the US.

An ‘all-terrain’ airplane

If there is something that makes the B 17 a remarkable design, it is the fact that modifications to its landing gear allows the plane to operate from any type of terrain… literally. The main landing gear configuration is that with wheels for normal operations in normal airstrips. But when winter comes, the wheels could be replaced with skis, allowing the airplane to operate even in harsh cold weather conditions with snow-covered airstrips. This might indicate that Sweden needed an all-time available air asset to defend its sovereignty and neutrality, or maybe that it absorbed the operational lessons the Swedish Volunteer squadron that took part during the Winter War, or the lessons provided by that same conflict. But the B 17 received another modification that allowed it to operate from the surface of any water body, as it could be fitted with two floats replacing the wheeled-landing gears, becoming the B 17BS. This variant was mainly used for water-borne aerial reconnaissance.

Close to War and the architect of an air force

Despite being a rather obscured airplane in history, the B 17 would have been one of the few neutral airplanes to take actual part in a conflict, besides those belonging to the Flygvapnet that took part during the Winter War. For instance, the Danish Brigade, a unit comprised of refugee Danish airmen supported and equipped by Sweden, would have been close to assist in the liberation of their country, if it weren’t for the fact that the Swedish government did not allow it to take off with the supplied B 17 units to Denmark. The B 17s were then offered to the Danish Air Force, but were rejected as the German surrender took place some days before the offering was made, being returned to the Flygvapnet.

But the adventures of the B 17 would not finish there, Ethiopian country was looking for assistance in building a more advanced air force of its own after WWII. Sweden became the main supporter of this small air force, supplying Saab Safir trainers and B 17 light bombers, as they later were being phased out in 1947. It also employed some former Flygvapnet personnel and under orders of Carl Gustav von Rosen, who also became the chief instructor of the rebuilt Imperial Ethiopian Air Force. It remained in service there until 1968.

Variants

L-10 – The prototype version of the B 17 under the denomination it had when ASJA was tasked with the design and development process. One unit was powered by a NOHAB-made Bristol Mercury XII 880hp engine and another was powered by a Pratt & Whitney R-1830 Twin Wasp engine.
B 17A – Bomber version powered by a Pratt & Whitney R-1830-S1C3G Twin Wasp engine of 1050 to 1200 hp. Some units were modified to carry air-to-ground rockets. The armament of this version became standard for the bombers and its other variants: 2x8mm machine guns placed on the wings and firing forwards, and an 8mm rear machine gun placed at the second crewman’s post, along a 500 kg (1,102 lb) bomb. 132 units delivered.
B 17B – Bomber version powered with a Swedish-built Bristol Mercury XXIV (Svenska Flygmotor Aktiebolaget SFA) engine, with the same armament configuration except for a 700 kg (1,500 lb) bomb. 55 units delivered.
B 17B I – Dive-bomber version fitted with a trapeze under the fuselage, carrying a 500 Kg (1,500 lb) bomb, and underwing hardpoints for bombs. It was equipped with the m/42 bombsight.
B 17B II – A light level bombing version fitted with an internal bomb bay and underwing hardpoints.
B 17BL – Reconnaissance version fitted with a wheeled landing gear and a camera in the fuselage, replacing the HE 5 Hansa and the Fokker C.VD/C.VE. 21 units delivered.
B 17BS – Reconnaissance floatplane version fitted with twin floats, aerodynamic struts, and endplates on the horizontal stabilizers. 38 units delivered.
B 17C – Another bomber version fitted with the Piaggio P.XIbis R.C.40D 1040hp engine, and carrying a 700 kg (1,500 lb) bomb. 77 units produced.

Operators

Sweden
The Flygvapnet was the main operator of the B 17, with 132 units of the B 17A model, 55 units of the B 17B and its modified sub-variants, and 77 of the B 17C variant. The first model was fitted with an inner bomb bay with some airframes modified to carry air-to-ground rockets. The following version was used as bomber – equipped with the advanced m/42 bombsight and some with the trapeze and underwing hardpoints – up until 1945. Some airframes were modified for reconnaissance duties and subsequently equipped with cameras. These modified aricraft served until 1949. Some airframes received further modifications such as the twin floats and other structural modifications. The B 17C was used for bombing missions, having an internal bomb bay and hardpoints until 1948, when they were withdrawn due to problems with the engines. The B 17 operated in six squadrons from 1942 to 1949 as it follows: the B 17 bomber and dive-bomber versions operated in F4 Frösön, F6 Karlsborg, F7 Stenäs, and F12 Kalmar. The B 17BS sea-based planes operated with F2 Hägernäs, and the land-based reconnaissance planes operated in the F3 Malmslätt.Following the B 17 withdrawal from service with the Flygvapnet, the airplane was operated by civilian companies for various purposes, target towing included. Two B 17BS were purchased by the Osterman Aero and used to carry fish and shellfish from Bergen (Norway) to the Swedish capital. In addition, 19 B 17A were loaned to AVIA and Svensk Flygtjänsk AB and modified for target towing; 5 of them received ECM equipment in 1959. One B 17A remains airworthy in airshows, with 2 additional airframes used as museum displays.
Finland
The Ilmavoimat (Finnish Air Force) received two B 17A for target towing tasks, which were lost in accidents.
Austria
The Österreischische Luftstreitkräfte (Austrian Air Force) received a B 17A via Svensk Flygtjänsk AB in 1957. This was done to facilitate the deal as it was a privately-owned airplane, considering the restrictions the Swedish government sets on sales abroad on Swedish-made military equipment.
Denmark
As this country was under German occupation, a Danish brigade was established in Sweden in 1943 with 15 pilots and equipped with 15 B 17C under loan, taking part in training and exercises with the Flygvapnet, being painted with Danish colors. They were not given permission to leave the Swedish territory despite being ready to enter action against the Germans; the 15 units were offered to Denmark, but this country never accepted them, with Germany surrendering some time after the offer was made. One remains as a display in a museum.
Ethiopia
The Ethiopian Air Force received 46 B 17As between 1947-1953 as the airplanes were being phased out in Sweden, and mainly as Sweden agreed to support the establishment of the Ethiopian Air Force under the lead of Carl Gustav von Rosen and with some former Flygvapnet personnel. The Ethiopian B 17 remained in service until 1968.

Specifications (B17C)
Wingspan	44 ft 11 in / 13.7 m
Length	32 ft 10 in / 10 m
Height	14 ft 9 in / 4.5 m
Wing Area	307 ft² / 28.5 m²
Engine	1x Piaggio P.XIbis R.C.40D 9 cylinders air-cooled radial piston engine, with a 3-bladed Piaggio P.1001 variable propeller.
Maximum Take-Off Weight	8,355 lb / 3,790 kg
Empty Weight	5,908 lb / 2,680 kg
Loaded Weight	8,532 lb / 3,870 kg
Climb Rate	2,000 ft/min / 10m/s
Maximum Speed	270 mph / 435 kmh
Range	1,056 miles / 1,700 km
Maximum Service Ceiling	32,200 ft / 9,800 m
Crew	2
Armament	2x 8mm Ksp m/22F machine guns, wing mounted, firing forwards An 8mm Ksp m/22R machine gun pintle mounted at the rear of the cabin and firing rearwards Up to 700 kg (1,500 lb) of bombs, the B 17B could carry a similar payload, while the B 17A could carry a 500-kg bomb (1,102 lb). The reconnaissance versions had a Type N2 Camera.