Dyle et Bacalan DB-70
Encyclopedia
The Dyle et Bacalan DB-70 was a large three engine French
airliner
with a thick airfoil
centre section which accommodated the passengers. Two fuselage
s, part of the centre section at the front but distinct further aft, carried the empennage
. First flown in 1929, only one was built.
, developed an aircraft manufacturing interest. They built several all-metal prototypes incorporating very thick wings. The DB-70 was the largest of these and the last to carry the company name: Dyle et Bacalan ceased trading in July 1929, before the DB-70 had flown, though the company reformed as Société Aérienne Bordelaise (SAB) that same month. As a result, the aircraft is sometimes referred to as the SAB DB-70; the letter prefix DB was retained, though aircraft designed later by SAB used the AB- form .
The DB-70 was a very large, all-metal aircraft built, like all Dyle et Bacalan aircraft, largely of duralumin
. As on the 1926 DB-10
, the centre section of the wing of the DB-70 was extremely thick and twice the chord of the outer wings, with a chord/thickness ratio of about 25%. The layout of the two designs was different, though; the otherwise conventionally laid-out DB-10 had thick wings inboard of its two engines, whereas the DB-70 was built around its thick centre section with twin fuselages, developed from it rearwards, carrying the empennage. The centre section also mounted the three 450 kW (600 hp) Hispano-Suiza
water-cooled inline engines and the pilots' cockpit and enclosed the passenger accommodation.
The 9.25 m span wide (30 ft) centre section, the structural core of the DB-70, was based on four steel transverse spars
, separated vertically by 2.30 m (7 ft 6 in), horizontally by 1.95 m (6 ft 5 in) and cross-braced into six frames, forming five transverse bays. The two pairs of outer frames defined the forward fuselages and the outer wings, engines and undercarriage legs were attached to the outermost frames. The centre engine was mounted on the central frame, positioned well forward of both the leading edge and of the planes of the two outer propellers. The whole structure was duralumin
skinned to form an aerofoil section with a chord of about 10 m (33 ft), the lower surface continuing to form the undersides of the fuselages.
The outer wings were mounted high on the fuselage sides, carried 3° of dihedral and were of parallel chord with rounded tips. Each was supported from below by a pair of struts mounted on the lower fuselage longeron
. The fuselages were simple rectangular cross section structures, built around four longerons and tapering rearwards. They carried the horizontal tail surfaces, both between them and extending outwards. The angle of incidence
of this 'fixed' tail could be adjusted in flight for trimming. It carried three linked and balanced elevators. Two rectangular fins carried balanced rudders. The DB-70 had a fixed conventional undercarriage with double mainwheels on V-shaped shock absorbing legs mounted on the lower longerons, with bracing struts to the centre of the centre section. This arrangement produced a wide undercarriage track of 6.65 m (21 ft 10 in). Sprung tailskids were placed the extreme ends of each fuselage.
The passenger accommodation was a rectangular area within the deepest part of the centre section, 5.35 m (17 ft 6 in) long, about 9.5 m (30 ft) wide and 1.88 m (6 ft 2 in) high. The structural bays divided this space laterally into three: two outer, 10 seat cabins 1.80 m (6 ft) wide, each lit by 5 windows in the outer fuselage walls, and a central saloon with eight arm chairs grouped around two tables. For night flights, the seats in each of the cabins were replaced by 8 berths, reducing the overall accommodation to 24. Aft of this central area were toilets, a kitchen and baggage space plus corridor access to a floor trapdoor which was the principal passenger entryway. A 'promenade' ran the width of the centre section ahead of the seating areas, lit by glazed wing leading edges, with further passenger access doors at either end. Adjacent to it in the centre section leading edge was a corridor that allowed the third crew member, a mechanic, to enter the engine compartments for in-flight servicing. The two pilots sat in an open cockpit, fitted with dual controls, at the centre section leading edge.
The first flight of the DB-70 was on 15 November 1929 from Merignac Aerodrome. Initial trial flights showed the aircraft could take of in about 120 m (400 ft) carrying a 5 tonne load. It flew around the airfield at Vincennes
on both days of the National Aviation meeting held there in June 1930. Photographs show that modifications were made after the early flights, including the provision of external exhaust pipes and an increase in passenger window size, done by making the original oval windows into square ones. Only one DB-70 was built, though the military, four engine SAB AB-20
and SAB AB-21 used very similar airframes.
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
airliner
Airliner
An airliner is a large fixed-wing aircraft for transporting passengers and cargo. Such aircraft are operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an aircraft intended for carrying multiple passengers in commercial...
with a thick airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
centre section which accommodated the passengers. Two fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
s, part of the centre section at the front but distinct further aft, carried the empennage
Empennage
The empennage , also known as the tail or tail assembly, of most aircraft gives stability to the aircraft, in a similar way to the feathers on an arrow...
. First flown in 1929, only one was built.
Design and Development
In 1925 the large naval ship builders Société Anonyme de Travaux Dyle et Bacalan, established in 1879 and based in BordeauxBordeaux
Bordeaux is a port city on the Garonne River in the Gironde department in southwestern France.The Bordeaux-Arcachon-Libourne metropolitan area, has a population of 1,010,000 and constitutes the sixth-largest urban area in France. It is the capital of the Aquitaine region, as well as the prefecture...
, developed an aircraft manufacturing interest. They built several all-metal prototypes incorporating very thick wings. The DB-70 was the largest of these and the last to carry the company name: Dyle et Bacalan ceased trading in July 1929, before the DB-70 had flown, though the company reformed as Société Aérienne Bordelaise (SAB) that same month. As a result, the aircraft is sometimes referred to as the SAB DB-70; the letter prefix DB was retained, though aircraft designed later by SAB used the AB- form .
The DB-70 was a very large, all-metal aircraft built, like all Dyle et Bacalan aircraft, largely of duralumin
Duralumin
Duralumin is the trade name of one of the earliest types of age-hardenable aluminium alloys. The main alloying constituents are copper, manganese, and magnesium. A commonly used modern equivalent of this alloy type is AA2024, which contains 4.4% copper, 1.5% magnesium, 0.6% manganese and 93.5%...
. As on the 1926 DB-10
Dyle et Bacalan DB-10
-External links:*...
, the centre section of the wing of the DB-70 was extremely thick and twice the chord of the outer wings, with a chord/thickness ratio of about 25%. The layout of the two designs was different, though; the otherwise conventionally laid-out DB-10 had thick wings inboard of its two engines, whereas the DB-70 was built around its thick centre section with twin fuselages, developed from it rearwards, carrying the empennage. The centre section also mounted the three 450 kW (600 hp) Hispano-Suiza
Hispano-Suiza
Hispano-Suiza was a Spanish automotive and engineering firm, best known for its luxury cars and aviation engines in the pre-World War II period of the twentieth century. In 1923, its French subsidiary became a semi-autonomous partnership with the parent company and is now part of the French SAFRAN...
water-cooled inline engines and the pilots' cockpit and enclosed the passenger accommodation.
The 9.25 m span wide (30 ft) centre section, the structural core of the DB-70, was based on four steel transverse spars
SPARS
SPARS was the United States Coast Guard Women's Reserve, created 23 November 1942 with the signing of Public Law 773 by President Franklin Delano Roosevelt. The name is a contraction of the Coast Guard motto: Semper Paratus and its English translation Always Ready...
, separated vertically by 2.30 m (7 ft 6 in), horizontally by 1.95 m (6 ft 5 in) and cross-braced into six frames, forming five transverse bays. The two pairs of outer frames defined the forward fuselages and the outer wings, engines and undercarriage legs were attached to the outermost frames. The centre engine was mounted on the central frame, positioned well forward of both the leading edge and of the planes of the two outer propellers. The whole structure was duralumin
Duralumin
Duralumin is the trade name of one of the earliest types of age-hardenable aluminium alloys. The main alloying constituents are copper, manganese, and magnesium. A commonly used modern equivalent of this alloy type is AA2024, which contains 4.4% copper, 1.5% magnesium, 0.6% manganese and 93.5%...
skinned to form an aerofoil section with a chord of about 10 m (33 ft), the lower surface continuing to form the undersides of the fuselages.
The outer wings were mounted high on the fuselage sides, carried 3° of dihedral and were of parallel chord with rounded tips. Each was supported from below by a pair of struts mounted on the lower fuselage longeron
Longeron
In aircraft construction, a longeron or stringer or stiffener is a thin strip of wood, metal or carbon fiber, to which the skin of the aircraft is fastened. In the fuselage, longerons are attached to formers and run the longitudinal direction of the aircraft...
. The fuselages were simple rectangular cross section structures, built around four longerons and tapering rearwards. They carried the horizontal tail surfaces, both between them and extending outwards. The angle of incidence
Incidence
Incidence may refer to:* Incidence , a measure of the risk of developing some new condition within a specified period of time* Incidence , the binary relations describing how subsets meet...
of this 'fixed' tail could be adjusted in flight for trimming. It carried three linked and balanced elevators. Two rectangular fins carried balanced rudders. The DB-70 had a fixed conventional undercarriage with double mainwheels on V-shaped shock absorbing legs mounted on the lower longerons, with bracing struts to the centre of the centre section. This arrangement produced a wide undercarriage track of 6.65 m (21 ft 10 in). Sprung tailskids were placed the extreme ends of each fuselage.
The passenger accommodation was a rectangular area within the deepest part of the centre section, 5.35 m (17 ft 6 in) long, about 9.5 m (30 ft) wide and 1.88 m (6 ft 2 in) high. The structural bays divided this space laterally into three: two outer, 10 seat cabins 1.80 m (6 ft) wide, each lit by 5 windows in the outer fuselage walls, and a central saloon with eight arm chairs grouped around two tables. For night flights, the seats in each of the cabins were replaced by 8 berths, reducing the overall accommodation to 24. Aft of this central area were toilets, a kitchen and baggage space plus corridor access to a floor trapdoor which was the principal passenger entryway. A 'promenade' ran the width of the centre section ahead of the seating areas, lit by glazed wing leading edges, with further passenger access doors at either end. Adjacent to it in the centre section leading edge was a corridor that allowed the third crew member, a mechanic, to enter the engine compartments for in-flight servicing. The two pilots sat in an open cockpit, fitted with dual controls, at the centre section leading edge.
The first flight of the DB-70 was on 15 November 1929 from Merignac Aerodrome. Initial trial flights showed the aircraft could take of in about 120 m (400 ft) carrying a 5 tonne load. It flew around the airfield at Vincennes
Vincennes
Vincennes is a commune in the Val-de-Marne department in the eastern suburbs of Paris, France. It is located from the centre of Paris. It is one of the most densely populated municipalities in Europe.-History:...
on both days of the National Aviation meeting held there in June 1930. Photographs show that modifications were made after the early flights, including the provision of external exhaust pipes and an increase in passenger window size, done by making the original oval windows into square ones. Only one DB-70 was built, though the military, four engine SAB AB-20
SAB AB-20
The SAB AB-20 was a large four engine French bomber built in the early 1930s as a development of the Dyle et Bacalan DB-70 airliner. It featured a lifting body of thick airfoil section between the inner engines...
and SAB AB-21 used very similar airframes.