SAB AB-20
Encyclopedia
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. It was later modified for the attack role; a second aircraft, the AB-21, had different engines and cleaner aerodynamics but no more were built.
airliner. The change of manufacturer's name was the result of the financial failure of Dyle et Bacalan in 1929, followed by its immediate reappearance as SAB, who took over DB-70 development. The latter was built around a thick, wide chord
airfoil centre section which provided generous internal space for passengers. The engines were mounted on this structure as were twin fuselage
s to carry the tail. Outer wings of normal thickness and chord, the cockpit and the under carriage were also attached to the centre section. The generous intra-wing volume equally offered crew, fuel and bomb room for military purposes. Initially the AB-20 was intended to have three engines like its forebear, but during the design phase there was a military request for a bombardier's position and a gunner's cockpit in the nose, which required the removal of the centre engine and its replacement by two extra engines wing mounted outboard of the centre section.
Apart from the extra engines and the very different crew compartment, together with the removal of passenger accommodation, the AB-20 and DB-70 had much in common: the thick centre section and high mounted outer wings, twin fuselages carrying a long horizontal stabilizer and twin fin
s and rudder
s. Both aircraft had conventional undercarriages with pairs of mainwheels widely separated on V-struts attached to the lower longerons of the centre section.
The new central crew pod was flat sided and tapered forwards to a complicated cylindrical nose, formed of a simple lower part with an overhanging, windowed cabin for the navigator/bombardier and an open gunner's cockpit, fitted with a machine gun
ring, directly above. The nose also carried a long, conical probe with fine extensions, possibly pressure sensors. Further aft there was an enclosed pilot's cabin. A second gunner was stationed rearwards, on top of the centre section and a third fired from a ventral turret.
By early 1934 a much developed version, the AB-21 had appeared. It had the newer V-12 Lorraine Petrel water-cooled engines and a tapered, filleted cantilever
wing without the struts used on the AB-20 and DB-70. The undercarriage had also been cleaned up with streamlined legs and wheels in long cowlings. The nose was further complicated, retaining the upper, open gunner's position but now with double underhanging windowed positions, though the conical probe had gone.
Trials of an airborne sideways-firing 75 mm gun were carried out with the AB-20 prototype modified as the AB-22. Firing trials were halted after damage was caused to the lower wing skin by blast from the gun muzzle.
SAB AB-21
SAB AB-22
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...
bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
built in the early 1930s as a development of the Dyle et Bacalan DB-70
Dyle et Bacalan DB-70
The Dyle et Bacalan DB-70 was a large three engine French airliner with a thick airfoil centre section which accommodated the passengers. Two fuselages, part of the centre section at the front but distinct further aft, carried the empennage...
airliner. It featured a lifting body of thick airfoil section between the inner engines. It was later modified for the attack role; a second aircraft, the AB-21, had different engines and cleaner aerodynamics but no more were built.
Design
The SAB AB-20 was a four engine night bomber development of the three engine Dyle et Bacalan DB-70Dyle et Bacalan DB-70
The Dyle et Bacalan DB-70 was a large three engine French airliner with a thick airfoil centre section which accommodated the passengers. Two fuselages, part of the centre section at the front but distinct further aft, carried the empennage...
airliner. The change of manufacturer's name was the result of the financial failure of Dyle et Bacalan in 1929, followed by its immediate reappearance as SAB, who took over DB-70 development. The latter was built around a thick, wide chord
Chord (aircraft)
In aeronautics, chord refers to the imaginary straight line joining the trailing edge and the center of curvature of the leading edge of the cross-section of an airfoil...
airfoil centre section which provided generous internal space for passengers. The engines were mounted on this structure as were twin 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 to carry the tail. Outer wings of normal thickness and chord, the cockpit and the under carriage were also attached to the centre section. The generous intra-wing volume equally offered crew, fuel and bomb room for military purposes. Initially the AB-20 was intended to have three engines like its forebear, but during the design phase there was a military request for a bombardier's position and a gunner's cockpit in the nose, which required the removal of the centre engine and its replacement by two extra engines wing mounted outboard of the centre section.
Apart from the extra engines and the very different crew compartment, together with the removal of passenger accommodation, the AB-20 and DB-70 had much in common: the thick centre section and high mounted outer wings, twin fuselages carrying a long horizontal stabilizer and twin fin
Fin
A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...
s and rudder
Rudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
s. Both aircraft had conventional undercarriages with pairs of mainwheels widely separated on V-struts attached to the lower longerons of the centre section.
The new central crew pod was flat sided and tapered forwards to a complicated cylindrical nose, formed of a simple lower part with an overhanging, windowed cabin for the navigator/bombardier and an open gunner's cockpit, fitted with a machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....
ring, directly above. The nose also carried a long, conical probe with fine extensions, possibly pressure sensors. Further aft there was an enclosed pilot's cabin. A second gunner was stationed rearwards, on top of the centre section and a third fired from a ventral turret.
Development
The first flight of the AB-20 was on 15 January 1932. The following year it was reported that it had been structurally modified for the attack role and was returning to Villacoublay for tests.By early 1934 a much developed version, the AB-21 had appeared. It had the newer V-12 Lorraine Petrel water-cooled engines and a tapered, filleted cantilever
Cantilever
A cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
wing without the struts used on the AB-20 and DB-70. The undercarriage had also been cleaned up with streamlined legs and wheels in long cowlings. The nose was further complicated, retaining the upper, open gunner's position but now with double underhanging windowed positions, though the conical probe had gone.
Trials of an airborne sideways-firing 75 mm gun were carried out with the AB-20 prototype modified as the AB-22. Firing trials were halted after damage was caused to the lower wing skin by blast from the gun muzzle.
Variants
SAB AB-20- A four-engined bomber derived from the three-engined Dyle et Bacalan DB-70Dyle et Bacalan DB-70The Dyle et Bacalan DB-70 was a large three engine French airliner with a thick airfoil centre section which accommodated the passengers. Two fuselages, part of the centre section at the front but distinct further aft, carried the empennage...
, powered by four Lorraine Courlis engines.
SAB AB-21
- Similar to the AB-20 and DB-70 but with cantilevered wings and powered by four Lorraine Petrel engines.
SAB AB-22
- The sole prototype AB-20, with a crew of five, modified with a 75 mm gun firing sideways. Test firing took place at CazauxCazauxCazaux is a commune of the Ariège department in southwestern France....
in September 1934, but was terminated after five rounds had been fired due to structural damage to the lower wing skin.
Specifications
External links
- "The Next War In The Air" Popular Mechanics, January 1936 photo bottom of pg 67