PUSH IT

While the concept of pusher designed planes is older than aviation, it wasn't applied to actual aircraft until 1908, when propellers mounted in the rear of the engine were used to power a biplane. During the course of this blog, we'll trace the development of pusher aircraft along with their current use.

Henri Farman, a French aircraft designer was responsible for the first practical application of the pusher engine concept. Farman bought his first plane from the Voisin brothers in 1907. He then modified the plane in 1908 as an equal-span pusher biplane with a single forward elevator and biplane tail surfaces mounted on booms. The Farman III made use of a converging boom design, placing the elevators on the booms, eliminating the covered nacelle for the pilot. The first flight of the Farman III was in 1909 and the aircraft was an instant success. The Farman III was further modified later that year with improved aileron control surfaces, as well as two new engines, the 50 hp. Gnome Omega rotary engine followed by the E.N.V., a water-cooled V-8 engine. The Farman design had a great influence on European aircraft as followed by the British Short S27, Bristol Boxkite and the Howard Wright 1910 biplane. Farman III aircraft were also produced in Germany, designated as the Albatros F-2. An elevator was added to the upper tailplane surface in 1910 to increase performance.

The Farman design saw service in World War I in the form of three distinct planes, which shared a common Farman pusher biplane layout. The F.E.2 (1) was designed by Geoffrey de Havilland in 1911 at the Royal Aircraft Factory. Although claimed to be a rebuild of the earlier F.E.1 pusher biplane, the F.E.2 was an entirely new aircraft. After its first flight by de Havilland in 1911, the F.E.2 (1) was fitted with floats the following year, but proved to be underpowered and its engine was replaced by a 70 hp. Gnome, which allowed it carry a passenger while utilizing floats. Later in 1912, the F.E. 2 (1) was refitted with a land plane undercarriage, and was subsequently modified to carry a flexible Maxim machine gun mount in the nose. The F.E. 2 (2) was produced in 1913 and heavier with a much more modern design. The F.E.2 (2) crashed in 1914 due to the use of wings instead of ailerons for lateral control. This problem was corrected with subsequent versions of the aircraft and it gave a good account in both fighter and bomber roles.

After World War I interest waned in pusher aircraft designs, but they had made a comeback in the 1930's. The Supermarine Walrus was a single-engine amphibious biplane designed to conduct maritime reconnaissance missions from either island bases or catapult launch from Royal Navy capital ships. The hull was constructed from aluminium alloy, with stainless steel forgings for the catapult spools and mountings. The wings could be folded, enabling stowage on a ship. The Walrus was powered by a 620 hp. Pegasus II M2 radial engine mounted between the wings behind the cockpit area in a pusher configuration. The pusher design gave the Walrus the benefits of keeping the engine and propeller clear of spray when operating on water, as well as reducing noise levels within the plane. Another advantage was the propeller was also to the rear of any crew standing on the front deck when picking up a mooring line. First flown in 1933, the Walrus entered production in 1936 with 740 examples built before production ended in 1944, making the design one of the most successful pusher aircraft. The pusher concept was applied to a new type of aircraft in the 1930's, the autogyro. The precursor to the later helicopter, the autogyro was developed in Spain in the early 1920's to meet a need for a type of aircraft which was capable of stable flight at low speeds without stalling, while also being able to make low speed landings on a short runway. The autogyro operates by a free-spinning rotor, which turns because of the passage of air through the rotor from below. While a helicopter works by forcing rotor blades through the air, drawing lift from above, the autogyro rotor blades induce lift in the same manner as a glider's wing. The autogyro is not capable of direct vertical flight, as with the helicopter, but is able to take off from a short runway since the autogyro configuration is a fuselage with a tail and short, stubby wings powered by a tail or frontal rotor with the large umbrella rotor above the craft providing lift. While a number of early autogyros were designed with a tractor arrangement, in which the engine and propeller are located at the front of the aircraft, ahead of the pilot and rotor, the majority of autogyros built after World War II use a pusher type configuration where the engine and propeller are located behind the pilot and rotor mast.

The pusher configuration offers several advantages. Unlike a tractor arrangement, a pusher propeller at the end of the fuselage has a stabilizing effect, and is less sensitive to crosswind while requiring less vertical tail area. A pusher aircraft may have a shorter fuselage with a reduction in both weight and wetted area. Wing profile drag is also reduced due to the absence of prop-wash over the wing areas. Propeller shafts are also shorter, allowing easier access than the tractor configuration. However, there are several key disadvantages to the use of a pusher configuration. Pusher engines take up rear wing area, which could be used for control surfaces. Secondly, with no prop wash streaming over the wing area, lift is reduced which increases takeoff roll length. With the propellers at the back of the engines, noise is increased with sound traveling to the rear and sides of the plane. This may also cause vibration due to engine exhaust fumes flowing through the propeller blades. Speaking of propellers, pusher aircraft have a different pitch rotation from tractor planes, requiring shorter blades or longer and heavier landing gear. Pusher aircraft are also more prone to pick up rocks or ground objects striking the engine or fuselage areas. Engine cooling is also an issue, since the airflow from the propellers moves away from the engine and radiator areas. In the event of a nose-on crash landing, the engine could travel through the fuselage area, injuring passengers. Finally, a pusher configuration, unlike a tractor plane, has the potential of spinning propellers making passenger access and loading from behind a risky activity.

In the late 1940's the USAF resurrected the pusher concept in the form of two new bomber aircraft designs, the Northrop XB-35 and the Convair B-36 Peacemaker. Jack Northrop, founder of Northrop Aircraft, had longed dreamed of a flying wing concept design for military aircraft. Northrop, as with a number of small aviation companies during World War II, built components for aircraft produced by other firms. However, this changed in 1941 when the USAAF awarded Project MX-140 to Northrop, the aim of which was to develop a high altitude, long range, heavy bombardment aircraft. The aircraft, designated the XB-35, was a flying wing, designed without the central fuselage and rear tail. The wing was powered by four Pratt & Whitney Wasp Major 3,000 hp. piston engines mounted in a pusher configuration. Though the first test flight in June 1946 was partially successful, the plane experienced problems with its propeller system, which limited its performance. The jet version of the plane, the XB-49, was unstable at high speeds due to faulty rudder control and a lack of reinforced structure, as the XB-49 was rushed to production with a XB-35 airframe. After several crashes, the project was discontinued in 1950.

The Convair B-36 Peacemaker had its origins in 1941 due to the threat of Britain falling to the German bombing campaign at the time, which dictated production of a large bomber aircraft having intercontinental range. Consolidated Aircraft approved construction of the B-36 in 1943, but delayed delivery until August 1945, due to its merger with Vultee and current production requirements for the B-24 Liberator. The B-36 was a unique aircraft, powered by six 28 cylinder Pratt & Whitney R-4360 radial engines mounted in a pusher configuration with twin General Electric J47-19 jet engines suspended by pylons near the end of each wing on D and later models. The Peacemaker's first test flight in August 1946 was successful, with the aircraft entering service in 1948. The B-36 served with the Strategic Air Command for ten years and proved to be a reliable aircraft, although prone to carburetor icing, due to engine heat moving away from the plane due to its pusher configuration. Once the ice melted, the engines became prone to fires because of excess fuel deposits around the carburetor .

While there are no pusher aircraft designs currently in service with either the military or the airlines, the pusher concept has made a comeback in the recreational aviation market. There are a number of pusher aircraft such as small amphibians, ultralights and sport planes which utilize the pusher concept and the trend appears unabated. A newcomer to the pusher aircraft family is the Celera 500L. The 500L makes use of laminar flow technology, which minimizes aerodynamic drag against an air surface by utilizing a smooth surface fuselage creating an optimum length to width ratio to maximize aircraft performance. The 500L, produced by Otto Aviation in Yorba Linda, California, touts a teardrop fuselage similar to that of the Bell X-1 with a cockpit windscreen blended into the fuselage, which gives the aircraft a large internal volume with high aerodynamic efficiency. Powered by the Red AO3 V12 liquid cooled aluminium engine, Otto claims the Celera offers in excess of 550 hp. takeoff power, as well as the best fuel efficiency in its class. Mounted in a pusher configuration with a five bladed prop, the Red AO3 engine delivers a cruising speed of 460 mph-comparable to a number executive jets in its class, with a range of 4,500 miles. The Celera is also decked with long, slender tail and wing surfaces to enhance laminar flow. The Celera 500L is proof that the pusher concept is alive and well today.