Aviation of World War II

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Patrol Flying Boat


Saro A.33

The A.33 patrol flying boat was designed to replace existing biplane flying boats. The powerful propulsion system consisted of four 830-horsepower Bristol Perseus XII air-cooled nine-cylinder radial engines mounted on the leading edge of the wing at equal distances from each other. The engines rotated three-blade variable-pitch propellers. The single-spar parasol wing with a span of 28.96 m was probably one of the largest ever built, taking bending loads directly through the spar, and twisting through a pyramidal system of guy wires. The wing was covered with canvas, although this method was already outdated by the end of the 1930s. Two large N-pillars connected the wing and sponsons located along the sides of the fuselage. Sponsons, 6.1 m long, contained fuel tanks and had a slight negative transverse V.

The A.33 all-metal twin-led hull was a beautiful streamlined design, 22.86 m long.The closed cockpit, like the cockpit of the A.27 London seaplane with side-by-side seats, was glazed on all sides and located with a height , provided pilots with excellent visibility.

A.33 was supposed to use powerful (for its time) defensive weapons. 7.7 mm Browning machine guns were to be installed in the bow and tail turret mounts. However, the tail turret installation was repaired immediately after the start of the test flights.

The plane provided for the accommodation of seven crew members: a pilot, a co-pilot, a flight engineer, a radio operator and three gunners. In the space behind the cockpit, under the center section, there were berths and a place for cooking. In accordance with the standard practice of those years, the front tower could be pulled back to facilitate docking.

The tail unit consisted of a conventional trapezoidal stabilizer with separate elevators and one large keel and rudder.

Crew 7
Length, m 22.87
Height, 6.92
Wing span, m 28.96
Wing area, m² 110.93
Weight, kg
Empty 14,320
Loaded weights 18,864
4 × PE radial Bristol Perseus XII, power, h. p. 4 × 830
Maximum speed, km/h 322
Cruising speed, km/h 280
Service ceilling, m 4353
3 × 7,7-мм пулемета Vickers, бомб, кг 909

Taxiing trials of the prototype A.33, numbered K4773, began on October 10, 1938 at East Cowes and continued until October 12, when a tendency to goats at high speeds was revealed. However, no changes were made, it was decided that the A.33 should complete flight tests as soon as possible in order to obtain a serial production contract.

On October 14, the K4773 made its maiden flight, flown by Frank Courtney, who had previously tested the A.3 Valkyrie for the company. The only problem we encountered in the air was a little shake of the tail, but on the water, due to the tendency to goats and splashing, takeoffs were difficult. Saro's hydrodynamic department was perplexed by the behavior of K4773 and Courtney was tasked with letting the goat develop a little if it would help to help observe and study the process. Why a series of tests on models was not carried out at this stage remains a mystery. Instead, testing of the K4773 prototype continued with disastrous consequences.

On October 25, during its fifth run at Solent, K4773 was traveling at high speed when it struck a ferry in its wake near Southampton. The plane immediately began to goat and made a huge jump, during which there was a break in the flow, the car fell down, losing control. On impact, the wing, being in a twisted position, was damaged by rolling down the motors of the right console. The right side of the wing literally spun around the spar so that the right inboard propeller hit the boat's hull and sponson, just inches away from Henry Knowler. The tail unit was damaged by flying debris from the wing.

Testing of the K4773 was terminated, while the aircraft itself did not sink, since all damage was above the waterline. None of the crew members were injured. The tests carried out were in the factory, MAEE * had not tested the K4773 before the accident. If this had been done before, then perhaps many design errors would have been discovered. In addition, by this time the development of the prototype of the smaller flying boat S.36 was more successful. At the time of the A.33 accident, the S.36 prototype had already been guaranteed series production. With this in mind, the A.33 program, which had already spent more than £ 80,000, compared with its original declared development cost of £ 68,000, was closed.

* MAEE - Marine Aircraft Experimental Establishment.

Photo Description
Drawing Saunders-Roe A.33

Drawing Saunders-Roe A.33

A.33 K4733 after test flight

A.33 K4733 after test flights


  • "All seaplanes of the Second World War" /Andrey Kharuk/
  • "Saunders and Saro Aircraft Since 1917" /Peter London./
  • "British Flying Boats" /Peter London/

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In 1934, Henry Knowler developed a single-spar parasol wing with sponsons instead of the conventional underwing floats. The high wing position was chosen to provide the sufficient distance from the water that a parasol wing can provide without creating the very deep hull that has become a feature of most monoplane flying boats. Comparatively small, Knowler's hull had less resistance and weight than the deep hull, which provided an increase in speed and range.