In the first decades of aviation development, the choice of the power plant was one of the main problems. In particular, the issue of the optimal number of engines was relevant. The single-engine aircraft was simpler and cheaper to manufacture and operate, but the twin-engine design provided more power and reliability. An original compromise between the two schemes was proposed by the American aircraft manufacturer Allan Haynes Lockheed in the Duo project.
Time of inventions
At the turn of the twenties and thirties, the aircraft business of brothers Allan and Malcolm Lockheed ran into problems. In 1929, their company Lockheed Aircraft Corp. came under the control of Detroir Aircaft Corp. This deal did not suit Allan, and he left his own company. Already in 1930, the brothers organized a new company - Lockheed Brothers Aircraft and continued their activities.
The Lockheeds understood that they would have to fight for a place in the market and for contracts. For this, it was necessary to develop new models of aviation technology, which have serious advantages over competitors. Accordingly, it was required to invent and develop fundamentally new solutions and designs that differ from the existing and mastered ones.
Already in 1930, the Lockheed brothers began designing an aircraft of unusual architecture, called the Duo-4 or Olympic. All the advantages of this project were associated with an unusual power plant. In the nose of the fuselage, it was proposed to install two engines under a common fairing. It was assumed that this would increase the total power and thrust, but at the same time reduce air resistance in comparison with the "traditional" twin-engine aircraft. In addition, the car could continue flying with one engine inoperative.
"Olympic" plane
The Duo-4 Olympic project proposed the construction of an all-wood high-wing aircraft with an original power plant and a fairly large cargo-passenger cabin. In the design and appearance of this machine, some features of the Lockheed Vega aircraft were visible, but there was no direct continuity.
The fuselage with a length of about 8, 5 m and a wing with a span of 12, 8 m were made on the basis of a wooden frame with plywood and linen sheathing. The tail unit of the traditional design was used. The three-point landing gear with a tailwheel received teardrop-shaped fairings. The main wheels were mounted on V-shaped frames and connected to the wing using vertical struts.
In the nose of the fuselage there was an original engine mount for two Menasco C4 Pirate gasoline engines (4 cylinders, 125 hp, air cooling). The motors "lay on their side" with their cylinder heads to the longitudinal axis of the aircraft; the crankshafts were spaced as far as possible. The power plant was covered with a metal hood of a characteristic shape with numerous slots for airflow. Two metal propellers were used. The propeller discs to be swept did not intersect, there was a distance of only 3 inches between them.
Behind the engine mount was a two-seater cockpit with side-by-side seats. The central part of the fuselage was given under a four-seater cockpit with an entrance through a door on the left side. Behind the passenger cabin there were two luggage compartments for 1, 1 cubic meters.
The empty plane had a mass of approx. 1030 kg, maximum take-off did not exceed 1500-1600 kg. According to calculations, two 125-horsepower engines were to provide high thrust-to-weight ratio and flight characteristics.
Duo-4 in the air
In 1930, Lockheed Brothers completed the design and built an experimental aircraft of a new type. Already at the end of the year, the aircraft with registration number NX962Y made its maiden flight. The tests were carried out on dry Lake Murok (now the Edwards base); pilot Frank Clark was at the helm. Despite the unusual design, the plane kept well in the air and showed good performance.
During the tests, it was possible to obtain a maximum speed of more than 220 km / h, the landing speed did not exceed 75-80 km / h. Other characteristics were planned to be removed later, but this was prevented by an accident.
In March 1931, during landing, a prototype aircraft was caught in a gust of wind and skapoted. Moreover, during such a "somersault" the car collided with a car parked next to it. Fortunately, no one was seriously injured, and the Duo-4 was subject to repair.
However, the investors did not begin to understand all the circumstances of the accident and refused to support the project. Lockheed Brothers found itself in a difficult position, since the Duo-4 was so far its only development with real prospects. Nevertheless, the Lockheed brothers did not give up and continued to work, proceeding from the available opportunities.
Superior Duo-6
The repair of the prototype aircraft dragged on for several years. However, for some time, the pace of work was affected not only by the lack of a resource, but also by plans for a serious revision of the project. During the renovation, the experienced Duo-4 was decided to be rebuilt according to the updated Duo-6 project. The improvements mainly affected the power plant and related units.
A new oversized motor mount was installed on the nose of the fuselage for two Menasco B6S Buccaneer engines. Six-cylinder engines developed a power of 230 hp each. Metal screws with a diameter of 2.3 m were placed on the output shafts. As before, there was a minimum gap between the rotating screws.
As a result of this update, the dimensions of the aircraft have not changed. The empty weight increased to 1300 kg, and the maximum take-off reached 2300 kg. Despite the increase in weight indicators, the thrust-to-weight ratio of the Duo-6 was higher than in the previous project.
1934 turned out to be eventful. In February A. Lockheed changed his surname from Loughead to Lockheed, in accordance with the pronunciation and spelling of the company name. Almost simultaneously, his company ran out of money and went bankrupt. However, the assembly of the experienced Duo-6 was completed and prepared for testing. The plane was delivered to the airport in Alhambra (California). F. Clark was to become the tester again.
In March, the Duo-6 was flown into the air, and the aircraft immediately showed the advantages of two more powerful engines. The cruising speed increased to 250-255 km / h, the maximum speed exceeded 290 km / h. The service ceiling was 5600 m. Due to the increased load on the wing, the landing speed exceeded 90-92 km / h.
In May, the plane was tested with one engine running. For the purity of the experiment, the screw was removed from the second motor. One engine made it possible to take off, although the takeoff run increased. The maximum speed dropped to 210 km / h, and the ceiling did not exceed 2 km. Despite the reduction in performance, the aircraft could fly in all main modes. The pilot noted only a slight drift towards the inoperative engine, easily parried by the pedals.
Way to the market
After "single-engine" tests A. Kh. Lockheed flew the Duo-6 across the country to the East Coast to demonstrate the aircraft to the military. The representatives of the army got acquainted with the new machine, but did not show any interest in it. Commercial air carriers, despite all the efforts of the former Lockheed Brothers, were also unwilling to buy a new plane.
In October 1934, the Duo project was given a new chance. Federal authorities have severely restricted the use of single-engine aircraft in commercial travel and effectively forced airlines to switch to twin-engine aircraft. It was assumed that this would increase the reliability of equipment and transport safety.
A. Lockheed began to promote the original idea. It was proposed not only to build new aircraft, but also to re-equip existing single-engine aircraft according to the Duo scheme. This would allow them to continue to operate without breaking the new rules. The experienced Duo-6 was used for promotional flights and showed all the usefulness and safety of the original power plant. However, such an advertising campaign lasted only a few months. In the next demonstration flight, Duo-6 crashed and could no longer be repaired.
A. Lockheed again did not abandon his ideas and launched a new project. In early 1937, he incorporated the Alcort Aircraft Corp. Its first development was a full-size passenger aircraft C-6-1 Junior Transport with a proven and proven twin-engine power plant. The development of existing ideas continued, and they got a real chance to come to use in practice.
