Kraków 2013-03-14
Outline of the history of navigation. Commercial Aircraft.
Boeing 247. 1933
At the beginning of the 1930s, several accidents occurred in postal and passenger aviation in which wooden aircraft burned down quickly. The most famous was the fire of the Fokker F.VII aircraft. Airlines began to look for aircraft with a metal structure, which are therefore more difficult to burn.
The first in the USA was the Ford Trimotor. The next was the Boeing 247. The Boeing 247 aircraft was built on the order of the United Airlines airline and the construction and production program was financed by it. It was characterized by a modern layout; a metal low-wing, twin-engine monoplane. The design was very modern. An anti-icing installation was used (the device was pneumatic, in the form of a rubber skirt on the leading edge, under which compressed air was pumped if necessary). The propeller blades were adjustable. The landing gear was retractable. The aircraft was very richly equipped. It had an autopilot, radio station, echo sounder (for measuring flight altitude), radio direction finder and special instruments for flights without visibility. It had a gyroscope panel for avionics instruments. The crew was 3 people. The plane took 10-14 passengers on board. It made its first flight on February 8, 1933. The plane turned out to be very fast on the go. It covered the New York-Los Angeles route (with seven landings between) in 7.5 hours less than previous planes.
Only 75 machines were built, because United Airlines had exclusive rights to this plane. This caused this successful design not to be widely distributed. In 1939, the German plague started another world war. Boeing 247 planes were converted into military transport planes and received the designation C-75. The Boeing 247 plane introduced speed, reliability, safety and comfort in passenger transport.
Douglas DC-2. 1934
The DC-2 was created based on similar assumptions as the Boeing 247. Due to Boeing’s close cooperation with United Airlines, Transcontinental and Western Air (TWA) was forced to look for another supplier. Douglas presented a prototype model DC-1 that met TWA’s requirements, which was built in a single copy. The production version DC-2 was created on its basis. TWA initially placed an order for 20 copies. Further orders were placed by other airlines from the USA and Europe. In Europe, the DC-2 flew, among others, in the colors of PLL LOT, KLM, Swissair. Aircraft for European customers were assembled in Fokker plants. There were also military versions, used by the US Air Force and Navy. A total of 156 copies were built. Based on the DC-2, in 1935, the Douglas B-18 Bolo bomber was designed.
Lockheed L-10 Electra 1934
Lockheed also had experience in building aircraft with metal fuselages. However, the wings had always been constructed using wood. Therefore, it was the third company, after Boeing and Douglas, to decide to build an all-metal passenger aircraft. A twin-engine low-wing system was used. The aircraft model was tested in a wind tunnel at the University of Michigan. As a result of these tests, it was decided to use a double vertical tail, which became a certain distinguishing feature of Lockheed. The L-10 prototype made its first flight on February 23, 1934. The commercial name “Electra” came from one of the stars in the Pleiades cluster. When the United States administration issued a ban on the carriage of passengers by airlines in single-engine aircraft and night flights for this type of aircraft, Lockheed, with the offer of its new aircraft, perfectly exploited the demand of the aviation market. Lockheed Electra L-10 aircraft were purchased and used by over 30 carriers around the world. A total of 149 machines were built. In the passenger version, the plane could carry 10 passengers. However, the cabin was not very spacious and did not provide passengers with a sense of comfort. In the period 1936-1939, Lockheed L-10-A planes also flew in the colors of PLL LOT. Eight countries (the United States, Argentina, Brazil, Honduras, Spain, Canada, Great Britain) also equipped their armed forces with these planes.
Paradoxically, the Lockheed L-10 Electra gained the greatest fame for its unsuccessful attempt to fly around the world along the equator, which was undertaken in 1937 by the famous pilot Amelia Earhart. After completing 3/4 of the route, she took off from New Guinea and disappeared flying over the Pacific.
Douglas DC-3. 1935
The Douglas DC-3 is a development of the Douglas DC-2, in response to a request from American Airlines for an aircraft with sleeping places (sleepers) for night transcontinental flights within the USA. Douglas developed the first version of the DC-3, called the DST (Douglas Sleeper Transport). The aircraft had 14 sleeping places. To achieve this, the fuselage had to be enlarged. In addition to the DST version, a traditional version was created, which accommodated 21 passengers in individual seats.
The first flight of the Douglas DC-3 aircraft took place on December 17, 1935, on the 32nd anniversary of the Wright brothers’ first flight. Scheduled flights of the DST variant were inaugurated on September 18, 1936. The aircraft turned out to be a great commercial success. American Airlines management believed that it was the first aircraft to make money on passenger transport, without government subsidies.
World War II saw the aircraft built in huge numbers for the needs of the Allied forces. They had various designations; C-47, R-4D and Dakota. Total production, including the licensed Lisunow Li-2 in CCCP and Showa L2D in Japan, amounted to at least 17,276 units. After the war, a large number of DC-3 aircraft were withdrawn from military service and were sold. Low price combined with simple and economical operation meant that these aircraft became the basis of the fleets of many airlines around the world. At the beginning of the 21st century, several dozen DC-3s are in service, mainly as transport aircraft, but also as passenger aircraft.
Polish RWD-11. 1936
In 1934, engineers Stanisław Rogalski and Jerzy Drzewiecki designed a twin-engine passenger plane RWD-11, which was to compete with the PZL-27. Due to low financial outlays, work progressed slowly. The first flight of the prototype with registration marks SP-ASX was performed in January 1936. The pilot was Aleksander Onoszka. The prototype underwent many tests, as a result of which many modifications were made. At the end of 1937, the aircraft was considered to be a very successful design. The introduction to serial production was delayed due to the tense political situation and the priority given to military aircraft. Ultimately, the attack of the German plague caused the program to be interrupted. The built aircraft were taken over by German troops in October 1939.
T-T data of the RWD-11 aircraft: Dimensions; span 16.20 m, length 10.65 m, height 3.30 m, wing area 25 m2, empty weight 1,740 kg, total weight 2,650 kg, max speed 305 km/h, ceiling 4,100 m, range 800 km.
Lockheed L-14 Super Electra. 1937
The success of the Lockheed L-10 Electra aircraft led the company to decide to further develop its designs. The new model was designated the L-14 Super Electra and was built at Lockheed’s Burbank plant. The lead designer was Don Palmer. The number 14, like in the previous model, meant the number of passengers. The Super Electra was essentially an enlarged version of the L-10 aircraft. The prototype first flew on July 29, 1937. Initially, the aircraft was offered with two Pratt & Whitney R-1690 Hornet radial engines. Over time, the option of installing more powerful Wright R-1820 Cyclone engines was introduced. 354 units were built between 1937 and 1940.
T-T Lockheed L-10 Electra data: Dimensions; span 19.97 m, length 13.52 m, height 3.48 m, wing area 51.2 m2, empty weight 4,886 kg, maximum 7,955 kg, maximum speed 402 km/h, ceiling 7,650 m, range 3,420 km, crew 2.
In 1937, LOT Polish Airlines decided to purchase 10 machines of the new, enlarged version of the Lockheed L-10 Electra. The first five machines arrived in Poland on board the transatlantic liners MS Batory and MS Piłsudski, in April and May 1938. The machines were assembled at the airport in Rumia.
The company’s authorities decided to use the purchase of the modern aircraft for propaganda purposes. It was decided that the last of the machines would be brought from the factory in Burbank to Warsaw by air. It was to be a test in the possible launch of an airline connecting Warsaw with New York and Chicago. Interestingly, the Atlantic Ocean was to be crossed at its narrowest point, i.e. from Natal, Brazil to Dakar, Senegal. The flight took place in May 1938. The crew consisting of Wacław Makowski (LOT director and first pilot), Zbigniew Wysiekierski (co-pilot), Szymon Piskorz (mechanic), Alfons Rzeczewski (radio navigator) and Jerzy Krassowski (assistant), took off in a brand new aircraft from Burbank, California on May 13, 1938. The flight passed through; Mazatlan, Mexico, Guatemala, Lima, Buenos Aires and Rio de Janeiro, and the aircraft reached Natal, Brazil. From there, in 11 hours and 10 minutes, the crew crossed the Atlantic Ocean and landed in Dakar, covering a record distance of 3,070 kilometers without stopovers. The route then led through Senegal, Casablanca, Tunis and Rome, from where the plane arrived on June 5, 1938, directly to Okęcie Airport in Warsaw. In total, during the flight from California to Poland, the plane spent 85 hours in the air. The flight over a record distance of 24,850 km had advertising and propaganda significance, but was also intended to be a preparation for the start of regular transatlantic flights in 1940. These plans were thwarted by the German plague, which started World War II, together with its Muscovite brothers.
Soon, LOT Polish Airlines lost two aircraft: SP-BNG crashed in July 1938 near Campulung in Romania, and SP-BNJ burned down at Bucharest airport a little later. To replenish the losses, in May 1939, four more Super Electra aircraft were brought to Poland. During the defensive war in 1939, all Lockheed Electra aircraft were mobilized by the Polish Army and performed courier and supply flights. Then four of them were evacuated to Romania, where they were interned. One aircraft was interned in Tallinn, Estonia. The remaining three aircraft of this type (SP-BPM, SP-LMK and SP-BNF) were evacuated to France, where they served as liaison aircraft for Polish diplomacy. The SP-BPM aircraft was destroyed during the German attack on France in June 1940, while SP-LMK and SP-BNF flew to Great Britain. There, they were planned to be rebuilt into aircraft for dropping Silent Unseen soldiers, but the idea was eventually abandoned and both aircraft were taken over by BOAC Airlines.
Boeing 307 Stratoliner. 1938
The Boeing 307 was practically the last passenger plane designed, built and put into service before World War II. In the second half of the 1930s, it was noticed that thinner air at an altitude of over 6,000 m, creating less resistance, allowed for a higher cruising speed. There were only two problems. First, thinner air caused a decrease in the power of the power unit. The solution was the use of turbochargers, which allowed the planes to reach an altitude of 10,000 m. Second, lower pressure meant less oxygen and difficulty breathing. The crew could put on masks, but the passenger could not be dressed in a mask. The solution turned out to be a pressurized passenger cabin. Boeing decided to use both solutions, developing the Model 307. In 1938, based on the B-17 C bomber, the manufacturer developed a passenger version, which became the first passenger plane with a pressurized cabin for the crew and passengers and engines equipped with turbocharging. The model also received its own name Stratoliner, which suggests the high altitude at which this type of aircraft was to fly. Flight at high altitudes is associated with experiments conducted by Trans World Airlines (TWA). It turned out that at altitudes above 6,000 m, weather conditions are more stable. There are definitely fewer clouds and much less turbulence. So, the flight is definitely more efficient.
The first work on the Boeing 307 Stratoliner aircraft began in 1935, but progressed relatively slowly. It gained momentum when the first order from an airline was received in 1937. It took some time to make a pressurized passenger cabin. Ultimately, Boeing chose the following solution. The fuselage was designed like a low-pressure tank, i.e. bulging. Two General Electric compressors were used, with a system of two pairs of valves. Thanks to these compressors, at an altitude of 7,000 m, the pressure in the fuselage was equivalent to an altitude of 3,600 m. There was no attempt to increase the pressure, because it would have forced the fuselage to increase in weight and the use of stronger, heavier compressors. The remaining structural elements, wings, tail, landing gear, engines and propellers were adapted directly from the B-17C bomber. The price of one aircraft in 1938 was $315,000. A total of 10 units were built.
The first flight of the prototype intended for Pan Am (PAA-307) took place on December 31, 1938. The aircraft crashed due to the pilot’s fault during the first flight, which did not delay its production in any way, but it did result in a significant design change. In the production version, the small vertical stabilizer of the B-17 C was replaced with a large stabilizer of a new design. The next airline to purchase the Model 307 was TWA. The aircraft served the route between New York and Los Angeles. The planes covered the route in 13 hours and 40 minutes, two hours faster than the DC-3.
The Boeing 307 Stratoliner was an all-metal, cantilever low-wing monoplane powered by four radial engines, with a power of 4 x 900 hp – 4 x 1,200 hp. The machine could carry 33 passengers on board in comfortable conditions, some of the seats were foldable, the walls of the fuselage were paneled, and the floor was carpeted. The fuselage was fully pressurized. The landing gear, wings, tail and engines along with the installation were adapted from the B-17 C bomber.
Flying boats.
Up to now we have not mentioned flying boats. At a certain period of aviation development they played a significant role. The main reason for their popularity was the possibility of landing on water, i.e. in almost every region of the world. Therefore, initially seaplanes were developed, i.e. aircraft equipped with floats instead of wheeled undercarriage. However, flying boats gained huge interest in the second half of the 1930s. Mainly due to their size and the possibility of performing long flights.
Short Empire. 1936
The Short Empire is a British mail and passenger flying boat developed in the second half of the 1930s by the Short Brothers company in response to the British government’s order for a seaplane that would provide postal communication with the possessions of the British Empire in Africa, Asia and Australia. The first aircraft flew on 4 July 1936 and in the same year, the first units were delivered to Imperial Airways. All aircraft received their own names. In total, 45 seaplanes were produced in four versions (S.23, S.26, S.30, S.33) by 1940, which, apart from Imperial Airways (since 1939, BOAC), served on QANTAS and TEAL. In 1937, one of the Short Empire aircraft, named Caledonia, made a flight over the Atlantic Ocean from England to the USA.
It was powered by four Bristol Pegasus X C (S.23) or XII (S.30) radial engines with a power of 4 x 919 hp (676 kW) (S.23) or 4 x 889 hp (654 kW) (S.30). Dimensions; span 34.75 m, length 26.82 m, load-bearing surface 139.35 m². max speed 322 km/h, ceiling 6,100 m, range 1,200 km, payload 3,500 kg. The aircraft could carry 24 passengers on seats or 16 passengers on bunks (sleepers).
Boeing 314 Clipper. 1938
The Boeing 314 Clipper is an American flying boat built by the Boeing Company, commissioned by the Pan American airline company. It was intended for commercial mail, cargo, and passenger flights from the USA to Europe. Hailed as the first transatlantic passenger aircraft. One of the largest aircraft in the world. In July 1936, Pan American signed a contract with Boeing to build six aircraft with an option for six more. A total of 12 were built; six Boeing B-314s and six Boeing B-314 A. In June 1938, the first of them took to the air. At first, they only carried mail on transatlantic flights, because it was necessary to prove that the machine was safe. Over time, passenger flights were launched. The aircraft’s development was interrupted by the Germans unleashing another world war. The aircraft were used by the army. They were used to transport important figures. For example; Franklin Delano Roosevelt and Winston Churchill. In February 1943, one of the planes crashed in Lisbon. The accident resulted in twenty-nine fatalities, but it was the only one in the history of this aircraft model.
The further development of commercial aviation was halted by the outbreak of World War II. Almost all of the planes went to the armed forces and took part in warfare in various ways. The development of navigation itself was also halted.
Written by Karol Placha Hetman