26 July 2015

Jaki Jakimiuk and the PZL Fighters: The Roots of the De Havilland Beaver

Jaki Jakimiuk
In telling the story of the development of the De Havilland Canada Beaver, there were many brilliant minds at De Havilland Canada and no story of the development of any aircraft can be fully told without looking at previous design influences. Often in aviation history, military aircraft have design influences on civilian aircraft- sometimes the design lineage is obvious, like the pathway from the Boeing B-29 Superfortress to the Boeing 377 Stratocruiser. Sometimes the path of development is parallel but intertwined, like that of the Lockheed C-5 Galaxy and the Boeing 747. And sometimes individual designers bring their experience to a project that leaves their stamp on it- like Jack Northrop's influence on Douglas designs from his time working for Donald Douglas. In the case of the De Havilland Canada Beaver, the experience of the company's chief design engineer, a gregarious Polish emigre named Wsiewolod "Jaki" Jakimiuk and his prior work before the Second World War with the PZL series of fighters, would, combined with the talents of his colleagues that the De Havilland's Downsview facility, create one of the greatest bush aircraft of the skies. 

Zygmunt Pulawski
The story begins with the Polish aeronautical engineer Zygmunt Pulawski. Born in 1901, Pulawski made a name for himself as a student at the Warsaw University of Technology designing and building his own gliders. Graduating in 1925, he went to work in France for Breguet, gaining valuable experience in aircraft design and construction. After two years he returned to Poland, became a pilot and by 1927 was the chief designer at the Central Aviation Workshops in Warsaw which was soon reorganized into PZL (the Polish abbreviation for State Aviation Works). It was in that capacity he submitted the winning design for a 1928 requirement from the Polish military for a new fighter aircraft, the PZL P.1. At PZL, Pulawski pushed his team to all-metal construction at a time when many fighter aircraft were still biplanes with fabric and wood components. At the time of its first flight in 1929, the P.1 was one of the most advanced fighter designs in the world with its gull winged monoplane wing, slim nose with a Hispano-Suiza V-12 engine and a finely corrugated metal skin that would be imitated by many contemporary designs. Pulawski's gull wing was so that the wing roots met the fuselage at the most aerodynamically optimum 90-degree angle and the cylinder heads of the V-12 engine matched the angle of the wing roots, giving the pilot excellent forward visibility compared to contemporary fighter designs. 

Model box art showing the P.1 configuration
The P.1 was showcased throughout Europe and even was demonstrated at the 1932 Cleveland Air Races in the United States. At a 1930 fighter competition in Bucharest, Romania, the P.1 made an excellent showing against contemporary types which included the Bristol Bulldog and the Dewoitine. The P.1, however, remained only a prototype as the Polish military preferred the Bristol Mercury radial engine which was being license built in Poland at the time. Pulawski, however, developed the P.1 design further with more powerful V-12 powered aircraft, the P.8, which first flew in August 1931. However, the two P.8 prototypes had cooling issues in the engine, but more importantly as a setback, Pulawski had perished in a crash on 31 March 1931. Lacking a strong proponent for streamlined in-line engine designs, the P.8 was canceled by the Polish government. 

The radial engine-powered P.6
At the time that the Polish military pushed for the incorporation of the Bristol Mercury radial engine into the P.1 design, Pulawski's assistant engineer was Jaki Jakimiuk. Prior to Pulawski's death, it was decided to forgo the Bristol Mercury engine and go with the more powerful nine-cylinder Bristol Jupiter engine with 500 horsepower which was also built under licence in Poland as well. The P.6 first flew in August 1930 and had a new, more streamlined fuselage and empennage and a Townend ring to improve the airflow over the protruding radial heads in the nose. Interestingly, the design of the DHC Beaver would go through the same transition, originally envisioned with an inline engine in a slim nose but ended up with a more robust radial engine. Like the P.1, the P.6 elicited quite a bit of interest in aeronautical circles worldwide- it was demonstrated at the 1931 Paris Air Show and it also won the 1931 National Air Races in the United States which were hosted by Cleveland, Ohio, that year. The P.6 also remained a prototype as a more refined design, the P.7, succeeded it. 
PZL P.7 in Polish Air Force markings

The P.7 was a P.6 with a more powerful variant of the Bristol Jupiter radial that had now had 520 horsepower, but more importantly, featured a supercharger for improved performance at altitudes over 10,000 feet. In addition, some of the aerodynamic refinements to the wings that were used on the P.8 were incorporated into the P.7. The Townend ring used on the P.6 was increased in chord for improved aerodynamics. One interesting feature of the design is that the main fuselage fuel tank which was located behind the engine but ahead of the cockpit, could jettisoned in case of an engine fire. The P.7 went into production and became operational in 1933 at which time the Polish Air Force became the first air force in the world to be completely equipped with all-metal monocoque fighter aircraft. By this time Jaki Jakimiuk had succeeded Pulawski upon his death and the PZL works in Warsaw were hosting technical delegations from aircraft companies throughout Europe. Jakimiuk himself often hosted the delegations who came to study PZL's techniques and discuss Jakimiuk's design philosophy. In 1937, a delegation from De Havilland came from the UK to meet with Jakimiuk for an exchange of ideas. At the time, De Havilland was working on its first all-metal airliner, the DH.95 Flamingo. One of the engineers doing an internship on the Flamingo project was Dick Hiscocks, a graduate of the University of Toronto who would eventually join Jakimiuk's team at De Havilland Canada as its aerodynamicist.

The PZL P.11, Poland's primary fighter at the outbreak of the war
At the outbreak of the Second World War with the invasion of Poland in September 1939, three Polish Air Force squadrons still flew the P.7- though more maneuverable than any Luftwaffe fighter and able to operated from grass fields with a takeoff run under 500 feet, the P.7s were simply outclassed by the Luftwaffe's Messerschmitt Bf 109s. But in 1931, the war was far in the future and Jakimiuk and his PZL team refined the P.7 further to create the P.11 which first flew in August 1931. Even before the P.11 was launched into production, Romania showed interest in the design and had arranged to license-build it as the IAR P.11 (the Romanians even incorporated the P.11's tail unit in their later IAR 80 fighter aircraft design). The P.11 used an even more powerful engine than the P.7, a 800-horsepower Bristol Mercury IV, combined with an even more robust structure based on the P.7 design. The first P.11s became operational with the Polish Air Force in 1935 as the primary fighter. 

Model box art of the P.24 in Royal Hellenic Air Force colors
Buoyed by the success of the P.11 and its export to Romania, Jakimiuk developed the P.11 further into a variant intended for export, the P.24. Since the license for the Bristol radial engines prohibited export, the P.24 was based on the P.11 but incorporated a 900-horsepower French Gnome-Rhône Mistral radial engine which was a fourteen-cylinder two-row engine. In addition, the P.24 had a fully-enclosed cockpit and heavier armament that could include two 20mm cannons. Greece took delivery of 36 aircraft, Turkey took 60 (in fact the world's only surviving P.24 is in a Turkish museum), Bulgaria took 36 and Romania got 50 with 44 of them license-built by IAR. The P.24's performance was quite a leap from the P.11 thanks to its more powerful engine and the first variable-pitch three bladed propeller fitted to a PZL fighter design. Turkey's P.24s were flown until the late 1940s as training aircraft, some getting retrofitted with the Pratt and Whitney Twin Wasp engines used on the Douglas DC-3. Romania's P.24s protected the Ploesti oil installations at the start of Operation Barbarossa and flew ground attack missions until 1942. The Royal Hellenic Air Force was the only air arm to use the P.24 as its primary fighter type and it gave a good account for itself against the numerically superior Regia Aeronautica during the Italian push in Albania. By the time of the German invasion in April 1941, though, only five P.24s remained. 

Model box art of the P.50
Given the leap in performance of the P.24, you might be asking yourself why the Polish Air Force never operated it and stuck with the P.11. When the P.11 became operational in 1935, that was around the same time that the prototypes of the Messerschmitt Bf 109 (1935) and the Supermarine Spitfire (1936) first flew. It was pretty obvious to the Polish military command that the P.11s were quickly going to be come obsolete, so Jakimiuk broke from PZL tradition to design a much more modern fighter- a low wing monoplane fighter with an enclosed cockpit and retractable undercarriage, the P.50 Jastrząb or Hawk- it looked a lot like the Curtiss P-36 Hawk, though this is purely coincidental given that common problems in aviation design result in common solutions. Again using the Bristol Mercury engine, Jakimiuk's design was enthusiastically accepted by the Polish Air Force and ordered into production in 1937. The 800-horsepower Bristol Mercury VIII engine was ordered direct from the UK until license production could get underway in Poland. The second prototype P.50 would have an even more powerful engine, the Bristol Taurus with 1,150 horsepower with plans for a P.50 export variant with French Gnome-Rhône engines. The first flight was made in February 1939. The following prototypes and production standard aircraft were planned to have a cut down rear fuselage to improve rearward visibility during air combat. 

At the end of August 1939 on the eve of the German invasion, only the unarmed P.50 prototype was flying. The second prototype P.50 still had not received its Taurus engine and the third prototype was about 80% complete. In addition, airframe sections for four more P.50s were under construction. Poland fell to the Nazi onslaught in two days with the P.50s being captured and studied before being scrapped in 1940. The sole P.50 prototype was flown out in an attempt to escape, but ran out of fuel and crashed. Jakimiuk and his family managed to escape Poland during the invasion and his prior contacts with De Havilland proved fruitful as they arranged for him to work at their Canada subsidiary at Downsview north of Toronto. Rather amusingly, Jakimiuk, his family, and a team of engineers from PZL that he brought with him, were denied a permanent visa by the Canadian government as Ottawa bureaucrats demanded to know who was covering the Poles' travel costs from the UK to Canada. De Havilland guaranteed the travel costs for Jakimiuk and his family and his team of engineers as a gesture of thanks for the their advice on the DH.95 Flamingo transport back in 1937. In all, De Havilland covered the costs of travel and relocation for forty PZL engineers and their families to Canada to work at the Downsview facility. Many of Jakimiuk's colleagues would go on to to have illustrious careers in both the Canadian and American aerospace industry for years to come after the war. As for Jaki Jakimiuk, by the end of the Second World War he would become De Havilland Canada's chief designer and his experience with the PZL fighter line would prove indispensable as DHC made the transition from wartime production to peacetime civilian aircraft designs. 

But that's a story for a future blog article!

Source: Immortal Beaver: The World's Greatest Bush Plane by Sean Rossiter. Douglas & McIntyre Books, 1996, pp 17-23. Photos: Wikipedia, Wings Palette, Internet Modeler

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