Douglas DC-3 Dakota
Europe’s most successful turboprop DC3 replacement
The Fokker F.27 Friendship is the best known aircraft from Dutch soil. Its design and construction was a huge gamble that exceeded expectations.
The birth of an iconic aircraft
In 1935, passengers and cargo were often transported by air on the DC-3, a highly successful aircraft built by Douglas Aircraft Company. After World War II, the need to transport passengers by air grew and aircraft manufacturers worldwide were busy developing a potential successor to the DC3.
Fokker, the Dutch aircraft manufacturer, was also one of them. A number of inspired designers and engineers came up with a very daring plan: the design of an aircraft that deviated greatly from the usual form and technology. The new aircraft had to be much better than the DC-3: more powerful, lighter and cheaper. It also had to offer much more comfort for passengers. Easier said than done, because Fokker had no real experience in the field of larger passenger aircraft.
Exciting choices, risky gamble
In the daring design, Fokker no longer wanted to use piston engines but turboprops. Although piston engines were cheap to operate and maintain, they were not powerful enough in Fokker’s view. For example, the safety requirements for aircraft were quite high, because the aircraft had to be able to take off, fly and land on 1 engine. In addition, piston engines were less powerful at higher altitudes.
That is why Fokker opted for so-called turboprop engines: these had fewer moving parts, were much more powerful, offered more comfort because they vibrated less and were also more reliable.
In 1955 this was quite a big gamble because in practice there were hardly any turboprop powered aircraft (in 1953 the Vickers Type 701 Viscount was the first passenger aircraft with turboprop engines). Many competitors therefore thought that turboprop engines were unreliable. Years later, practice proved that the turboprop aircraft were actually much more reliable.
Another innovation was the placement of the wings above the fuselage. This would reduce drag and make it possible to use longer propeller blades. A larger propeller has the advantage that more power can be delivered at less rpm.
This also had the advantage that the landing gear in the nacelle could be retracted behind the engine, which in turn had the advantage of less air resistance.
The disadvantage of an upper decker was that longer and therefore heavier landing legs were needed. To make sure they didn’t get too long, the hull was made a bit flatter at the bottom. That was also a risk, because a cylindrical shape is the best for a pressurized cabin.
A glued-on plane?
Another very important innovation was the gluing of the skin plates instead of riveting. This made the aircraft not only lighter but also much more streamlined, which reduced the air resistance again.
Gluing did bring more challenges because metal gluing was fairly new. Fokker developed his own method in which glue was cured in an autoclave. The disadvantage was that Fokker himself had to devise a method to inspect the glued parts; an in-house measuring device was developed for this purpose, the Fokker bond tester. It is still used under that name today.