Propellers Still Going Strong After Over 120 Years

Propellers are the world's preferred way of generating propulsion for an aircraft. They come in many varieties, from pusher propellers on the tail of an aircraft to pull propellers on the nose or on the front (or rear) sides of the wings. The propellers of tiltrotor aircraft such as the V-22 Osprey or Leonardo's AW609 are special in that they serve as either propellers or rotors, depending on the phase of flight. In either case, the rotating propeller "scoops" air and thereby moves the aircraft. 

Although the Wright brothers used propellers in their early aircraft, anyone who thinks that this technology is therefore old fashioned is mistaken. It is experiencing a renaissance due to aviation's drive for ever greater efficiency and the pressure to make flying more sustainable. 

The emerging market for drones is also driving new research and technological approaches to propellers, which will also find their way into manned aviation in the future, particularly General Aviation. The Wright Brothers' Wright Flyer was initially pulled through the air by two two-bladed propellers, setting a standard that endured for decades. Today, most General Aviation piston engine aircraft still have two-blade propellers. 

But with more powerful engines and newer aerodynamic discoveries, the number of propeller blades increased. During World War II, many fighter aircraft such as the mighty P-51 Mustang, the heavy P-47 Thunderbolt or the sleek Supermarine Spitfire flew with four-blade or, like the Messerschmitt Bf 109, three-blade propellers. These props were made of wood and metal, respectively. 

Over the years, physical knowledge and practical experience led to new propeller designs. On the one hand, designers worked on the shape of the propellers to increase efficiency and designed and built sickle-shaped propellers or propellers with curved blade tips. On the other hand, designers increased the number of propeller blades, resulting in smoother running with less vibration and reduced noise emissions. 

Five-blade propellers are now standard on many turboprop aircraft, but propellers with seven blades are also already available as retrofits for production aircraft. And that’s not the end: The Airbus A400M military transporter flies with four turboprop engines, each driving an eight-blade propeller. 

MT-Propeller, a company based in Straubing, Germany, has once again done pioneering work in propellers over the past year: Recently, a twin-engine Piper PA-31T1 Cheyenne flew with propellers with eleven propeller blades each for the first time in the world! Until now, a nine-bladed propeller – also from MT-Propeller – was the propeller with the most blades ever flown on a General Aviation aircraft. 

Basically, the more blades installed on a propeller, the lower the noise emissions. In addition, the propeller diameter can be smaller for the same power output, thus increasing the ground clearance of the propeller. However, props with more blades are usually also heavier than those with a smaller number of blades. MT-Propeller is testing the eleven-blade prop extensively to learn in detail the advantages and possible disadvantages of this propeller. 

In addition to the classic materials of wood and metal, fiber composites have also found their way into propeller manufacturing. They are usually lightweight and corrosion-resistant. At the front of plastic blades is usually incorporated a metal leading edge, which is to prevent propeller erosion by dust. As long as aircraft fly, there will be propellers.