A helicopter flies by and to a great surprise of your friends you immediately identify it as a Robinson. With confidence too, even if it is flying quite far away from you. And that’s because Robinson helicopters have a distinctive feature – a tall rotor mast.
A rotor mast is a platform, a column, which separates the fouselage of a helicopter and its main rotor. It’s hardly a technical term, but people do use it (we asked). Especially to describe helicopters that have low-mounted engines.
Some details about Robinson helicopters
Frank D. Robinson founded the Robinson Helicopter Company at the age of 43 in 1973. Prior to that, Robinson worked on a number of exciting helicopter projects at companies like Cessna, McCulloch, Kaman, Bell and Hughes. Robinson was often regarded as a tail rotor expert. He was a talented engineer and a real wizard when it came to helicopter aerodynamics.
In his namesake company Robinson aimed to create an affordable, easy-to-operate and easy-to-maintain helicopter. He wished his aircraft to be a bit like a car – suitable for a variety of different tasks, not taking up too much space when parked and able to be repaired with relatively simple tools. Robinson’s first helicopter R22 took off for its maiden flight in 1975. As you may imagine, it was piloted by mr. Robinson himself. In 1979 the Robinson R22 went into series production and soon became the most popular two-seater helicopter in the world.
The R22 is a very compact two-seat helicopter, perfectly suited for pilot training, personal recreational flights, work on large cattle farms and a wide variety of other tasks. It is 8.74 meters long and is equipped with a four-cylinder 92 kW Lycoming engine, mounted behind the cockpit. The diameter of the twin-blade rotor is 7.67 meters. Such dimensions allow the R22 to be transported on a car trailer without taking off its rotor – an experienced pilot can land his R22 directly on a trailer. This is one of the reasons why Robinson chose a two-bladed rather than a three-bladed rotor – it doesn’t have to be taken off or folded for transport.
In 1990, a larger, more powerful and more comfortable version of the R22 came along, called R44. This 11.66 meter long Robinson seats 4 people and has a Lycoming 6 cylinder 183 kW engine that powers a 10 meter twin-bladed rotor. The Robinson R44 is one of the best-selling general aviation helicopters in the world.
In 2007, an even more spacious Robinson model – the five-seater R66 – came off the ground. At 8.99 meters long, it is shorter than the R44 and has the same diameter main rotor. The biggest mechanical difference is that the R66 has a turboshaft engine instead of a piston engine.
Robinson helicopters are very popular and easily recognized by that interesting column on which the main rotor is situated.
Robinson helicopters and the tall rotor mast
Robinson’s first model, the R22, was designed as a cheap and easy-to-maintain helicopter. Thus, the manufacturer had to look for ways to simplify the construction of the aircraft and its controls.
The R22 has a simple welded steel tube frame covered with an aluminum, fiberglass and plexiglass skin. Its cabin is quite cramped, which is understandable, having in mind how compact this helicopter is. Robinson had to find some creative ways to make this work. Instead of the two separate cyclic sticks (joysticks, sort of) that would normally be between each pilot’s knees, Robinson helicopters have what’s known as a T-Bar – one teetering stick, mounted between the pilots, which splits into two handles. The larger Robinson R44 and R66 use hydraulic controls, while the R22 has a mechanical control system.
By the way, an interesting fact – the lack of hydraulics on the R22 is actually an advantage for pilot schools. Young pilots get used to more sensitive handling characteristics, which require more attention, more care and smoother movements. At the same time, of course, the lack of a hydraulic system reduces the cost and mechanical complexity of the R22. However, pilots often say that the Robinson R22 is surprisingly tricky to control due to its light weight, lack of hydraulics and stabilization systems. Once you master the R22, other helicopters seem quite easy.
Robinson helicopters use two-bladed main rotors, while many other small helicopters use a three-bladed rotor design. A two-bladed rotor is technically cheaper and makes transporting the helicopter a lot easier. The Robinson rotor uses a teetering hinge mechanism – as one blade rises, the other goes down. This mechanism, reminiscent of a seesaw, is relatively simple (remember – they tried to cust the costs down), but the helicopter is not as maneuverable as it could be with a multi-hinge main rotor. Because of the teetering hinge mechanism the tips of the Robinson rotor blades have a greater amplitude of vertical movement, which is one of the reasons why the manufacturer had to raise the main rotor up. If we add all of this together, the teetering main rotor, low-mounted engine and small fuselage result in a larger gap under the rotor. And that is why Robinson helicopters have a tall rotor mast.
There are other helicopters that have teetering main rotors, but they do not have such distinctive rotor masts like Robinsons. This is because many such helicopters are larger and more powerful and have their engines above the cockpit. For example, the Bell 206 has a two-bladed teetering rotor, which is also mounted quite high, but this visual tower is not created because the engine compartment is right under the rotor. If the engine of the Bell 206 was behind the cockpit, that section between the fuselage and the rotor would also be a tall mast.
The tall main rotor mast has some advantages. It reduces the risk of the rotor blades colliding with obstacles. Robinson R22 is 2.72 meters high. In comparison, another popular two-seater Guimbal Cabri G2 is 2.37 meters tall. Those extra centimeters make it less likely that the tip of the rotor blades will catch on a bush or a fence. After all, the R22 was developed as a very versatile helicopter, suitable for pilot schools (students sometimes do not land quite straight and stable) and for farmers. The Australians use their R22 helicopters to herd cattle, expertly maneuvering between trees, fences, buildings and cows. Obviously, this advantage is less important for the larger R44 and R66, but it is still nice to have that teetering main rotor away from the ground.
Of course, there are downsides to Robinson’s tall rotor mast design. Pilots sometimes say that Robinson helicopters can be caught by the pendulum effect, when the helicopter starts swinging and becomes difficult to control.