Flight initiation course

The helicopter has three different controls: the cyclic one, which controls the inclination (left and right) and the pitch (nose down and up), varying the plane of rotation of the main rotor; the collective, which controls the power (the angle of the main rotor blades) to go up and down and the pedals, which control turning left and right by varying the angle of the tail rotor blades. In addition, there is control of the engine or engines, generally automatic, although some are manual.

To date, an effective system has not been achieved that allows launching from a helicopter as is done from a fighter plane, with an ejection seat. (The Kamov Ka-50 military helicopter has this system incorporated). In reality, the parachute is the helicopter itself, and more specifically the main rotor.

Unfortunately, the helicopter cannot glide, but rather "controlled fall." The maneuver called autorotation allows you to land with the engine stopped or without power applied to the rotors due to the entry into operation of a system similar to that of bicycles (when you stop pedaling, the rear wheel continues rotating) called freewheel. This system allows the main rotor (and the tail rotor associated with it) to rotate in the same way that a windmill does due to the flow of air from bottom to top as the helicopter descends.

To enter autorotation, the collective control must be lowered completely and in a very short time (of the order of two seconds) since if this is not done, the main rotor would be braked due to air resistance until it loses revolutions and would no longer be able to operate. support the helicopter. Hence a saying among helicopter pilots: "when in doubt, autorotation."

Although autorotation allows you to reach the ground safely, it is an extremely difficult maneuver, since the descent rate during it is close to 2000 ft./min. (about 600 m/min. or 10 m/sec.) and the indicated speed remains around 650 KIAS (120 Km./h) (approximate R22 conditions).

If contact with the ground were made under these conditions, the result would be catastrophic. For this reason, at the end of the autorotation and very close to the ground (about 30 m.), a "flare" or aerodynamic braking is carried out by quickly raising the nose of the helicopter to about 20º. This achieves three things: a moderate increase in rotor rpm (and therefore lift), a large decrease in the indicated speed (ideally 0 KIAS) and a large decrease in the descent rate (below 500 ft./min.).

Once braking is completed, the pilot lowers the nose until it is slightly above the horizon and applies the collective control to cushion the entry into the ground, changing rotor lift for descent rate (the higher the collective rises, the slower the descent will be, provided the rotor rpm loss is within limits).

Training in autorotation must be continuous, especially in single-engine helicopters. In the basic helicopter course, these maneuvers are practiced regularly in the R22, entering autorotation from 600 ft. on the ground and trying to enter a square of about 15x15 m. Without breaking the helicopter!

It cannot be said that one is more difficult to pilot than the other, each one has its peculiarities. The helicopter requires great coordination between the hands and feet, and the movements of the controls generally have to be very small, so "fine hands" are needed.

Assuming that the helicopter was invented to fill the gap between the surface vehicle and the airplane, great speed is not needed. The fundamental problem is the helicopter's rotor, which at high speeds suffers a series of aerodynamic phenomena that limit its maximum speed. Even so, modern helicopters have acceptable speeds, which allow them to "rub shoulders" with conventional aircraft, and even with some fighters, when landing at airports.

Theoretically yes, as long as the maneuvers are within the resistance limits of its components (rotor, structure). Even so, the maneuvers would not be as attractive as in conventional airplanes (for example, the curl or looping is much more similar to an ellipse than a circle) due to the aerodynamic problems inherent to the helicopter design.

No. Due to the aerodynamic problems that appear in lateral and backward flight, the speed in these cases is much lower than forward (about a quarter of this in "normal" helicopters and a 50% in combat models ).

Regarding the power plant, there are no major differences with a conventional internal combustion engine or turbine/turboprop aircraft except that helicopter turbines do not have an afterburner. However, the rest of the powertrain components are much more complicated.

 

In multi-engine helicopters (generally twin engines), the main transmission box must be capable of absorbing, combining and transforming the power supplied by the engines (which do not always rotate at the same rpm and therefore do not provide the same torque). To get an idea, it is enough to say that some turbines operate at about 30,000 rpm and the main rotor at about 300 rpm. All this is achieved through sets of reduction gears.

 

Regarding the flight controls, the difference with the conventional airplane is much greater since it is the lifting surfaces (blades) themselves that at the same time constitute the control surfaces.

 

Rotor heads are of great technical complexity, although the use of composite materials tends to simplify their design and maintenance. An articulated rotor (the type generally most used due to its efficiency) allows rotation movements on the longitudinal axis, up/down and forward/reverse. In addition, the blades themselves suffer deformations and bending while they rotate. All this makes the maintenance of the rotors a very important aspect.

 

The blades must be paired so that their weight is as uniform as possible (they must all weigh the same), with the tolerance for the difference in weight being a few tens of grams since an imbalance of masses in rotation causes vibrations. and, ultimately, structural damage to them and the rest of the helicopter components.