Principle of Operation and Control

The helicopter derives lift from rotating an airfoil called the rotor. Usually it is equipped with one or more power-driven rotors. When the angle of attack of rotating rotor blades attains a certain value, the lift overcomes the weight of the aircraft and then it takes off vertically.

To achieve horizontal flight, the pilot tilts the rotor forward at a certain angle. This is done by what is known as cyclic pitch change, i.e. changing the pitch of each blade once per revolution. More particularly, the angle of attack of each blade is increased every time it sweeps over the tail of the machine, thereby temporarily developing a greater amount of thrust than the other blades.

Additionally each blade can swivel about its longitudinal axis and its pitch is changed cyclically, through a linkage system, by a so called swash-plate, which performs a sort of wobbling rotary motion around the shaft and swivels the blades to and fro as they rotate. The tilt of the swash-plate can be varied by the pilot, and the tilt of the rotor follows the tilt of the plate.

So, by changing the pitch angle of the main rotor blades, by manipulating the engine speed and by tilting the main rotor, the pilot controls the helicopter's flight in any direction.

Hovering over one point is done by selecting the correct speed and setting the rotor blades so that their vertical lift is exactly equal to the weight of the helicopter.

Classification of Military Helicopters

Hels are a separate group of acft and have now begun to displace mil fixed-wing acft in many roles. They are classified as atk, obsn, utility, cbt assault transport, electronic warfare and target acquisition, antiarmor, etc.

AIRCRAFT ARMAMENT SYSTEMS

General

The art of air-to-air cbt and air-to-ground atk was born in the smoke and flames of WW I battlefields, when low-flying ftr plts used MG's to strafe en trps in the trenches or to fire at en acft. Later on some kind of gunsight was installed on the ftrs to ensure the accuracy of aim and bomb racks were fitted so that they could atk any "tgts of opportunity" spotted on the gnd. And then came a never-ending succession of other devices to make them more formidable.

Today, cockpit video displays, navigation rdos, sensors, on-board computers, ground-mapping rdr, forward-looking infrared (FLIR) systems, inertial navigation sets, integrated tactical ECM devices, and programmable armt con sets are std equip aboard modern acft such as USAF's F-15E. These enable the ftr plt strike a tgt with precision. In many cases, they can employ certain types of ordnance without having to fly over a heavily defended tgt.

Using the two-pod Low-Altitude Navigation and Targeting Infrared for Night (LANTIRN) system, a two-man F-15E crew can take off from a blacked-out airfield and fly a moonless night atk msn only 100 feet above rough terrain, traveling at airspeeds greater than 500 knots. The IR picture, which the plt sees through the head-up display (HUD) in his windscreen, "reads" heat emissions to show him the terrain ahead, which shows up almost as bright as in daylight.

The terrain-following equip enables the plt to stay below en rdr acquisition horizons. Once in the atk area, the aircrew can "see" the tgt, using ground-mapping rdr or IR return data displayed on one or more of their cockpit multifunction displays (MFDs), and atk it before the defenders know they are threatened.

Staying beneath en rdr, the plt uses gnd clutter to fool any searching acft that might be equipped with look-down/ shoot-down rdr systems.

The glass cockpit is one more crucial innovation. Several cathode-ray tubes replace most of old round "steam gauge" dials familiar to generations of plts. These screens display all the info the plt needs to fly the plane and use it as a fighting machine. Whatever info the plt needs at any moment can be projected onto his HUD, so it appears to be floating out in space, where his eyes focused in his search for en planes.

Coupled with the programmable rdr and the glass cockpit is the hands on throttle and stick, or HOTAS, system. With all the critical con switches on the stick or throttle, the plt never has to let go of the controls to fly or fight.

Once the plt drops his bombs, he immediately switches his rdr and all his wpn systems from air-to-gnd to air-to-air with a slight movement of the thumb of his right hand where it rests on the con stick to prepare to deal with en ftrs. In the past, if he could do it at all, it took the plt many seconds to reconfigure the plane as a ftr and in a dogfight he had to estimate the distance to his tgt and then use his gunsight to calculate how far in front of the other plane to aim so the bullets would arrive at the right moment. At present the plane's rdr measures the distance to the other plane and the computers do all the calculations with much more precision than the plt could do them in his own mind.

When the rdr is locked on to the en plane and it is within range of the gun or one of the msls, a strobe light on the HUD flashes "SHOOT ... SHOOT ... SHOOT". If the plt presses the trigger on the stick, a hit is almost certain.

So the term "aircraft armament system" covers a wide variety of equip and comps designed to carry, arm, release, and maintain overall control of the various explosive items of ordnance which are frequently referred to as "stores" for brevity. According to the stores used and the method of their employment the aircraft armament may be classified as guns, bombs, rkts and GM's, mines, torpedoes and depth charges, and special purpose wpn systems.

AERIAL ARMORY

It was the gun which led the way in abn weaponry to be followed by the bomb and abn rkt. Over the years, however, these simple categories have become more complex and developments have produced precision-guided wpns and submunition dispensers, overflight and stand-off wpns.

Guns

About the only wpn which has remained, essentially, the same is the abn gun, which reigned supreme as the principal ftr wpn until the mid-1950s, when the first air-to-air msls (AAMs) entered service. Such were the advances that by the mid-1960s, several major nations had entirely abandoned the abn gun in air def acft. Yet from the reality of modern air cbt in the late-1960s, the lessons of history were re-learnt and guns rapidly re-introduced. The resurgence was led by General Electric's 20 mm M61 Vulcan rotary cannon. This wpn was rapidly integrated on board a Phantom and has been on virtually every major US ftr since. Of course, the M61 is not the only GE product. The company produces a wide range of abn wpns varying from 30 mm down to 7.62 mm with the rate of fire from 300 up to 6000 rd/min that can be selected by the gnr.

Lighter wpns, including pintle- and pod-mounted machine guns, are used on hels. They can also be installed in chin turrets and are available in single- to six-barrel forms.

Fixed-wing acft can carry heavier cannon than the average hel, but firing opportunities are generally restricted in duration. Number of barrels is usually from five to seven.

Short-Range AAMs

Defending battlefield hels are variants of man-portable air def sys (MANPADS) msls. First in the field was the General Dynamics FIM-92 in a version known as Air-to-Air Stinger (ATAS). Undoubtedly the classic 'dogfight' AAM must be the AIM-9 Sidewinder series.