"Like all novices, we began with the helicopter (in childhood) but soon saw that it had no future and dropped it. The helicopter does with great labor only what the balloon does without labor, and is no more fitted than the balloon for rapid horizontal flight. If its engine stops it must fall with deathly violence for it can neither float like the balloon nor glide like the aeroplane. The helicopter is much easier to design than the aeroplane but is worthless when done."

Wilbur Wright
Davton,Ohio, January 15, 1909

Rotary Aircraft

Helicopter Types Military Service
H-1 X X   X X
H-3   X      
H-6       X  
H-46 X X      
H-47       X  
H-53 X X      
H-57 X        
H-58       X  
H-60 X X X X X
H-64       X  
H-65     X    
H-67       X  
H-72       X  
Helicopters are different from airplanes. Helicopters don't fly -- they beat the air into submission. An airplane by its nature wants to fly, and if not interfered with too strongly by unusual events or by a deliberately incompetent pilot, it will fly. A helicopter does not want to fly. It is maintained in the air by a variety of forces and controls working in opposition to each other, and if there is any disturbance in this delicate balance the helicopter stops flying; immediately and disastrously. This is why being a helicopter pilot is so different from being an airplane pilot, and why helicopter pilots are brooding introspective anticipators of trouble. They know if something bad has not happened it is about to.

The quite favorable trend of fewer and fewer helicopter accidents per year, even as the number of helicopters flying has increased over the past six decades, is a heartwarming story to relate. However, the industry did learn an expensive lesson when it introduced helicopters powered by single turbine engines, which caused a wide spike in accidents per year. This spike distorted the yearly trend in accidents per 100,000 flight hours. The current trend is to sell four helicopters and have an accident with one of them. Loss of engine power due to running out of gas is quite common, and the upward trend in loss-ofcontrol accidents per year is very, very disturbing.

Helicopters are considered high-value items by military commanders because of their mobility, operation flexibility, rapid response, and lethality. To transporters, however, helicopters are extremely fragile, high-dollar materiel requiring extreme care to ensure proper and safe transport.

By convention used worldwide, helicopters are categorized by weight. Specifically, "light", "medium lift", and "heavy lift" helicopters. Light helicopters are those generally considered below 12,000 pounds maximum gross weight. "Medium lift" are generally considered those from about 14,000 pounds to 45,000. There is some disagreement in terminology regarding the use of "heavy lift." Some within the industry refer to helicopters above 50,000 pounds as "heavy lift" while others reserve this term for the very largest helicopters, those above 80,000 pounds. Within Army aviation the largest helicopter is the 54,000 pound CH-47D Chinook, most often referred to as a medium lift helicopter.

The cost of helicopters both in terms of purchase price and operational cost, increases geometrically with size. As a consequence of both cost and use, over 95% of the civil helicopters in use worldwide are "light." During the first two decades of helicopter development, the military adopted commercial designs. The design expertise for helicopters has remained with the five domestic firms that supply military helicopters: Bell, Boeing, Kaman, McDonnell-Douglas, and Sikorsky. Although Kaman supplies USN helicopters and some Army helicopter components (notably, the AH-1 Cobra rotor blades), the Army does not have any Kaman helicopters. The "big 4" US helicopter firms are the other four listed. Military helicopters tend to be both larger and heavier, with many more "systems" on board (e.g., sensors, weapons, communications) and more "crashworthy" features. A small news or traffic helicopter (typically a Bell Jet Ranger) costs from $700K to $1.2M. An Apache costs approximately $14M (1997 figures).

Military helicopters are designated by use. The designation "OH" refers to observation helicopter. These are light helicopters used predominantly for reconnaissance and courier requirements (e.g., OH-58C). General use helicopters are designated as "utility" and have a "UH" prefix (e.g., UH-60L). "CH" refers to cargo helicopters. They are designed to move cargo both internal and external ("sling loads"). Attack helicopters have an "AH" prefix. There are two in the Army, the AH-1 Cobra and the AH-64 Apache. And finally, the next generation Comanche helicopters has an "RAH" prefix to designate it as a reconnaissance and attack helicopter. With the exception of helicopters used for medical evacuation, all have some armament (e.g., door guns, rocket pods).

The major sub-categories of helicopters are the 1) rotor system, gearboxes and drive train components; 2) engine; 3) avionics; 4) "systems," a.k.a. "Mission Equipment Package (MEP)"; and, 5) airframe. The Viet Nam era helicopters generally have two bladed (teetering) rotor systems while the newer aircraft have four or five rotor blades ("fully articulated" rotor systems). The turboshaft engines used in helicopters have commercial applications. In some aircraft, there are more engines in civil use than in the Army fleet. Avionics for navigation, communications, and flight instrumentation are similar or identical to those used in civil aviation. There are however, some military unique avionics or modifications (e.g., blue - green lighting compatible with night vision goggles). As a general statement, the predominant developments over the past two decades have been in the on-board "systems," rather than in rotor systems, engines, or airframes.

There are some 5,000 to 30,000 parts on an Army helicopter. The great majority of these are not essential to flight. However, there are 200 - 400 parts, whose failure results in a catastrophic crash (e.g., separation of a rotor blade). These parts are designated as "flight critical." In all aspects of design, testing, configuration control, and spares procurement, "flight critical parts" receive significantly more attention than others. If operators in the field report the failure, or impending failure of a flight critical part, an immediate investigation is undertaken (led by the AMRDEC and coordinated by the flight safety office). Frequently an Aviation Safety Action Message (ASAM) is distributed which grounds the fleet pending a complete investigation. These events, though infrequent, result in a cessation of normal activity and a comprehensive focus on a remedy. "Flight safety part" is synonymous with "flight critical part."

Helicopters have a large number of moving parts, designed to minimal weight and high stress (fatigue) conditions. This, combined with a low tolerance for failure, results in high maintenance. Ratios of Maintenance Man Hours (MMH) to flight hours is often 3.5 to 4.5. That is, four hours of maintenance is conducted for every flight hour. Parts are replaced well before expected failure. Many parts are machined to very close tolerances. Metal used to manufacture parts have certifications regarding the source, treatments, and inspections. It is not unusual for spare parts to cost $5,000 to $15,000 with a few exceeding $50,000. Consequently, the current parts cost (in 1996) per flight hour of a Black Hawk is $1,602.70 ($351.54 consumable and $1,251.16 reparable). The Longbow Apache spares cost per flight hour is $3,851.18 ($444.20 consumable and $3,406.98 reparable).

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