¶ … CH-47D helicopters. It focuses on five subsections during the development process until the implementation stage. The paper further looks at how the helicopter was developed, how it was developed and its future. Besides, the paper looks at the significance of the helicopter and major issues experienced during the development and how they were overcome. The Development Process

The department of defense announced in 1956 plans for the replacement of the CH-37 helicopters with an improved edition CH-47D helicopters. This decision was reached after several army aviation corps voted in favor of the creation of helicopters powered by piston engines. In addition, the army corps recommended that the new helicopters be large enough to airlift large military equipment (Spenser, 1998).

Following the army's decision to use bigger and more powerful helicopters, Vertol was contracted to start the design and building of a new tandem-rotor helicopter known as the V-107 in the year 1957. The following year, Vertol was further contracted to design the YHC-1A; V-107's successor, with capacity to carry up to 20 troops. The YHC-1A seemed better enhanced than the V-107, however it was considered heavy for air assaults and light for transport leading to the decision of procuring a heavier transport helicopter by the army. Consequently, modification and improvement of the YHC-1A commenced paving way for the CH-46 Sea Knight in 1962 which was used by the U.S. Marines.

During the same period, the American army ordered a large helicopter Model 114 referred to as the HC-1B. The HC-1B was later renamed CH-47A in 1962 in accordance to the United States Tri-Service Aircraft Designation System. The CH-47A helicopter was propelled by double turbo shaft engines attached at the helicopter's rear connected by drive shafts to the helicopters rotors. In addition, these helicopters were fitted with engines that had 2,200 horsepower output (Anderton & Miller, 1989).

The American army further opted for the upgrade of the CH-47A helicopters leading to the creation of the more powerful and larger CH-47C helicopters. The CH-47D helicopters were upgraded from the CH-47C's. The CH-47C helicopters had upgraded engines, composite rotor blades, redesigned cockpit to reduce pilot workload, improved but redundant electrical systems, an advanced flight control system and improved avionics. This overhaul of the CH-47C helicopters led to the creation of the CH-47D helicopters. The CH-47D helicopters were further upgraded to reduce maintenance costs, digitalize flight controls.

The CH-47D upgrade program was initiated in 1976 in an effort to upgrade the Army's fleet of CH-47A/B/C helicopters to a common standard. The first flight by a prototype rebuilt CH-47D occurred in 1979 and after evaluations and testing, the Army placed its first production CH-47D order in 1980; the first production flight being in 1982. The CH-47D officially entered service with the U.S. Army in the year 1984.

During the upgrade of the CH-47D's the aircrafts were stripped down to the frame and rebuilt afresh. Some of the upgrade included the inclusion of Honeywell T55-L-712 turbo shaft engines, improved and uprated transmissions, improved avionics and flight control systems, composite rotor blades, and three external cargo hooks. In addition, equipment reliability was improved by simplifying the transmission lubrication system by rerouting hydraulic lines to reduce potential leakages.

Though originally fitted with double T55-L-712 engines, the current CH-47D models have T55-GA-714A engines. With the three-hook cargo system, the CH-47D is able to carry heavy loads internally more than 25,000 pounds at speeds higher than 150 mph. The D-model is the principal mover of 155mm M198 howitzer firing 30 rounds of ammunition per minute during air assault operations. Like most American army helicopters, the CH-47D has advanced avionics and electronics, including the Global Positioning System (GPS).

Reasons for the Development

The first in the long line of CH-47D helicopters was the YHC-1B tandem-rotor transport helicopter that was majorly used in 1961. It was designed to serve the Army and Air Force as a medium-lift helicopter and evolved into several versions. Immediately after the Gulf War, Boeing and the U.S. Army rolled out the plan for a major fleet upgrade that led to development of the CH-47D. During the upgrade period, more than 500 early models underwent extensive modernization process in Philadelphia, producing completely new CH-47 fleet (Dunstan, 2003).

The CH-47D helicopters were developed since the predecessors such as the YHC-1A had tandem-rotor blades which were not effective during flights. The predecessors were further having poor avionics and communication systems and low power engines, having horsepower of 2,200 which were insufficient to power the helicopters making the helicopters unlikely for the U.S. Army. Besides, the former helicopters engines could not handle a 25,000-pound worth of load during shipments of...

This led to the modification and improvement of the YHC-1A to CH-46 Sea Knight in 1962 which was used by the U.S. Marines which were further improved leading to the creation of the CH-47D helicopters.
The CH-47D helicopters were created since they could be easily upgraded to suit the specifications of the army and the air force. The CH-47D helicopters were created to provide the army and air force personnel with increased engine power during flights, improved and uprated transmissions and improved avionics and flight control systems.

In addition, the CH-47D helicopters were developed given their reliability. By rerouting hydraulic lines and simplifying the transmission lubrication system, leakages are reduced leading to lowered operation and maintenance costs.

Future of the CH-47D Helicopter

It has been ascertained that the CH-47D helicopters fulfill vital service roles around the world, not only moving troops and equipment but also flying missions for medical evacuation, aircraft recovery, firefighting, heavy construction, disaster relief as well as search and rescue missions. The improvement of the CH-47D helicopters has had a great impact in supporting U.S. troops during their operations. The helicopters have made the transport and dispatch of troops during warfare and disasters incredible safer and cheaper for the American army (Crawford, 2003).

The CH-47D helicopters were the central element in U.S. Army operations Gulf War, where more than 160 CH-47Ds carried U.S. And Allied troops to outdo Iraqi forces and restrain their retreat from Kuwait. Recently in 2002, the helicopters high speed and large load capacity gave it the lowest cost-per-ton-mile of any transport helicopter available. This shows that despite being mostly used in military operations, the CH-47Ds can be used in transport with minimal operation costs required.

In addition, there have been speculations that Boeing had developed CH-47F helicopters in 2004. Besides, the aircraft manufacturer has been contracted to modernize CH-47D helicopters to the newer F-model crafts standards. Features such as reduced vibration effects, an integrated cockpit control system and more powerful engines with digital fuel controls are likely to make the CH-47D helicopters fully compatible with 21st century operational and war-fighting requirements thus improving the aircraft's efficiency and effectiveness.

In addition, the United States Army Special Operations Forces have built special helicopters; the MH-47Ds and MH-47Es which are the most advanced rotorcraft in operation today. They have fully integrated digital cockpits; forward-looking infrared, terrain-following and terrain-avoidance radar; long-range fuel tanks; and aerial refueling capability (U.S. Department of the Navy, 1982). The MH-7E's integrated avionics system permits global communications and navigation. The upgrading of the CH-47D helicopters to the MH-models aircrafts is likely to increase the efficiency of the CH-47D.

Significance of the CH-47D helicopters

The CH-47D helicopter is significant in modern aircraft operations due to the several capabilities it has over other helicopters. The reasons include improved engine capabilities, high speeding capabilities among other capabilities.

The CH-47D is a twin-engine, twin-rotor heavy lift transport helicopter. It is equipped with a two 3-bladed contra-rotating rotors and no tail rotor. The rotor blades are fabricated from composite materials and are resistant to AAA (anti-aircraft artillery) fire up to 23mm. The engines are mounted externally on the after section of the fuselage, at the base of the stern. They have flight deck access door mounted behind the cockpit. This door is of a split design, with the upper half opening upward and inward, and the lower half opening downward. The lower door portion features molded in steps for access to the helicopter. The upper portion of the door can be jettisoned in flight.

The rear of the aircraft is equipped with a large cargo ramp that can be left open or partially closed while in flight to accommodate long cargo. The CH-47D's triple-hook system, provides stability to large external loads such as 155mm howitzers which can be transported at speeds of up to 260 km/h.

The CH-47D helicopters have two T55-L-712 turbo shaft engines affixed to them each having an output of 3,750 shaft horsepower. In addition, the engines; mounted on the sides of the planes under the rotors, are to provide the helicopter's rotors horsepower via a central gearbox. The engines, providing a continuous horsepower of 3,750 are equipped with Full Authority Digital Electronic Control (FADEC) to regulate the flow of power to the rotors. Furthermore, the engines having internal fuel tanks…