C-17 Globemaster III - Design
Airborne forces are the spearhead of a force projection Army. They may be employed during strategic, operational, or tactical missions. Airborne forces have a worldwide contingency mission, must be prepared to deploy with little notice, and fight immediately upon arrival at the drop zone. Tactical operations include personnel static-line and military freefall (MFF) airdrops, A7/A21 containers airdrop, Low Velocity Air Drop (LVAD) of heavy equipment, container delivery system (CDS), and Low Altitude Parachute Extraction System (LAPES).
The C-17 can carry 102 parachutists at any one time. Dual door exists allow these parachutists to deploy the aircraft in 55 seconds. On 12 August 1994, during routine development flight testing at Edwards AFB, CA, of mass paratroop operations, a pair of Army jumpers encountered a high-altitude parachute entanglement. Both jumpers landed safely without injury following the event, and the Army and Air Force immediately began work to understand and resolve the phenomenon, which is not unique to the C-17. The aircraft's "vacuum effect" on paratroopers, caused by the draft of a wide-body aircraft's wake and design, tends to "suck" paratroopers into a single file behind the aircraft where they could bump into each other. Parachute testing resumed in March 1995 at the US Army's Yuma Proving Ground, AZ, with a series of three, dual-door paratroop missions. During April 1995, the final jump involving more than 100 jumpers occurred with all jumpers safely exiting the aircraft without incident.
During a mass tactical airdrop, a static line is the piece of heavy-duty nylon fabric that connects the paratrooper to the aircraft and deploys the parachute after he or she jumps out of it. The 15-foot static line is a World War II-era design that has been successfully used on the Air Force C-130 and C-141. Troops line up and one by one exit the aircraft with a safety monitoring each person. The standard 15-foot length is too short to use with the new Air Force C-17, which led to the development of the Universal Static Line. The US Army's Universal Static Line (USL) is intended to be suitable for airborne operations from all current Army, Air Force, Navy and Marine aircraft. The USL program investigated several candidate items that could potentially meet the requirement. A single length 20' line was shown to be suitable on the C-17, however, it induced an increased safety risk on the C-130. The program strategy included static line options such as adjustable/convertible candidates that were produced for testing. The Universal Static Line is 15-feet long for use on the C-130, but a 5-foot extra piece of line can be attached in girth-like fashion to meet the needs of the C-17. Fielding of the Universal Static Line began in March 2001, with a total of 85,000 being supplied within a year to all Army airborne units.
Eight C-17 Globemaster IIIs lived up to their name 14 September 1997 they flew 7,780 miles non-stop to airdrop more than 500 members of the Army's 82nd Airborne Division at a drop zone in Central Asia. The C-17s took off from Pope Air Force Base, NC, to begin the nearly 20-hour non-stop flight to the drop zone at Kazakhstan. The airdrop, part of an exercise dubbed "CENTRAZBAT '97," was not only the longest-distance airborne operation in history, but also the first field training exercise to use the C-17 to airdrop U.S. troops over Central Asia. In 1998, before Air Mobility Command's airlift fleet acquired refueling capabilities, about 45 airplanes picked up the airborne troops at Fort Bragg, NC. They had to land in Milan, Italy, for refueling, any maintenance needed and to change aircrews. Then they flew into the drop zone in Turkey. Those C-141 missions were part of an annual exercise known as Deep Furrow.
With the help of aerial refueling, the C-17 is capable of direct delivery to drop zones or austere airfields. Another unique point to the CENTRAZBAT '97 mission was the triple aerial refueling. Originally, only two aerial refuelings were scheduled as weather forecasters predicted a tailwind for the C-17s as they crossed the Atlantic. Hurricane Erika's position off the East Coast took away the tailwind and added a head wind. To compensate for the change, a third refueling rendezvous was added during the pre-mission crew brief 09 September 1997. Tankers from McConnell AFB, Kan., McGuire AFB, N.J., MacDill AFB, Fla., and Travis AFB, Calif., supported the mission flown by aircrews from Charleston's 14th, 17th and 317th Airlift Squadrons, the 315th Operations Support Flight and the 97th Air Mobility Wing at Altus AFB, Okla.
The nature and magnitude of the realistic threat environment is highly dependent on the C-17's concept of operations. As a result, the primary threats to the C-17 are those that cannot be readily avoided without sacrificing C-17 mission effectiveness. Airlift aircraft are generally vulnerable to most antiaircraft weapons. The C-17 will reduce its susceptibility to these weapons through the use of current intelligence, mission planning, and avoidance tactics. Low-level terrain masking will be used to enhance survivability, gain the element of surprise, evade detection, and reduce exposure to hostile fire. The C-17 is not a covered system and was therefore not subject to Live Fire Test legislation. Instead, a C-17 vulnerability assessment was conducted and completed prior to Milestone IIIB. The assessment included engineering analysis, component and subsystem level tests, and testing of a full scale test section, using 12.7mm API, and 23mm HEI projectiles. The Infrared Flare for C-17 Aircraft Foreign Comparative Testing [FCT] evaluation of an Infrared Flare developed by Buck Industries of Germany is intended to extend combat mission profiles against current, highly capable surface-to-air missile threats. This FCT facilitates the concurrent comparative testing of the German flare and U.S.-produced infrared flares.
A vulnerability analysis of the C-17 to bird strikes, conducted by Air Force engineers, disclosed that the likelihood of losing a C-17 to a bird strike is remote. Analysis of historical data of large aircraft bird strikes revealed that of the 125 incidents of wing leading edge penetration, no fires resulted. Such a scenario (wing leading edge penetration causing a fire) is the primary vulnerability of the C-17, per analysis conducted under the C-17 survivability program. Additionally, the C-17's powerplant, the F-117 engine, is a derivative of the Pratt and Whitney PW2040 commercial powerplant. To be certified by the FAA, the PW2040 has successfully undergone qualification testing for bird strike tolerance.
Maximum use has been made of off-the-shelf and commercial equipment, including Air Force standardized avionics. The C-17 has a variety of mission configurations as well as flexibility in the choice of air delivery methods. Highly automated, the cockpit is designed for a two-pilot crew with physically and functionally integrated controls and displays. Many flight crew instruments are automated by computer. Redundant hardware configurations are provided throughout the computer subsystems to ensure survivability and successful mission completion. The interface network communicates all data to related elements and utilizes MIL-STD-1553B data buses. In the cockpit, nearly all devices are duplicated and located for left-right flight crew split. Although these identical units interface with the same subsystems, each pilot can operate control panels and configure electronic displays independently of the other pilot. Redundancy applied in the configuration provides multiple data sources, controls, and displays.
Maintenance data collected on the C-17 aircraft (to include engine health data, built-in-test (BIT) data, and structural integrity data) are loaded into a ground support system operated by AMC and AFMC. Aircraft data is downloaded to the base level computer equipment by either tape cassettes, portable computers, 3 1/2" diskettes, or by manual collection and data entry. The data are then transferred to the central database management systems (DBMS) for processing, analysis, and utilization by maintenance personnel.
Mission planning is accomplished by AMC pilots using the Advanced Computer Flight Plan (ACFP) program operating on AFGWC computer systems. After a flight plan is generated by the ACFP program, the digital flight plans is downloaded from AFGWC to the Base Flight Planning Computer or a portable laptop computer. Additional data, not available in the AFGWC system, is added to the flight plan on the Base Flight Planning Computer or the laptop computer; the flight plan is then uploaded to the C-17 Mission Computer for flight preparation.
The C-17 intermediate-level automatic test system (ATS) consists of the C-17A Digital Analog Video (DAV) test stations, interface test adapters (ITAs), test program (TPs), and a photometric test bench (PTB). The automatic test equipment (ATE) component of the ATS is a five-rack test station providing stimuli, measurement, power and switching. TPs provide a set of coded instructions that control testing of Unit Under Test (UUTs) and are implemented through the use of the ATLAS IEEE 716 test language. This test software, when used with the ATE, provides end-to-end and diagnostic execution of UUT tests. The ITAs, which interface the avionics UUT with the ATE, the TP software and the PTB are newly developed items that support UUT fault detection/fault isolation to the SRU level.
The mission-essential functions implemented in software include flight control through the flight control computers, bus control of the MIL-STD-1553B data buses by the mission computer, flight plan manipulation, and display control of computer operated flight crew instruments. Interoperability requirements that impact the C-17's software are divided into two classes, operations and maintenance. For operations, the Mission Computer software manages the navigation and communication databases, be capable of loading and manipulating the data from the mission planning system, and is fully compatible with the Base Flight Planning Computer. The Aircrew Laptop Computer (ALC) System software provides for Loadmaster Form F (weight & balance) calculations, uphold mission data and download avionics and some non-avionics fault data. For maintenance, the software which manages the data collection on the aircraft must interface with the systems on the ground.
The wings, flaps, and slats combine with high thrust engines and the electronic flight control system for short take-off and landing (STOL). Exhaust from the jet engines force air over wings and flaps, generating additional lift. Engines on the C-17 are mounted under the wings and large flaps protrude down into the exhaust stream. The engine exhaust is forced through the flap and down both sides of the flap, creating significant added lift. The externally blown flap system and the full-span leading edge slats enable the C-17 to operate at low approach speeds for short-field landings and for airdrops (Henderson, 1990). Powered lift enables the C-17 to land on shorter runways than current, large-capacity transports by allowing it to fly slow, steep approaches to highly accurate touchdown points.
The F117-PW-100, a 41,000 lb. thrust class engine, powers the C-17 aircraft. It is a derivative of the commercial PW2037/2040 engines used on the B757 aircraft. The F117 is designed and manufactured by United Technologies' Pratt & Whitney Division. Pratt & Whitney also produces spare engines and provides logistics support to the user, Air Mobility Command. In 1980, McDonnell Douglas Aircraft (MDA) selected the F117-PW-100 engine to power the C-17 aircraft. MDA purchased the engine as Contractor Furnished Equipment (CFE) for the first three aircraft production lots. MDA drove engine performance improvements in the form of engine control enhancements, lighter weight, and better fuel economy. Pratt & Whitney undertook all the design and development of the improvements at their expense. The Air Force took over engine procurement and made it Government Furnished Equipment (GFE) supplied to MDA beginning with the Lot IV buy in November 1992. The contract type is fixed price plus Economic Price Adjustment (EPA) in keeping with the commercial acquisition methodology.
In July 1993, the F117 engine was nominated as a pilot program by the Under Secretary of Defense (Acquisition and Technology) to demonstrate the advantages of using derivatives of commercial engines to satisfy military requirements. One of the primary advantages of procuring a commercial engine is that the Government does not directly pay for the development of the basic engine and product enhancements after the engine is fielded. The baseline is the development cost of the TF39 engine on the C-5. The TF39 was certified in 1969, and the F117 passed FAA testing in 1984. In FY84 dollars, the TF39 development cost is $775M whereas P&W invested $900M in certifying the PW2040/F117. However, since the Government does not directly pay for development, the direct cost of developing the F117 engine is zero.
The Air Force significantly reduced the cost of constructing the C-17 Globemaster aircraft by using a pollution prevention approach, which also eliminated a source of hazardous waste. Each C-17 uses more than 730,000 rivets and 590,000 titanium pins. In the past, these parts were coated with a sealant before being fitted. The Air Force disposed of the empty sealant tubes as hazardous waste at the cost of $10 each. By using a new sealant, the Air Force reduced labor hours by 2.3 million and decreased supply and disposal costs by $2.2 million.
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