Military

JTF10 / TF30

The first afterburning turbofan, Pratt and Whitney's TF30, powered the F-111 multirole fighter. Inlet air is supplied to two bypass ratio 1.1 Pratt & Whitney TF30-P-9 afterburning turbofan engines of 20,840 pounds thrust each. Afterburning turbofans, with bypass ratios of one or less, provide both good subsonic cruise fuel efficiency and high augmented thrust for supersonic flight. Even today, the afterburning turbofan remains the dominant cycle for all fighters.

The development of the F-111 began more than 30 years ago. In 1962, General Dynamics (now Lockheed Martin) won a Department of Defense contract to develop a supersonic aircraft called the TFX. This aircraft originally was expected to be a joint services fighter, also operating as an aircraft carrier based Navy fighter. Production of the F-111 prototype began in the fall of 1963, and the first F-111 rolled out on Oct. 15, 1964, 16 days ahead of schedule. After the Pratt & Whitney TF30-P103 turbofan engines were tested in AEDS's Engine Test Facility [ETF], the propulsion system was integrated into the airframe. Propulsion Wind Tunnel [PWT] again was used for engine inlet compatibility tests in 1964. The F-111 first flew in December 1964. The first operational F-111 was delivered to the Air Force in October 1967.

The F-14 Tomcat is a supersonic, twin-engine, variable sweep wing, two-place strike fighter manufactured by Grumman Aircraft Corporation. The F-14A is powered by a pair of TF30-414A Afterburning Turbofans with over 40,000 lb Total Thrust, while the F-14B/D is powered by a a pair of F110-GE400 Afterburning Turbofans with over 54,000 lb Total Thrust.

Because of NASA Dryden's previous F-111A propulsion experience, the United States Air Force (USAF) asked NASA in 1973 to assist in developing and flight-test ing a digital IPCS. The IPCS, installed on an F-111E airplane, was the first integrated digital propulsion control system flown. The Boeing Company (Seattle, Washington), Pratt & Whitney (East Hartford, Connecticut), and Honeywell (Minneapolis, Minnesota), were the major contractors.

In 1978 an F-111E Aardvark (#67-0115) was flown at the NASA Flight Research Center to investigate an electronic versus a conventional hydro-mechanical controlled engine. The program called integrated propulsion control system (IPCS) was a joint effort by NASA's Lewis Research Center and Flight Research Center, the Air Force's Flight Propulsion Laboratory and the Boeing, Honeywell and Pratt & Whitney companies. The left engine of the F-111E was selected for modification to an all electronic system. A Pratt & Whitney TF30-P-9 engine was modified and extensively laboratory, and ground-tested before installation into the F-111E. There were 14 IPCS flights made from 1975 through 1976. The flight demonstration program proved an engine could be controlled electronically, leading to a more efficient Digital Electronic Engine Control System flown in the F-15.

The TF30 (Pratt & Whitney) afterburning turbofan engine had a full-authority digital control and was integrated with the control of the variable-geometry external compression inlet. Controlled variables in the inlet were the translating spike and expanding cone. Controlled variables in the engine were the main and five zones of augmentor fuel, the compressor bleeds, and the nozzle area. The engine control featured two modes: one a digital implementation of the hydromechanical controller; the other a new research digital engine control mode. The controller was remotely mounted in a cooled weapons bay. Significant performance benefits included stall-free operation, faster throttle response, increased thrust, and increased range at a Mach number of 1.8.

The IPCS program achieved its planned objectives on schedule and within budget. The flexibility of the software was used to develop additional capabilities, such as an on-line thrust calculation that had not been planned; and overall, the IPCS program was viewed as more successful than planned. This rather humble beginning led to widely used military and commercial digital engine control technology that has made a major improvement in reliability, maintainability, and engine operability and efficiency. The IPCS program also demonstrated the capability and flexibility of digital engine control technology.

The successful application of advanced composites as the structural material for aircraft jet engine rotating parts will significantly reduce engine weight and improve engine performance characteristics. To solve the component design, manufacturing, and quality assurance problems associated with such an application, in 1978 a program was conducted to design and develop BORSIC/Aluminum third-stage fan blades, which would operate satisfactorily in the TF30-P-7 or P-9 engine models. Program objectives successfully were to improve the existing design of a composite material fan blade, manufacture the blade, and demonstrate its quality by bench and engine environment testing. The scope of the program required to meet these objectives included establishing design and fabrication procedures, developing special tooling, evaluating current nondestructive inspection techniques and adapting these techniques to composite materials, establishing quality assurance criteria, and developing comprehensive bench and engine environment test programs to adequately demonstrate fan-blade quality. During the program, several sets of BORSIC/Aluminum blades weighing 40 percent less than comparable TF30 bill of material titanium blades were successfully produced and tested. On the basis of extensive test program, and with the establishment of quality control criteria and repair procedures, the blades were deemed acceptable for evaluation in a flight program.^During the total program, 246 engine-configuration blades were manufactured and non-destructively inspected; with an overall acceptance rate of 92.3%.

In 1978 the noise of the TF30 afterburning turbofan engine in an F-111 airplane was determined from static (ground) and flyover tests. A survey was made to measure the exhaust temperature and velocity profiles for a range of power settings. Comparisons were made between predicted and measured jet mixing, internal, and shock noise. It was found that the noise produced at static conditions was dominated by jet mixing noise, and was adequately predicted by existing methods. The noise produced during flyovers exhibited large contributions from internally generated noise in the forward arc. For flyovers with the engine at nonafterburning power, the internal noise, shock noise, and jet mixing noise were accurately predicted. During flyovers with afterburning power settings, however, additional internal noise believed to be due to the afterburning process was evident; its level was as much as 8 decibels above the nonafterburning internal noise. Power settings that produced exhausts with inverted velocity profiles appeared to be slightly less noisy than power settings of equal thrust that produced uniform exhaust velocity profiles both in flight and in static testing.

The Chrome Product Substitution initiative replaced chrome with a less hazardous or non-hazardous solution for plating processes, to reduce the amount of the wastestream generated. In September 1989 tests were condcucted to to substitute electroless nickel plating for chrome plating on several parts have begun. Initial emphasis was on turbine shafts and gear shafts for the TF30 engine. Pratt & Whitney was given limited approval to use a high efficiency chrome plating solution, HEEF 25. This solution was reported to be twice as efficient, thus requiring up to 50 percent less tank capacity. Tests were initially limited to bearing journals. This process was closely monitored for 4-6 months before changing additional tanks to this solution. In October 1989 project information from OC-ALC to JDMAG was distributed to all depots.

By January 1990 the testing on the TF30 gear shafts was completed. A funding request was forwarded so OC-ALC can proceed with the process on production parts. The high efficiency chrome coating proved to be too brittle, and that particular application was abandoned. Testing continued on other forms of chrome application. By July 1990 testing of TF30 gear shafts and low speed shafts had been completed. OC-ALC qualified the TF30 parts with a standard electroless nickel process which had been in use for approximately ten years. Air Force Technical Order (TO) changes were prepared to allow the use of this process on TF30 parts in production.

By October 1990 four TF30 parts had electroless nickel authorized as a substitute for chrome plating. Approximately 30 more parts required TO changes to be submitted. All of the parts had been approved for the electroless nickel plating process. TO changes were in process for TF33, J57, TF41, and J79 engine components. By January 1991 technical order approval had been obtained for substitution of chrome plating with electroless nickel for 50 TF30 parts. The main delay in obtaining more approvals was the time required to prepare Air Force TO Form (AFTO) 22s for each part and have them added to the TO repair manual.

Disk burst is described as a rotor failure that results in engine rotor fragments and blade fragments exiting the engine case during engine operating conditions. This phenomenon is a threat to commercial and military aircraft. Uncontained disk failures in military or commercial aircraft are frequently the result of corrosion, material flaws, or maintenance error. In a hostile threat environment, disk burst can be the result of a penetrating ballistic projectile. To address this issue, China Lake has leveraged funding with the DoD and the FAA.

Under DoD funding, China Lake initiated disk burst testing in 1997 to identify the first order effects of ballistic penetration of turbine engine disks. Testing conducted on an F404 engine resulted in a spectacular event, which has had a significant effect on understanding the importance of engine vulnerability. Additional testing conducted on the T56, T406, and TF30 engines has yielded somewhat different results. These tests indicated that engines are much less susceptible to disk burst than previously thought.

The TF-30-P414A engines had a habit of experiencing a compressor stall at high angles of attack if the throttles were moved, especially in afterburner, causing a flame out. In 1992 and again in 1993, the Congress provided funds to the Navy to install F-110 engines on early model F-14A aircraft to replace the original TF-30 engines introduced to the fleet with F-14A deliveries in the mid-1970s. This was done to improve the F-14A fleet's safety and reliability, and to afford full use of the F-14 envelope in air-to-air engagements. At the time TF-30 engine compressor stall susceptibility was the number one operational and safety concern within the F-14 community. This initiative was very successful, resulting in 47 reengined F-14B aircraft for the fleet that would have not been fielded had Congress not acted.

Lt. Kara Hultgreen was the first woman to qualify in a combat-ready F-14 Tomcat, graduating third in her pilot training class. She was a member of the Black Lions of VF-213 readying to deploy to the Persian Gulf. As she was approaching the flight deck of the USS Abraham Lincoln on 25 Oct 1994, her aircraft began losing altitude. Her radar intercept officer ejected successfully. Hultgreen ejected immediately after, but the jet had already rolled. After an exhaustive search, her body and the plane were not recovered. She received full military honors upon her death. The Navy salvaged the plane and recovered her body, still strapped inside the ejector seat. A four-month investigation found that engine malfunction caused the crash and that almost no pilot could have saved the plane after the left engine stalled. The Navy indicated the crash resulted from a number of factors but principally left-engine failure due to engine stall.

In 1995 the Navy testified that over the past ten years, there had been a total of 52 F-14A Class A mishaps, of which 12 (23 percent) were related to TF-30 malfunction. Over the past 21 years, there had been 34 Class A TF-30 engine-related F-14A mishaps which have claimed the lives of five Naval aviators. Mishap causes were undetermined in other F-14A mishaps which resulted in ten fatalities. The Navy further testified in 1995 that it will keep F-14A aircraft in the active inventory for nine more years and for an additional six years in the reserves. In the year 2004, the Navy will, under 1995 plans, still have 24 TF-30 equipped F-14A aircraft to support one 14-aircraft squadron, which would be retained until at least the year 2010.

The TF30 engine breather-pressure modification consists of an engine sensor that detects an abnormal condition to allow the pilot time to take action to prevent engine failure. The TF30 Engine Breather Pressure Modification incorporates a new sensor in the engine that detects an abnormal increase in breather pressure and allows the pilot time to take appropriate action to prevent catastrophic engine failure. Installation began in November 1996 and will complete in 1997. The F-14s digital flight control system (DFCS) has demonstrated significant improvements in departure resistance/spin recovery and improved flying qualities during shipboard recovery. Installation of the DFCS began in June 1998.




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