Sigh~
However, problems have surfaced related to some overheating concerns during high-speed flight-testing, reliability, avionics that perform radar, communication, navigation, identification and electronic warfare functions as well as excess movement of the vertical tails. Modifications are being made to some test aircraft to address some of these problems. For now, however, testing in some areas is restricted. In 2001, we reported on continuing increases in aircraft weight and that more frequent maintenance than planned on the aircraft was being required. We also reported on structural inadequacies in the aft (rear) fuselage and on problems with the separation of some materials within the horizontal tail section and cracking of the clear section of the canopy. In 2002, we again reported that the F/A-22’s performance could be affected by increased aircraft weight and maintenance needs as well as a potential problem with “buffeting”, or excessive movement, of the aircraft’s vertical tails. We also continued to report on problems with the separation of materials within the horizontal tail section and cracking of the clear section of the canopy. We reported last month that the F/A-22 developmental program did not meet key performance goals established for fiscal year 2002 and continues to confront numerous technical challenges, specifically:
• Avionics instability: Software instability has hampered efforts to integrate advanced avionics capabilities into the F/A-22 system. Avionics control and integrated airborne electronics and sensors are designed to provide an increased awareness of the situation around the pilot. The Air Force told us avionics have failed or shut down during numerous tests of F/A-22 aircraft due to software problems. The shutdowns have occurred when the pilot attempts to use the radar, communication, navigation, identification, The cost limitation, before adjustment under the act’s provisions, was $43.4 billon. Performance Issues and electronic warfare systems concurrently. Although the plane can still be flown after the avionics have failed, the pilot is unable to successfully demonstrate the performance of the avionics. Therefore, the Air Force has had to extend the test program schedule. The Air Force has recognized that the avionics problems pose a high technical risk to the F/A-22 program, and in June 2002 the Air Force convened a special team to address the problem. According to the team, the unpredictable nature of the shutdowns was not surprising considering the complexity of the avionics system. The team recommended that the software be stabilized in the laboratory before releasing it to flight-testing. The team further recommended conducting a stress test on the software system architecture to reduce problems and ensure it is operating properly. The Air Force implemented these recommendations. Further, the Air Force extended the avionics schedule to accommodate avionics stability testing and it now plans to complete avionics testing in the first quarter of 2005. However, Air Force officials stated they do not yet understand the problems associated with the instability of the avionics software well enough to predict when they will be able to resolve this problem.
• Vertical fin buffeting: Under some circumstances, the F/A-22 experiences violent movement, or buffeting, of the vertical fins in the tail section of the
aircraft. Buffeting occurs as air, moving first over the body and the wings of the aircraft, places unequal pressures on the vertical fins and rudders.
The buffeting problem has restricted the testing of aerial maneuvers of the aircraft. In addition, unless the violent movement is resolved or the fins strengthened, the fins will break over time because the pressures experienced exceed the strength limits of the fins. This could have an impact on the expected structural life of the aircraft. Lockheed Martin has developed several modifications to strengthen the vertical fins.
• Overheating concerns: Overheating in the rear portions of the aircraft has significantly restricted the duration of high-speed flight-testing. As the F/A-22 flies, heat builds up inside several areas in the rear of the aircraft. Continued exposure to high temperatures would weaken these areas. For example, a portion of the airframe that sits between the engines’ exhausts experiences the highest temperatures. This intense heat could weaken or damage the airframe. To prevent this heat buildup during flight-testing, the aircraft is restricted to flying just over 500 miles per hour, about the same of the speed as a modern jet liner, and significantly below the supercruise requirement. Currently, the F/A-22 flies with temperature sensors in those areas of the aircraft and slows down whenever the temperature approaches a certain level. The Air Force may incorporate a modification that adds copper sheets to the rear of the aircraft to alleviate the problem. The Air Force began these modifications in January 2003 and plans to complete them by July 2003.
• Horizontal tail material separations: F/A-22 aircraft have experienced separations of materials in the horizontal tail and the shaft, which allow the tail to pivot. Because the separations reduce tail strength, the Air Force restricted flight-testing of some aircraft until it had determined that this problem would not affect flight safety during testing. The Air Force and the contractor initially believed that improvements to the aircraft’s manufacturing process would solve this problem. However, the Air Force has determined that it could only solve this problem by redesigning the aircraft’s tail. The Air Force plans to conduct flight-testing of the redesigned tail between February 2004 and April 2004.
• Airlift support requirements: The Air Force estimates it will not meet the F/A-22 airlift support requirement—a key performance parameter.8 The
airlift support requirement is that 8 C-141 aircraft or their equivalents would be sufficient to deploy a squadron of 24 F/A-22s for 30 days without resupply. Today, the Air Force estimates that 8.8 C-141 equivalents will be necessary.
• Impact of maintenance needs on performance: The F/A-22’s performance may also be affected by maintenance needs that exceed established
objectives. The Air Force estimates that the F/A-22 should, at this point in its development, be able to complete 1.67 flying hours between maintenance actions and 1.95 flying hours by the end of development. However, aircraft are requiring five times the maintenance actions expected at this point in development. As of November 2002, the development test aircraft have been completing only .29 flying hours between maintenance actions. Therefore, the development test aircraft are spending more time than planned on the ground undergoing maintenance.
GAO 2003 - http://www.gao.gov/new.items/d03603t.pdf
If you read the underscore part of the text, can you accept that F-22 had some problem with the tail section ? and by reading previous post, they still have.
This was back in 2003, by that time, the restriction was 500 mph, or cessna speed if you will.
I have read a report from 2007/2008, and i guess Scorpion82 has as well, that nowadays the speed limit is M1.7, i just can't find it now
I'm aware this is not a proof it has a speed limitation, but it is proof they have problem with the tail, and at least last time, they solved it by imposing speed limit.
However, problems have surfaced related to some overheating concerns during high-speed flight-testing, reliability, avionics that perform radar, communication, navigation, identification and electronic warfare functions as well as excess movement of the vertical tails. Modifications are being made to some test aircraft to address some of these problems. For now, however, testing in some areas is restricted. In 2001, we reported on continuing increases in aircraft weight and that more frequent maintenance than planned on the aircraft was being required. We also reported on structural inadequacies in the aft (rear) fuselage and on problems with the separation of some materials within the horizontal tail section and cracking of the clear section of the canopy. In 2002, we again reported that the F/A-22’s performance could be affected by increased aircraft weight and maintenance needs as well as a potential problem with “buffeting”, or excessive movement, of the aircraft’s vertical tails. We also continued to report on problems with the separation of materials within the horizontal tail section and cracking of the clear section of the canopy. We reported last month that the F/A-22 developmental program did not meet key performance goals established for fiscal year 2002 and continues to confront numerous technical challenges, specifically:
• Avionics instability: Software instability has hampered efforts to integrate advanced avionics capabilities into the F/A-22 system. Avionics control and integrated airborne electronics and sensors are designed to provide an increased awareness of the situation around the pilot. The Air Force told us avionics have failed or shut down during numerous tests of F/A-22 aircraft due to software problems. The shutdowns have occurred when the pilot attempts to use the radar, communication, navigation, identification, The cost limitation, before adjustment under the act’s provisions, was $43.4 billon. Performance Issues and electronic warfare systems concurrently. Although the plane can still be flown after the avionics have failed, the pilot is unable to successfully demonstrate the performance of the avionics. Therefore, the Air Force has had to extend the test program schedule. The Air Force has recognized that the avionics problems pose a high technical risk to the F/A-22 program, and in June 2002 the Air Force convened a special team to address the problem. According to the team, the unpredictable nature of the shutdowns was not surprising considering the complexity of the avionics system. The team recommended that the software be stabilized in the laboratory before releasing it to flight-testing. The team further recommended conducting a stress test on the software system architecture to reduce problems and ensure it is operating properly. The Air Force implemented these recommendations. Further, the Air Force extended the avionics schedule to accommodate avionics stability testing and it now plans to complete avionics testing in the first quarter of 2005. However, Air Force officials stated they do not yet understand the problems associated with the instability of the avionics software well enough to predict when they will be able to resolve this problem.
• Vertical fin buffeting: Under some circumstances, the F/A-22 experiences violent movement, or buffeting, of the vertical fins in the tail section of the
aircraft. Buffeting occurs as air, moving first over the body and the wings of the aircraft, places unequal pressures on the vertical fins and rudders.
The buffeting problem has restricted the testing of aerial maneuvers of the aircraft. In addition, unless the violent movement is resolved or the fins strengthened, the fins will break over time because the pressures experienced exceed the strength limits of the fins. This could have an impact on the expected structural life of the aircraft. Lockheed Martin has developed several modifications to strengthen the vertical fins.
• Overheating concerns: Overheating in the rear portions of the aircraft has significantly restricted the duration of high-speed flight-testing. As the F/A-22 flies, heat builds up inside several areas in the rear of the aircraft. Continued exposure to high temperatures would weaken these areas. For example, a portion of the airframe that sits between the engines’ exhausts experiences the highest temperatures. This intense heat could weaken or damage the airframe. To prevent this heat buildup during flight-testing, the aircraft is restricted to flying just over 500 miles per hour, about the same of the speed as a modern jet liner, and significantly below the supercruise requirement. Currently, the F/A-22 flies with temperature sensors in those areas of the aircraft and slows down whenever the temperature approaches a certain level. The Air Force may incorporate a modification that adds copper sheets to the rear of the aircraft to alleviate the problem. The Air Force began these modifications in January 2003 and plans to complete them by July 2003.
• Horizontal tail material separations: F/A-22 aircraft have experienced separations of materials in the horizontal tail and the shaft, which allow the tail to pivot. Because the separations reduce tail strength, the Air Force restricted flight-testing of some aircraft until it had determined that this problem would not affect flight safety during testing. The Air Force and the contractor initially believed that improvements to the aircraft’s manufacturing process would solve this problem. However, the Air Force has determined that it could only solve this problem by redesigning the aircraft’s tail. The Air Force plans to conduct flight-testing of the redesigned tail between February 2004 and April 2004.
• Airlift support requirements: The Air Force estimates it will not meet the F/A-22 airlift support requirement—a key performance parameter.8 The
airlift support requirement is that 8 C-141 aircraft or their equivalents would be sufficient to deploy a squadron of 24 F/A-22s for 30 days without resupply. Today, the Air Force estimates that 8.8 C-141 equivalents will be necessary.
• Impact of maintenance needs on performance: The F/A-22’s performance may also be affected by maintenance needs that exceed established
objectives. The Air Force estimates that the F/A-22 should, at this point in its development, be able to complete 1.67 flying hours between maintenance actions and 1.95 flying hours by the end of development. However, aircraft are requiring five times the maintenance actions expected at this point in development. As of November 2002, the development test aircraft have been completing only .29 flying hours between maintenance actions. Therefore, the development test aircraft are spending more time than planned on the ground undergoing maintenance.
GAO 2003 - http://www.gao.gov/new.items/d03603t.pdf
If you read the underscore part of the text, can you accept that F-22 had some problem with the tail section ? and by reading previous post, they still have.
This was back in 2003, by that time, the restriction was 500 mph, or cessna speed if you will.
I have read a report from 2007/2008, and i guess Scorpion82 has as well, that nowadays the speed limit is M1.7, i just can't find it now
I'm aware this is not a proof it has a speed limitation, but it is proof they have problem with the tail, and at least last time, they solved it by imposing speed limit.
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