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Originally Posted by ORAC
(Post 10493412)
The link below leads to a long list of articles posted yesterday explicating various issues. I’ve chosen just one to post separately to give an example...... http://www.defensenews.com/smr/hidden-troubles-f35/ The Hidden Troubles of the F-35 https://www.defensenews.com/air/2019...-environments/ The Marine Corps’ ‘No. 1 priority’ for the F-35 involves a rough landing in hot environments WASHINGTON — It was a hot day aboard the amphibious assault ship Essex when a pilot brought his F-35B in for what is known as a “mode four” flight operation, where the jet enters hover mode near a landing spot, slides over to the target area and then vertically lands onto the ship. It’s a key part of the F-35B’s short-takeoff-and-vertical-landing capability, known as STOVL. And normally, everything in a “mode four” landing goes smoothly. But on this day, when the pilot triggered the thrust to slow his descent, something went wrong. The engine, working hard on a day that temperatures cracked 90 degrees Fahrenheit while trying to lift a plane that was heavier than most returning to base, wouldn’t generate the needed thrust for a safe, ideal landing. The pilot got the plane down, but was shaken enough by the situation to write up an incident report that would eventually be marked as “high” concern by the F-35 program office. “May result in unanticipated and uncontrolled sink, leading to hard landing or potential ejection/loss of aircraft, particularly in the presence of HGI [hot gas ingestion],” reads a summary of the issue, which was obtained by Defense News as part of a cache of “for official use only” documents that detail major concerns with the F-35 Joint Strike Fighter..... The issue seems to stem from two factors: the heat, and the fact that much of the testing for the “mode four” maneuver was done with planes that were lighter, as they weren’t armed with heavy stores of weaponry. Feedback from the Marine Corps highlighted that while the average engine should not see this issue until around 750 flight hours, “several engines are at/near the point of concern,” and that number will continue to grow with the extended use of older planes......... Winter said engineers have identified an issue in the design of the control software that the pilot uses to generate demand for thrust from the propulsion system. “There’s no redesign of the engine [necessary]. The engine is doing what the engine is supposed to do,” Winter emphasized, before acknowledging that in addition to the software fix, the program office has worked with Honeywell to change how the company calibrates the throttle valve on the engine. “We’ve identified the software fix for the control system, the calibration fix to the throttle valve and some near-term fleet actions that could be taken for very hot days to ensure that the pilot gets the performance he or she needs on those hot days,” he said. That software fix will be a rolling target, as the first increment of the software release is due in June, followed by another at the end of this year or early next year. “We’ve given them tighter tolerances to tune them more precisely, so that when it goes on the engine it’s no longer not giving the command the way it’s supposed to be,” Winter explained. “It wasn’t tuned correctly for this high-demand phase of flight. Now, we fixed that. That’s fixed. The software is going in to make sure that the pilot can command that thrust and understand the heat and the loading.” Those fixes won’t be cheap, and when asked who would pay for them, Winter was blunt, saying it is his office’s belief the thrust issue is a “design deficiency” that merits “consideration” from industry. “In this case it doesn’t matter that the design was done back in 2002, it’s still pragmatistic, so you owe consideration because we’re fixing it right now,” Winter said of industry.......... |
Originally Posted by GeeRam
(Post 10493462)
Err.........I maybe being a bit thick here, but isn't this 'problem' why UK is going down the SRVL route for B ops.....??
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and the fact that much of the testing for the “mode four” maneuver was done with planes that were lighter, as they weren’t armed with heavy stores of weaponry. |
A quick shufti at the JPT gauge should sort that problem; JPT too high - burn some gas off. In the old days the duty pilot would calculate the max VL fuel weight for the worst engine and post it on the board. Individual pilots would then confirm their own limits on the VSTOL computer (wizz-wheel). A free-air hover can be attained at a greater gross weight than a VL. SRVL increases the bring-back weight by allowing the wing to develop some lift (a bit) and reducing hot gas recirculation into the intake close to the deck. Can't be that difficult. mog BTW, 37 years ago today the Falkland Islands were liberated, thanks in no small measure to the Sea Harrier. BZ guys. |
Educated guess here, but it sounds to me like it the engine became EGT limited and cut back thrust unexpectedly.
Assuming that's correct (or at least close), the 'fix' would be easy - get rid of EGT limiting except during starting. We did that in the commercial world 35 years ago, assuming that the pilot is in a better position to judge if they need to exceed the EGT limit for safety reasons than the FADEC was. |
Originally Posted by Two's in
(Post 10493747)
I had no idea you could perform trials and Release to Service testing in a more benign environment than is likely to be encountered by operational users. Must be a new thing...
I believe there was a large amount of crowing about the skips ability to return to deck with unexpended ordinance.. |
Originally Posted by weemonkey
(Post 10494385)
"the fact that much of the testing for the “mode four” maneuver was done with planes that were lighter, as they weren’t armed with heavy stores of weaponry. "
I believe there was a large amount of crowing about the skips ability to return to deck with unexpended ordinance.. |
Originally posted by tdracer Educated guess here, but it sounds to me like it the engine became EGT limited and cut back thrust unexpectedly. |
Originally Posted by Turbine D
(Post 10494450)
I'm not sure about the turbine temperature control architecture used on F135 engines, but in some other military engines like the F101 or F110, EGT isn't used to control turbine temperature upper limits. In military engines, there is less turbine temperature margins when operating on a normal fan speed schedule. To protect the high pressure turbine from excessive over temperature the control system incorporates a turbine blade temperature limiting function known as T4B. A dedicated optical infrared pyrometer is used to measure the temperature of the HPT turbine blade. This signal is fed to the electronic control which reduces core fuel flow to limit the turbine temperature. T4B anticipation logic is built in to prevent excessive overshoots during power bursts.
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The RB199 in the Tornado was one of the first to use optical pyrometers to record and control EGT. They were more accurate than conventional downstream thermocouples but they were much higher maintenance because of the tendency to soot up. They were supposed to be cleaned every 25 hrs, calibrated every 50 hours and performance tested every 100 hrs. The 25 hr cleans were frequently "cuffed off" but you can see why such a regime would be prohibitive for civilian applications. I've not really kept up with the civilian engine sector over the past 15 years and I'd be interested to know if any modern civvy turbofan uses pyrometers.
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I've not really kept up with the civilian engine sector over the past 15 years and I'd be interested to know if any modern civvy turbofan uses pyrometers. The GE90-94B was a pretty lousy engine out of the box (unreliable and high maintenance), but matured very nicely providing the basis for the -115B. |
F-35 display, from the cockpit...
Some nice footage from the cockpit of an F-35A during a display over Miami Beach during the Hyundai Air & Sea Show May 26, 2019.
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Just an uninformed comment but I would assume from looking at the video that an override to the control software permits a robust pull to the wrong edge of the buffet, not to mention the pedal turn. Perhaps it's just a result of the camera being set on a flexible mounting.
IG |
If it was a solid mount, you wouldn't see any movement, other than the pilot. So there is a bit of both. There is some buffet apparent, airflow boundary layer, laminar flow and all that stuff. The video seems to make it out to be a lot more than it actually is.
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https://www.defensenews.com/smr/hidden-troubles-f35/2019/06/12/when-us-navy-and-marine-f-35-pilots-most-need-performance-the-aircraft-becomes-erratic/
See the info on the link above, not very reassuring regarding Bs and Cs. Best regards, FB |
In that video - thanks Rhino power, btw, I enjoyed it - but why is the pilot using both hands on the stick at one stage? Anyone know?
airsound |
Presumably to push the aircraft outside the normal control law limits and hold the pitch and roll at that level for the pedal turn.
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Just a shame if you operate the F35B........ http://aviationweek.com/defense/lock...-upgrade-f-35a Lockheed Martin Proposes 40% Fuel Capacity Upgrade for F-35A Lockheed Martin has started engineering studies focused on substantially extending the range of the F-35A by increasing the total onboard fuel capacity by 40% and improving the aircraft’s fuel efficiency, Aviation Week has learned. The studies would resurrect a long-abandoned plan to install external fuel tanks under the wings of the conventional takeoff-and-landing variant. The range-extension study also could benefit from proposed propulsion improvements, such as Pratt & Whitney’s Growth Option upgrade offer for the F135 engine........ Not all customers wanted to rely on the range provided by internal fuel capacity alone, though. When the U.S. State Department approved the Israeli export configuration in 2011, the F-35I included external fuel tanks. But the impact on the cost and schedule for the aircraft forced Israeli officials to defer the requirement. Nonetheless, work continued on the project within Israel’s aircraft industry. In April, Israel Aerospace Industries (IAI) and Elbit Systems’ Cyclone subsidiary confirmed that they had completed initial design studies on different fuel tank designs. IAI studied a conformal fuel tank design, while Cyclone examined a design for a 600-gal. external fuel tank. The latter would likely help preserve the F-35I’s stealthy profile on radar. Lockheed confirms that it is now engaged in a study about the option for a 600-gal. fuel tank and a wing pylon that can be jettisoned. The tank is designed to be integrated on the inboard stations—3 and 9—on each wing, the company says. Although the pilot can restore the F-35A’s stealth signature to radar by jettisoning the tank and pylon, it is not clear how the radar cross-section is affected with the equipment attached to the wing. Given that the 18,500-lb. internal fuel capacity of the F-35A is equivalent to 3,000 gal., adding two 600-gal. external tanks on an F-35A would raise overall fuel volume onboard to 4,200 gal., or 25,700 lb. That still falls short of the 35,500-lb. capacity for an F-15E configured for a ferry flight but should dramatically increase the single-engine fighter’s endurance. “While exact ranges depend on mission profiles, our studies show a significant increase in both range and loiter time—or mission persistence,” a Lockheed spokesman says. So far, the company has completed feasibility studies and conducted initial analysis, as well as early design of the range-extension upgrades. The industry-funded work was done in advance of an approved customer requirement, but Lockheed plans to present the range extension as a candidate upgrade through the Continuous Capability, Development and Delivery framework for the F-35’s follow-on modernization program, also known as Block 4. The remaining work required includes detailed design and qualification of the fuel tank and pylon, as well as software integration, flight testing and airworthiness certification, Lockheed says. |
Wow, 600 gallon tank on each side, that's the same size as the big F-4 Phantom centerline tank.
I can think of a few scenarios where Israel and other users might find these handy. As for the "it is not clear how the radar cross-section is affected with the equipment attached to the wing..." I have an idea. |
About the same size as the Tornado 2250L underwing tanks. https://cimg2.ibsrv.net/gimg/pprune....b2438bf39.jpeg |
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