F-35 Replan Adds Time, Resources For Testing

Discuss the F-35 Lightning II
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alloycowboy

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Unread post09 Feb 2011, 05:10

Gee, I wonder if it would be possible to create a generic plug and play computer operating system for use on multiple aircraft. It should would reduce the future cost and time of develope on future aircraft if you could.
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Unread post09 Feb 2011, 05:20

spazsinbad wrote:bsac: Why is there a significant difference in the avionics for the Navy variant? Yes the airframe is different (as are the three different in many major/minor ways) but AFAIK the avionics & flight control laws are the same (with addition of perhaps 'minor' features such as STOVL). The only major difference in the 3 cockpits is the 'RED BUTTON' in the F-35B to go into STOVL mode. Whereas a similar button will lower the hook in the F-35C and lower the emergency hook in the F-35A.


My terminology sucks. By 'avionics' I mean the fly-by-wire systems. Or the computer coding that operates the fighter's flight controls. I mistakenly referred to all electronics, but I meant the computers and programing which actually fly the aircraft.

They should be able to use the same coding for both the air force and marine variants, but the larger wings of the navy variant are what would be a major difference. That would essentially make the navy variant a completely different fighter, needing its own coding that can't be used by the other two. The A variant should share the B variant's flight coding, save the VSTOL systems.
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Unread post09 Feb 2011, 05:51

bsac, I don't believe what you have stated about flight control laws/coding is correct. Why do the larger wings make a difference when there are other differences in airframe between A & B models for example. Whatever differences are essentially accounted for in the same flight control model for all variants as I understand. You have made an erroneous assumption based on what for the F-35C - that the wings are larger therefore...? I'll look for the usual suspect references.... :D

Here is onesuch: http://www.nt.ntnu.no/users/skoge/prost ... _ECC03.ppt (5.6Mb)
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Unread post09 Feb 2011, 06:15

Two versions of F-35 undergo test flights over 2 days by Bob Cox, Monday, Jun. 07, 2010

http://www.star-telegram.com/2010/06/07 ... -test.html

"...Compared with the other F-35 models, the F-35C model that flew Sunday has larger wings to allow for slower flight speeds and a heavier structure to absorb the rigors of carrier landings.

"The flight went exactly as planned, more so than any test flight I've been on," test pilot Jeff Knowles said in a conference call. "There were no anomalies."

He said the plane [F-35C] flew largely the same as the other two versions, a result of Lockheed's extensive use of simulation in writing the flight control software and incorporating results of tests on earlier versions."
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Some F-35 Flight Control Gibberish here: (0.5Mb)

Flight Control Law Development for the F-35 Joint Strike Fighter by David W. Nixon - Lockheed-Martin Aeronautics - 5 October 2004

http://www.mathworks.com/aerospace-defe ... eNixon.pdf
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Tons of words about stuff:
Ride the Lightning: Testing the Marine Corps' latest fighter
http://www.leatherneck.com/forums/archi ... 81456.html

"...Other than the reduced G-limit, in conventional flight the F-35B handles almost exactly like the F-35A, Tomlinson explained. The F-35B retains the same outstanding low-speed, high angle of attack handling qualities as well as the same incredible acceleration as the F-35A. “You struggle to tell the difference between the CTOL and the STOVL in the cockpit,” Tomlinson said, adding that test pilots are trained to notice even minute differences in aircraft handling qualities. Tomlinson noted that while the F-35B’s lift-fan causes a visible bump in the aircraft’s outer mold line, the only cue in the cockpit is a slightly different wind noise. “STOVL only applies below 10 thousand feet and below 250 knots,” Tomlinson notes...."
Last edited by spazsinbad on 09 Feb 2011, 08:17, edited 3 times in total.
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Unread post09 Feb 2011, 06:21

battleshipagincourt wrote:Why not develop software that works for all three?
The same software does work in all three.

Where are you getting your bad information?
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spazsinbad

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Unread post09 Feb 2011, 06:36

Always a classic:
New Fighter Jet: Controversial Future of the U.S. Fleet By Dave Majumdar, Special to LiveScience.com posted: 07 November 2008

http://www.livescience.com/technology/0 ... -jets.html

"...In terms of aerodynamic performance, the F-35 is an excellent machine, Beesley said. Having previously been only the second man ever to have flown the F-22 Raptor, Beesley became the first pilot ever to fly the F-35 in late 2006. As such, Beesley is intimately familiar with both programs. According to Beesley, the four current test pilots for F-35 have been most impressed by the aircraft's thrust and acceleration. In the subsonic flight regime, the F-35 very nearly matches the performance of its' larger, more powerful cousin, the F-22 Raptor, Beesley explained. The "subsonic acceleration is about as good as a clean Block 50 F-16 or a Raptor- which is about as good as you can get." Beesley said.

The aircraft flies in "large measure like the F-22, but it's smaller, and stiffer" than the Raptor however, Beesley explained, adding that the aircraft handles superbly. The reason for the similar flight characteristics, explained the test pilot, is because the man who designed the flight control laws for the Raptor, is also the same man who is responsible for the flight control software for the F-35. As Beesley explains, the flight control laws of modern fighters determine to large extent the flight characteristics of a given aircraft. Beesley said that the aircraft is so stable and so comfortable that the test pilots find themselves inadvertently drifting too close to their wingmen in formation.

What Beesley expects will surprise future F-35 pilots is the jets' superb low speed handling characteristics and post-stall manoeuvrability. While the F-22 with its thrust vectored controls performs better at the slow speeds and high angle of attack (AOA) flight regime, the F-35 will be able match most of the same high AOA manoeuvres as the Raptor, although it will not be able to do so as quickly as the more powerful jet in some cases. Turning at the higher Gs and higher speed portions of the flight envelope, the F-35 will "almost exactly match a clean Block 50 F-16 and comes very close to the Raptor", Beesley said.

Ironically, the Navy version, which has larger wings but a lower G limit of 7.5G, has the best turning capability of the three F-35 versions Beesley explained. The Air Force version, meanwhile, has the best acceleration and is rated for 9Gs, Beesley said. Davis, explaining that the Marine Corps deemphasizes manoeuvrability in its air combat doctrine, said that the short take off, vertical landing (STOVL) USMC plane has a 7G limit. Beesley said that the aircraft makes up for the lower G limit by offering the flexibility in basing required by the Marines. Nor does the STOVL give up too much in range because of the engine driven lift fan installed behind the cockpit, Beesley said. The jet has "a range of more than 500 miles", while the Air Force and Navy planes both have ranges greater than 600 miles, Beesley explained, adding that the USAF version has as much internal fuel capacity as the larger twin engined F-22 Raptor.

While supersonically the F-35 is limited to a seemingly unimpressive Mach 1.6 in level flight, Davis explains that the JSF is optimized for exceptional subsonic to supersonic acceleration. Transonic acceleration is much more relevant to a fighter pilot than the absolute max speed of the jet, Davis said. Davis, who was previously the program manager for the F-15 Eagle, explains that while the Eagle is a Mach 2 class fighter, it has rarely exceed the threshold of Mach 1.2 to Mach 1.3 during it's entire 30 year life span. Additionally, the time the aircraft has spent in the supersonic flight regime can be measured in minutes rather than hours- most of the supersonic flights were in fact during specialized flights such as Functional Check Flights (FCF). "I don't see how that gets you an advantage" Davis said, referring to the Mach 2+ capability. Beesley said that in terms of supersonic flight that the F-35 is still more than competitive with existing designs.

Comparisons to the F-22 Raptor are unfair as "supersonically, the Raptor is in a class by itself. It lives there," Beesley explained. "In many ways the Raptor is the first true supersonic fighter," Beesley added, referring to that aircrafts' much publicized and unique supersonic cruise capability...."
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spazsinbad

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Unread post09 Feb 2011, 08:50

Interesting poster for UNI project in Holland?: http://www.lr.tudelft.nl/live/pagina.js ... poster.pdf (1Mb)
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F-35 Reconfigurable Flight Control Design and Evaluation

http://www.lr.tudelft.nl/live/pagina.js ... 07&lang=en

"Background
At this moment the Netherlands are considering to replace the current fleet of F-16 Multi-Role Fighters with the Lockheed-Martin F-35 Lightning II, formerly known as Joint Strike Fighter (JSF). The single-engine F-35 will fly a set of flight control laws based on nonlinear dynamic inversion (NDI). This control law design methodology allows direct mapping of flying qualities to the control laws over the entire flight envelope reducing the need for aerodynamic gain scheduling. Although flight test results on the X-35 prototype have proven the strength of this control design methodology, the nonlinear dynamic inversion does rely heavily on a precise onboard dynamic aircraft model. Within the available computing power an adaptive control law with on-line model identification can be designed that can adapt to changes in the aircraft dynamics and/or failures of aircraft subsystems. The overall result of the application of such a reconfigurable flight control (RFC) system will be an improvement of safety in operations, survivability and performance as part of the F-35 program requirements.

Project Goals
The main goal of this project is to develop a reconfigurable flight control system for F-35 Lightning II, based on the latest adaptive control approaches. Since no F-35 dynamic model is publicly available, the flight control system will be designed for a generic high-performance modern fighter aircraft model. Software packages and tuning rules will be developed which facilitate the RFC law design and tuning for any type of aircraft including the F-35. The designed control system will have the following properties:

Sufficient pilot handling qualities are maintained during several stages of degradation due to various types of realistic system failures/damages.

The flight control system will protect the aircraft from entering flight envelope regions where recovery is no longer possible or handling qualities are to severely degraded.

Based on well founded mathematical stability and robustness proofs.

To help achieve these objectives several realistic failure models will be developed for the generic fighter aircraft model."

I guess they would hope their work will eventually be used by the F-35?
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Unread post09 Feb 2011, 09:10

Good PDF to peruse: http://sstc-online.org/proceedings/2002 ... /p1417.pdf (0.7Mb)

Model-Based Development of X-35 Flight Control Software Greg Walker 2 May 2002

"Flight Control Objectives
• Proactive Approach to Flying Qualities Design
• Enforce a Criteria-Centered Process
• Leverage Advanced Control Design Methodology
• Maximize Commonality in Control Laws Across the Variants...
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Unread post09 Feb 2011, 14:48

From the avweek article that Spudman posted:
"regression testing of mission-system software changes."

This is the toughest part of the program, as each software change is implemented, the testing time can increase exponentially.

Forget the flight control software. As each mission system is added, the integration of that system requires weeks of testing. This is not a program where having the OFP auto-restart is an option.
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