*The F-14’s CADC* *Central Air Data Computer* Designed by Steve Geller and Ray Holt, the Central Air Data Computer’s primary function was to manage the variable-sweep wing, glove vanes, maneuvering flaps/slats, and limit allowable controllable inputs. Signals were both digital and analog. The automatic sweep wing was optimized as a function of Mach speed and altitude biasing, affording the F-14 stability and efficient lift/drag characteristics throughout different flight regimes. Two sweep wing programs allowed the pilot to choose whether to augment the wings for excess energy or capitalize on maximum usable lift for effective maneuvering. Built using the same principles as a primary flight control system, the CADC featured a dual redundant fly-by-wire system with a mechanical backup. *What is Fly-By-Wire?* That depends on the definition you use: _Aerospace Recommended Practice (ARP) defines FBW as a flight control system wherein vehicle control information is transmitted completely by electrical means._ _A fly-by-wire flight control system is an electrical primary flight control system employing feedback such that vehicle motion is the controlled parameter._ _…Fly-by-wire is the generally accepted name for the flight control systems [that] process the flight control inputs made by the pilot or autopilot using computers and submit suitable electrical signals to each actuator of the flight control surfaces._ _Fly-by-wire (FBW) systems are semi-automatic, computer-regulated aircraft flight control systems that replace mechanical flight controls with an electronic interface. (BAE)_ Why is there more than one definition? Because FBW philosophy changed over time. My college degree’s main focus was Aeronautical Science. Yet, we didn’t analyze flight control systems as profoundly as we should have (maybe we did; I was more interested in aerodynamics anyway). But college wasn’t where I first heard the term “fly-by-wire.” As a kid, I watched a documentary that noted FBW technology and its advancements. I asked my father-a pilot and aviation attorney-what FBW was. He tersely explained that instead of conventional controls (pulleys, cables, etc.), the aircraft’s flight controls used a flight control computer (FCC) to interpret the pilot’s commands and move the control surfaces accordingly. 12-year-old me didn’t grasp the concept immediately, but I still felt I got the “gist” of FBW. As I ventured into an aviation career, I recognized how FBW definitions polyfurcated amongst pilots of different generations. If you ask them what the “first” FBW aircraft was, there are either thirty or none. My definition of FBW flipped-flopped often. I grew tired of the generally trite back-and-forth and researched why so many definitions existed. *The Aerospace & Defense Industry* FBW's original goal was to replace the conventional control system. In the 1950s, as jets got faster, conventional systems weren’t doing enough to keep up with the rapidly changing conditions a fighter jet may experience. Furthermore, conventional systems were heavy and intricate. Thus, aerospace engineers sought lighter, more efficient alternatives for next-generation aircraft. The Avro Arrow incorporated the technology with an Analog FBW system in the late 1950s. Concorde, often cited in these discussions, gets credit for using an analog FBW FCS. NASA’s Dryden Digital Fly-by-Wire (DFBW) program and the Air Force’s Survivable Flight Control System (SFCS) tests provided the industry with more intel on FBW, eventually culminating into the F-16’s Analog FBW FCS. Aerospace engineers realized that DFBW could use software to program and tailor flight control systems to correct aerodynamically unstable designs. The added functionality fostered Relaxed Static Stability (RSS) aircraft with Active FCS exploiting the maneuverability characteristics of an unstable platform. *Flight Envelope Protection* _Flight Envelope Protection warns or prevents pilots from exceeding flight envelope limits through either aural or visual cues or rejecting a pilot’s commands to fly the aircraft outside those limits._ The amalgamation of FCS and Flight Envelope Protection (FEP) was possible because of the advancements in DFBW. However, FEP is not a new concept. Before integrating FEP and FBW (creating an Active FCS), it existed in the form of visual or aural warnings (e.g., the stall tone in an aircraft). This means FEP is _not_ exclusive to FBW. Furthermore, manufacturers applied different philosophies to FEP. For example, Airbus chose “hard” limits preventing pilots from overriding normal control laws. Whereas Boeing chose a “soft” limit approach, warning the crew of flight envelope margins but still allowing them to override FEP. *Perspectives Today* Newer generations of pilots may only be aware of the exceedingly advanced Active FCS that typically accompany 4th-and 5th-generation fighters. Occasionally, this leads to misimpressions and misinterpretations of control systems that pioneered the technology so commonly embedded in today's platforms. Analyze the argument that the “first FBW” fighter is the F-16. When it first entered service, it used an Analog FBW FCS system. The Legacy Hornet went into production with a DFBW FCS, which invites the counterargument: maybe it’s the F/A-18 that was the first DFBW aircraft? An extreme version of this argument (or perhaps merely a distinction) accounts for whether a mechanical backup exists. This argument restores the F-16 as the first production AFBW fighter. On the other end of the spectrum are those who want to go as far back as the B-17’s “formation stick” as the earliest form of FBW. On some level, I’m sure that argument is acceptable as well. Manufacturers must hit moving targets with each new design. The FCS needs to account for the design’s respective objective. Employing the F-117’s FBW system in a 737 wouldn't make sense. The natural evolution of priorities and threats, integration of FEP/FCS, and diverging philosophies of FEP are how we reached varying degrees of FBW concepts. In a semi-recent discussion regarding the F-14, a friend asked if it was a FBW airframe. I answered, “No.” My answer didn't convince him, so we dug deeper into the subject, leading us to discover Geller's and Holt's creation: The CADC. We agreed that the F-14 still isn’t FBW _in the modern sense_ (no _active_ FCS). But we also recognized that it wasn’t exactly a Sopwith Camel either. The F-14 isn’t a traditional aircraft. So, I don’t judge it in a traditional way. For clarity, the aim of this piece isn’t to correct or persuade others to call the F-14 a “hybrid” or “semi” AFBW aircraft. This argument tends to err more on the philosophical side of the spectrum. The objective here is to show how nomenclature can be ambiguous or misleading (like _computer_ and _October_ - it doesn’t refer to the tenth month; three other months are also out of order). Additionally, debating the progeny of FBW systems throughout history and which one should be considered “first” or how one aircraft is classified in terms of its FCS doesn’t make pilots better operators. Pilots focus on flying their aircraft to the best of their ability, wholly irrespective of which aircraft they think maintains “true” FBW. _A special thanks to my friend and former Naval Aviator, "Coach," for reviewing and fact-checking my information._ People discussing FBW: groups.google.com/g/rec.aviation.military/c/c_x_qgS4veI www.pprune.org/tech-log/510768-fly-wire.html Some References: www.f-16.net/articles_article13.html#:~:text=(The%20F%2D16%20was%20eventually,norm%20for%20high%2Dperformance%20aircraft spinoff.nasa.gov/Spinoff2011/t_5.html ntrs.nasa.gov/api/citations/19760024050/downloads/19760024050.pdf ntrs.nasa.gov/api/citations/19680023697/downloads/19680023697.pdf warfarehistorynetwork.com/article/the-norden-bombsight-was-it-truly-accurate-beyond-belief/ web.archive.org/web/20120419001851/www.firstmicroprocessor.com/thereviewers/russell-fish/ kzfaq.info/get/bejne/hLSGjMh4v57Lh2g.htmlsi=7df052eJmkiidXSh kzfaq.info/get/bejne/l7x1oJiEuLu5fJc.htmlsi=uBV1sTGAWI8oDP1k kzfaq.info/get/bejne/aNmKm72q166ahn0.htmlsi=M45NyPyqYCFYzA22 kzfaq.info/get/bejne/ZquEdrN5mbi0oHk.html

TOMCATS!