The FCS for the legacy hornet used two computers with 701E processors. This full-authority control system moved hydraulic actuators. The differential stabilator on the hornet was used as a yaw device at AOA over 30 degrees due to the adverse yaw generated. With the stabilator deflected Tail-Edge down a large yawing moment was created due to the high induced drag that was opposite the roll command. Leading and trailing edge flaps are used for carrier operations, maneuvering and cruise.[^3] The flaps are scheduled with Mach number and AOA.[^3] The all-moving stabilators are mounted below and behind the wing for better stability at high AOA.[^3] There is a speedbrake between the twin vertical tails.[^3] The speed brake has deflection limits at 0 degrees and 60 degrees.[^3] The control surfaces are all hydraulically powered.[^3] The initial force command architecture was modified into a position command.[^3] This allowed the removal of forward path structural filters as well as stick pre-filters, which decreased the total time delay.[^3] The F-18A has around 120ms of equivalent time delay.[^3] Each Aileron is driven by 2 of the 4 identical channels.[^4] The aileron systems can withstand one electrical and one hydraulic failure and still function.[^4] After two failures of either the electrical or hydraulic system, they revert to a “trail-damped” mode where it fairs into the airstream to prevent flutter.[^4] If an actuator fails with the flaps down, the flight control system will bring up the opposite flaperon to maintain symmetry while the surface is blown into a faired position.[^4] The Hornet flight control system used lessons learned from the F-4 SFCS, F-4 PACT, F-15, and YF-17.[^5] The requirements development came from experiences with the A-7 and F-4 aircraft.[^5] The digital fly-by-wire system is quad-redundant.[^5] This drives the ailerons, rudders, leading-edge flaps, trailing-edge flaps, and stabilators.[^5] The stabilators have a mechanical backup.[^5] The twin rudders are used for yaw and pitch control.[^5] leading-edge flaps, trailing-edge flaps, and flaperons are used for flap and roll control.[^5] The stabilators are used for pitch and roll control.[^5] The actuators used force summing single-stage electrohydraulic servos.[^5] The thin wings and tail surfaces limited the envelope for the aileron and rudder actuators.[^5] The FCS contained autopilot and datalink modes.[^5] I also had a built-in test feature.[^5] The digital systems allowed for multi-purpose control surface usage, and optimal scheduling of control laws.[^5]
It also used a rudder schedule to improve longitudinal handling.[^5]
Another modification was to reduce the wing bending moments and the wing-fold hinge bending moments by increasing the trailing-edge flap deflection.[^5] This moved more of the lift inboard thereby reducing the bending moments.
[[A-7 Fuel-Saving Equipment Changes]] – suggested replacing IMU with F-18 IMU
[[Advanced Continuous Simulation Language]] – used to develop nonlinear simulations
[[mdcf18 Program]] – used the 8.3.3 flight control laws
[[Force Command Architecture]] – used on F-18A
[[Tacit Blue Flight Control System]] – used digital computers from the F-18
[[F-18 Aileron Actuator]]
[[F-18 Smart Actuator]] – used in experimental NASA program
[[F-18 Flight Control Requirements]]
[[F-18 EMC Design]]
[[F-18 FCS Redundancy]]
[[F-18 longitudinal Mechanical Controls]]
[[F-18 Stabilator and TE Flap Actuator]]
[[F-18 Leading-Edge Flap System]]
[[F-18 Hydraulic System]]
[[F-18 Electrical System]]
[[F-18 Flight Tests]]
[[F-18 Roll Performance Improvements]]
[[F-18 Inertial Coupling Compensation]]
[[F-18 Dutch Roll Mode]]
[[B-2 Gust Load Alleviation System]] – also uses control surfaces to reduce the bending moment
Sources
- [1] E. J. Mitchell, “F/A-18A-D Flight Control Computer OFP Versions 10.6.1 and 10.7 Developmental Flight Testing: Out-of-Controlled Flight Test Program Yields Reduced Falling Leaf Departure Susceptibility and Enhanced Aircraft Maneuverability”.
- [2] W. Mallett and M. Herskovitz, “A synopsis of the Navy A-7 Aircraft Fuel Conservation program,” in Aircraft Systems and Technology Conference, Dayton,OH,U.S.A.: American Institute of Aeronautics and Astronautics, Aug. 1981. doi: 10.2514/6.1981-1681.
- [3] C. S. Buttrill, P. D. Arbuckle, and K. D. Hoffler, “Simulation model of a twin-tail, high performance airplane,” NASA-TM-107601, Jul. 1992. Accessed: Feb. 24, 2024. [Online]. Available: https://ntrs.nasa.gov/citations/19920024293
- [4] S. C. Jensen, G. D. Jenney, and D. Dawson, “Flight test experience with an electromechanical actuator on the F-18 Systems Research Aircraft,” in 19th DASC. 19th Digital Avionics Systems Conference. Proceedings (Cat. No.00CH37126), Philadelphia, PA, USA: IEEE, 2000, p. 2E3/1-2E310. doi: 10.1109/DASC.2000.886914.
- [5] H. Harschburger, “MIT Subject 16.885J/ESD.35J Aircraft Systems Engineering,” Flight Control Systems, 2002.
Backlinks
[[A-4 Skyhawk]]
[[A-7 Corsair 2]]
[[Adverse Yaw]]
[[Aeroservoelasticity and Structural Mode Filter Best Practices]]
[[AN_AYK-14 Digital Computer]]
[[Angle of Attack]]
Built-in Self Test
[[Electrohydrostatic Actuator]]
[[Equivalent System Time Delay]]
[[F-4 PACT]]
[[F-4 Phantom Flight Control System]]
[[F-4 Survivable Flight Control System]]
[[F-15 Flight Control System]]
F-18 Legacy Hornet
[[Flaperons]]
[[Flutter]]
[[Force Summation Redundancy]]
[[Gain Scheduling]]
[[Mach Number]]
[[Redundancy]]
[[YF-17 Cobra]]