The Initial flight control system for the demonstrator used an eigenstructure assignment design. The command structure was similar to the F-16.[^6] After a crash during a flight test go-around, the FCS was re-designed. It used the classical control combined with eigenstructure assignment but removed the pitch integrator. In addition, a filter for first-order pitch stick command was used to achieve sufficient flying qualities. This reduced to a pole-placement algorithm.[^6] This led to a tradeoff between the pitch attitude and the flight path angle bandwidth. Eliminating the integrator dynamics from the closed-loop increases the bandwidth of the system.[^6] With these changes, the control law was able to achieve Level 1 Handling for all tasks involving closed-loop tracking. FFT analysis was used to develop the pitch attitude and pitch force-frequency response. The actual flight control system was ready a year before the first flight. It augmented the pitch control of the aircraft with the thrust-vectoring nozzles. A cockpit switch is used to engage/disengage the thrust-vectoring.[^6] The initial feedback gains were calculated with an eigenstructure assignment algorithm. It combined the pitching moment control power into a single pole placement algorithm. 600 hours of flight testing spanned sl-50kft and 90kts to M1.5. The G loading tested was from -1 to 7. The flight control system used Gibson, Neal-Smith, Bandwidth, and Smith-Geddes methods to design the system. A pitch integrator was used to provide a set point for control and to minimize the need for trimming the aircraft. The additional integrator pole and zero can limit the effective bandwidth of a closed-loop system. This pole was the dominant mode for the load factor and pitch-rate response. The pitch axis was designed to have a low second-order equivalent response. To do this, the proportional and integral path gains were designed to cancel out the integrator pole using the integrator zero zero so that there were no observed integrator dynamics in the short-period response.[^6] The YF-22 used a MACH DI controller in engineering simulations from 1993-1996. The accelerometers for the flight control system are near the cockpit station, and the gyroscopes are 150in behind the cockpit. The F-22 does not have a speed brake and instead uses TEU ailerons, TED flaperons, and trailing-edge outboard differential rudders as a brake.[^5] The trailing-edge wing surfaces were not used for the direct lift control effectors.[^6]
[[F-22 Initial Short-Period Mode Specifications]] – not the dominant mode
[[F-22 Handling Qualities Simulator]]
F-22 PIO – crashed during landing
[[F-22 FCS design Philosophy]] – used to incorporate YF-22 lessons learned into the production aircraft
Eigenvalues of State-Space System -Eigenstructure refers to the set of eigenvalues of the system
[[F-22 Structural Filters]]
F-22 Lateral Directional Flight Control System
[[F-22 Longitudinal Flight Control System]]
[[Oblique Wing Aircraft]] – eigenstructure techniques were studied in oblique wing aircraft
[[B-1 Roll Control Channel]] – inboard spoilers are used for deceleration.
F-16 VISTA (X-62) – was used to simulate the F-22 control system
[[YF-23 Control Surfaces]] – also used differential flaperons for speed brakes
JAS-39 Longitudinal Control Laws – also used a pitch integrator to automatically trim the aircraft
F-16 Flight Control System – shows a diagram of a pitch integrator
B-2 Aerodynamics] – also uses differential deflection as a brake
Sources
- [1] “Flight Control Law Design: An Industry Perspective – ppt video online download.” Accessed: Feb. 11, 2023. [Online]. Available: https://slideplayer.com/slide/5738737/
- [2] RTO-TR-029
- [3] _20100033140
- [4] W. R. Wray, “F-22 Structural Coupling Lessons Learned”.
- [5] J. Abercrombie, F-15 Eagle The Early Years.
- [6] J. Harris and G. Black, “F-22 control law development and flying qualities,” in 21st Atmospheric Flight Mechanics Conference, San Diego,CA,U.S.A.: American Institute of Aeronautics and Astronautics, Jul. 1996. doi: 10.2514/6.1996-3379.
Backlinks
Aircraft Trim
[[Bandwidth Limitations of Controllers]]
[[Closed-Loop Tracking]]
[[Direct Lift]]
[[F-16 Flight Control System]]
F-22 Raptor
[[Fast Fourier Transform]]
[[Gibson Criteria]]
[[Honeywell Multi-Application Control (MACH)]]
[[Integrty RTOS]]
[[Pole Placement for Helicopter Flight Systems]]
[[Pole-Zero Cancellation]]
Poles of a System
[[Second-Order Systems]]
[[Z-Domain Integrator]]