The pitch axis uses AOA, pitch rate, and normal acceleration feedbacks to stabilize the aircraft.[^1] The canards and elevons are distributed evenly for redundancy and to reduce the required control surface rates.[^1] It uses a center-mounted damped ministick that has a 10.8 degree displacement.[^1] The maximum nose-down displacement is -7 degrees.[^1] When the aircraft is above its corner speed (600km/h) the stick commands load factor.[^1] Below the corner speed the stick commands AOA.[^1] The soft-stop can be overridden by 135N of force to gain an extra commanded 3G when above the corner speed.[^1] The control laws use a PI pilot command with a PI adjustment of the aircraft response.[^1] Linear Quadratic design methods were used to design these control laws.[^1] The AOA and Pitch rates are used in the proportional feedback for canards and elevons.[^1] This augmentation changes the aircraft response to a simple second-order model.[^1]
The pitch rate response for control surface pulses between light and heavy aircraft are almost identical.[^2]
In this block diagram the proportional command is shown with green pathways, the integral command is in blue, and the feedback paths are shown in red.[^1] The integral path will adjust the normal load factor by adding elevon position until it agrees with the commanded load factor if the gear is up.[^1] The AOA and pitch rate are determined by a voting scheme. The load factor response follows a first-order system.[^1]
For AOA, a similar structure to the G-command is used.[^1] to prevent AOA overshoots during rapid maneuvers a predicted AOA signal is used.[^1]
$$\alpha_p=\alpha_{cv}+q-(N_{zcor}-\cos\theta\cos\phi)\times g\times \frac{57.3}{V}-p\times\frac{\beta_F}{57.3}-0.005V_{dot}$$
For light loads the AOA limit is 26 degrees and is reduced to 20 deg for heavy stores.[^1]
Sources
- [1] R. H. Saab ab, “CAREFREE MANOEUVRING AND AUTOMATIC RETURN TO NORMAL FLIGHT ENVELOPE JAS 39 GRIPEN.,” IFAC Proceedings Volumes, vol. 40, no. 7, pp. 115–120, Jan. 2007, doi: 10.3182/20070625-5-FR-2916.00021.
- [2] L. Rundqwist and R. Hillgren, “Phase compensation of rate limiters in JAS 39 Gripen,” in 21st Atmospheric Flight Mechanics Conference, San Diego,CA,U.S.A.: American Institute of Aeronautics and Astronautics, Jul. 1996. doi: 10.2514/6.1996-3368.
Backlinks
[[C* Flight Control Law]]
[[Corner Speed]]
F-22 Flight Control System
[[Feedforward Control]]
[[First-Order Systems]]
[[JAS-39 maneuver Load Limiters]]
[[LQG]]
[[LQR Controller Design]]
[[PI Controller]]
[[SAAB Gripen JAS-39 Flight Control System]]
[[Second-Order Systems]]
[[Superaugmentation Architecture]]