BMS F-16C/D 4.34, Flight Manual

Page: 136 / 234

T.O. BMS1F-16CM-1 BMS 4.34 Change 2.00
BMS 4.34 Dash 1
© Red Dog 2012-2019
Page: 136
1.12 FLIGHT CONTROL SYSTEM (FLCS)
The FLCS is a digital fly-by-wire system which controls the flight surfaces hydraulically. The main
component of the FLCS is the Flight Control Computer (FLCC) that translates electrical signals
generated at the flight controls to hydraulic pressure moving all primary and secondary flight controls,
taking into account other sources of data such as AOA, air data probes, INS, etc.
Pitch motion is provided by symmetrical movement of the horizontal tails, Roll is controlled by
differential movement of the flaperons and horizontal tails and Yaw is controlled by the rudder.
The FLCS provides roll coordination automatically through the ARI (Aileron Rudder Interconnect)
system which is not active on the ground with WOW and until a few seconds after gear retraction.
The FLCS is meticulously coded in BMS as it is one of the main components of the BMS Advanced
Flight Model. It is a combination of three modules:
- Pitch FLCS
- Roll FLCS
- Yaw FLCS
FLCS limiters are provided in all three axes to help prevent departure/spins.
The FLCS has three operational modes that are called GAINS:
- Standby gains
- Takeoff & Landing gains
- Cruise gains (normal operating mode)
The normal mode of operation is Cruise gains. Takeoff and Landing gains is activated whenever the
following conditions are met:
1. Landing Gear handle in Down position.
2. ALT FLAPS switch in EXTEND position and airspeed less than 400 knots.
3. AIR REFUEL door switch in OPEN position and airspeed less than 400 knots.
The Standby gains are coded in BMS but are relatively transparent to the user. They kick in
automatically when the FLCC detects a FLCS failure indicated by the FLCS FAULT caution light.
1.12.1 CRUISE GAINS
1.12.1.1 Pitch FLCS
The purpose of the Pitch FLCS is to limit requested G to control the natural pitch instability of the F-16.
It is important to understand that when the pilot applies pressure on the sidestick in the pitch axis he is
actually commanding an amount of G. The FLCS translates this into flight control surface motion to
deliver the intended G number, taking into account other flight parameters such as AOA.
At low AOA (below 15°) the maximum positive G is 9G, but as AOA increases maximum G decreases.
The limit also depends on the position of the STORES CONFIG switch. Two settings are possible:
CATI and CAT III.
CAT I is the least limiting position and is intended for a clean configuration (centreline and A-A
weapons can be carried). CAT III is the most limiting position to protect the aircraft from departure
when carrying loads on the wing stations (fuel tanks, A-G bombs, etc).
In CAT I the pilot can request from -3G to +9G. The AOA remains a factor in the maximum possible G.
At 20° AOA it will reach 7.3G and at 25°AOA the max G reachable is 1G (level flight).
In CAT III the AOA is limited from a certain angle to prevent higher G being reached. This AOA limit is
around 15.5
– 15.8° AOA. That means that in CAT III below 15° AOA, the airframe might be able to
pull 9G but as soon as the AOA reaches 15° the CAT III limits additional AOA increase therefore
limiting the number of available G.
The CAT config does not limit G, it limits AOA which as a consequence limits maximum G available.