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constant forward stick force is required to maintain a constant pitch attitude and load factor. Again,
if pitch trim is used to eliminate these stick forces, additional short trim inputs will be required to
re-establish 1g flight, further increasing pilot workload. Another task with a slightly increased
workload is the instrument penetration/approach where neutral speed stability may cause difficulty in
maintaining a desired airspeed.
The longitudinal handling qualities are excellent with good pitch rate and damping that combine to
allow very aggressive maneuvering. FCS control laws modify aircraft response to stick inputs, creating
the effect of changing stick forces to provide pilot cueing in maneuvering flight. Actual stick forces for
a given stick displacement do not change with flight condition. Full forward and aft stick requires a 20
pound push and 37 pound pull, respectively. At high airspeeds, the FCS is a g-command system
requiring 3.5 pounds of stick force per g. At medium airspeeds, the FCS acts as a hybrid pitch rate and
g-command system. Pitch rate feedback is used to increase apparent stick force per g as a cue of
decaying airspeed and available load factor. At low airspeed, the FCS is primarily an AOA command
system using AOA feedback above 22 degrees to provide increasing stick force with increasing AOA.
The maximum commanded AOA is approximately 45-50 degrees at full aft stick. Combined with the
capability to command high AOA is the ability to generate high nose-down pitch rates with large
forward stick to rapidly reduce AOA, particularly below approximately 200 KCAS. This nose-down
pitch rate capability is further enhanced as airspeed decreases to 150 KCAS. However, due to
departure resistance concerns, the additional nose-down capability is reduced somewhat when large
forward stick inputs are accompanied by even moderate lateral stick inputs (>1/3 stick).
The g-limiter function in the FCS limits commanded load factor under most flight conditions to the
symmetric load limit (NzREF) based on gross weight below 57,400 pounds gross weight. Above 57,400
pounds, NzREF is held constant at 5.5g even though the allowable load factor may be below NzREF
(see G-Limiter). Above 57,400 pounds gross weight, the g-limiter does not provide adequate over-g
protection and pilot action may be required to prevent an aircraft overstress.
Very abrupt full aft stick commands with aft CG conditions can beat the g-limiter and cause a
positive over-g (811 MSP code). Likewise, very abrupt pushes can result in a negative over-g (925 MSP
code). Flight test showed the most sensitive area for over-g to be localized around 20,000 ft and 0.93
Mach number even with a nominal CG. Care should be taken during all abrupt maneuvers. During
rolling maneuvers, the g-limiter also reduces commanded load factor to 80% of NzREF. This feature
can also be defeated with abrupt lateral stick inputs at elevated-g. Abrupt full lateral stick inputs at
NzREF may result in an aircraft overstress without setting an 811 or 925 over-g MSP code (see figure
4-7, Acceleration Limits - Basic Aircraft, Note 2).
Another flight characteristic related to g-limiter performance occurs during very high bleed rate
turns where even with full aft stick, load factor may be slightly less than NzREF. This can happen
when the aircraft decelerates much faster than the FCS can position the stabilators to maintain
NzREF. Additionally, during elevated-g maneuvering at transonic flight conditions, the g-limiter
unloads the aircraft (and NzREF) by as much as 1.0 to 1.7g. This feature helps prevent an aircraft
overstress that could result from the classic aerodynamic phenomenon known as ``transonic pitch-up''
experienced during elevated-g decelerations at transonic flight conditions.
At low angles of attack, the aircraft is extremely smooth with little sensation of changing airspeed
or Mach. However, at transonic flight conditions, the aircraft may exhibit a mild buffet, which is more
pronounced with empty wing pylons or interdiction loadings but is almost nonexistent with clean
wings. Buffet begins at approximately 0.88M, subsides by 0.95M, and presents a sensation much like
A1-F18EA-NFM-000
IV-11-3 ORIGINAL
riding on a ²gravel road². Airframe buffet is also noticeable in the cockpit while maneuvering at tactical
speeds between approximately 6° and 11° AOA. At low altitudes, this AOA range begins at
approximately 6 g but at high altitude begins at 2g to 3g. Above this AOA range, the buffet sensation
at the cockpit subsides slightly but is still apparent in the airframe. Although this buffet at elevated-g
is present in all configurations, it is most apparent with empty wing pylons at transonic flight
conditions. Additionally, persistent but bounded wing rock or roll-off may occur at some flight
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本文链接地址：
NATOPS Flight Manual 飞行手册 2(5)
