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provides, pilots must understand the difference between ²design limit-g² and ²reference load factor (Nz
REF).² See the Acceleration Limitations chart in the Operating Limitations chapter for a plot of Nz
REF versus gross weight, for g-limiter specifics, and for gross weight related g-restrictions.
2.9.7.1 Design Limit-g. The aircraft was designed to sustain a limit-g of +7.5g or -3.0g (symmetric)
only at or below its fighter design gross weight of 42,097 lb. At higher gross weights, design limit-g is
reduced to keep from exceeding the structural limitations of the airframe. An ²overstress² is defined as
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a g-level that exceeds the design limit-g at the aircraft's current gross weight. Above 42,097 lb gross
weight, design limit-g is reduced by the aircraft's relative gross weight (42,097/GW), such that the
positive design limit is +7.5g * (42,097/GW) and the negative design limit is -0.4 * (positive limit-g). At
the aircraft's maximum gross weight (66,000 lb), design limit-g is only +4.8g or -1.9g.
Due to the increased airframe and pylon loads that accompany high-g rolling maneuvers, the aircraft
also has a design limit-g for abrupt full-stick rolls (FSR). Abrupt FSRs are defined as full lateral stick
in less than 1 second. The positive design FSR limit is +6.0g below 42,097 lb GW and 80% of the
symmetric design limit-g above 42,097 lb. The negative design FSR limit is -1.0g at all gross weights.
At 66,000 lb GW, the positive design FSR limit is only +3.8g.
2.9.7.2 Reference Load Factor (Nz REF). Reference load factor (Nz REF) is the value that the MC
uses to set the g-limiter when outside of the transonic g-bucket (described below). With increasing
gross weight, Nz REF is the same as design limit-g until the gross weight where +5.5g (-2.2g) is
available (57,405 lb GW). Above 57,405 lb GW, Nz REF is held fixed at +5.5g (-2.2g) in order to assure
that the pilot always has those g-levels available even if they would result in an overstress. Since the
g-limiter may not prevent an overstress at gross weights above 57,405 lb, the pilot must be responsible
for preventing an overstress in this gross weight region.
2.9.7.3 G-Limiter. The g-limiter essentially limits the amount of positive and negative g that can be
commanded by the pilot at a particular gross weight in order to prevent an aircraft overstress. Once the
pilot reaches the stick displacement required to attain the Nz REF g-limit, further stick inputs do not
increase g. This is commonly called ²being on the limiter.² Once the stick is relaxed to the limit
displacement, g-control below Nz REF is regained. The g-limiter functions to maintain both the
positive and negative Nz REF limits.
During abrupt longitudinal stick inputs, g-limiter overshoots are not uncommon. G-limiter overshoots
of up to +0.5g or -0.2g are allowed and do not constitute an over-g. An ²over-g² is defined as a
g-level which exceeds the overshoot thresholds and sets MSP code 811 (positive exceedance) or 925
(negative exceedance). An over-g condition requires a postflight inspection to determine if an
²overstress² occurred.
For rolling maneuvers commenced above the positive FSR limit, the g-limiter also provides some
protection. In this region, the g-limiter attempts to reduce commanded-g towards the positive FSR
limit to prevent an overstress. However, if the rate of lateral stick input exceeds the capability of the
g-limiter, an actual rolling overstress may result without setting an 811 MSP code (set only if the
symmetric over-g threshold is exceeded). The g-limiter treats rolling maneuvers with less than ¾ inch
lateral stick as symmetric maneuvers.
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A FUEL XFER, R-LIM OFF, CAUT DEGD, or MC2 caution; an SMS failure, or an invalid fuel
quantity sets a G-LIM 7.5G caution along with the ²Flight controls, Flight controls² voice alert. A
G-LIM 7.5G caution indicates that the positive symmetrical command limit has been set to +7.5g
regardless of gross weight or stores loading. If the G-LIM 7.5G caution is set, the pilot must limit
commanded g-level to prevent an overstress.
Very high g-onset rates are possible with rapid aft stick movement, with
or without g-limiter override. A very high g-onset rate can cause immediate
loss of consciousness (G-LOC) without the usual warning symptoms
of tunnel vision, greyout, and blackout. The effects of G-LOC may last 20
seconds or longer after the g level is reduced to near 1 g.
2.9.7.4 G-Bucket. Due to the aerodynamic phenomenon known as transonic pitchup, the g-limiter
incorporates a ²g-bucket² designed to prevent an aircraft over-g during transonic deceleration. ²In the
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NATOPS Flight Manual 飞行手册 1(64)
