Aero Chapter 04, Stability
T-45 Aerodynamics Student Workbook
MEAN AERODYNAMIC CHORD (MAC)
The mean aerodynamic chord is located on the reference axis of the aircraft and is used by the
aeronautical engineer as a primary reference for longitudinal stability considerations. The limitations of
the allowable location aircraft’s center of gravity are customarily referenced to the MAC (Figure 66).
The T-45’s leading edge of the mean aerodynamic chord (LEMAC) is located 240.9" aft of datum (which is
the tip of the nose boom). The MAC extends aft of the LEMAC 74.03" and the CG location will be
measured as a percentage of the entire MAC that the CG is aft of LEMAC.
T-45 CENTER OF GRAVITY (CG) LIMITATIONS
The CG is the point at which the weight of an
object can be considered to be concentrated.
The aircraft is viewed as rotating about the CG
in response to the forces of lift, weight, thrust,
and drag. The aeronautical engineers design
each aircraft for a certain range of CG
movement. Factors such as landing gear
repositioning, the ejection of one pilot, fuel
burn, wing sweep, and ordnance release can
affect the CG location while in flight.
The T-45 was designed to have the CG move
Mean
between 14% and 25% of the mean
AERODYNAMIC CENTER
Aerodynamic
aerodynamic chord (MAC). The only
Chord
CENTER OF PRESSURE
significant CG variables the T-45 pilot has are
Figure 66: MEAN AERODYNAMIC CHORD
gear positioning, speed, fuel burn, and dual or
solo manning (Figure 67). Some of the larger
factors that affect the CG movement
follow:
• Extending the T-45’s landing gear
13,500
moves the CG aft 2% of MAC or
1.4 inches. Raising the gear
Upper
causes a forward shift of equal
13,000
Fuselage
Fuel
• Fuel burn causes the CG to move
12,500
slightly forward from full fuel to
AIRCRAFT
Lower
minimum fuel. CG shifts aft 1% of
Fuselage
WEIGHT 12,000
MAC or 0.7 “during lower fuselage
Fuel
(LBS.)
tank burn and 3% or 2.1” forward
11,500
during outer wing fuel burn.
Outer
Wing
• Note: Weapons release has little
Fuel
11,000
effect on the T-45’s CG due to the
suspension points’ relationship to
Center
the CG.
10,500
Wing
Fuel
The pilot does not control these CG
shifts directly but does respond to
10,000
them with trim.
9
11
13
15
17
19
21
23
25
C. G. - %M.A.C.
Figure 67: CENTER OF GRAVITY TRAVEL
Page 44
(7-99) Original
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