forward CG (load forward) v.s aftward CG (load aftward)

[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 5-13, 5-15, 5-16, 5-19, 5-25, 5-43]

Aircraft designers tend to locate the aircraft’s CG as nearly as possible to the 20 percent point of the mean aerodynamic chord (MAC). Actually, it is common that the wing’s CL is to the rear of the CG – “CG-CL-T” design (positive longitudinal stability). However, there are few more considerations.

 

Forward CG

  • (Pros) positive directional stability – when the side surface greater aft than ahead of the CG
  • (Pros) Higher longitundinal stability and better in stall recovery – an aircraft becomes less controllable, especially at slow flight speeds, as the CG is moved aft. The recovery from a stall in any aircraft becomes progressively more difficult as its CG moves aft. Failure in stall recovery can lead to spin. Indeed, the most critical CG violation would occur when operating with a CG that exceeds the rear limit.
  • (Cons) Higher stall speed – stalling AOA is reached at a higher speed due to increased wing loading.
  • (Cons) need for greater back elevator pressure – the elevator may no longer be able to oppose any increase in nose-down pitching.

 

Aft CG

  • (Pros) Faster cruising speed – produces the most efficient overall performance (but it would also result in instability)
  • (Pros) Lower Stalling speed – “nose-up” trim is required less to maintain level cruising flight. This means produce a lighter wing loading. Also, this requires a lower AOA of the wing, which results in less drag
  • (Cons) Poor in stall recovery
  • (Cons) Poor response in sideward force (Such as Cross wind)

 

Read More –

Loading both forward and aftward cargo compartment

In real operations, sometimes both forward and aft compartment may be loaded. Actually, it cause impact on the controllability, which is related to moment arm in lieu of CG.

Greater control forces required when the load is dispersed!

Long moment arms to the positions of heavy equipment  and cargo requires the application of greater control forces.

Example:

tip tanks tends to be sluggish in roll when control situations are marginal;

With full nose and aft cargo bins tends to be less responsive to the elevator controls

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