## Center of Gravity:

- One of the most significant components of aircraft design is CG
- It is the specific point where the mass or weight of an aircraft may be said to center; that is, a point around which, if the aircraft could be suspended or balanced, the aircraft would remain in place at any attitude
- In other words, the CG may be considered as a point at which all the weight of the aircraft is concentrated

- It will be noted that CG is of major importance in an aircraft, for its position (within a designed range) has a great bearing upon stability
- As the CG moves rearward (towards the tail), the aircraft becomes more and more dynamically unstable
- In aircraft with fuel tanks situated in front of the CG, it is important that the CG is set with the fuel tank empty
- Otherwise, as the fuel is used, the aircraft becomes unstable
- The CG is computed during initial design and construction and is further affected by the installation of onboard equipment, aircraft loading, and other factors

- It is the specific point where the mass or weight of an aircraft may be said to center; that is, a point around which, if the aircraft could be suspended or balanced, the aircraft would remain in place at any attitude
- The C.G. must always be within limits, however, depending where in the allowable range the C.G. falls will effect performance [Figure 1]
### Forward CG: [Figure 2]

- Stable feeling
- Nose Heavy
- Longer takeoff distance (more airflow required to provide more force to lift heavy nose)
- High stall speeds (more airflow deflection of the elevator required to maintain altitude at slower airspeeds resulting in high AOAs)

### Rearward CG: [Figure 3]

- Less stable
- Tail heavy
- Hard to recover from stall or spin
- Higher true airspeed
- More tail down force

- Center of Pressure:
- It is important to understand that an aircraft’s weight is concentrated at the CG and the aerodynamic forces of lift occur at the CP
- When the CG is forward of the CP, there is a natural tendency for the aircraft to want to pitch nose down
- If the CP is forward of the CG, a nose up pitching moment is created
- Therefore, designers fix the aft limit of the CG forward of the CP for the corresponding flight speed in order to retain flight equilibrium

## Overweight Aircraft:

- Most aircraft will never be too light to fly however overweight aircraft pose very serious safety threats
- People like R&B https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20010907X01905&key=1 have died when pilots neglect to complete a proper preflight
**Limitations:**- Longer takeoff run
- Higher takeoff speed
- Reduced angle and rate of climb
- Reduced cruising speed
- Shorter range
- Higher stalling speed
- Longer landing roll

## Definitions:

**Center of Gravity:**imaginary point where the aircraft would balance if suspended**CG Limits:**the forward and aft center of gravity locations for a given weight**Reference Datum:**imaginary vertical plane from which all horizontal distances are measured (firewall, leading edge, etc.)**Basic Empty Weight (BEW):**weight of standard airplane, optional equipment, unusable fuel, and full operating fluids, including full engine oil. Any changes must be documented**Unusable Fuel:**fuel that cannot be drained**Licensed Empty Weight:**like BEW, but does not count full engine oil, only undrainable oil**Ramp Weight:**airplane loaded for flight prior to engine start**Gross Takeoff Weight:**weight of the airplane just before brake release to begin takeoff roll**Gross Landing Weight:**takeoff weight minus the fuel burned en-route**Zero Fuel Weight:**weight of the aircraft before addition of fuel**Payload:**weight of only the passengers, baggage, and cargo**Useful Load:**weight of crew and usable fuel**Maximum Ramp Weight:**max weight for ground operations**Maximum Takeoff Weight:**max weight for takeoff**Maximum Landing Weight:**max weight for landing based on stress of impact on gear**Usable Fuel:**fuel available for flight**Arm:**distance from the datum**Moment:**measurement of the tendency of the weight to cause rotation at the fulcrum**Loading Graph:**used to find the moment for loads in the airplane**Center of Gravity Moment Envelope:**shows limits with proposed loading

## Determining Weight and Balance:

- Weight and balance specifics are unique to different aircraft
- A weight and balance example should be included with your POH

- Most pilots however, will learn and therefore be able to relate to the Cessna 172: [Figure 4]
**Block 1:**Determine the Basic Empty Weight (BEW) of the airplane (found in POH)**Block 2:**Determine the basic empty weight moment of the airplane (found in POH)**Block 3:**Determine the weight of the pilot and passenger**Block 4:**Determine the moment of the pilot and passenger (weight x arm = moment)**Block 5:**Determine the weight of the rear passengers**Block 6:**Determine the moment of the rear passengers (weight x arm = moment)**Block 7:**Determine the weight of the baggage**Block 8:**Determine the moment of the baggage (weight x arm = moment)**Block 9:**Determine the weight of the baggage as in step 7**Block 10:**Determine the moment of the baggage as in step 8, using the new arm**Block 11:**Add all weights together to get the Zero Fuel Weight (Z.F.W.)**Block 12:**Add all moments together**Block 13:**Determine the weight of the ramp fuel**Block 14:**Determine the moment of the ramp fuel (weight x arm = moment)**Block 15:**Determine the ramp weight (Z.F.W. + Ramp Fuel)**Block 16:**Determine the ramp moment (Z.F.W. moment + Ramp Fuel moment)**Block 17:**Subtract taxi fuel used (~8 lbs)**Block 18:**Subtract taxi fuel moment (~384)**Block 19:**Add Z.F.W. and Ramp Weight together, then subtract Taxi Fuel to get the Gross Takeoff Weight (G.T.W.)**Block 20:**Add Z.F.W. moment and Ramp Weight moment together, then subtract Taxi Fuel moment**Block 21:**Estimate trip fuel weight**Block 22:**Determine the moment of the trip fuel (weight x arm = moment)**Block 23:**Subtract trip fuel weight from G.T.W. to get the Gross Landing Weight (G.L.W.)**Block 24:**Subtract trip fuel moment from G.T.W. moment**Block 25:**Divide block 12 by block 11**Block 26:**Divide block 20 by block 19**Block 27:**Divide block 24 by block 23**Block 28:**Determine maneuvering speed (V_{a})- Instructions found on the performance calculations page

## Weight Shift Formula

- If you shift weight after determining the aircrafts weight and balance then verify your calculations with the weight shift formula

Weight Moved |
= | Distance C.G.Moves |

Aircraft Weight | Distance Between Arm Locations |

## Case Studies:

- National Transportation Safety Board Identification: ANC13FA091: The NTSB determines the probable cause(s) of this accident to be:
- The pilot's improper decision to load the airplane beyond its allowable takeoff weight and center of gravity limits, which resulted in a loss of control during the initial climb. Contributing to the accident was the external load and the downwind takeoff

- National Transportation Safety Board Identification: ERA14LA450: The NTSB determines the probable cause(s) of this accident as follows:
- The pilot's inadequate preflight planning, which resulted in a takeoff with the airplane's center of gravity aft of its limit and led the airplane to exceed its critical angle of attack and experience an aerodynamic stall during the initial climb. Contributing to the accident was the pilot's lack of flight experience in the aircraft make and model

- National Transportation Safety Board Identification: ERA14CA408: The NTSB determines the probable cause(s) of this accident as follows:
- The pilot/owner/builder's improper weight and balance calculations, which rendered the airplane uncontrollable in the pitch axis

- National Transportation Safety Board identification: ERA14FA343: The NTSB determines the probable cause(s) of this accident as follows:
- The pilot’s failure to secure the cargo in the cargo compartment, which resulted in a weight shift that led to the center of gravity exceeding its aft limit during a go-around attempt and a subsequent aerodynamic stall. Also causal to the accident were the pilot’s inadequate preflight inspection and his loading the airplane beyond the cargo compartment weight limit

- National Transportation Safety Board Identification: CEN13IA563: The NTSB determines the probable cause(s) of this incident as follows:
- The pilot’s improper weight and balance calculations, which resulted in the airplane exceeding its weight and center-of-gravity limits and led to a loss of pitch control during takeoff, and the operator’s failure to obtain required weight information and to ensure that the flight was properly loaded

## Conclusion:

- Weight and balance is an easy subject to become complacent with over time as most flights are nearly identical but referencing our case studies, its always important
- The weight and balance document is the "W" in the acronym "ARROW," which helps us remember the documents required for flight