PHAK 10: Weight and Balance Flashcards
Introduction
Why is compliance with weight and balance limits critical?
To ensure flight safety and avoid compromising the structural integrity of the aircraft.
Introduction
What are the effects of operating above the maximum weight limitation?
It compromises the structural integrity and adversely affects performance.
Introduction
What happens if the center of gravity (CG) is outside the approved limits?
It results in control difficulty.
Weight Control: Effects of Weight
What is weight in the context of flight?
The force with which gravity attracts a body toward the center of the Earth, a product of mass and acceleration.
Weight Control: Effects of Weight
Why is weight significant in aircraft construction and operation?
It affects the aircraft’s performance and safety, requiring respect from all pilots.
Weight Control: Effects of Weight
What force counteracts weight to sustain an aircraft in flight?
Lift.
Weight Control: Effects of Weight
What factors influence the amount of lift produced by an airfoil?
Airfoil design, angle of attack (AOA), airspeed, and air density.
Weight Control: Effects of Weight
What happens if an aircraft is loaded beyond the manufacturer’s recommended weight?
The lift generated may be insufficient, making the aircraft incapable of flight.
Weight Control: Effects of Weight
Why do manufacturers prioritize minimizing aircraft weight?
To enhance performance while maintaining strength and safety.
Weight Control: Effects of Weight
What are three potential consequences of overloading an aircraft?
- Inability to leave the ground
- Poor flight characteristics if airborne
- Degraded takeoff and overall performance
Weight Control: Effects of Weight
What are eleven key performance deficiencies of an overloaded aircraft?
- Higher takeoff speed
- Longer takeoff run
- Reduced rate/angle of climb
- Lower maximum altitude
- Shorter range
- Reduced cruising speed
- Reduced maneuverability
- Higher stalling speed
- Higher approach/landing speed
- Longer landing roll
- Excessive weight on the nose or tail wheel
Weight Control: Effects of Weight
When do poor performance indications due to overloading typically appear?
During takeoff.
Weight Control: Effects of Weight
Why should preflight planning include performance chart checks?
To assess if the aircraft’s weight could lead to hazardous flight operations.
Weight Control: Effects of Weight
Why is excessive weight especially dangerous in emergency situations?
It reduces safety margins, making it difficult to handle engine failure or airframe ice formation during critical phases like takeoff.
Weight Control: Weight Changes
How can the operating weight of an aircraft be altered?
By adjusting the fuel load or changing fixed equipment.
Weight Control: Weight Changes
How much does gasoline weigh per gallon?
6 pounds per gallon.
Weight Control: Weight Changes
What should pilots consider when reducing fuel weight?
The decrease in range and its impact on flight planning.
Weight Control: Weight Changes
What is the primary weight change during flight?
Fuel burn, which lightens the aircraft and improves performance.
Weight Control: Weight Changes
How do changes in fixed equipment affect an aircraft?
Adding radios, instruments, or making repairs/modifications increases the aircraft’s weight.
Balance, Stability, and Center of Gravity
What is the definition of balance in aviation?
Balance refers to the location of the CG (center of gravity) of an aircraft, which is critical for stability and safety.
Balance, Stability, and Center of Gravity
What is the CG (center of gravity)?
The point at which the aircraft would balance if suspended.
Balance, Stability, and Center of Gravity
Why is the fore-and-aft CG location important?
It determines if the aircraft is nose-heavy (forward CG) or tail-heavy (aft CG), both of which can affect control and stability.
Balance, Stability, and Center of Gravity
What happens if the CG is too far forward?
A nose-heavy condition, which may require excessive control pressure to maintain stability.
Balance, Stability, and Center of Gravity
What happens if the CG is too far aft?
A tail-heavy condition, which can make the aircraft unstable and potentially uncontrollable.
Balance, Stability, and Center of Gravity
How does lateral unbalance occur in an airplane?
By uneven fuel distribution or weight imbalance left-to-right across the fuselage.
Balance, Stability, and Center of Gravity
What is the effect of lateral unbalance on flight?
It requires trim adjustments or constant control pressure, increasing drag and reducing efficiency.
Balance, Stability, and Center of Gravity
How does flying out of balance affect the pilot and flight?
It increases pilot fatigue, decreases aerodynamic efficiency, and reduces primary control travel in the trimmed direction.
Balance, Stability, and Center of Gravity
What does the term “balance” typically refer to in this context?
The longitudinal location of the CG.
Balance, Stability, and Center of Gravity: Effects of Adverse Balance
How do adverse balance conditions affect flight characteristics?
They affect flight in a manner similar to excess weight, impacting stability, control, and performance.
Balance, Stability, and Center of Gravity: Effects of Adverse Balance
What happens when the aircraft operates above the maximum weight limit?
It compromises the structural integrity of the aircraft and adversely affects performance.
Balance, Stability, and Center of Gravity: Effects of Adverse Balance
What is the impact of improper balance on stability and control?
It decreases stability and makes the aircraft harder to control.
Balance, Stability, and Center of Gravity: Stability
What are three effects of loading in a nose-heavy condition?
- Difficulty controlling and raising the nose, especially during takeoff and landing.
- Increased stalling speeds.
- Higher control forces.
Balance, Stability, and Center of Gravity: Stability
Who establishes the limits for the center of gravity (CG) location?
The manufacturer, and the limits are published in the Type Certificate Data Sheet (TCDS), AFM, or POH.
Balance, Stability, and Center of Gravity: Stability
Why is the forward CG limit critical during landing? (5)
Exceeding it can cause:
- Excessive loads on the nosewheel.
- A tendency to nose over on tailwheel airplanes.
- Decreased performance.
- Higher stalling speeds.
- Increased control forces.
Balance, Stability, and Center of Gravity: Stability
What must be done if the CG is outside allowable limits?
Relocate some items before flight to bring the CG within limits.
Balance, Stability, and Center of Gravity: Control
What are the effects of an aft CG location? (3)
- Decreased static and dynamic longitudinal stability.
- Extreme control difficulty and violent stall characteristics.
- Very light control forces, increasing the risk of overstressing the aircraft.
Balance, Stability, and Center of Gravity: Control
What is the aft CG limit?
- The most rearward position of the CG for safe maneuvering or operation.
Balance, Stability, and Center of Gravity: Control
Why do CG limits vary in some aircraft?
Limits may change with gross weight or for specific operations, such as acrobatic flight, gear retraction, or installation of special loads.
Management of Weight and Balance Control
What does 14 CFR part 23, section 23.23 require?
Establishment of weight and CG ranges for safe aircraft operation, provided in the AFM, TCDS, or aircraft specifications.
Management of Weight and Balance Control
Are pilots required to calculate weight and balance before each flight under 14 CFR part 91?
No, but the PIC must comply with operating limits in the approved AFM, including weight and balance.
Management of Weight and Balance Control
What two factors controlled by the pilot can affect total weight and CG location?
- Loading
- Fuel management
Management of Weight and Balance Control
What must aircraft owners ensure regarding weight and balance records? (3)
- Records are up to date.
- Proper entries are made after repairs or modifications.
- Equipment lists are updated as needed.
Management of Weight and Balance Control
What weight changes are considered negligible and do not require a weight and balance check?
- 1 lb or less for aircraft < 5,000 lbs empty weight.
- 2 lbs or less for aircraft 5,000–50,000 lbs empty weight.
- 5 lbs or less for aircraft > 50,000 lbs empty weight.
Management of Weight and Balance Control
What is negligible CG change?
- < 0.05% Mean Aerodynamic Chord (MAC) for fixed-wing aircraft.
- < 0.2% MAC for rotary-wing aircraft.
Management of Weight and Balance Control
What should a pilot determine before any flight regarding weight and balance?
The aircraft’s weight and balance condition using manufacturer-provided procedures.
Management of Weight and Balance Control
What may be required if an aircraft is fully loaded with passengers, baggage, and fuel?
Reduce fuel load or baggage to remain within approved weight and balance limits.
Management of Weight and Balance Control
What does 14 CFR part 125 require for aircraft with 20+ seats or 6,000+ lbs payload? (2)
- Weighing every 36 calendar months.
- Multi-engine aircraft under 14 CFR part 135 are also subject to this unless operating under an approved weight and balance system.
Management of Weight and Balance Control
What must mechanics ensure after a 100-hour or annual inspection?
Weight and balance data in aircraft records is current and accurate.
Terms and Definitions
What is the “arm” (moment arm)?
- The horizontal distance in inches from the reference datum line to the CG of an item.
- Positive (+) if aft of the datum, negative (–) if forward of the datum.
Terms and Definitions
Define “basic empty weight” (GAMA).
The standard empty weight plus the weight of optional and special equipment installed.
Terms and Definitions
What is the “center of gravity” (CG)?
The point at which an aircraft would balance if suspended, representing the mass center. It may be expressed in inches from the datum or as a percentage of MAC.
Terms and Definitions
What are CG limits?
The specified forward and aft points within which the CG must be located during flight, as indicated in aircraft specifications.
Terms and Definitions
Define “CG range.”
The distance between the forward and aft CG limits indicated on pertinent aircraft specifications.
Terms and Definitions
Define “datum” (reference datum).
An imaginary vertical plane or line from which all measurements of arm are taken, established by the manufacturer.
Terms and Definitions
What does “fuel load” include?
The expendable part of the load, including usable fuel but excluding trapped or line-fill fuel.
Terms and Definitions
Define “delta.”
A Greek letter (Δ) indicating a change in values. For example, ΔCG represents a change or movement of the CG.
Terms and Definitions
What is the “floor load limit”?
The maximum weight the floor can sustain per square inch/foot, as provided by the manufacturer.
Terms and Definitions
What is “licensed empty weight”?
The empty weight consisting of the airframe, engine(s), unusable fuel, undrainable oil, and optional equipment, used before GAMA standardization.
Terms and Definitions
What is the “maximum landing weight”?
The greatest weight an aircraft is allowed to have at landing.
Terms and Definitions
Define “maximum ramp weight.”
The total weight of a loaded aircraft including all fuel. It accounts for fuel burned during taxi and run-up operations.
Terms and Definitions
What is “maximum takeoff weight”?
The maximum allowable weight for takeoff.
Terms and Definitions
Define “maximum weight.”
The maximum authorized weight of the aircraft and all its equipment as specified in the TCDS.
Terms and Definitions
What is “maximum zero fuel weight” (GAMA)?
The maximum allowable weight of the aircraft, excluding usable fuel.
Terms and Definitions
What is the “mean aerodynamic chord” (MAC)?
The average distance from the leading edge to the trailing edge of the wing.
Terms and Definitions
Explain “moment.”
The product of an item’s weight multiplied by its arm, expressed in pound-inches (in-lb).
Terms and Definitions
What is the “moment index”?
A moment divided by a constant (e.g., 100, 1,000) to simplify weight and balance calculations involving large numbers.
Terms and Definitions
What is “payload” (GAMA)?
The weight of occupants, cargo, and baggage.
Terms and Definitions
What is “standard empty weight” (GAMA)?
The weight of the airframe, engines, and all fixed items, including unusable fuel and full engine oil.
Terms and Definitions
What are “standard weights”?
Established weights for items in weight and balance calculations, such as:
- Gasoline: 6 lb/US gal
- Jet A: 6.8 lb/US gal
- Oil: 7.5 lb/US gal
- Water: 8.35 lb/US gal
Terms and Definitions
Define “station.”
A location in the aircraft designated by its distance in inches from the datum, with the datum identified as station zero.
Terms and Definitions
Define “useful load.”
The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. Calculated as basic empty weight subtracted from the maximum allowable gross weight.
Principles of Weight and Balance Computations
How is the total weight of an aircraft determined?
The total weight is calculated by adding the aircraft’s empty weight to the weight of everything loaded onto it, including fuel, passengers, and cargo.
Principles of Weight and Balance Computations
How is balance achieved in weight and balance computations?
Balance is achieved when the moments on both sides of the datum equalize. For example, if a 50-pound weight is at 100 inches from the datum, producing a 5,000 in-lb moment, another set of weights can balance it as long as their combined moments total 5,000 in-lb.
Weight and Balance Restrictions
Are all aircraft equally prone to CG imbalances?
No. Some small aircraft are designed with seats, fuel, and baggage areas near the CG, making it difficult to load them out of CG limits, though they can still be overloaded in weight. Other aircraft can exceed CG limits even when the useful load is not exceeded.
Determining Loaded Weight and CG
What are the methods for determining the loaded weight and center of gravity (CG) of an aircraft?
The loaded weight and CG of an aircraft can be determined using:
- Computational Method – Performing mathematical calculations based on the weights and arms of individual components.
- Graphs and Tables – Using manufacturer-provided graphical or tabular tools to simplify the process.
Determining Loaded Weight and CG: Computational Method
How is the computational method for determining the loaded weight and CG of an aircraft applied?
The computational method involves the following steps:
- Determine and List Weights: Include weights for the aircraft, occupants, fuel, and baggage.
Example:
Weight of front seat occupants: 340 lbs
Weight of rear seat occupants: 350 lbs
Fuel: 75 gallons (AVGAS weighs 6 lbs/gallon) = 450 lbs
Weight of baggage in area 1: 80 lbs - Calculate Moments: Use the formula
Moment = Weight × Arm.
Moments are calculated for each item based on its arm distance from the datum. - Find Total Weight and Moment: Sum up the weights and moments of all components.
- Calculate CG: Use the formula
CG = TotalWeight / TotalMoment
Example: If the total weight is 3,320 lbs and the total moment is 281,216 in-lb, then:
CG = 281,216 / 3,320 = 84.8 inches - Check Limits: Verify the total weight does not exceed the maximum gross weight and ensure the CG is within the specified range (e.g., 78–86 inches in this example).
Result: If both conditions are met, the aircraft is loaded within limits.
Determining Loaded Weight and CG: Graph Method
Graph Method for Determining Loaded Weight and CG
- Gather Weight Information: List the weights for all components:
Front seat occupants: 340 lbs
Rear seat occupants: 300 lbs
Fuel: 40 gallons (AVGAS weighs 6 lbs/gallon) = 240 lbs
Baggage area 1: 20 lbs - Use the Loading Graph to Determine Moments:
Locate the weight of each item on the loading graph.
Draw a horizontal line from the weight until it intersects the line for the specific item (e.g., pilot and front passenger, fuel, baggage area).
From the intersection point, draw a vertical line downward to find the corresponding moment.
Repeat this process for all items. (See the red line example in the loading graph for the front seat occupants.) - Calculate Total Weight and Total Moment:
Add up the weights of all components to get the total weight.
Sum all the moments to determine the total moment. - Plot on the CG Envelope Graph:
Using the total weight and total moment, locate the point on the CG envelope graph.
Verify whether the point falls within the envelope. - Result: If the point is within the envelope, the aircraft is loaded within limits. In this example, the aircraft is properly loaded within the CG and weight limits.
Determining Loaded Weight and CG: Table Method
Table Method for Determining Loaded Weight and CG
- Understand the Table: The manufacturer provides tables that include allowable weights, moments, and CG limits for various configurations. Each entry in the table correlates weight with its associated moment.
- Gather Information: List the weights for all components to be loaded onto the aircraft:
Example:
Front seat occupants: 340 lbs
Rear seat occupants: 300 lbs
Fuel: 40 gallons (AVGAS weighs 6 lbs/gallon = 240 lbs)
Baggage: 20 lbs - Use the Table to Find Moments: For each weight, use the table to find the corresponding moment. Tables are designed so you can locate a weight in one column and find its moment in another.
- Calculate Total Weight and Moment:
Add up all weights to get the total loaded weight.
Sum all moments from the table to get the total moment. - Check Limits: Compare the total weight and moment with the limits provided in the table.
Ensure the weight does not exceed the maximum allowable weight.
Ensure the moment falls within the allowable range for that weight. - Example Result: In the given example, the total weight of 2,799 lbs and moment of 2,278/100 (i.e., 22,780 inch-pounds) fall within the specified limits of the table, confirming the aircraft is loaded within limits.
Determining Loaded Weight and CG: Computations With a Negative Arm
How do computations with a negative arm differ?
It is important to remember that a positive times a negative equals a negative, and a negative would be subtracted from the total moments.
Determining Loaded Weight and CG: Computations With a Negative Arm
What is the purpose of computing zero fuel weight (ZFW)?
To ensure that the total weight of the aircraft, excluding usable fuel, does not exceed the maximum zero fuel weight limit, preventing structural overloading.
Determining Loaded Weight and CG: Computations With a Negative Arm
How do you compute the zero fuel weight (ZFW)?
Add the basic empty weight, occupants, baggage, and other payload items, excluding usable fuel.
Determining Loaded Weight and CG: Computations With a Negative Arm
What must you do if the zero fuel weight exceeds the limit?
Reduce payload, such as passengers or cargo, to bring the weight within the allowable limit.
Shifting, Adding, and Removing Weight
What can a pilot do if the aircraft is loaded within the allowable weight limit but exceeds CG limits?
Shift baggage, passengers, or cargo to correct the CG imbalance.
Shifting, Adding, and Removing Weight
What is the formula for calculating the amount of weight to shift to correct a CG imbalance?
Weight to Shift = (Total Weight × ΔCG) / Distance Moved
Where:
* Total Weight is the total weight of the aircraft.
* ΔCG is the difference between the current CG and the desired CG.
* Distance Moved is the distance between the current location of the weight and the new location.
Shifting, Adding, and Removing Weight
How do you determine if adding weight to a new location will correct a CG imbalance?
Calculate the new moment of the aircraft after adding the weight and check if the resulting CG falls within the allowable range.
Shifting, Adding, and Removing Weight
What should be done if removing weight is required to bring the CG within limits?
Recalculate the total weight and CG after removing the specified weight and ensure the new CG is within the acceptable range.
Shifting, Adding, and Removing Weight
What happens to the total weight and total moments of the aircraft when weight is shifted?
The total weight remains unchanged, but the total moments change in relation and proportion to the direction and distance the weight is moved.
Shifting, Adding, and Removing Weight
What happens to the total moments when weight is moved forward?
Total moments decrease.
Shifting, Adding, and Removing Weight
What happens to the total moments when weight is moved aft?
Total moments increase.
Shifting, Adding, and Removing Weight
How do you calculate the change in moments when weight is shifted?
Change in Moments = (Weight) × (Difference in Stations)
For example:
* If 100 lb is shifted from station 30 to station 150:
* Moment at station 150 = 100 × 150 = 15,000 in-lb
* Moment at station 30 = 100 × 30 = 3,000 in-lb
* Moment change = 15,000 - 3,000 = 12,000 in-lb
Shifting, Adding, and Removing Weight
How do you find the new total moments after weight is shifted?
New Total Moments = Original Moments ± Moment Change
For example:
* Original Moments = 616,000 in-lb
* Moment Change = +12,000 in-lb
* New Total Moments = 616,000 + 12,000 = 628,000 in-lb
Shifting, Adding, and Removing Weight
How do you calculate the new CG after weight is shifted?
New CG = (New Total Moments) ÷ (Total Weight)
For example:
* New Total Moments = 628,000 in-lb
* Total Weight = 8,000 lb
* New CG = 628,000 ÷ 8,000 = 78.5 in
Shifting, Adding, and Removing Weight
What is a proportional formula for calculating the shift in CG due to weight movement?
Shift in CG = (Weight Shifted × Distance Shifted) ÷ Total Weight
For example:
* Weight Shifted = 100 lb
* Distance Shifted = 150 in - 30 in = 120 in
* Total Weight = 8,000 lb
* Shift in CG = (100 × 120) ÷ 8,000 = 1.5 in
New CG = Original CG ± Shift in CG.
Shifting, Adding, and Removing Weight
How do you calculate the new CG when weight is added or removed?
- Calculate the moment for the added/removed weight:
Moment = Weight × Arm (distance from the datum) - Adjust the total weight and total moments:
New Total Weight = Original Weight ± Added/Removed Weight
New Total Moments = Original Moments ± Added/Removed Moments - Calculate the new CG:
New CG = New Total Moments ÷ New Total Weight
Shifting, Adding, and Removing Weight
What determines whether the moment of added or removed weight is added to or subtracted from the total moments? (3)
- If weight is added aft of the CG, the moment is added to the total moments.
- If weight is added forward of the CG, the moment is subtracted from the total moments.
- If weight is removed, the opposite adjustments are made.
Shifting, Adding, and Removing Weight
How do you decide whether to add or subtract the change in CG (
Δ
𝐶
𝐺
ΔCG) to/from the old CG?
- If the CG shifts aft, add ΔCG to the old CG.
- If the CG shifts forward, subtract Δ𝐶𝐺 from the old CG.
