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Presented by: Kyle Black Carol Cushman. Weight & Balance. Weight & Balance. Why is weight and balance so important?. Center of Gravity (CG). What does Center of Gravity mean? The imaginary point where the aircraft would balance if suspended.
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Presented by: Kyle Black Carol Cushman Weight & Balance
Weight & Balance Why is weight and balance so important?
Center of Gravity (CG) • What does Center of Gravity mean? • The imaginary point where the aircraft would balance if suspended. • The location of this point is critical to an airplane’s stability and elevator effectiveness. • Greatly impacts how the aircraft performs.
Center of Gravity Envelope • What is meant by the Center of Gravity envelope of an airplane? • Why is this envelope so important?
Center of Gravity Envelope • How do we determine if our aircraft’s CG is within the envelope?? • We calculate our Center of Gravity before every flight!
Weight & Balance Terminology Basic Empty Weight: • Includes the weight of the standard airplane, optional equipment, unusable fuel, and full operating fluids including full engine oil. Unusable Fuel: • The smallest amount of fuel in the tanks and fuel lines that cannot be used in flight or drained on the ground. Licensed Empty Weight: • Similar to Basic Empty Weight, except that it does not include full engine oil. It counts only undrainable oil. • Used on older aircraft.
Weight & Balance Terminology Ramp Weight: • The term used to describe the airplane loaded for flight prior to engine start. The total weight of the aircraft as it sits on the ramp. Takeoff Weight: • The weight of the aircraft just before you release the brakes to begin the takeoff roll. • Subtract the fuel burned during engine start, runup, and taxi. Landing Weight: • The weight of the aircraft just before touchdown. • Takeoff weight minus the fuel burned in route.
Weight & Balance Terminology Max Ramp Weight: 803,000 lbs. Max Takeoff Weight: 800,000 lbs. Max Landing Weight: 654,000 lbs.
Weight & Balance Terminology Max Ramp Weight: 2558 lbs. Max Takeoff Weight: 2550 lbs. Max Landing Weight: 2550 lbs.
Weight & Balance Terminology Useful Load: • The amount of weight that the aircraft can carry in flight crew, passengers, baggage, cargo, and usable fuel. • Max Takeoff Weight – Basic Empty Weight = Useful Load Payload: • The weight of passengers, baggage, and cargo. • Anything the person is “paid to transport.” Useable Fuel: • The fuel available for use during flight. • Must account for it’s weight while computing weight and balance.
Weight & Balance Terminology Standard Weights: Fuel: 6 lb/US Gal Jet A / Jet A-1: 6.8 lb/US Gal Oil: 7.5 lb/US Gal Water: 8.35 lb/US Gal
Weight & Balance Terminology Terms for Calculating Weight & Balance: • Datum • Weight • Arm • Moment
Weight & Balance Terminology • Reference Datum: • An imaginary vertical plane from which all horizontal distances are measured for balance purposes.
Weight & Balance Terminology • Weight: • A measure of the heaviness of a particular object. • Accuracy counts when computing aircraft weight and balance. • How much do you trust your passengers??
Weight & Balance Terminology • Arm: • The horizontal distance in inches from the reference datum line to the center of gravity of an item. • The algebraic sign is plus (+) if measured aft of the datum, and minus (–) if measured forward of the datum. • Experiment: • Try holding your Jeppesen book with your arm extended straight out for 5 minutes. • What happens if you bring the book to your chest and try to hold it for 5 minutes?
Weight & Balance Terminology • Moment: • The product of the weight of an object multiplied by its arm. • Expressed in pound-inches (lb.-in). • Total moment of an aircraft is it’s weight multiplied by the distance between the datum and the CG. • Moment Index (Index) • The moment divided by a constant such as 100, 1000, or 10,000. • The purpose of using an index is to simplify weight and balance calculations. • Makes huge numbers more manageable.
Calculating the Position of the CG • Computation Method • Listing all weights, their respective arms, and calculate the moment of each. • Must include: • Airplane • Pilot • Passengers • Baggage • Fuel • Cargo
Computation Method • Step 1: • List each item and their weight • Then total the weights to ensure the total weight is below the Max Ramp Weight.
Computation Method • Step 2: • Determine the Arm (Station) for each item
Computation Method • Step 3: • Calculate the moments of each item. • Then total all of the moments.
Computation Method • Step 4: • Determine the Center of Gravity by dividing the Total Moment by the Total Weight. • This will give you the location of the CG in inches aft of the datum.
Computation Method • Step 5: • Verify that the computed Center of Gravity is within the Center of Gravity envelope. • How do we check to ensure we are within limits?
Calculating Weight & Balance • What other way could we calculate Weight & Balance? The Table Method Graph Method
Table Method • The idea is the same, but instead of calculating Moments they are listed in tables next to the corresponding weights. • See next slide.
Graph Method • Instead of calculating by hand or using a table, the graphing method utilizes a graph to make the calculation for you. • See next slide.
Advantages/Disadvantages • Discuss some Advantages/Disadvantages of: • The Computation Method • The Table Method • The Graph Method
What now? • During your preflight, being the responsible pilot that you are, you calculate weight and balance for your flight and realize that you are over the Max Weight allowable by the Pilot Operating Handbook. What can you do to get the airplane within limits? • Kick your significant other out of the airplane? • Quick do 20 laps around the ramp to lose as much weight as you can before the flight? • Take a reduced fuel load, leave some baggage…
What now? • You figured out a way to lose the extra weight and bring your total weight within limits, but you realize that your Center of Gravity is just aft of the limit allowed by the Center of Gravity envelope. You decide you’re going to move passengers and bags around to bring the CG within range. Does this mean you have to go through the entire process of calculating your new CG??
Weight-Shift Formula • Following the Weight-Shift formula helps you to compute exactly what is necessary to bring the CG within limits.
Weight Shift Formula • Example: • Your CG is aft by 2 inches so you decide to move weight from the back seat to the front seat. What is the minimum amount of weight you must move forward to bring the CG in range? • Airplane weights 2500 lbs. • The difference between the front seat and back seat is 36 inches.
What now? • While preparing the night before your flight you decide to complete the weight and balance in order to save time before your flight. The next day you meet your friend at the airport for the flight. When you arrive you are completely shocked by the size of suitcase she brought for the weekend trip. You had planned for a 30 lb. bag but her bag is clearly pushing 100 lbs. Is your CG going to be affected? How much?
Weight Addition/Removal • Luckily you are an intelligent, competent pilot and this problem doesn’t even phase you. Using the Weight Addition/Removal formula you are easily able to make sure that her ridiculously large suitcase won’t be an issue.
Weight Addition/Removal • Aircraft Weight = 2430 lbs. (Max Takeoff Weight for Cessna 172 is 2550) • Current CG = 44.5 (CG Range for Cessna 172 is 41.0” to 47.3”) • Expected Baggage = 30 lbs. • Actual Baggage = 100 lbs. • Baggage Area A arm is 95.0” • How much will the CG change? • Will the CG move forward or aft? • What is the new CG? • Is it within limits?
Effect of Weight & Balance on Performance/Stability • How will our airplane be affected by weight? • How will our airplane be affected by the location of the Center of Gravity?
Effect of Weight & Balance on Performance/Stability • How will an increased weight affect performance? • Higher takeoff speed required • Longer takeoff run required • Reduced rate and angle of climb • Shorter range • Reduced cruising speed • Reduced maneuverability • Higher stalling speed • Higher landing speed required • Longer landing roll required
Effect of Weight & Balance on Performance/Stability • How will a forward Center of Gravity affect performance? • Performance DECREASE • With a forward center of gravity, a greater downward force on the tail is required to maintain level cruising flight. • The total lift required from the wing is increased. • The wing must fly at a higher angle of attack, which results in more drag and a higher indicated stall speed. • How will a forward Center of Gravity affect stability? • Stability INCREASES • Essentially the aircraft “feels” or behaves as if it is heavier. A heavier aircraft resists movement to outside forces. • As the CG moves forward, the airplane becomes more nose-heavy. • If the CG is moved beyond the forward limit, the elevator may no longer be able to hold the nose up, particularly at low airspeeds, e.g., takeoff, landing, and power-off glides.
Effect of Weight & Balance on Performance/Stability • How will an aft Center of Gravity affect performance? • Performance INCREASES • With an aft center of gravity, less downward force on the tail is required, resulting in less lift required by the wing. • The wing flies at a lower angle of attack with less drag and a higher cruise speed. • How will an aft Center of Gravity affect stability? • Stability DECREASE • An airplane becomes less stable as the CG moves aft. • The elevator has a shorter arm (i.e., distance) from the CG and requires greater deflection to produce the same result. • Recovery from a stall is more difficult because the airplane’s tendency to pitch down is reduced. • If the CG is moved beyond the aft limit, stall and spin recovery may become impossible.
Time to Practice • Time to practice a weight and balance calculation for a Cessna 172! • Aircraft (As calculated by maintenance) • Weight = 1733.7 • Moment = 71,907.0 • Weights: • Pilot = 200 lbs. • Front Passenger = 145 lbs. • Rear Passenger = 125 lbs. • Baggage = 50 lbs. • Fuel = 35 US Gal. • Fuel Used in Flight = 25 US Gal • CG Range: • 4o.o” to 47.3”
The End! • Any questions??