Lesson 5 Weight and Balance

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The Top 10 Actual Transmissions Made in the O’Hare TRACON

  1. “Citation 123, if you quit calling me center, I’ll quit calling you twin Cessna.”
  2. “If you hear me, traffic is no longer a factor.”
  3. “I am way too busy for anybody to cancel on me.”
  4. “Don’t anybody maintain anything.”
  5. “Air Force One, I told you to expedite.”

The Top 10 Actual Transmissions Made in the O’Hare TRACON

  1. “Put your compass on ‘E’ and get out of my airspace.”
  2. “You got any more smart remarks, we can do this over South Bend…go ahead.”
  3. “Climb like your life depends on it…Because it does.”
  4. “You’re gonna have to key the mike, I can’t see you when you nod your head.”
  5. “Listen up, gentlemen, or something’s going to happen that none of us wants to see. Besides that your p–ing me off.”

Terms

Reference datum- imaginary vertical plane from which all horizontal distances are measured

Station- a designated location on the fuselage measured from the reference datum

Terms

Empty weight- the weight of the aircraft with all the necessary equipment installed does not include people or baggage

Basic empty weight- the weight of the aircraft with all equipment, oil and unusable fuel does not include people or baggage

Terms

Max ramp weight- max weight of aircraft for taxi operations (it includes start taxi and runup fuel)

Max takeoff weight- max weight approved for the start of the takeoff run

Terms

Useful load- difference between take off weight and basic empty weight

Payload- weight of the occupants, cargo and baggage

Zero fuel weight- weight exclusive of usable fuel useful for calculations when fuel is a variable

Terms

Tare- weight of chocks, blocks, stands ect used when weighing an aircraft

Arm- the horizontal distance from the reference datum

Moment- the force exerted by a weight using an arm usually measured in in/lbs or foot/lbs

Terms

Center of gravity- the point at which an airplane would balance if suspended from that point

Principles Of Weight And Balance

Principles Of Weight And Balance

Useful Facts

Fuel weighs 6lbs per gallon

Oil weighs 7.5lbs per gallon

That’s 1.875lbs per quart

Weight x Arm = Moment

Where Do I Start?

Start by finding the Basic Empty Weight, Arm and Moment

Located in the Aircraft POH (Weight and Balance Chapter) in that particular airplane

BEW = 1520.85 lbs

ARM = 111.71 inches

MOM = 1698.94

Second Step, Front Seats

170@108 and 190@112

Third Step, Rear Seat

10@142

Fourth Step, Usable Fuel

40-2.6=37.4 gallons

Be Aware!

Note: the baggage and rear seat are the same arm

Fifth Step

Subtract out fuel for taxi and takeoff

We use 1 gallon or 6 lbs

 

Where’s The Beef?

Find your weight and see if your moment is within the two moment values listed

For takeoff W=2109.25 M=2365.07

For landing W=2037.25 M=2280.83

The Cessna Way

Always read the fine print!

High Gross Weights

Longer takeoff run

Shallower climbs

Faster touchdown speed

Longer landing roll

Overheating in climb

High Gross Weights

Added wear on engine

Increased fuel consumption

Slower cruising speeds

Reduced range

High Gross Weights

It is a violation of FAR’s to exceed gross weight limits

Limit load factors normal 3.8 -1.52 utility 4.4 -1.76 aerobatic 6.0 -3.0

These can be exceeded easily if overloaded

High Gross Weights

For example,2150 lbs. At 3.8 g’s is 8170 lbs.

At 100lbs over gross, 2250 at 3.8g’s is 8550

For a difference of 380 lbs!

Stall, spin, die

High Gross Weights

Over loading may accelerate metallic fatigue failures

Baggage floor may have limits on weight for structural reasons

Stability may be effected to the negative if overloaded

High gross weights

The higher the gross weight the higher the stall speed

Less reserve angle of attack

Load distribution

Safety

Manufacturer sets limits for controllability and maneuverability

Certification procedures demand a certain amount of oscillations before dampening out this determines where the aft cg is located

W&B Aerodynamics

Tail down force

Forward cg gives:

Higher stall speed,

Higher elevator control forces (critical in takeoff and landing phase),

W&B Aerodynamics

Slower cruise,

More overall stability,

Longer takeoff and landing distance,

With an aft cg recovery from a stall spin harder or impossible.

Opposites are true for aft cg

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