Ch 6 - The Effect Of Mass An Its Distribution Flashcards
If an aircraft is too heavy:
V speeds will be impacted
Rate of climb decreases
Gradient of climb decreases
Lower cruise ceiling therefore decreased efficiency
Increased Fuel Burn
Decreased Range
Too Heavy effects 2:
Landing roll will be longer
Lower approach speed, margins above the threshold will be lower
Increased breaks and tire wear
Increased landing speed
CG Too Far Aft effects
Pitching up moment which could be a problem for TO - Tailstrike
Decreased longitudinal Static Stability
Decreased cruise fuel burn due to there being less trim drag
Stall speed will reduce
Poor landing characteristics
Range and endurance increased
Insufficient nose down authority
Forces Experienced by an airframe
Twisting (Torsion)
Tension (stretching)
Compression
Shear
An AC will be exposed to multiple stress inputs at the same time
If there is a large enough stress - the airframe could fail (break/snap)
Ultimate Load Limit
Is based on the load factor
The airframe will start to fail at this point
Design load limit has a 50% safety factors over and above the ultimate load limit
Fatigue
Metal fatigue is caused by multiple applications of stress below the ultimate load limit
Can cause the structure to eventually fail well below the ultimate limit
Cycles of compression/tensions produce fatigue rapidly when the stresses are larger
A med-long term source of damage
Fatigue Life
Determined by the manufacturer based on the number of hours flown or number of fatigue cycles (TO and landings)
How do we protect against failure
Observe mass limits
AC have multiple load bearing paths so if something breaks somewhere, the structure isn’t totally failed
Overloading on performance
The basic stall speed will increase along with all other v speeds apart from V1
Reduced acceleration and deceleration
Reduces the rate and angle of climb
Overloading on TO
Reluctant to rotate and lift off
Takes longer to accelerate and rotate
Fail to become airborne
Overloading on Climb
Unable to achieve the required obstacle clearance
Lift off point closer to the obstacles
Climb gradient becomes shallower
Overloading on Cruise
Decreased Max speed
Decreased max ceiling
Increased Drag
Increased Fuel consumption
Decreased range and endurance
Decreased manoeuvrability
Overloading on Landing
Faster approach speed
Increased landing speed
Longer landing run
Brake fade caused by heating of the breaks
Overloading on Landing Gear
Can cause SEV tyre wear
Tyres may fail
Severe break wear
Wing spar failure (in the most extreme cases)
CG and CG position
Where the mass is considered to be concentrated
Weight acts through CG
Pitches/rolls/yaws around CG (in flight)
CG changes with mass distribution (fuel consumption)
Acceptable range of CG is determined by manufacturer (%MAC)