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Airworthiness
and
Aircraft Loads
13-Mar-14 1 RM
The airworthiness of an a/c is concerned
with safety incorporation/application in all
aspects of its:
construction
operation.
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These range from structural strength to the
provision of certain safeguards in the events
crash landing.
It include design requirements relating to
aerodynamics, performance and electrical
and hydraulic systems.
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Structural aspect of airworthiness of a flying
vehicle depends mainly on:
strength
stiffness
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Strength problems arise from
ground loads
air loads
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Strength problems arise from
ground loads
air loads
and their
magnitude depends on the
selection of maneuvering
other conditions applicable
to the operational requirements of a
particular a/c.
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What is Load Analysis
The task of loads analysis
o Loads analysis largely means establishing
appropriate loads for design and testing
The goal or purpose of loads analysis
o Nearly always to support design or to verify
requirements for designed or built hardware.
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Airplanes loads come from diverse sources.
These include:
Component and payload weight
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Airplanes loads come from diverse sources.
These include:
Component and payload weight
Air loads
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Airplanes loads come from diverse sources.
These include:
Component and payload weight
Air loads:
Lift
Drag
gusts
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Drag Drag
Lift Lift
Mo
CP AC
CP
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Drag Drag
Lift Lift
Mo
CP AC
CP
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Span-wise
Lift
Distribution
Chord-wise
Lift
Distribution
Wing lift distribution
Span-wise
Lift
Distribution
Chord-wise
Lift
Distribution
Span-wise
lift distribution
Chord-wise
lift distribution
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Span-wise
Lift
Distribution
Chord-wise
Lift
Distribution
Wing lift distribution
Span-wise
Lift
Distribution
Chord-wise
Lift
Distribution
Span-wise
lift distribution
Chord-wise
lift distribution
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Airplanes loads come from diverse sources.
These include:
Component and payload weight
Air loads:
lift, drag, gusts
Acoustic loads
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Acoustic Loads
During the lift off and the early phases of the
launch an extremely high level of acoustic
noise surrounds the payload
The principal sources of noise are:
Engine running
Aerodynamic turbulence
Acoustic noise (as pressure waves) affecting
on light weight panel-like structures produce
high response
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Airplanes loads come from diverse sources.
These include:
Component and payload weight
Air loads:
lift, drag, gusts
Acoustic loads
Thermal loads
13-Mar-14 RM 18
Airplanes loads come from diverse sources.
These include:
Component and payload weight
Air loads:
lift, drag, gusts
Acoustic loads
Thermal loads
space
fast vehicles
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Airplanes loads come from diverse sources.
These include:
Component and payload weight
Air loads:
lift, drag, gusts
Acoustic loads
Thermal loads
Landing loads
13-Mar-14 RM 20
Airplanes loads come from diverse sources.
These include:
Component and payload weight
Air loads:
lift, drag, gusts
Acoustic loads
Thermal loads
Landing loads:
touchdown
arresting 13-Mar-14 RM 21
Take-off loads
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Take-off loads:
runway taxi
assisted (e.g. jet/rocket) take-off
catapult
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Catapult
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Take-off loads:
runway taxi, catapult, assisted (e.g.
jet or rocket) take-off
Power plant loads
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Take-off loads:
runway taxi, catapult, assisted (e.g.
jet or rocket) take-off
Power plant loads:
thrust
engine torque
gyroscopic effects
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Gyroscopic effects
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Take-off loads:
runway taxi, catapult, assisted (e.g.
jet or rocket) take-off
Power plant loads:
thrust, engine torque, gyroscopic effects
special loads:
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special loads:
towing
refueling
cargo
weapons recoil
bomb release
missile/rocket fired
blast effects
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Other loads:
cabin pressure
Turbulences
crash safety…
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Flight Loads
Maneuver
Gust
Control deflection
Buffets (winds strike)
Inertia
Vibration
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Ground Loads
Vertical load factor
Braking
Bumps
Turns
Catapult
Arrested landing
Aborted take off
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Spin-up gears
Spring back gears
One wheel/two wheel
Towing
Ground winds
Break away
Other Loads & Conditions
Fatigue
Fall safety
Damage tolerance
Bird strikes
Lightning
Wind milling
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Thermal
Jacking
Pressurization
Power plant
Hail
Ground handling
Principal Aerodynamic loads on an Aircraft
Wings, tail-plane and fuselage are
subjected to:
bending loads
shear loads
torsion loads
and must be designed to withstand
them at minimum weight
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For spacecraft, the following additional loads
are encountered:
Launch loads
boost
orbit transfer
On orbit loads
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Aircraft Mission and Stages
Applied loads depends on the mission of the
aircraft, e.g.:
Transport
Fighter
Aerobatic mission
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The stages during any aircraft mission can be
roughly divided into:
Taxi and take off
Cruising
Maneuver
Landing
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Design loads must be carefully established
for every stage of the aircraft mission.
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The objectives of structural design is to
maintain the shape and integrity of the
aircraft during each part of the mission and
stage.
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Factor of Safety
Flight Envelope
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The a/c designer is constantly seeking to
reduce the a/c weight to a minimum
compatible with safety.
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To ensure general minimum standards of
strength and safety, airworthiness regulations
(CAA) lay down several factors which the
primary structure of the a/c must satisfy.
These are
limit loads
proof loads
ultimate loads
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Limit load is the maximum load that an a/c is
expected to experience in normal operation.
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Limit load is the maximum load that an a/c is
expected to experience in normal operation.
The proof load is product of the limit load
and the proof factor (1 - 1.25)
13-Mar-14 44 RM
Limit load is the maximum load that an a/c is
expected to experience in normal operation.
The proof load is product of the limit load
and the proof factor (1 - 1.25)
Ultimate load is product of limit load and the
ultimate factor (usually 1.5)
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The a/c structure must:
withstand the proof load without
damaging distortion
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The a/c structure must:
withstand the proof load without
damaging distortion
not fail until the ultimate load has
been achieved.
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The proof and ultimate loads may be
regarded as
factors of safety
and provide for various contingencies &
uncertainties etc.
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Factor of safety =
FoS =
MoS = - 1
= FoS - 1
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= Margin of Safety =
