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ASAE > Chapter 3 External Loads > Flashcards

Chapter 3 External Loads Flashcards

1
Q

external loads

A

applied loads like aerodynamics, inertia, engine thrust, etc.

external and internal forces are in equilibrium

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2
Q

internal loads

A

counter react to the external forces

external and internal forces are in equilibrium

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3
Q

design loads (aerospace context)

A

forces applied to the structure components to establish the strength safety level of the complete aerospace vehicle

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4
Q

4 aircraft load cases

A

manoeuver

dynamic: gust, turbulence, buffer

ground handling: landing impact, taxi, break, turn, tow, jack, hoist

special: crash, failure

depend on the aircraft type and planned usage described in the Structur Design Criteria (SDC)

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5
Q

5 aircraft load sources

A

aerodynamics: lift, drag, speed, altitude, airfoil, trimming conditions

inertia: mass distribution, centre of gravity, accelerations

engine: thrust

landing gear: aircraft mass, sink rate, type of landing gear

special loads: engine and control surface faults

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6
Q

aircraft loads analysis

A

sources -> load case -> trimming (equilibrium) -> load case categories

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7
Q

Mach number

A

quantity defined as the ratio of the local flow velocity to the local speed of sound

indicates the flow compressibility (air is compressible from around M = 0.3)

M < 0.8 subsonic
0.8 < M < 1.2 transonic
1.2 < M < 5.0 supersonic
5.0 < M < 10 hypersonic
10 < M < 25 high hypersonic
25 < M re-entry speeds

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8
Q

Reynold’s number

A

helps to predict the flow patterns in different fluid flow situations

represents the importance of viscosity

low R: laminar flow, low drag
high R: turbulent flow, high drag

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9
Q

optimal lift distribution

A

for rigid wings: elliptic

but wings are not rigid

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10
Q

infinite vs finite wing

A

lift and drag polars are determined for infinite wings

in finite wings - due to tip vortices the lift slope curve is reduced (downwash effect) and induced drag is generated

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11
Q

aircraft mass categories

A

75% non-structural mass (engine, fuel, equipment, painting, fairings, etc.)

25% structural mass (primary structure (skin, stringers, spars, ribs, frames, floors, joints, etc.), secondary structure (pad-ups, rivets, bolts, nuts, etc.))

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12
Q

aircraft mass configurations

A
  1. minimum take-off weight
  2. basic flight design mass
  3. maximum wing zero fuel mass
  4. maximum design mass
  5. minimum flying mass
  6. landing design mass

mass changes during operation

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13
Q

XYZ

A

X: roll
Y: pitch
Z: yaw

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14
Q

trimming

A

procedure of bringing all the applied external loads into equilibrium in order to fly a steady manoeuver

main contributors:
F_x -> thrust, drag, inertia
F_y -> rudder, lift, thrust, inertia
F_z -> lift, weight
M_x -> aileron, inertia
M_y -> elevator
M_z -> rudder

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15
Q

unknown trimming variables

A
  1. angle of attack (alfa)
  2. yaw angle (beta)
  3. tailplane angle of attack (alfa_T)
  4. rudder deflection (chi)
  5. deflection of elevator (eta)
  6. deflection of any other control surface (gamma)
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16
Q

structure design criteria (SDC)

A

define, among others, the maneuvers, speeds, useful load, aircraft design weights

include V-n diagram (flight envelope)

17
Q

V-n diagram

A

flight envelope

V: velocity
n: load factor

shows the capabilities of a design in therms of airspeed and load factor

defined for each critical combination of altitude and weight

18
Q

load factor n

A

n = lift / inertia force = L / mg

ratio of the lift of an aircraft to its weight

represents a global measure of the “load” to which the structure of the aircraft is subjected

19
Q

limit load

A

maximum expected load during operation

no permanent structural deformation or damage allowed

NEVER DESIGN FOR LIMIT LOADING

20
Q

ultimate load

A

limit load x safetu factor (1.5)

maximum structural load above which structural failure can occur

between limit load and ultimate load local damages and permanent deformations are allowed

21
Q

gust

A

sudden, brief increase in speed of the wind

dynamic load case

the faster the aircraft the less severe the gust

sharp edge gust, ramped gust, 1-cos gust

different gust speeds at different altitudes

22
Q

landing gear loads categories

A
  1. landing impact
  2. other ground handling (taxi, take-off, etc.)
23
Q

landing conditions

A
  1. level landing conditions (three-point landing, two-point landing, one-point landing)
  2. taildown landing
24
Q

sink rate

A

velocity of aircraft descend

design limits:
3.05 m/s at landing weight
1.83 m/s at maximum take-off weight

25
Q

assumed friction coefficient between the tires and the ground

A

0.8

26
Q

landing speed

A

at a standard day (15 C) at sea level:
V_landing = V_stall_speed + V_tail_wind = V x L_1

at a hot day (37.8 C) at the highest altitude the aircraft is allowed to land:
V_landing = 1.25 x V x L_2 + V_tail_wind

V_stall_speed is the slowest an aircraft is allowed to fly

V_tail_wind = 0 when aircraft is certified for tail winds of <19 km/h
V_tail_wind =/= 0 when aircraft is certified for tail winds >19 km/h

27
Q

on a hot day …

A

… you need higher speed to achieve the same lift as on a standard day

28
Q

standard day parameters

A

temperature: 15 C
density: 1.225 kg/m^3
pressure: 1 atm = 101.325 kPa
viscosity: 17.3 x 10 ^ (-6) Ns/m^2

29
Q

two-point landing conditions

A

main wheels contact the ground with the nose wheel just clear of the ground

provides maximum loads at main landing gear

30
Q

three-point landing conditions

A

nose and main wheels contact the ground simultaneously

provides maximum loads at the nose gear

31
Q

inertia (bezwładność)

A

capacity of an object to resist changes in motion (Newton’s First Law)

force is required to initiate or terminate motion; in absence of force constant velocity is maintained

force acting against acceleration of a mass m

added in the context of non-inertial reference frames to account for the effects of acceleration of the frame itself

fictitious force

32
Q

inertial reference frame

A

an object we assume is not moving and with respect to which we assess motion

e.g. earth

33
Q

aerodynamic loads depend on …

A

… air density, air speed, structure geometry and orientation

34
Q

aerodynamic loads

A

normal stress due to fluid pressure

shear stress due to skin friction (viscosity + surface roughness)

35
Q

airspeeds

A

GS: ground speed - speed relative to the ground
IAS: indicated airspeed - uncorrected airspeed
CAS: calibrated airspeed - IAS corrected for installation and instrument errors
TAS: true airspeed - CAS corrected for deviations from standard atmosphere conditions and compressibility effects
EAS: equivalent airspeed - speed of equivalent dynamic pressure at sea level as TAS at currsent altitude

36
Q

control surfaces

A
  1. ailerons: roll and increase drag on one of the wings and increase lift on the other
  2. elevator: pitch
  3. rudder: yaw
  4. spoiler: reduces lift
  5. flaps: raise max. lift coefficient
  6. slats: reduce stalling speed
  7. air brakes: increase drag

ASAE (9 decks)

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