Fatigue and Stress | Landing Gear Flashcards
Side loads in cross winds should be __% of the vertical load combined with __% of the maximum ground reaction and __% of drag load
25 75 40
__ft/sec at the design landing weight should be capable of being absorbed
10, combined with a maximum aft drag component of 25%
__ft/sec at the design take off weight should be capable of being absorbed
6, combined with a maximum aft drag component of 25%
Fatigue life of a gear assembly is expressed as mean times between ___ and ___.
overhaul or replacement
The fatigue life of a gear assembly is affected by ___
- Gear up and down cycle
- Vibration from
- Wheels out of balance
- Airframe
- Corrosion
Surfaces used for aircraft must be ___ and ___
strong drained
The runway must be cored with grooves _ inches apart
2
ACN must not exceed the ___
PCN
The ___ expresses the relative effect of an aircraft on a runway pavement for a specified standard sub grade category
ACN
The ACN is twice the ___ ___-___ ___ expressed in kilograms, with single wheel tyre pressure standardised at 1.25 megapascals.
derived single-wheel load
The derived single-wheel load is a function of the ___-___ ___
sub-grade strength
The ACN covers four subgrades for flexible or rigid pavements:
- High
- Medium
- Low
- Ulta low
The reported PCN indicates that an aircraft with an ACN ____ ____ ____ ____ ____that can operate on the pavement, subject to tyre pressures and all up mass.
equal to or less than
For an aircraft with a ramp mass equal to or less than 5700kg, the following information is reported.
- Max allowable aircraft mass
- Max allowable tyre pressure
The PCN is expressed as a ___ part code, separated by forward slashes
5
The first letter expresses the ___ ___ of the pavement
assessed strength
The second letter is a _ or _, and shows whether the pavement has a rigid or flexible design
R F
A rigid surface is made of ___
concrete
A flexible surface is made of ___
asphalt
The third letter is a letter from _ to _ expressing the strength of what is underneath the pavement, called the ___.
A D subgrade
A subgrade of A is ___
very strong
A subgrade of D is ___
very weak
The fourth part of the code can be a letter or number expressing the ____
maximum tyre pressure that the pavement can support
Class W has a max tyre pressure of ___
No limit
Class X has a max tyre pressure of ___
1.5 MPa
1.5 MPa is ___ psi
217
Class Y has a max tyre pressure of ___
1.0 MPa
1.0 MPa is ___ psi
145
Class Z has a max tyre pressure of ___
0.5 MPa
0.5 MPa is ___ psi
72
The fifth part describes how the ___ value was worked out
first
A fifth letter T means a ___ ___
technical evaluation
A fifth letter T means ___
usage
A PCN of 80/R/B/W/T means that ___
- The underlying concrete has a bearing strength of 80
- Rigid
- Medium subgrade
- No limit on tyre pressure
- Calculated via technical evaluation
One reason why multiple gear systems are used on jets is to distribute weight and ___ the ACNs
lower
Conventional landing gear are those with a pair of wheels ___ of the centre of gravity with a ___ tailwheel
ahead swivelling
Tricycle undercarriage has the main gear ___ the centre of gravity
behind
Tricycle undercarriage allow you to use __ speeds for takeoff and landing
higher
Slender machines are held down on the ground aerodynamically as the wings are held ___ the zero lift line
below
Slender aeroplanes with large pitching inertia take ___ to respond to elevator inputs, so the undercarriage must be made ___ in case of a late flare on landing.
longer, stronger
Emergency extension can be done using ___ ___
compressed nitrogen
Main undercarriage units are locked down by ____ and ___ ___ ___ ___
mechanical and overcentre geometric locks
The overcentre mechanism stops the lever from moving back to its original position once it has passed the ___ ___ of its arc without more effort than was used in the first place
mid point
Landing gear cannot be retracted on the ground because the electrical control system is either routed through the ___ __ ___ switch or a latch on the main gear.
weight on wheels
Undercarriage safety switches are aka ___ switches
squat
Weight-on-wheels switches are normally micro or magnetic proximity switches mounted on the ___ ___
torsion link
A secondary method of stopping the gear being selected up when on the ground is with ___ ___ ___
ground locking pins
Ground locking pins can also be used for:
- Prevent use of reverse thrust in flight
- Control outflow valves on the ground
- Stop air-frame anti-icing being used on the ground
- Enable auto-spoilers to deploy, plus autobrakes
- Control electrical output to some anti-icing systems
- Record landing
A retractable landing gear unit will normally have an oleo-pneumatic shock absorber strut, supported by a ___ ___ which is fixed to a strengthened box section in the fuselage.
trunnion bearing
Wheel bays are ____
unpressurised
The oil supplies a ___ effect and the nitrogen a ___ effect in the oleo-pneumatic strut by absorbing the initial shock of landing.
damping, springing
The bounce or release of landing inertia is called ___
recoil
The rate of oleo extension is controlled by the ___
oil
If the oleo leg is too ___, you have not enough nitrogen
short
The landing gear assembly is braced longitudinally by ___ and laterally by ___
drag struts side struts
A scissor link, aka ___ ___, stops the oleo in the shock absorber from ___
torsion link, rotating
The highest loads on the torsion link occur when making ___ ___ during taxi manoeuvres
tight turns
The _ types of wheel attachment are:
4
- Cantilever
- Half Fork
- Fork
- Dual Wheel
The greatest wear on tyres occurs ___
on landing
The _ types of bogie are:
4
- Single wheel
- Twin wheel
- Tandem wheel
- Twin axle bogie
Bogie tilt allows the landing gear to ___
fit into a smaller wheel space.
The rear set of wheels hanging down is accomplished by using ___
hop and damper linkages
The reason the rear set of wheels hangs down is that ___
upon contacting the runway first, the wheel spin can be made to absorb up to 16% of the energy before the oleos begins to compress. Allowing for a shorter oleo, saving weight and space.
The nose wheel generally carries around __% of the aircraft weight
10
Self-centering nose wheels use a ____ system
roller/spring
The tiller should be used for ___
sharp taxi turns
Tiller centering is done with a ___
pair of cams in the upper and lower parts of the strut engaging with each other and turning the wheel as it comes up.
The maximum castoring angles are about __ degrees
55
Some nose wheels use a ___ on each side of the upper sidewall of the tyre to deflect water from the engines.
chine
A shimmy is the ___
rapid oscillation of a wheel during ground manoeuvres and takeoff.
A shimmy might be caused by ___
- Uneven tyre pressures
- Unbalanced wheels
- Worn shimmy damper/wheel bearings
- Worn torque links
Anty-shimmy designs include:
- Twin wheels
- Marstrand tyres
- Shimmy damper (friction for small, hydraulic for big)
- Limiting the castoring ability of the nose wheel
Gear on the wing are called ___ gears
wing
Gear on the fuselage are called ___ gears
body
The main wheels turn in the ____ direction as/to the nose wheel to reduce side loads
opposite
Main wheel steering operates only when ___
it is armed
During pushback, the nosewheel is locked out from the main system with a ___
pin
If sharp turns are involved with the pushback, the nosewheel steering can be disconnected at the nosegear torsion links with an ____
APEX pin
A red gear light indicates that ___
there has been a malfunction, or any gear is not locked
During an overweight landing, damage will primarily be caused to the ___
- Landing gear
- Support structures in wings/fuselage
- Wing/tailplane attachments
- Front pressure bulkhead
- Nose wheel drag
- Shock struts
During an overweight landing, damage will secondarily be caused to the ___
- Fuselage structure (upper/lower skin)
- Wing structures
- Upper and lower skins
Following an overweight landing, if no damage is found in the primary areas, the secondary areas ___
do not need to be inspected
