UC and suspension

Question 1

UC weight and price

Answer 1

3%-7% gross weight
2%-4% of sales price

Question 2

UC design requirements

Answer 2

-provide flotation and clearance from the ground
-absorb and dissipate landing load
-brake park and tow AC
-taxi takeoff and landing
-stability during maximum braking, crosswinds and high speed taxi

Question 3

desirable UC characteristic

Answer 3

-low rolling friction
-maximum traction for braking
-min drag while airborne
-min weight and coast while achieving above

Question 4

tail dragger

Answer 4

torque- roles left
precession- up and left

Question 5

tricycle

Answer 5

tread - wheel base
caster angle - perpendicular to longitudinal and compare to angle of front wheel gear
offset - wheel center distance from line of nose gear to ground
wheel base- front to back wheel

-main wheels aft of CoG but forward enough to take load off of nose wheel.
-nose wheel as far forward as possible
-tread and wheelbase configuration dependent on turn over angle (will plane flip in wind or at high speeds)

Question 6

nose wheel considerations

Answer 6

-normal load is 10-20% AC weight
- high nose wheel load requires high elevator download for rotation
- low nose load can make steering ineffectual
- can cause pourpouesing (oscillation in pitch)
- ground clearance requirements

Question 7

Nose wheel UC advantages

Answer 7

-directional stability
-better braking
-better vis on ground
-fuselage floor angle closer to horizontal
-good control in crosswinds
-prop protected from ground contact
-short wheel base gives small turn radius
- good acceleration on takeoff due low AoA

Question 8

nose wheel disadvantages

Answer 8

-heavier nose wheel
-high drag if fixed
-steering mechanism more complex
-higher cost
-nose wheel shimmy more likely

Question 9

shimmy

Answer 9

usually in nose while
high speed oscillation from side to side
shimmy dampener similar to oleo used to assist

Question 10

Landing Loads

Answer 10

-potential energy carried in wing lift
-Kinetic energy function of descent velocity
-vertical descent velocity is constant
FACTORS EFFECTING THE MAGNITUDE OF LG LOADSS
-weight
-speed
-shock absorber travel
-tyre deflection
-runway surface roughness
-angle of approach
angle of drift or yaw

Question 11

shock absorbers

Answer 11

-rubber cords
-rubber discs
-springs
limited dissipation leads to recoil

Question 12

telescopic strut (Oleo Pneumatic)

Answer 12

two cylinders (one oil one air. air compressible oil is not)
flutter valve
plunger tube
gland
torque links
oil forced through flutter valve as load is acquired, slowly released back into oil chamber to avoid rebound
torque links set limits at mins and max and prevent rotation and misalignment

Question 13

oleo-pneumatic shock extension

Answer 13

light a/c approx. 100mm for main and 80mm for nose gear

Question 14

shimmy damper

Answer 14

oleo pneumatic shock absorber that dampens lateral movement using push rod and oil chamber