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Sunday, May 2, 2010

Steering Systems

Some a/c have free castering nose wheels; most have steerable.

Mechanical Steering Systems

Uses foot power to steer the aircraft – no assistance

Some types will disengage when the gear is retracted

Some types have an automatic centering device when weight is off the a/c

Tail Wheel

Conventional gear use the tail wheel to steer

May be a castering type with no steering capabilities (rudder steers)

May be lockable, for parking purposes

Power Steering Systems

Used where large amounts of force are required to steer

Controlled by pilots rudder pedals, OR

By a steering wheel, OR

By a combination of both

Most will require a towing bypass valve which allows

Ground crews to to the a/c without damaging the system

Retraction Systems

Purpose: reduce drag, or adapt a/c for landing on different surfaces

(consider retractable wheels on float systems)

Mechanical Systems

Crank mechanism, or uses a lever pulled by the pilot

This method may use a mechanical latch system to lock wheels “up”

No emergency backup available for this system

Electrical Retraction Systems

Uses a central motor and push-pull rods

Uses microswitches to detect when gear is down/locked, or up/locked

Hydraulic Retraction Systems

Most common system of retraction for most sizes of a/c

Used exclusively where landing gear is too large to be retracted by other methods

May use ED pumps, electric pumps, hand or wind-driven pumps

Emergency Landing Gear Systems

4 possible methods of dropping gear when hydraulics are lost:

air bottle “blows” the gear down

hand crank or ratched

separate hydraulic system (may be hand pump)

mechanical system which releases UP locks, and gear free-falls

Landing Gear Operation

4 main components:

shock strut

the wheel

the brake assembly

the trunnion and side/drag brace

scissors (torque links)

actuating cylinder

down & up locks

the bungee system

Using hydraulics, landing gear retraction requires greater energy than lowering

Gear rotates on the trunnion pin

Extending landing gear requires a release of the UP lock first, then

The gear can begin free falling, slowed by the snubber in the orifice check valve

Final few degrees of travel may require hydraulic pressure assistance

Bungee system is used for emergency operation:

Gear doors must be operated before extension & after retraction

Landing Gear Position Indicator Systems

Positive indication must be provided to the pilot that gear is down & locked

Safety system includes squat switches and other microswitches

Squat switches tell pilot when weight of a/c is on the wheels

Squate switches are electrically “open” when on the ground

Some a/c use warning horns: they sound when:

If gear is retracted, and throttle retarded to below cruise

Landing gear position indicators: show position of Landing gear

May use a system of different color indicator lights

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nothing can fly without airfoil...

but i try my best to do it

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