Black Oar Studio · Engine Room 04

Landing Gear Test Bench

The main landing gear of a fictional twin-engine turboprop aircraft, part by part. A retraction actuator swings the shock strut into the nacelle through a drag brace with an over-centre lock. The gear doors move in a fixed sequence. On touchdown, a two-mass model calculates stroke, force and load factor.

L Nose R

0°Swing angle

In flight · gear extended

Drag to rotate · after a click, the mouse wheel zooms · the “Side” camera shows the kinematics

Sequence At rest

Mode

In flight Landing

Landing is only possible with the gear extended and locked.

Gear lever

Sequence 0%

extendedretracted

Nacelle

Lines Off

Landing mass 5,000 kg

3,5005,700 kg

Sink rate 1.5 m/s

gentle3.05 = design value

Pre-charge pressure 30 bar

1545 bar

Landing

1/10 1/3 Real time

Camera

Cockpit indicator

Extended and locked, all three gears
In transit or not locked
Retracted and locked in the uplock

Main landing gear

Extended

Swing angle: 0°
Retraction actuator: –
Stroke: –
Shock strut force: –
Peak force: –
Load factor: –

Shock strut: force over stroke–

Air spring, static
Air spring, under impact
Last landing

Touchdown impact over timefrom ground contact

Force (kN, left)
Stroke (mm, right)

Static compression: –
Max. stroke: –
Tyre max.: –
Efficiency: –

Retraction actuatorForce over swing angle

Data sheet

Type: Main landing gear, fictional design for a light twin-engine turboprop aircraft
Retraction: Forward, 90° swing into the engine nacelle, gear doors open beforehand and close afterwards
Shock strut: Oleo-pneumatic shock strut, piston Ø 70 mm, stroke 220 mm, air column 300 mm
Tyre: Ø 560 mm, progressive spring rate
Drag brace: 500 + 460 mm, locked 4° over centre when extended, secured by a lock link and downlock spring
Retraction actuator: Piston Ø 40 mm, stroke 311 mm, lever arm 220 mm at the top of the shock strut
Moving mass: 70 kg (shock strut, wheel, brake)
Airstream: 65 m/s during retraction and extension
Touchdown: 50% of the landing mass on this gear, lift 2/3 of the weight, wheel spins up from 0 to 42 m/s
On the ground: 45% of the mass static on this gear, retraction inhibited by the weight-on-wheels switch

How the model calculates

The shock strut rotates about the pivot. In every frame, the drag brace, lock link and torque links are solved as four-bar linkages through circle intersections. The actuator force is the required moment from weight and airstream, divided by the lever arm of the actuator.
The air spring follows p·Vⁿ = const. with n = 1.1 for static compression and n = 1.3 under impact. The oil flows through an orifice, F = k·v·|v|, with four times the damping on rebound.
The touchdown impact runs as a two-mass model (aircraft share and wheel) in steps of 0.02 ms. The tyre is a progressive spring with light damping. Friction brings the wheel up to rolling speed.
During emergency extension there is no hydraulic pressure. The shock strut falls under gravity and airstream, an orifice slows it, and the spring pulls the lock over centre. The gear doors stay open afterwards.
All dimensions are chosen to be plausible, but they belong to no real aircraft. The model shows the principle and the order of magnitude. It does not replace a formal proof.