Aircraft Retracting Main Landing Gear

A-17 Zephyr Main Landing Gear (MLG) Cranfield University, MSc Aerospace Vehicle Design, October 2017 Intake   Background: As part of the MSc in Aerospace Vehicle Design at Cranfield University, a group of students performs the preliminary and detail design of an aircraft conceptual design provided by the staff. Each member of the group focuses on one area of the aircraft. This author did the design work of the Main Landing Gear Structure of the A-17 Zephyr and as part of this work produced a very complex CAD assembly of a functional MLG. It is important to note that producing the CAD model was only a small part of the design work since a lot of effort went into calculating the structure and justifying the dimensions implemented.   The CATIA V5 project of the A-17 MLG is quite complex albeit for reasons that may not be obvious. It is a functional, moving (retracting and extending) model of a Landing Gear that not only retracts sideways into the fuselage bay but also shortens in length by means of a length shortening mechanism composed of several smaller parts. This shortening mechanism achieves a reduction in length of the unit of 33% from 2.7 (extended) to 1.8 metres (retracted). Due to this reduction in length, the volume required for stowage is reduced and the frontal area of the fuselage cross section is minimised, therefore reducing the size of the potential MLG fairing and consequently fuel consumption and environmental impact. Please note that the strength of this project does not lie in the geometry of the parts per se; the geometries involved are not that complex, the key achievement was defining the main dimensions to achieve a functional, structurally suitable and moving assembly. The model has been brought to life via the Kinematics module. A 1 degree of freedom solution was achieved, meaning that only one parameter (command) drives the state of the entire assembly. The retraction sequence is as follows:

• Hydraulic pressure on the retraction/extension actuator commences the retraction sequence.
• The actuator shortens thereby pulling on the main strut into the fuselage.
• Rotation of the main strut forces the direction rod to pivot with respect to its airframe fixed end.
• The direction rod forces the crank to pivot about its cylindrical bearing axis.
• The crank pivots clockwise (seen from the front) with respect to the main strut, thereby pulling the shock absorber outboard and upward.
• The shock absorber is spherically hinged to the lever arm on its lower end and pulls on it upward with respect to the main strut achieving the desired shortening rotation.

Some key facts of the A-17 MLG CAD model:

• Designed between October 2017 and March 2018.
• Modules used: Part, Assembly, Generative Shape Design, Kinematics, Drafting
• Complex file structure composed of over 30 .CATPart and .CATProduct files.
• 15 kinematics joints and 1 command. Spherical joints were implemented using the "universal joint" tool.
• Inspired by the solution of the BAe 146.
• Design of parts was initially dimensioned using "simple" hand calculations, with some areas sized via semi-empiral methods (ESDU) and then refined via iterative Finite Element Analysis.

For any further information regarding this project please contact the author at:

• Jaime Beneyto
• jaimebeneyto@cranfield.ac.uk
• +447547946758
• +34637851181

  Note: I did not design the fuselage structure which is shown in the video/drawings for reference. This work was done by fellow student Geoffrey Rayter. Nor did I do the design of the brake assembly, work of Alice Williams-Allden.