Miscellaneous Considerations

This chapter discussing undercarriage design is a relatively large, complex, and standalone chapter without which an aircraft design cannot be completed. Only the preliminary information – what is needed by aircraft designers to conduct a con­ceptual study – is presented here. Details of the undercarriage design are imple­mented by specialists after the go-ahead on a project is obtained. Aircraft designers and undercarriage designers maintain communication to integrate the undercar­riage with the aircraft, doing it right the first time.

There is a tendency to minimize undercarriage design work in coursework exer­cises, possibly because of time constraints. As now understood, this is an involved procedure; if time is a constraint, then the undercarriage should be addressed in a second term, using CAD and including work on retraction kinematics. A good spreadsheet must be prepared for the calculations because they are required for subsequent iterations.

In summary, the chosen undercarriage should be the tricycle type with retrac­tion. The runway LCN and ESWL decide tire pressure (the higher level of inflation pressure may be necessary), which in turn decides the number of wheels and struts required. Tire manufacturers’ catalogs list the correct sizes of the tires.

The methodologies for civil and military aircraft undercarriages and tire sizing are nearly the same. The differences are in operational requirements. In general, civil aircraft design poses more difficulty in maintaining component commonality

within the variants. The cost options for component commonality for variant designs must be decided early during the conceptual design phase. Trade-off studies on cost versus weight must be conducted.

7.13 Undercarriage and Tire Data

Table 7.8 gives some production aircraft undercarriage and tire data.

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