FUSELAGE: ROLE AND STRUCTURAL LAYOUT

Hendri Syamsudin

Main Reference

Niu, M. C. (1999), "Airframe structural design : practical design information and data on aircraft structures", Conmilit Press, Hong Kong.

Cutler, J. and Liber, J. (2005), "Understanding Aircraft Structures", 4th ed, Blackwell Pub., Oxford; Malden, MA.

Objectives of this chapter:

To able to describe Fuselage Structure Roles and Layout

To be able to design Fuselage Layout based on Specific Requirements

Key Design Parameters

CONFIGURATION?

MATERIAL?

SIZE?

Fuselage Structural Requirements

To provide an envelope to support the payload, crew, equipment, systems & possibly powerplant.

To react against the in-flight manoeuvre, pressurisation and gust loads; also the landing gear and possibly powerplant loads.

To transmit control & trimming loads from stability/control surfaces.

Fuselage - Mass-Boom & Longeron Layout

Fundamentally similar to mass-boom wing-box concept.

Used when the overall loading is relatively low or when there are extensive cut-outs in the shell.

Comprises four or more continuous heavy booms (longerons) to react against direct stresses due to vertical and lateral bending loads.

Frames or bulkheads used at direction changes and elsewhere along length of members.

Fuselage - Mass-Boom & Longeron Layout

Outer shell supports longerons against compression loads & aids shear-carrying.

• Floors needed at cut-outs.

• Skin stabilised with frames and bulkheads.

Fuselage - Semi-Monocoque Layout

Most common layout, used with small number & size of cut-outs.

• Skin carries most of the loading.

• Skin thickness determined by pressurisation, shear loading & fatigue considerations.

Semi-Monocoque Layout (Cont.)

Longitudinal stringers provide skin stabilisation and contribute to load carrying capacity.

Increased stringer x-sections & skin thicknesses used around edges of cut-outs.

Less integral machining possible than on wing structure.

Semi-Monocoque Layout (Cont.) - Frames

Used to stabilise skin-stringer elements & transmit shear loads into structure.

May also help to react against any pressurisation loads.

Usually manufactured as pressings with reinforced edges.

Spacing (pitch) usually determined by crack-stopping requirements.

Frames usually in direct contact with skin - stringers pass through and cleated in place.

Typical Bulkhead Designs

Fuselage Layout Considerations

Particularly affected in accordance with whether: combat aircraft, or

transport aircraft.

Fuselage Layout Considerations - Fighters

Main features affecting layout include: Powerplant installation Fuel/undercarriage installation Weapons carriage/integration

Area ruling on transonic/supersonic fighters also significantly affects fuselage section.

Pressurisation only required locally in crew compartment.

Fuselage Layout Considerations - Fighters

Effect of Powerplant Installation Number & location of engines directly influences

shape & sectional area. May have single central location (e.g. F16, F102,

F106, Mirage, Gnat, MiG-17, etc.) May have twin side-by-side installation (e.g. F5,

F14, F15, F18, Jaguar, MiG-19, Su-15, etc.) Rarely twin vertical installation (e.g. Lightning).

Fuselage Layout Considerations - Fighters

Weapons Carriage Selection of internal or external carriage

significantly affects fuselage structure. Internal advantages include:

Improved stealth characteristics. Reduced wave drag. Constant area rule.

F22 Raptor

Fuselage Layout Considerations - Fighters

Weapons Carriage Internal carriage disadvantages include:

Reduced flexibility to different roles and changed specifications.

Significant volume and mass penalty with empty weapon compartment.

Structural penalties due to large cut-outs.

Fuselage Layout Considerations - Transports

Longer “in-service” lifetimes than fighters lead to two potential problem areas: Fatigue Corrosion

Boeing 737 accident due to corrosion/fatigue in 1998

Fuselage Layout Considerations - Transports

Fatigue prevention involves: Careful material selection. Reduction of loads, stress levels and concentrations. Eased inspection and maintenance procedures.

Corrosion prevention involves: Adequate provision for moisture drainage. Maintenance of surface finish and protective

treatment integrity.

Fuselage Layout Considerations - Transports

Fuselage Cross-Section Selection involves compromises between weight,

drag, systems, stowage & comfort considerations (also stealth & weapons integration for military transports).

For pressurised aircraft a circular section is most efficient in purely structural terms - however, often wasteful of volume.

Fuselage Layout Considerations - Transports

Fuselage Cross-Section (Cont.) For low pressurisation

requirements, flat-sided fuselages often used - cheap to build.

For large transports, “double-bubble” or ovoid designs popular.

Shorts 330

Fuselage Layout Considerations - Transports

Circular Fuselage Cross-Section Examples

Fuselage Layout Considerations - Transports

“Double-Bubble” Fuselage X-Section Examples

Fuselage Layout Considerations - Transports

Ovoid Fuselage Cross-Section Example

Airbus A380