SKIN STRINGERS IN AN AIRCRAFT

MS MS&E 06ATTAULLAH KHAN,

MUHAMMAD SUBHAN, WAJAHAT ALI

WHAT IS SKIN STRINGER?

• Stringer is a stiffening member which supports a section of the load carrying skin, to prevent buckling under compression or shear loads.• Stringers keep the skin

from bending.• Longitudinal members

are sometimes referred to as longitudinal, stringers, or stiffeners.

ROLE OF STRINGERS IN AIRCRAFT WINGS• In aircraft construction, a stringer is a thin strip

of material to which the skin of the aircraft is fastened. In the fuselage, stringers are attached to formers (also called frames) and run in the longitudinal direction of the aircraft. • They are primarily responsible for transferring

the aerodynamic loads acting on the skin onto the frames and formers. In the wings or horizontal stabilizer, longerons run span wise and attach between the ribs. • The primary function here also is to transfer the

bending loads acting on the wings onto the ribs and spar.

MATERIAL SPECIFICATION

• Mostly aluminum 2024 T3 is used for skin stringers and frames. Airframe designers still demand strong, stiff material at an acceptable weight and cost .So alloys of aluminum, steel and titanium will probably use for airframe design.

• Other aluminum alloys i.e. aluminum iron molybdenum zirconium, function well enough at high temperature to be competitive with titanium up to near 600oF.

STRINGER AND LONGERONS• A longeron is part of the structure of an aircraft,

designed to add rigidity and strength to the frame. • Materials like wood, carbon fiber, and metal can be

used in longeron construction. • Each longeron attaches directly to the frame of the

aircraft using bolts.• In some planes, shorter longitudinal supports called

stiffeners or stringers are fastened to the longerons• Sometimes the specifications longeron and stringer

are applied interchangeably

STRINGER VS. LONGERONS

Stringer Longeron• If the longitudinal

participants are countless (usually 50 to 100), they are named stringers.• Generally, stringers are

of smaller cross-section once contrasted to longerons .• Stringers frequently

take smaller stacks compared to longerons construction.

• If the longitudinal participants in a fuselage are limited (usually 4 to 8), they are named longerons.

• Generally, longerons are of greater cross-section once contrasted to stringers.

• Longerons frequently take greater stacks compared to stringers construction.

It is not unusual to have a blend of longerons and stringers in the similar chief structural part.

DIFFERENT SHAPES OFSTRINGERS• The stringers on an aluminum airplane are normally

extruded or bent into shape, and can have a number of different cross sections. • Typically Shapes for stringers are

i. HAT Stringerii. I-Stringeriii. J-Stringeriv. Y-Stringerv. Z Stringer

• On wooden airplanes, they are usually spruce square or rectangular cross sections.

DIFFERENT SHAPES OF STRINGERS(CONT…)

DIFFERENT SHAPES OF STRINGERS(CONT…)

DIFFERENT SHAPES OF STRINGERS(CONT…)

DIFFERENT SHAPES OF STRINGERS(CONT…)

CURRENT DEVLOPMENTS• An effective Optimization routine has been

developed to design a compressive skin stringers panel for minimum while guarding against important failure made such as stringer buckling, compression in stringer outstanding and beam column eccentricity.• The above optimization routines have been

successfully used to design Wing stringers of different shapes by CATIA(Computer Aided Three-dimensional Interactive Application) software. • A good preliminary design of wing box having

different types of configuration was implemented by different stages of design process.

RECOMMENDATION FORFUTURE WORK

• Although the design of a lower wing panel for simple case of single straight crack is a good start, it can be extended to design for a case of multiple cracks.

• Instead of using adhesive material to join stringer with skin, it would be interesting to design by replacing adhesive material with rivets (fasteners).

RECOMMENDATION FORFUTURE WORK (CONT…)

• The drag forces can also be included while generating the design load curves.• As the dimensions for spars and their corresponding

web caps are taken with reasonable assumption, the design can be refined by taking actual dimensions for them.• This design process can be repeated at different

stations along the wing semi-spar to design a complete preliminary of wing box and stringers or skin-stringer pane