B. Baumeister, D. Kalal

The conventional method of construction for wing spars used in light business aircraft is little changed from the techniques that have been used in aircraft dating back to the 1950s, and earlier. Machined extrusions are used for the spar caps, which are then riveted to a web stiffened by uprights and rib attachments, all using dedicated tooling to create the final spar assembly. A monolithic spar combines the web and both the upper and lower caps into a single machined part (generally from plate stock). Such a design offers several advantages over the conventional design: a significant parts-count reduction through unitized structure and the elimination of hundreds of fasteners, a reduction in assembly tools, reduced assembly time, and reduced floor space requirements. The challenge is to design a monolithic spar so that it remains damage tolerant-particularly for the most severe cases, where the level of damage is large. A wing with fully monolithic wing spars does not possess obvious classic fail-safe capability - in which the failure of an entire element (a full spar, in this case) can be withstood - without the use of multiple, redundant, spars (an approach which may not be weight-efficient). However, this apparent limitation can be addressed by ensuring that a crack in a spar will not result in the failure of the entire spar. Consequently, a crack-arrest feature of the monolithic spar must ensure that the wing will be able to maintain a safe level of strength, even in the event that the spar cap is completely failed. This crack-arrest member could be either a separate, fastened element, or it could be an integrally machined part of the spar. A separate element has the advantage of crack-arrest efficiency (as with a crack stopper band at a fuselage frame), while an integral machined feature has the advantage of better durability(through the elimination of fasteners) and higher structural efficiency. An important consideration in the selected analysis method is that it allows frequent and rapid tum-around times that are required in the optimization of new airplane. Full-scale wing box test results indicate that an approach based on stress intensity, which is compared against a limiting value appropriate for the material, will accurately predict the crack arrest and residual strength of a monolithic spar.

23rd ICAF Symposium of the international Committee on Aeronautical Fatique, 2005, Hamburg

Conference Paper

englisch

A5, 12 Seiten

DGLR-Bericht, 2005, 2005-03, 23rd ICAF Symposium of the international Committee on Aeronautical Fatique - Proceedings; S.177-188; 2005; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

design optimization, damage tolerance

Bestellbar

2005