Chapitre Charges et calcul des structures

2 CHARGES Pression Inertie Poids Réactions du sol

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4 Charges distribuées

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7 Facteur de charge ‘n’: exprime le rapport de la charge aérodynamique par rapport au poids. Pour l’aviation générale: 2.5 < n < 3.8 Et n= -1

8 Facteur de charge due aux rafales: exprime la charge aérodynamique causée par la turbulence dans l’air. Cette charge est importante pour l’aviation civile d’où

9 On introduit un facteur de correction pour tenir compte de : avec et

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11 Structure

12 Tension, compression et cisaillement: En flexion: En torsion:

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20 Flambement d’un panneau mince: t: l’épaisseur, b: le côté le plus petit, K dépend de la fixation (k= 3.62 simplement supporté et K= 6.31 fixé des deux côtés). Pour les coques avec un rayon de courbure R:

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26 Conceptual Structure Design Guidelines Every structure design problem is different, but the following general guidelines suggest pitfalls to avoid and goals to strive for when laying out an aircraft structure: 1. Never attach anything to skin alone. Even thick aluminum skin has relatively little strength against point loads perpendicular to its surface. Pylons, landing gear, control surfaces, etc. must be attached through the skin to major structural components (spars, ribs, frames, keels, etc.) within the structure. 2. Structural members should not pass through air inlets, passenger cabins, cargo bays, etc. 3. Major load-bearing members such as spars should carry completely through a structure. Putting unnecessary joints at the boundaries of fuselages, nacelles, etc. weakens the structure and adds weight. 4. Whenever possible, attach engines, equipment, landing gear, systems, seats, pylons, etc. to existing structural members. Adding structures to beef up attachment points adds weight. Plan the positions of major structural members so that as many systems as possible can be attached to them, and so the structures can carry as many different loads as is practical. 5. Design redundancy into your structures so that there are multiple paths for loads to be transmitted. In this way, damage or failure of a structural member will not cause loss of the aircraft. 6. Mount control surfaces and high-lift devices to a spar, not just the rear ends of ribs. 7. Structural layout is a very creative process. Innovation can often save complexity, weight, and cost. Follow the suggestions on creative problem solving in Chapter 1.

27 Figure 7.12 Partially Completed Structural Layout of a Jet Fighter