Another disadvantage of the resins is their limited shelf life, i.e., if the resin is not used within the specified time lapse after manufacturing, the results may be unsatisfactory and unsafe. HEAVY AIRCRAFT RAW MATERIALS 1. Magnesium: An expensive material. Castings are the only readily available forms. Special precaution must be taken when machining magnesium because this metal burns when hot. 2. Titanium: A very expensive material. Very tough material and difficult to machine. 3. Carbon Fibers: Still very expensive materials.
ADP-II HEAVY-LIFT MILITARY CARGO AIRCRAFT 75 4. Kevlar Fibers: Very expensive and also critical to work with because it is hard to "soak" in the resin. A number of properties are important to the selection of materials for an aircraft structure. The selection of the best material depends upon the application. Factors to be considered include yield and ultimate strength, stiffness, density, fracture toughness, fatigue, crack resistance, temperature limits, producibility, repairability, cost and availability. The gust loads, landing impact and vibrations of the engine and propeller cause fatigue failure which is the single most common cause of aircraft material failure. For most aerospace materials, creep is a problem only at the elevated temperature. However some titanium plastics and composites will exhibit creep at room temperatures. Taking all the above factors into considerations, the following aluminium alloys which have excellent strength to weight ratio and are abundant in nature are considered. S.No Aluminium Alloy Yield strength MPa Ultimate strength MPa 1 Al 2024- T35 280 470 2 Al 2024- T3 276 427 3 Al 7075- T6 476 538 4 Al7075- T651 462 538 5 Al 6061-0 55 112 6 Al6064-T4 110 207 7 Al6061-T6 241 290 8 AA6082T6 210 340
ADP-II HEAVY-LIFT MILITARY CARGO AIRCRAFT 76 DESIGN REPORT
ADP-II HEAVY-LIFT MILITARY CARGO AIRCRAFT 77 Design Report: ParametersValuesSpan 70 m Planform area 549 m2Aspect ratio 8.92 Empty weight 160000 kg Maximum takeoff weight 359331 kg Oswald efficiency factor 0.7852 Chord at root 12.54 m Chord at tip 3.135 m Taper ratio 0.25 Sweepback angle 3.843 Wing loading 654 kg/m2 Power delivered by motor 54 hp Thrust-to-weight ratio 0.158 Rate of climb 5.22 m/s Endurance 3 hours Range 4500 km Stall speed 69.44 m/s Landing distance 1450 m Takeoff distance 2277.46 m Maximum +ve Load factor 3 Maximum –ve Load factor 1.2 Design dive speed 312.5 m/s
ADP-II HEAVY-LIFT MILITARY CARGO AIRCRAFT 78 Lift coefficient(flaps down) 1.138 Minimum radius of turn 688.698 m Maximum bending moment 261419642.5 Nm Front spar bending moment 118989368.5 Nm Rear spar bending moment 99406322.85 Nm Bending moment in fuselage 33827996.63 Nm
ADP-II HEAVY-LIFT MILITARY CARGO AIRCRAFT 79 Three view digram:
ADP-II HEAVY-LIFT MILITARY CARGO AIRCRAFT 80 CONCLUSION: The structural design of the Heavy-lift military cargo aircraft which is a continuation of the aerodynamic design part carried out last semester is completed satisfactorily. The aeroplane has gone through many design modifications since its early conceptual designs expected, among these was a growth in weight.