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Airship Structural Analysis Lin Liao Aeronautical Engineer, PhD Worldwide Aeros Corp., Montebello, CA 1 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011

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Introduction Analysis of airships Rigid body motion analysis Static bending moment Aerodynamic bending moment Envelope stress analysis Stress analysis of empennage attachment Cable_truss structures Summary 2 Overview The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011

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Non-rigid airships Empirical experiences “Airship Design”, “Airship Technology” Finite Element modeling NASTRAN,ABAQUS Rigid airships Bulkhead construction No FEA model of rigid airships 3 Introduction The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 4 Vertical & Longitudinal Directions

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 5 Lateral Direction

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6 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 Calculation of lift, drag, and pitching moment Sum of forces and moments in vertical & longitudinal directions Vertical & Longitudinal Directions

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7 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 Sum of forces and moments in lateral direction Lateral Direction

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 8 Flight Maneuver Conditions ConditionSpeedWeightAttitude Load Factor and Acceleration 1Level FlightVHVH WtWt Horizontaln x, n y, n z =0;χ,ø=0 2 Level Flight Reverse Thrust N/A 3Nose DownVHVH WoWo Θ=+30 n y =0;n z >0;χ, ø=0 4Nose UpVHVH WoWo Θ=-30 n y =0;n z <0;χ, ø=0 5Descent & Pull-UpVHVH WtWt Θ<0n y =0;n z >0;χ,ø=0 6Turn EntryV SH WoWo Horizontaln y ≠0;ø>0 7Turn & ReverseV SH WoWo Horizontaln y ≠0;ø<0 8Dive EntryVHVH WoWo Horizontaln y =0;χ<0;ø=0 9Climb EntryVHVH WoWo Horizontaln y =0;χ>0;ø=0 10Turn & ClimbVHVH WoWo Horizontal χ>0;ø>0 11Turn & DiveVHVH WoWo Horizontal χ 0 12TurnV SH WoWo Horizontaln x, n z =0;n y< 0;χ,ψ=0 13Turn RecoveryV SH WoWo Horizontaln x, n z =0;n y <0;χ,ψ=0 14Turn Rec. & ClimbVHVH WoWo Horizontaln y 0 15Turn Rec. & DiveVHVH WoWo Horizontaln y <0;χ<0 16Light FlightVHVH W min Θ<0n y =0; n z >0; ø=0

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9 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 The envelope is divided into longitudinal segments. Distribution of buoyancy force is obtained by multiplying the segment volume by the Helium (96% purity as specified by ADC) unit lift. The buoyancy forces is given the (+) sign. The segment envelope weight is obtained in proportion to the segment surface area, and given the (-) sign to denote weight downward. The components (nose cone, helium, etc.) are placed in their nearest segment, and given the (-) sign. The segment load F is obtained by summing up the above forces and weights. The envelope shear at each segment, S, is obtained by summing the above F from the nose up to the segment where shear is determined. The envelope bending moment at each segment, M, is obtained by summing the above S multiplied by the segment length, from the nose up to the segment where bending moment is determined. Calculation of Static Bending Moment

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 10 Static Bending Moment Case 1 Envelope: 30% Car: 55% Case 2 Envelope: 36% Car: 50%

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 11 Static Bending Moment Static bending moment increases from zero to maximum along the longitudinal length of airships and then decreases to negative maximum. Maximum static bending moment decreases with the increase of envelope weight. Case 3 Envelope: 37% Car: 48%

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 12 Aerodynamic Bending Moment Gust 1, Gust 2, and Gust 3: 20 ft/s, 25 ft/s, 30 ft/s

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 13 Aerodynamic Bending Moment

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 14 Envelope Stress Analysis Envelope stresses due to internal pressure & bending moment Pressurized airships and rigid airships

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15 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 Stress Analysis of Empennage Attachment

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16 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 Stress Analysis of Empennage Attachment

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17 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 Cable_truss Structures Restraints: fixed Nodes1, 4, and 5 Applied loads: Fx =1000 lbs at Nodes 9, 10, 11, 12 Cable pretension: 100 lbs Cable tension in the deformed configuration CableC1C2C3C4C5C6C7C8C9 Tension (lbs)156.9643.07113.3886.79200.9507.79192.9243.72 CableC10C11C12C13C14C15C16C17C18 Tension (lbs)156.1782.68116.8995.04104.26263.120235.790

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 18 Cable_truss Structures Restraints: fixed Nodes1-5, 9-13 Applied loads: Fz =400 lbs at Nodes 7, 8, 15, 16 Cable pretension: 100lbs Three Design Configurations: Design A: no cables are used Design B: six cables are included Design C: 14 cables (Each of four truss members is replaced by two cables)

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 19 Cable_truss Structures Node 7Node 8 ABCABC U X (1E-3)-2.4040-2.02390.2537-0.9174-0.7827-0.0552 U Y (1E-4)0.00183.16813.08360.00242.30542.3075 U Z (1E-3)5.30294.17542.13583.44122.62962.7121 U T (1E-3)5.82234.65092.17283.56132.75332.7225 Displacements in the deformed configuration

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The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 20 Cable_truss Structures DesignNode 5Node 6 UxUyUzUtUxUyUzUt A (all)-2.88820.6030-4.3362 5.2448 -2.52970.36406-2.5316 3.5973 B(1/2)-1.01610.4342-1.5344 1.8909 -0.57510.1376-0.5817 0.8295 C(1/2/3/4)-2.83420.1595-4.2621 5.1209 -2.5728-0.01747-2.5788 3.6428 D(5/6)-0.3899-0.05827-0.5891 0.7088 -0.3134-0.1107-0.3155 0.4583 E(9/10)-0.48380.09942-0.7368 0.8870 -0.2231-0.07710-0.2292 0.3290 F(7/8/9/10)-0.48780.06495-0.7428 0.8910 -0.2172-0.1181-0.2233 0.3331 Displacements in the deformed configuration

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21 The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011 Rigid body motion analysis has been utilized to study a variety of flight maneuver conditions of airships. Static bending moment and aerodynamic bending moment are calculated. Aerodynamic bending moment increases with the increase of airship length and increases with the decrease of equivalent max diameter for the same volume and prismatic coefficients. Airship envelope stress is expressed as a function of bending moment and internal pressure. Finite element model of empennage attachment of airships is presented. Cable tension changes significantly in contrast with pretension and cables could completely lose tension. Optimal cable pretension and configuration are helpful for the minimization of structural deformation. Summary

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22 Thank You! Questions? Suggestions? The Eighth Annual AIAA Southern California Aerospace Systems and Technology (ASAT) Conference Santa Ana, CA, May 21, 2011

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