2008 International ANSYS Conference · 2008 International ANSYS Conference Design and Analysis of the ACES 5 Ejection Seat Park O. Cover, Jr. Mechanical Engineer. Concurrent Technologies

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2008 International ANSYS Conference

Design and Analysis of the ACES 5 Ejection Seat

Park O. Cover, Jr.Mechanical EngineerConcurrent Technologies Corporation (CTC)


Background

• ACES II – Designed in 1970’s by

McDonnell Douglas– Currently used in

USAF aircraft• F-15, F-16, F-22, F-117,

B-1, B-2, A-10– Monocoque structure

constructed from sheet metal


Background

• ACES Modular– CTC / Goodrich design– Designed for B-2 retrofit

• Modular design reduces maintenance cost and B-2 downtime

• Machined structure reduces part count / assembly costs

• Common pyrotechnics with legacy ACES II

• New structure analyzed with ANSYS • Successful 1st test

October 2007


Background

• ACES 5– CTC / Goodrich design– Designed for F-35 Joint

Strike Fighter (JSF)• Modular design• Machined structure• Reduced weight• Common pyro w/ ACES II• Enhanced safety

– Accommodates 103 lb to 245 lb pilot

• Meets JSF specific requirements

• Blank sheet design January 2007

• Successful 1st test April 2008

• Made possible with ANSYS


Requirements

• Performance Envelope– Speed: Zero airspeed to 600 KEAS (~750 mph)– Altitude: Zero feet to 60,000 feet

• Major load cases– Loads applied for a fraction of a second

• Catapult load (16g x 1.5 safety factor)• Aerodynamic loads• Crash loads (30g)• Drogue parachute load

• One time use


Approach

• Truly concurrent design and analysis– Meet structural and weight requirements on

tight schedule• System level analysis built directly from CAD

models– Minimize preprocessing– Run on Dell XP64 workstation w/ 32GB RAM– Quickly analyze changes as the design

evolved• Detailed submodels of high stress areas

– Local yielding allowed


Method

• Designed with ProE • Analyzed with ANSYS


Concurrent Design / Analysis

• Windblast pushes legs apart with 3,300 lb force

• Design goals– Optimize weight– Meet quickly changing

design requirements• Linear static with elastic

material properties• Used Design Modeler to

slice bucket sides for load application areas


Bucket Structure Evolution

• REV 1 bucket side structure• 2.1 lb weight










Elastic stress exceeds allowable ultimate


Bucket Sub-Model

• Sub-model of bucket side structure• Multi-linear isotropic hardening material properties

– Aluminum 7050-T7451• Used “commands” object to interpolate

displacements from system model onto submodel boundaries


Bucket Sub-Model

• Verified that submodel deformation matches system model

System ModelTotal Deformation

Sub Model Total Deformation648,148 Nodes173,483 ElementsHex Dominant 0.03” Element Sizing


Bucket Leg Guard Submodel

• Max stress of 71.4 ksi indicates permanent deformation. Margin of safety to failure is +0.01

Equivalent Stress Equivalent Plastic Strain


System Level Analysis

• Solid 3D geometry imported to Design Modeler– Minimal defeaturing– Some shell geometry created with auto-

midplane feature• 175 contact regions manually applied

– Reactions used to size rivets / fasteners• Point masses applied to represent subsystems• Acceleration / loads applied to simulate desired

load condition


System Analysis Details

• Mesh– Hex dominant for all

solid components– Global element size

0.125”– 1,252,376 Nodes – 406,164 Elements– Run time of 27.7min

for linear static structural analysis


Method Verification

Shell0.535” Max Deflection

Solid – Hex Dominant0.531” Max Deflection

• Thin Machined Parts (0.06” thick)

Shell0.125” Global Size4,236 Nodes4,097 Elements100 lb Applied force

Solid – Hex Dominant0.125” Global Size32,792 Nodes6,144 Elements100 lb Applied force


Catapult System Analysis

24g Ultimate load

Pressure due to windblast at 600 KEAS

• Catapult ejection load at 600 KEAS (Tipoff)• Linear static with elastic material properties



Catapult Sub-Model

• Submodel of seat side using multi-linear isotropic hardening material properties

–111,508 Nodes–26,177 Elements



Drogue Parachute System Analysis

• 16,000 lb drogue parachute load at 30 deg yaw• Inertia Relief, requires accurate mass properties• Elastic material properties

Representative occupant included to achieve accurate mass moments of inertia


Drogue Parachute System Analysis

• Equivalent stress for system model with elastic material properties



Drogue Parachute Sub-Model

• Submodel of seat side using multi-linear isotropic hardening material properties

–551,880 Nodes–127,462 Elements


Equivalent Stress


Conclusion

• ANSYS was used to:– Optimize the seat structure – Show that all structural components have a

positive margin of safety

• ANSYS enabled CTC and Goodrich to meet project goals and aggressive deadlines– Less than 1.5 years from concept to test– Flawless ejection test on the first try


Questions

Park O. Cover, Jr.Concurrent Technologies Corporation100 CTC Drive Johnstown, PA 15904

Documents

2008 International ANSYS Conference · 2008 International ANSYS Conference Design and Analysis of the ACES 5 Ejection Seat Park O. Cover, Jr. Mechanical Engineer. Concurrent Technologies