Functional Design Principles Applied to Amphibious Aircraft Patrick McNally, VI-grade
Agenda About VI-grade and VI-Aircraft About Wipaire and Aircraft Float Design Template Methods Common Parts and Interchangeability Design Space Considerations Adaptability of Designs Application to Landing Gear Design for Floats Summary and Conclusions 2
Why VI-grade? VI is the maximum climbing difficulty grade according to the original Welzenbach scale VI for Virtual Innovation Climbing the peaks of simulation and testing 3
Industry Focus of VI-grade VI-Sportscar VI-Motorcycle VI-Rail ADAMS + Template Building VI-Aircraft 4
Industry Focus of VI-grade ADAMS + Template Building 5
System Approach Landing Gear Design Virtual Test Lab Validation Full Aircraft Full Aircraft Full A/C Simulation Full A/C Simulation Flight Tests Flight Tests Subsystem Subsystem Virtual Drop Virtual Drop Drop Tests Drop Tests Component Component Stress Analysis Stress Analysis Component Tests Component Tests Correlation Correlation 6
VI-Aircraft for Landing Gear: Complete Set of Pre-defined Subsystems, Assemblies, Simulations Subsystems Assemblies Simulations component Wheel(s) Wheel Wheel/Tire LGR Brakes Hydraulics Control Laws Engine Airframe LGR Structure (w/o wheels) LGR Dynamics (w/ wheels) Full Aircraft subsystem subsystem full vehicle Steady Axle Load Drop Retract-Extend Attitude Dyn. Tipback Taxi & Shimmy Braking Turning Co-Simulation Landing Catapult Arrestment Towing In-flight 7
Template Library Wheel subsystem templates 1, 1x1, 2x1, 1, 2x3 Landing gear subsystem templates NLG post, NLG articulated, MLG post, MLG trailing arm, MLG tripod Airframe subsystem templates rigid F-xx, flexible F-xx, flexible civil A-2, Brake subsystem templates simple single antilock, multi rotor/stator... Other subsystem templates... 8
Example Drop Double Strut Gear 1. Create rigid or flexible assembly from library 2. Specify load-stroke curve or orifice settings 3. Specify drop height and impact angles 4. Use spun or stationary tire 5. Run virtual drop to determine energy absorbed 9
Wipaire, Inc. Manufactures Aircraft Floats World s largest float manufacturer Conversion kits for standard aircraft Pilot training Based in St. Paul, MN 10
Anatomy of Amphibious Float Aircraft hull Float with gear Note nose retract system Float Step Aircraft modifications include structural attachments, ventral fins, controls Amphibious STC kits include hulls, spreader bars, rigging, hydraulics 11
Design Problem Develop a new float system for a new aircraft Take advantage of previous designs Part commonality Existing strut design Existing drop test data Move from paper-based approach to virtual approach CAD transition complete Structural analysis transition 75% System analysis transition not started Limited engineering staff and resources Enterprise engineering and design can fit in one 50 x 50 room Blend of old and new 12
Template Based Philosophy and Methods Common Parts and Interchangeability Common parts and assemblies identification Unique parts and assemblies Validation and usage constraints Design Space Considerations Design assumption limitations Tolerable variation of parameters Adaptability of Designs Heritage and Certification considerations Recent changes in FAR 25 requirements allow analysis and simulation of previously certified designs 13
Common Parts/Interchangeability 14
Overall Comparison of Key System Parameters Aircraft Cessna Cessna DHC-2, Caravan, 182 185 Pil. PC-6 DHC-3 Otter Floats 3000 3450 6100 8000 Length 20 2 23 3 22 7 30 4 Length nose to step 9 4 10 6 11 5 14 Height 29 29 34 38 Width 32 32 40 40 Weight, exchange 455 lbs 507 lbs 924 lbs 976 lbs Oleo pressure N/A N/A 175 PSI 210 PSI Tire, Main 6.00x6-8 6.00x6-8 8.00x8-8 6.00x6-8 Tire, Nose 4.1x4-4 4.1x4-4 5.00x5-8 5.00x5-10 15
Tolerable Variations: Example Limits in Load-Stroke Curves Load-Stroke Curve Load, Lbs. 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 Polytropic from Static Isothermal Compression Polytropic Compression (Total) static 0 1 2 3 4 5 6 7 Stroke, Inches Adaptable Changes Static pressure Orifice size Metering pin 16
Tolerable Variations: Example Limits in Load-Stroke Curves Load-Stroke Curve: Increased Static Pressure 10000 9000 8000 Polytropic from Static Adaptable Changes Load, Lbs. 7000 6000 5000 Isothermal Compression Polytropic Compression (Total) ` Static pressure 4000 3000 Orifice size 2000 Metering pin 1000 0 0 1 2 3 4 5 6 7 Stroke, Inches 17
Tolerable Variations: Example Limits in Load-Stroke Curves Load-Stroke Curve Load, Lbs. 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 Polytropic from Static Isothermal Compression Polytropic Compression (Total) Adaptable Changes Static pressure Orifice size Metering pin 0 0 1 2 3 4 5 6 7 Stroke, Inches 18
Approach to Strut Design Goal: Determine minimal number of forgings which gives best performance over the design space Initial variations Nominal operating pressure Orifice size (fixed) Metering pin shapes Follow-on variations Air-Oil Volumes Cylinder diameters Total stroke 19
FAR Part 25 Design and Construction of Landing Gear Sec. 25.723 Shock absorption tests. [(a) The analytical representation of the landing gear dynamic characteristics that is used in determining the landing loads must be validated by energy absorption tests. A range of tests must be conducted to ensure that the analytical representation is valid for the design conditions specified in Sec. 25.473. (1) The configurations subjected to energy absorption tests at limit design conditions must include at least the design landing weight or the design takeoff weight, whichever produces the greater value of landing impact energy. (2) The test attitude of the landing gear unit and the application of appropriate drag loads during the test must simulate the airplane landing conditions in a manner consistent with the development of rational or conservative limit loads. (b) The landing gear may not fail in a test, demonstrating its reserve energy absorption capacity, simulating a descent velocity of 12 f.p.s. at design landing weight, assuming airplane lift not greater than airplane weight acting during the landing impact. (c) In lieu of the tests prescribed in this section, changes in previously approved design weights and minor changes in design may be substantiated by analyses based on previous tests conducted on the same basic landing gear system that has similar energy absorption characteristics.] 20
Two Steps to Certification Previous Design Cert Test Results Delta Design New Cert Test Results Physical No physical drop required!!! Virtual Step 1 Step 2 21
Early Models: New Design Main Gear Main strut compressed 4 Main strut extended to stop VI-Aircraft Assembly compressed 4 22
Summary and Conclusions Taking template approach to allow easy substitution of alternate designs, including component curve characteristics Including design limit information with virtual components and subsystems Virtual approach is allowing faster certification of new designs with demonstrated heritage more acceptance is anticipated 23
Acknowledgements VI-grade would like to acknowledge Chuck Wiplinger, Chief Engineer, and Ryan Nordell, Design Engineer of Wipaire, Inc. for their support of this project as well as MSC.Software in supporting VI-grade 24