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Personal Airbag System Investigation

Orion Alternative Landing Attenuation Concept Study. Personal Airbag System Investigation. Progress Update. October 21 st , 2009. Principle Investigator: Professor Olivier de Weck Graduate Student: Sydney Do Undergraduate Students: Josh Gafford Jack Weinstein.

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Personal Airbag System Investigation

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  1. Orion Alternative Landing Attenuation Concept Study • Personal Airbag System Investigation Progress Update October 21st, 2009 Principle Investigator: Professor Olivier de Weck Graduate Student: Sydney Do Undergraduate Students: Josh Gafford Jack Weinstein

  2. Since Our Last Progress Update

  3. Orion Alternative Landing Attenuation Concept Study • Airbag Venting Mechanism Parametric Study

  4. Airbag Venting Mechanism Parametric Study Aim – Using the updated 1-DOF model, investigate the sensitivity of the overall attenuation performance to perturbations in: • Initial Airbag Inflation Pressure • Total External Orifice Area • Burst Acceleration for a head sized airbag (Ø220mm x 350mm), and determine approximate values for use in the design and testing of the single airbag drop article Approach: • Start with baselined values from Gen 1 airbag study (initial guess) • For parameter A, fix the values of all other parameters and run 1DOF model over varying A • Fix A to the best performing value, and vary B • Repeat Steps 2-3 until A, B, … etc. are “optimized” individually • Repeat Steps 1-4 starting with the latest refined A, B,… from Step 4 • For Step 2, start with the most sensitive value found in the previous Step 3, followed by the second most sensitive, etc. • Stop when the solution converges (best performing values remain consistent between iterations) • This method assumes that general trends hold, this needs to be checked with every iteration

  5. Baseline Airbag Venting Parameter Definition - Results Initial Inflation Pressure Orifice Diameter Burst Acceleration Observations: Orifice area is most sensitive to perturbations. Other parameters seem invariant to perturbations Step 3 – Fixed Orifice Diameter to 2” Initial Inflation Pressure Burst Acceleration Observations: Burst acceleration sensitivity appears to increase at “optimal” orifice diameter Step 2:

  6. Baseline Airbag Venting Parameter Definition - Results Step 5 – Check that General Trends Hold for Orifice Area Initial Inflation Pressure Orifice Diameter Observations: Brinkley DRI seems to improve slightly with increasing initial inflation pressure. This improvement begins to level off at approximately 125kPa Observations: Best performing orifice diameter is similar to that originally found. Trends are also very similar, indicating relative insensitivity of other studied parameters Baseline Parameter Values • Summary & Conclusions: • For a fixed geometry, external orifice area has the most influence on the overall performance of the airbag system • Burst acceleration is the next most influential parameter, but its influence is far overshadowed by that of the external orifice area • The system performance is essentially insensitive to the initial airbag pressure (over the low pressure range investigated) Step 4 – Fixed Orifice Diameter to 2” and Burst Acceleration to 15G’s

  7. Orion Alternative Landing Attenuation Concept Study • Flapper Valve Development

  8. Flapper Valve Requirements • Based on the results of the parametric study we need a valve: • Which has a large outlet diameter (≥Ø2”); and • Opens at low pressures (≈130kPa, ≈4psig) • A survey of available valves found that: • Pressure relief valves with large outlet diameters are typically used in industrial applications and operate at a high pressure • Low pressure valves have very small outlet diameters • “Low pressure” valves typically refer to pressures higher than our required opening pressure • Valves that meet our requirements are custom designed and built • 18-26 week delivery times • Very costly • Decided to develop our own valves based on the design of those custom designed to meet similar requirements

  9. Flapper Valve Design • Personal Airbag System Valve • Flapper Valve P/N 11070 • Outlet area size to be between 2 and 2.5” • Springs sized to open at a pressure of approximately 130kPa • Leakage has been problematic, but we are close to getting acceptable performance • Developed for the Orbital Sciences X-34 Propulsion System Tanks • Low pressure operation • Low leakage with gaseous helium

  10. Flapper ValveLeakage – Test Setup Data Recording Computer Pressure Transducer Test Valve DAQ Fitting for Pressure Measurement Power Supply Gasket Airtight Container Container Inlet Valve Leak detection fluid is applied to the seat edge. Leaks are indicated by bubbling of the fluid

  11. Flapper Valve Leakage Testing - Results

  12. Flapper Valve Leakage Testing - Results

  13. Flapper Valve Leakage Testing - Results

  14. Flapper Valve Leakage Testing - Summary • Summary • Leakage has been a significant issue in the development of the flapper valve • We have not found a final solution yet, but we think we are close • A good sealing material for this application: • Is viscoelastic • Has a completely closed cell, non-porous structure • Is applied such that there are no imperfections in its seal (assembly sensitive) • Vinyl foam rubber shows promise for our sealing purposes • We are in the process of procuring it in a more fabrication-friendly form

  15. Preliminary Single Airbag Test Article Design

  16. Preliminary Single Airbag Test Article Design Drop Article to Drop Rig Interface (Same as that used in Gen 1 System) Inflation Valve Flapper Valve Pressure Transducer Hard Point for Mounting Impact Angle Control (Same as that used in Gen 1 System) Test Mass (5lb) Simulated Floor (Constructed of the same extrusions used in the Gen 1 frame) Test Airbag Airbag-Floor Interface PEM Blind Self-Clinching Fasteners

  17. Actively Controlled Flapper Valve DevelopmentJack Weinstein

  18. Design Objectives • Electronically controlled valve • Precisely controlled, easily adjusted set pressure • First pass: Testing oriented • Cheap, simple to produce • Blow open/stay open design • Integrates with current prototype • Maintain tight seal

  19. Concepts

  20. Concepts Force from electromagnet Magnet Distributed load from differential pressure • Electromagnet • Estimated Actuator Cost: $30-40 • Features: Simple, fast response time. Ease of integration into existing flapper. • Design obstacles: Incorporating magnets without changing area of flap; finding small, powerful, affordable electromagnets. Magnet might introduce gaps into sealing foam.

  21. Concepts Actuator Reaction force from pin Pin motion Distributed load from differential pressure • Release Pin • Estimated Actuator Cost: $10-15 • Features: Simple, good response time. Doesn’t require powerful (expensive) actuator. • Design obstacles: Torque against pin causes friction; reaction force doesn’t compress foam, so sealing difficulties are likely.

  22. Concepts Sprint torque Pin motion Θ Distributed load from differential pressure • Adjustable Spring • Estimated Actuator Cost: $50? • Features: Makes good use of existing framework. • Criticism: Doesn’t actually provide electronically controlled opening; as such, no benefit to using actuator over hand-turned linear screw. Retains imprecision of spring; requires actuator to be very small, strong, precise (read: costly).

  23. Concepts Torque from motor Distributed load from differential pressure • Direct Control • Servomotor • Estimated Actuator Cost: $30-40 • Features: High degree of control. • Design obstacles: Requires high torque from servo. Opposite motion required for flappers requires creativity (two motors? Gear system?). Control not necessary for first-pass test valves.

  24. Short-term Goals • Continue research: available actuators, examples from industry • Refine concepts: detailed designs, modeling, analysis • Begin build testing

  25. Generation 2 Seat Frame DevelopmentJosh Gafford

  26. Seat Design • Critical Modules • Airbag interface / mounting plates (maximizing load distribution and airbag stroke) • Interface between seat and testing rig • Foldable joints for stowing away • Angle adjustment / sectional elongation mechanism Design Considerations • Weight minimization (material and geometry considerations) • Structural stiffness, resistance to impulse loads (system should hold its shape during impact) • Adjustable angle/section lengths to accommodate range of expected body sizes (without use of tools) • Ability to collapse when not in use • Most importantly: MINIMIZE RISK OF INJURY to occupant under loads experienced during rapid deceleration

  27. Folding Joint Concepts Threaded Peg Quick-Release Latch Spring-Loaded Peg

  28. Folding Joint Concepts Future Tasks: • Exploring other joint folding methods • ELIMINATING shear loading situations on joints/bolts/pegs/fasteners • Alter configuration of fasteners to take primarily tensile/compressive loads, or translate shear loading to structural members • Keeping design as simple and robust as possible, without sacrificing functionality, rigidity, and weight minimization • Controlling vibration (damping elements) • Fabrication considerations (bridge gap between idea and reality) • First order analyses, benchmark experiments, FEA

  29. Orion Alternative Landing Attenuation Concept Study • Moving Forward

  30. Moving Forward • Near-term Tasks (Over the next month): • Complete leak-proofing of flapper valves (by Nov. 9th) • Fabricate test airbag and interfaces (by Nov. 9th) • Finalize design of single airbag drop test article (by end Oct. 28th) • Conduct small scale drop testing to validate results of parametric study (Start Nov. 16th) • Longer-term Tasks • Improve models based on drop test results • Continue development of seat frame structure • Continue development of actively actuated flapper valves

  31. Orion Alternative Landing Attenuation Concept Study • Questions?

  32. Orion Alternative Landing Attenuation Concept Study • End of Presentation

  33. Orion Alternative Landing Attenuation Concept Study • Backup Slides

  34. Brinkley Model X Y Z These values are used to calculate the β-Number, which gives an overall indication of the risk to injury during a drop. β < 1 indicates that the Brinkley criteria for the inputted level of injury risk has been satisfied • Metric used to gauge the risk of injury to an occupant in an accelerating frame of reference • Based on approximating the human as a spring-mass-damper system: • Brinkley Direct Response Index is obtained from: • Risk of injury is measured by comparison with predefined Brinkley Limits, with a lower Brinkley Number corresponding to a lower risk of injury:

  35. Pressure Transducer Control Test Results Test Performed at ~2pmOctober 14th 2009 Approximate Pressure Containment Limit of Container NOTES: Calibration Function Used: Pressure (kPa) = 206.842719/5*(Voltage(V)-1) Filter Used: 3rd Order Butterworth Filter with a cut-off frequency of 2Hz (0.01*sampling rate)

  36. NOAA Buoy Station 44013 (LLNR 420) Air Pressure DataLocated: BOSTON 16 NM East of Boston, MA P[atm]: ~102.13kPa No Pressure Data at this buoy Approximate time of test REF: http://www.ndbc.noaa.gov/station_page.php?station=44013&unit=M&tz=STN

  37. Discussion and Conclusions • Container • Maximum pressure able to be maintained in container is approximately 110kPa < 128kPa burst valve designed opening pressure • Need a stronger container for valve opening characterization testing • Pressure Transducer • Discrepancy of approximately 0.5-0.6kPa between atmospheric pressures measured by NOAA and by our pressure transducer • Note that these measurements were taken in different locations • Conclusion is that accuracy of pressure transducer and calibration function used is good enough for our purposes

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