Personal Airbag System Investigation

October 21st, 2009

Progress Update

Principle Investigator: Professor Olivier de Weck

Graduate Student: Sydney Do

Undergraduate Students: Josh Gafford

Jack Weinstein

Orion Alternative Landing Attenuation Concept Study

Since Our Last Progress Update

Tasks Moving Forward Listed in Last Progress Update (August 6th, 2009)

Progress Made Since Last Update

• Complete definition of baseline airbag venting parameters for small scale testing

• Determine appropriate pressure relief and solenoid valves for use in small scale testing

• Develop fabric-type burst disk

• Develop small scale anti-bottoming airbag implementation techniques

• Complete Vectran tensile testing results analysis• Conduct small scale drop testing and determine

appropriate venting mechanism

• Completed

• Completed. Flapper-type pressure relief valve selected

• Completed. Leakage testing and leak-proofing is underway

• Deferred until after single airbag drop testing.

• Deferred until after single airbag drop testing.• Preliminary design of single airbag drop apparatus

is complete. Final design nearing completion

Additional Progress• Completed and presented a paper on this work at

Space 2009 (AIAA 2009-6438)• Commenced concept exploration of actively

controlled valves (Jack)• Commenced concept exploration of Gen 2 seat

frame (Josh)

Airbag Venting Mechanism Parametric Study

Orion Alternative Landing Attenuation Concept Study

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 Accelerationfor 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:1. Start with baselined values from Gen 1 airbag study (initial guess)2. For parameter A, fix the values of all other parameters and run 1DOF model over varying

A3. Fix A to the best performing value, and vary B4. Repeat Steps 2-3 until A, B, … etc. are “optimized” individually5. 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

Baseline Airbag Venting Parameter Definition - Results

Step 2:Initial Inflation Pressure Orifice Diameter

Observations: Orifice area is most sensitive to perturbations. Other parameters seem invariant to perturbations

Burst Acceleration

Step 3 – Fixed Orifice Diameter to 2”Initial Inflation Pressure Burst Acceleration Observations:

Burst acceleration sensitivity appears to increase at “optimal” orifice diameter

Baseline Airbag Venting Parameter Definition - Results

Step 4 – Fixed Orifice Diameter to 2” and Burst Acceleration to 15G’s

Initial Inflation PressureObservations: Best performing orifice diameter is similar to that originally found. Trends are also very similar, indicating relative insensitivity of other studied parameters

Observations: Brinkley DRI seems to improve slightly with increasing initial inflation pressure. This improvement begins to level off at approximately 125kPa

Step 5 – Check that General Trends Hold for Orifice Area

Orifice Diameter

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)

Parameter Value

Test Mass 5 lbs (2.27kg)

Radius 110mm

Length 350mm

Total Vent Orifice Area 2 x Ø(2-2.5”) holes

Initial Airbag Pressure 125kPa = 1.23atm

Burst Acceleration -15G’s

Corresponding Burst Pressure

Approx. 130kPa (4psig)

Baseline Parameter Values

Flapper Valve Development

Orion Alternative Landing Attenuation Concept Study

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

Flapper Valve Design

• Developed for the Orbital Sciences X-34 Propulsion System Tanks

• Low pressure operation• Low leakage with gaseous

helium

Flapper Valve P/N 11070

Personal Airbag System Valve

• 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

Flapper ValveLeakage – Test Setup

Airtight Container

Test Valve

Gasket

Pressure Transducer

Container Inlet Valve

Fitting for Pressure Measurement

Leak detection fluid is applied to the seat edge. Leaks are indicated by bubbling of the fluid

Data Recording Computer

DAQ

Power Supply

TestNo.

ValveConfig.

Observations Conclusion Image

1 Original (metal to metal seat)

Significant leaking felt by hand. Leak fluid seeped throughPressure transducer indicated no change in container pressure

Perform control test of pressure transducer.Sealing required at seat

2 Dummy Valve (Control Test)

Pressure transducer indicated expected increase in container pressureContainer bulged significantly

Pressure transducer has an adequate accuracy and works as expectedContainer cannot withstand our burst pressures

3 Neoprene Backed Flaps

Slight improvement on Test 1. Significant leaking observed. Leak fluid seeped throughPressure transducer indicated no major pressure increase

Covering entire hatch restricts room for material to deform and hence sealNeoprene is too firm for our purposes

4 Dow CorningSilicone Sealant on Seat

Performance similar to the observed in Test 3

Silicone rubber did not fill all gaps in seat. Silicone sealant is not viscous enough for our purposesPreloading required on spring to provide downward force

Flapper Valve Leakage Testing - Results

TestNo.

ValveConfig.

Observations Conclusion Image

5a Memory foam backed flaps with preloaded springs

Leakage still observed, however it is improved upon the initial testsSignificant leak fluid bubbling observed

Although this material conforms well to the seat and flap, its porosity causes it to leak.Hence this material has been ruled out.

5b Ear plug foam backed (vinyl foam) flaps with preloaded springs

Much improved performance over previous testsSome leak fluid bubbling observed from areas of imperfect material application

This material has potential for providing the sealing capability we need. Leakage was traced to imperfections in fabrication We are in the process of procuring it in a sheet form

6a Marian Chicago Vinyl foam tape backed flaps with preloaded springs

See 5b This material has potential for providing the sealing capability we need. See 5b

Flapper Valve Leakage Testing - Results

TestNo.

ValveConfig.

Observations Conclusion Image

6b Dennis RCR Vinyl foam tape backed flaps with preloaded springs

Leakage analogous to that observed in Test 5a

This material has been ruled out. See 5a

7a ULine Vinyl Foam backed flaps with preloaded springs

Sealing capability is better than un-preloaded springs however its leakage is greatest relative to all previous conducted preloaded tests

The firmness of this material is too high for this application. This causes it to not conform well to the seat surfaces.Hence, this material has been ruled out

7b Original Neoprene backed flaps with preloaded springs

Leakage analogous to that observed in Test 7a

Preloading the springs did not significantly improve the sealing ability of this material. Hence, this material has been ruled outSee 7a

Flapper Valve Leakage Testing - Results

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

Preliminary Single Airbag

Test Article Design

Preliminary Single Airbag Test Article Design

Flapper Valve

Hard Point for Mounting

Test Mass (5lb)

Drop Article to Drop Rig Interface(Same as that used in Gen 1 System)

Simulated Floor(Constructed of the same extrusions used in the Gen 1 frame)

Test Airbag

Pressure Transducer

Impact Angle Control(Same as that used in Gen 1 System)

Airbag-Floor Interface

Inflation Valve

Actively Controlled Flapper

Valve DevelopmentJack Weinstein

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

Concepts

Possible Designs Pros/Cons

Electromagnet holds flap down

Simple, fast. Small, strong electromagnets prohibitively expensive.

Solenoid/linear servo pulls pin to release flap

Simple, effective. Concerns about friction and sealing.

Linear actuator controls pre-load angle of spring

Takes full advantage of existing hardware. Imprecise, requires special actuator; philosophical objections.

Servomotor directly controls flap angle

High degree of control; high-torque servos are expensive, response control unnecessary.

Concepts

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.

Distributed load from differential pressure

Force from electromagnet

Magnet

Concepts

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.

Pin motion

Distributed load from differential pressure

Reaction force from pinActuator

Concepts

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).

Distributed load from differential pressure

Pin motion

Θ

Sprint torque

Concepts

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.

Distributed load from differential pressure

Torque from motor

Short-term Goals

• Continue research: available actuators, examples from industry

• Refine concepts: detailed designs, modeling, analysis

• Begin build testing

Generation 2 Seat Frame

DevelopmentJosh Gafford

Seat Design

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

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

Folding Joint Concepts

Threaded Peg

Quick-Release Latch

Spring-Loaded Peg

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

Moving Forward

Orion Alternative Landing Attenuation Concept Study

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

Questions?

Orion Alternative Landing Attenuation Concept Study

End of Presentation

Orion Alternative Landing Attenuation Concept Study

Backup Slides

Orion Alternative Landing Attenuation Concept Study

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

105

110

115

120

125

X: 0.003Y: 127.6

Bottom Bag Pressure vs Time

Time (s)

Pre

ssur

e (k

Pa)

X: 0.0034Y: 127.9

Orifice Dia. = 2"

Orifice Dia. = 2.5"

Brinkley Model

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:

)()()(2)( 2 tAtxtxtx nn

gtxDR n /)(2

X

Y

ZX Y Z

Direct Response Level DRX < 0 DRX > 0 DRY < 0 DRY > 0 DRZ < 0 DRZ > 0

Very Low (Nominal) -22.4 31 -11.8 11.8 -11 13.1

Low (Off-Nominal) -28 35 -14 14 -13.4 15.2

Moderate -35 40 -17 17 -16.5 18

High Risk -46 46 -22 22 -20.4 22.4

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

2

lim

2

lim

2

lim

)()()(

x

x

x

x

x

x

DR

tDR

DR

tDR

DR

tDR

Pressure Transducer Control Test Results

0 25 50 75 100 125 150 175 200 225 250 275 300102

104

106

108

110

112

X: 204.6Y: 110.3

Time (s)

Abs

olut

e P

ress

ure

(kP

a)

Pressure Transducer Control Test Results - October 14th 2009

X: 26.02Y: 102.7

Results 1

Results 2Results 3

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)

Approximate Pressure Containment Limit of Container

Test Performed at ~2pm October 14th 2009

NOAA Buoy Station 44013 (LLNR 420) Air Pressure DataLocated: BOSTON 16 NM East of Boston, MA

REF: http://www.ndbc.noaa.gov/station_page.php?station=44013&unit=M&tz=STN

P[atm]:~102.13kPa

Approximate time of test

No Pressure Data at this buoy

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