Be careful, you just might find Be careful, you just might find what you are looking forwhat you are looking for

SQNLDR Darren HughesSQNLDR Darren HughesTest PilotTest Pilot

ARDUARDUFLTLT Dane PetersenFLTLT Dane PetersenFlight Test EngineerFlight Test Engineer

ARDUARDU

An F/A-18 AOC Interaction during asymmetric carriage of An F/A-18 AOC Interaction during asymmetric carriage of underwing storesunderwing stores

IntroductionIntroduction• 2006 2006

• Hornet Upgrade programHornet Upgrade program

• End to End assessment of GBU-16End to End assessment of GBU-16

• ““excessive and objectionable lateral cockpit excessive and objectionable lateral cockpit vibration”vibration”

• 20102010

• Investigate for a full clearanceInvestigate for a full clearance

• It was probably just an “anomaly”It was probably just an “anomaly”

The investigationThe investigation• Hornet unique stores clearance considerations.Hornet unique stores clearance considerations.

• A conservative approach.A conservative approach.

• What we found!What we found!

• Lessons learned.Lessons learned.

Limit cycle oscillationLimit cycle oscillation

AsymmetriAsymmetric wing c wing motionmotion

Pilot’s Pilot’s experienceexperience

A 5.6 Hz oscillation that is bounded for a given A 5.6 Hz oscillation that is bounded for a given dynamic pressure, and only present during carriage dynamic pressure, and only present during carriage of High pitch inertia stores & wingtip missilesof High pitch inertia stores & wingtip missiles

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Helmet mounted Helmet mounted cameracamera

• (±0.05/±0.06g) moderate level LCO from the pilot’s perspective(±0.05/±0.06g) moderate level LCO from the pilot’s perspective

Increasing amplitude = Increasing amplitude = degradationdegradation

A human factors issue!A human factors issue!±0.05 g±0.05 g ±0.10 g±0.10 g ±0.15 g±0.15 g

Very Very distractingdistracting

Displays Displays blurredblurred

Difficult to Difficult to select upfront select upfront

controlscontrols

OperationOperational Limital Limit ±0.10 g±0.10 g

Flight Flight Test LimitTest Limit ±0.15 g±0.15 g

LCO ABORT is Throttles to LCO ABORT is Throttles to IDLEIDLE

Active Oscillation Active Oscillation ControlControlThe ailerons move to dynamically suppress The ailerons move to dynamically suppress

LCOLCOThe ailerons move to dynamically suppress The ailerons move to dynamically suppress

LCOLCO

AOC mode AOC mode selectionselection

> > ±0.15 g±0.15 g can not reliably select the AOC can not reliably select the AOC mode!mode!

AOC uses an AOC uses an upfront upfront

controllercontroller

AOC uses an AOC uses an upfront upfront

controllercontroller

Task ObjectiveTask Objective

Investigate the ‘objectionable vibration’ to support Investigate the ‘objectionable vibration’ to support an full envelope clearance for the GBU-16.an full envelope clearance for the GBU-16.

A ‘one-off’ event?A ‘one-off’ event?• The GBU-16 was The GBU-16 was

cleared by other F-18 cleared by other F-18 users: users: why would we why would we be different?be different?

• Qualitative description Qualitative description was not compelling: was not compelling: turbulence seemed turbulence seemed like a plausible like a plausible explanationexplanation

Almost heart Almost heart of the of the

envelope envelope

Almost heart Almost heart of the of the

envelope envelope

Risk AssessmentRisk Assessment• Cause unknown = proceed with caution & LCO safety caseCause unknown = proceed with caution & LCO safety case

Safety Chase

available

Standard LCO abort

limit

±0.15 g lateral

acceleration

No Safety Chase

LCO limit reduced by

50%

±0.08 g lateral

acceleration

Standard LCO abort Standard LCO abort actions:actions:

1. Throttles IDLE1. Throttles IDLE2. AOC 2. AOC OFFOFF

Happy!Happy!

A slow build-up in speed...A slow build-up in speed...Slow downSlow down for undesirable response for undesirable response

Test ConfigurationTest Configuration

Test TechniqueTest Technique Slow Slow

accelerations:accelerations:0.73 M0.73 M 0.93 M0.93 M

Level / +1.5g / +2.0g / +3.0gLevel / +1.5g / +2.0g / +3.0g

Stick Stick raprap

Stick Stick raprap

SpeedSpeed(hold/increase)(hold/increase)

SpeedSpeed(hold/increase)(hold/increase)

TerminateTerminate(0.08g)(0.08g)

TerminateTerminate(0.08g)(0.08g)

TelemetTelemetryry Test aircraftTest aircraft

ResultsResults

AOC OFFAOC OFF StandarStandard Hornetd Hornet==

ONON - this was - this was another matter another matter

entirely!entirely!

ONON - this was - this was another matter another matter

entirely!entirely!

0.08g

Aileron reduces

immediately with AOC OFF

selection

Reduces 0.5 sec after AOC OFF selection

IDLE had no effect on recovery

IDLE AOC OFF

Outboard wingOutboard wing

BothBothemptyempty

Both Both occupiedoccupied

What if Safety Chase What if Safety Chase was used?was used?

Safety Chase

available

Standard LCO abort

limit

±0.15 g lateral

acceleration

No Safety Chase

LCO limit reduced by

50%

±0.08 g lateral

acceleration

AOC selection may AOC selection may not have been not have been

possible!possible!

±0.15 g±0.15 g an ineffective and inappropriate an ineffective and inappropriate terminate limit terminate limit

A structural issue as A structural issue as well!well!

Lateral acceleration should Lateral acceleration should notnot have been have been the sole terminate limit!the sole terminate limit!

LCO - asymmetric movementLCO - asymmetric movement AOC driven - symmetric movementAOC driven - symmetric movement

Lateral Lateral accelerationacceleration

Wing Wing responseresponse

±0.15 g < ±3.0 g< ±3.0 g

Lateral Lateral accelerationacceleration

Wing Wing responseresponse

±0.15 g > ±9.0 g> ±9.0 g

Qualitative similar ‘feel’ to LCO, but almost Qualitative similar ‘feel’ to LCO, but almost unrelated! unrelated!

ConclusionConclusion

0.10 g/s0.10 g/srate ofrate ofincreasincreas

ee

2 seconds2 secondsLateral acceleration at pilot’s seat double the

operational limit, at ±0.20 g!

Asymmetric captive carriage of the Asymmetric captive carriage of the GBU-16 was GBU-16 was UNACCEPTABLEUNACCEPTABLE above above 0.75 M0.75 M

Presence of ‘objectionable vibration’ Presence of ‘objectionable vibration’ confirmedconfirmed

Lessons LearntLessons Learnt

‘‘Be careful, you just might find what you’re Be careful, you just might find what you’re looking for’.looking for’.

Take time to critically reevaluate the plan when Take time to critically reevaluate the plan when unexpected results are encountered.unexpected results are encountered.

Understand the System Under TestUnderstand the System Under Test

Where to from here?Where to from here?

• Check 2000 lbs weaponsCheck 2000 lbs weapons

• Disable the AOC?Disable the AOC?

Questions?Questions?