Be careful, you just might find what you are looking for An F/A-18 AOC Interaction during asymmetric carriage of underwing stores SQNLDR Darren Hughes Test Pilot ARDU FLTLT Dane Petersen Flight Test Engineer ARDU

Introduction • 2006 • Hornet Upgrade program • • End to End assessment of GBU-16 “excessive and objectionable lateral cockpit vibration” • 2010 • • Investigate for a full clearance It was probably just an “anomaly”

The investigation • Hornet unique stores clearance considerations.

• A conservative approach.

• What we found!

• Lessons learned.

Limit cycle oscillation A 5.6 Hz oscillation that is bounded for a given dynamic pressure, and only present during carriage of High pitch inertia stores & wingtip missiles Asymmetric wing motion Pilot’s experience

Helmet mounted camera QuickTime™ and a YUV420 codec decompressor are needed to see this picture.

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

A human factors issue!

±0.05 g Very distracting ±0.10 g Displays blurred ±0.15 g Difficult to select upfront controls Increasing amplitude = degradation Operational Limit Flight Test Limit ±0.10 g

±0.15 g

LCO ABORT is Throttles to IDLE

Active Oscillation Control The ailerons move to dynamically suppress LCO AOC mode selection AOC uses an upfront controller >

±0.15 g

can not reliably select the AOC mode!

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

A ‘one-off’ event?

• • The GBU-16 was cleared by other F-18 users:

why would we be different?

Qualitative description was not compelling:

turbulence seemed like a plausible explanation

pe envelo of the ost heart Alm

Risk Assessment • Cause 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 actions: 1. Throttles IDLE 2. AOC

OFF

Happy!

A slow build-up in speed...

Slow down

for undesirable response

Test Configuration

Test Technique 0.73 M 0.93 M Slow accelerations: Level / +1.5g / +2.0g / +3.0g

Telemetry Stick rap Speed (hold/increase) Terminate (0.08g) Test aircraft

Results AOC OFF = Standard Hornet

ON

- this was another matter entirely!

Aileron reduces immediately with AOC OFF selection 0.08g

IDLE had no effect on recovery IDLE AOC OFF Reduces 0.5 sec after AOC OFF selection

Outboard wing Both empty Both occupied

What if Safety Chase 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 not have been possible!

±0.15 g

an ineffective and inappropriate

terminate limit

A structural issue as well!

Qualitative similar ‘feel’ to LCO, but almost unrelated! LCO - asymmetric movement Lateral acceleration ±0.15 g Wing response < ±3.0 g AOC driven - symmetric movement Lateral acceleration ±0.15 g Wing response

> ±9.0 g

Lateral acceleration should

not

terminate limit!

have been the sole

Conclusion Presence of ‘objectionable vibration’ confirmed 0.10 g/s rate of increase 2 seconds Lateral acceleration at pilot’s seat double the operational limit, at ±0.20 g!

Asymmetric captive carriage of the GBU 16 was

UNACCEPTABLE

above 0.75 M

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

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

 Understand the System Under Test

Where to from here?

• Check 2000 lbs weapons • Disable the AOC?

Questions?