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Be careful, you just might find what you are looking for SQNLDR Darren Hughes Test Pilot ARDU FLTLT Dane Petersen Flight Test Engineer ARDU An F/A-18 AOC.

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Presentation on theme: "Be careful, you just might find what you are looking for SQNLDR Darren Hughes Test Pilot ARDU FLTLT Dane Petersen Flight Test Engineer ARDU An F/A-18 AOC."— Presentation transcript:

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

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

3 The 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.

4 Limit cycle oscillation Asymmetric wing motion Pilot’s experience 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

5 Helmet mounted camera (±0.05/±0.06g) moderate level LCO from the pilot’s perspective (±0.05/±0.06g) moderate level LCO from the pilot’s perspective

6 Increasing amplitude = degradation A human factors issue! ±0.05 g ±0.10 g ±0.15 g Very distracting Displays blurred Difficult to select upfront controls Operational Limit ±0.10 g Flight Test Limit ±0.15 g LCO ABORT is Throttles to IDLE

7 Active Oscillation Control The ailerons move to dynamically suppress LCO AOC mode selection > ±0.15 g can not reliably select the AOC mode! AOC uses an upfront controller

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

9 A ‘one-off’ event? The GBU-16 was cleared by other F-18 users: why would we be different? 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 Qualitative description was not compelling: turbulence seemed like a plausible explanation Almost heart of the envelope

10 Risk Assessment Cause unknown = proceed with caution & LCO safety case 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

11 Happy! A slow build-up in speed... A slow build-up in speed... Slow down for undesirable response

12 Test Configuration

13 Test Technique Slow accelerations: Slow accelerations: 0.73 M 0.93 M Level / +1.5g / +2.0g / +3.0g Stick rap Speed(hold/increase)Speed(hold/increase) Terminate(0.08g)Terminate(0.08g) Telemetry Test aircraft

14 Results AOC OFF Standard Hornet = ON - this was another matter entirely!

15

16 0.08g Aileron reduces immediately with AOC OFF selection Reduces 0.5 sec after AOC OFF selection IDLE had no effect on recovery IDLEAOC OFF

17 Outboard wing Bothempty Bothoccupied

18 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

19 A structural issue as well! Lateral acceleration should not have been the sole terminate limit! LCO - asymmetric movement AOC driven - symmetric movement Lateral acceleration Wingresponse ±0.15 g < ±3.0 g Lateral acceleration Wingresponse ±0.15 g > ±9.0 g Qualitative similar ‘feel’ to LCO, but almost unrelated!

20 Conclusion 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 Presence of ‘objectionable vibration’ confirmed

21 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

22 Where to from here? Check 2000 lbs weapons Check 2000 lbs weapons Disable the AOC? Disable the AOC?

23 Questions?


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