Reverse Engineering Crosswind Limits - A New Flight Test Technique?

A New Flight Test Technique?

Troy Asher (M), Tim Williams (M), and Brian Strovers

Reverse Engineering Crosswind Limits

Outline

Background: Fly without spoilers?! Build-up approach Math A New Flight Test Technique, the SS2B Flight test/simulator results Lessons Learned 27 Sept 2013 –

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SETP

Background

Experimental flight research project within larger ERA project NASA and Air Force Research Laboratory joint effort Seamless transition between trailing edge surfaces Reduce noise during takeoffs and landings Improve aircraft aerodynamic efficiency

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Adaptive Compliant Trailing Edge (ACTE) project Composite flexible trailing-edge wing flaps Environmentally Responsible Aviation – 27 Sept 2013 –

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ERA SETP

NASA 804

Test Article

Ground spoilers, speed brakes and low speed roll control – NASA Dryden Gulfstream III, N804NA (NASA 804) is a G-1159A Designated as a SubsoniC Research Aircraft Testbed (SCRAT) Low-wing, twin fanjet, pressurized transport category aircraft Lateral control: ailerons and 3 spoilers on each wing Flight controls hydraulically powered with a manual reversion mode Demonstrated max x-wind 21 knots 45,000 feet; 340 KIAS/0.85M 38,570 lbs empty; 69,700 lbs max Fowler flaps – 0°, 10°, 20°, 39° 27 Sept 2013 – • • • • • • • • • SETP

The Problem

All wing spoilers had to be removed Some aileron also needed to counter lateral asymmetries inherent in ACTE Be sufficient for control in crosswinds Be sufficient for control in failure states

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Replace fowler flaps on a G-III with ACTE flaps Would ‘residual roll capability’ Is this a suitable testbed?

27 Sept 2013 –

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SETP

“Stock” configuration

Spoilers Off ‘Up-and-Away’

Spoilers Disabled

Buildup

throughout program iteratively

Simulator

Used transport category sim Basic aeromodel from pilot training sim Updated Normal flight mode Stability & Control, Performance, Aeromodeling data Manual Reversion mode – Four flights – SS2B FTT, aero-model, bank-to-bank, HQ – – – – – – – Building a Phase 0A – Baseline Aircraft in Phase 0B – Fowler flaps, Back to the Simulator – revalidation of HQ 27 Sept 2013 –

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SETP 200 ft 200 ft 3º L

Offset Landing Task

On Centerline Wings level 1500 ft from the approach end Vref -10 knots – – – – Setup on ILS approach 1-dot width right (~200 ft) of Localizer; on Glidepath At 200 ft AGL, correct to land 27 Sept 2013 –

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SETP ±500 ft ±250 ft L 1500 ft -10 ref

Offset Landing Task -10

ref 75 ft of runway centerline 10 ft of runway centerline

Performance Criteria

±5kts of V ± ± ± 250 ft downrange* Smooth touchdown ± 500 ft downrange* +10/-5kts of V Desired Adequate * Note: started with ±200 ft but concluded downrange wasn’t relevant to the task other than to increase pilot gains. Therefore, increased this to 250 feet.

27 Sept 2013 – SETP

Stock Aircraft

Phase 0A HQ Results

Simulator aeromodel still immature at this point Sim improved over time Aircraft, as expected No HQ in Man Reversion mode – open loop only 27 Sept 2013 –

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SETP ܽɁ ܽɁ ܽɁ ܽɁ ܽɁ ܽɁ ) ܰ൅ ݎɁ ܮ ൅ ݎɁ ܻ൅ ݎɁ β ݎɁ ஔ௔ ݎɁ ݎɁ ܰ൅ Ⱦ Ⱦ ൅ ܮ  ݀݊ܽǡ ܻ൅ Ⱦ Ⱦ Ⱦ Ⱦ β ஔ௥ , β థ Ͳ ൌ ܮ ܰൌ Ͳ ܻൌ ߶ ݃ (75% for Mil-Std-1797) - ࣘ ࢇࢾࢊ࢔ࢇ ǡ࢘ࢾ ǡ ࢼǡ ܽɁݎ݋ ǡݎɁ ǡ߶ = 0 Ⱦሶ to lateral velocity ઺ P, R, Ṗ, Ṙ, Side force reduces to Roll reduces to Yaw reduces to Solve each unknown as a function of β ( Find β at the limit for

Phase 0B Crosswind Predictions

• • • • • • Use lateral directional equations of motion 3 equations 4 unknowns Convert – – –

Wing low crosswind landing is a steady heading sideslip

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SETP First Flight Limit 5 knots

Limit With 75% Aileron Deflection

Predictions

Skeptical that 25% aileron deflection would be sufficient 27 Sept 2013 – SETP No Spoilers No Spoilers / No Flap

Pre-Phase 0B

Simulator included all Phase 0A data including man reversion Crosswind landings done with up to 10 knots of crosswind

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Flew test profile and several scenarios in the simulator

27 Sept 2013 –

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SETP

Determining Residual Roll Rate

Is 5 knots crosswind too conservative? Is 25% residual aileron deflection enough? How much residual roll rate is enough? Steady Heading Sideslip + Bank-to-Bank Roll Calculate resulting residual roll rate

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Crosswind limit questions Original plan Why not just measure it!

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(SS2B)

The Sideslip-to-Bank Maneuver

Establish desired bank angle first Then feed in rudder to maintain heading Stabilize for 10 seconds Full yoke into established bank Rudder fixed Backwards “Steady-Heading Sideslip” “Bank-to-Bank Roll” Terminate at max bank angle Recover to wings level

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27 Sept 2013 – 1. 2. 3. 4.

SETP = 133 KIAS stall No Flap 1.2 V 3/8 initial yoke deflection - - -

Sideslip-to-Bank Maneuver

27 Sept 2013 – SETP

Test Matrix

0°

3/8 1/2 5/8 10° 20° (man rev limit)

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10,000 ft; 1.2 Vstall Heavy weight – early in flight (≈ 58,500 lbs) Light weight – end of flight (≈ 44,000 lbs) Yoke deflections (both left and right) Flap Positions Terminate roll at 20° bank 27 Sept 2013 –

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SETP = 115 KIAS stall Flaps 20-deg 1.2 V 1/2 initial yoke deflection - - -

Sideslip-to-Bank Maneuver

27 Sept 2013 – SETP

Sideslip-to-Bank Time History

Sideslip used for crosswind Aileron usage Residual roll rate – – – SHSS, time < 2 s Full aileron, time 3 to 9 s Return to wings level coordinated flight, time > 10s 27 Sept 2013 –

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SETP No Spoilers 10K ft 20K ft Mil-Std-1797 Lateral FQ Results environment with

vs. Usability

Initial Phase 0B Results

Aircraft acceptable for flight in controlled ≤ 50% yoke deflection Easily handle > 5 kts wind

Safety

 

Phase 0B pilot comments Need to expand the crosswind limit

27 Sept 2013 –

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SETP

Research

No “exceptional pilot skill, alertness, or strength” < 75% roll control authority (retains level II FQ) No roll rate guidance Roll rates > 5°/sec had “acceptable” pilot ratings 45%-60% control deflection was Satisfactory • • • • •

14 CFR Part 25 Mil-Std-1797 NASA TN-7062

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How much roll rate is needed for crosswind landings? Tire Speed (182 knots) FAA handbook 8110.8 allows (4° crab) 27 Sept 2013 –

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SETP

Design Criteria

Maximum 50% control wheel deflection to maintain runway alignment Takeoff and landing does not require “exceptional pilot skill, alertness, or strength” Touch down at less than 182 knots ground speed Maximum of 2 degrees crab angle at touch down 27 Sept 2013 – 1. 2. 3. 4.

SETP

Flight Data

50% yoke deflection criteria Resulted in 4 deg/s roll rate minimum

27 Sept 2013 –

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SETP

Results

27 Sept 2013 – SETP 120 130 140 150 160 (KIAS) Min Vref 12 13 14 15 16 (knots) Crosswind ) ref

New Crosswind Limit

to 10 times the crosswind component (“Pilot Math”) ref Added 2° crab angle to increase usability (+ 4 to 5 knots) – Crosswind limit is based on landing speed (V Adjust V • •

Offset Landings

Aircraft with Spoilers Deactivated

Phase 0B

New Crosswind Limits

in the sim

st (with action at 250 ft) – offset landings – 8 knot crosswind st nd 1 2 – – Practiced 1 2 Flights Data gathered in-flight was minimal to support results Returned to the simulator 27 Sept 2013 –

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SETP Simulator Flight Test

Validation

Simulation Handling Quality

Evaluate HQ in the simulation with 10-20 knot crosswinds Compare HQ using offset landing task Enabled the team to focus primary safety concerns on crosswind landing capability Enabled a scaled degradation of a aileron authority to determine handling quality limits Supported flight test and in return flight test data supported a more accurate simulator model – – – – – How do we know these crosswind limits are safe yet useable? Does simulation accurately represents the aircraft? Flight simulation 27 Sept 2013 –

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SETP

Back in the Sim

27 Sept 2013 – SETP It will pay for itself 10 times over.

Lessons Learned

For a modified G-III, it resulted in a limit that is safe yet useable Chosen criteria are critical to the final outcome Practice/refine FTTs without wasting precious flight time Evaluate modified aircraft before taking any in-flight risk Accurate evaluation of analytical predictions Continue research in a meaningful way after flying was over • • • • • • Fight for a simulator for your project and do what is necessary to keep it!

The Sideslip-to-Bank maneuver can be an accurate predictor of residual roll rate capability in the presence of sideslip An accurate flight simulator is an essential tool 27 Sept 2013 –

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SETP

Program Summary in Video

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Questions?

Back-up

27 Sept 2013 – SETP

Prediction versus Actual

27 Sept 2013 – SETP

G-III Flight Envelope

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Flight to Simulation Comparison

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Technique Comparison

27 Sept 2013 – SETP 10K ft 20K ft 40K ft

Qualities

Spoilerless Roll Handling

27 Sept 2013 – SETP Cockpit Instrumentation Hot Films

Instrumentation

Leading Edge Wiring 27 Sept 2013 – SETP

Instrumentation

27 Sept 2013 – SETP