Handling Qualities Optimization for Rotorcraft Conceptual Design

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Handling Qualities Optimization for Rotorcraft

Conceptual Design

Ben Lawrence Colin Theodore

San Jose State University

Wayne Johnson

NASA Ames Research Center National Aeronautics and Space Administration NASA Ames Research Center

Tom Berger

U.S. Army Aviation Development Directorate Moffett Field Rotorcraft Virtual Engineering Conference,

Liverpool, UK

November 8 - 10, 2016

NASA Revolutionary Vertical Lift Technology Project (RVLT)

Develop and Validate Tools, Technologies and Concepts

to Overcome Key Barriers for Vertical Lift Vehicles

Vision • Enable next generation of vehicles to expand capabilities and develop commercial markets with technologies for noise, speed, safety, mobility, payload, efficiency, environment Scope • Spectrum of configurations from very light (UAS) to ultra - heavy (transport size) Conceptual Design Tool Development • Developing an OpenMDAO framework to integrate High - fidelity, validated CFD discipline analyses: Sizing , propulsion, acoustics, structural loads and handling qualities Advanced measurement techniques Conceptual Design Tool Development Advanced propulsion and drive systems Noise Modeling

Handling Qualities in Conceptual Design

Stability, control and handling qualities (HQ) historically given little attention in conceptual design – “not given their proper place in the early design trade - space, and often left until flight test to discover and ‘put † right ’” – Weight savings by addressing over - design Development of toolset: “SIMPLI - FLYD” Exploring HQ in conceptual design † Padfield, G. D ., 1988. and 2012 – integrate in a MDAO framework

• SIMPLI - FLYD

– CONDUIT optimization and HQ design margins

• NDARC/SIMPLI - FLYD coupling

• Results

– Tiltrotor

– Helicopter

• Lessons l earned

• Future developments

SIMPLI - FLYD

• “ SIMPLIfied FLight dYnamics for conceptual Design” – NASA/U.S. Army collaboration – NDARC: NASA Design and Analysis of RotorCraft Automated process that: • Calculates linear flight dynamics models • Integrates control system optimization for roll, pitch, vertical and yaw response axes • Calculates stability and control parameters for handling qualities metrics • Generates a real - time flight dynamics and control model for piloted simulation in X - Plane

Control System Model

• Full - authority fly - by - wire • Model - following architecture – Generic architecture that can be applied to multiple vehicle configurations

K , K …

p q – Feedback to stabilize, provide gust rejection – Feed - forward for piloted response, command shaping Rotor - Borne Wing - Borne • Appropriate piloted response Hover Forward - Flight Forward - Flight types chosen automatically Roll RCAH RCAH RCAH Angle - of - Attack - based on flight regime Pitch RCAH RCAH Command Sideslip - Sideslip - Yaw RCDH Command Command Thrust RCHH Open - loop Open - loop • Control system gains need to be RCAH = Rate - Command/Attitude - Hold optimized RCDH = Rate - Command/Direction - Hold RCHH = Rate - Command/Height - Hold

Control System Optimization - CONDUIT

ADS - 33E MIL - STD - 1797B • Control Designer’s Unified Interface ® (CONDUIT ) – Optimizes control system parameters to meet handling qualities specifications • Automatic selection of different specification sets from ADS - 33E and MIL - STD - 1797B criteria for control optimization Rotor - borne Wing - borne – 17 to 23 specs per axis • Design margin Piloted Bandwidth Handling qualities levels – % over - /under - design based on ability 0.4 of aircraft to meet metrics in each axis ■ Level 1 - Good ■ Level 2 - Adequate • 0% Just meets Level 1 0.3 ■ Level 3 - Unsatisfactory • - 100% on Level 2/3 boundary 0.2 • Most limiting specification determines - 100% +100% 0% design margin for each axis 0.1 Phase delay [sec] Design – 2 per axis Margin 0 1 2 3 4 5 Bandwidth [rad/sec]

Objectives and example cases

• Evaluate NDARC/SIMPLI - FLYD coupled analysis to explore

handling qualities in conceptual design

• Example aircraft/HQ scenarios chosen:

– NDARC models with typical missions for sizing task

– Varied a mix of design and actuator parameters

• Tiltrotor pitch axis

– Forward flight only

– Varied horizontal tail size, location, flap area ratio, actuator rate limit

• Single Main R otor (SMR) helicopter yaw axis

– H over & forward flight

– Varied tail rotor size, location, collective actuator bandwidth and rate

limit

NDARC/SIMPLI - FLYD coupling

• NDARC s izes aircraft for design mission PYTHON Design Parameters • Python scripting used to SIMPLI - FLYD Geometry, trim, integrate NDARC and aerodynamic data Flight dynamics SIMPLI - FLYD in single NDARC modeling process (MATLAB) Inertia • Design parameter, Stability and control Empty Weight, Power etc.

derivatives actuator characteristic and flight condition ± % HQ Design Margins sweeps CONDUIT DESIGN • Outputs: – CONDUIT computed HQ Actuator Characteristics Design Margins – NDARC empty weight • Moments of inertia derived from fixed radii of gyration and weight

Handling Qualities Design Margin Data

PITCH AXIS Tail area =25.25ft Tail area =49.245ft Tail area =75.375ft

Handling Qualities Design Margin Data

• Compact visualization

of 3 - D/4 - D data

• Primary intent is to

illustrate trends and

sensitivities

Tiltrotor Pitch Axis HQ - Introduction

PITCH AXIS • Feed - forward: – Maneuver response • Feedback: – Stabilization , disturbance rejection

• Tail size varied at constant

Aspect Ratio

• Elevator flap area ratio: – 1.0 = all moving tail – 0.0 = no flap

• Elevator flap control

actuator rate limit

Tiltrotor Pitch Axis HQ – Effect of Speed

PITCH AXIS Small tail, Small flap Small flap Large tail, small flap Small tail 300 kts 230 kts 160kts Reducing Speed Low airspeed is critical for sizing tail but important to check whole envelope

Tiltrotor Pitch Axis HQ vs. Empty Weight

Weight mostly sensitive to tail size Small tail 160kts Tradeoff between minimum weight and handling qualities constraints

Tiltrotor Pitch Axis HQ – Tail length Variation

Weight sensitive Rate limit = 20 deg /s, Tail length varied to tail size and location Longer tail 160kts Tradeoff between minimum weight and handling qualities constraints

Single Main Rotor Yaw Axis HQ - Introduction

• Tail rotor size varied at

constant solidity and tip

speed

• Tail rotor longitudinal

location

• Actuator bandwidth limit

for tail rotor collective

• Region of no data for

non - converged NDARC

cases

Single Main Rotor Yaw Axis HQ – Effect of Speed

Longer tail, greater BW ≈ +10% Nominal design ≈ - 20% 0 kts 80 kts (hover) Increasing Speed Speed change includes change of control mode and HQ spec requirements

Single Main Rotor Yaw Axis HQ – Larger Tail Rotors

Nominal design 0 kts 80 kts (hover) Increasing Speed

Single Main Rotor – Empty Weight

Weight minimum Smaller tail rotors lead to heavier aircraft Trading weight via trim/performance aspects

Lessons Learned From Application Of The Tools

• Handling qualities vary with flight condition:

– Due to different characteristics and different HQ requirements

– CONDUIT Design Margin helps to provide a consistent metric

• Actuator characteristics important factor

– “Cost” (weight) needs to be accounted for in design

• Inertia modeling probably not sensitive enough to design

changes relevant to HQs

• Ensuring geometry “consistency” also important

• Current SIMPLI - FLYD process approx. 15 - 20 min per flight

condition

OpenVSP and ALPINE

• OpenVSP is a 3D geometry tool with a focus on conceptual design • ALPINE tool ( Automated Layout with a Python Integrated NDARC Environment ) developed by US Army ADD to generate OpenVSP models from NDARC output Geometry “fixed” • OpenVSP sub functions: – mass properties tool offers a higher resolution prediction of moments of inertia – Integration plans underway • OpenVSP offers possibilities to address geometry management

Overview

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