Post on 15-May-2018
transcript
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Electric VTOL Aircraft
Subscale Prototyping Overview
Francesco Giannini
fgiannini@aurora.aero
08 June 8th, 2017 ©2017 AURORA FLIGHT SCIENCES
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Contents
• Intro to Aurora
• Motivation & approach for the full-scale vehicle
• Technical challenges
• Design and building the subscale models
• Lessons learned
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Aurora has been developing autonomous aircraft systems for 28 years
Heritage
28Years in Business
UAS Design
30+Built and Flown
Hours
80Endurance Record
Feet
103KHighest Altitude Flown
Locations
8Worldwide
Patents
100+Issued & Pending
AUTONOMY ELECTRICPROPULSION
AIRFRAMEDESIGN
AURORA BY THE NUMBERS
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Three principles used in concept design
LARGE NUMBER OFREQUIREMENTS TO CONSIDER
Keep it simple
Design for efficient cruise
Base design on existing technology
USE THREE DESIGN PRINCIPLES
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Detailed Concept Modelling and Selection
Traditional and novel promising configurations were modeled and analyzed before selecting a lift + cruise configuration
https://vertipedia.vtol.org/vstol/wheel.htm
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Takeoff noise comparable to road traffic Inaudible in
cruise flight
>3x as efficient as a multi-copter in cruise
Light-weight, rigid structure avoids induced vibrations
No safety critical single points of failure
Optionally piloted – can be flown fully autonomously or piloted
Aurora – BCG DV concept:All-Electric VTOL Aircraft Design
Eliminates mechanical complexity –Direct drive, fixed pitch rotors/prop
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Video at: https://www.youtube.com/watch?v=BSFVvhQP7ws&t=6s
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Design challenges: Need to look out for negative wing-rotor interactions during transition
HOVER TRANSITION
Rotors placed so that rotor wash does not impinge on the wing
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Wing lift
Download from rotor wash
• As aircraft gains forward speed, rotor wash impinges on the wing to create a download
• Rotor-wing interaction reduces lift generated by the rotor, requiring rotor to increase power output
Rotor lift (reduced due to wing interaction)
Rotor lift
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Three main test objectives for the sub-scale model
Prove that configuration is able to perform the full mission1
Verify power consumption and controllability throughout mission is as expected, particularly transition
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Determine suitable sequence of reducing rotor thrust to support low-power transitions
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Limited experience in industry with low disc loading vs. high wing loading design. Need to verify rotor-wing interactions are manageable.
Furthermore, flight testing helps us identify any unknown “unknowns” early
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Sizing the Subscale VehicleFor data obtained from scale-model to be representative of full-scale aircraft, need to observe “similitude requirements” and scaling relationships for both the aircraft and test conditions:
Full-scale Sub-scale
span = 8 m span = 2 m
M = 800 kg M = 12.5 kg
v = 180 km/h v = 90 km/h
Note: For rigid, free-flight models where compressibility and Mach number effects not of concern
Linear dimension n 1/4Relative density (m/ρl3 ) 1Froude number (V2 /lg) 1Angle of attack 1Linear acceleration 1Weight, mass n^3 /σ (1/4)^3 = 1/64Moment of inertia n^5 /σLinear velocity n^1/2 (1/4)^(1/2) = 1/2Angular velocity 1/ (n^1/2)Time n^1/2 Reynolds number (Vl/ν) n^1.5 * (ν/ν0)
Scale Factor
Chambers, J. Modeling Flight: The Role of Dynamically Scaled Free-Flight Models in Support of NASA’s Aerospace Programs NASA SP 2009-575
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Subscale Vehicle Design2.0 m
2.0 m
Mass, kg 12.5Span, m 2.0Rotor diameter, cm 35.5Cruise prop diameter, cm 30.5Cruise motor, max, kW 2.0Lift motors (max/cont), W 600/300 Max Speed, km/h 90Hover time, min. 7.0
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10% subscale design
• The aerodynamics of the three-lifting surface configuration were analyzed using a Vortex-lattice method.
• However, much uncertainty remained regarding the extent of the de-stabilizing effect of the fuselage, as well as the desired cg location
• A 10% scale model was built and flown with and without the fuselage, providing useful information on cg position and desired engine thrust line
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Subscale Materials and Construction
100+ 3D printed parts(High Temperature PLA with carbon fiber fill)
COTS carbon tube
Flying surfaces : CNC Foam core/balsa skin/Ultracote
COTS RC landing gear
Electronics: COTS RC batteries, servos , motors, propellers, ESCs, autopilot boards and software, computer for telemetry and logging
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Lessons Learned
• A properly-sized subscale model is a very good development tool
• Brings to light “unknown unknowns”• Even very small subscale models can represent
substantial “bang for the buck” value • Adjustable features on the model prevent time-
consuming rebuilds• Have high-def video of all flights for post-flight review• Size controllers, motors, servos, with ample margin• Next-day shipping and in-house AM capability
compressed our schedule
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Questions?