electric vtol aircraft - ahs...

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Electric VTOL Aircraft

Subscale Prototyping Overview

Francesco Giannini

[email protected]

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

©2017 AURORA FLIGHT SCIENCES

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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


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?

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