DARPA TX Industry Day Moore.pdf


Moore TX Industry Day Briefing
Original Source
Contract Opportunity
Date Originally Posted
Jan. 20, 2010, 12:28 p.m.
Profiled People



Personal Air Vehicles

Mark D. Moore
NASA Langley Research Center
Systems Analysis Branch

Prepared for the
DARPA TX Industry Day
January 14th, 2010

No ITAR Restrictions - Public

What’s Changed in 10 Years

Garmin G300

Cessna SkyCatcher

Prior generation mechanical gyro vs.
Current piezo crystal miniaturized gyro
(smaller, lighter, less power, reliable, cheap)

Cockpit Avionics

Digital Sensors and Systems

Vehicle Intelligence

Electric Motors/Controllers

Scale-Free Power
Distributed Power Solutions

Heavy Fuel Engines
Small Turbines
Lightweight IC Engines

Highly Coupled Aero-Propulsive-Control Analysis

Noise Can’t Be Wished Away

Dual Air-Road VTOL Concept Study, 2002

MD500 NOTAR-based Concept

Pulsed Ejector Thrust Augmentor (PETA) Concept

Information from “Dual Air-Road Transportation System (DARTS)” Public SAE Presentation, Nov 7
Not All Ducts are Created Equal

DARPA SoloTrek VTOL Demonstrator,
Disc loading ~ 35 lb/ft2
Thrust / HP ~ 7.6 lbf/hp

NASA Tailfan
Low Noise
Duct, 2006

Disc Loading Rules

Cruise and Hover Nacelle Shape Mismatch

Tilt-Nacelle VTOL Concept Study, 2004

Problem: Ducted VTOL concepts suffer from the nacelle requiring

two different shapes for best static and cruise performance.

Use of circulation control on inlet lip and diffuser could provide

• Cruise shaped nacelle to act as a bell mouth at static
• Increase duct lip suction at static (sizing) condition
• Increase effective exit area and mass flow in hover
• Decrease downwash velocity on ground plane
• Prevent flow separation in V/STOL transition
• Lower cruise spillage drag with turn down


Gas Generators

Hover CC blowing

CC blowing

Virtual diffuser area

Quantity Has a Quality of It’s Own

Design for Affordability, Tailfan Study, 2005

– Lean design to reduce touch labor
– Designed for automated manufacturing (higher

production volumes than typical aircraft production)

– Use of COTS products
– Extensive use of symmetry for reduced parts count
– Simplified concepts for minimum gage structures

– Foam core composite
– Honeycomb composite
– Spanwise and chordwise beading to achieve

skin-stiffened structures

NASA STTR Facetmobile Conceptual Study

Don’t Forget the Ilities

Many other factors

– Visibility critical for safe VTOL operations
– TO/Landing footprint
– Ground personnel safety
– Cabin environment NVH
– CG variability
– Mission flexibility
– Vehicle robustness and damage tolerance
– Altitude, temperature sensitivities

Electric Propulsion is a VTOL Enabler

• Problem: Small VTOL aircraft platforms are plagued with mechanical

powertrain problems due to small turbine and reciprocating engines integration issues;
resulting in complex, inefficient, noisy, and poor performance vehicles which are not
capable of satisfying the current and future mission needs.
Poor efficiency and reliability of small engines, must be designed to accommodate engine-

out through cross-shafting to multiple propulsors, highly sensitive to altitude and
temperature, power only available at a single rpm, …

High VTOL power requirement is for less than 2 minute duration, with throttle down to 20-

30% power for endurance missions.

High / Hot capability degrades air breathing engines by up to 30%
VTOL missions are typically in close proximity to people, so noise is a key concern.

• Solution: Electric propulsion offers a scale-free technology integration path,

with new degrees of aircraft integration freedom.
Scale-Free: Electric motors have the same efficiencies (>90%) and power to weight (2

hp/lbm) across large changes in size (from 1 hp to 300 hp).

New Integration DOF: Able to design highly redundant propulsion systems that eliminate

need to cross-shaft, able to design entire system for low noise.

Electric Propulsion is a VTOL Enabler

Puffin VTOL Tailsitter Study, 2009

– Gross weight ~600 lb
– Useful load of 280 lb
– Hover power 60 hp
– Control power margin up to 120 hp (2 min)
– Cruise power 20 hp
– Cruise speed 150 mph
– Cruise L/D 14.5
– Cruise Range 50 nm with SOA batteries
– High altitude dash of 300 mph @ 30k ft

Electric Propulsion Attributes
Extremely Quiet
Scale-free Integration
Safety through Redundancy
Low Cooling Drag
High Reliability
No thrust lapse with altitude
No warm up ground idle delay
Variable RPM Capability
Permits Low Tip-Speed Cruise

Electric Propulsion is a VTOL Enabler

• Designed 5 Redundant Electric Motor Systems

– Integral motor and gearbox to achieve 30 hp at 500 rpm
– Ring motors without gear reduction were shown to be infeasible at
this power level (too heavy/power, too large of diameter for the
required rpm).

– 36 Pole Motor with Belt Drive weighs 28.6 lbs, 92% efficiency, can
fail up to 4 poles and/or half of belts and still produce full power.
Failure of 5th pole permits rated power for 2 minutes prior to thermal

– Quad Motor with Planetary weighs 58.0 lbs, 92% efficiency, can fail
1 motor and/or a single gear planet and still produce full power.
Failure of another motor permits rated power for 2 minutes prior to
thermal runaway.

• Analysis to Satisfy FAA Multi-Engine Reliability

– Fault tree analysis utilizing Navy reliability tool set, including

individual component by component build-up to capture parts count,
complexity, and failure rates of specific components.

– Reliability during 1st 500 hour period of 99.8% (with no inspections
or replacement during that period), with probability of success (no
subsequent critical failure during 2 minute period emergency period)
of 99.99997.

36 Pole Motor Reliability Dependance on Pole Count Required for Operation
motor only

Mission Duration, hour

36/36 Poles Working

34/36 Poles Working
32/36 Poles Working
30/36 Poles Working

28/36 Poles Working
22/36 Poles Working
16/36 Poles Working

Electric Propulsion is a VTOL Enabler

36 Pole Motor with 8 Belt Reduction Redundant System

All VTOLs Can Fly, But Can They Transition

Dos Samara VTOL UAV Concept Study, 2009

Proof of a VTOL is successful transition through a robust corridor; sub-scale
demonstrations can be very useful to validate the many transition control
assumptions required during conceptual design.

All VTOLs Can Fly, But Can They Transition

Samarai Roadable VTOL Concept Study, 2010

Attempts to achieve redundancy through the entire propulsion system (even blade
failure), while maintaining lower disc loading without the need for cyclic (and
maybe even collective) rotor control.

Tight Packaging Requires Creativity

Vehicle Sketch Pad (VSP) Facilitates Rapid, Creative Design
Rapid and intuitive conceptual geometry front-end to design that using parametric

input (Aspect Ratio, Sweep, Twist, etc– not like CAD). Available from NASA to
U.S. citizens, including source, models, manuals, etc at no cost through a
Software Users Agreement.

Tight Packaging Requires Creativity

VSP Example

(4) Person accommodations
with single width fuselage
(seat and head position shown)

Wing root hover/climb peak
battery energy storage
(50 kW hrs)

(4) Poster tilting circulation control nacelle
configuration with dual, redundant electric
motors and damped-brake rotation mechanism
(100 hp / motor, 200 hp / nacelle)

CG located JP fuel tank

Adaptive autonomy avionics
system with bay accessible
to 2nd seat passenger.

(3) Surface control system
for max CG excursion

Allison 250 Turboshaft
coupled to high speed
alternator (400 hp)

Wide track front wheels
(18” diameter)

Dual main, center gear
wheels with pancake
electric motor drive

Inflatable outer panel wings
with no control linkages

Tight Packaging Requires Creativity

VSP Example