System Studies of Unconventional Aircraft

July 24-26, 2007Workshop on Revolutionary Aircraft for Quiet

Communities

Mark GuynnAeronautics Systems Analysis Branch

NASA Langley Research Center

Aeronautics Systems Analysis BranchObjective Analytical Services for Aircraft and Airspace Operations Systems

Airspace OperationsAircraft

Systems Analysis

Airspace System Engr & Analysis

Subsonic Transports

Personal Air Vehicles

Supersonic & High Performance Aircraft

Planetary Flyers

EnvironmentalImpact

VehicleSynthesis

MissionPerformance

TechnologySensitivity

AirportCapacity

Av safety/security Analysis

∆ Technology

∆ Cost∆ Weight

∆ etc.

Introduction

• Advanced aircraft concept studies provide a vision of the possible – what could be, not necessarily what will be

• Future, unconventional aircraft concepts offer both opportunities and challenges from an aircraft noise perspective

• This presentation provides a glimpse of possible future aircraft based on ASAB and other NASA studies

• “Realism” of concepts presented varies from notional sketches to the output of conceptual design studies

Jet Transports: Over Wing Nacelle*

• New installation appears to eliminate drag penalty

• Easy clearance for large bypass engines

• Wing shielding of lower hemisphere engine noise

• No gaps in flaps (noise & performance benefit)

• Issues include maintenance access, cabin noise

Shielding Effect is Approximately 4 EPNdB to Community for Pylon Mount, Fan Exit Dominates

*Berton, J.J.: “Noise Reduction Potential of Large, Over-the-Wing Mounted, Advanced Turbofan Engines”NASA TM-2000-210025, April 2000; and Hill, G. A.; Kandil, O. A.: “Aerodynamic Investigation of an Advanced Over-the-Wing Nacelle Transport Aircraft Configuration” AIAA 2007-670, January 2007.

Jet Transports: Blended Wing Body

• Typical over-body engine placement provides opportunity for noise shielding

• Improvement in aerodynamic efficiency compared to wing-body-tail configuration

• Key technical issues such as stability and control and non-circular pressure vessel continue to be worked

• Basic configuration for numerous low noise and/or high efficiency aircraft concepts

• Extension provides a noise shield between engines and observers on the ground

• Length ranges from 1/2 to 3 times the fan exit diameter (largest extension possible to avoid tail strike on takeoff)

• Systems Impacts– Increased weight and drag due to larger “tail” area– Additional tail weight penalty due to retractable mechanism– Thrust reverser operation could be a problem

BWB with Extension for Shielding*

*Hill, G.A.; Brown, S.A.; Geiselhart, K.A.: “Integration of Propulsion-Airframe-Aeroacoustic Technologies and Design Concepts for a Quiet Blended-Wing-Body Transport” AIAA 2004-6403, September 2004.

• Low pressure ratio internally blown flap (IBF) for quiet powered lift and pitch control

• Preliminary results indicate significant noise reduction

• Systems Impacts– Increased overall propulsion system weight– Reduced engine efficiency– Increased maintenance costs– Increased noise from IBF?

Study conducted by Boeing under Revolutionary Aero-Space Engine Research (RASER) Contract

NASA Task Manager: Hyun Dae Kim (NASA Glenn Research Center)

*More at: http://www-psao.grc.nasa.gov/presentations/CESTOL.pptand http://www-psao.grc.nasa.gov/publications/AIAA-2006-CESTOL.pdf

CESTOL Concept*

Jet Transports: Notional Concepts

• Advanced Vehicle Configuration Workshop held at Langley in 2003

• Structured brainstorming of unconventional propulsion-airframe integration for low noise

• Qualitative assessment of concepts using Pugh Decision Matrix

Fuel Efficiency vs. Noise?

• Economic and environmental pressures could lead to a search for higher fuel efficiency

• Concepts for increased fuel efficiency may have negative noise implications…

Image from www.globalsecurity.org

• Noise challenges for unducted fan / propfan include airport noise, interior noise, and even cruise overflight noise

Striking an Environmental Balance…

• What is the right balance between fuel efficiency, emissions, and noise?– Pursue concepts which benefit all three areas?– Accept penalty in one area to realize significant gains in

another?

• Ultimately the right balance depends on many external drivers, not just technology

Noise

Fuel Efficiency

EmissionsNoise

Fuel Efficiency

Emissions

Quiet Green Transport Concept A*

Scarf Inlet

Fuselage LH2 TanksStrut-Braced Wing

Ultra-High Bypass Ratio H2 Turbofan

Over-wing Engines

• Steep Approach• “Contrail Avoidance” Cruise

CO2, CO, SOX, soot, hydrocarbons, contrails

0.0

0.5

1.0

1.5

2.0

2.5

Impa

cted

Pop

ulat

ion

(Mill

ions

)Potential 90% Reduction*

* With Concept A benefit assumed for all aircraft types

Community Noise (11 Study Airports)Sound Exposure Level Contours

55 dBA Contour(Area –53%)

*Guynn, M.D. and Olson, E. D.: “Evaluation of an Aircraft Concept With Over-Wing, Hydrogen-Fueled Engines for Reduced Noise and Emissions” NASA TM-2002-211926, September 2002

Quiet Green Transport Concept B*

• Steep Approach • “Contrail Avoidance” Cruise

Blended Wing Body

Distributed H2 Fuel Cell Propulsion(H2O only emission)

Forward and Aft Noise Shielding

Continuous Moldline Flaps

Fuselage LH2 Tanks

• Advanced technology (25-30 yr) fuel cell propulsion system• 30% red. in structural, systems & equipment, fuel tank weight• 15% red. in drag beyond current BWB designs

*Guynn, M.D.; Freeh, J. E.; and Olson, E. D.: “Evaluation of a Hydrogen Fuel Cell Powered Blended-Wing-Body Aircraft Concept for Reduced Noise and Emissions” NASA TM-2004-212989, February 2004

General Aviation: Civetta Concept*

Class: 4-seat, single engineWing Span: 39.0 ftWing Area: 162.5 ft2

Gross Weight: 3600 lbEmpty Weight: 2450 lbEngine: Chevrolet LS-1 V8Power: 300 hpCruise Speed: 163 ktsLanding Speed: 52 kts

*Hahn, A. S.: “Next Generation NASA GA Advanced Concept” SAE 2006-01-2430, presented at SAE General Aviation Technology Conference, August 2006.

General Aviation: Propeller Noise*

• Low noise propulsorstudies performed by Hamilton-Standard in 1970-80’s

• Low noise propulsor is heavier, costlier, less efficient

• Quiet propeller is not retrofitable & requires a gearbox

• Quiet fan is not retrofitablebut does not require a gearbox

*Hahn, A. S.: “Next Generation NASA GA Advanced Concept” SAE 2006-01-2430, presented at SAE General Aviation Technology Conference, August 2006.

Supersonic Business Jet

• “Time is money” principle provides a motivation for supersonic travel

• Low bypass ratio engines make meeting airport noise regulations very challenging

• Must fly supersonic over land to be economically viable– Sonic boom mitigation – Regulatory changes

Unmanned Aerial Vehicles

• Potential civil, commercial, and military applications of unmanned aerial vehicles seem almost limitless

• Focus of current UAV debate largely on safety issues, could community noise be an obstacle as well?

• Many of the postulated missions could spread aircraft noise issues beyond airport communities

UAV: Border Eye Concept*

“Mothership”

Releasable Drone

• Originally designed for border surveillance• Commercial uses? Automated package delivery?

*Developed by AVID, LLC under NASA Revolutionary Systems Concepts for Aeronautics (RSCA) project; NASA Technical Monitor Dennis Bartlett; presentation available at http://sacd.larc.nasa.gov/projects/RSCA.htm

UAV: “Aerobots”*

Small Package Delivery Courier-Bot

Pizza Delivery*Young, L. A.: “Aerobots as a Ubiquitous Part of Society” Presented at AHS Vertical Lift Aircraft Design Conference. San Francisco, California, January 2006.

Summary

• ASAB, along with sister branches at other NASA Centers, continues to explore unconventional aircraft concepts

• New, unconventional aircraft concepts may mitigate or exasperate noise issues

• Future community noise concerns may extend beyond the airport area, e.g., small UAVs, sonic boom, propfanoverflight

• Successful implementation of an unconventional concept depends as much or more on the market and regulatory environment as on the availability of technology

“Prediction is very difficult, especially if it’s about the future.”Niels Bohr, physicist (1885 – 1962)