AURA MITHRA

INDIA

FACULTY ADVISER

Ascot. Prof. SURENDRA BOGADI

STUDENT LEAD

NIKHIL JOHN

DATE SUBMITTED

1st MAY, 2012

AURA MITHRA Page 2

THE TEAM

NIKHIL JOHN

3RD YEAR B.E. AERONAUTICAL ENGINEERING STUDENTS, HITS, INDIA Email: nikhilsjohn@gmail.com

ARAVIND SASIKUMAR

3RD YEAR B.E. AERONAUTICAL ENGINEERING STUDENTS, HITS, INDIA Email: aravindaero@gmail.com

MANISH KUMAR

3RD YEAR B.E. AERONAUTICAL ENGINEERING STUDENTS, HITS, INDIA Email:

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ABSTRACT

Aura Mithra is an aircraft designed with the primary aim of reducing fuel

consumption. Noise reduction is also part of the objective. The aircraft mainly

features a Blended Wing Body design. It is powered with three engines-two open

fan engines and one ultra high bypass engine. The two open fan engines are

placed at the wingtips while the ultra high bypass engine is buried in the rear

fuselage. The aircraft is provided with elevators and flaperons. It is also equipped

with technologies such as micro vortex generators and pneumatic landing gear

fairings-all aimed at reducing the drag throughout the mission profile. By

combining all these technologies Aura Mithra is estimated to have an increase in

fuel efficiency by around 93%. It also reduces the noise produced by certain

components without affecting the performance significantly making it less noisier

than conventional aircrafts.

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CONTENTS

1. INTRODUCTION……………………………………………………………………………. 2. THE DESIGN…………………………………………………………………………………..

a. HIGHLIGHTS OF AURA MITHRA…………………………………………….. b. WHY WAS A BWB DESIGN CHOSEN?.................................... c. BODY LAYOUT…………………………………………………………………….. d. BASIC DIMENSIONS…………………………………………………………….. e. WHY DELTA WING INSTEAD OF SWEPTWING?...................... f. THE ENGINES………………………………………………………………………

i. INTRODUCTION………………………………………………………… ii. ADVANTAGES…………………………………………………………….

iii. CHALLENGES…………………………………………………………….. iv. OUR ENGINE CONFIGURATION…………………………………. v. TWO OPENFAN ENGINES……………………………………………

vi. WHY ARE OPEN FAN ENGINES PLACED AT WINGTIPS?.. vii. WINGTIP ENGINE MOUNTING ADVANTAGE………………. viii. THIRD ENGINE…………………………………………………………..

ix. ADVANTAGES OF THE THIRD ENGINE………………………... g. VORTEX GENERATORS………………………………………………………… h. RETRACTABLE LANDING GEAR WITH FAIRING……………………..

i. CHALLENGES…………………………………………………………….. ii. ADVANTAGES…………………………………………………………….

3. SUMMARY AND RESULT………………………………………………………………… a. FEATURES THAT INCREASE THE FUEL EFFICIENCY……………….. b. FEATURES THAT REDUCE NOISE………………………………………….. c. FEATURES THAT CONTRIBUTE TO LIFT………………………………….

4. CONCLUSION……………………………………………………………………………….. 5. REFERENCES………………………………………………………………………………….

5 6 6 7 8 9 9 10 10 10 11 11 12 12 16 16 19 19 20 20 21 22 22 22 23 24 25

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INTRODUCTION

AURA MITHRA is an aircraft designed to make flying more efficient and greener. It

combines many of the well know and proven technologies along with some

innovations blended into one design to make it as efficient as possible.

In this design increasing the fuel efficiency of the aircraft was given the

prime importance followed by noise reduction. Some features in the aircraft also

add on more safety.

CHAPTER 1

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THE DESIGN

Our design is based on the BWB concept combined with various other technologies that makes the aircraft highly fuel efficient. The aircraft is designed to have maximum takeoff weight of 374504 kg (i.e. 300 passengers and cargo) and fly at mach 0.8.

Fig 1 : Aura Mithra

HIGHLIGHTS OF AURA MITHRA

It has a blended wing body. The fuselage and the wings use NACA 7 series laminar flow airfoils which reduce drag at high speeds.

It has three engines: o Two Open Fan Engines located at the wing tips providing 80% of the

required thrust. o One Ultra High Bypass Engine buried in the fuselage providing 20% of

the required thrust.

CHAPTER 2

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The wings have no swept back. Instead it is designed similar to a delta wing, giving the wings high structural strength at the same time maintaining the required leading edge sweptback angle.

It has four rudders, two on each side. The elevators are placed in the areas in between the two rudders. In this arrangement no gap is formed between the trailing edge of the elevator and the trailing edge of the wing, creating a clean flow.

The centre engine’s exhaust exit is located on the upper surface of the fuselage reducing noise and helps in controlling boundary layer and increase lift during take-off (By vectoring thrust).

The centre engine’s inlet is also located on the upper surface of the fuselage. This helps in boundary layer energizing and increased lift.

The retractable landing gears are designed with pneumatic fairings that can also act as spoilers. This reduces drag while take-off and increases drag while landing.

Why was a Blended Body Design chosen?

Blended Wing Body (BWB) aircrafts has aerofoil shaped fuselage blended into the

wing. Most of the lift is produced by the body while the wing is used to balance it.

In the recent years BWB concepts proved to have vast potential as the

aircrafts of the future.

THEIR ADVANTAGES INCLUDE:

Significant payload advantages in strategic airlift/air freight and aerial

refueling roles.

Structurally Superior.

Reduced empty weight compared to conventional aircrafts (by about 18%).

Reduced noise due to the smooth flow over the blended surface.

Reduced wetted surface area for the same volume of payload.

High values of L/D.

Cheaper to Build (by about 25%).

Cheaper to Operate (by about 32%).

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Requires Lesser Thrust.

Easily matches with the present airport conditions.

All the capabilities of BWB design have already been demonstrated through

various designs such as the SAX (MIT), X-15, Vela Series and many more.

In short a BWB design in general can be considered about 30% more fuel efficient

than conventional designs.

In order to take advantage of the capabilities mentioned above it was

decided to use the BWB concept as the basis of our design also.

BODY LAYOUT

Fig 2: Body Layout

The main body is shaped using NACA 07-610 laminar flow airfoil with a t/c ratio of

11.7%. The wing is made up of NACA 07-606 and NACA 07-306. The t/c ratio was

decided on the basis of the payload capacity required. The payload capacity

required includes 300 passengers and cargo, the engine size, fuel etc and the

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amount of lift required. The wing is not a swept back wing; instead it has a delta

wing configuration.

BASIC DIMENSIONS:

Aircraft Length : 42m

Wingspan : 56m

Height : 10m

Aspect Ratio : 2.4

From preliminary estimates it was found that this body layout of the aircraft is

about 20% more fuel efficient and less noisy than conventional aircrafts of its

same capacity.

Why is a delta wing configuration used instead of

swept wing?

In our configuration the two main engines are placed at the wing tips. It order to

make full advantage of this setup, it is required to have an efficient wing

structure.

A delta wing is superior to sweptback wing in case of structure. The main reason

for this is because in delta wing the spars can be normal to the fuselage making

them shorter and stronger.

One main drawback of delta wing over sweptback wing is that they have a lower

aspect ratio and thus higher induced drag at lower operation speeds. However, in

our configuration the engines placed at the wingtips compensates for this

drawback.

Hence it was decided to use delta wing for the wing section.

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Fig 3 Showing the unswept, delta like wing configuration

THE ENGINES

Introduction

Turbofan engines are one of the most efficient engines that are used by today’s

airliners. The efficiency of the engine increases with the increase in its Bypass

ratio. But after certain limit the drag etc caused by the large nacelles or ducts

seems to outweigh the advantages of the engines. It is at this point that Open Fan

Engines came up. In this concept the fan is not covered inside a duct.

Also known as Prop Fans the concept is about three decades old. Recently the

concepts potential of increasing the fuel efficiency has revived interest in it. Many

of the engine manufactures have already developed the scale models of this

concept.

ADVANTAGES:

Increased fuel efficiency (up to 30 %) [6].

Reduced noise if engine is placed above the fuselage [5].

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CHALLENGES [4]:

Increase in noise due to the absence of duct.

Increase in noise due to the interaction between the counter-rotating

blades.

Installation. Absence of an engine nacelle requires that the fan’s interaction

with the fuselage or wing wakes must be taken into account for improved

performance.

OUR ENGINE CONFIGURATION

We used a total of three engines.

Two Open fan engines providing 70% of thrust.

One Ultra High Bypass engine providing 30% of the thrust.

The engines used in our design are based on the Rolls Royce Sage 2 engine. It is a

counter rotating twin open fan engine which is expected to be 30% more fuel

efficient and has noise levels well under the limits of the regulations [7].

Fig 2: Rolls Royce Sage 2 Open Fan Engine (Courtesy of Rolls Royce)

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However in our design, this concept is implemented with some modifications.

The TWO OPEN FAN ENGINES are placed at the wing tips and although they are

based Rolls Royce Sage 2 they have only one fan each.

Fig 4 (a) wingtip mounted engines

Why is the open fan engines placed at the wingtips?

Induced Drag of the wing is created due to the pressure difference between

the upper and the lower surface of the wing. This induced vortex reduces

the effective wing span and also creates dangerous wakes behind an

aircraft.

In any open fan engine when the air exits from a fan, it has an axial velocity

and a radial velocity giving the air a twist in the same direction as of the

fan. The axial velocity gives the thrust while the radial velocity does not

contribute to any thrust. It can be considered as a waste of energy. In

counter rotating open fan engines the second fan reduces the twist of the

air from first fan and thereby improves the thrust. But the drawback of this

technique is that two counter rotating fans interact and create a lot of

noise.

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By placing the open fan engines at the wingtip both these problems can be solved

efficiently.

+

=

In a wing, say the right wing, the induced vortex will be in rotating in

anticlockwise direction. Imagine at a certain velocity the induced vortex produced

is 10o inclined to the relative flow. This 10o inclined induced vortex enters the fan

which is rotating in the clockwise direction (the fan produces a vortex also with a

twist of 10o. But in this case the fan is going to impart a 10o clockwise twist to a

Fig 1(a) Induced vortex being created in the

anticlockwise direction.

Fig 1(b) Twisted flow (clockwise direction) leaving a fan

kept in free stream.

Fig 1(c) Synchronizing both the wake to cancel each other will decrease drag an increase

thrust (both of which will contribute to increased fuel efficiency)

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flow which is already twisted by 10o in the anticlockwise direction. The result is

that we get an almost untwisted flow that exits the fan giving more thrust for the

same amount of fuel. Untwisted flow also means that the dangerous wakes are

not formed behind the aircraft making it safer for other aircrafts to operate in the

vicinity.

It also eliminates the need for a second fan thereby reducing engine weight,

complexity, fuel required, and also eliminating the noise produced by dual blade

interaction while giving almost same performance.

The above mentioned concept is based on a patent by Mr. Patterson Jr.

dated Aug 6, 1985 [2]. It is also given in his patent that by placing the engines at

the wingtips of a wing with coefficient of lift as 0.3, the thrust produced by the

engine increased by 23% for the same amount of fuel and the induced drag

reduces by 25% which account to 10% of the total drag. As a whole the

performance increased by 33%.

In our design Mr. Patterson’s concept is enhanced by using a simple

flaperon mechanism (combination of aileron and flaps).

The limitation with Mr. Patterson’s original concept is that the induced

vortex is not synchronized with the propeller. Due to this the two vortexes does

not cancel out each other completely throughout the operational regime. By

using the flaperon it is possible to control the coefficient of lift of the wing tips

and thus the strength of the induced vortex. This ensures that whatever may be

the rpm at which the fan is rotating, the induced vortex almost cancels out by the

fan vortex producing a nearly untwisted flow exiting from the fan at all times. This

increases the efficient operational range of the wingtip engines. Theoretically, it

can reduce the induced drag by about 85% that accounts to about 34% of the total

drag (where induced drag accounts to 40% of the total drag) and increase the

thrust produced by about 30%. This accounts to a total performance increase of

about 64% for the same amount of fuel.

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Although 64% increase in performance is achievable, since no experimental

evidence was obtained at the time of this report we will be sticking to Mr.

Patterson’s 33% increase in performance throughout the remaining report. With

the flaperon this 33% improvement can be maintained throughout the mission

profile.

There are also many operational advantages of the wingtip engines which

are enumerated below:

1. When the aircraft is turning, say to the right, the left side aileron

deflects downwards thereby increasing the induced drag and hence

thrust. Vice-versa happens on the right side. This differential thrust

due to the extreme positions of the engines creates a significant yaw

moment towards the turning direction, reducing the adverse yaw

(presently this is reduced by using differential spoilers which work by

increasing drag on one side).

2. During a turn if the thrust of the inner engine is reduced by some

amount by integrating the aileron control with the engine throttle,

then this help the aircraft make sharper turns while saving some

amount of fuel in the process.

3. Able to make sharper turns means the aircrafts is more

maneuverable while maintain good inherent stability and will need to

cover only lesser distance in situations like go around etc which can

further save on fuel and time to some amount.

4. During take-off, with the deployment of flaps and higher angle of

attack increases the induced drag and thus the thrust produced when

it is most required, without any additional fuel consumption.

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SUMMARY OF THE ADVANTAGES OF WINGTIP ENGINE

MOUNTING:

Reduces induced drag by 25% (by synchronizing about 85%).

Increases thrust produced by engine for the same fuel by 23% (by

synchronizing 30%).

Considerable reduction in noise due to the elimination of the second fan.

Improves the maneuverability while having good degree of inherent

stability.

Increases fuel efficiency by about 33% (will be more with synchronization).

Increase in L/D due to increased effective span.

Produces clean flow over the entire wing unlike in case of conventional

under wing mounting.

The combined drag of the wing plus engine configuration is less for a

wingtip mounting when compared to under wing or over wing mounting,

even without considering the effect of the fan.

So, a BWB design which by itself is 20% more efficient than conventional aircrafts,

combined with an open fan engine, which due to its ultra high bypass ratio is

about 20% more fuel efficient than today’s turbofans, along with the wingtip

engine mounting, which makes it 33% improved performance, will make this

aircraft 73% more efficient and also more silent than conventional airplanes of

today.

The THIRD ULTRA HIGH BYPASS engine which is buried in the rear segment of the

fuselage produces 30% of the required thrust. By burying the engine in the

fuselage the engines ram impact drag and nacelle drag can be significantly

reduced.

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Fig 4 (b) center engine buried inside the body

This engine has an inlet placed at 70% of the fuselage length. The air flowing

above the fuselage including the boundary layer gets sucked into this inlet. This

helps in reducing the parasite drag as the boundary layer gets enhanced due to

the suction of the engine. Such methods of enhancing the boundary layer has

already been demonstrated in many BWB designs.

The main limitation of this technique is that too turbulent boundary layer

entering the engine could adversely affect the engines performance. However, in

our design the air (including boundary layer) entering the inlet does not directly

go into the fan and compressor, instead this air, after entering the inlet is made to

swirl using micro vortex generators and it is this vortex that then enters the fan

and compressor.

Unlike the wingtip mounting here the vortex and the fan will be rotating in the

same direction.

Why is the air made to swirl inside the inlet before entering

the engine?

When the air swirls the weak boundary layer gets mixed with the energetic

free stream air from above. This equalizes the energy of the air entering the

engine enabling a smooth functioning of the engine.

Also, a weak vortex rotating in the same direction as the first fan would

produces an effect similar to that of guide vanes of the old engines. This

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reduces the chance of the first blade to surge without adding the weight or

complexity of an actual guide vane.

In short by creating a swirl inside the inlet before the air enters the engine it is

possible to energize the boundary layer without adversely affecting the engine

performance.

Since the center engine is completely buried in the fuselage it is possible to

significantly reduce noise with the help of mufflers etc. This also permits the use

of counter rotating fan which are highly fuel efficient.

In addition to this the nozzle exit is also located on the upper surface of the

fuselage. This also reduces the noise created by the exit making the aircraft more

silent. The exhaust also acts as a blower and helps in energizing the boundary

layers.

Apart from the drag and noise this arrangement of engine also helps in lift

augmentation.

The air from the upper surface of the aircraft is sucked into the engines inlet. This

suction increases the velocity of flow over the upper surface and thereby lowering

the pressure on the upper surface while the flow over the lower surface remains

the same and hence the pressure. This increased differential pressure gives an

increase in the lift produced by the aircraft.

This is based the concept of the channel wings developed by Mr. William Custer

and others which first came up in the 1940s [3].

Also the surface that is extending from the exit of the nozzle is made in such a

way that it can be deflected like a simple flap (will be termed as nozzle exit flap).

During Take-Off, when this nozzle exit flap is deployed. It vectors the thrust from

the engine downwards due to the coanda effect. This helps the aircraft to

perform shorter take-offs.

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The nozzle exit flap is also designed to serve as the thrust reverses during landing.

SUMMARY OF THE ADVANTAGES OF THE CENTER ENGINE:

Boundary layer energizing and thereby reduction in drag (by around 5%).

Significant reduction in noise due to buried engine and upper surface

nozzle exit.

Lift augmentation due to channel wing concept.

Lift augmentation by thrust vectoring during take-off etc.

VORTEX GENERATORS

The design also features vortex generators placed along the line as shown in the

figure to avoid flow separation and thereby reduce drag.

The vortex generators proposed to be used in this design are the Micro Vortex

Generators developed by NASA [11]. These vortex generators can reduce

aerodynamic drag by 50%, increase the lift by 10% and increase the L/D as much

as 100%.

For preliminary calculation a 30% reduction in the drag is considered.

Fig 6: The red line indicates the position of the vortex generators

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RETRACTABLE LANDING GEAR WITH FAIRING

Almost all conventional airliners traveling at high subsonic speeds have

retractable landing gear. Landing gears typically produce 4% -7% of the total drag.

When we use a retractable landing gear it eliminates the drag created by the

landing gear completely during cruise. But these landing gears produce lot of drag

during take- off and landing.

Typical retractable landing gear system consists of the landing gear, retraction

mechanism and the doors.

But in our design we opted for a retractable landing gear with fairing as its

advantages outweighed the increase in weight.

Normally fairing is not opted for retractable landing gear due to the following

reasons.

1. It adds more weight.

2. Landing gear will be exposed only for a short duration of time.

These problems are resolved to some extent by the following means:

With the use of pneumatically activated fairing for the wheels. This type of

fairings will be build with the materials used for deicing boots, ram air

parachutes etc with a light frame for support and a mechanism to restore it

after deflation.

The pneumatically activated fairing will not add significant weight to the

system. Being flexible can be easily folded and stowed along with the

landing gear.

The Strut fairing can be made from light weight composite materials.

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The pneumatic fairing for wheels is deployed only during take-off and not during

landing. The strut fairing can be deployed as spoilers. This increases the landing

drag to 6%- 9% which will improved the braking effect during landing.

Since the pneumatic fairing for the wheel is not deployed during landing, it will

not affect the brake pad cooling process adversely.

ADVANTAGES

It reduces the landing gear drag to 1%-2% during take-off against the

current value of 4% -7%, thereby increasing fuel efficiency during take-off.

It increases the landing gear drag to 6%-9% during landing against the

current value of 4% -7% by increasing the frontal area and thereby

increasing the braking effect.

Reduction in noise during take-off.

Due to the materials used and design of the fairings, the weight increase is

not significantly high.

Take-off configuration Landing configuration

Fig 5: A proposed concept for landing gear fairing assembly

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SUMMARY AND RESULT

FEATURES THAT CONTRIBUTE TO INCREASE IN FUEL EFFICIENCY

Combining all the above mentioned technologies AURA MITRA can attain 93%

more efficiency than conventional aircrafts.

During take-off the landing gear fairing reduces further 3% drag.

FEATURES THAT CONTRIBUTE TO REDUCTION IN NOISE

Blended Wing Body design itself reduces noise due the smooth flow

created over it.

Reduction of the secondary fan from the wingtip engines reduces a

significant amount of noise while maintain performance [2].

The buried center engine reduces the noise produced by the engine.

The nozzle exit of the third engine on the upper surface of the fuselage.

0

10

20

30

40

50

60

70

80

90

100

Estimated Contribution of Each Feature

Conventional Aircrafts (Reference)

BWB Layuot

Open Fan Engines

Wingtip Engine Mounting

Micro Vortex Generators and Boundary layer Control by Center Engine

INCREASE IN FUEL

EFFICIENCY (%)

(DURING CRUISE)

0 %

20 %

+10 %

+33 %

+30 %

CHAPTER 3

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The landing gear fairing also reduces noise during take of as flow over it

gets smoothened.

A thread like feature at the trailing edge used in SAX to reduce the

aerodynamic noise caused due the mixing of upper and lower surface flow

can be implemented in the design to further reduce noise.

FEATURES THAT CONTRIBUTE TO LIFT

During Cruise

The fuselage produces most of the lift required (around 74%), similar to

other BWBs.

The wings contribute to around 24-25% of the lift.

The Inlet of the center buried engine also contributes to lift (around 2-1%).

During Take-Off

The fuselage

The wings.

The Inlet of the center buried engine’s contribution increases due to low fre

stream velocity

Vectored Thrust from the third engine.

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CONCLUSION

This project although is still in its preliminary stage has proved to be very

successful and the satisfactory.

We were also able to revive some of the forgotten technologies and put them to

proper application.

There is still a lot more room for development. For instance, there are many more

technologies that are implemented in aircrafts like SAX etc that could reduce

noise and improve some more performance if added to AURA MITRA.

Also the estimation of some of the features was done using the minimum values.

A more detailed development can likely improve the present performance.

CHAPTER 4

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REFERENCES

1. Data Sheets of:

A310-300

A330-300

A340-500

A350-1000

A380-800

B747-400

B767-400

B777-200LR

B787-9

2. US Patent no. 4,533,101 by Patterson, Jr. “WINGTIP VORTEX PROPELLER”.(

Aug. 6th, 1985)

3. “Channel Wing as a Potential VTOL/STOL Aero-Vehicle Concept” by Zeki O.

Gokce and Cengiz Camci.

4. “Sustainable and Green Energy” by Mark Pacey, Programme Manager,

Rolls-Royce plc.

5. http://www.dae.mi.th/aero-update/05_Boeing,%20Rolls-

Royce,%20RUAG%20to%20Investigate%20Open-

Fan%20Propulsion%20Technology_EN.htm

6. http://www.psmag.com/business-economics/prop-planes-the-future-of-

eco-friendly-aviation-39649/

7. http://www.rolls-royce.com/sustainability/markets/aviation/

8. http://en.wikipedia.org/wiki/Propfan#Jet_aircraft_fuel_economy

AURA MITHRA Page 26

9. http://en.wikipedia.org/wiki/General_Electric_GE90

10. Drag Reduction by Shock and Boundary Layer Control: Results of the

Project ... By E. Stanewsky

11. http://www.nasa.gov/centers/langley/news/factsheets/Micro-VG.html

12. http://www.geaviation.com/engines/commercial/ge90/ge90-115b.html

13. www.geaviation.com/engines/commercial/ge90/

14. http://www.flightglobal.com/news/articles/whatever-happened-to-

propfans-214520/