ALMAULY_WALEED_LINKREPORT

A STUDY OF AIRCRAFT CLIMB PERFORMANCE USING
FLIGHT SIMULATION
BACHELOR OF ENGINEERING DEGREE IN AEROSPACE
ENGINNERING WITH SPACE TECHNOLOGY HONOURS

School of Engineering and Technology BEng Final Year Project Report
A STUDY OF CLIMB PERFORMANCE USING FLIGHT SIMULATION
i
BACHELOR OF ENGINEERING DEGREE IN AEROSPACE
ENGINNERING WITH SPACE TECHNOLOGY HONOURS
A STUDY OF AIRCRAFT CLIMB PERFORMANCEUSING
FLIGHT SIMULATION
Reportby
WALEED ALMAULY
Supervisor
DR LIZ BYRNE
Date 12/04/2016

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DECLARATION STATEMENT
I certify that the work submitted is my own and that any material derived or quoted
from the published or unpublished work of other persons has been duly
acknowledged (ref. UPR AS/C/6.1, Appendix I, Section 2 – Section on cheating and
plagiarism)
Student Full Name: WALEED AHMED ALMAULY
Student Registration Number: 13032830
Signed: …………………………………………………
Date: SELECT DATE OF SUBMISSION HERE

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ABSTRACT
The use of flight simulators provides an effective and cheaper way of analysing a near
accurate portrayal of aircraft performance. Simulators also provide a virtual reality
allowing one to experience real flight as accurately as possible without actually flying.
This report presents a series of tests to investigate and identify how the angle of attack,
weight and centre of gravity affects the climb performance of the aircraft, CESSNA 172
SKYHAWK.
The experimental study carried out identifies which simulator, out of the Merlin simulator
and X-plane 10 simulator, produced a near accurate portrayal of the CESSNA 172
SKYHAWK climb performance.
Finally, the data gathered from the simulators were compared with each other and also the
Pilot Operating Handbook for validation.

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ACKNOWLEDGEMENTS
Above all, praise goes to the Almighty, ALLAH for giving me the opportunity and strength
necessary for me to complete this report. I would also like to thank him for providing me with
such amazing people in my life, as without them, the completion of this report would have not
been possible.
I, the author would like to take this opportunity to express sincere gratitude to Dr LIZ BYRNE for
providing the support, guidance and knowledge throughout this year.
I would also like to express my gratitude to LAURENCE TAYLOR for the support and help
towards my undergraduate affairs.
Sincere thanks to MUNA AZIZ for the encouragement and moral support throughout the most
important stages of my life. I would also like to thank all my friends especially HARSHIL MUGRA
and EZEKIEL K IBITOYE for their kindness and support during my studies.
My deepest appreciation goes to my parents; Mr AHMED MOHAMMED ALMAULY and MRS
NAIMA SAID CABDALLA as well as all my brothers and sisters for their prayers, love and
encouragement throughout my life, not forgetting BISHARA NASSOR.
Last but not least, I would like to extend my gratitude to the UNIVERSITY OF HERTFORDSHIRE
for providing me the facilities that enabled me to complete my report.

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TABLE OF CONTENTS
DECLARATION STATEMENT...............................................................................................ii
ABSTRACT.........................................................................................................................iii
ACKNOWLEDGEMENTS..................................................................................................... iv
TABLE OF CONTENTS ........................................................................................................v
LIST OF FIGURES .............................................................................................................viii
LIST OF TABLES ................................................................................................................ x
LIST OF EQUATIONS .........................................................................................................xi
GLOSSARY .......................................................................................................................xii
1. INTRODUCTION ......................................................................................................... 1
1.1 Project Outline ...................................................................................................... 1
1.2 Project Aims and Objectives .................................................................................. 2
1.3 Project Outline Block Diagram ............................................................................... 2
2 Literature Review......................................................................................................... 3
2.1 Flight Simulators through the Ages ......................................................................... 3
2.2 Area of Application ................................................................................................ 4
2.3 Types of Simulators .............................................................................................. 5
2.3.1 Components of a Flight Simulator ................................................................... 5
2.4 The Simulators: X-plane and Merlin........................................................................ 6
2.4.1 X-Plane 10 .................................................................................................... 6
2.4.2 Merlin MP520 ................................................................................................ 7
3 Aircraft Performance .................................................................................................... 9
3.1 Equation of motion ................................................................................................ 9
3.2 Climb Performance ..............................................................................................10
3.2.1 Climb angle ..................................................................................................11
3.2.2 Climb gradient ..............................................................................................11
3.2.3 Rate of climb ................................................................................................11
3.2.4 Time to climb................................................................................................12
3.2.5 Fuel burn during climb...................................................................................12
3.2.6 Distanced travelled .......................................................................................12
3.3 Factors affecting climb performance ......................................................................12
3.3.1 Power, speed and weight ..............................................................................12
3.3.2 Pressure Altitude and Air Density...................................................................13
3.3.3 Temperature.................................................................................................13
3.3.4 Humidity.......................................................................................................13
3.3.5 Turbulence and manoeuvring ........................................................................14
3.3.6 Wind............................................................................................................14
4 DESIGN OF EXPERIMENTS ......................................................................................15
4.1 Cessna 172 SP Skyhawk .....................................................................................16

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4.2 X-Plane Setup .....................................................................................................17
4.3 Merlin Setup ........................................................................................................19
4.3.1 Experiment 1................................................................................................21
4.3.2 Experiment 2 ................................................................................................21
5 PROCEDURE ............................................................................................................22
6 PERFORMANCE AND OUTPUT ANALYSIS ................................................................23
7 RESULTS AND ANALYSIS EXERIMENT 1 ..................................................................25
7.1 X-Plane ...............................................................................................................25
7.1.1 Average Time and Speed ..............................................................................25
7.1.2 Rate of Climb ...............................................................................................26
7.1.3 Ground Distance...........................................................................................27
7.1.4 Fuel Consumption.........................................................................................28
7.2 Merlin..................................................................................................................29
7.2.1 Average Time and Speed ..............................................................................29
7.2.2 Rate of Climb ...............................................................................................30
7.2.3 Ground Distance...........................................................................................31
7.2.4 Fuel Consumption.........................................................................................32
7.3 Discussion...........................................................................................................33
7.4 Validation- X-plane & Merlin vs POH .....................................................................35
7.4.1 Analysis and Discussion................................................................................35
7.4.2 Conclusion ...................................................................................................39
8 RESULTS AND ANALYSIS EXERIMENT 2 ..................................................................40
8.1 Analytical overview...............................................................................................40
8.2 Discussion...........................................................................................................43
9 FINAL PROJECT DISCUSSION ..................................................................................44
10 CONCLUSION ...........................................................................................................47
REFERENCES ...................................................................................................................48
BIBLIOGRAPHY .................................................................................................................50
APPENDIX A-Excalibur I Parameters..................................................................................... I
APPENDIX B- Christopher J Neal Email.................................................................................II
APPENDIX C- Cessna 172 Skyhawk POH Data ....................................................................III
APPENDIX D- X-Plane Altitude Vs Time ...............................................................................V
APPENDIX E – X-Plane ROC.............................................................................................. VI
APPENDIX F – X-Plane Ground Distance ........................................................................... VII
APPENDIX G – X-Plane Fuel Consumed ...........................................................................VIII
APPENDIX H – X-Plane 10- Drag vs Density.........................................................................IX
APPENDIX I– Merlin – 2.5 Degrees ...................................................................................... X
APPENDIX J– Merlin – 5 Degrees ........................................................................................XI
APPENDIX K– Merlin – 7.5 Degrees ....................................................................................XII
APPENDIX L– Merlin – 10 Degrees .................................................................................... XIII

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APPENDIX M– Merlin – 12.5 Degrees ............................................................................... XIV
APPENDIX N– Flight Simulation Analysis Performa ............................................................. XV
APPENDIX O– X-Plane Altitude Vs Time Matlab Scripts ..................................................... XVI
APPENDIX P– X-Plane 10 Other Matlab Scripts ................................................................ XXIII
APPENDIX Q– Merlin Matlab Scripts ................................................................................XXXI

viii
LIST OF FIGURES
Figure 1:1- Project flowchart ................................................................................................. 2
Figure 2:1[2] - The First Flight Simulator ................................................................................. 3
Figure 2:2[4] - CAE training simulator ..................................................................................... 3
Figure 2:3- Cockpit of the A350 XWB flight simulator. (Source: A350 XWB)............................. 4
Figure 2:4- A functional model of the flight simulator showing a flow diagram of the interactions
between the operator and pilot. Source (Vepa,R) ................................................................... 5
Figure 2:5-X-plane Simulations (Source: ANON).................................................................... 6
Figure 2:6- X-plane interface (Source: X-plane flight manual) ................................................. 7
Figure 3:1- Aircraft forces and geometry (adapted from 6ENT1010 lecture notes) .................... 9
Figure 3:2-Balanced forces around an aircraft (adapted from 6ENT1010 lecture notes) ...........10
Figure 3:3-Velocity vectors ..................................................................................................11
Figure 3:4- Altitude vs Density Graph (Source: Engineering toolbox) ......................................13
Figure 3:5- Climb Performance (Source: Chapter 7 Climb Performance) ................................14
Figure 4:1 - Experimental design .........................................................................................15
Figure 4:2-Experiment 1 approach .......................................................................................15
Figure 4:3-Experiment 2 approach .......................................................................................16
Figure 4:4-Boeing 737 simulator ..........................................................................................17
Figure 4:5 -X-Plane 10 file layout configuration .....................................................................17
Figure 4:6 - Systematic steps to initiate the simulations .........................................................18
Figure 4:7 - Main toolbar .....................................................................................................18
Figure 4:8- Data recording applications on X-plane ...............................................................19
Figure 4:9- Excalibur l Editor................................................................................................20
Figure 4:10- Aircraft modelling components ..........................................................................20
Figure 4:11- Main Control display.........................................................................................21
Figure 6:1- Time vs altitude graphs for different angles for pilot and auto pilot .........................23
Figure 7:1- Average Time and Speed Vs Altitude ..................................................................25
Figure 7:2-Rate of climb ......................................................................................................26
Figure 7:3 - Average Ground distance travelled at each AoA .................................................27
Figure 7:4 - Average Fuel consumption over different AoA ....................................................28
Figure 7:5- Graphs of Airspeed vs time and Airspeed vs Altitude ...........................................29
Figure 7:6- Shows the average ROC achieved over three trials at different AoA......................30
Figure 7:7 Calculating ground distance in meters ..................................................................31
Figure 7:8- Average ground distances travelled by each AoA ................................................31
Figure 7:9- Fuel consumption at different AoA ......................................................................32
Figure 7:10 -Power required and available for AoA 2.5° vs Altitude (Magenta Pr, Blue Pa) ......34
Figure 7:11- Time vs altitude simulators comparison with POH ..............................................36
Figure 7:12 -Speed vs altitude simulators comparison with POH ............................................37
Figure 7:13- ROC vs altitude simulators comparison with POH ..............................................37

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Figure 7:14- Ground distance vs altitude simulators comparison with POH .............................38
Figure 7:15 - Fuel consumed vs altitude simulators comparison with POH ..............................38
Figure 8:1- Time vs COG for different weight values .............................................................40
Figure 8:2- Average speed vs COG at different weights ........................................................41
Figure 8:3- ROC vs COG at different weights .......................................................................41
Figure 8:4- Ground distance vs COG for different weights .....................................................42
Figure 8:5- Fuel consumed vs COG at different weights ........................................................42
Figure 8:6 - Longitudinal forces acting on an aircraft .............................................................43

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LIST OF TABLES
Table 1- Summary of the X-plane and Merlin ......................................................................... 8
Table 2- Geometric features of a Cessna 172 acquired from POH .........................................16
Table 3- Changed parameters .............................................................................................20
Table 4- Experiment 1 steps ................................................................................................22
Table 5- Experiment 2 steps ................................................................................................22
Table 6- Average time for each AoA – Pilot vs Autopilot ........................................................24
Table 7- Angle of Attack vs Climb rate from start to end altitude. ............................................26
Table 8- Average ground distances over different AoA ..........................................................27
Table 9- Change in Fuel consumption with AoA (Fuel units (lb)).............................................28
Table 10- Comparison in average time and speeds between the two simulators .....................29
Table 11 –Change in ROC with increasing AoA ....................................................................30
Table 12-Total ground distance travelled at various altitudes .................................................31
Table 13 Power Required (Pr) and Power Available (Pa) with Altitude ....................................35

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LIST OF EQUATIONS
Equation 1- Newton’s 2nd law of motion with parallel and perpendicular forces present ............10
Equation 2- Climb Angle......................................................................................................11
Equation 3- Climb gradient ..................................................................................................11
Equation 4- Rate of Climb ...................................................................................................11
Equation 5- Climb time........................................................................................................12

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GLOSSARY
AGL – Above Ground Level
AoA- Angle of Attack
AR- Aspect Ratio
GUI- Graphical User Interface
MTOW- Max Take-Off Weight
POH- Pilot Operating Handbook
Vx – Best Angle-of-climb
Vy- Best Rate of Climb

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1. INTRODUCTION
1.1 Project Outline
The flight simulation test phase is one of the most critical stages in the design and
manufacturing of an aircraft. A series of rigorous flight simulations are needed to determine the
efficiency and overall performance of the designed vehicle. Flight simulators are used to gather
data that describe how a particular aircraft will perform within different flight stages, such as
climb. The purpose of such simulations is to understand and identify design flaws and
limitations in order to resolve them. Aircraft testing methods have become sufficiently advanced
that aircraft developers are able to turn a conceptual design to an actual aircraft using
inexpensive and effective means.
Flight simulators give the developers freedom to manipulate physical aircraft design parameters
together with environmental factors to run simulations. The output data of such tests can then
be used to improve the initial design. This is a cost effective method as the physical prototype
is only manufactured after a highly effective theoretical design is produced from the simulations.
Flight simulation uses sophisticated algorithms to imitate real life scenarios without the use of
physical resources thus saving costs, such as fuel. Since no physical testing takes place, risks
and associated hazards are avoided. Within the last few decades, flight simulators have
improved technologically and are able to simulate conditions close enough to real life situations.
They have not only become more accurate, but their use in the aerospace industry and higher
education institutions is on the rise.
One of the tests performed using a flight simulator is investigating the ability of an aircraft to
climb. This is also known as the climb performance and is a measure of how well aircrafts can
travel on an increased gradient, gaining altitude. Depending on the aircraft mission, climb
performance is assessed in various ways. Different aircraft will require different optimisations
of a climb. A commercial aircraft is only developed for one purpose and that is to transport
passengers and cargo and not to perform acrobatic/evasive maneuverers, unlike military
aircraft. For example, a strategic bomber is designed to descend to a suitable bomb disposal
altitude and ascend to normal height ceiling as fast as possible for effective weapons delivery
and to avoid surface to air munition.
This research uses X-plane 10 and the Merlin simulator to demonstrate how different climb
angles of attack affect the climb performance of the Cessna 172 Skyhawk. Both set of results
gathered will be used to indicate the best angle of attack and to evaluate whether the results
corresponds to the Pilot Operating Handbook performance data. The results gathered will
indicate which simulator out of the two will be best suitable for such aircraft performance tests.
This report will also look at how and whether weight and the centre of gravity of the Cessna
172 affect climb performance. This test will reveal whether the two variables are crucial during
a climb. The purpose of this report is to investigate whether the flight simulators provided at the

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University of Hertfordshire are viable enough to be able to provide a near portrayal of the climb
performance of the Cessna 172 Skyhawk.
1.2 ProjectAimsand Objectives
Aims
 Determine the best AoA for optimum climb performance using X-Plane 10 and
Merlin Flight simulators for the Cessna 172 Skyhawk.
 Determine the effects of Weight and COG on the climb performance on the
Cessna 172 Skyhawk.
 Determine the most suitable flight simulator to use for such investigations
Objectives
 Run preliminary simulations to become familiar with the use of the simulators
 Run simulations and obtain effective results from both simulators.
 Present results in an effective way for analysis.
1.3 ProjectOutline Block Diagram
The block diagram in Fig 1:1 below, illustrates the systematic approach taken to accomplish
this investigation.
Figure 1:1- Project flowchart

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2 Literature Review
2.1 FlightSimulators throughthe Ages
Since the beginning of manned flight, the
importance of training has been clear. The need
for training has grown with the increasing
pressures on the safety and environmental
issues associated with transportation [1]. During
the 1980s, simulators were almost non-existent.
The only way an aviator could learn is by
actually being on an aircraft and flying in it. That
said, 1910 was the year the first ever flight
simulator was produced [1] .This breakthrough allowed future aviators to train on land before
exposing them to high risk in the air. This simulator was made of two half-sections of a barrel,
mounted and moved manually to represent the pitch and roll of an aircraft [2]. Figure 2:1 shows
the first ever advertised flight simulator apparatus in a catalogue dated 1910, which allowed
pilots to be trained to fly the Antoinette VII [1].
With the outbreak of WWI in 1914, the demand for pilots was high; however there was a lack
of resources to accommodate all potential airmen. Flight simulators allowed the improved
selection of potential trainee pilots, aiding the air force in picking the strongest candidates. The
Link Trainer developed between 1927-1929, provided future pilots with realistic conditions by
replicating the motion of an actual flying aircraft.
This was done by using a small fuselage that was
mounted responsively to a universal joint and
control base [3]. The simulator consisted of a
control column, control wheel, two-foot pedals
which were used to simulate banking, pitching,
turning and the use of navigation instruments [3].
It is understandable that only a few years after the
Wright Brothers made history with flight
aeroplane- constructors were quick to produce
more advanced training devices which were used as safety measures for both people and the
equipment which could cause harm by unprepared aviators. With the development of highly
sophisticated systems in today’s aviation industry, flight simulators vary significantly, coming in
all shapes and sizes with different degrees of motion and different purposes. Figure 2:2 shows
a CAE training simulator which is able to accurately represent several aircrafts with realistic
flight deck instrumentation and a 6° of freedom axis. The Full Flight Simulator uses
mathematical models in which aerodynamic characteristics of the aircraft are used to determine
the avionics, motion and visual system responses [4].
Figure 2:1[2]
- The First Flight Simulator
Figure 2:2[4]
- CAE training simulator

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Figure 2:3- Cockpit of the A350 XWB flight
simulator. (Source: A350 XWB)
2.2 Area of Application
In general, a flight simulator models the flight dynamics and characteristics of an aircraft. There
are three categories of flight simulators in use today.
Engineering simulators are used during the development of an aircraft. Such simulators will
frequently be used to observe human behaviour as controllers and to examine the properties
of the aircraft to predict any problems associated with design. Due to the enhancement of new
aircraft systems, several tests have to be done in order to understand how they work and
understand their limitations to design with human interface [5]. An example of an engineering
simulator is shown in Figure 2:3. This is the cockpit of the new Airbus A350 XWB. During the
development phase, the flight desk is presented to
test pilots where several tests are carried out to
investigate primary flight control. Modifications are
made to the functionality of new systems to see
how pilots respond to them. The setup of the
simulator will have a similar structure to the actual
aircraft allowing the pilot to experience a real life
aircraft environment.
Training simulators are used to develop control skills of pilots for a particular type of aircraft.
This is done by replicating the workstation of the pilot during actual flight missions. The main
purpose of a training simulator is to help the pilot understand the aircraft properties from the
information that is fed back to the pilot from the simulator. This gives the pilot a prospective
understanding of how the aircraft is functionally operated and provides them with a feeling of
the aircraft’s behaviour. Furthermore, training simulators are also used to examine the pilot’s
ability, such as manual control and procedural flight management [5]. However, not all flight
simulators are ‘fit’ for training. A Flight Simulation Training Device (FSTD) has to be licenced
and approved by the Federal Aviation Administration/Civil Aviation Authority.
Research simulators are often used to investigate interactions between the pilot and the
aircraft. They are also used to carry out research in human perception where information can
be gathered about the aircraft to improve emergency and operational procedures [5]. This allows
humans to understand more about the properties of the aircraft under simulation and could
even contribute to creating and innovating new ways in which different parts and different
systems of the aircraft can be optimised for future aircrafts. As well as that, research simulators
are used to evaluate the effectiveness of the flight simulator itself, on how well it is capable in
replicating the flight, allowing researchers to refine and develop improved simulators in order
to increase the precision of the data gathered.

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2.3 Types of Simulators
There are several different types of simulators which have different purposes with various
systems. The most used and inexpensive simulator is a software package that can easily be
installed on a desktop computer. This type of simulator is used as an engineering and research
tool to predict flying ability as well as for leisure purposes. A common setup for this would
consist of a screen, joystick, rudder pedals and a throttle that all connect to the user’s computer
to allow flight control inputs. The software package usually contains several aircraft to choose
from as well as several airports. Other types of simulators will involve a full cockpit set-up
simulator which contain actual control components of the real aircraft without motion. The most
robust type of simulator provides full motion capabilities through an ideal cockpit set-up with a
motion-controlled platform [4].
In order for a flight to provide a similar environment to the actual aircraft, it has to be integrated
with several sub-systems to create a simulation of the actual aircraft flying [7]. For this to
happen, the flight simulators are divided into various sub-systems each contributing towards
creating a sense of flying. Figure 2:4 illustrates how a full motion simulator transfers information
from the cockpit controls to the rest of the subsystem.
2.3.1 Components of a Flight Simulator
The flight simulators must be able to simulate the same forces an aircraft would experience
during flight and should also be able to replicate the same environmental stimuli which
correspond to the motion of the aircraft while exposed to different environmental conditions [7].
In principle, a flight simulator is a framework that approximates information given from the pilot’s
control panel to be converted into mathematical approximations.
The following components are found in a typical flight simulator:
Interior – The inside of a full cockpit simulator, with or without motion, will have the same or
similar interior as the actual aircraft itself
Figure 2:4- A functional model of the flight simulator showing a flow diagram of the interactions
between the operator and pilot. Source (Vepa,R)

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Visual system- Several simulators have a wind screen attached right in front of the simulators
cockpit. However, depending on what simulator it is, the visual system may even be projected
on the simulator at different angles to give the pilot a feel of actual flying scenery. Another way
this is done is to have more than one screen at different angles connected to each other
surrounding the pilot.
Instruments- Training simulators usually have the exact instrumentation that the pilots would
have in the real aircraft. However, other simulators, such as the MERLIN and X-plane, will have
primary instruments that are present such as a joystick, rudder pedals, throttle stick and a few
switches for flap configurations as well as brakes.
Motion systems- For a motion based simulator, the simulator will generate forces such as
accelerations that the pilot will experience as if they were on the actual aircraft.
Audio system- Every simulator, whether it be a desktop simulator or a full motion simulator,
may have some kind of audio system. The audio system generates sound from the actual
simulated aircraft together with its environment. This adds to the overall feeling of flying an
actual aircraft.
2.4 The Simulators: X-plane and Merlin
2.4.1 X-Plane 10
Laminar Research’s X-plane is thought to be one of the world’s most advanced flight simulator
available to the public [8]. Its software package can be installed on desktop computers and runs
on the Aerofoil-Maker and Plane Maker Graphical User Interface (GUI). X-plane utilises an
aerodynamic model called the blade element theory to establish flight characteristics, whereby
it assigns constraints to very small elements which together form the geometric shape of the
aircraft [9]. The blade element theory works by dividing the aircraft into several components
which consist of the wings, horizontal stabilisers, vertical stabilisers and propeller. X-plane then
breaks the parts down into a finite number of elements [9]. The maximum number of elements
that could be assigned to the aircraft per side per component is ten. The blade element theory
then evaluates each element individually calculating the forces acting on each element using
flow calculations several times per second to calculate how the selected aircraft flies in the
simulated environment [9].
Fig 2:5 -X-plane performing flow calculations
several times per second to figure how the
selected aircraft flies in the simulated
environment. The picture also shows the
flowing air acting on the aircraft.
Figure 2:5-X-plane Simulations (Source:
ANON)

7
Figure 2:6 shows the interface on X-plane
that allows the user to view all the forces
calculated on different components of the
aircraft. The green bars from the control
surfaces of the aircraft show how much lift is
being generated, the longer the lines the
greater the force. The red lines show how
much drag is being generated and the
yellow lines show lift from vertical control surfaces [9]. X-plane is so advanced that with a certified
X-plane software hardware, the Federal Aviation Administration can allow logged hours on the
flight simulator if the simulator is approved. These can then be used to work towards a pilot
licence [8]. The software package includes a wide range of different aircrafts and locations. It
also allows the user to set the weather and the time of day. The user can also manipulate flight
conditions and flight failures.
2.4.2 Merlin MP520
Manufactured by Merlin Flight Simulation group, these flight simulators give students and
potential pilots the ability to design and test their aircraft flight dynamics, allowing them to gain
a true experience which can only be learnt through practice. The software incorporated in the
simulator allows the designer to modify different aircraft parameters to see how it will affect the
flight dynamics of the aircraft.
The aerodynamic coefficients are highly dependent on a large number of variables, which
poses modelling, as well as measurement problems. To minimise complications, Merlin forms
an aerodynamic coefficient from a sum of components which provide physical insight that
requires only a single type of test and a wind tunnel model [10]. The aerodynamic coefficient is
also convenient to handle mathematically. The Merlin is also governed by technical equations
that are used in order to calculate atmospheric conditions, system parameters, mass properties,
and numerical integration to propagate the equation of motion forward at each frame rate,
equation of motion, aerodynamic equations and propulsion equations [10].
The Merlin flight simulator is a full motion simulator with a single-seat capsule including a visual
and HUD displays and control systems. The Merlin has the ability to simulate a wide range of
aircraft, from a glider to an Airbus A320. The simulator uses a build-up coefficient method to be
able to model the characteristics of the aircraft.
All Merlin simulators operate on a graphical user interface called EXCALIBUR with two forms,
EXCALIBUR I AND EXCALIBUR II. Excalibur allows the user to create an aerodynamic model
that the user can input aircraft parameters to simulate an aircraft which can include everything
from wing aerofoil to fuselage drag coefficients. EXCALIBUR II contains a more detailed
analysis than EXCALIBUR I and uses a different technique to model wings, fins and tailplane
of the aircraft. Appendix A shows the parameter that needs to be inputted when using
EXCALIBUR I.
Figure 2:6- X-plane interface (Source: X-
plane flight manual)

A STUDY OF CLIMB PERFORMANCE USING FLIGHT SIMULATION 8
FLIGHT
SIMULATOR
Use Graphical
User interface
Motion Head’s
up
Display
Flightdynamic
modelling
method
Method of calculating Graphics and simulator
overview
Source to get
information
Availability
MERLIN Aircraft design/research
for institutions
Excalibur Yes Yes Coefficient
build up
method
EXCALIBURI- simulates
wing, engine andprop
configurationas a whole
section
- Blurriness appears
during simulation
-Graphics are not clear
- Scenery is not realistic
- Few airports totakeoff
from andto land
-Variable weather
-University
manual available
-Contact withthe
company
-University
(through
bookings)
X-plane -Leisure purposes
-Data collecting
-Research
-Pilot Lessons (from
verifiedFAA approved
x-plane simulators)
Plane Maker
andAerofoil
Maker
No No Blade Element
Theory
Breaks down the wings,
rotors, horizontalandvertical
surfaces into several
components
-No blurriness
-Uses real terrainhaze
freeware givingrealistic
atmospheric visuals
-X-plane sceneryuses
OpenStreetMap to give
detailedscenery
-Variety of airports to
take off from
-Variable weather and
atmospheric conditions
-User guides and
forums available
online
-University
(through
bookings)
-Personally
ownedprogram
Table 1- Summary of the X-plane and Merlin

9
Figure 3:1- Aircraft forces and geometry (adapted from 6ENT1010 lecture notes)
3 Aircraft Performance
Aircraft performance analysis is the procedure undertaken to examine different properties of an
aircraft during different operations. Depending on the design requirement of an aircraft, it will
require different operational optimisations. For example, the climb performance for a fighter
aircraft will be far more agile than a commercial aircraft. This is due to the fact that military
aircraft are designed to reach specified heights and speed within the shortest time. In this case,
the specification on aircraft performance is highly dependent on the customer’s needs. In order
to satisfy the customer needs, aircraft performance analysis is undertaken to make sure that
the aircraft is ‘fit for purpose’.
3.1 Equation of motion
Climb performance is the ability of an aircraft to gain altitude. Figure 3:1 shows the forces and
geometry acting on an aircraft during a climb.
The four main forces that determine the performance of climb is Thrust (T), Lift (L), Drag (D)
and Weight (W). In general, thrust is what increases the velocity of an aircraft, when taking off
the runway. It plays a huge role in bringing the plane to a speed such that the aircraft produces
lift. In flight thrust is used to overcome the overall drag experienced. Lift is the force produced
when air flows over the wing and is used to overcome the weight, with higher airflow velocity
meaning more lift is generated. Drag is the backwards acting force generated by the resistance
of the air as the aircraft moves through it and weight is the force generated by gravity that pulls
the aircraft at an angle to the centre of Earth. The equation of motion for the aircraft in figure
3:1 is derived by summing up the forces that are acting parallel and perpendicular to the
aircraft’s velocity vector.

10
Figure 3:2-Balanced forces around an aircraft (adapted from 6ENT1010 lecture notes)
Using Newton’s second law of motion and summing the parallel and perpendicular forces gives
rise to the Equations below.
∑ 𝐹 = 𝑚𝑎
∑ 𝐹 = 𝑚𝑎 = 0 = 𝑇 − 𝐷 − 𝑊𝑠𝑖𝑛 𝜃
∑ 𝐹 = 𝑚𝑎 = 0 = 𝑇 + 𝐿 − 𝑊𝑐𝑜𝑠 𝜃
Equation 1- Newton’s 2nd law of motion with parallel and perpendicular forces present
Where: F= Force (N), D = Drag (N), L =Lift (N), m = Mass (kg), W = Weight (N), a =
Acceleration (m/s2), and T = Thrust (N)
3.2 Climb Performance
When the aircraft is in steady flight ( 𝜃 = 0), not accelerating, all the forces are in equilibrium
thus, Thrust=Drag & Lift=Weight (see Fig 3:2)
When trying to achieve climb, the forces act on the aircraft in different ways. As the angle of
attack is changed (the angle of the wing to the relative wind direction), the whole aircraft’s pitch
is changed which in turn changes the positioning and the magnitude of the acting forces. As a
result of this, more drag is experienced by the aircraft as more surface area is directly facing
the direction of the wind. The direction at which the lifting force acts is only in one direction
because the wings don’t move, so when the aircraft is pitching, the direction of the lift
component also changes unless the aircraft lifting power changes [11]. Changing the angle also
results in a loss of lift which results in the weight component of the aircraft increasing because
the weight component works more directly against the thrust.
To overcome changes in the four forces and increase altitude, energy must be added to the
aircraft by increasing the thrust output of the engines. This will ultimately increase the kinetic
energy that will result in the aircraft climbing in altitude [11]. To summarise, the use of excess
power above the required amount is what defines the characteristics of a climb [12]. An aircraft
engine capable of producing 300 horsepower (at a given altitude) but uses 210 horsepower to
sustain level flight (at a given speed) has 90 excess horsepower available for climbing[12].

11
The velocity vectors seen during
climb are represented in Fig 3:3.
Where V=velocity, Vv = Vertical
Velocity, Vhor= Horizontal velocity
and 𝜃 = climb angle
3.2.1 Climb angle
With sufficient excess power, the aircraft pitches up creating an angle between the reference
plane and the nose of the aircraft (see figure 3:2). The climb angle is given by rearranging
Equation 2 below:
∑ 𝐹 = 𝑚𝑎 = 0 = 𝑇 − 𝐷 − 𝑊𝑠𝑖𝑛 𝜃
𝑠𝑖𝑛𝜃 =
𝑇 − 𝐷
𝑊
Equation 2- Climb Angle
The equation above states that for a given aircraft weight, the climb angle is determined by the
difference between thrust and drag, in other words, the excess power. The maximum
sustainable climb angle that the aircraft can perform is achieved when the aircraft is able to
produce the highest amount of excess power (T-D) and the minimum aircraft weight (W) [11].
When the excess power of the aircraft equals zero (T=D) then the angle at which the aircraft
pitches will also be zero. If drag is greater than thrust then the aircraft will descent but if thrust
is greater than drag this will lead to an ascend.
3.2.2 Climb gradient
The climb gradient is the ratio of altitude gained per ground distance covered. In other words,
it is a measure of how steeply an aircraft is climbing. The climb gradient is expressed as:
𝐶𝑙𝑖𝑚𝑏 𝐺𝑟𝑎𝑑𝑖𝑒𝑛𝑡 = 𝑡𝑎𝑛( 𝜃) × 100
Equation 3- Climb gradient
The gradient is expressed as a percentage where 100 % occurs when Vv =Vhor or when tan( 𝜃)
=1 or 450.
3.2.3 Rate of climb
The rate of climb is the change in the vertical velocity by definition and is given by Equation 4
below:
𝑅𝑂𝐶 =
[( 𝑇−𝐷)]𝑉
𝑊
= Vsin 𝜃
Equation 4- Rate of Climb
Figure 3:3-Velocity vectors

12
Equation 4, demonstrates that the rate of climb depends upon the specific excess power. In
other words, this is the excess thrust that the aircraft can provide in order to produce a climb.
This is given by taking the difference between the power available from the engine and the work
done against drag in a unit of time[13].From Equation 4, it can be seen that the maximum rate
of climb for a given angle occurs at the velocity where excess power is greatest.
The velocity at which the aircraft is travelling impacts the rate at which an aircraft is climbing as
the specific excess power is directly dependent on the true airspeed. The true airspeed also
affects the climb performance as drag and thrust are functions on velocity.
3.2.4 Time to climb
The time to climb is the time rate for an aircraft to reach a certain altitude. The time to climb
could be worked out by the integral:
𝑡 = ∫
1
𝑅𝑂𝐶
ℎ2
ℎ1
𝑑ℎ
Equation 5- Climb time
Where: ROC = Rate of climb, h1 and h2= total altitude change and t=time taken.
3.2.5 Fuel burn during climb
The fuel burn is the change of fuel weight as the altitude changes and is used by the aircraft
in order to facilitate a climb. In order to calculate the fuel burn, readings at every altitude
increment have to be recorded.
3.2.6 Distanced travelled
The distance travelled by an aircraft is the total ground distance covered during a climb. This
can be calculated by multiplying the ground speed at which the aircraft is travelling by the
total time spent to reach the specified altitude.
3.3 Factors affecting climb performance
The following sub-sections discuss the factors which affect the overall climb performance of
an aircraft.
3.3.1 Power, speed and weight
From the equations seen in Section 3:2, it can be said that the amount of excess power used
in a climb directly influences different climb profiles. Flying higher or lower than the optimum
specified airspeed as illustrated in the pilot handbook will result in a lower climb performance.
The maximum constant climb is achieved for the lowest possible weight and the airspeed for
minimum excess power required (refer to equation 4), however, a heavy aircraft will decrease
the climb performance as there would be an insufficient amount of excess power required to
maintain a given flight speed.

13
3.3.2 Pressure Altitude and Air Density
Density is affected in different ways and is influenced by pressure altitude and temperature.
Pressure altitude is the international standard height above the 1013.25 hPa pressure reference
which is 29.92 in Hg (inches of mercury). All aircraft pilot handbooks performance tables use
this value as its baseline pressure at sea level [12].
Figure 3:4, shows that as the pressure altitude
above sea level increases the specific volume of
air also increases resulting in a decrease in the
density of air molecules. As a result of this, the
power that the engine provides is decreased due
to the minimised air intake of the engine and the
fixed fuel/air ratio at which the aircraft engine
operates at. The power required for the aircraft to
perform at higher altitudes goes up which
ultimately affects the efficiency of the propeller
which affects the overall thrust that the aircraft
produces.
The change in density is directly proportional to lift, as density increases more lift is being
generated by the aerofoil. Climbing at an altitude where the air is less dense will generate less
lift force on the aerofoil. For a pilot to compensate for the reduced climb rate at lower densities,
they will require to operate at higher speeds [15].On the other hand, density is inversely
proportional to drag, as density increases more drag is being experienced by the aerofoil.
3.3.3 Temperature
Temperature decreases as altitude increases. On a warm day, the density decreases further
due to the gas molecules expanding, therefore, acquiring much more volume than at sea level,
resulting in a lower density [16]. The warmer it is, the less efficient the aircraft engine is due to
its dependency on the surrounding air. This means the higher the temperature is, the less thrust
the engine is able to produce. As a result of this, the pilot will experience a reduction in the rate
of climb and climb gradient achieved. The pilot will then have to compensate for this by using
much more power than is required to attain a normal climb as at sea level [16].
3.3.4 Humidity
Humidity refers to the amount of water molecules occupying the atmosphere. Depending on
the temperature, when it’s hot the atmosphere can hold much more water vapour than on a
colder day. This contributes in determining the density altitude and climb performance of the
aircraft [12].
Figure 3:4- Altitude vs Density Graph
(Source: Engineering toolbox)

14
3.3.5 Turbulence and manoeuvring
To perform an efficient climb, the aircraft requires all of its excess power to be used to help the
aircraft achieve the desired altitude. Any turning or movement from a constant heading will limit
the aircraft from performing a climb using the full power available.
3.3.6 Wind
A steady wind will have no effect on the climb angle of the aircraft. However, by using the exact
power setting and climb speeds, a wind which is blowing in the direction the aircraft is travelling
(tail wind) will lead to an overall increased ground distance than a steady wind. But the wind
that blows against the direction of travel, will have the complete opposite effect. Figure 3:5
shows how wind affects climb angle and distance travelled.
Figure 3:5- Climb Performance (Source: Chapter 7 Climb Performance)

15
4 DESIGN OF EXPERIMENTS
To investigate the climb performance of a Cessna 172 Skyhawk, a one factorial experiment
design and a two factorial design method was used. Figure 4:1 below shows the experimental
design process that was executed.
A design of experiment provides a structured way to change multiple settings in order to
understand their impact. The foundation of the tests investigated consisted of two variables,
the controllable and uncontrollable input factors. The controllable factors are the parameters
that one can control such as the power/thrust inputted in each run. On the other hand, the
uncontrollable factors are factors that cannot be controlled but still affect the response to the
experiment. The aim of such tests is to gather valid data/responses in order to understand how
different controllable factors could affect the performance of an aircraft, which could be used to
predict aircraft performance. However, uncontrollable factors like pilot skills must be minimised
or even eliminated if possible. Doing this will remove and decrease any uncontrolled variation
in the data to be measured.
Experiment 1 and Experiment 2
Figure 4:2-Experiment 1 approach
Determine
Objectives
Identify
the best
angle to
climb
Independant
Variables
Set
standard
conditions
Full throttle
Flaps up
Dependant
Variables
Climb
angle
(AoA)
Experiment
Investigate
how the AoA
affects climb
performance
High andLow
Level
2.5 - 12.5
degrees
Data
Collecting
Collect
data from
both
simulators
Analysis
Create graph
representation of
the data gathered
from both
simulators and
analyse how the
different pitch
angle affects the
climb
performanceand
comparethebest
climb angleto the
POH data
Controllable
input factors
Uncontrollable input factors
Response/Output MeasureProcess
Figure 4:1 - Experimental design

16
Figure 4:3-Experiment 2 approach
4.1 Cessna 172 SP Skyhawk
The flight simulators used were the X-plane 10 and the Merlin. The aircraft that was used to do
the tests was a high-wing piston engine aircraft (Cessna 172 SP Skyhawk). To be able to model
the Cessna 172 Skyhawk in a flight simulator and compare the data collected to the Pilot
Operating Handbook (POH), a check had to be made to ensure that both aircraft characteristics
and dimensions of both models from both simulators were identical to the pilot handbook. The
table below shows the general geometry of the Cessna 172 Skyhawk taken from the POH.
Geometry
Maximum take of weight 2558 lb (1160kg)
Empty Weight 1721 lb
Fuel Weight 350 lb
Payload weight 487 lb
Wing Span 11m
Tip chord 1.58 m
Root chord 1.1m
Mean Aerodynamic Centre (calculated) 3.739 m
Taper ratio (calculated) 0.7
Aspect ratio (calculated) 7.48
Wing area 49m2
Fuselage length 8.28m
Engine Power 180 BHP
Table 2- Geometric features of a Cessna 172 acquired from POH
Determine
Objectives
Identify
the effects
of the
change in
weight and
centre of
gravity
Independant
Variables
Set
standard
conditions
Full
throttle
Flaps Up
Dependant
Variables
Weight of
aircraft
and centre
of gravity
position
Experiment
Investigate
how the
change in
both weight
and centre of
gravityaffect
the climb
performance
High and
Low Level
Weight:
900kg,
1160.3kg
and
1270kg
Centre Of
Gravity
Range -5
to +5 from
datum
Data
Collecting
Collect
data from
selected
simulator
Analysis
Create
graph
representa
-tion of the
data
gathered
from
simulator
and
analyse

17
4.2 X-Plane Setup
The simulations were carried out at the University of Hertfordshire flight simulator lab. The lab
has four flight simulators which include the MERLIN, Cessna 152 simulator and a desktop setup
running X-plane 9. The last simulator available is the Boeing 737 simulator running on X-plane
10. For the purpose of this experiment the tests were carried out using the latest version, X-
plane 10.
Figure 4:4-Boeing 737 simulator
The Boeing 737 simulator has three screens used for the visual system and is configured in
such a way that these surround the user. It also has three screens which are used to display
the primary flight display which shows the attitude indicator, vertical speed indicator, indicated
airspeed, vertical speed, heading with navigational information and an engine-indicating and
crew-alerting system as seen in Figure 4:4, in (light blue). A joystick (green) and trim option
(orange) located on the side were used to control pitch and roll. Rudder pedals presented in
yellow were used to control yaw. The throttle was used to control the power (red). A glare shield
panel used to set autopilot options (dark blue) and an audio control panel (purple). The X-Plane
arranges its component files in a specific way as seen in Figure 4:5
Figure 4:5 -X-Plane 10 file layout configuration
This project used the X-plane 10 version which included the model maker (Plane maker) and
Aerofoil Maker. X-plane 10 is designed so that information from both GUIs is integrated to
create the aircraft. X-plane 10 has several aircraft models with their unique aerofoil already
included in the software, including the Cessna 172 SP.

18
Figure 4:6 - Systematic steps to initiate the simulations
Figure 4:7 - Main toolbar
As seen in Fig 4:6, a common route to start the simulations were used for each trial using
tools from the main menu (Fig 4:7)
Once the X-plane 10 application had been launched, the following steps were taken:
1) To select the aircraft, the ‘aircraft’ button located on the toolbar was selected and the
type of aircraft then picked from the drop down menu.
2) The Cessna 172 Skyhawk aircraft was located in the ‘General Aviation’ folder. Once the
aircraft had been selected, the location at which the simulation took place was chosen
by clicking on ‘Location’ on the toolbar. The ‘Select Global Airport’ on the drop link was
clicked to allow simulation runs from a variety of airports. The airport selected for this
was London Heathrow, as this was the only airport available on both simulators.
3) To manipulate the weight of the aircraft, the ‘Aircraft’ button on the toolbar was used.
There the option to manipulate the centre of gravity, payload weight and fuel weight was
possible. For this experiment, the weight of the aircraft selected was 2558lb, which is
the maximum take-off weight of the Cessna 172 SP.
4) The test was conducted so that the results gathered were the outcomes of the tested
variables. The ‘Environment’ button on the toolbar opened a drop down menu that
allowed the atmospheric parameters to be changed. The test was set to standard
atmospheric conditions of 15°C with a pressure of 29.92 inch Hg. There were several
other parameters that could be simulated, for example the wind speed, wind gust, shear
direction and turbulence could be changed. However for this experiment, everything
was kept at zero.
On completion of the above steps, the simulations were started. X-plane 10 also gave the
author freedom to change the pilot ‘viewing’ allowing a view of the aircraft with a pilot point of
view or an outside view of the aircraft.
Data Acquisition
As soon as the flight reached the required altitude, the simulation has to be paused by pressing
‘P’ on the keyboard. X-plane 10 data acquisition programme was enabled from the tool bar
Settings > Data Input & Output. After ‘Data input & Output’ was selected, the parameters
needed were recorded.

19
On simulation start up, X-plane 10 records the desired parameters ten times per second using
the blade element theory [8]. The parameters selected on the X plane 10 were as seen in Figure
4:8.
Figure 4:8- Data recording applications on X-plane
Once the user has quit the X-plane application, all the data recorded is available on an external
file called, ‘Data.txt’. The data is arranged in the same order selected by the user. X-plane 10
also has different data files such as ‘Data.see’ which plots graphs. All the data collected from
X-plane 10 was analysed on Matlab and MS-Excel.
4.3 MerlinSetup
This project also used the Merlin Flight Simulator MP520, which has the capability of running
on both Excalibur Editor I and Excalibur Editor II GUI. The Merlin MP250 is a capsule simulator
fitted with two axis electric motion system. The inside of the capsule has a 19’’ visual display
with two 8.4’’ screens which are used to display the primary flight display. The simulator uses
a joystick, two throttle control sticks and two rudder pedals to control the aircraft during
simulation.
During the course of the year, there was contact between the author and the managing director,
Christopher J D Neal. Due to the complexity of Excalibur Editor II and the limited timescale it
was identified that the best software to go for was Excalibur l.
In reply to the author’s inquiry on the best interface to use, the director responded that, ‘‘The
Excalibur I has a Cessna design on the simulator but is not a specific Cessna, it is a
representation of a high-wing piston aircraft based upon the Cessna configuration. The aircraft
used in X-plane was the Cessna 172 SP model and in order to make a fair comparison between
the Merlin and X-plane, both aircraft simulated have to be the same’’ (see appendix B). The
geometric data for the Cessna 172 SP was gathered and the existing model named

20
Figure 4:10- Aircraft modelling components
‘Cessna172MGK.mdl’ was modified to the Cessna 172 SP. The primary parameters changed
were summarised in Table 3, by manipulating the variables in the editor as seen in Figure 4:9.
Overall Weight 1160 Kg
Wing length 11m
Wing Area 16.1651 m2
Engine Power 180 HP
Prop diameter 1 m
Fuselage length 8.28m
Table 3- Changed parameters
The configuration of the file layout of the Excalibur I works similar to the way X-plane 10 works.
Excalibur I works by taking information from each component (figure 4:10) and editing the
model is done by selecting the value and retyping the new value on the top menu of the interface
as seen in Figure 4:9.
Once the model had been modified and saved. The simulation was initialised from the main
menu. Figure 4:11 shows the main control.
To start the simulation, the ‘Init’ button (red) was selected, this was where the starting altitude,
speed, heading and location were selected. On selection of the initial starting parameters, the
simulation were started by clicking on ‘Run’.
Figure 4:9- Excalibur l Editor

21
Outputting Data
After the simulation had reached the required altitude, the simulation was stopped. The data
was then obtained and saved by selecting the ‘Export Data’ function (in purple). The data
gathered was then analysed on Matlab or Excel where each column represented the different
parameters being measured.
4.3.1 Experiment 1
The objective of this experiment was to investigate how the AoA of the Cessna 172 Skyhawk
affected the climb performance. However, uncontrollable variations caused by human factors
such as pilot skills had to be eliminated/minimised during the tests. The uncontrollable input
varied from person to person due to their independent pilot skills. This results in inconsistency
of results as different pilots will all produce different results. After all, the experiment could not
be influenced by only controllable input factors so there was always variations in results due to
human factors. To minimise these factors a series of practice runs were conducted on both
simulators so that the author could get familiar with the control equipment.
In the process of trying to identify the effects of different AoA, it was crucial that nothing else
was changed. There were several variables that influenced the data collected. The variables
discussed earlier were wind, speed and direction, atmospheric conditions, weight and
configuration of flaps.
4.3.2 Experiment 2
The main objective of this experiment was to determine if weight and the centre of gravity affects
the climb performance of the Cessna 172 Skyhawk. In order to observe a realistic
representation, the simulator that performed closest to the data in the POH in experiment one
was selected to carry out the two factorial test.
Figure 4:11- Main Control display

22
5 PROCEDURE
Experiment 1
This chapter describes the procedure used to test on how different Angles of attack (alpha)
affect the overall climb performance of the Cessna 172 Skyhawk. Table 4 shows the steps.
Procedure Test
Step 1 Initialise flight simulator – Setting standard conditions with no wind speed,
set the location and maximum take-off weight.
Step 2 Throughout the experiment full throttle should be applied with flaps up.
Step 3 From 0-1000ft the pilot should ensure that the angle being tested and the
heading is maintained.
Step 4 To ensure the heading and AoA remain constant the pilot should use pitch
control, and where it’s needed, trim should be used.
Step 5 Once the aircraft reaches 10000 feet, stop the simulations and gather data
from simulator.
Step 6 Repeat the test three times for each AoA (2.5, 5, 7.5,10 and12.5).
Table 4- Experiment 1 steps
Once all the different AoA had been tested three times on both simulators. The data was
extracted and analysed graphically using a series of plots. The test showed how different
angles affected the climb performance of the aircraft. The two simulators were compared with
each other to see which result was most similar to those of a real aircraft. The effects of
different AoA was highlighted, and the best angle was compared to the data in the POH.
Experiment 2
This experiment was a two factorial design which was done to observe how the weight and
the centre of gravity point affect climb performance in order to understand their impact. Table
5 shows the method used:
Procedure Test
Step 1 Initialise flight simulator – Setting Standard conditions with no wind speed,
set the location, set the tested weight and centre of gravity.
Step 2 Throughout the experiment full throttle should be applied with flaps up.
Step 3 From 2000-3000 feet the pilot should ensure that the angle being tested
and the heading is maintained.
Step 4 To ensure the heading and AoA remains constant the pilot should use pitch
control, and where it’s needed, trim should be used.
Step 5 Once the aircraft reaches 3000 feet, stop the simulations and gather data
from simulator.
Step 6 Repeat for different centre of gravity points and weight.
Table 5- Experiment 2 steps

23
6 PERFORMANCE AND OUTPUT ANALYSIS
In order to demonstrate how much uncontrollable factors affect the overall test, two tests were
conducted on the X-plane 10, one with a pilot and one with the auto-pilot setting. To initiate the
auto-pilot on X-plane 10, the glare shield panel was used. On take-off, auto pilot was initiated.
When the pitching at the desired angle was reached, the CMD > HED SEL was clicked which
allowed both the AoA and the heading to remain constant throughout. Apart from using the
autopilot, the method used for both experiments were the same.
a) Pilot b) Autopilot
Figure 6:1- Time vs altitude graphs for different angles for pilot and auto pilot
Key - Red= Trail 1, Magenta= Trail 2, Blue= Trail 4 Black=Av erage of the three trials (Green= Autopilot plotted on pilot trials)

24
Three trials per angle were conducted. The left column in Figure 6:1 shows the pilot results
while the right shows the autopilot results. An autopilot system is designed to guide a vehicle
without any assistance; therefore, uncontrollable input factors are eliminated. Comparing the
two sets of results we see a similarity within the range of values apart from the results gathered
for the angle at 2.5°. All the tests gathered were plotted with error bars to show how much
variation/error there is in each measurement. Table 6 shows the average time taken to reach
10,000 feet on both tests with percentage errors.
Looking at the graphs in Fig 6:1 and the values in Table 6, it was seen that apart from the AoA
of 2.5°, a similar time was recorded to reach 10,000 feet across the three trials. This anomaly
could be due to the awkward hand position which had to be maintained throughout the 2.5°
trials.
The autopilot showed little variation in the three trial runs for a given AoA. It was also observed
that the data recorded for the autopilot were precise as all the trials lay within the average and
that there was not a lot of difference between the data produced from each trial, this is shown
by the length of the error bars located on the graphs.
On the other hand, the trials done by the pilot showed a greater variation in the results recorded.
Although these results seemed fairly consistent, the error bars showed that the data collected
had a greater difference in each trial run. This was mainly due to the skills possessed by the
pilot, and the knowledge the pilot has in using the flight simulator. Table 6 shows the percentage
error obtained throughout the different AoA between the pilots controlled trials and autopilot
controlled trials.
It was observed that repeating the test three times and taking the average, uncontrollable input
factors such as pilot skills were minimised to give values close to those of the autopilot.
Last but not least, the consistency of the autopilot varied from time to time and was not 100%
consistent; this could be due to software errors such as not having the most updated software
of X-plane 10 (numerical instability).
Unfortunately, the Merlin did not have an autopilot option, but according to the data comparison
between the autopilot generated by the simulator itself and the data generated by the pilot, it
can be assumed that manually controlling the flight over three trials and trying to maintain
equivalent condition each time on the Merlin would produce a fair representation.
AoA
(Degrees)
Pilot (seconds) Autopilot(seconds) Percentage Error
2.5 2286 1616.8 41 %
5 1396 1438.1 2.9%
7.5 1195 1265 5.5%
10 1413 1508.5 6.3%
12.5 1447 1496.72 3.3%
Table 6- Average time for each AoA – Pilot vs Autopilot

25
7 RESULTS AND ANALYSIS EXERIMENT 1
7.1 X-Plane
7.1.1 Average Time and Speed
After successfully running the simulations, results were gathered from three trials from X-
plane 10 and Merlin. The results gathered were for the AoA ranging from 2.5°-12.5° in
increments of 2.5°. Figure 7:1 shows the average speed and time taken over three trials at
different AoA.
As was seen in Figure 7:1, there was a positive correlation between the time taken and the
altitude. Time overall increased exponentially with altitude. From 1000-2000ft, all the angles
apart from 2.5° show a similar gradient. The time taken for the angles to reach 2000ft was 89.2s
(7.5°), 92.1s (5°), 102.7s (10°), 104.5s (12.5°) and 156s (2.5°). Once the plane had reached
2000ft, it continued with a unique increasing gradient depending on its AoA. The angle
corresponding to the longest climb was 2.5° despite having achieved the highest speed
compared to all the other angles throughout the 1000-10,000 feet run. This was because it
covered more horizontal distance than any of the other angles. The AoA that took the least time
to reach 10000ft was 7.5° taking 1265.4s. 2.5° took about 2285.82s with a manual pilot while
with auto pilot it took 1616.8seconds, which was the longest time taken. Overall 5° took less
time than 10°, however with only a small variation. 12.5° took the second longest time to reach
1000 feet with 1496.72s.
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
60
65
70
75
80
85
90
95
100
Altitude (feet)
Speed(knots)
Averages speed vs time for different attack angles (X-plane)
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
0
500
1000
1500
2000
2500
Altitude (feet)
Time(s)
Averages altitude vs time for different attack angles (X-plane)
2.5
5
7.5
10
12.5
4000 5000 6000 7000 8000 9000 10000
Altitude (feet)
2.5
5
7.5
10
12.5
Figure 7:1- Average Time and Speed Vs Altitude

26
7.1.2 Rate of Climb
The rate of climb (ROC) is the measure of how fast the aircraft is able to increase its altitude
with respect to time. Figure 7:2 shows the average rate of climb achieved over three trials at
different AoA.
Figure 7:2-Rate of climb
Angle (degrees) X-plane feet /min (difference in
fpm)
2.5 452.1-94.78 (357.32)
5 569.1-304 (265.1)
7.5 765.1-320.2 (444.9)
10 614.3-259.2 (355.1)
12.5 670.9-176.3 (494.6)
Table 7- Angle of Attack vs Climb rate from start to end altitude.
It was observed that there was an inverse relationship, as the altitude increased, the ROC
decreased. The angle that achieved the lowest ROC was the angle at 2.5°. Whereas 7.5°
achieved the highest ROC .It can be noted that the difference in ROC between 2.5 ° and 7.5 °
ranged between 312.9-225.22 fpm throughout the trials. It can also be noted that there was a
small variation difference in the ROC achieved by the angles 5°, 10° and 12.5° degrees. Also,
at altitudes of 1500, 4000 and 8000 there are periods where the lines intersect showing that
they achieved the same ROC.
Table 7 shows the angle that achieved the greatest difference in the ROC was 12.5 °. Whereas
the smallest difference in the ROC was 5°. ROC climb achieved is directly linked to the time
taken to reach a certain altitude and therefore, the order of the angles, from the shortest to the
lowest time taken corresponds to the ROC achieved by each angle.
0.9 0.95 1 1.05 1.1 1.15 1.2 1.25
650
700
750
density (kgm-3
)
0
0
5
10
0 2000 4000 6000 8000 10000
0
100
200
300
400
500
600
700
800
Altitude (ft)
RateofClimb(ft/min)
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
x 10
5
Altitude(ft)

27
7.1.3 Ground Distance
Ground distance is the horizontal distanced covered during a climb. Figure 7:3 and Table 8
shows the average ground distance achieved over three trials at different AoA.
From plotting ground distance against altitude, it was observed that as the altitude increased
so did the ground distance. The angle that had the greatest ground distance was 2.5 °, when
reaching 10,000 feet above the ground level (AGL), 2.5° travelled a total of 427000 feet when
flown by a pilot and 293400 feet when flown with autopilot, which is still the greatest distance.
On the other hand, it was observed that 7.5° covered the least ground distance overall however
at altitudes of 1000-4000 feet AGL there was only a slight variation in the ground distance
covered by the angles 7.5,10 and 12.5 degrees but overall 12.5° covered a shorter distance
than 10 degrees. The graph also shows that 5°covered the second highest ground distance
travelling a total distance of 197900 feet. Although trigonometrically speaking an angle of 12.5°
would potentially travel the least distance, the speed achieved was the lowest and the drag
experienced was the highest due to the fact that more surface area is exposed to the incoming
air (refer to Appendix H). As a result of this more ground distance had to be covered to reach
the desired altitude.
Altitude(feet)
Angle
(degrees)
2000 4000 6000 8000 10000
2.5 50570 101700 171700 269300 427000
5 33010 62860 101500 143800 197900
7.5 23950 49670 79110 113300 158200
10 25620 52190 84040 124800 176600
12.5 24240 50440 85240 124300 168590
Table 8- Average ground distances over different AoA
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
x 10
5
Altitude(feet)
Distance(feet)
8000 9000 10000
2.5
5
7.5
10
12.5
Figure 7:3 - Average Ground distance travelled at each AoA

28
7.1.4 Fuel Consumption
Fuel consumed is the amount of fuel the aircraft used to travel at a particular time. Figure 7:4
and Table 9 shows the average fuel consumed over three trials at different AoA.
Altitude
(feet)
Angle(degrees) 1000 2000 4000 6000 8000 10000
2.5 3.046 5.56 10.81 17.64 26.63 40.56
5 2.54 5 10.03 15.63 20.81 27.02
7.5 2.2 3.847 7.392 11.37 15.86 21.92
10 2.29 4.151 8.41 13.31 19.26 26.37
12.5 2.44 4.4 8.81 14.39 19.92 26.67
Table 9- Change in Fuel consumption with AoA (Fuel units (lb))
As observed in Figure 7:4 and Table 9, an increase in altitude led to an increase in fuel
consumption. It can be observed that the angle that used the least amount of fuel was 7.5°,
using a total amount of 21.92 lbs. On the other hand 2.5º used the most amount of fuel using
40.56lbs, this can also be verified by the autopilot results which used up 30.7 lbs of fuel. At
10,000 feet, 5 degrees used up the most fuel compared to both 12.5° and 10°, using up a total
fuel of 27.02 lbs. Whereas 10° and 12.5° used a total of 26.37 lbs and 26.67 lbs.
4000 5000 6000 7000 8000 9000 10000
Altitude (feet)
2.5
5
7.5
10
12.5
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
0
5
10
15
20
25
30
35
40
45
Altitude(feet)
Fuelconsumed(lb)
Figure 7:4 - Average Fuel consumption over different AoA

29
7.2 Merlin
7.2.1 Average Time and Speed
Results were then gathered for the Merlin simulator using the same steps and criteria in section
7:1. Figure 7:5 shows the average time and speed achieved over three trials at different AoA.
Key= red=2.5, blue=5 magenta= 7.5 green=10 and 12.5 =black
Table 10- Comparison in average time and speeds between the two simulators
The variables in Figure 7.5 and Table 10, have a linear relationship, as shown by the constant
gradients that each angle possesses. The overall trend was similar to the X-plane 10. From
1000ft to 2000ft despite, all the angles having different speed, apart from the 2.5 degree angle,
they all appear to have a similar gradient and arrived at similar times. Once an altitude of 2000
feet was reached the angles at 2.5°, 7.5° and 10° achieved different gradients. The Merlin
showed that the angles of 12.5° and 5°, travelling at an average speed of 54.9 knots and 75
knots reached 10,000 feet in 532 seconds. The angle that took the longest to reach 10,000ft
was 2.5° taking 1016 s, even though the average speed achieved was 84.5 knots. The 7.5
degrees didn’t perform as well as it did for the X-plane 10, it achieved an average speed of 68.5
Figure 7:5- Graphs of Airspeed vs time and Airspeed vs Altitude

30
degrees taking 609s. At an AoA of 10 degrees the average speed achieved was 60.16 knots
taking 545s to reach 10,000 feet.
7.2.2 Rate of Climb
KEY = red=2.5, blue=5 magenta= 7.5 green=10 and 12.5 =black
Angle Merlin feet/min (difference in fpm)
2.5 626.6-433.1 (193.5)
5 870.1-642.4 (227.7)
7.5 1131-727.7 (403.3)
10 1333-821.5 (511.5)
12.5 1301-849.7 (451.3)
Table 11 –Change in ROC with increasing AoA
The Merlin results in figure 7:6 shows that the ROC for each angle decreased with altitude.
Compared to X-plane 10 the highest ROC was achieved at an AoA of 7.5° whereas for Merlin
it was 12.5°. However at approximately 6000 feet AGL the AoA of 10 degrees achieved a similar
ROC to the angle at 12.5°. On the other hand, the angle that achieved the lowest ROC was
2.5° with 12.5° achieving more than twice the ROC than the angle of 2.5°.The difference
between the ROC achieved by the 2.5 ºangle was much larger compared to the other angles.
Compared to the X-plane 10, the 7.5 degrees did not achieve the best ROC, at 1000 feet it
achieved a ROC of 1131 fpm which achieved the third best out of all the angles. The angle of
5° achieved a ROC of 870.1 fpm at 1000ft and 642.4 fpm which came second to last. However
there was a large difference between the ROC achieved at 5° and 2.5° which ranged between
209.3fpm-243.5fpm. The angle that achieved the greatest difference in the ROC during 3 runs
was 10º achieving a difference of 511.5 fpm between 1000-10,000feet.
Figure 7:6- Shows the average ROC achieved over three trials at different AoA.

31
× Time
7.2.3 Ground Distance
The data extracted from the Merlin simulators did not have some parameters recorded as with
X-plane such as ground distance. However, the Merlin provided parameters in different units
which allowed the author to calculate the needed parameters in desired units. For example in
order to determine the ground distance achieved by each angle for the Merlin, the ground speed
in knots was provided. Figure 7:7 shows how the ground distance was calculated.
KEY = red=2.5, blue=5 magenta= 7.5 green=10 and 12.5 =black
As observed in Figure 7:8 and Table 12, the Merlin simulator also showed that the ground
distance increasing with time. It can also be observed that as the altitude increased, the rate at
which the increment of ground distance also increased. The angle that covered the most ground
distance was 2.5° reaching a ground distance of 43,440m. The angle that achieved the lowest
ground distance was 12.5°, achieving 14,850m when reaching an altitude of 10,000 feet AGL.
Angle 2000ft 4000ft 6000ft 8000ft 10000ft
2.5 4357m 13560m 23400m 33250m 43440m
5 3216m 8972m 14990m 21060m 27410m
7.5 2134m 6424m 11050m 16100m 21350m
10 2000m 5170m 8761m 12680m 16700m
12.5 1412m 4365m 7444m 10690m 14850m
Table 12-Total ground distance travelled at various altitudes
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
50
60
70
80
90
altitude (ft)
Trueairspeed(kn)
True airspeed Vs altitude
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 10
4
0
2000
4000
6000
8000
10000
Ground distance (m)
Altitude(ft)
Altitude vs Ground distance
Ground Distance in
metres
× 0.514
Ground Speed
in m/s
Ground Speed
in Knots
Figure 7:7 Calculating ground distance in meters
Figure 7:8- Average ground distances travelled by each AoA

32
7.2.4 Fuel Consumption
The Merlin simulator did not collect the fuel consumption directly. In order to obtain the fuel
consumption of each trial, the following calculations had to be done.
𝐹𝑢𝑒𝑙 𝐶𝑜𝑛𝑠𝑢𝑚𝑒𝑑 =Aircraft MTOW - Aircraft Current Weight kg (at different altitudes) × 2.20462lb
Where 2.20462lb = 1kg
Using MS-Excel, the average of all three trials was determined and were plotted on the graph
in Figure 7:9.
Figure 7:9- Fuel consumption at different AoA
As seen in Figure 7:9, fuel consumed increased with altitude. It can be observed that the angle
that used the most amount of fuel was 2.5°, using a total of 20 lbs of fuel presumably as it took
the longest, this was shown by the steep gradient. On the other hand, the angle that used up
the least amount of fuel was 12.5°, where only 10.14 lbs of fuel was used.
5° started with a low fuel consumption at 1000ft AGL, however, the gradient of the line at which
fuel was consumed was steeper compared to the rest. Between 1000-7000 feet AGL, 5°
achieved the second least fuel consumption. However when reaching 7000ft, it became the
third least as at 10,000ft it consumed a total fuel of 13.69 lbs.
Even though from 1000-7000 feet 10° consumed more fuel, 10° had a less steep gradient which
resulted in it having a lower fuel consumption at 10,000ft AGL. Finally, 7.5° showed to have the
second largest fuel consumption.
0
5
10
15
20
25
0 2000 4000 6000 8000 10000 12000
FuelConsumption(lb)
Altitude
2.5
5
7.5
10
12.5

33
7.3 Discussion
The climb performance of an aircraft depends on many factors such as the aerodynamic forces
experienced and the environmental conditions as well as the flap configuration. As mentioned
in the methods, section 5 of this report, the variation between the wing’s chord line and the
relative wind will be used to assess the climb performance as it governs the pressure
distributions across the wings. It is expected that the deflection of the airstream in the downward
direction (downwash) by the wing, together with the negative pressure distribution across the
top surface of the wing, to be the main contribution to the lifting force at low positive angles of
attack.
At 2.5 degrees the aircraft would be expected to exhibit the behaviour of a steady level flight,
whereby the lift and weight have a small variation and thus are nearly identical in magnitude.
At 12.5 degrees we expect the airflow over the wing to still be laminar and thus, still follow the
shape of the wing. There would be a greater negative pressure distribution over the upper
surface of the wing and as a result the pressure difference between the upper and lower surface
of the aerofoil would yield a greater lift force.
Looking at both simulators, it can be observed that 2.5 degrees obtained the greatest speed,
fuel consumption and time taken to reach 10,000 feet. It can be deduced that most of the thrust
produced by the engine is used mostly in the horizontal component of the climb. With a small
vertical component, maximum forward velocity was achieved. Both simulators also showed that
at this angle the fuel consumed was the highest, this is due to the engine accelerating the
aircraft at high speed over long periods of time at a greater ground distance. For X-plane 10,
2.5 degrees consumed approximately 1.5 times more fuel and achieved 2.5 times more ground
distance compared to the best rate of climb (7.5 degrees). Whereby the Merlin used up two
times more fuel and travelled three times more distance than its best rate of climb (12.5/5
degrees).
The AoA that achieved the best rate of climb for the X-plane 10 was 7.5 degrees. At this angle
the simulated speed ranged between 73-73.42 knots, taking 1195s to reach 10,000 feet. As
well as achieving the best ROC it also achieved the best angle of climb as it covered 10,000
feet with the minimum ground distance covered thus resulted to it having consumed the least
amount of fuel which was 21.92 lbs. This is due to the aircraft experiencing the least drag at
this angle with sufficient speeds.
On the other hand, the best ROC on the Merlin was achieved by both 12.5 degrees and 5
degrees taking 532s to reach 10,000 feet which is less than twice as much as the time taken
on the X-plane 10. This can be due to the fact that X-plane 10 is a more robust system
compared to Merlin due to its faster rate of calculation. Both 12.5 degrees and 5 degrees
produced different magnitudes in speed of 58 knots and 78.9 knots. However, the ground
distance travelled by 5 degrees (27410m) was much greater than of that of 12.5 degrees
(14850m). Although the time taken to reach 10,000 feet was the same, 12.5 degrees
corresponds to a shorter ground distance making it also the best angle of climb. The fuel
consumption at 12.5 degrees was 10.14 lbs of fuel whereas 5 degrees used 4.1 lbs more, this

34
makes 12.5 degrees the best angle to climb for the Merlin as it achieved the best ROC, the
least ground distance covered and the least fuel consumed making it more efficient.
If all the data is compared together, then X-plane time values are at least two times greater
even though the average speed of both simulators was roughly the same. This is because the
flight simulators use different equations and methods used to calculate the time taken. It should
also be noted that the calculated ROC on the Merlin is much greater than the ROC achieved
on the X-plane 10.
Altitude plays a significant role, in the ROC and climb angle of an aircraft due to the density of
air decreasing and pressure increasing, although the experiment was simulated in the
troposphere (0-12000feet) the effect of these changes in density and pressure can be
observed. The ROC climb decreases as the altitude increases; this is due to the decrease in
excess power at higher altitudes where the plane approaches its absolute ceiling.
Unfortunately, the Merlin did provide thrust and drag values but we can observe this from X-
plane 10 using the thrust, drag and velocity values at different altitudes. We can see that the
difference between the power available (Pa) and the power required (Pr) decreases as altitude
increases. For example, for a set trial at an angle of 2.5 degrees the power required and power
available can be observed in Figure 7:10.
Figure 7:10 -Power required and available for AoA 2.5° vs Altitude (Magenta Pr, Blue
Pa)
Referring back to equation 4, the power required is obtained by multiplying drag by the speed
and power available is obtained, by multiplying thrust with speed. It can be observed by the
graph in figure 7:10 that as the altitude increases the amount of excess power decreases (the
difference between Pr and Pa). At the point where the power available curve intersects the
power required, climb is no longer achievable. Another reason for the ROC and the power
available decreasing is the fact that the air density decreases with increase in altitude, therefore
there is a low amount of oxygen molecules to support the combustion process in the engines.

35
Altitude Thrust(N)
PowerAvailable
(Pa) Drag(N)
PowerRequired
(Pr)
1000 1623.109129 78766.25538 966.9003 46921.74849
2000 1542.591663 76401.67283 968.7495 47980.34458
3000 1472.134297 74079.52856 964.4344 48531.4716
4000 1396.637869 71531.35132 959.4938 49142.22121
5000 1328.043786 69148.05764 954.574 49702.38201
6000 1265.328785 66918.37286 949.8883 50235.93733
7000 1196.83273 64421.63858 944.5074 50839.78045
8000 1131.325251 61968.34769 938.9794 51432.60407
9000 1075.610177 59826.1862 933.8579 51941.82677
10000 1016.074291 57465.40655 927.3344 52446.60751
Table 13 Power Required (Pr) and Power Available (Pa) with Altitude
As each climb for all angles progresses, fuel is used up and the aircraft weight decreases. It
can be observed that the fuel consumed is directly proportional to the work done to move the
aircraft forward and how long it took for each angle to reach 10,000 feet. It was also observed
that even though the aircraft weight decreased due to fuel being consumed, the climb gradient
and the climb angle also decreased with altitude. This is because thrust decreased with altitude
too.
In general, the graph plotted using the Merlin (figure 7:6) shows a lot of fluctuation compared
to X-plane 10. This was caused due to the difficulties encountered when trying to maintain a
steady heading and climb angle when motion is enabled. Another cause for this may be due to
the fact that when trim is applied to the Merlin, it does not respond instantly and therefore when
too much trim is applied, trim has to be applied in the opposite direction in order to correct the
angle.
It should also be noted that some of the data gathered, such as fuel consumed are derived from
data that may have been extracted from linearly interpolated look-up tables. This is derived
from the fact that the fuel consumed graph is increasing in steps. This can be seen by the zig-
zag stair pattern created in figure 7:9.
7.4 Validation-X-plane& Merlinvs POH
7.4.1 Analysis and Discussion
To determine which simulator performed closest to the actual aircraft, the pilot handbook was
used for comparison. The pilot handbook is provided by the aircraft manufacturers and is
approved by the Federal Aviation Administration (FAA) to provide the pilot with the safest and
most efficient procedures that the aircraft should operate at. The POH also provides
breakdowns on sections such as:
- Normal Procedures
- Emergency Procedures
- Operating Limits

36
- Flight Characteristics
- Performance Data
- Adverse Weather Operations
The performance data was used to compare the findings on both simulators. The POH provides
the pilot with several performance data, however for the purpose of this report, only the climb
data at standard conditions was used even though standard procedures for a normal take-off
was used. Both experiments for both simulators were done so that the conditions were the
same as the POH data. The data provided from the POH were based on standard conditions,
full throttle, flaps up and zero wind.
The Cessna 172 Skyhawk POH was obtained through the internet. Referring to the Section 5,
Fig 5-7(see Appendix C), time, fuel and distance information was gathered and graphs were
plotted and compared to the angle that performed the best. Using the average values gathered
from the three trials from 7.5 degrees and 12.5 degrees for X-plane 10 and Merlin, as seen in
Fig7:11, a comparison between the averages of those results were compared with the POH.
The colours green, blue and magenta in the Figures 7:11-7:15 represent POH, X-plane 10 and
Merlin respectively.
As with the time, the graph in Fig 7:11 shows that X-plane 10 is more consistent with the POH
data. The data gathered by X-plane 10 shows a percentage error from 1000 feet to 10,000 feet
decreasing for X-plane 10, whereas for the Merlin it increased. Additionally, both sets of
simulation showed results less than the POH data but overall X-plane 10 presents data that
was close to the POH data.
Figure 7:11- Time vs altitude simulators comparison with POH

37
Figure 7:12 -Speed vs altitude simulators comparison with POH
Comparing the two simulators, it can be observed in Fig 7:12 that the speed obtained by the X-
plane 10 was much closer to the POH data than of that of the Merlin. It can also be noted that
the speed difference between the Merlin and the POH data is much greater and deviates more
as it increases in altitude. Whereby for the X-plane 10 the difference between the POH data
decreases with altitude.
Both the simulator and the POH data show that as the altitude increases, the ROC decreases.
From Figure 7:13, it can be seen that the ROC achieved by the Merlin was much greater
compared to the POH and X-plane 10. Overall, X-plane 10 shows that the ROC achieved
overall demonstrates a small variation in the value and decreased as the altitude increases.
Figure 7:13- ROC vs altitude simulators comparison with POH

38
Figure 7:14- Ground distance vs altitude simulators comparison with POH
As with the ground distance travelled, the Merlin shows a consistent deviation between the
values obtained on the Merlin and POH data. The percentage error for the Merlin ranges
between 61-70 percent whereas the percentage error between the X-plane 10 and the POH
data is considerably small compared to the Merlin, ranging between 0-3.5 percent. This shows
that X-plane 10 is able to simulate an accurate representation of how much ground distance
will be covered if flying at 7.5 degrees.
Figure 7:15 shows that the data recorded for both simulators did not produce a similar fuel
consumption close to the POH data values. Even though X-plane 10 proved to have calculated
the fuel consumed close to the POH data, there was still a large difference in the values.
However with the Merlin, as it achieved the lowest ground distance and the lowest speed it also
resulted in the aircraft not consuming as much fuel. Comparing the fuel consumed by the Merlin
to the POH data, there was a significant difference.
Figure 7:15 - Fuel consumed vs altitude simulators comparison with POH

39
7.4.2 Conclusion
From the graphs, it was observed that the data produced from the virtual simulation of the
Cessna 172 Skyhawk evidently shows X-plane 10 produced more viable data than the Merlin
software. The advantages of using the PlaneMaker and AirfoilMaker GUI configuration of flight
dynamics by X-plane 10 over the Excalibur I GUI configuration by Merlin can be seen by the
offset of data from the pilot handbook data. The blade element theory produced data very close
to the pilot handbook due to the fact that it divides the aircraft components such as the wing
into small finite elements, each having its own constraints. As a result of this method more
comprehensive results are produced.
The Merlin software however, although it uses aerodynamic coefficients and technical
equations to obtain parameters such as atmospheric conditions it doesn’t match the complexity
of the X-plane 10. Merlin simulates the different aircraft components such as the wing as a
whole. So the results of data such as pressure distribution across the wing are averaged and
thus has the same values across the section of the wing. Whereas on the other hand, X-plane
10 pressure values over the wing differ across different locations on the wing because of the
use of the Blade Element theory and the flow equation. Each element across the wing
experiences different aerodynamic forces depending on their location. Thus, the detail and
complexity of X-plane 10 is much more than that of Merlin.
In conclusion, X-Plane 10 proved to provide climb performance much closer to the POH
compared to Merlin.

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