engine sizing
TRANSCRIPT
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Air Force Institute Of
Technology
Basheer Ibraheem
LIGHT TRAINER AIRCRAFT RESEARCH
(AFIT01)
Engine Sizing, Installation and performance
DEPARTMENT OF AIRCRAFT ENGINEERING
PGD THESIS
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Air Force Institute Of Technology
DEPARTMENT OF AIRCRAFT ENGINEERING
PGD THESIS
Academic Year 2011-2012
Basheer Ibraheem
Light Trainer Aircraft Research(AFIT 01)
Engine Sizing, Installation and Performance
Supervisor:..This thesis is submitted in partial fulfillment of
the requirements for post graduate diploma
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ABSTRACT
This report outlines the Engine Sizing, Installation and Performance of
the AFIT Light Trainer Aircraft. The AFIT Light Trainer aircraft Design is a
Group Design Project undertaken in order to meet Nigerian Air Forces
ambition of self reliance in pilot training whilst still satisfying one of the
requirements of the PGD in Aerospace Vehicle Design from AFIT. The
first section given in this report is the introduction and background to
the project. This is subsequently followed by a literature review into
piston engine sizing, engine installation and aircraft performance. The
design stages commenced with a comprehensive engine sizing,
followed by engine selection and propeller sizing. Installation type was
selected based on what the engine was machined for by the
manufacturer. The work in progress is engine performance. The
designer faced some limitations such as absence of past research
articles of similar field of interest.
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CONTENTS
LIST OF FIGURES................................................................................6
1.0 INTRODUCTION .................................................. 61.1 Project Background ................................................................ 7
1.2 AFIT Light Trainer Concept ..................................................... 8
1.3 Project Specifications ............................................................. 9
1.4 Authors Responsibility ........................................................ 11
1.5 Design requirements ............................................................ 11
1.5.1 Certification Requirements ............................................. 12
1.5.2 Functional Requirement ................................................. 12
2.0 LITERATURE REVIEW ............................................................... 13
2.1 Aero Engines ....................................................................... 13
2.1.1 Gas Turbine Engines ....................................................... 13
2.1.1.1 Turbojet ..10
2.1.1.2 Turboprop.11
2.1.1.3 Turbofan12
2.1.2 Reciprocating Engine ...................................................... 17
2.2 Light trainer Aircraft Engines ............................................... 18
2.2.1 Selection of Engine Type ................................................. 18
2.2.2 Determination of Engine Size ........................................ 20
2.2.3 Getting the Required Engine ......................................... 21
2.3 Engine Installation ............................................................... 21
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2.3.1 Management of Exhaust Gasses .................................... 22
2.3.2 Management of Cooling Air ............................................ 23
2.3.3 Stability and Control Considerations ............................. 25
2.3.4 Safety Considerations .................................................... 25
2.3.5 Noise Considerations ...................................................... 25
2.3.6 Structural Considerations ............................................... 26
2.4 Engine Mount ...................................................................... 27
2.4.1 Types of Engine Mount ................................................... 28
2.4.1.1 Conical Mounts.24
2.4.1.2 Dynafocal Mounts..25
2.4.1.3 Bed Mounts.26
2.5 Aircraft Performance ............................................................ 31
2.5.1 Introduction .................................................................... 31
2.5.2 Engine and Aircraft Performance. 32
2.5.2.1 Maximum Speed..29
2.5.2.2 Climb Rate29
2.5.2.3 Range30
2.5.2.4 Take off Distance.30
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LIST OF FIGURES
Figure 1: AFIT Light Trainer Aircraft........................................................9
Figure 2: A Turbojet Engine [18]......................................................14
Figure 3: A Turboprop Engine [18]...................................................15
Figure 4: A Turbofan Engine [18].....................................17
Figure 5: Principles of Piston Engine [18]...................................18
Figure 6: A Bad Way of Mounting Exhaust [6].......................................22
Figure 7: An Improved Way of mounting Exhaust [6]............................23
Figure 8: A Downdraft Cooling *6+.................................................24
Figure 9: An Updraft Cooling [6]......24
Figure 10: A Shock Mount.....................................................27
Figure 11: A Conical Mount........................................29Figure 12: A Dynafocal Mount............................................30
Figure 13: A Bed Mount...........................................31
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1.0 INTRODUCTION
1.1 Project Background
Ab initio flying training aircraft are a class of aircraft specifically
designed to facilitate transition of pilots-in-training (student pilots) to
pilots [19]. Ab initio flying training aircrafts are characterised by
additional safety features which include; forgiving flight characteristics,
stiff structure, simplified cockpit arrangement, excess power and good
visibility. These characteristics serve to accommodate the mistakes by
the inexperienced and enable instructors to allow students more time
to correct their own errors which increase learning speed [5]. The
above mentioned qualities however are considered together with the
operators requirement of cost effectiveness.
A cost effective aircraft must have comparatively lower sum of initial
investment and operating costs [19]. Additionally, availability of parts
and ease of maintenance are major considerations to the operator.
In search of a good trainer, the NAF incorporated the Scottish Aviation
Bulldog into service in the early 80s for use as trainer. However, the
high operating cost, which comprises of cost of fuel and spares made if
impossible for the NAF to sustain the use of Bulldog as trainer.
Consequently the ABT-18 aircraft was introduced in 1995 to replace the
Bulldog. Since then, the air beetle has been the ab initio trainer of the
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NAF. The air beetle is known to have many inadequacies, the major of
which are the unforgiving nature of its nose wheel strut, and frequent
high cylinder head temperature. These maintenance problems made it
impossible for the NAF to sustain local training. Replacing the air beetle
therefore, with an easier to maintain, more robust aircraft would assist
the NAF to actualize its dream of self reliance in pilot training.
1.2 AFIT Light Trainer Concept
The department of Air Engineering, Air Force Institute of Technology is
exploring the possibility of designing a light trainer aircraft for the
Nigerian Air Force. The project when successful is going to replace the
ABT-18 Aircraft currently in service as the ab initio trainer of the NAF.
The AFIT light trainer aircraft project considers a two seater low wing
light aircraft. It is intended to be an engineering data gathering
research to lay the grounds for future development work in subsequent
years. The project consists of a number of individual research topics
that stand in their own right
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Figure 1: AFIT LIGHT TRAINER AIRCRAFT
1.3 Project Specifications
The conceptual design of the aircraft has been carried out by a team of
instructors. The conceptual design was able to establish all the features
of the aircraft. The following are the established parameters and
payload configuration of the light aircraft:
SPECIFICATIONS
Interior Layout
Accommodation and capacity
Maximum specified passenger capacity: 2
Configuration: side by side
Doors: 1 overhead canopy
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Powerplant
Type: Piston Engine
Capacity: To be determined
Configuration: Tractor
Performance:
Max take-off weight: 1,066 kg
Empty weight: 669 kg
Range: 540 nm
Service ceiling: 10,000 ft
Cruise speed: 46.96 m/s
AERODYNAMIC INFORMATION
Lift Characteristics
Maximum lift coefficient: 1.448
Basic wing Max CL angle 15o
Stall angle 9o
Drag Polar:
Cruise condition M = 0.14
Sea level takeoff, undercarriage and flaps extended
Landing gear increment
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1.4 Authors Responsibility
The author was primarily responsible for engine sizing (determining
power required), engine selection, installation and performance
calculation for the AFIT light trainer aircraft. Engine selection is an
important part of the aircraft design process. Because the engine size
was not determined during the conceptual design, this requires the
determination of power required by the aircraft, selecting an engine
capable of producing that amount of power, determining how it will be
installed and calculating the key performance indicators.
Evidently, certain interface issues are present with components such as
fuselage, nose landing gear and systems such as the fuel system and
the mass and C.G of the aircraft. Thus, it is paramount to work in
collaboration with the various designers with which interface issues
exist for synchronization of efforts.
1.5 Design requirements
Definition of necessary air worthiness requirements and goals are key
aspects of an aircraft design. This provides a means of monitoring the
project goals and ensuring that the design outcome is not conflicting
with the pre-stated requirements.
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1.5.1 Certification Requirements
The marketability and the integrity of a design are ensured by it strict
adherence to standard design regulations as documented by the
appropriate governing bodies. In this case, AFIT light trainer aircraft is
designed in conformity with design requirements of EASA certification
Specification for normal, utility, aerobatic and commuter category
airplanes (CS - 23) [7]. The air worthiness code ofCS 23 is applicable
to this class of aircraft as it is an aerobatic aircraft with maximum
certified takeoff weight of greater than 750kg (which is the limit for
CSVLA), and less than 56kg. The sections of the regulatory document
that apply to the power plant are as listed in Appendix A.
1.5.2 Functional Requirement
It can be argued that the correct choice of power plant is half the
success of an aircraft design. It does not matter if you build a really
efficient structure or have the best aerodynamics if the choice of
power plant is poor, then the design will not be successful [5].
The primary role assigned to the aircraft engine is to provide the
required thrust to move the aircraft. In addition, there is the need for
the engine weight and fuel consumption to be within acceptable limits
of todays technology.
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2.0 LITERATURE REVIEW
2.1 Aero Engines
Aircraft need some form of power to keep them flying. Since the first
powered flight, numerous types and models of engines have been
developed. Aviation propulsion system varies according to
construction, configuration and purpose and has gone through several
changes over the years. The most popular propulsion systems are Gas
Turbine and Reciprocating Engines.
2.1.1 Gas Turbine Engines
Most modern passenger and military aircraft are powered by gas
turbine engines, which are also called jet engines. The gas turbine
engine is essentially a heat engine using air as a working fluid to provide
thrust. To achieve this, the air passing through the engine has to be
accelerated; this means that the velocity or kinetic energy of the air is
increased. To obtain this increase, the pressure energy is first of all
increased, followed by the addition of heat energy, before final
conversion back to kinetic Energy in the form of a high velocity jet
efflux. There are several types of jet engines. They include:
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2.1.1.1 Turbojet Engines
The first and simplest type of gas turbine is the turbojet [18]. Turbojet
engine derives its thrust by highly accelerating a mass of air, all of
which goes through the engine. Since a high jet" velocity is required to
obtain an acceptable thrust, the turbine of turbo jet is designed to
extract only enough power from the hot gas stream to drive the
compressor and accessories . All of the propulsive force (100% of
thrust) produced by a jet engine is derived from the exhaust gas.
Figure 2: A TURBOJET ENGINE
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2.1.1.2 Turboprop Engines
Many low speed transport aircraft and small commuter aircraft
use turboprop propulsion. There are two main parts to a turboprop
propulsion system, the core engine and the propeller. The core is very
similar to a basic turbojet except that instead of expanding all the hot
gasses through the nozzle to produce thrust, most of the energy of the
exhaust is used to turn the turbine. The shaft on which the turbine is
mounted drives the propeller through the propeller reduction gear
system. The propeller produces most of the thrust in a turboprop and
the exhaust contributes little thrust. Approximately 90% of thrust
comes from propeller and about only 10% comes from exhaust gas [18].
Figure 3: A TURBOPROP ENGINE
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2.1.1.3 Turbofan Engines
A turbofan engine is the most modern variation of the basic gas turbine
engine. As with other gas turbines, there is a core engine. In the
turbofan engine, the core engine is surrounded by a fan in the front and
an additional turbine at the rear dedicated for driving the fan. The
incoming air is captured by the engine inlet. Some of the incoming air
passes through the fan and continues on into the core compressor and
then the burner, where it is mixed with fuel and combustion occurs.
The hot exhaust passes through the core and fan turbines and then out
the nozzle, as in a basic turbojet. The rest of the incoming air passes
through the fan and bypasses, or goes around the engine, just like the
air through a propeller. The air that goes through the fan has a velocity
that is slightly increased from free stream. So a turbofan gets some of
its thrust from the core and some of its thrust from the fan. The ratio of
the air that goes around the engine to the air that goes through the
core is called the bypass ratio. Because the fuel flow rate for the core is
changed only a small amount by the addition of the fan, a turbofan
generates more thrust for nearly the same amount of fuel used by the
core. This means that a turbofan is very fuel efficient. Most modern
airliners use turbofan engines because of their high thrust and good
fuel efficiency [16].
http://www.pilotfriend.com/training/flight_training/tech/turbo/inlets.htmhttp://www.pilotfriend.com/training/flight_training/tech/turbo/burner.htmhttp://www.pilotfriend.com/training/flight_training/tech/turbo/nozzles.htmhttp://www.pilotfriend.com/training/flight_training/tech/turbo/nozzles.htmhttp://www.pilotfriend.com/training/flight_training/tech/turbo/burner.htmhttp://www.pilotfriend.com/training/flight_training/tech/turbo/inlets.htm -
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Figure 4: A TURBOFAN ENGINE
2.1.2 Reciprocating Engine
A reciprocating aero engine is a fuel-burning internal combustion piston
engine specially designed and built for minimum fuel consumption and
light weight in proportion to developed shaft power [21]. Reciprocating
aircraft engines operate on a four-stroke cycle, where each piston
travels from one end of its stroke to the other four times in two
crankshaft revolutions to complete one cycle. The cycle is composed of
four distinguishable events called intake, compression, expansion (or
power), and exhaust, with ignition taking place late in the compression
stroke and combustion of the fuel-air charge occurring early in the
expansion stroke. These reciprocating engines burn specially
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formulated aviation gasoline and produce shaft power by the force of
combustion gas pressure on pistons acting on connecting rods turning a
crankshaft. Major parts are the crankcase, crankshaft, connecting rods,
pistons, cylinders with intake and exhaust valves, camshafts, and
auxiliary operating systems such as ignition, fuel injection or
carburetion, and fuel and oil pumps.
Figure 5: PISTON ENGINE PRINCIPLES
2.2 Light trainer Aircraft Engines
2.2.1 Selection of Engine Type
The following factors play a role in selecting the type of propulsion
system to be used [6]:
1. Required cruise speed and/or maximum speed
2. Required maximum operating altitude
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3. Required range and range economy
4 Noise regulations
5. Installed weight
6. Reliability and maintainability
7. Fuel amount needed
8. Fuel cost
9. Fuel availability
10. Specific customer or market demands
Overall fuel efficiency, cost and installed weight often dominate the
arguments about the pros and cons of a certain type of propulsion
system [6].
Most modern aircraft using engines with up to 450hp output are
powered by air-cooled, horizontally opposed, reciprocating engines.
The biggest reason for this is cost: other than avionics, the system that
contributes most to a vehicles price is its propulsion system, and a
turbine engine can cost up to five times more than a comparable piston
engine [3]. Additionally, recent years have seen large technological
advances in piston engine manufacturing, making them lighter, more
powerful, and more efficient. Finally, piston engines are known to have
greater flexibility with respect to transient power requirements than
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turbine engines, which not only increases safety, but also performance
and efficiency [4]. Because of these factors, many general aviation
manufacturers are using piston engines in an attempt to reduce vehicle
price and increase the potential market.
The smaller turbine engines that fall below 450hp have failed to meet
the low cost and fuel economy necessary to compete with existing
reciprocating engines. Therefore reciprocating engines are the cost
effective choice for light trainer aircraft like the AFIT Light Trainer
Aircraft.
2.2.2 Determination of Engine Size
Before choosing an engine for an aircraft, the total thrust (power)
required must be known. The thrust-to-weight ratio (power loading for
propeller-powered aircraft) and wing loading (w/s) are the two most
important parameters affecting aircraft performance [13]. Wing loading
and thrust-to weight ratio are interconnected for a number of
performance calculations, such as takeoff distance, climb rate andmaximum speed. These performances are critical design drivers used to
size the engine.
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2.2.3 Getting the Required Engine
An aircraft can be designed using some existing engine or a new to-be-
designed engine. However, rarely is a new general aviation airplane
design enough incentive for engine manufacturers to go for the time
and expense of designing a new engine. This only happens in the case
of major military fighter or bomber program [1]. Designer of a general
aviation or aerobatic aircraft mostly rely on selecting the best of the
existing engines. To do this, the designer determines the performance
characteristics he needs and search for an engine that is capable of
delivering those parameters.
2.3 Engine Installation
Haven decided on the type and the number of engines to be used, the
next decision is: how should these engines be installed? There are a
number of possible options. The following factors play a role in deciding
on the engine installation [6]:
1. Management of exhaust gases
2. Management of cooling air
3. Stability and control considerations
4. Safety Considerations
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5. Noise considerations, and
6. Structural Considerations
2.3.1 Management of Exhaust Gasses
When the exhaust stack is mounted perpendicular to the free stream, it
is very bad from a drag viewpoint. Figure 7 shows how this can be
improved somewhat. Reference 6, shows that poorly designed exhaust
configurations can increase the zero lift drag coefficient of an airplane
by 16 percent. By directing the exhaust rearward, drag can be reduced
and some thrust can be recovered as well.
Figure 6: A BAD WAY OF MOUNTING EXHAUST PIPE
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Figure 7: AN IMPROVED WAY OF MOUNTING EXHAUST
2.3.2 Management of Cooling Air
Most piston engines are designed with the assumption that the cooling
air will flow from top to bottom: downdraft, as shown in figure 8.
Updraft cooling arrangement, as shown in figure 9, may look good, but
can result in the cooling air being heated by the exhaust stack thereby
reducing cooling effectiveness. Mismanagement of cooling air can
cause drag Increase of up to 9 percent of zero lift drag [6].
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Figure 8: A DOWNDRAFT COOLING
Figure 9: AN UPDRAFT COOLING
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2.3.3 Stability and Control Considerations
The stability and control effect that should be considered in a tractor
engine is the effect of engine/propeller thrust line location and
inclination. In preliminary design, a good rule of thumb is: if the engine
disposition differs significantly from that of existing certified airplanes,
considerable power effects on stability and control characteristics can
be expected [6]. In such cases the safest thing to do is to perform the
necessary stability and control calculations before freezing the design.
2.3.4 Safety Considerations
AII engines and other heat generating equipment must be isolated from
the rest of the airplane by means of firewalls and/or other suitable
shrouds. This requirement is of great importance in isolating engines
from fuel tanks. Fire walls should be made out of stainless steel and/or
titanium [6].
2.3.5 Noise Considerations
Airplanes and their engines create a substantial amount of both interior
and exterior noise. The interior noise levels should not be so high as to
cause discomfort to the passengers or to make safe operation by the
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crew impossible. The exterior noise levels should meet the
requirements of Certification Specifications for Aircraft Noise CS-36.
These requirements impose severe restrictions on the type of engine
and/or propeller technology which can be utilized.
2.3.6 Structural Considerations
The structural consideration that plays an important role in the
integration of the propulsion system into the airframe is the
transmission of thrust into the airframe [6]. To transmit thrust forces
into the airframe it is necessary to have a number of 'hard points'
where the engine is physically attached to the airframe. The number of
these hard points depends on the type of engine used. Figure 12 shows
an example of the principal method used to mount piston engines in
airframes. This is accomplished with a truss (usually made of welded
steel tubes).
It is important to note that the attachment (mounting) points on the
engine itself cannot be changed easily. Their location depends on the
internal design of the engine which is determined by the engine
manufacturer. Changing these attachment points is very expensive [20].
Also, since most piston engines transmit significant vibrations into the
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airframe it is essential to use some type of shock mount(s) to reduce
these vibrations.
Figure 10: A SHOCK MOUNT
2.4 Engine Mount
The engine mount is primarily used to connect the engine to the
airframe or fuselage. Some of its secondary features are to distribute
the weight of the engine and spread the torque and vibration
generated by the engine [20]. Most engine mounts are made from
tubular steel chrome-molybdenum welded together. This is a
lightweight and strong construction. After welding, the structure is
sandblasted and power-coated in bright color, which makes it easy to
spot any cracks should they develop.
The engine is not bolted directly onto the mount; this would result in
vibrations from the engine to the aircraft. Instead, rubber shock
mounts of varying strength and thicknesses are used. This dampens the
vibration and movement, giving a much smoother flight and running
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engine. Any fatigue due to vibration is also not a factor with this
construction.
2.4.1 Types of Engine Mount
Most four cylinder engines today use mounts that look similar. The
engine is bolted to the mount at the back or at the underside of the
engine. The common types of piston engine mount are conical,
dynafocal and bed mounts.
2.4.1.1 Conical Mounts
This is the easiest mount to fabricate. It has four attach point for the
engine and usually four points to bolt the mount to the firewall. The
engine mount points are parallel with the firewall, so there is no
awkward angle when installing the engine bolts and shock mounts.
The disadvantage of this type of mount is that it is not effective in
cushioning vibration and engine torque [20].
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Figure 11: A CONICAL MOUNT
2.4.1.2 Dynafocal Mounts
These are the best types of mounts, and they do a perfect job of
cushioning the vibrations and movements from the engine. Dynafocal
mounts also produce lower cockpit noise. However, they are more
expensive to build and construct [20]. The engine is held in four attach
points (located in a ring), under a certain angle and point to the center
of gravity of the engine. During welding this angle must be held in
perfect alignment or else the four bolts will not fit when installing the
engine in the mount.
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There are two types of dynafocal engine mounts: Type 1 and Type 2.
Type 1 is used in Lycoming engines up to 180 hp and the type 2 is used
in the IO-320 and IO-360 model engines from Lycoming [20].
Figure 12: ADYNAFOCAL MOUNT
2.4.1.3 Bed mount
In a Bed mount, the engine is mounted using four points underneath
the crankcase and then hang to the firewall, as shown below:
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Figure 13: A BED MOUNT
2.5 Aircraft Performance
2.5.1 Introduction
Performance is a term used to describe the ability of an airplane to
accomplish certain things that make it useful for certain purposes [22].
For example, the ability of the airplane to land and take off in a very
short distance is an important factor to the pilot or operator who
operates in and out of short, airfields. The ability to climb fast, carry
heavy loads, fly at high altitudes at fast speeds, or travel long distances
are essential performance parameters for operators.
The main elements of performance are the takeoff and landing
distance, rate of climb, ceiling, payload, range, speed, maneuverability,
stability, and fuel economy. Some of these factors are often directly
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opposed: for example, high speed versus shortness of landing distance;
long range versus great payload. It is the compromise between two or
more of these factors which dictates differences between airplanes and
explains the degree of specialization of modern airplanes.
Therefore, whenever the question of aircraft performance is asked,
what the questioner wants to find out are:
How fast can the airplane go?How high can it go?How fast can it climb?How far can it travel without refueling?What length of airfield is required to operate it?
2.5.2 Engine and Aircraft Performance
The various items of aircraft performance result from the combination
of airplane and engine characteristics.
The aerodynamic characteristics of the airplane generally define the
power and thrust requirements at various conditions of flight while
engine characteristics define the power and thrust available at various
conditions of flight. The matching of the aerodynamic configuration
with the engine is accomplished by the designer to provide maximum
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performance at the specific design condition; e.g. range, endurance,
and climb.
Below are examples of engine role in key performance parameters:
2.5.2.1 Maximum Speed
The maximum level flight speed for the airplane will be obtained when
the power or thrust required equals the maximum power or thrust
available from the powerplant. So maximum speed is directly related to
the engine capacity. On the other hand, the minimum level flight
airspeed is not usually defined by thrust or power requirements.
Instead, it is determined by conditions of stall or stability and control
problems [22].
2.5.2.2 Climb Rate
Climb depends upon the reserve power or thrust. Reserve power is the
available power over that required to maintain horizontal flight at a
given speed. Thus, if an airplane is equipped with an engine that
produces 200 total available horsepower and the airplane requires only
130 horsepower at a certain level flight speed, the power available for
climb is 70 horsepower.
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2.5.2.3 Range Performance
The ability of an airplane to convert fuel energy into flying distance is
one of the most important items of aircraft performance. Range isanother performance parameter that is determined partly by the
engine; the specific fuel consumption (SFC) of the engine.
2.5.2.4 Takeoff performance
The minimum takeoff distance is of primary interest in the operation of
any airplane because it defines the runway requirements. The
minimum takeoff distance is obtained by taking off at some minimum
safe speed that allows sufficient margin above stall and provides
satisfactory control and initial rate of climb.
To obtain minimum takeoff distance at the specific lift-off speed, the
forces that act on the airplane must provide the maximum acceleration
during the takeoff roll. The powerplant thrust is the principal force in
providing the acceleration and, for minimum takeoff distance, the
maximum output thrust should be high.
When the wing loading (w/s) of an aircraft and other aerodynamic
characteristics are known, the required maximum speed, climb rate and
takeoff distance are used to size the engine [1].
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APPENDIX A: APPLICABLE SECTIONS OF CS-23.
1. CS-23.45 PERFORMANCE GENERAL2. CS-23.51 TAKE OFF APEED3. CS-23.53 TAKE OFF PERFORMANCE4. CS-23.75 LANDING DISTANCECS-23.655. CS-23.335 DESIGN AIRSPEEDS6. CS-23.361 ENGINE TORQUE7. CS-23.363 SIDE LOAD ON ENGINE MOUNT8. CS-23.371 GYROSCOPIC AND AERODYNAMIC LOAD9. CS-23.611 ACCESSIBILITY PROVISIONS10. CS-23.901 POWERPLANT INSTALLATION11. CS-23.905 PROPELLERS12. CS-23.925 PROPELLER CLEARANCE13. CS-23.1121 EXHAUST SYSTEM14. CS-23.1191 FIRE WALLS