Basic knowledge for categories A, B1 and B2 are indicated by the allocation of knowledge levels indicators (1, 2 or
3) against each applicable subject. Category C applicants must meet either the category 81 or the category 82
basic knowledge levels.
The knowledge level indicators are defined as follows:
LEVEL 1
A familiarisation with the principal elements of the subject. Objectives:
The applicant should be familiar with the basic elements of the subject.
The applicant should be able to give a simple description of the whole subject, using common words and examples.
The applicant should be able to use typical terms.
LEVEL 2
A general knowledge of the theoretical and practical aspects of the subject.
An ability to apply that knowledge.
Objectives:
The applicant should be able to understand the theoretical fundamentals of the subject.
The applicant should be able to give a general description of the subject using, as appropriate, typical examples.
The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject.
The applicant should be able to read and understand sketches, drawings and schematics describing the
subject.
The applicant should be able to apply his knowledge in a practical manner using detailed procedures.
LEVEL 3
A detailed knowledge of the theoretical and practical aspects of the subject.
A capacity to combine and apply the separate elements of knowledge in a logical and comprehensive
manner. Objectives:
The applicant should know the theory of the subject and interrelationships with other subjects.
The applicant should be able to give a detailed description of the subject using theoretical fundamentals
and specific examples.
The applicant should understand and be able to use mathematical formulae related to the subject.
The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject.
The applicant should be able to apply his knowledge in a practical manner using manufacturer's
instructions.
The applicant should be able to interpret results from various sources and measurements and apply
corrective action where appropriate.
3.2 Module 15.3 Inlet
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Table of Contents
Module 15.3 - lnlets
General~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-5 Description 5 Purpose 5 Ram 7 Definitions 7 Intake Momentum Drag 7 Intake Design 9 Pitot Intakes 9Divided Entrance Intakes 1 O
Supersonic Intakes 13
The Shock Wave 13
Variable Throat Area Inlet 13
External I Internal Intake 16
Intake Ice Protection 17
Hot Air Anti Icing 17
Electrical Intake De-icing I Anti-icing systems 18
Module 15.3 Inlet 3.3
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Module 15.3 Enabling Objectives and Certification Statement
Certification Statement
These Study Notes comply with the syllabus of EASA Regulation 2042/2003 Annex Ill (Part-66)
A ppen di I rx , an d th e assoc1a e . t d K nowe I d 1qe eve s as spec: 1e L I if d b I eow:
Objective EASA66 Level
Reference 81
Inlet 15.3 2
Compressor inlet ducts
Effects of various inlet configurations;
Ice protection.
3.4 Module 15.3 Inlet
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Module 15.3 - Inlet
General
Description
The main air intake is often part of the airframe structure, delivering the air to the engine air intake casing.
The intake is designed to convert kinetic energy into pressure reduce the velocity at the
compressor inlet to no more than between 0.4 and 0.5 Mach. Any inefficiency in the intake
results in a pressure loss at the compressor inlet and reduced compressor outlet pressure. Purpose
To deliver the air to the compressor with the minimum loss of energy The intake system should meet the following requirements:-
1 Deliver to the engine an adequate mass flow of air under any engine operating condition.
2 The air must be delivered evenly across the face of the compressor, free from turbulence
at approximately M
=
0.4.3 Must make maximum use of RAM pressure.
4 Produce minimum airframe drag.
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Module 15.3 Inlet 3.5
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3.6 Module 15.3 Inlet
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Ram
Definitions
Total Head Pressure
The pressure of the air when brought to rest in front of the intakes. Ram Ratio
The ratio of the total pressure (Pt) at the compressor entry to static pressure (P s) at the intake entry i.e. Ptf P s (See figure 3.1)
Ram Recovery
To convert as much of the intake air velocity as possible to pressure at the face of the engine. If all available ram pressure is converted, it is known as "TOTAL PRESSURE RECOVERY". Ram Compression
Ram Compression increases in pressure within the intake at substantial forward speeds.
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When an aircraft is stationary, the engine intake is of little interest, in fact, a slight depression exists within it. Ram compression causes redistribution of the energy existing in the air stream. As the air in the intake slows in endeavouring to pass into and through the compressor element against the air, increasing pressure and density which exists therein, so the kinetic energy of the air in the intake decreases. This is accompanied by a corresponding increase in its pressure and internal energies and consequently compression of the air stream is achieved within the intake, thus converting the unfavourable intake lip conditions into the compressor inlet requirements.
Although ram compression improves the performance of the engine, it must be realised that during the process there is a drag force on the engine and hence the aircraft. This drag must be accepted, since it is a penalty inherent in a ram compression process. The added thrust more than makes up for the increase in drag.
The degree of ram compression depends on the following:-
1 The frictional losses at those surfaces ahead of the intake which are "wetted" by the intake airflow.
2 Frictional losses at the intake duct walls.
3 Turbulence losses due to accessories or structural members located in the intake. 4 Aircraft speed.
5 In a turbo-prop engine, drag and turbulence losses due to the propeller, blades and spinner.
Intake Momentum Drag
As forward speed increases, thrust decreases, this is due to the momentum of the air passing into the engine in relation to the aircraft's forward speed.
Module 15.3 Inlet 3.7
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3.8 Module 15.3 Inlet
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Intake Design
The following types of intake can be seen on modern aircraft:- 1 2 3 4 Pi tot Divided Entrance Variable Geometry External/Internal Compression Pitot Intakes
This intake is suitable for subsonic or low supersonic speeds. The intake is usually short and is very efficient because the duct inlet is located directly ahead of the compressor. The duct is
divergent from front to rear with smooth gradual changes in shape
Efficiency will fall rapidly at sonic speeds due to shock wave formation at the lip. With increased speeds above sonic, this shock wave will move backwards towards the compressor face. If the shock wave enters the compressor, damage may occur and there is a high risk of compressor surge.
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---:-- Static Pressure (Ps) Total Pressure (Pt)Figure 3.1: A pitot intake
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Module 15.3 Inlet 3.9
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Figure 3.2: A pitot intake
Divided Entrance Intakes
This type is used on some single engined aircraft with a fuselage mounted engine and can be either side scoop or wing root mounted. The side scoop inlet is placed as far forward of the compressor as possible to approach the straight line effect of the single inlet. The wing root inlet presents problems to the designer in the forming of the curvature necessary to deliver the air to the engine compressor.
One major problem with both of these inlet types is a loss of ram pressure occurs on one side of the intake and as a result separated turbulent air is fed to the compressor.
The intake will be divergent from front to rear.
3.10 Module 15.3 Inlet
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