飞机设计AIRCRAFT DESIGN(2)

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2021hen the engine company finalize the design for the new engine, it becomes fixed in size and thrust ( fixed-engine );
In Chapter 3 a quick method based on minimal information was introduced . This chapter presents a more refined method capable of detail with most types of aircraftsizing problems.
AIRCRAFT DESIGN ( 2 ):
A Conceptual Approach Daniel P. Raymer
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Chapter 6 Initial Sizing
CONTENTS 6.1 Introduction 6.2 Rubber-Engine Sizing 6.3 Fixed-Engine Sizing 6.4 Geometry Sizing 6.5 Control-Surface Sizing
The rubber engine can be scaled to any thrust so the thrust-to-weight ratio can be held to some desired value even as the aircraft weight is varied.
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The designer will use a rubber engine in the early stages of design, specially for a major military fighter, bomber program, or SST ( the second supersonic transport ). And then, with the customer, tell the engine company what characteristics the new engine should be have;
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2021年3月11日10时3分
6.1 Introduction(2)
An aircraft can be sized using some existing engine or a new design engine. The existing engine is fixed in size and thrust, and is referred to as a “fixed-sizeengine” or “fixed-engine”. The new design engine can be built in any size and thrust required, and is called a “rubber-engine”.
Developing a new jet engine costs several billion dollars. Developing and certifying a new piston engine is also very expensive. Most aircraft projects do not rate development of a new engine, and so must rely on selecting the best of the existing engines;
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2021年3月11日10时3分
6.2 Rubber-Engine Sizing(1)
Review of Sizing :
Chapter 3 presented a quick method of sizing an aircraft using a configuration sketch and the selected aspect ratio ASwet / SrefAwet(L/D)max ( W i+1 / W i ) Wf We WTO ( iteration solution ) Refined Sizing Equation
2021年3月11日10时3分
6.1 Introduction(5)
The rubber engine sizing approach allows the designer to size the aircraft to meet both performance and range goals, for example, by solving for takeoff gross weight while holding the T/W required to meet performance objectives.
This is not possible for fixed-engine aircraft sizing. When a fixed size engine is used, either the mission range or the performance of the aircraft must become a fallout parameter.
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2021年3月11日10时3分
6.1 Introduction(4)
Even projects that must use an existing engine may begin with a rubber-engine design study to determine what characteristics to look for in the selection of an existing engine.
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2021年3月11日10时3分
6.1 Introduction(1)
Aircraft sizing is the process of determining the takeoff gross weight and fuel weight required for an aircraft concept to perform its design mission.