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In the same way, click on the left menu to access to the airfoil database. You select an airfoil in the
list. And all the information about this airfoil is displayed in the window. This information concerns the
coordinates of the airfoil profile and the aerodynamic data. The aerodynamic data are given for
different Reynolds numbers. The design module of ADS uses at any time this information to compute,
at a given flight speed, the drag and the lift of any lifting surface.
That ends this very quick tour of ADS. If you wish, we can go further in the design module itself or we
can speak about the algorithms used to compute the specific weights, the specific drags or the
propeller efficiency. We can also simulate the work done in a research department of a company.
Optimal Aircraft Design
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2 Conceptual design
Introduction
With ADS the design process in itself is divided in 3 phases (3 levels). The first level is called the
design with “given objectives”. The second level is called the design with “given means”. And the third
level is called the design with “given geometry”.
Level 1
For designing a new aircraft, the designer may start with a set of specifications and use this
information as input data. His goal is to find the parameters of the most optimized aircraft configuration
which will meet the design specification.
Initially, the designer should start without prejudice and keep all options open. He should consider any
imaginable and possible solution (fixed or retractable landing gear, two stroke or four stroke engine,
rotary or turbine engine, taildragger or tricycle landing gear, canard or tandem configuration, etc…),
including those which may appear unconventional.
To achieve this, he will study a limited set of parameters. Only “1st order parameters” will be evaluated,
i.e. those parameters which will significantly affect the results. For example, he will not assume a
predetermined engine, but instead he will assume an engine of a predetermined technology.
Optimal Aircraft Design
Optimal Aircraft Design SPRL Tél.: (32) 81 21 26 87 TVA.: BE 887 679 266
Rue de l’Yser, 31 Fax.: (32) 81 21 26 87 Banque : ING 363-0097122-65
5020 Namur E-Mail: info@oad.aero IBAN : BE18 3630 0971 2265
Belgique Code BIC : BBRUBEBB
The level 1 analysis uses a “flexible engine” (rubber engine) The engine power required to meet the
design specification will be calculated. At a later stage, the designer will search in an engine database
to find “the real engine” which will best match the “flexible engine”.
The results of the level 1 design process will allow the designer to define an aircraft configuration
which will meet the design specification. The geometry (wing and tail sizing, etc…) of the aircraft is
calculated as well as the thrust (engine power, propeller properties). Only the main flight condition
(typically cruise flight) will be explored, as the input data are not accurate enough to explore other
flight conditions (climb, take-off, descent).
We do not compute the maximum lift coefficient but we choose a given value keeping in mind the KIS
approach (Keep It Simple). We do the same with the aerodynamic efficiency of the aircraft. We know
that a high value of lift coefficient will lead to a sophisticated and expensive wing design. This is the
same for the aerodynamic efficiency. A low value of surface roughness will lead to expensive molds or
expensive manufacturing methods.
Optimization
While making the conceptual study of a new design, it is important to plan as many solutions as
possible to be able, in the end, to keep the best one, i.e. the one that responds in an optimal way to
the specifications requirements.
ADS offers a specific module to carry out this optimization. In order to do that, the user has to specify
the variables that he wishes to make vary from a lower limit to an upper limit as well as the variation
pitch
Given the fact that there are so many results and in order to facilitate their analyses, the user can also
determine some limits so that only the results that fit within those limits will be taken into consideration.
Those limits are determined, most of the time, through an in-depth analysis of the existing aircraft.
Once the optimized design is finished, only a limited number of about ten different configurations will
remain.
Level2
Once satisfied with the results obtained, the designer proceeds to the second stage of the process:
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