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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
4 Algorithms
Maximum lift coefficient
Wing lift is found by computing the spanwise distribution of the lift coefficient, based on the theory of a
“loaded line”. The local lift is computed taking into account the wing planform and other properties
such as airfoil profile, twist and incidence. The maximum wing lift is generated when somewhere along
the span, the local lift coefficient reaches the maximum lift coefficient of the wing section.
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
Specific weights
An estimate of the empty weight of the aircraft is made by making a weight breakdown for the major
components of the aircraft: wing, engine installation, propeller, fuselage, horizontal tailplane, vertical
tailplane, foreplane (canard), main landing gear, nose or tail landing gear, fuel system, hydraulic
system, control systems, electrical systems, instruments.
The weight breakdown is made by using formulas. Most often these formulas were derived in an
empirical way from the analysis of a large number of existing aircraft. Each result is mulitplied by a
correction coefficient in order to take into account several aspects, such as materials used, the ability
of the designer to build lighter, etc… These correction coefficients are generally found after a detailed
analysis of existing aircraft which are similar in concept to what the designer has in mind.
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
Specific drags
A traditional drag breakdown is made as follows:
- CD0 : zero-lift drag (friction drag),
- CDL : induced drag,
- CDint : interference drag caused by interaction of the different parts of the aircraft.
The drag coefficient is therefore: CD = CD0 + CDL + CDint.
The total drag of the aircraft is calculated as the sum of the drag of each major part of the aircraft:
wing, trailing edge devices, horizontal tailplane, vertical tailplane, foreplane (canard), fuselage,
propulsion (engine installation), propeller, nacelle, landing gear, interference.
During the conceptual design of the aircraft, the interference drag is difficult if not impossible to
determine. ADS uses a method based on reference aircraft as described below:
- The designer has specified the “aerodynamic quality” of the aircraft for the design flight
condition being considered. This value was determined from the analysis of similar aircraft. As
a reminder, the “aerodynamic quality” is the total drag coefficient of the aircraft.
- During the design process, the drag breakdown for the major aircraft components is initially
worked out for the design flight condition.
- Next, the interference drag is computed for the design flight condition by subtracting the total
drag (the “aerodynamic quality” specified by the designer) and the sum of the drag breakdown
calculated above.
- Then, the relative interference drag is calculated and expressed as a fraction of the total drag.
It is assumed that the relative intereference drag is constant for all flight conditions.
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
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
Propeller characteristics
The propeller properties (diameter, pitch, number of blades, blade section) are determined using
Propeller chart extracted from NACA reports. A blind test has been conducted with MT-Propeller in
Germany. We sent to them the propeller specifications. They calculated the new propeller using their
own methods and, in our side, we calculated the new propeller using ADS. The results concerning the
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