Chapter 2: Conceptual Design
The framework of a conceptual design process is a long and tedious process but on the contrary; A conceptual design is the first and most important phase of the aircraft system design and development process. A brief description of the conceptual designing process is given in the following section.
Selection of the Design Layout
Comparing and analyzing many historical models our aircraft was designed to have configuration similar to the figure below:
Some of the important features of this modeling is the canard configuration. Some of the advantages of this configuration are listed below.
Selection of Propulsion System
Ducted fan configuration was selected for our aircraft. A ducted fan is a propulsion arrangement whereby a fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tip vortices of the fan.
Design Parameter Estimation
The fundamental parameters calculated during the conceptual design phase are as follows:
(1) Aircraft maximum take-off weight (WTO),
(2) Wing reference area (Sw or Sref or S), and
(3) Engine thrust (TE or T) or engine power (PE or P)
Takeoff Weight Estimation
Normally, the EPUAVs were found to have a mass of 3 kg. But since we were using two ducted fan engines which may require two batteries, we estimated takeoff weight to be less or equal to 4 kg.
Wing Planform Design
During this stage reference area of the wing (Swref) was calculated i.e. the projection of the trapezoidal portion of the wing. Using available formulas and design requirements i.e. from our assumption, W/S = 11.5 kg/m2, W ≤ 4 kg ,
SWref ≤ WW/S ≤ 0.3478 m2
Using, ARw=5, we get Wing Span (b) = 1.28m
Wing Sweep: At transonic and supersonic speed, wing sweep is the primarily desirable factor. Especially when using FSW configuration, wing sweep angle is a most. In accordance to the aspect ratio of 5, sweep angle of -20 degree was selected.
Taper Ratio: Usually for unswept wing taper ratio of 0.45 is idle. But according to our precision of -20 degree sweep angle, historical trend graph suggests it to be 0.9. But analyzing other possible problematic criterion, taper ratio for our wing was selected yo be 0.6.
Twist Angle: Since taper ratio was chosen to be far less than the one needed in our aircraft, despite its forward swept configuration, so to provide elliptical lift distribution, a twist angle of 3 degrees (tip- positive 1 degree to root- negative 2 degree) was chosen.
Dihedral and Incidence Angle: For -20 degree sweep angle dihedral angle is required and to minimize drag at cruise 1 to 2 degree incidence angle is required which will be fulfilled by selecting suitable airfoil. From the wing span calculated, other requirements satisfied and carefully designing space for placing the control surface, below is the wing planform final design parameters:
From the takeoff weight estimation, fuselage length was found to be 1.5m, Using fuselage fineness ratio about 10 with following parameters, our fuselage will be designed.
Canard was configured with following parameters:
Airfoil selection is a very important stage during design process since overall aerodynamic efficiency during all phases of flight depends on this factor.
Overlooking different selection criterion like maximum lift coefficient, the range of angle of attack, airfoil thickness, etc., MEG-6263137 is selected idle for our wing configuration. Below are the parameters of this airfoil.
Vertical Stabilizer Sizing
Tail sizing is done by using historical approach. Since the effectiveness of vertical tail proportionally lies in the force produced by the tail and tail moment arm about the center of gravity, from estimations and calculations below listed tail parameters, are found out.
Landing Gear Design
Tricycle landing gear is chosen to be in our design. The landing gear parameters are found to be as follows:
CAD Model Of The Design
After all the parameters were determined a CAD model of each individual components and whole aircraft is created in CATIA which is shown below in the following figures: