DESIGN SELECTION
Designing the R.C plane with all proper dimensions with a good ratio and keeping all aspects related to theory of flight and aerodynamic calculations and structures a design was produced.
We design our plane according to the available engine size. i.e. 0.46 and drive other relative parameters from it, like wing span, chord, fuselage length etc.
A wing on a trainer is 5 to 1, that's span to chord. According to our engine size we decided 64" span wing. With a 5 to 1 aspect ratio it would have almost 10" chord. That's 640 sq in, or about 4.44 sq ft.
Pick a wing span of 64", aspect ratio should be 5 to 1 so the chord is 10" and the wing area is 640 sq.in. The balance point is about 25% back from the leading edge i.e. 7.5" from the back, and an airfoil thickness about 12% to 15% of chord.
Fuselage is 75% span so 43.6" long fuselage. Nose length is from back of prop to wing leading edge, should be 20% fuselage length so its 11.2" Tail length is from wing trailing edge to leading edge of horizontal stab, should be 40% of fuselage length so its 24".
Horizontal Stab area is 22% of wing area or 133.1 sq in. Horizontal Stab aspect ratio should be 3 to 1, say 'c' is the chord, then 3c is the span of the horizontal stab, so 3c * c = 133.1. 3c * c = 133.1 3 times c squared = 133.1
c = 6.66 ~7". So make it 20" long with a 7" chord.
Elevator is 20% of the area of the stab i.e. 26.6 (20” long with 1.333” wide)
Vertical Stab area is 1/3 Horizontal Stab are or 44.36 sq in. Vertical Stab is about as tall as it is wide, so 7" wide and 7" tall, adjust shape, height, width to look right and keep the area.
Rudder is 1/3 to 1/2 of the vertical stab area i.e. 14.78 sq in. (7” tall with 1.333” wide)
That's about what I need to build my trainer.
Summary of Basic Airplane Design:
Wing:
Balance point 25% average chord length back from leading edge, no more than 33% back from leading edge Aileron area 10% of total wing area. Aileron length 8 times its width. Strip ailerons are 1/8 the width of the cord of the wing. Barn Door ailerons are 1/4 the span and 1/4 the cord. Landing gear axle even with leading edge of wing for tail dragger. Landing gear main axle just after balance point for tricycle gear.
Airfoil:
Airfoil high point 25% back of leading edge. Airfoil thickness 12% to 15% of chord, including covering. (Clark Y - using Profili software)
Fuselage:
Fuselage length is 75% wing length. Nose length from prop to wing leading edge is 20% fuselage length. Tail length from wing back edge to horizontal surface front edge is 40% fuselage length. Fuselage height 10% to 15% of fuselage length.
Horizontal Stab:
20% to 22% of wing area. Has a 3 to 1 aspect ratio. Elevator is 20% of the area of the stab.
Vertical Fin and Rudder:
Vertical stab is 33% of horizontal stab. Vertical stab is about as wide as it is high. Rudder is 1/3 to 1/2 of that area.
Thrust Line:
2 to 3 degrees down thrust. 2 to 3 degrees right thrust. A thrust offset of 3 degrees is about 1/4 inch over 5 inches.
Technical Aspects:
Wing Profile:
We chose the Clark-Y (Flat bottom) airfoil because of its good low speed lift and high angle of attack stall characteristics. The following diagram shows how a Clark y airfoil behaves in different angle of attacks.
Angle of Attack/Angle of Incidence:
Angle of Attack is used to define the angle between the wing chord line (zero lift axis) and the flight path (relative motion)
Max angle of attack of Clark Y airfoil is 12 degree after that it stalls.
Critical or stalling angle of attack: The critical angle of attack is the angle of attack which produces maximum lift coefficient i.e. angle of attack increases beyond a certain point such that the lift begins to decrease. This is also called the "stall angle of attack".
Typically greater than 12 degree for Clark Y airfoil.
Coefficient of lift:
CL is a function of the angle of the body to the flow. The lift coefficient varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases.
The coefficient of lift for model RC Plane is around 1 to 1.5.
Team ZEETA Project Report:
Engine: Heli Engine
A thorough study related to the selection of engine was done in order to select the optimum engine for the model that could be able to give the required thrust. Several engines were taken into consideration. However, due to their unavailability, selection had be done among the available ones. So, two stroke 0.46 cu.in Heli engine is selected because of its easy start and set.
Empennage: Conventional
The tail plays an important role in the stability of the aircraft. Different configuration were studied and conventional tail was selected because of its overall balanced performance.
Wing Position: High Wing
The type of wing, which gives the most stability, was to be selected. The data shows high wing offers the best stability; however, it has a moderate weight and increased take-off distances.
Manufacturing and Material Selection:
Material selection is the basic step in manufacturing process. Different materials were used in each of the three major components.
Fuselage - ply wood; Horizontal and vertical stabilizer - balsa; Wing - Thermopol & Balsa
Undercarriage: Tricycle
The tricycle has good ground handling characteristics and is suitable for small take off distance. There is much more clearance for the placement of the main wheels to maintain center of gravity.
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