The Design Philosophy was centric on few main factors namely
•Generate Maximum Lift Force
•Minimize drag effects
•Adequate Vertical, Longitudinal and Directional
•Achieve the optimal structural strength while
•Minimize the all-up- weight
Step 1: Lets Make the Wing
Airfoil Name: S1223
1) High Cl v/s α.
2) Cl v/s Cd ratio.
On experimenting it was observed that this airfoil has brilliant glide slope, which becomes a very essential factor when we approach the plane to land with high amount of payload.
Therefore, S1223 was chosen to meet the requirement of high payload.
The wing is made up of two main spar and two trailing spars which provides adequate strength to the wing , but if the payload is above 1.5 kg a 5mm carbon rod along the wing is necessary.
The wing is made up with 10 ribs of balsa wood and covered with monocot. Additionally, lighting holes are made throughout the ribs along with the slot for the spars and the carbon rod.
Winglets can be provided to reduce the intensity of tip vortices to make the airflow more efficient and reduce energy loss due to induced drag, but one has to optimize between weight and aerodynamics.
Top wing configuration would allow locating the payload near the center of gravity of the entire airplane and provide positive longitude stability, both being very advantageous from a longitudinal stability perspective.Also it leaves space for electronics and payload mounting.
Step 2: It All Connects to the Fuselage, So Lets Make It!!!
FUSELAGE: BULKHEAD DESIGN
The fuselage design has 6 longerons running along with 10 bulkheads tapering at the end providing the fuse more than required structural strength to carry the payload. Care has been taken to provide sufficient reinforcement at the place where the wing and payload will be attached to the fuselage as these places have maximum stress. It is covered with monocot. Also the bulkhead and longeron structure makes the fuselage extremely light weight.
A aerodynamic fuselage design was chosen to reduce 3D drag mitigation.
The picture doesn't show the fuselage as it was the first prototype and the above described fuse is was used in the final model.!!
Step 3: Lets Stabilize the Plane
The horizontal stabilizer provides longitudinal stability in pitch; Flat bottom stabilizer is preferred as it offers low drag and weight along with an added component in improving pitching ability.
The vertical stabilizer provides stability in yaw; Symmetrical airfoils are preferred as it provides exceptional drag reduction and equal pressure distribution on both the sides resulting in improved directional stability.
Horizontal and Vertical stabilizers are made with ribs ,with spars passing through them to make them light and strong.
Step 4: TIme to Power Everything Up!!
A differential servo is used for the ailerons to minimize weight, as a cargo plane need not be highly maneuverable.
MOTOR , PROPELLER
Emax motor, 1100KV GT 2215/09 was used as it weighed only 70g and met the thrust requirement of 1250gm for 10*5 propeller.
ELECTRONIC SPEED CONTROLLER
Emax ESC, 40 amps was chosen to be on the safer side and prevent any shorting of equipment in case the motor would draw higher amp of current while carrying payload.
Battery depends on the flight time required, I personally used a 2000mah 11.1V 40C LIPO battery which gave me a flight time of 4 min.
Step 5: Testing!!
THE PLANE WEIGHED 400 GM AND COULD CARRY A WEIGHT OF 1200GM WITH THE SPECIFIED ELECTRONICS USED.
IT COULD COVER THE ENTIRE FOOTBALL FIELD CIRCUMCIALLY IN ABOUT A MINUTE
AND FLY FOR A MAXIMUM TIME FOR ABOUT 3 - 4 MIN.