The goal was to produce a simple, robust conceptually designed VTOL (vertical takeoff and landing) UAV (unmanned aerial vehicle) for package delivery. The end result had to be buildable using proven, existing, tested, and reliable fixed wing and quadcopter technology without years of research trying to make a crazy design that might work a little better.
The goal is not to use complex CFD (computational fluid dynamics) programs, FEA (finite element analysis), or any other complex method to create the final perfected design down to the last detail. That is pointless, since it is impossible for me, an engineering student (2 years completed of 4), or anyone else for that matter to do a better analysis than a company with the tools, experience, experts, time, and money. For this reason, the design presented has only the basic mathematics required for the frame sheet such as wing loading and mass of components, and the drag was given conservative estimates. Likewise, the perfect airfoil shapes and aerodynamics were left out. The design outlined uses basic concepts to show one way to create a UAV called the Bamberga-V5 that meets the projects requirement outlined in the requirements and guidelines.
Since most of the flight time is in cruise mode, it was decided early on to use a single propeller on the Bamberga-V5 for efficiency since they are theoretically more efficient than multiple propellers. A pusher motor was used as opposed to a tractor in order that the propeller would not obstruct the sensors in the nose of the aircraft. While pushers can be at a disadvantage since the propellers flows through disturbed airflow from the rest of the airplane [1, pp.317], the pusher has the benefit of reducing skin friction drag by avoiding scrubbing drag since the fuselage is not flowing through the propeller wake [1, pp. 316-317 and 407]. A pusher also allows a steeper longitudinal contour angles and thus a shorter fuselage and wetted area since the pusher minimizes the airflow separation on the back of the fuselage by pulling in the air [1, pp.216-218].
A conventional aft-tail geometry was rejected in favor of a control canard. This keeps the horizontal stabilizers further ahead than an aft-tail would to minimize airflow disturbance from the stabilizers at the propeller. Other boom mounted tail configurations that put the stabilizers behind or to either side of the propeller were rejected because of their added surface area, weight, and complexity. However, the vertical stabilizer and rudder were inverted and placed in the rear. This allows the advantage of the inherent stability of a rear mounted rudder and also allowed the stabilizer to act as the rear landing strut. For simplicity and reliability a fixed landing gear is used at the front.
As a trade-off between aerodynamics and useful volume, an oval fuselage was chosen. A large fuselage upsweep was incorporated in order to lift the aft of the UAV up to be able to use a larger 1 meter pusher propeller for reduced disc loading and increased efficiency [1, pp. 476-477]. In order to prevent the wing from flowing through the downwash of the stabilizer, the stabilizer and main wing are low and high wing mounted respectively. The main wing is chosen as the high wing in order to reduce the likelihood of the wing striking the ground as it lands if the UAV does not land perfectly level because of a sudden gust or other cause. The high main wing is also naturally stable since the COG (center of gravity) is below the main lifting force of the wing.
A straight elliptical wing with no sweep or dihedral was chosen with a higher wing loading of 30kg/m2 for minimum lift induced drag and increased efficiency [1, pp.79-83 and 124-125]. The reduced inherent stability can be counteracted with modern computer controlled flight. The wings are 2 meters long each which was the maximum length of any part when broken down for transport. This helps keep the design simple by eliminating an extra connection in the wings.
The lifting propellers are attached to the wings in order to reduce the number appendages sticking out of the fuselage. Since the horizontal stabilizer is low mounted, the propeller must go on the upper side of the wing to keep it away from hitting ground or tall grass when landing in non-deal areas. However, for the main wing the propeller can be mounted on the underside which is preferred since the upper side of the wing produces 2/3 of the lift so it is best left undisturbed [1, pp.57-58].
The construction is graphite-reinforced polymer for its high strength to weight ratio. Its density was assumed to be 1.63g/cm3 with an average thickness of 0.5mm for the fuselage and wings for purposes of estimating the UAV’s mass. A ladder frame in the fuselage transfers the structural loading across the modular joint of the UAV through interlocking tubes. Other tubes transfer the wing loading to the main ladder frame that all the mandatory internal equipment as well as the parachute recovery system is attached to with room to spare for any future equipment changes. All the parts break down to 2 meters or less for transport and storage.
The payload area is located at the COG in front of the main wing so it does not vary much with differing load masses. The COG can be fine-tuned by adjusting the position of the internal equipment such as the flight control computer. The payload is accessible from and upper and lower hatches and held down with bungee straps. The lower hatch is ideal for surveillance equipment, air dropping packages, and accessibility for automatic loading and battery changing landing pads. The upper hatch is useful for when humans are loading or changing batteries or when maintenance is required. The battery area is just aft of the payload compartment with easy access through the same aforementioned hatches. The compartment is designed with plenty of room for standard lithium polymer batteries such as Kokam 3200SHD or any similar battery. This way the turnaround time can less than a minute since all that needs to be done is to open the hatch, unplug the spent battery, plug in the new battery, and replace the hatch.
Using the frame sheet calculations, 432 W were required for cruise which is provided by a standard 900 W Neu 1907 motor. 7124 W were required for hover which is provided by two 2100 W Neu 1917 motors on the main wing which do more of the lifting since they are closer to the COG and two 1500 W Neu 1912 motors on the horizontal stabilizers. Although the mass of the frame, fuselage, and wings were just under 5kg; the mass entered in the frame sheet was 7kg to cover for extra hardware and servos. An extra 1kg is added under the miscellaneous. This leeway gives the extra weight needed to modify the design for extremes weather situations and waterproofing. According to the frame sheet, a 4.1kg payload can be carried 100km at 25m/s (90km/h) and a 5.9kg payload 60km at 25m/s. These results exceed the project’s minimum requirements. The frame sheet for both ranges can be found here Bamberga-V5 Frame Sheet 60km.xlsx Bamberga-V5 Frame Sheet 100km.xlsx
and under the files tab. Isometric renderings, exploded views, 3-view with major dimensions, and labelled renderings can be found under images and downloaded here.
The resulting UAV is a one of many ways to design an aircraft to meet the requirements. The Bamberga-V5 uses a tail pusher canard layout with vertical lifting propellers attached to the wings and horizontal stabilizers. It has an inverted vertical stabilizer that doubles as the rear landing gear, while the front landing gear is fixed. Its construction is graphite-reinforced polymer shell, with graphite-reinforced polymer ladder frame to transfer loads across each modular part. It uses off the shelf batteries and motors for propulsion and has an estimated payload of 4.1kg for 100km, or 5.9kg for 60km at a speed of 90km/h. The resulting Bamberga-V5 does not use any overly complex and unreliable system, but sticks with well-developed and dependable existing technology which is what makes the design functionally feasible.
 Raymer, Daniel P. Aircraft design: a conceptual approach
. Reston, VA: American Institute of Aeronautics and Astronautics, 2012. Print.