General inspiration for design
A lot of the inspiration for materials came from the RC industry, and the overall design idea comes from helicopter design, especially the VTOL fan unit and how it is connected to the fuselage to a single connection point above CG point, it resembles a helicopter rotor.
That design gives the drone a very good stability and structural strength. It also makes it possible to easily disassemble it from the fuselage, transforming the drone to a taildragger airplane for conventional take-off and landing. This makes it possible to transport heavier cargo than the usual VTOL configuration allows.
The cargo unit is easily interchangeable with a censor unit. The cargo unit is a fiberglass shell with Styrofoam core which contains the cargo.
The interchangeable units are connected to the fuselage with 4 of the shelf latches, easy to detach but reliable locking method. It is widely used in all industries for its good locking capabilities, and there is no reason to develop something new and complex and/or unproved at this point. Later in the future when there is need for automatic loading and unloading, it is possible to switch the laches to something else. The locking mechanism is external; which simplifies the switch to other locking system relatively easy.
Materials used in the project are mainly fiberglass, carbon fiber, plywood and Styrofoam. These are the materials also widely used in the RC industry, which makes it easy to get and affordable to build and repair.
In conclusion, all aspects of the design are made with proven and widely used materials and parts, to keep cost down and reliability high and also allow easy maintenance of the drone.
Explanation of design details
Landing gear concept is kept simple and light and easily replaceable, to enable to modify the drone specifically for the mission. Important aspect of the design of the landing gear was not to have any moving parts that could easily malfunction in a freezing weather.
When the drone is used as VTOL aircraft, then it’s best to remove the wheels that create a lot of drag, and add a significant amount of weight to the plane. When used for conventional take-off and landing, then the wheels are easily connected to the landing gear. Here the weight and drag of the wheels are not causing too much problems, because the fan unit has been removed, saving a lot of weight and reducing drag significantly.
This landing gear concept also allows mounting different mission specific wheels. Big and fat for take-off in off runway conditions, like dirt road, or assemble small thin wheels for paved runways.
All the materials used in the design are or are prepared to be waterproof. Plywood parts are cowered with a thin layer of epoxy, the same epoxy used to manufacture the fiberglass fuselage.
Cargo is protected inside a Styrofoam box with a lid taped around edges to prevent water entering the container in case of water landing.
Electronics have moderate protection against rain from the closed fuselage, but it can be better protected if the electronics are shielded, for example inside a plastic container.
There is also an option to use protective sealant chemicals that are sprayed in servos and speed controllers. Here is an introduction video of this type of chemicals used:
This drone is easily disassembled into small components for easy transport. The wings, tail boom and tail are attached with latches, to allow assembly without the help of tools.
The fan unit can be disassembled from the fuselage and the individual arms can also be disassembled from the central hub of the unit. Here it is possible to use variety of locking screws to connect the parts.
Ease of handling
Handling the drone is no harder than an average RC airplane. There is no need for any external systems or a crew to maintain and operate the drone. One person should be capable of assembling, installing the cargo bay and operating the drone.
The drone has a max takeoff weight (with 5kg cargo) just under 25kg. The majority of weight is the Lipo batteries, which weigh almost 10kg. Even if there might be a lighter and with higher Wh/kg power pack available, it would not be of the shelf. Lipo is widely used around the world. These batteries are very rapidly developed with higher capacity’s coming out every year, hereby enhancing the performance of the craft every year.
Fail Safe components
This drone has 8 lifting propellers 2 in its corner, which gives it a reasonable control of the drone even if one motor would malfunction.
In this drone there are both, flight termination parachute and a parachute for safe return to the ground. In case of total loss of control and power of the drone, these parachutes are deployed.
When working around the drone you are also near the propellers, which are a potential safety hazard. This drone has protective rings just above the propellers, that works as a visual barrier for the operator to stay clear from the propeller blades.
As an extra safety measure it could be a good idea to install a safety switch outside the fuselage, that disables the fan unit while operator is working around the drone.
Configurability concept to change from cargo to sensor payload
This is the most mission specific drone possible, and changing from cargo payload to sensor payload is no different than changing from one cargo payload to other. Unlock the latches, remove the cargo unit, insert the sensor unit and lock it on place. It makes no difference for the drone if it’s hauling cargo or flying around with sensor bay.
This drone is affordable to build and all parts are available from RC shops around the world. It’s easily configured to meet the mission objectives, and can be repaired with basic knowledge about RC airplanes.