Voting Result: 3.1927467194
Overview for Minerva
I give you: Minerva
Named after the ancient Roman goddess of medicine and wisdom this UAV shall bring supplies to those in need.
Even though not directly visible, this is a spanloader concept!
The twin boom layout is often used for UAVs, but it is applied in new context here: Because heavy parts as the lifting motors and the batteries are placed inside the boom structure a spanloading effect is achieved. This gives a lower wing root bending moment and consequently a lighter wing structure.
For a maximum lift-to-drag ratio (L/D) much effort was spend on reducing the wetted area, and obtaining a high wetted aspect ratio.
The fuselage is kept as small as possible. It is sized by the cargo compartment and the avionics and flight termination equipment. A transparent bulge is added for the camera system. The boundary layer is ingested/energized by the pusher cruise propeller. This will decreases the fuselage drag and improve flight performance.
The high aspect ratio wings are smoothly blended into the fuselage for minimal interference. This is more visible on the concept art – I was unable to replicate the idea properly in OpenVSP. Right now it looks a little bit jagged. The wings incorporate the inverse gull-wing shape to keep the landing gear as short as possible. I “stole” that idea for Chance-Vought’s F4U Corsair. This will help to keep the impact of the landing gear on weight minimal. The packaging requirements are satisfied by splitting the wings at the boom-attachments.
For airfoils NACA 6-series sections are used to lower the friction drag by keeping the boundary layer laminar as long as possible. Therefore aggressive 66 sections are used inboard. To get an acceptable stall behavior the more docile 64 and 63 sections are used outboard with aerodynamic and geometric twist. Efficiency is further optimized by winglets.
The lifting rotors (low disk loading for minimal power) on the booms arrest their propellers in flight direction during cruise flight and thus minimize the drag impact.
For the landing gear the quad layout is selected. With a very simple (and therefore light) retraction mechanism and short legs the aerodynamic impact is minimal. The landing gear incorporates another idea I “stole”, this time from Douglas: The DC-3’s gear would not completely retract, but rather still allow “belly landings on the wheels”. For Minerva the wheels tilt aft to the side of the booms and still allow emergency landings.
Safety is improved further by having redundant control surfaces. Even the elevator is split to mitigate the risk of failure.
As most of the other designs I am fighting the 25kg MTOM limit, but right now the first analysis looks very promising, both in terms of payload/range and energy requirements.
Of course I’ll keep you all updated on the ongoing design process.