## 5 Conclusions  
This research aimed to design, build, and test a unique UAV in flight: optimized for efficient hover, but able to fly in long-range missions. We chose a tandem-wing configuration because it is the most compact variant of a VTOL drone compared to a fixed-wing one. We proved in our test flights that the drone could fly very fast (in plane mode) using the same electric power as in hover (in quadcopter mode). That feature lets it cover a longer distance than a typical multi-rotor could do. Additionally, we could optimize motors and propellers for a single purpose, unlike motor-tilting constructions. The tandem-wing configuration is also significantly smaller and lighter than a typical quadplane of the same wing area.  
Figure 30: Telemetry log from an in-flight experiment: top speed test in a horizontal flight in Elka1Q mode.  
Eventually, we designed, calculated, simulated, built, and tested the Elka1Q drone in static tests and in flight. We also identified a model of the drone dynamics to improve its attitude controller implementation and experiment with custom-made MPC controllers.  
The flights proved the wings almost do not affect the drone behaviour in hover and VTOL manoeuvres.  
Fast horizontal flights using the pusher motor and transitioning to plane mode proved the drone could cover a significant distance in a short amount of time, i.e., it can operate in long-range missions. We measured the electric power usage and concluded that the prototype drone offers a \(5\times\) more extended range than a typical VTOL-only UAV (e.g., a multirotor). The compact mechanical construction of the tandem-wing and the fuselage proved to be extremely robust--it survived some crash landings with very little damage, having a take-off weight of ca. 2900 g!  
The most significant disadvantages of the Elka1Q drone are related to its pitch stability issues. Some were caused by a misplaced CG, some plausibly by inefficient elevons, but some remain unexplained. We suggest examining the pitch controller in a wide range of conditions and possibly tuning it further.  
Future research could optimize the wings and measure all the physical limits of such a drone, such as the actual top speed and range with a selected mission scenario.  
There is a Supplementary Material available--a video summary of the research.  
The following supporting information (Video: Elka1Q UAV--a Tandem-Wing Quadplane.) can be downloaded at: [[https://www.youtube.com/watch?v=2](https://www.youtube.com/watch?v=2) cdPLeVac24]([https://www.youtube.com/watch?v=2](https://www.youtube.com/watch?v=2) cdPLeVac24), accessed on 19 May 2022.  
Conceptualization, M.O. and M.L.; methodology, M.O. and M.L.; software, M.O.; validation, M.O.; formal analysis, M.O. and M.L.; investigation, M.O.; resources, M.O.; data curation, M.O.; writing--original draft preparation, M.O.; writing--review and editing, M.O. and M.L.; visualization, M.O.; supervision, M.L.; project administration, M.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} UAV & Unmanned Aerial Vehicle \\ SAR & Search-And-Rescue \\ PID & Proportional-Integral-Derivative \\ IMU & Inertial Measurement Unit \\ MPC & Model Predictive Controller \\ GPC & Generalized Predictive Controller \\ FC & Flight Controller \\ CG & Centre of Gravity \\ AoA & Angle of Attack \\ ESC & Electronic Speed Controller \\ \end{tabular}