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VTOL

Thomas Leitgeb, the vice team leader of Team Drone Tech, tells the story of how this project came to live:

The idea of a tri-rotor tiltable Vertical Take-Off and Landing (VTOL) in flying wing configuration started out 1 year ago.

The thought of being able to take-off in your backyard always fascinated me, but until last spring (2018) I never acted on this dream. To big was the challenge, I thought. But after researching a bit, it did not seem impossible and I decided to start small. So, I looked in my box with random drone parts, fished out 3 motors, ESCs and a few servos and started designing. The result was a small completely 3D printed VTOL.

The plane flew quite well but its design was not very efficient. The 3D printed wings and fuselage made the plane heavy and not very robust. That’s why I decided to build a new version.
Taking use of a self-programmed optimization software, the wing-shape of the new VTOL was tuned to achieve maximum range for a given motor, propeller and battery combination. The result was a wing with quite a big aspect ratio and twice the span of the first VTOL. This time a Pixhawk 2.1 was used as a flight controller. This makes it possible to let the plane fly completely autonomous. The setup of the Pixhawk for VTOLs is harder, compared to the simple KK2.1 flight controller, used in the first version. But after a few PID tuning sessions a very stable flight was achieved in multirotor and fixed wing mode.  The flight performance surprises. While the 2200mAh battery just allows for about 4 minutes of hovering, flight times of up to 30 minutes are possible in fixed wing mode.
The next step is building an even bigger VTOL. And maybe in a few iterations, a dream becomes reality.

Automatic Gliding for Unmanned Aerial Vehicles

The increased use of unmanned aerial vehicles raises the question of how their range and time of flight can be improved. Raphael Vierhauser and Luis Trojer, two team members who are excellent FPV racers and knowledgeable about drone building, face up to this topic in their bachelor’s thesis. One possibility is the use of thermals. To create the necessary simulation environment for the development of centering algorithms, the air movements found in the atmosphere were incorporated. Statistical values were used to implement an almost realistic simulation in MATLAB®.

In order to simulate the flight of an unmanned aerial vehicle a simulation of the aircraft was developed using flight mechanics. The developed autopilot for unpowered airplanes controls the unmanned aerial vehicle. This compensates for disturbances and converts the control commands received from the centering algorithms derived in this work into commands to the actuators of the rudders. The centering algorithms must decide whether the vehicle is in a thermal and whether the thermals are strong and wide enough to gain altitude. If a thermal is detected, the program directs the aircraft in circular orbits around the thermal center. The flightpath must be constantly corrected, as the thermal bubbles move relative to the air. With various centering strategies, height gains of several hundred meters can usually be achieved in the simulations.

 

In order to test the algorithm, a test platform is needed: In this case, a model sailplane is being used. To calibrate the autopilot, the aerodynamic and geometric characteristics of the plane have to be determined. This was achieved by simulating the aircraft in XFLR5, a program for analyzing profiles, wings and entire airplanes. The flight controller that is being used is a Teensy 3.2 microcontroller board that runs on Arduino C and can be programmed via the Arduino IDE; it runs the program containing autopilot and centering algorithm, as well as reading data from the sensors and sending PWM (Pulse Width Modulation) signals to the actuators. The sensors used are two pressure sensors to calculate airspeed and angle of attack, a combined accelerometer and gyroscope to determine the attitude of the aircraft and a GPS receiver to get the aircraft´s position.

The testing phase is planned to be during spring. We will keep you up to date and hope to be able to report successful first flights.

Demonstration of a Reverse Engineering Process for a Historic Aircraft Model Based on 2D-Drawings

Michael Lampesberger, a team member, was analysing the design process of an aircraft in his bachelor’s thesis. He performed his task by creating a historical flight model through reverse engineering. The foundation is the 1932 published blueprint of the so called ‘Hochdecker-Rumpfmodell’. To optimize the flight performance of the ‘Hochdecker’ (high winged aircraft), the model will be designed according to essential adaptive aircraft features.
Nowadays the CAD-Software CATIA V5®, developed by Dassault Systems, is usually used in aviation. To design and digitize, the 87 years old blueprint must be prepared due to its poor condition. To be able to do so, several steps and software tools are necessary. Due to the inaccuracies of the blueprint, appropriate actions must be taken.
The entire ‘Hochdecker-Rumpfmodell’ had been drawn with CATIA V5®. This was realized using the Generative Shape Design and the Part Design development environments. Additionally, the material to all parts created were properly allocated in order to analyse the aircraft mass.
With the described procedures, a complex CAD model was created, which can be adapted quickly to the required geometrical conditions by using Adaptive Design.
Furthermore, the Airplane performance was analysed with xflr5.

Concept and Design of a Modular CNS / ATM Receiver System

A high-frequency receiver must be designed very careful and well-considered to get useful signals. Jakob Bauer designed a receiver chain that is additionally modular constructed to be used as an illustrative material in lectures as well as a generally usable flexible receiver. The design process starts with the selection of the most useful receiver structure. For this the elements for a certain application, in this case the reception of GPS-frequency at 1.5 GHz and the reception of the hydrogen line at about 1.4 GHz must be chosen. This concerns a radio frequency bandpass filter, a low-noise amplifier, mixer with a local oscillator and an intermediate frequency receiver in the use receiver chain.

 

The chosen circuit must be controlled for his efficiency and the signal quality. At first the needed microstrip width of the circuit board must be calculated. Following this a link-budget calculation takes place which adds up all gains and losses of the single elements. Additionally, the noise of the elements is considered. With those two values the signal to noise ratio can be calculated, which gives a good overview of the whole circuit and the output signal.

The second test is about the so-called S-parameters, which are very important at high frequencies. For that a simulations program is used, in which a schematic circuit with all important values around the operating point gets calculated. The output of this analysis takes place via a smith-chart.

After a successful analysis the circuit is constructed in EAGLE and gets manufactured. At the end it gets assembled and tested for its functionality.

Concept Development for a Heavy-Duty Drone

The need for drones is growing steadily. Therefore, new and more efficient concepts are needed especially for increasing payloads and as a replacement for helicopters. Benjamin Haller, a team member, wrote his bachelor’s thesis about such heavy-duty drones.

A scientifically proven drone design requires a close look at the individual components and the interaction in the overall system. It starts with an analysis of weight and geometry and goes into bigger detail in calculations of propulsion and structural analysis. In the overall design, the determination of an optimal propulsion system with modern power supply, efficient propellers and sufficient flight performance is a big point. In this bachelor’s thesis, the actuator disc model is used primarily. Furthermore, a special system is designed for the automatic pickup and dropdown of payloads. The construction together with structure calculations are done with a modern CAD program.

The design and structure calculations with FEM methods visualize the appearance and strength of the drone. The final result is a parts list with the most important components, the costs and the suitable suppliers to produce the heavy-lift drone.

The conventional hover-drones are relatively inefficient but accomplish their purpose without big problems. The result is a good solution for a heavy-lift drone for lifting or carrying payloads over short distances.

Mechanical Conception and Construction of a Dualcopter

Klaus Graf, a team member who is currently doing his master’s degree in aviation, worked on a very interesting project in his first bachelor thesis. A dualcopter in general is an exotic type of multicopter. The realization can pursue in different ways. This project focuses on the concept of the tilt-rotor approach and contains the design, preliminary calculation methods and the manufacturing of two prototypes.

The first and smaller prototype was made to get an inside view of the in-flight-behaviour and to test early control unit designs. To fulfil the requirement of easy replacement, RotorBits® and some 3D printed parts were used. A detailed CAD model in CATIA® also provides the moment of inertia for further control unit designs and simulation purposes.

Expertise and weak points of the first prototype were analysed and taken into consideration for the development of the final prototype. The tilt mechanism was designed to be as rigid as possible, fast and precise to handle the 15” propeller and its deviation moments. Frame plates were milled out of CFRP and aluminium components were manufactured on a lathe to withstand the enormous forces.