Konzeptuntersuchungen für ein zukünftiges unbemanntes Lufttransportsystem

Im Rahmen dieser Masterarbeit werden zwei unbemannte Flugzeugkonfigurationen für die im DLR-Projekt ALAADy (Automated Low Altitude Air Delivery) vorgesehene Transportaufgabe ausgewählt und entworfen. Dafür werden eine Vielzahl von Konfigurationen betrachtet und qualitativ im Hinblick auf die in ALAADy formulierten Anforderungen bewertet. Die konventionelle Drachenkonfiguration, ein Entenflugzeug, ein Doppelleitwerksträger, ein Doppeldecker sowie ein Boxwing werden für genauere Untersuchungen ausgewählt. Die gewählten Konfigurationen werden im Rahmen von Flugleistungsbetrachtungen verglichen. Dabei werden diese für verschiedene Werte der Spannweite derart ausgelegt, dass die ALAADy-Anforderungen an die maximalen Start- und Landestrecken sowie die minimale Reichweite eingehalten werden. Zusätzlich wird ein Konzept untersucht, bei dem der Maximalauftrieb durch die Integration zusätzlicher elektrischer Triebwerke vergrößert wird. Im Anschluss werden die Geometrien der Konfigurationen im Hinblick auf statische Stabilität und Steuerbarkeit modifiziert sowie die resultierenden Änderungen der Flugleistungen ermittelt. Darüber hinaus werden Untersuchungen zur dynamischen Stabilität in der Reiseflugkonfiguration angestellt. Abschließend werden ein Regler für die Längsbewegung implementiert sowie Reiseflug und Startvorgang simuliert

Evaluation of the controllability of a remotely piloted high-altitude platform in atmospheric disturbances based on pilot-in-the-loop simulations

In the context of the project HAP, the German Aerospace Center (DLR) is currently developing a solar-powered high-altitude platform that is supposed to be stationed in the stratosphere for 30 days. The development process includes the design of the aircraft, its manufacturing and a flight test campaign. Furthermore, a high-altitude demonstration flight is planned. While the high-altitude flight will be performed using a flight control and management system, during take-off and landing and at the beginning of the low-altitude flight test campaign, the aircraft will be remotely piloted. The aircraft has a wing span of 27 m and operates at extremely low airspeeds, being in the magnitude of around 10 m/s equivalent airspeed, and is therefore profoundly susceptible to atmospheric disturbances. This is particularly critical at low altitudes, where the airspeed is lowest. Hence, both time and location for take-off, landing or low-altitude flight test campaigns need to be selected thoroughly to reduce the risk of a loss of aircraft. In this regard, the knowledge about the operational limits of the aircraft with respect to atmospheric conditions is crucial. The less these limits are known, the more conservative the decision about whether to perform a flight on a certain day or not tends to be. On the contrary, if these limits have been adequately investigated, the amount of days and locations that are assessed as suitable for performing a flight might increase. This paper deals with a pilot-in-the-loop simulation campaign that is conducted to assess the controllability of the high-altitude platform in atmospheric disturbances. Within this campaign, the pilots are requested to perform practical tasks like maintaining track or altitude, flying a teardrop turn or performing a landing while the aircraft is subject to different atmospheric disturbances including constant wind, wind shear, continuous turbulence, and discrete gusts of different magnitudes. This paper describes the desktop simulator used for the campaign, outlines the entity of investigated test points and presents the assessment method used to evaluate the criticality of the respective disturbances. Finally, a set of restrictions on the acceptable wind conditions for the high-altitude platform are found. The underlying limits comprise a constant wind speed of 3.0 m/s in any direction, except during landing, maximum wind shear of 0.5 m/s^2 and gusts with peak speeds of 1.5 to 2.0 m/s, depending on the direction

Evaluation of Landing Procedures for a High-Altitude Platform with Skid-Type Landing Gear Based on Pilot-in-the-Loop Simulations

In the context of the project HAP, the German Aerospace Center (DLR) is currently developing a solar-powered high-altitude platform. The underlying vehicle is a fixed-wing aircraft that is supposed to be stationed in the stratosphere for 30 days. Due to, among others, low achievable rates of descent, the use of skids as landing gear and its high susceptibility to wind, landing this aircraft is a very challenging task. Hence, it requires a landing procedure, which is specifically tailored to the aircraft's particularities. In addition, this procedure needs to be relatively easy to follow by pilots especially in adverse atmospheric conditions. This paper deals with a pilot-in-the-loop simulation campaign that is conducted in order to assess a landing procedure which has been developed for the high-altitude platform in earlier works. Within this campaign, the pilots are supposed to land the aircraft following this specifically developed procedure in atmospheric turbulence conditions. In addition, they also land the aircraft following a reference procedure, which is based on a conventional landing. In doing so, the altitude at which a flare is performed and/or the propellers are shut down is varied. Finally, the novel procedure's overall feasibility from a piloting point of view and its potential to reduce the risks during landing are assessed. The results show that the developed procedure proves to reduce the risk of inadvertent ground contact of the aircraft payload compartment, which is associated with serious damage to aircraft structure and payload. However, since the novel procedure is challenging for the pilots, some improvements to the procedure are proposed to make it easier to follow

Numerical Parameter Study of a Strake on a Turboprop Engine in Active High-Lift Configuration

The engine integration into the wing of an aircraft often has a significant impact on lift generation in high-lift configuration. Within this project, the SFB 880 aircraft, equipped with a droop nose and an active Coanda flap is analysed in the landing configuration. The integration of large turboprop engines leads to strong nacelle vortices that cause a wake burst above the flap inboard of the engine and therefore reduces C_{L,max} recognisably. Therefore, a nacelle strake parameter study is performed, based on an initial strake. The strake optimisation allows for a lift recovery of C_{L,max} by around 17 LC and an increase of Alpha_{max} by 2° compared to the configuration without strake. Since nacelle strakes have not been extensively investigated for aircraft with turboprop engines and an active high-lift system, particular attention is paid to the effects of the parameter variations and to the nature of the improvements. It turns out that the lift recovery arises from an effective weakening of the nacelle vortex. This is particularly achieved thanks to a smaller distance between the nacelle and the strake vortex compared to the case with the initial strake. Thereby, the strake vortex shows a very good interaction with the nacelle vortex while its impact on the flow close to the surface is kept low. Hence, a final enlargement of the strake area also allows for an increase of lift. In addition, further potential for an augmentation of C_{L,max} by the utilisation of a supplementary outboard strake is revealed. Finally, the impact of the strake integration on drag in cruise configuration is analysed. Hereby, a drag increase at the beginning of cruise of 0.222% is determined

Performance-Based Preliminary Design and Selection of Aircraft Configurations for Unmanned Cargo Operations

This chapter deals with the selection process of three different aircraft configurations that are appropriate for automated cargo operations at low altitudes and above loosely inhabited areas. The selection process starts with a conceptual assessment of various aircraft types with respect to their suitability as an unmanned cargo aircraft (UCA) and subject to a set of specific top level aircraft requirements (TLAR's). Based on the TLAR's and further characteristics like fuel efficiency, cargo space accessibility, technical simplicity or size, five fixed-wing aircraft and two rotorcraft are chosen for further investigations. A subsequent preliminary design study dimensions the fixed-wing aircraft for different wing spans based on flight performance requirements according to the TLAR's. A possible mean to enhance take-off and landing performances is the integration of additional small propellers and to make use of the propeller slipstream effect. Therefore, this chapter furthermore investigates the benefits from the integration of additional electrically driven propellers. The second part of the study focusses on the comparison of a helicopter and a gyrocopter, presenting performance key parameters and discussing their respective advantages and disadvantages. This chapter concludes with the selection of a twin boom aircraft of 16 m wing span, a box wing of 12 m span and a gyrocopter with a rotor radius of 7 m and small supplementary wings for the use as UCA

Nacelle Strake Design for Short Takeoff and Landing Configuration with Turboprop Engines

The scope of this Paper is to investigate the Integration effects of turboprop engines on a high-lift wing with an internally blown plain flap system with Reynolds-averaged Navier–Stokes computations. It is shown that the resulting nacelle vortices can significantly reduce the high-lift performance at zero thrust conditions. To limit the negative impact, an inboard nacelle strake was designed with the aim of maximizing the lift coefficient of the landing configuration at zero thrust. To reach this goal, a sensitivity study on basic geometric strake parameters was carried out. The best nacelle strake is able to improve the maximum lift coefficient by ΔCL,max � 0.17 and the maximum angle of attack by 3 deg. The study also reveals the further potential of improvement due to an additional outboard strake. First simulations with outboard strake lead to a further improvement of ΔCL; max � 0.13 and 4 deg in the maximum angle of attack. It is also shown that the installation of an inboard strake does not negatively impact the high-lift performance at a moderate thrust level

Landing Simulation of a High-Altitude Platform with Skid-Type Landing Gear - Flight Procedure, Controller, and Loads

The German Aerospace Center (DLR) is currently developing a solar-powered high-altitude platform. The underlying vehicle is a fixed-wing aircraft designated to be stationed in the stratosphere for several days and to carry payload used to perform Earth observation missions. The project HAP addresses the complete design process of the aircraft, from conceptual studies and detailed design up to its construction, flight test campaigns and its final operational clearance. The aircraft operates at very low airspeeds, in the order of 10 m/s equivalent airspeed, and is therefore very susceptible to atmospheric disturbances, particularly in ground proximity. In addition, due to the absence of air brakes and due to the the very high glide ratio, the aircraft only reaches low sink rates, which additionally prolongates the landing duration. Altogether, the landing is a highly critical flight phase that needs thorough consideration. This paper addresses three issues associated with the landing: first, it presents a landing procedure that has a potential of reducing the risk of the landing, second, it describes the positioning process of skids that are used as landing gear, and third, it includes the resulting landing loads in the aeroelastic design. A high number of landing simulations of the aircraft in atmospheric disturbances is performed using a 6 degrees-of-freedom flight dynamics model. For this purpose, a landing controller based on an outer energy management loop and an inner pitch loop is implemented. During the simulations, the best main skid position is found to be around 40 cm in front of the centre of gravity. A dynamic aeroelasticity simulation is performed to analyse the associated loads. The results show that the landing loads obtained with this landing procedure are not sizing and thus do not influence the structural weight

Evaluation of the Controllability of a High-Altitude Platform in Atmospheric Disturbances Based on Pilot-in-the-Loop Simulations

In the context of the project HAP, the German Aerospace Center (DLR) is currently developing a solar-powered high-altitude platform that is supposed to be stationed in the stratosphere for 30 days. The development process includes the design of the aircraft, its manufacturing and a flight test campaign. Furthermore, a high-altitude demonstration flight is planned. The aircraft operates at extremely low airspeeds, being in the magnitude of around 10 m/s equivalent airspeed, and is therefore profoundly susceptible to atmospheric disturbances. This is particularly critical at low altitudes, where the airspeed is lowest. Hence, both time and location for take-off, landing or low-altitude flight test campaigns need to be selected thoroughly in order to reduce the risk of a loss of aircraft. In this regard, the knowledge about the operational limits of the aircraft with respect to atmospheric conditions is crucial. The less these limits are known, the more conservative the decision about whether to perform a flight on a certain day or not tends to be. On the contrary, if these limits have been adequately investigated, the amount of days and locations that are assessed as suitable for performing a flight might increase. This paper deals with a pilot-in-the-loop simulation campaign that is conducted in order to assess the controllability of the high-altitude platform in atmospheric disturbances. Within this campaign, the pilots are requested to perform practical tasks like maintaining track or altitude, flying a teardrop turn or perform a landing while the aircraft is subject to different atmospheric disturbances including constant wind, wind shear, continuous turbulence, and discrete gusts of different magnitudes. This paper describes the desktop simulator used for the campaign, outlines the entity of investigated test points and presents the assessment method used to evaluate the criticality of the respective disturbances. Finally, a set of restrictions on the acceptable wind conditions for the high-altitude platform are found. The underlying limits comprise a constant wind speed of 3.0 m/s in any direction, except during landing, maximum wind shear of 0.5 m/s^2 and gusts with peak speeds of 1.5 m/s to 2.0 m/s, depending on the direction

DEVELOPMENT AND TESTING OF A SURROGATE UNMANNED AIRCRAFT FOR CREW TRAINING AND EVALUATION OF FLIGHT TEST PROCEDURES FOR A HIGH-ALTITUDE PLATFORM

The German Aerospace Center (DLR) is currently developing a solar-powered high-altitude platform (HAP) in the context of the DLR-internal project HAP-alpha. The project addresses the complete development process of the aircraft, from conceptual studies and detailed design up to its construction, flight test campaigns, and the final operation procedures. Generally, HAPs are in terms of flight characteristics and flight performance unconventional due to their highly flexible structure, extremely low weight, and high glide ratio. Furthermore, the flight test of such a highly fragile aircraft poses significant challenges in terms of flight test procedures, system identification maneuvers as well as the Beyond Visual Line of Sight (BVLOS) operation. Therefore, a surrogate aircraft was developed to train the crew and evaluate suitable flight test procedures. This surrogate aircraft is a highly modified commercial off-the-shelf (COTS) radio controlled (RC) sail plane. The aircraft features a flight controller to approximate the maneuverability and flight performance of the HAP and a FirstPerson View (FPV) system comparable to the HAP. The surrogate aircraft is modified to have a comparable engine arrangement to that of the HAP, and the controller is tuned such that similar angular rates, and climb performances are obtained. In this paper the design considerations, development tests and a brief overview of the crew training is given. In addition, the results of flight tests are presented. These include a general feasibility test of performing system identification maneuvers with the aircraft and a test dealing with turning flight in HAP mode