Manned-Unmanned Teaming creates opportunities to increase mission performance of close formation flight for military and civil uses. Currently, the close flight of two helicopters, one manned aircraft and one unmanned aircraft system (UAS), within a shared airspace organized as a mixed formation creates high pilot workload due to maintaining the formation and avoiding collisions at the same time. The work presented in this paper approaches this high workload and safety problem and introduces two different strategies implemented as controllers to automate the UAS for the formation flight. In addition to flight results, this paper presents the design and implementation of the formation strategies and highlights the process within a simulation framework of their development, tuning, and testing. The simulation framework also facilitated finding of suitable safety constraints for the formation controllers and the flight test. One developed strategy, the so called Corridor Mode, reduces crew workload, increases flight safety, and enabled the coupling of a manned and an unmanned helicopter in a close formation during a real flight test campaign.

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 $$\text { m/s}^{2}$$ m/s 2 and gusts with peak speeds of 1.5 to 2.0 m/s, depending on the direction.

Determining the flight envelope is a crucial step in the development process for Unmanned Aerial Vehicle (UAV). Research in the recent years focused on extending the useable flight envelope safely. As the number of available unmanned helicopters increases, maintaining low development costs is a key aspect to enable many civil business cases. Therefore, this paper presents a method to detect flight envelope limits tailored to commercially available unmanned helicopters. The proposed method consists of the following two steps: First, a set of dominating limiting effects of the flight envelope is identified and the concrete thresholds are determined. For the helicopter example used in this paper, these effects are engine power, actuator authority, rotor hub moments, load factor limitations, and the vortex ring state. Second, we propose to use indicators to measure the margin to these limits for each flight condition. A comprehensive rotorcraft model is used to calculate the indicators for the flight conditions. This model determines steady state responses or trim points. Thus, the margin for each trim point to the limit of the flight envelope can be estimated. In this paper, we apply this method to a helicopter in intermeshing rotor configuration and present a verification of the method. Furthermore, we compare the flight envelope of the proposed method to the known of this specific rotorcraft to assess the potential in respect of flight envelope expansion.

Manned-unmanned teaming is a key aspect for improving the efficiency of civil and military operations. This paper provides an overview of a four-year project to develop and evaluate methods for manned-unmanned teaming formation flight. The formation flight scenarios are tailored towards manned and unmanned rotorcraft performing a close formation flight. This paper explains use cases as well as the test methodology. Two formation flight algorithms were developed and evaluated against a preprogrammed waypoint-based baseline. The evaluation was done in a simulator campaign with different pilots and in a flight test campaign with one evaluation pilot. During the final flight test campaign the first coupled close formation flight between a manned and an unmanned helicopter was achieved. Finally, this paper contains the results of both the flight test and simulator campaign.