# Integration and Flight Test of a 7 kW Turboelectric Vertical Take-Off and Landing Unmanned Aircraft
###### Abstract  
This paper evaluates the performance and practical challenges associated with fabricating and flight testing an unmanned aircraft powered by a turboelectric system based on a 7 kW turbine engine. Emerging hybrid gas-electric aircraft concepts have been the subject of numerous design studies and analytical evaluations; however, there is a critical need to identify and assess practical issues associated with integrating a hybrid turboelectric power system into an aircraft. The purpose of this study, relevant to emerging hybrid-powered aircraft, is to evaluate and retrofit a prototype turboelectric power system to an existing 391 N gross take-off weight unmanned airframe. The representative 7 kW turboelectric system was installed to identify challenges and to formulate data-driven recommendations for general application to urban air mobility. This work addresses performance, power and thermal management, vibration, and acoustic emissions. Results include a weight breakdown with the turboelectric system making up 21% of the total aircraft weight, in-flight voltage and current measurements with maximum loads observed during a dive pull-out, temperature measurements, accelerometer measurements, and far field sound pressure level measurements. Practical recommendations from this study are applicable to power system reliability, electronic component selection, cooling requirements, and peak power behavior, informing the design of future hybrid gas-electric aircraft. simulate different airspeeds. There have been many conceptual and analytical studies done to evaluate designs and predict performance for turboelectric transport aircraft, but there is a critical need for a sub-scale, unmanned demonstrator aircraft to safely identify and evaluate practical integration challenges, which is the aim of this current study. Subsequent studies to evaluate and improve the aircraft-system-level performance are enabled by incorporating recommendations from this current effort. Whereas most of the turboelectric research has been focused on large commercial fixed-wing transport aircraft, there also has been research published on smaller-scale systems. Urban Air Mobility (UAM) is a quickly emerging field of small-scale aircraft that aims to allow for convenient short length flights around cities. The key advantages of these \"air taxis\" include facilitating rapid transportation within cities to avoid ground transportation traffic delays. Current battery technology is one of the most significant obstacles facing UAM systems. Though batteries offer sufficient power output for UAM vehicles, they lack the necessary energy density and recharge rates to sustain a viable vehicle for most missions. As of 2018, state-of-the-art battery energy density is around 170 Wh/kg after lithium-ion batteries are put into packs [6]. Energy density is a complicated figure of merit because it depends on how batteries are implemented in a particular aircraft application, accounting for all associated electrical components. There is typically a 30-40% reduction in Wh/kg once the installation of the batteries has been accounted for [6]. Recent estimates for the minimum required energy density of batteries for UAM systems is around 300 Wh/kg to 400 Wh/kg after installation [6; 7]. Notably, work has also been done on structural batteries to decrease installation losses by using the battery as a load-bearing component of the airframe [8]. As of this publication, the state of battery technology has not significantly increased from 170 Wh/kg, but there are several emerging technologies that aim to improve or replace lithium-ion batteries to extend aircraft range and endurance [8]. However, the requirement for a power source with higher energy density has prompted the development of hybrid systems to leverage the high energy density of hydrocarbon fuels for UAM systems. Another major advantage of utilizing traditional fuels is the ability to execute rapid refueling, allowing for more operating time to transport people or cargo.