Abstract
The article aims to prove the effectiveness of the proposed unmanned air vehicle design (The Propulsive Wing) through numerical and experimental means. The propulsive wing unmanned air vehicle is a completely new class of unmanned air vehicle, making disruptive changes in the aircraft industry. It is based on a distributed cross-flow electric fan propulsion system. When the fan starts to operate, the flow is drawn from the suction surface, provided by energy through the fan and expelled out of the airfoil trailing edge (TE). This causes a significant lift increase and drag reduction with respect to ordinary aircrafts, making it perfect for applications requiring low cruise speed such as firefighting, agriculture, and aerial photography. In this early stage of the investigation, our main aim is to prove that this design is applicable and the expected aerodynamic and propulsion improvements are achievable. This is done through a two-dimensional computational fluid dynamics investigation of the flow around an airfoil with an embedded cross-flow fan near its TE. A scaled wind tunnel model of the same geometry used in the computational fluid dynamics investigation was manufactured and used to perform wind tunnel testing. The computational fluid dynamics and wind tunnel results are compared for validation. Furthermore, an unmanned air vehicle model was designed and manufactured to prove that the propulsive wing concept is flyable. The article shows that the aerodynamic forces developed on the cross-flow fan airfoil are not only functions of Reynolds number and angle of attack as for standard airfoils but also function of the fan rotational speed. The results show the great effect of the rotational speed of fan on lift augmentation and thrust generation through the high momentum flow getting out of the fan nozzle. Wind tunnel tests show that the suction effect of the fan provides stall free operation up to very high angles of attack (40 degrees) leading to unprecedented values of lift coefficient up to 5.8. The flight test conducted showed the great potential of the new aircraft to perform the expected low cruise speed and high angles of attack flight.
Highlights
Introduction and literature reviewThe propulsive wing concept has many advantages at both cruising and high angles of attack
The study succeeded to apply and prove the benefits of embedding a cross-flow fan (CFF) in a thick airfoil section in order to be used for thrust generation, lift augmentation, and circulation control
The computational fluid dynamics (CFD) simulations and wind tunnel tests showed that the propulsive wing can fly up to an angle of attack of 408 with no signs of separation and with very high lift coefficients which was not possible using conventional airfoil sections
Summary
The propulsive wing concept has many advantages at both cruising and high angles of attack. In case of 2000 r/min, the lift coefficient at a = 30° is less than that at a = 20° since the rotational speed of the fan is less than the reattachment value There is a noticeable lift augmentation at cruising angles of attack (5°, 10°) as the fan starts to operate at 2000 r/min which is the minimum rotational speed used. The intersection of a constant rotational speed curve with the x-axis indicates the angle of attack at which the Cdnet = 0 and this means that the generated thrust is equal to the drag. It is noticed that the maximum velocity ratio decreases by 16% as the angle of attack increases from 5° to 30° at 4000 r/min
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