Recent interest in high-angle-of-attack flight, aerobatic maneuvering, vertical/short takeoff and landing, etc., of small unmanned aerial vehicles necessitates more detailed modeling of the complex aerodynamics associated with these flight regimes. This includes modeling the effect of the propeller slipstream, also called prop wash, which is the main source of airflow that helps maintain lift and control during near-zero forward-speed flight like that encountered during vertical/short takeoff and landing, as well as during high-angle-of-attack flight/aerobatic maneuvering like hovering. Propeller slipstream models based on conventional theories, such as the momentum theory, have been used extensively in the literature to predict the induced air velocity within the slipstream. However, because these conventional theories consider only acceleration of air within the slipstream and not diffusion, their applicability in regions far downstream of the propeller where diffusion is dominant, is questionable. This...

Development and Validation of a Propeller Slipstream Model for Unmanned Aerial Vehicles

A potential-flow model for conceptual design and vertical tail sizing purposes, currently under development, has been applied and tested in an investigation of the influence of the propeller slipstream on the empennage flowfield. Additionally, the model is intended to increase the understanding of the phenomena arising in propeller-empennage interaction. For verification purposes and complementation to limited wind-tunnel results in open literature, dedicated measurements were performed and supplemented by a Reynolds-averaged Navier-Stokes analysis. From wind-tunnel measurements, in one-engine-inoperative condition, it is found that the empennage experiences a propeller-induced crossflowfield, which is found to be the main contributor to the additional yawing moment experienced by the measured multiengine propeller aircraft. The most probable cause for deviation in yawing moments in measurements and the potential-flow model is incorrect modeling of the flowfield behind the wing. This was verified by a comparison of the measured and computed flowfield behind the wing and in front of the vertical tail. Efforts to create a potential model to aid in conceptual vertical tail sizing should, therefore, focus on achieving realistic wing-wake behavior. In this respect, the effect of the propeller on the wing-lift distribution, as well as the wing-wake aircraft interaction, should be treated with care.

Propeller Empennage Interaction Effects on Vertical Tail Design of Multiengine Aircraft

Numerical Simulation of Propeller Slipstream Effect on A Propeller-driven Unmanned Aerial Vehicle

: An investigation into the effects of the propeller slipstream on a flexible wing micro-air-vehicle (MAV) was conducted. The Air Force Research Lab, Munitions Directorate designed a man-portable MAV with a 24 in. wingspan and 6 in. root chord to be used for battle damage assessment and reconnaissance. Two wings have been developed for this MAV. One is a rigid carbon-fiber wing and the other consists of flexible parachute material attached to a carbon-fiber skeleton. Experimental methods were implemented to investigate propeller and wing interactions, characterizing torque and thrust requirements on the motor along with aerodynamic forces on the aircraft as the wing was placed in various locations. Initially, the motor and propeller were mounted on an air bearing table and connected to a torque and load cell. A fuselage prototype was developed and built to mount the wing at multiple heights and distances from the propeller while keeping the same angle of attack. The airframe was attached to a six degree-of-freedom balance. A tri-axial hot-wire anemometer was used to capture velocity profiles in the wind tunnel to characterize propeller wake interactions. Momentum theory provided a method to extract drag and thrust from the velocity profiles. Propeller wake results indicate 12-18% of propeller thrust translates into aircraft drag while 25-45% of motor torque is countered by aircraft roll moment. Values depend on wing location. Results indicate that changing wing location is a viable option for improving pitch and yaw stability, without increasing power requirements.

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Experimental Analysis of Propeller Interactions With a Flexible Wing Micro-Air-Vehicle

Anthropogenic environmental impact is growing despite large technical efforts to reduce it. Its dependency on technology induced human behaviour makes designing for environmental impact reduction particularly difficult. Despite the fact that the sustainable conundrum is characterized as a “no technical solution problem”, a framework is proposed in support of environmental impact reducing technology design. The goal is to provide a means to allow a priori evaluations of product design in a true stakeholder setting. The basis of the framework is formed by Quality Function Deployment (QFD), Value Engineering (VE) and Multidisciplinary Design Optimization (MDO), which allow for addressing the complexities at system and system-of-systems level by dedicated and tailored tools. This set of tools consists of Agent Based Modelling and Simulation (ABMS), Bi-Level Integrated Systems Synthesis (BLISS) and Bayesian Statistics. The design for sustainability support provided by each of these tools is illustrated by a different realistic show case. Since aviation possesses all complexities of the sustainable conundrum, it is used as a challenging example to illustrate the proposed tools. The show cases used, MagLev launch system, Prandtl Plane, Blended Wing Body, Propeller aircraft and Coand? plane, are a subset of the diverse range of solutions proposed to reduce environmental impact. This framework is a first step on the long way required to arrive at a truly sustainable product design process.

/pdf/complexity-aspects-in-design-for-sustainability-5et2ks7zck.pdf

Complexity Aspects in Design for Sustainability

The panel method was used for the numerical calculations in this study. The propeller vortex system rotating with its blades, and the steady horseshoe vortex system distributed on the aircraft surface were used as the mathematical model. Neumann boundary conditions were satis ed at the panel control points of the blade and the aircraft panel to achieve coupling of propeller slipstream with the whole  ow eld of the aircraft. At each corresponding azimuth angle of the propeller, pressure coef cients and induced velocities by the two vortex systems at the panel control points were calculated; from this, the average aerodynamic characteristics of the aircraft in one revolution period were obtained. The contraction effect of the three-dimensional propeller slipstream and its in uence on the  ow eld were considered in the computation. Results of numerical examples showed that the slipstream had a signi cant effect on aircraft lift characteristics such as  ap de ecting, resulting in relatively large changes of the aircraft moment performance. Numerical results were in good agreement with the experimental data. The method presented here is suitable for both singleand multiple-propeller aircraft.

Guowei Yang

Papers

Numerical Analysis of the Interference Effect of Propeller Slipstream on Aircraft Flowfield