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General Statements
Published in Pylyp Volodin, Blade Element Rotor Theory, 2023
2.4.6 Air blowing of a blade element generates aerodynamic forces acting on this element. Aerodynamic forces of a blade element consist of the element lift force and the element profile (parasitic) drag. The element lift force is directed perpendicular to the element oncoming airflow velocity and to the blade longitudinal axis. The profile drag is directed along the element oncoming airflow velocity: this is opposite to the element velocity relative to the oncoming airflow. The element aerodynamic force components proportionally depend on dynamic pressure of the element oncoming airflow and the element planform area with proportionality coefficients: the element lift coefficient CLe for the element lift force, and the element profile drag coefficient CDe for the element profile drag. It is assumed that: an element lift coefficient depends only on attack angle of the element in its oncoming airflow and this dependence is increasing linearly with a lift coefficient slope CLeα; and an element profile drag coefficient is constant. It is assumed here that an element does not create any lift force if the element has zero attack angle.
UAS Airframe Design
Published in R. Kurt Barnhart, Douglas M. Marshall, Eric J. Shappee, Introduction to Unmanned Aircraft Systems, 2021
Michael T. Most, Michael Stroup
The aerodynamics and flight physics associated with a helicopter are very complex. A helicopter simultaneously produces both lift, to oppose the weight of the aircraft, and thrust, represented by a vector acting in the direction of flight, by accelerating a mass of air through the rotor disk. The energy imparted to the air mass is provided by the fuel or battery, converted to mechanical power by the aircraft powerplant, and transmitted through gear reduction (e.g., in a transmission) to the main shaft that supports the main rotor blades. The helicopter gear reduction (transmission) is necessary to convert the high rpm, low torque output of the motor to low rpm, for aerodynamic efficiency (generally, the transonic regime should not be entered), and high torque to move the blades through the viscous fluid of the atmosphere. In a hover, 60%–70% of this power is consumed in producing lift (referred to as induced power), while the remainder (referred to as profile drag power) is expended in overcoming parasite drag (Gessow and Myers 1985). Because low Reynolds numbers are characteristic of narrow chord/short span blades (Schafroth 1980) and the energy required to accelerate an air mass increases as the square of the acceleration, increasingly larger diameter rotors become increasingly efficient due to the ability to process greater amounts of air through the rotor disk (Gessow and Myers 1985). Another contributing factor is that increasing the length, and therefore the aspect ratio, of the rotor blades reduces the drag induced by producing lift. The trade-offs are increased parasitic drag and the reduction in rotor rpm, which will reduce dynamic pressure and tend to diminish lift, necessary to keep tip speeds subsonic.
UAS Airframe and Powerplant Design
Published in Douglas M. Marshall, R. Kurt Barnhart, Eric Shappee, Michael Most, Introduction to Unmanned Aircraft Systems, 2016
The aerodynamics and flight physics associated with a helicopter are very complex. A helicopter simultaneously produces both lift, to oppose the weight of the aircraft, and thrust, represented by a vector acting in the direction opposite that of flight, by accelerating a mass of air through the rotor disk. The energy imparted to the air mass is provided by the fuel or battery, converted to mechanical power by the aircraft powerplant, and transmitted through gear reduction (e.g., in a transmission) to the mast which supports the main rotor blades. The helicopter gear reduction (transmission) is necessary to convert the high rpm, low torque output of the motor to low rpm, to maintain a low rotor rpm for aerodynamic efficiency (generally, the transonic regime should not be entered), and high torque to move the blades through the viscous fluid of the atmosphere. In a hover, 60%–70% of this power is consumed in producing lift (referred to as induced power), while the remainder (referred to as profile drag power) is expended in overcoming parasite drag (Gessow and Myers 1985). Because low Reynolds numbers are characteristic of narrow chord/short span blades (Schafroth 1980) and the energy required to accelerate an air mass increases as the square of the acceleration, increasingly larger diameter rotors become increasingly efficient due to the ability to process greater amounts of air through rotor disk (Gessow and Myers 1985). Another contributing factor is that increasing the length, and therefore the aspect ratio, of the rotor blades reduces the drag induced by producing lift. The tradeoffs are increased parasitic drag and the reduction in rotor rpm, which will reduce dynamic pressure and tend to diminish lift, necessary to keep tip speeds subsonic.
Modeling and performance evaluation of sustainable arresting gear energy recovery system for commercial aircraft
Published in International Journal of Green Energy, 2023
Jakub Deja, Iman Dayyani, Martin Skote
where is the mass of the aircraft, is the resultant ground speed of an aircraft, is the moment of inertia and is the angular velocity of landing gear rotary components. During a landing roll, the aircraft is continuously subjected to drag which can be divided into parasitic and induced drag. Induced drag is assumed to be negligible whereas parasitic drag equation formula is given as:
Numerical investigation of aerodynamic characteristics of naca 23112 using passive flow control technique – gurney flaps
Published in Cogent Engineering, 2023
Experiments were carried out on a multielement airfoil having gurney flaps on the trailing element (Katz & Largman, 1989; Papadakis et al., 1996, 1997), the primary element alone (Papadakis et al., 1996, 1997; Ross et al., 1995), or on both (Papadakis et al., 1996, 1997; Storms & Ross, 1995). The performance was enhanced in the case of flaps on the trailing element but not in the case of the flaps on the main element (Myose et al., 1996, 1998) experimented on three-dimensional cambered wings with gurney flaps with single and multiple elements. The angle of attack for zero lift increases negatively, and the lift curve shifts upwards in the presence of the flaps. Although the stall angle reduces with increased flap height, the maximum lift coefficient increases. A 25%, 36% and 47% increase were reported with flap heights of 0.01c, 0.02c and 0.04c, respectively. For the cambered case, a 22% increase in lift coefficient was obtained for a flap of 0.01c height. Their study of three-dimensional wings found that the shape of the lift-curve slope is altered totally due to gurney flaps, as opposed to a mere shift in the curve for two-dimensional cases. Also, positioning the flaps in the inboard position is more favourable than the outboard position. A study by (Storms & Jang, 1994) on a NACA4412 airfoil with vortex generators and Gurney flaps showed that the two devices could be used to yield better results. The combination’s lift-to-drag ratio was higher at higher AOA but lower at moderate and low AOA. As a result, vortex generators can be hidden within high-lift devices to decrease parasitic drag during cruising mode (J. Kentfield, 1993). investigated the use of Gurney flaps on helicopter rotors and discovered a 20% improvement in the lift with no extra power or propeller diameter increase. The overall efficiency increases by 10% with the addition of flaps. With a focus on improving the lifting capability of an airfoil with a minimal penalty, Gurney flaps could be an ideal choice. The geometry and deployment methods are simple to achieve. Gurney flaps enhance the lift coefficient with minimum drag penalty by enhancing airfoil circulation, delaying flow separation, and raising the pressure coefficient ahead on the pressure side. The lift coefficient remains near or over-unity due to the high pressure on the pressure side post-stall, which might be helpful for aviation applications. Gurney flaps reduce the power consumed by a considerable amount for application in compressor blades. Applications in helicopter blades can also enhance the flight envelope and increase payload carrying capacity. Wind turbine applications of gurney flaps can be beneficial to decrease starting speed when used near the root, controlling loads by deflectable flaps, combined with vortex generators to adapt to high-power machinery (Salcedo et al., 2006) etc.