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Aerodynamic Forces – Subsonic Flight
Published in Rose G. Davies, Aerodynamics Principles for Air Transport Pilots, 2020
Aspect ratio (AR) of an aerofoil is the ratio of wing span b to the chord c. The aspect ratio is a feature of the basic geometric shape of an airplane’s planform. A high aspect ratio means the airplane with a long or narrow wing. For example, the aspect ratio of a glider can be as high as 33, and the aspect ratio of a passenger jet is about 10. A low aspect ratio means a short wing, or wide wing. For example, an aspect ratio of small subsonic aircraft can be approximately 5 or 6, and the aspect ratio of a jet fighter could be as low as 2 to 3.5.
Hypersonic Aircraft
Published in G. Daniel Brewer, Hydrogen Aircraft Technology, 2017
The major conclusions drawn from the detail analysis of HYCAT configurations -1 and -4 can be summarized as follows:The landing field length is a critical sizing constraint.Turbojet accelerator engines should be buried within the airframe when they are not in use. This serves to minimize both drag and nacelle weight.The arrangement of the propulsion system in HYCAT-1 blocks the scramjet inlet flow in the Mach 0 to 3.5 speed range. The inlet retraction and stowage system is too complex.Lift provided by a flattened vehicle forebody (or by use of strakes) is important to improve hypersonic lift/drag.It is important to keep wing aspect ratio low in order to minimize weight. Higher aspect ratios provide higher low speed lift but incur excessive weight penalty.The use of a horizontal tail or a canard is required to provide trim for changes in e.g. relative to aerodynamic center of pressure. A further advantage is that they allow use of drooped ailerons (flaperons) for low speed lift.The forward passenger compartment location on HYCAT-1 is not efficient and e.g. movement is too large.
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 drivers of L/D (lift divided by drag) are fundamentally the wing span and wetted area (the surface area that is in contact with the external airflow). This is called the “wetted aspect ratio” and defined as the span^2/total wetted area. This parameter, like aspect ratio, is to be maximized for increased L/D until other physical constraints dominate the design (Raymer 1992). High aspect ratio wings are long and narrow. Think about it this way: An infinitely long wing would have no tips, produce no vortices, and induce no drag. As the span of the wing goes to infinity so, too, does the aspect ratio. Just as high aspect ratio wings decrease induced drag, so, too, does a high fineness ratio fuselage reduce form drag. The fineness ratio is a comparison of the length of the fuselage to its width. A short wide fuselage has a low fineness ratio; a long narrow one exhibits a high fineness ratio. When one carefully examines the design of the fixed-wing UAS, high aspect and fineness ratios are frequently very apparent (examples include the Aeromapper EV2, the Hi Aero Gabbiano, General Atomics MQ-9 series, and the IDETEC Stardust). A high-wing aircraft suffers less interference drag than a mid-wing design as the adverse pressure gradient over the aft top region of the wing has no interfering fuselage boundary layer. However, the presence of the fuselage, as mentioned above, impairs upwash, downwash, and thus lift. See Figure 10.3 (High-wing UASs include several Israeli Aerospace Industry [IAI], designs, e.g., Heron, Searcher, Mastiff, and Hunter, and the designs they influenced, e.g., the RQ-2 Pioneer and the RQ-7 Shadow.) Control surface hinges of sUAS are sometimes nothing more than an extension of the airframe material (e.g., carbon fiber cloth) or covering; these surfaces are attached by a thin skin of plastic film or composite and run the length of the surface, thus completely eliminating leakage drag. Larger UASs tend to employ hinge and actuation schemes similar to manned aircraft. Additional characteristics will subsequently be discussed, but the necessity to minimize drag will always be among the factors to be given careful consideration in the design of any UAS, but most particularly those of fixed-wing configuration.
RANS simulation of the tip vortex flow generated around a NACA 0015 hydrofoil and examination of its hydrodynamic characteristics
Published in Journal of Marine Engineering & Technology, 2018
Parviz Ghadimi, Araz Tanha, Sasan Tavakoli, Mohammad A. Feizi Chekab
The diagram in Figure 9 is presented to render the stated conclusion in terms of CL versus CD. This figure indicates that at a fixed lift magnitude, the drag coefficient for two-dimensional foil is greater than that of three-dimensional foil. On the other hand, at a fixed lift coefficient, increase in aspect ratio results in higher drag coefficient. Overall, the 2D simulations have shortcomings in comparison with 3D models. In 2D cases, vortices and their effects cannot be simulated and thus their effects would be neglected on hydrodynamic characteristic of the hydrofoil.