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Introduction
Published in James DeLaurier, Aircraft Design Concepts, 2022
The choice of the material for a structure also depends on the loading and the cross-sectional space available. If, for example, the column is constrained to the dimensions of the compressed spruce example, but the imposed load is larger than what spruce can take, then the material must simply be changed. Recall that the spruce column with a 4.4774cm square cross-section could carry a maximum load of 51831.8N. However, an aluminum column with the same cross-section can carry a maximum load of 288,837N, which is 5.6 times greater. The weight of the aluminum column is also 5.3 times greater but, as was seen, re-configuring the cross-section can reduce this number. Nonetheless, the higher stresses experienced by high-performance aircraft require materials that can accommodate these stresses, even at a weight penalty. This is why high-performance airplanes generally have higher wing loadings. Using wood for an F-14 fighter would be ridiculous.
Straight-level flight
Published in Mohammad H. Sadraey, Aircraft Performance, 2017
The ratio between the aircraft weight and the wing area (W/S) is called wing loading. The wing loading is an important parameter in aircraft performance evaluation. For example, for an aircraft with a weight of 2650 lb and wing area of 160 ft2, the wing loading is 2650/160 or 17.67 pound per square foot (lb/ft2). Another term that appears in many performance equations is T/W, which is called the thrust-to-weight ratio. This ratio for the majority of jet aircraft is less than 1 (about 0.2–0.3). For a vertical takeoff and landing (VTOL) aircraft, this ratio is more than unity.
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 preceding highlights several of the ways sUAS designs are similar to those of manned aircraft. However, due to scale effects among other factors, certain differences also exist. On average, the size (mass) of both unmanned fixed- and rotary-wing aircraft are orders of magnitude less than their manned counterparts (Austin 2010). As we “scale down” aircraft to smaller sizes, all attributes are not affected in the same way. For example, wing surface area, being two dimensional, will vary inversely as the square of the scaling factor, whereas volume, a cubic, will vary inversely as the cube of the scaling factor. Thus, all other factors held constant, wing loading—that is, weight (mass in the gravitational field of the earth) divided by wing area—tends to increase with a decrease in UA size. Higher wing loading affects aircraft performance, decreasing the rate of climb and increasing stall speed. Decreasing the rate of climb may negatively affect endurance, and consequently, range. Increased stall speed increases stress on all recovery structures (main and nose landing gear system primarily). Higher wing loading may compel the designer to use a catapult launch system in lieu of the less equipment intensive hand launch. Higher wing loading also reduces maneuverability. Conversely, any reduction in mass affects the ability of the UAS to resist the disturbing or upset force of wind gusts, an important consideration in many data gathering missions. Neither are rotorcraft immune to the effects of reduced scale. Narrower blade chords and smaller rotor disks produce low Reynolds numbers, which reduce the efficiency and lift of the rotor system (Seddon 1990) that, in turn, decreases range, endurance, and payload. Thus, in UAS design, size is important, affecting several operational characteristics that may, in turn, affect the ability of the platform to meet mission requirements.
Fluid-structure interaction simulation for performance prediction and design optimization of parafoils
Published in Engineering Applications of Computational Fluid Mechanics, 2023
Hong Zhu, Qinglin Sun, Jin Tao, Hao Sun, Zengqiang Chen, Xianyi Zeng, Damien Soulat
During actual flight, the installation angle can be adjusted by the length of suspension ropes so that the parafoil system can be steady in a gliding state. Figure 19 shows the predicted velocities of Model A parafoil system with different suspended weights. Wing loading is the ratio of suspended weight to wing area. Horizontal and descent velocities increased with wing loading–the higher the attack angle, the smaller the velocities. The horizontal velocity can reach 8 m/s to 10 m/s with a payload in the range of 10 kg to 20 kg. With a 13 kg payload, horizontal and descent velocities at a steady angle of attack were about 9.9 m/s and 4.7 m/s, respectively.