Low Speed Aerodynamics

Stability in Aviation. By Prof. G. H. Bryan, F.E.S. Pp. X + 192. 5S. net. 1911. (Macmillan.)

Flight Vehicle System Identification: A Time-Domain MethodologyJategaonkarR. V., Progress in Aeronautics and Astronautics, 2nd ed., AIAA, Reston, VA, 2015, 648 pp., $119.95.

A brief review of some of the more pertinent applications of analytical pilot models to the prediction of aircraft handling qualities is undertaken. The relative ease with which multiloop piloting tasks can be modeled via the optimal control formulation makes the use of optimal pilot models particularly attractive for handling qualities research. To this end, a rating hypothesis is introduced which relates the numerical pilot opinion rating assigned to a particular vehicle and task to the numerical value of the index of performance resulting from an optimal pilot modeling procedure as applied to that vehicle and task. This hypothesis is tested using data from piloted simulations and is shown to be reasonable. An example concerning a helicopter landing approach is introduced to outline the predictive capability of the rating hypothesis in multiaxis piloting tasks.

Prediction of pilot opinion ratings using an optimal pilot model. [of aircraft handling qualities in multiaxis tasks

A review of recent shape memory alloy (SMA) aeronautical applications is highlighted. To date, SMAs have not been successfully employed in critical aircraft actuation due to several technological and infrastructure challenges. Albeit fully functional SMA prototypes were demonstrated in aerospace environments over a decade ago, other critical elements such as material form, certification, and other crucial design tools have not progressed with the same level of maturity. The applications presented here have acknowledged these shortcomings and are built on previous successes to thrust SMAs a step closer to aircraft adoption. The spanwise adaptive wing (SAW) project and the wind tunnel remote control actuation (RCA) are the new applications that employ new advancement. First, the SAW project is the first ever, fully integrated flight test employing high-temperature SMAs with flight-relevant properties. The project utilized NiTiHf alloys with suitable actuation temperatures, and scalable to commercially available lots/forms. Second, the RCA project represents the next paradigm shift in wind tunnel testing. This application employs NiTi torque tubes capable of moving and controlling the model parts, enabling increased productivity, improved data quality, and reduced cost of wind tunnel testing. An overview of each application is provided here, with insights into system-level successes, challenges, and lessons learned.

Recent Advancements in Rotary Shape Memory Alloy Actuators for Aeronautics

Wingtip folding is a means by which an aircraft’s wingspan can be extended, allowing designers to take advantage of the associated reduction in induced drag. This type of device can provide other benefits if used in flight, such as flight control and load alleviation. In this paper, the authors present a method to develop reduced order flight dynamic models for in-flight wingtip folding, which are suitable for implementation in real-time pilot-in-the-loop simulations. Aspects such as the impact of wingtip size and folding angle on aircraft roll dynamics are investigated along with failure scenarios using a time domain aeroservoelastic framework and an established system identification method. The process discussed in this paper helps remove the need for direct connection of complex physics based models to engineering flight simulators and the need for tedious programming of large look-up-tables in simulators. Instead, it has been shown that a generic polynomial model for roll aeroderivatives can be used in small roll perturbation conditions to simulate the roll characteristics of an aerodynamic derivative based large transport aircraft equipped with varying fold hinge lines and tip deflections. Moreover, the effects of wing flexibility are also considered.

https://www.mdpi.com/2226-4310/6/6/63/pdf

Identification of in-flight wingtip folding effects on the roll characteristics of a flexible aircraft

The drive for aircraft efficiency and minimum environmental impact is requiring the aerospace industry to generate technologically innovative and highly integrated aircraft concepts. This has changed the approach towards conceptual design and highlighted the need for modular low fidelity aircraft simulation models that not only capture conventional flight dynamics but also provide insight into aeroservoelasticity and flight loads. The key aspects that drive the need for modularity are discussed alongside integration aspects related to coupling aerodynamic models, flight dynamic equations of motion and structural dynamic models. The details of developing such a simulation framework are presented and the utility of such a tool is illustrated through two test cases. The first case focuses on aircraft response to a gust that has a spanwise varying profile. The second investigates aircraft dynamics during control surface failure scenarios. The Cranfield Accelerated Aeroplane Loads Model (CA2LM) forms the basis of the presented discussion.

/pdf/flight-dynamic-modelling-and-simulation-of-large-flexible-2pgdf4io3o.pdf

Flight Dynamic Modelling and Simulation of Large Flexible Aircraft

Aircraft concepts of tomorrow, such as high aspect ratio wing aircraft, are far more integrated between technical disciplines and thus require multi-disciplinary design approaches. Design tools able to predict associated dynamics need to be developed if such wing concepts are to be matured for use on future transport aircraft. The Cranfield University Beam Reduction and Dynamic Scaling (BeaRDS ) Programme provides a framework that scales a conceptual full size aircraft to a cantilevered wing model of wind tunnel dimensions, such that there is similitude between the static and dynamic behaviour of the model and the full size aircraft. This process of aeroelastically scaled testing combines the technical disciplines of aerodynamics, flight mechanics and structural dynamics, to provide a means by which future concept aircraft can be de-risked and explored. Data acquisition from wind tunnel testing can then be used to validate fluid-structure interaction frameworks that model the aeroelastic effect on the flight dynamics of the aircraft. This paper provides an overview of the BeaRDSmethodology, and focuses on the Phase I of the programme, being the development of a reduced Cranfield A-13 aircraft cantilevered wing, to mitigate risk associated with the manufacturing and instrumentation approach. It is shown that a low cost acquisition system of commercial Inertial Measurement Units (IMUs) can measure the response of the wing within the desired frequency range. Issues associated with the Phase I testing are discussed, and methods are proposed for the Phase II programme that allow these problems to be resolved for a larger scale flexible wing with active control surfaces.

/pdf/flexible-high-aspect-ratio-wing-low-cost-experimental-model-3q734i0rri.pdf

Flexible high aspect ratio wing: Low cost experimental model and computational framework

It is well known that increasing wing span leads to improved aerodynamic performances. To comply with airport infrastructure limits, ground folding wingtips are implemented as a solution for wing span extension. To further justify the mechanism’s weight penalty the concept of in-flight folding is investigated here. A time domain aeroservoelastic simulation framework is used to asses its impact on lateral flight dynamics. An established system identification method, was used to derive key lateral aerodynamic derivatives and investigate the aircraft’s roll handling qualities. A range of wingtip deflections and various flight conditions were used to generate a sufficiently large database of coefficients to assess the effect of wingtip morphing as a function of airframe flexibility and flight conditions. Results show that overall, small changes in lateral aerodynamic derivatives are introduced with wingtip morphing. Different trends in aerodynamic derivatives were identified as a function of flight condition and wingtip deflection, leading to the derivation of prediction models to replace the aerodynamic derivatives database.

/pdf/effect-of-wingtip-morphing-on-the-roll-mode-of-a-flexible-59pp8n8ucb.pdf

Effect of wingtip morphing on the roll mode of a flexible aircraft

The drive for increasing flight efficiency is resulting in wing designs that are of higher aspect ratios, lower in weight, increased wingspans and, consequently, require greater attention in the disciplines of aeroelastics and loads. This trend in aircraft design, along with past research experience with flexible aircraft, motivate a review of assumptions in gust models; especially, that of the gust maintaining a uniform spanwise profile. In this paper, the authors investigate the use of spanwise varying 1−cos gust models for loads prediction using a non-linear aeroelastic model of a conventional large transport aircraft. The comparison between a test case using conventional uni-dimensional approach and another, using multidimensional gusts, illustrates the impact of stepping away from traditional discrete tuned gust processes and adding a spanwise varying gust component. A methodology for processing and analysing the loads data arising due to the added dimension is also developed and both envelope and correlated loads are considered. Gust characteristics and resulting load factor are, respectively, considered for comparison between the two models, as both metrics define realistic gust encounters. In this case, it has been shown that spanwise variation of gust profiles leads to lower envelope loads if viewed in terms of conventional gust gradients. However, higher envelope loads are found if the maximum load factors are matched.

Gaétan X. Dussart

Papers

Identification of in-flight wingtip folding effects on the roll characteristics of a flexible aircraft

Flight Dynamic Modelling and Simulation of Large Flexible Aircraft

Flexible high aspect ratio wing: Low cost experimental model and computational framework

Effect of wingtip morphing on the roll mode of a flexible aircraft

Impact of spanwise non-uniform discrete gusts on civil aircraft loads