Peter M. Render

Design methodology and performance of an indraft wind tunnel

The design methodology and performance of Loughborough University’s new 1·9m × 1·3m, indraft wind tunnel is discussed in the following paper. To overcome severe spatial and financial constraints, a novel configuration was employed, with the inlet and exit placed adjacent to each other and opened to atmosphere. Using a fine filter mesh, honeycomb, two turbulence reduction screens and a contraction ratio of 7·3, flow uniformity in the working area of the jet at 40ms-1 is shown to be within 0·3% deviation from the mean velocity, with turbulence intensity in the region of 0·15%. Working section boundary layer characteristics are shown to be consistent with that of a turbulent boundary layer growing along a flat plate, which originates at the point of inflection of the contraction. A maximum velocity of 46ms-1 was achieved from a 140kW motor, compared to a prediction of 44ms-1, giving an energy ratio of 1·42. Comparison between theoretical and measured performance metrics indicate differences between the way modules perform when part of a wind tunnel system compared to data gathered from test rigs.

Experimental Investigation into the Aerodynamics of Battle Damaged Airfoils

Wind tunnel tests are reported that investigate three aspects of aerodynamic flows through battle damaged airfoils. The first aspect investigated was the effect of camber. This showed that reducing camber weakened the strength of the jet flow through the damage and delayed the onset of strong jet flows to higher incidences. The second investigation used five hole probe measurements to survey the flow field on a battle damaged flat plate airfoil. The measurements indicated that the use of the jet-to-freestream velocity ratio is a poor criteria for determining whether damage flows have undergone transition to strong jets. Finally, the influence of a star shaped hole to simulate more realistic battle damage was investigated. It was shown that in terms of damage flow characteristics and changes in lift, drag, and pitching moment coefficients, the use of a circular hole is a reasonable simulation of battle damage.

Development of an autopilot system for rapid prototyping of high level control algorithms

This paper describes the development of a system for the rapid prototyping of high level control algorithms using an Arduino based commercial off the shelf autopilot called ArduPilot. It is capable of controlling multiple vehicle types, including fixed, and rotary wing aircraft as well as ground vehicles. The inner loop control is performed by ArduPilot, so the high level control can be rapidly prototyped and tested in Simulink, or an embedded system. The ability to conduct tests in software and hardware in the loop has also be developed, to enable safe testing of algorithms, which will speed up the development process. To show its functionality and ability to assist with the development process of algorithms, ArduPilot is used with a remote controlled aircraft in simulation and in real world testing to verify newly developed high level algorithms for UAVs.

Reachability Analysis of Landing Sites for Forced Landing of a UAS

This paper details a method to ascertain the reachability of known emergency landing sites for any fixed wing aircraft in a forced landing situation. With a knowledge of the aircraft’s state and parameters, as well as a known wind profile, the area of maximum glide range can be calculated using aircraft equations of motion for gliding flight. A landing descent circuit technique used by human pilots carrying out forced landings called high key low key is employed to account for the extra glide distance required for an approach and landing. By combining maximum glide range analysis with the descent circuit, all the reachable landing sites can be determined. X-Plane flight simulator is used to demonstrate and validate the techniques presented.

Aerodynamics of battle damaged finite aspect ratio wings

Wind-tunnel tests have been carried out on a battle-damaged NACA 641412 half-wing aspect ratio of 8.2. The simulated gunfire damage had a diameter of 0.2 wing chord and was located at midchord and at one of two spanwise locations. Tests were carried out at a Reynolds number of 5:5 105. Compared with an undamaged wing, the damage resulted in reduced lift, increased drag and a positive increase in pitching moment at zero lift. Moving the damage to near the tip reduced the magnitude of these effects. Using the static pressure difference between the upper and lower surfaces of the undamaged wing allowed the data from the present study to be successfully compared with previously published drag and lift data for a two-dimensional damaged airfoil. Tests on wings with aspect ratios of 6.2 and 10.3 produced similar trends in the aerodynamic characteristics and showed that the use of static pressure difference was equally effective in allowing comparisons with two-dimensional data.

Effects of target curvature on the impact characteristics of simulated hailstones

As hail ingestion tests are introduced into aero-engine certification procedures, there is an increasing need for an understanding of ice particle behaviour within an engine. In this paper, the possible effects that ingested ice may have on a turbofan engine are briefly discussed. The objective of this paper is to study the effect of target curvature on ice-ball (simulated hailstone) impact characteristics. The target curvature effect was studied on the concave side of two curved plates using the experimental techniques of patternator and still photography. The results are compared with those from a flat plate. The comparison shows that the curvature has a small effect on post-impact particle sizes, and significantly decelerates the movement of the particles after an impact.

Reachability analysis of landing sites for forced landing of a UAS

This paper details a method to ascertain the reachability of known emergency landing sites for any fixed wing aircraft in a forced landing due to engine failure in steady uniform wind conditions. With knowledge of the aircrafts state and parameters, and landing site location and landing direction, the minimum height loss path can be defined. This uses glide performance calculations and a trajectory planner to give a minimum height loss to each landing site. Based on the aircrafts initial altitude it can calculate if the site is reachable, and how reachable it is. The path definition takes into account wind and uses a geometric shape called a trochoid to define the gliding turns in wind. This method is generic enough for use by any aircraft in any wind conditions.

The influence of mid-chord battle damage on the aerodynamic characterstics of two-dimensional wings

This paper briefly considers the method of simulating gunfire damage to a wing and outlines the key basic assumptions used in modelling. The results of qualitative and quantitative investigations into the aerodynamic characteristics of a wing damaged at quarter chord are then presented. The results are discussed in terms of flow mechanisms, changes to surface pressure distributions and increments in lift, drag and pitching moment coefficients. For the damaged wing, the influence on force and moment coefficients was attributed to flow through the damage. This through flow was driven by the pressure differential between the upper and lower wing surfaces, and took one of two forms. The first form was a ‘weak-jet’ which formed an attached wake and resulted in small changes in force and moment coefficients. The second form resulted from either increased incidence, or damage size. This was the ‘strong-jet’, where through flow penetrated into the freestream flow, resulting in separation of the oncoming surface flow, and the development of a larger separated wake with reverse flow. The effect on force and moment coefficients was significant. The paper also compares the structure of the damage through flow with previously published results for jets in crossflows. Many similarities in the flow features were identified, although there were significant differences in the surface pressure distributions for the two cases.

Aerodynamics of Battle Damaged Wings - the Influence of Flaps, Camber and Repair Schemes

Two dimensional wind tunnel tests were conducted on NACA aerofoils with simulated battle damage. The first set of tests showed that positive deflection of a trailing edge flap increased the strength of the flow through the damage For a given incidence, increasing flap deflection increased the drag coefficient relative to the undamaged aerofoil and reduced the lift coefficient. The second set of tests demonstrated that similar effects can be obtained by increasing camber. The final set of tests investigated the effectiveness of battle damage repair schemes. Realistic schemes, incorporating both upper and lower surfaces repairs, were shown to achieve reductions in drag coefficient and increases in lift coefficient, which in both cases were significant. Repairs to only one surface (i,e, upper or lower) were also shown to make significant aerodynamic improvements, which were attributed to the lack of flow through the damage.

Landing Site Reachability in a Forced Landing of Unmanned Aircraft in Wind

Autonomous contingency management systems, such as a forced-landing system, which reacts appropriately to an engine failure, are important for the safe operation of unmanned aircraft systems. This paper details a method to ascertain the reachability of any possible emergency landing site for a forced landing in steady uniform wind conditions. With knowledge of the aircraft’s state, such as speed, heading, location, and orientation of a landing site, a method to calculate a minimum height loss path is developed based on aircraft glide performance. Wind direction and speed are taken into account using a trochoidal approach by defining the minimum height loss turn path. To facilitate real-time implementation, simplified gliding equations are developed without accuracy loss. The reachability of each site can be calculated as well as how much safety margin an aircraft would have. This method is generic and could also provide decision support for human pilots in forced-landing situations. Two types of aircraft,...