National Aeronautical Establishment Research Articles

Snow parameters derived from microwave measurements during the BOREAS winter field campaign

Passive microwave data have been used to infer the snow‐covered area and snow water equivalent (SWE) over forested areas, but the accuracy of these retrieved snow parameters cannot be easily validated for heterogeneous vegetated regions. The Boreal Ecosystem‐Atmosphere Study Winter Field Campaign provided the opportunity to study the effect of boreal forests on snow parameter retrieval in detail. Microwave radiometers (18, 37, and 92 GHz) were flown on board the Canadian National Aeronautical Establishment's Twin Otter. Flight lines covered both the southern study area near Prince Albert and the northern study area near Thompson, Canada. During the 1994 winter campaign, extensive ground‐based snow cover information, including depth, density, and grain size, was collected along most of the flight lines, jointly by U.S. and Canadian investigators. Satellite data collected by the special sensor microwave imager are also used for comparison. Preliminary results reconfirmed the relationship between microwave brightness temperature and SWE. However, the effect of forest cover observed by the aircraft sensors is different from that of the satellite observations. This is probably due to the difference in footprint averaging. There were also several flight lines flown over Candle Lake and Waskesiu Lake to assess lake ice signatures. Preliminary results show the thickness of the lake ice may be inferred from the airborne microwave observations. The microwave signature relationship between lake ice and snow matches the results from radiative transfer calculations.

Volume‐imaging lidar observations of the convective structure surrounding the flight path of a flux‐measuring aircraft

The University of Wisconsin volume imaging lidar has been used to portray images of the three‐dimensional structure of clear air convective plumes in the atmosphere surrounding the flight path of the instrumented Twin Otter aircraft operated by the National Aeronautical Establishment (NAE) of Canada. Lidar images provide a context for interpretation of the aircraft measurements. The position of data points within a convective element can be determined and the temporal development of the plume can be observed to time the observation with respect to the life cycle of the plume. Plots of the vertical flux of water vapor, q′w′, superimposed on lidar images clearly demonstrate the well‐known sampling difficulties encountered when attempting to measure fluxes near the top of the convective layer. When Loran was used to determine average aircraft velocity, flight‐leg‐averaged horizontal winds measured by the aircraft and area‐averaged winds measured by lidar agree to within 0.2 m s−1 in speed and 1° in direction.

An Application of Kalman Filtering to Airborne Wind Measurement

Airborne wind measurement techniques currently being used onboard the National Aeronautical Establishment (NAE) Twin Otter Atmospheric Research Aircraft are described and their fundamental limitations are discussed. In particular, a recently acquired LTN-90-100 strapdown Inertial Reference System (IRS) exhibits significant low frequency errors in its velocity components (primarily Schuler oscillation errors that can attain peak values of 2 to 3 m s−1), actually degrading wind computation accuracy compared with older techniques. A new wind measurement technique, based on a Kalman filter integrated navigation approach, is shown to mitigate this problem and provide wind computation accuracy superior to previous methods. Preliminary results, based on applying the Kalman filter to Twin Otter flight test data, indicate that inertial velocity accuracies of 0.3 m s−1 rms (per axis) are attainable under ideal conditions, with a corresponding improvement in the accuracy of earth-referenced wind components.

Transonic buffet on a supercritical aerofoil

The buffet characteristics of a supercritical aerofoil were investigated in the High Reynolds Number Two-Dimensional Test Facility of the National Aeronautical Establishment (NAE). The test was performed quite deep into the buffet régime. The buffet onset boundary was determined from the divergence of the unsteady balance normal force. Steady and unsteady pressure measurements were obtained for shock-induced separation with reattachment as well as fully separated flows. For flow conditions where discrete shock wave oscillations occurred, ensemble-averaging of the unsteady pressures determined the propagation velocity of the pressure wave induced by periodic shock motion. A model of the self-sustained oscillatory shock motion due to shock-boundary layer interaction was formulated. Broad-band cross-correlations of the pressure field determined the downstream convection velocities of the turbulent eddies of separated flows.

Investigation of flow separation on a supercritical airfoil

Transonic shock/boundary-layer interaction on the upper surface of a supercritical airfoil was investigated in the National Aeronautical Establishment High Reynolds Number Two-Dimensional Test Facility. Skin-friction coefficient measurements on the airfoil surface were carried out using a Preston tube. At the lower Mach number range of the experiments, shock-induced and trailing-edge separation regions were found to exist simultaneously. Detailed experimental measurements were carried out at M = 0.688 and various values of a to investigate the merging of the two separated-flow regions. Steady and unsteady pressure measurements were made for various types of shock/boundary-layer interaction. Pressure power spectra were computed to study the characteristics of pressure fluctuations in the separated-flow regions. Fluctuating normal forces were measured for different types of flow separation, and the behavior of the unsteady load experienced by the airfoil was presented. Broadband cross-correlations of the pressure field were carried out to determine the convection velocities for attached and separated flows.

Parametric investigation of wind-induced cable-stayed bridge motion using an aeroelastic model

This paper presents the results of an aeroelastic model test of a cable-stayed bridge. The model, built at a geometric scale of 1:75 was tested in the National Aeronautical Establishment's (NAE) 9 m x 9 m low speed wind tunnel (Ref. 1). Nine deck section configurations were tested in three different flows; two of which were properly scaled atmospheric turbulence, and the third being smooth flow.

Flight investigation of helicopter low-speed response requirements

A flight experiment has been conducted using the Canadian National Aeronautical Establishment's variable-stability airborne simulator to define the dynamic response requirements for operations at hover and low speeds. Fourteen Attitude Command/Attitude Hold, Rate, and Rate Command/Attitude Hold configurations were evaluated by six pilots using both conventional controls and a four-axis integrated sidestick over a low-speed course consisting of precision hover, landing, sidestep, and dash/quickstop tasks. The results indicate that with conventional controls all three response-types were acceptable as long as their response bandwidth was sufficiently high, and higher bandwidths were required in roll than in pitch. With the four-axis sidestick, there was a preference for the Rate systems. The range of acceptable bandwidths was lower, and the spread in pilot ratings smaller, than were found in a similar ground-based simulation.

Prediction of tubular projectile aerodynamics using the ZEUS Euler code

A subcaliber spinning tubular projectile was developed as a range-limited training ammunition for rifled tank guns, providing a ballistic match with the kinetic-energy-penetrator round. The supersonic shock-swallowed aerodynamics of the tubular projectile were obtained from wind-tunnel and free-flight experiments, extended linear theory, and subsequently the ZEUS Euler code. This paper presents a summary of results and makes comparison between experimental results and ZEUS for the cases of the subcaliber tubular projectile, the Royal Aircraft Establishment tubular inlet, and the National Aeronautical Establishment tubular projectile—Model A. The Euler code matched tunnel results for the subcaliber tubular projectile as follows: CW« = 10%, Cma = 15%, and the center of pressure position Xcp to within 0.2 diam. Shock/boundary-layer interactions were shown to move the internal shock reflection points slightly ahead of the positions calculated by the inviscid ZEUS code; however, the net effect of this was small because of the dominance of the external forces on the tube. Pressurecontour maps display internal and external flowfields in axial and crossflow planes, and internal pressure contours matched experimental data well.

Investigation of the buffet characteristics of two supercritical airfoils

The buffet characteristics of two supercritical airfoils were investigated at the high Reynolds number twodimensional test facility of the National Aeronautical Establishment. The design conditions of these two airfoils were quite similar. The thickness-to-chord ratio differed from each other by approximately 35%. The buffet onset boundaries were determined from the divergence of the unsteady balance normal force. They were compared to show the effect of thickness-to-chord ratio on buffet onset. One of the airfoils was instrumented with fast-response pressure transducers on the upper surface. Pressure intensities for shock-induced separation with reattachment as well as fully separated flows were measured. For flow conditions where discrete-frequency shock wave oscillations occurred, ensemble averaging of the unsteady pressure were carried out to determine the propagation of the pressure wave induced by periodic shock motion. Spectral analyzes of the pressure and normal force fluctuations were carried out quite deep into the buffet regime. Broadband convection velocities of the turbulent eddies were measured for fully separated flows.

Transonic buffet of a supercritical airfoil with trailing-edge flap

A supercritical airfoil with a trailing-edge flap was tested at the High Reynolds Number Two-Dimensional Test Facility of the National Aeronautical Establishment. Buffet boundaries at various flap angles were determined from the divergence of the indicated normal-force fluctuations. The test was performed quite deep into the buffet regime of the airfoil, and spectral analyses of the unsteady normal force showed shock-wave oscillations of approximately 50-80 Hz for Mach numbers between 0.612 and 0.792. The drag of the airfoil was measured from wake probes, and the drag penalties for the large flap angles were quite significant. This study illustrates the use of trailing-edge flaps for buffet alleviation at transonic conditions.

Greenland ice cap aeromagnetic survey 1987: completion of the survey over the southern end of the Greenland ice cap

The Geological Survey of Greenland (GGU), the Geological Survey of Canada (GSC), and the National Aeronautical Establishment (NAE) of the National Research Council of Canada are cooperating in the GICAS project. The objective of the project is to achieve a regional, aeromagnetic coverage of the Greenland ice cap, and to produce magnetic anomaly maps for use in research on the large scale geological structures. Field work was carried out in 1983, 1984, and 1985 (Thorning et al. , 1984, 1985, 1986). The work reported in this note was originally planned for April 1986, but for technical reasons it had to be postponed until April 1987. Consequently, the subsequent processing of all the data into a regional magnetic anomaly map has been correspondingly delayed.

Aircraft Flow Effects on Cloud Drop Images and Concentrations Measured by the NAE Twin Otter

A theoretical model for the local flow velocity ahead of the wing quarter-chord point on the National Aeronautical Establishment Twin Otter has been developed and experimentally verified by flight measurements using a pitot-static equipped Particle Measuring Systems (PMS) canister. This flow velocity model was used to calculate drop trajectories and the resulting airflow effects on drop images and concentrations. Results indicate that drop images and concentrations measured by the Twin Otter are distorted in the worst case by no more than 25% for an unusually high aircraft lift coefficient (CL) of 0.79, and by only a few percent for lower values of CL typical of normal flight. A method to correct water drop images and concentrations is described and results for a PMS probe mounted at one underwing station are presented.

Nonlinear simulation of flight along wind compensating curved glidepaths

A technique for defining curved glidepath geometries that compensate for some of the undesirable effects of low altitude winds is described. This technique uses an a priori estimate of the wind conditions present at the time of the landing approach to define a suitable glidepath geometry. The results of closed-loop, six degree-of-freedom simulation of a twoengined STOL transport conducting landing approaches on such curved approaches are summarized, and a number of recommendations for future work are made. Contents D evelopments in microwave landing system technology have given rise to the possibility of defining curved precision approach trajectories. Since the early 1970's a considerable amount of work has been carried out on curved approach trajectories defined in the horizontal plane. This new landing aid technology has also made possible curved approaches in the vertical plane (Fig. 1). The literature has occasionally made reference to such trajectories (e.g., the ''ideal descending route of Ling 1). These might be used for constant rate of descent procedures for portions of the approach and a steep initial approach gradually transitioning to a shallow approach for the last segment prior to landing. This paper briefly summarizes the key results of an evaluation of a particular subset of such vertical plane modified approach geometries. [For brevity, such approach trajectories will be referred to as curved glidepath geometries (CGG).] This subset is based on an estimate of the wind conditions present at the time of the approach through an algorithm that compensates for some of the undesirable effects of wind on aircraft, and potentially reduces pilot workload. Preliminary study of the problem from this viewpoint was undertaken by Hindson and Gould2 in 1974. Their results suggested that CGG may be desirable in the presence of wind gradients in order to alleviate pilot workload, particularly for V/STOL aircraft. This was followed by flight test evaluations in the National Aeronautical Establishment airborne simulator in 1975—76, with encouraging results.3 Method The source of Hindson and Gould's proposal was the observation that vertical wind gradients of the horizontal

Non-Oriented Cesium Sensors for Airborne Magnetometry and Gradiometry

Optically pumped magnetometers are characterized by an optimal angle between their optical axes and the direction of the magnetic field they are sensing. Departure from the optimal angle causes a shift in the Larmor frequency with a corresponding error in the scalar value of the magnetic field being measured. To minimize this error, magnetometers are conventionally either mounted in multiple sensor clusters such that the errors tend to cancel, or they are mechanically oriented to maintain the optimal angle with respect to the magnetic field vector. Recent cesium vapor magnetometers using a split-beam technique have a sufficiently flat error characteristic that they can be flown in a non-oriented or “strap-down” configuration. This configuration has advantages with respect to conventional methods in terms of reduced size and weight and of greatly reduced cost. This paper describes two fixed orientations for a particular split-beam magnetometer and calculates the allowable maneuver envelope for all dip angles from 0 to 90 degrees. It is shown that the residual orientation errors can best be handled by the conventional type of magnetic interference compensation model that must, in any case, be implemented in digital form for high-sensitivity magnetometry or for any type of gradiometry. The National Aeronautical Establishment (NAE) of the National Research Council of Canada has flown strap-down magnetometers in a three-axis gradiometer array in a Convair 580 for several years. Results for the entire normal maneuver envelope of the aircraft, including 30 degree bank turns, have equalled or surpassed those obtained with oriented magnetometers. Several typical maneuver compensation results are presented that gave root-mean-square (rms) (one-sigma) residual errors as low as 0.03 gammas (Γ) for total field and 3.5 mgammas/m(mγ/m) for lateral gradient.

Non‐oriented cesium sensors for airborne magnetometry and gradiometry

Optically pumped magnetometers are characterized by an optimal angle between their optical axes and the direction of the magnetic field they are sensing. Departure from the optimal angle causes a shift in the Larmor frequency with a corresponding error in the scalar value of the magnetic field being measured. To minimize this error, magnetometers are conventionally either mounted in multiple sensor clusters such that the errors tend to cancel, or they are mechanically oriented to maintain the optimal angle with respect to the magnetic field vector. Recent cesium vapor magnetometers using a split‐beam technique have a sufficiently flat error characteristic that they can be flown in a non‐oriented or “strap‐down” configuration. This configuration has advantages with respect to conventional methods in terms of reduced size and weight and of greatly reduced cost. This paper describes two fixed orientations for a particular split‐beam magnetometer and calculates the allowable maneuver envelope for all dip angles from 0 to 90 degrees. It is shown that the residual orientation errors can best be handled by the conventional type of magnetic interference compensation model that must, in any case, be implemented in digital form for high‐sensitivity magnetometry or for any type of gradiometry. The National Aeronautical Establishment (NAE) of the National Research Council of Canada has flown strap‐down magnetometers in a three‐axis gradiometer array in a Convair 580 for several years. Results for the entire normal maneuver envelope of the aircraft, including 30 degree bank turns, have equalled or surpassed those obtained with oriented magnetometers. Several typical maneuver compensation results are presented that gave root‐mean‐square (rms) (one‐sigma) residual errors as low as 0.03 gammas (γ) for total field and 3.5 mgammas/m (mγ/m) for lateral gradient.

Aircraft measurements of CO2 exchange over various ecosystems

The National Aeronautical Establishment's Twin Otter Atmospheric Research Aircraft has been equipped with open-path CO2 analyzers in order to obtain estimates of CO2 exchange over a corn field, a forest and a lake using the eddy correlation technique. On the 18th of August 1980, mean uptakes obtained over corn and forest were 12 and 8 kg CO2 ha-1 hr-1, respectively. On the 28th of August, mean uptakes obtained over corn, forest and the lake were 36, 14, and 1 kg CO2 ha-1 hr-1, respectively. The data are discussed in the light of general conditions on the two days.

Effect of edge-tone noise on supercritical airfoil data

A N investigation has recently been carried out in the National Aeronautical Establishment (NAE) 0.38x1.5 m two-dimensional test section1 to determine: 1) The possibility of edge-tone noise suppression by overlaying the perforated floor and ceiling with a fine gauze or screen. 2) The change in wall interference characteristics due to the application of point 1. 3) The effect of edge-tone noise suppression on twodimensional airfoil test data. The investigation was performed with a 0.254 m chord model of the BGK No. 1 airfoil and covered the Mach number range of 0.3-0.8 at chord Reynolds numbers of 10-21 x 106. A full account of the investigation is given in Ref. 2. This Note deals primarily with selected data related to point 3. However, first some brief comments on points 1 and 2. The fine gauze technique, first demonstrated by Vaucheret,3 was found to be both a practical and an effective means for edge-tone suppression, as demonstrated in Figs. 1 and 2, respectively. It was also found that the presence of the gauze, although reducing the geometric porosity from 20.5 to 8%, had a very minor effect on the wall interference characteristics. Measurements on the BGK No. 1 airfoil comprised balance, wake, and surface pressure. Only the latter two are discussed here. The data depicted in Fig. 2 were obtained by a sidewallmounted differential pressure transducer, with the reference side detuned and connected to the plenum chamber. The frequency response of the active side was flat up to 16 kHz. The data are presented in the form of the root mean square of the fluctuating wall static pressure coefficient, Cpj^, referenced to the mean value of the freestream dynamic pressure. The significant reduction in noise level due to the edge-tone suppression is clearly evident. In fact, at the higher Mach number the measured noise level is reduced to a level comparable to that inherent in the wall boundary layer itself. For a well-developed turbulent boundary layer, the wall CPRMS (referenced to the dynamic pressure at the edge of the boundary layer) is known to be about 0.6-0.7%. To what degree then are model test data influenced by this improvement in flow quality? The obvious thought that comes to mind is that the edge tones could excite the TollmienSchlichting waves and thus cause early transition. A cursory investigation reveals that, at the Reynolds numbers here of interest, the dangerous frequencies are an order of magnitude higher than the edge-tone frequencies. Thus the edge tones are not expected to influence the boundary-layer transition. However, we may speculate that they could interfere with, for instance, a turbulent boundary layer close to separation, although the mechanism in such a case would be far from clear. We shall first examine drag data obtained from wake pressure measurements. In Fig. 3 we have plotted the drag coefficient vs freestream Mach number, both corrected for wall interference effects, for two values of the normal force coefficient CN, 0.3 and 0.6. The data points are obtained by a

The translation velocity of convective plumes

AbstractDuring July 1971, an intensive experimental programme was undertaken in south‐eastern Alberta to measure the turbulence statistics in the planetary boundary layer (PBL), using a 92‐m tower, an array of four smaller towers and an instrumented T‐33 aircraft from the National Aeronautical Establishment of the National Research Council, Ottawa.In this first paper is reported the measurement of the translation velocity of convective plumes, determined by means of an array of towers, at a height of 3.5 m. The direction of plume motion was found to be close to that of the surface wind. The speed of plume motion was found to be close to the wind speed near the top of the surface shear zone; this result is different from previous estimates using different techniques. A dynamic model of the plume was used to show that a translation speed close to the wind speed near the top of the surface shear zone (as observed) allows plumes to exist at a lower thermal instability level than any other possible translation speed.These results mean that Taylor's frozen field hypothesis is not applicable to plume scales since the plumes (although not the air inside them) move at a speed independent of height.

Three-Dimensional Flow Separations on Aircraft and Missiles

William J. Rainbird; received his B.E.(Mech) at Canterbury University, Christchurch, New Zealand in 1947, and was awarded a Government scholarship to the College of Aeronautices, Cranfield, England, where he left in 1950 with a Post Graduate Diploma, with distinction, specializing in aerodynamics. After a year in Stockholm, Sweden working on transonic and supersonic wind-tunnel design at F.F.A., he returned to New Zealand and lectured at Canterbury University until September 1954. Returning to the College of Aeronautics, Cranfield that year, he was Lecturer in General and Experimental Aerodynamics for 3 years. Mr. Rainbird worked at the National Aeronautical Establishment, a Division of the National Research Council, Ottawa, from January 1958 to July 1970 and was a Senior Research Officer and Head of the High Speed Aerodynamics Section. In July 1970, Mr. Rainbird was appointed Professor of Engineering and Chairman of the Division of Aerothermodynamics, at Carleton University, Ottawa. In 1967, Mr. Rainbird spent a year’s study and refresher leave at the University of California, San Diego, Department of Aerospace and Mechanical Engineering Sciences. He is a Fellow of the C ASI, Associate Fellow of the Royal Aeronautical Society, Member of the AIAA, and was a Canadian Member of the AGARD Fluid Dynamics Panel from 1964-1969. His main field of specialization and interest in aerodynamics is in threedimensional boundary layers and separation. David J. Peake is a graduate of University of Bristol, England, Department of Aeronautical Engineering [B.Sc., 1960 (First Class Honors); M.Sc., 1962], Concurrent with University training, Mr. Peake completed an Engineering Student Apprenticeship at National Gas Turbine Establishment, Pyestock, Farnborough, England, during 1956- 1960. He remained at NGTE until May 1962 as Scientific Officer, working with Dr. Brian Stratford on the control of supersonic turbulent boundary layers with tangential air injection, and supersonic inlet design. Mr. Peake moved to National Research Council, Ottawa, Canada in May 1962, joining the Council's National Aeronautical Establishment in January 1964, in the High Speed Aerodynamics Laboratory. He worked with W. J. Rainbird in the investigation of three-dimensional separations in both subsonic and supersonic flow; transonic jet-flapped aerofoils, and axisymmetric turbulent boundary layers, all at high Reynolds numbers. Mr. Peake is studying for Ph.D. (parttime) at Carleton University, Ottawa and has membership in AIAA, RAeS and CASI. He has recently been awarded a Ph.D. from the University of Bristol for submitted published work. Edward G. Atraghji is a graduate of University of London (B.Sc., 1962). He conducted research on slender delta wing configurations at Queen Mary College, London, between 1962 and 1966. He joined the National Research Council, NAE Division, High Speed Aerodynamics Laboratory, 1966. Topics of research have included the flows about various aircraft and missile configurations.

Discussion of paper by Bruce M. Irons

International Journal for Numerical Methods in EngineeringVolume 2, Issue 3 p. 453-454 Comment Discussion of paper by Bruce M. Irons† G. R. Cowper, G. R. Cowper National Aeronautical Establishment, Ottawa, Ontario, CanadaSearch for more papers by this authorG. M. Lindberg, G. M. Lindberg National Aeronautical Establishment, Ottawa, Ontario, CanadaSearch for more papers by this authorM. D. Olson, M. D. Olson National Aeronautical Establishment, Ottawa, Ontario, CanadaSearch for more papers by this author G. R. Cowper, G. R. Cowper National Aeronautical Establishment, Ottawa, Ontario, CanadaSearch for more papers by this authorG. M. Lindberg, G. M. Lindberg National Aeronautical Establishment, Ottawa, Ontario, CanadaSearch for more papers by this authorM. D. Olson, M. D. Olson National Aeronautical Establishment, Ottawa, Ontario, CanadaSearch for more papers by this author First published: July/September 1970 https://doi.org/10.1002/nme.1620020311Citations: 3 † Bruce M. Irons, ‘A conforming quartic triangular element for plate bending’, Int. J. num. Meth. Engng, 1, 29–45 (1969). AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume2, Issue3July/September 1970Pages 453-454 RelatedInformation