5 Replies Latest reply: Nov 29, 2012 8:46 PM by mohammedfromvellore
cmadness Level 1 Level 1 (0 points)

I've got an epub validating with the latest version of epubcheck, yet Apple is rejecting with the following error:



[9780160897443]: ERROR ITMS-9000: "Wrong namespace in 9780160897443.epub:\OEBPS\Text\index_split_003.xht ml : null - expecting http://www.w3.org/1999/xhtml" at Book (MZItmspBookPackage)


Any ideas? This is getting frustrating because we're not getting more specific info. If we had some type of offline validation tool made by Apple, we could better troubleshoot them.

 

Here are the contents of the xhtml file in question:

 


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  <title>Modeling Flight</title>

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<body class="calibre">

  <h1 class="chapter-title" id="calibre_toc_5"><span class="chapter-title1">CHAPTER 1:<br class="calibre1" /></span> BACKGROUND</h1>

 

 

  <div class="calibre1">

    <p class="subhead">Objectives</p>

 

 

    <p class="paragraph"><span class="charCAP">D</span>ynamically scaled free-flying models are especially well suited for investigations of the flight dynamics of aircraft and spacecraft configurations. Flight dynamics focuses on the behavior of vehicles in flight and the causal factors that influence the motions exhibited in response to atmospheric disturbances or pilot inputs. The science includes aspects of applied aerodynamics, static and dynamic stability and control, flight control systems, and handling qualities. Applications of the free-flight test capability in flight dynamics have ranged from fundamental studies—such as investigations of the effects of wing sweep on dynamic stability and control—to detailed evaluations of the flight behavior of specific configurations—such as the spin resistance and spin recovery characteristics of highly maneuverable military aircraft. During these investigations, the test crew assesses the general controllability of the model and inherent problems such as uncontrollable oscillations or failure to recover from spins. The crewmembers also evaluate the effects of artificial stability augmentation systems, airframe modifications, and auxiliary devices, such as emergency spin recovery parachutes. Time histories of motion parameters—including model attitudes, angular rates, linear accelerations, angles of attack and sideslip, airspeed, and control positions—are recorded for analysis and correlation with full-scale results and other analysis methods. Aerodynamic data for the free-flight model can be extracted from the modelflight results, and most models can be used in conventional static wind tunnel tests as well as specialized dynamic force tests. The results of free flight testing are extremely valuable during aerospace vehicle development programs because potentially undesirable or even catastrophic behavior can be identified at an early design stage, permitting modifications to be incorporated into the design for satisfactory characteristics. In addition, the data provide awareness and guidance to test and evaluation organizations of potential problems in preparation for and during subsequent flight tests of the full-scale vehicle. The payoff is especially high for unconventional or radical configurations with no existing experience base.</p>

 

 

    <div class="image"><img alt="Fig 5- Bowman Patton Burk L-74-07645.tif" class="calibre3" src="../Images/fig_5-_bowman_patton_b_fmt.jpeg" /></div>

 

 

    <div class="calibre1">

      <p class="caption">Predictions obtained from dynamic model tests are routinely correlated with results from aircraft flight-testing. In a classic NASA study of spinning characteristics of general-aviation configurations, tests were conducted with, right to left: a spin tunnel model, a radio-controlled model, and the full-scale aircraft. Langley test pilot Jim Patton, center, and researchers Jim Bowman, left, and Todd Burk pose with the test articles.</p>

    </div>

 

 

    <p class="subhead">Role of Free-Flight Testing</p>

 

 

    <p class="paragraph">Free-flight models are complementary to other tools used in aeronautical engineering. In the absence of adverse scale effects, the aerodynamic characteristics of the models have been found to agree very well with data obtained from other types of wind tunnel tests and theoretical analyses. By providing insight as to the impact of aerodynamics on vehicle dynamics, the free-flight results help build the necessary understanding of critical aerodynamic parameters and the impact of modifications to resolve problems. The ability to conduct free-flight tests and aerodynamic measurements with the same model is a powerful advantage for the testing technique. When coupled with more sophisticated static wind tunnel tests, computational fluid dynamics methods, and piloted simulator technology, these tests are extremely informative. Finally, the very visual results of free-flight tests are impressive, whether they demonstrate to critics and naysayers that radical and unconventional designs can be flown or identify a critical flight problem for a new configuration.</p>

 

 

    <p class="paragraph">As might be expected, conducting and interpreting the results of free-flying model tests requires expertise gained by continual feedback and correlation with fight results obtained with many full-scale aircraft. Model construction techniques, instrumentation, and control technologies are constantly being improved. Facilities and equipment must be updated, and radical unconventional aircraft configurations may require modifications to the facilities and testing techniques. NASA staff members have accumulated extensive expertise and experience with the technology of free-flight models, and as a result, the aerospace community seeks them out for consultation, advice, and cooperative studies. The physical facilities and human resources acquired and nurtured by the Agency in the science and art of free-flight testing has made extremely valuable contributions to civil and military programs.</p>

 

 

    <p class="paragraph">Later sections of the document will provide overviews of the conception and development of free-flight testing techniques by NACA and NASA researchers as well as selected contributions made to specific aerospace programs. Before these topics are discussed, however, a review of the specific scaling procedures required for dynamic free-flight models will provide additional background and understanding of the model construction details and the testing procedure. In addition, observations regarding the constraints and limitations involved in free-flight model testing are presented.</p>

 

 

    <p class="subhead">Principles of Dynamic Scaling</p>

 

 

    <p class="paragraph">To obtain valid results from free-flight model test programs, the model must be designed and constructed in a specific manner that will ensure that its motions are similar to motions that would be exhibited by the full-scale article. Dynamically scaled free-flight models are not only geometrically scaled replicas; they are specially designed to ensure motion similitude between the subscale model and the full-scale subject. When a geometrically similar model of an aircraft reacts to external forces and moves in such a manner that the relative positions of its components are geometrically similar to those of a full-scale airplane after a proportional period of time, the model and airplane are referred to as “dynamically similar,” bringing about a condition known as dynamic similitude. When properly constructed and tested, the flight path and angular displacements of the model and vehicle will be geometrically identical, although the time required for selected motions of each will be different and require the application of mathematical factors for interpretation of the results.</p>

 

 

    <p class="paragraph">The requirements for scaling may be visualized with the help of the accompanying graphic, which shows the interaction between aerodynamic and inertial moments for an aircraft in a steady spin. The sketches indicate the physical mechanisms that determine the balance of moments that occur about the pitch axis during the spin. The sketch on the left shows that, at spin attitudes, an airplane experiences very high angles of attack, which usually results in a nose-down aerodynamic pitching moment. This nose-down moment is balanced by the inertial pitching moment depicted in the sketch at the right. In the right-hand sketch, the mass distribution of the airplane is represented by a system of weights along the fuselage and wings. As the weights rotate about the spin axis, centrifugal forces acting perpendicular to the spin axis create a nose-up inertial pitching moment, attempting to align the fuselage perpendicular to the spin axis. For the steady developed spin, the nose-up inertial moment balances the nose-down aerodynamic moment.</p>

 

 

    <div class="image"><img alt="Fig 6- Aero and Inertia Spin copy.tif" class="calibre3" src="../Images/fig_6-_aero_and_inerti_fmt.jpeg" /></div>

 

 

    <div class="calibre1">

      <p class="caption">Sketch illustrating the balance of nose-down aerodynamic pitching moments and nose-up inertial pitching moments during a steady spin. The balance of these moments will largely determine the spin rate and angle of attack of the spin.</p>

    </div>

 

 

    <p class="paragraph">It is readily apparent that the balance of aerodynamic and inertial parameters must be similar between the model and full-scale aircraft if the spin rate and angle of attack are to be dynamically reproduced. If, for example, the mass distribution of the model results in inertial nose-up loads that are too low compared with scaled airplane loads, the aerodynamics of the model will be grossly out of balance and possibly dominate the conditions of motion. On the other hand, if the aerodynamic moments are insufficient, the inertial moments will unrealistically determine the motions. Obviously, predictions of full-scale characteristics based on these conditions would be in error.</p>

 

 

    <p class="paragraph">In addition to geometric scale requirements for the model (such as wingspan, length, and wing area), scale ratios of force, mass, and time must also be maintained between the model and full-scale article for dynamic similitude.<span><a href="../Text/index_split_012.xhtml#anchor-5-anchor-chp01">1</a></span> The fundamental theories and derivation of scaling factors for similitude for free-flight models are based on the broad science known as dimensional analysis. The derivations of dynamic-model scale factors from dimensional analysis were developed during the earliest days of flight and will not be repeated here. Rather, the following discussion provides an overview of the critical scaling laws that must be maintained for rigid (nonaeroelastic) free-flight models in incompressible and compressible flow fields.<span><a href="../Text/index_split_012.xhtml#anchor-4-anchor-chp01">2</a></span></p>

 

 

    <p class="subhead">Rigid-Body Dynamic Models</p>

 

 

    <p class="paragraph">The simplest type of dynamic free-flight model is known as the rigid-body model. As implied by the name, a rigid-body model does not attempt to simulate flexible structural properties such as aeroelastic bending modes or flutter properties of the full-scale article. However, even these simple models must be scaled according to mandatory relationships in each of the primary units of mass, length, and time to provide flight motions and test results directly applicable to the corresponding full-scale aircraft. Units of model length such as wingspan are, of course, scaled from geometric ratios between the model and full-scale vehicle, units of model mass (weight) are scaled from those of the full-scale vehicle on the basis of a parameter known as the relative density factor (measure of model mass density relative to an atmospheric sample), and model time is scaled on the basis of a parameter known as the Froude number (ratio of inertial to gravitational effects). From these relationships, other physical quantities such as linear velocity and angular velocity can be derived. For most applications, the model and full-scale aircraft are tested in the same gravitational field, and therefore linear accelerations are equal between model and full scale. To conduct meaningful tests using free-flight models, the scaling procedures must be followed during the construction, testing, and data analysis of a dynamic model. Simply scaling geometric dimensional characteristics without regard for other parameters can produce completely misleading results.</p>

 

 

    <p class="subhead">Incompressible Flow</p>

 

 

    <p class="paragraph">Many of the free-flight dynamic model tests conducted by the NACA and NASA in research efforts have involved investigations of rigid models for conditions in which Mach number and compressibility were not major concerns. For these incompressible flow conditions, the required scale factors for dynamic models are given in the following table:</p>

    <hr class="calibre4" />

    <!-- Begin Table Info-->

 

 

    <p class="tableHeadings">Scale Factor</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Linear dimension</span> = n</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Relative density (m/&#961;l3)</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Froude number (V2/lg)</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Angle of attack</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Linear acceleration</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Weight, mass</span> = n3/&#963;</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Moment of inertia</span> = n5/&#963;</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Linear velocity</span> = n1/2</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Angular velocity</span> = 1/ n1/2</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Time</span> = n1/2</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Reynolds number</span> = (Vl/&#957;) n1.5&#957;/&#957;0</p>

 

 

    <p class="paragraph"><em class="calibre5">Scale factors for rigid dynamic models tested at sea level. Multiply full-scale values by the indicated scale factors to determine model values, where n is the ratio of model-to-full-scale dimensions, &#963; is the ratio of air density to that at sea level (&#961;/&#961;0), and &#957; is the value of kinematic viscosity.</em></p><!-- End Table Info-->

    <hr class="calibre4" />

 

 

    <p class="paragraph">Certain characteristics of rigid-body dynamic models are apparent upon examination of the factors given in the table. The required parameters of relative density and Froude number are maintained equal between model and aircraft (scale factor of 1), as are linear accelerations such as gravitational acceleration. The model and aircraft will exhibit similar flight behavior for the same angles of attack and dynamic motions. For example, following a disturbance at a specific angle of attack, the ensuing damped oscillations will be identical in terms of the number of cycles required to damp the motions for the model and aircraft.</p>

 

 

    <p class="paragraph">As shown in the below table, however, other motion parameters vary markedly between model and aircraft. For example, for a 1/9-scale model (n=1/9), the linear velocities of the model (flight speeds) will only be 1/3 of those of the aircraft, but the angular velocities exhibited by the model in roll, pitch, and yaw will be 3 times faster than those of the airplane. Because the model’s angular motions are so much faster than those of the airplane, the models may be difficult to control. Many dynamic model testing techniques developed by NASA meet this challenge by using more than one human pilot to share the piloting tasks.</p>

 

 

    <p class="paragraph">Another important result of dynamic scaling is that large differences in the magnitude of the nondimensional aerodynamic parameter known as Reynolds number (ratio of inertial to viscous forces within the fluid medium) will occur. In other words, as a result of dynamic scaling, the model is tested at a much lower value of Reynolds number than that of the full-scale airplane for comparable flight conditions. A 1/9-scale dynamic model is typically tested at a value of Reynolds number that is only 1/27 that of the airplane for sea level conditions. As will be discussed, this deficiency in the magnitude of Reynolds number between model and aircraft can sometimes result in significant differences in aerodynamic behavior and lead to erroneous conclusions for certain aircraft configurations.</p>

 

 

    <p class="paragraph">An examination of design specifications for dynamically scaled models of a typical high-performance military fighter and a representative general-aviation aircraft provides an appreciation for the impact of dynamic scaling on the physical properties of the models:</p>

    <hr class="calibre4" />

    <!--Begin Table Info-->

 

 

    <p class="paragraph"><span class="tableHeadings1">Fighter Model (n=1/9)</span> = Geometric scale<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 1.0<br class="calibre1" />

    <span class="tableHeadings1">Model</span> = 1/9</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Fighter Model (n=1/9)</span> = Wingspan<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 42.8 ft<br class="calibre1" />

    <span class="tableHeadings1">Model</span> = 4.8 ft</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Fighter Model (n=1/9)</span> = Weight (a)<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 55,000 lbs<br class="calibre1" />

    <span class="tableHeadings1">Model</span> = 75.5 lbs</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Fighter Model (n=1/9)</span> = Weight (b)<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 55,000 lbs<br class="calibre1" />

    <span class="tableHeadings1">Model</span>= 201.9 lbs</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">General-Aviation Model (n=1/5)</span> = Geometric scale<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 1.0<br class="calibre1" />

    <span class="tableHeadings1">Model</span> = 1/5</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">General-Aviation Model (n=1/5)</span> = Wingspan<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 36 ft<br class="calibre1" />

    <strong class="calibre6">Model</strong> = 7.2 ft</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">General-Aviation Model (n=1/5)</span> = Weight (c)<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 2,500 lbs<br class="calibre1" />

    <span class="tableHeadings1">Model</span> = 20 lbs</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">General-Aviation Model (n=1/5)</span> = Weight (d)<br class="calibre1" />

    <span class="tableHeadings1">Airplane</span> = 2,500 lbs<br class="calibre1" />

    <span class="tableHeadings1">Model</span> = 27 lbs</p>

 

 

    <p class="paragraph"><em class="calibre5">Design results for models of representative rigid-body, general-aviation, and fighter models. Notes for weight data = (a) denotes full-scale airplane at sea level and model at sea level, (b) full-scale airplane at 30,000 ft and model at sea level, (c) full-scale airplane at sea level and model at sea level, and (d) full-scale airplane at 10,000 ft and model at sea level.</em></p><!---End Table Info-->

    <hr class="calibre4" />

 

 

    <p class="paragraph">These data vividly demonstrate that dynamically scaled free-flight models weigh considerably more than would conventional hobbyist-type, radio-controlled models of the same geometric scale, and that the task of using a model at sea level to simulate the flight of a full-scale aircraft at altitude significantly increases the design weight (and therefore flight speed) of the model. The scaling relationships result in challenges for the dynamic-model designer, including ensuring adequate structural strength to withstand operational loads and crashes; providing adequate onboard space for instrumentation, recovery parachutes, and control actuators while staying within weight constraints; and matching flight speeds with those of wind tunnel facilities. Typically, a large number of preliminary trade studies are conducted to arrive at a feasible model scale for the altitude to be simulated in the flight tests. In some cases, the final analysis may conclude that the weight/payload/strength compatibility issues cannot be met for the type of testing under consideration.</p>

 

 

    <p class="paragraph">In addition to addressing weight considerations, the designer must also meet scaling laws to simulate the mass distribution properties (moments of inertia) expected for the full-scale aircraft. Using data or estimates of the weight and center of gravity of various model components and equipment, calculations are initially made of mass moments of inertia about each of the three aircraft axes to determine inertias in pitch, roll, and yaw for the model. After the model is fabricated, experimental methods are used to measure the moments of inertia of the model, with all systems installed to ensure that the values obtained approach the values prescribed by the scaling requirements. The experimental methods used to measure inertias are based on observations of the times required for periodic oscillations of the model when forced by a mechanical spring apparatus, or pendulum-type motions of the model mounted to suspension lines. Using theoretical relationships for the motions and period of the oscillation, the inertias can be calculated. The inertia requirements and distribution of mass in the model can be a very severe design challenge, especially for powered models with heavy engines displaced along the wing.<span><a href="../Text/index_split_012.xhtml#anchor-3-anchor-chp01">3</a></span></p>

 

 

    <p class="paragraph">While the model satisfied geometrical, mass, and weight scaling constraints, the designer may also have to provide an appropriate propulsion system. Propulsion techniques used by NASA in its flying models have included unpowered gliders, conventional internal-combustion engines, tip-driven fans powered by compressed air, compressed-air thrust tubes and ejectors, turbojets, and electric-powered turbofans. The use of power systems and the degree of sophistication involved depends on the nature of the tests and the type of data desired. For example, free-flight investigations of spinning and spin recovery are conducted with unpowered models, whereas free-flight studies of powered-lift vertical take-off and landing (VTOL) aircraft require relatively complex simulation of the large effects of engine exhaust on the aerodynamic behavior of a model. Model propulsion units used to simulate current-day turbofan engines are especially complex.</p>

 

 

    <p class="paragraph">Another challenge for the designer of a dynamic free-flight model is the selection of control actuators for aerodynamic control surfaces. The use of a proportional control system in which a deflection of the control stick results in a proportional deflection of the control surface may be suitable for precision control of larger models. However, because small, dynamically scaled models exhibit rapid angular motions, the use of rapid full-on, full-off “flicker” type controls may be required.</p>

 

 

    <p class="subhead">Compressible Flow</p>

 

 

    <p class="paragraph">Critical aerodynamic parameters for aerospace vehicles may change markedly when compressibility effects are experienced as flight speeds increase. Mach number, the ratio of aircraft velocity to the velocity of sound in the compressible fluid medium in which the aircraft is flying, is required to be the same for aircraft and model for similitude when compressibility effects dominate. Although the Mach number based on the speed of the complete aircraft may be low, in some cases, significant compressibility effects may be present on components of the vehicle. For example, flow over the upper surface of a wing with a thick high-lift airfoil at high angles of attack may experience Mach numbers approaching 1, even though the aircraft’s flight speed may be as low as Mach 0.3. As the local flow approaches transonic Mach numbers, severe flow separation can occur because of interactions of shock waves formed on the wing and the wing’s boundary layer flow. In turn, flow separation can cause undesirable dynamic motions such as wing drop or instability in pitch. When Mach number effects are expected to dominate, another set of scaling laws must be used for compressible-flow conditions:</p>

    <hr class="calibre4" />

    <!--Beging Table Info-->

 

 

    <p class="subhead">Scale Factor</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Linear dimension</span> = n</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Relative density (m/&#961;l3)</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Mach number</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Froude number (V2/lg)</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Angle of attack</span> = Dependent on Froude scaling</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Linear acceleration</span> = 1</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Weight, mass</span> = n3/&#963;</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Moment of inertia</span> = n5/&#963;</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Linear velocity</span> = n1/2</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Angular velocity</span> = 1/n1/2</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Time</span> = n1/2</p>

 

 

    <p class="paragraph"><span class="tableHeadings1">Reynolds number</span> = (Vl/&#957;) n1.5&#957;/&#957;0</p>

 

 

    <p class="paragraph"><em class="calibre5">Scale factors for rigid dynamic models when matching Mach number. Multiply full-scale values by scale factors to determine model values, where n is the ratio of model-to-full-scale dimensions, &#963; is the ratio of air density to that at sea level (&#961;/&#961;0), and &#957; is the value of kinematic viscosity.</em></p><!--End Table Info-->

    <hr class="calibre4" />

 

 

    <p class="paragraph">To maintain equivalent Mach numbers between model and aircraft, the previously discussed similitude requirements for Froude number (V2/lg) can no longer be met without an unfeasible change in the gravitational field. One result of this deficiency is that the model must be flown at a different angle of attack than the full-scale vehicle. The model will be at a lower angle of attack than the full-scale aircraft while flying at the same Mach number. With this discrepancy in mind, NASA’s applications and experiences with free-flying models for dynamic motion studies have included incompressible and compressible conditions with properly scaled models.<span><a href="../Text/index_split_012.xhtml#anchor-2-anchor-chp01">4</a></span></p>

 

 

    <p class="subhead">Limitations and Interpretation of Results</p>

 

 

    <p class="paragraph">Unfortunately, all the similitude requirements previously discussed cannot be duplicated in every respect during model testing. Use of the dynamic model test techniques therefore requires an awareness of the limitations inherent to the techniques and an accumulation of experience in the art of extrapolating results to conditions that cannot be directly simulated. In addition, results should not be extended beyond their intended areas of application.</p>

 

 

    <p class="paragraph">Unquestionably, the most significant issue involved in free-flight testing is the discrepancy in values of Reynolds number between the model and full-scale vehicle.<span><a href="../Text/index_split_012.xhtml#anchor-1-anchor-chp01">5</a></span> Most of the critical flight issues studied by NASA in dynamic free-flight model tests involve partially or fully separated flow conditions, which may be significantly affected by Reynolds number. Reynolds number effects are generally configuration dependent and may be very complex.</p>

 

 

    <p class="paragraph">One of the more common Reynolds number effects of concern involves its potential effects on the variation of the magnitude and angle of attack for maximum lift. Shown in the accompanying figure are lift data measured in wind tunnel tests of a general-aviation model at values of Reynolds number representative of those used in dynamic free-flight model tests and Reynolds numbers representative of full-scale flight.</p>

 

 

    <div class="image"><img alt="Fig 7- RN on Lift copy.tif" class="calibre3" src="../Images/fig_7-_rn_on_lift_copy_fmt.jpeg" /></div>

 

 

    <div class="calibre1">

      <p class="caption">Effect of Reynolds number on lift of a general-aviation model as measured in wind tunnel tests. Data were obtained at relatively low values of Reynolds number corresponding to model free-flight tests and high values representative of full-scale flight tests. The full-scale data show a markedly higher magnitude and angle of attack for maximum lift. Primarily a function of wing geometric features, such scale effects can lead to erroneous model results.</p>

    </div>

 

 

    <p class="paragraph">The data show significant increases in the magnitude and angle of attack for maximum lift as Reynolds number increases from model conditions to the full-scale value. Such results can significantly affect the prediction of flight characteristics of the airplane near and above stall. For example, the trends shown by the data might significantly influence critical characteristics, such as spin resistance. When an aircraft is flown near the angle of maximum lift, any disturbance that results in one wing dropping will subject that wing panel to a local increase in angle of attack. If the variation of lift with angle of attack is negative (as it normally is immediately beyond maximum lift), the down-going wing will experience a loss of lift, further increasing the tendency for the wing to drop and resulting in a pro-spin propelling phenomenon known as wing autorotation. If the configuration has large Reynolds number effects, such as those shown in the sketch, the extension of the angle of attack for maximum lift at full-scale conditions may delay the spin angle of attack for the airplane to a higher value. As a consequence, the model might exhibit a steeper spin from which recovery might be relatively easy, whereas the full-scale airplane might exhibit a more dangerous spin at higher angles of attack and unsatisfactory spin recovery.</p>

 

 

    <p class="paragraph">Finally, a consideration of the primary areas of application of free-flight dynamic model testing is in order to provide a cautionary note regarding extrapolating free-flight results to other issues that are best analyzed using other engineering tools. In particular, caution is emphasized when attempting to predict pilot handling quality evaluations by using remotely piloted free-flight models. NASA’s experience has shown that remotely controlled models do not provide suitable physical cues for the pilot when trying to quantitatively rate flying qualities. Instead, these studies are best conducted with the pilot situated in the simulator cockpit, with appropriate visual and motion cues provided at full-scale values of time. Investigations of handling characteristics for precision maneuvers are much more suitably conducted using fixed or moving-base piloted simulators.</p>

 

 

    <p class="paragraph">With NASA’s awareness and cautious respect for scale effects, its success in applying dynamic free-flight models for evaluations of conventional and radical aerospace configurations over the years has been extremely good. Thousands of configurations have been tested to date using several techniques, and the results of many of the NASA investigations have included correlation with subsequent flight tests of full-scale vehicles. Subsequent sections provide overviews of some of the success stories involved in this research as well as notable lessons learned.</p>

  </div>

 

 

  <div class="calibre1" id="x5-historical-development-vers-2"></div>

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