1、1. Report No. 2. Government Accession No. 3. Recipients Catalog No.NASA TN D-82065. Report DateJune 19764. Title and SubtitleREVIEW OF DRAG CLEANUP TESTS IN LANGLEY FULL-SCALE TUNNEL (FROM 1935 TO 1945) APPLICABLE TOCURRENT GENERAL AVIATION AIRPLANES7. Author(s)Paul L. Coe, Jr.9. Performing Organiza
2、tion Name and AddressNASA Langley Research CenterHampton, Va. 2366512. Sponsoring Agency Name and AddressNational Aeronautics and Space AdministrationWashington, D.C. 205466. Performing Organization Code8. Performing Orgamzation Report No.L-1073510. Work Unit No.505-10-11-0711. Contract or Grant No.
3、13. Type of Report and Period CoveredTechnical Note14. Sponsoring Agency Code15 Supplementary Notes16. AbstractResults of drag cleanup tests conducted in the Langley full-scale tunnel during theperiod from 1935 to 1945 have been summarized for potential application to currentpropeller-driven general
4、 aviation airplanes. Data from tests on 23 airplanes indicatethat the drag increments produced by many individual configuration features - such as,power-plant installation, air leakage, cockpit canopies, control-surface gaps, and antennainstallations - are not large; however, when the increments are
5、 summed, the resultingtotal drag increase is significant. On the basis of results of the investigation, it appearsthat considerable reduction in drag can be obtained by proper attention to details in aero-dynamic design and by adherence to the guidelines discussed in the present paper.i17. Key Words
6、 (Suggested by Author(s)Drag cleanupGeneral aviation19. Security Classif. (of this report 20. Security Classif. (of this page)Unclassified Unclassified18. Distribution StatementUnclassified - UnlimitedSubject Category 02*For sale by the National Technical Information Service, Springfield, Virginia 2
7、2161: :,- ,:,.: :!i!i!iii .i!ii i: .: - . 2: : : ,;%. _ :_“ i .iI_ _: _i_i_i:i_:_.:_IIi:(:i:i? _!.:(_:. :i.: .:= :2:.!i;, :.?:-:.:. :. _ii_ :. :):iProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-_!_ii_,_iI _ I_ii_?i_ _,_Provided by IHSNot for ResaleN
8、o reproduction or networking permitted without license from IHS-,-,-REVIEW OF DRAG CLEANUP TESTS IN LANGLEY FULL-SCALE TUNNEL(FROM 1935 TO 1945) APPLICABLE TO CURRENTGENERAL AVIATION AIRPLANESPaul L. Coe, Jr.Langley Research CenterSUMMARYResults of drag cleanup tests conducted in the Langley full-sc
9、ale tunnel during theperiod from 1935 to 1945 have been summarized for potential application to currentpropeller-driven general aviation airplanes. Data from tests on 23 airplanes indicatethat the drag increments produced by many individual configuration features - such as,power-plant installation,
10、air leakage, cockpit canopies, control surface gaps, and antennainstallations - are not large; however, when the increments are summed, the resultingtotal drag increase is significant. On the basis of results of the investigation, it appearsthat considerable reduction in drag can be obtained by prop
11、er attention to details in aero-dynamic design and by adherence to the guidelines discussed in the present paper.INTRODUCTIONThe Langley Research Center of the National Aeronautics and Space Administrationis currently engaged in a broad research program to provide the technology required forthe desi
12、gn of safe, efficient general aviation airplanes. Recently, considerable interesthas been expressed in drag reduction for general aviation airplanes. (See ref. 1.) Reduc-tions in drag would be expected to offer significant improvements in fuel economy and per-formance, and would thereby insure a str
13、ong competitive position in the domestic andforeign market for light airplanes.From 1935 to 1945, a large number of full-scale military airplanes were subjectedto drag cleanup tests in the Langley full-scale tunnel. Such tests identified sources ofdrag due both to poor design and to manufacturing pr
14、ocesses, and in addition, allowed thedetermination of suitable modifications for these poor design features. For example,cleanup tests for the Army P-39 fighter resulted in modifications which reduced the dragcoefficient of the airplane by about 35 percent and indicated a potential increase in thema
15、ximum speed of the airplane of over 44 knots. The results of cleanup tests for 23 ofthe configurations studied were summarized in reports by C. H. Dearborn, Abe Silverstein,-? 2.:i.2 : ( - .i?:C:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-stacks,
16、 etc.) was typically found to produce the largest drag increment of the items inves-tigated. Specific examples of drag-coefficient increments associated with power-plantinstallations are presented in appendix A. The drag increments may be discussed interms of drag produced by internal and external a
17、irflows.The drag increment associated with internal airflow is primarily a function of thetotal-pressure loss in ducts. For example, in a cooling duct some total-pressure lossis attributed to the cooling unit itself; however, the actual pressure loss of the installa-tion includes the losses associat
18、ed with the entire duct system, including features relatedto flow turning. If heat transfer is ignored, the power absorbed in a duct is given byP = Q Apt (1)Therefore, an efficient duct design is one for which total-pressure loss is minimized andvolumetric flow rate does not exceed the amount requir
19、ed for satisfactory cooling. Aspreviously noted, equation (1) was obtained by ignoring heat transfer; however, as shownin reference 7, some thrust is provided by the transfer of heat to the cooling air.Reference 2 indicates that, in general, efficient duct design may be obtained byadhering to the fo
20、llowing guidelines:(1) Whenever possible, duct inlets should be located on a stagnation point. Inletsat other locations should be designed to recover the full total pressure correspondingto the flight speed.(2) Bends, particularly in the high-speed section of the duct, should be avoided.If bends are
21、 required, guide vanes should be installed.(3) The duct should have a smooth internal surface with cylindrical cross sections.(4) In general, sudden changes in cross-sectional area should be avoided. Two-dimensional expansions should be limited to an included angle of 10 o, and three-dimensionalexpa
22、nsions should be limited to an included angle of 7 . An exception to this general ruleis a low-velocity expansion just ahead of a high-resistance area, in which case the expan-sion angles may be considerably higher. Also, as explained in reference 8, the expansionangles can be higher if the streamwi
23、se curvature of the duct walls is used to reduce theadverse pressure gradients and if the cooling block is located downstream to straightenthe flow.(5) The volumetric flow rate of air passing through the duct should not exceed theamount required for cooling. Since the volumetric flow rate depends up
24、on the flightcondition, provisions should be made for controlling airflow rate.(6) The volumetric flow rate of air through a duct can be efficiently controlled byvarying the area of the duct outlet. Internal shutters should be avoided.Provided by IHSNot for ResaleNo reproduction or networking permit
25、ted without license from IHS-,-,-(7) The airflow should be discharged along the contour of the aerodynamic body atthe duct outlet, and the afterbody at the duct outlet should be slightly undercut.The drag penalties due to departures from the ideal streamline shape, which areimplemented to meet power
26、-plant installation requirements, are considered power-plantdrag increments associated with external airflow. The drag increments produced byengine-associated protuberances may therefore be charged to the power-plant installa-tion. It should be noted that in the case of engine exhaust stacks, a drag
27、 increment iscaused by ejecting the exhaust gases at an angle relative to the airstream, as well as bythe actual protuberance. Furthermore, experience has shown that directing the exhaustgases rearward may provide a thrust component which is equal to about 10 percent of theinstalled thrust. Failure
28、to utilize this thrust force properly may be considered a dragpenalty.Air leakage.- The leakage of air through gaps in airplane surfaces may be properlyassociated with drag increments due to internal and/or external airflows. For example,leakage from air ducts essentially represents a reduction in m
29、omentum and is, therefore,a contributor to total-pressure loss. Furthermore, since leakage is generally normal tothe airstream, it produces a significant disturbance to the external airflow and therebyincreases the aerodynamic drag. Specific examples of drag-coefficient increments dueto leakage are
30、presented in appendix B. Because of the difficulty of isolating the dragcontribution produced solely by leakage, additional results related to this problem arediscussed under other headings. The significance of these results, in terms of dragpenalties, emphasizes the importance of sealing surfaces a
31、cross which a pressure dif-ferential exists.Wing surface irregularities.- The wing profile drag, which includes the effects ofskin friction and surface irregularities, was measured for airplanes 1 to 11. The incre-ment in drag coefficient due to roughness, rivets, joints, construction deviations, an
32、dother items was estimated by subtracting the calculated drag coefficients (based on two-dimensional smooth airfoil data) from the measured profile drag coefficient. The result-ing incremental drag coefficients and the measured boundary-layer transition points arepresented in table V. Additional exa
33、mples of the effects of surface irregularities and-roughness on wing profile drag are shown and discussed in appendix C.Investigations conducted to determine the location of the boundary-layer transitionpoints for both the smooth wings and the service-condition wings of airplanes 1 to 11showed that
34、irregularities of the production wings were generally located behind thetransition points, and were therefore in a region of turbulent flow. Comparison of themeasured profile drag coefficients for the service-condition wings with the calculatedprofile drag coefficients of the smooth wings indicates
35、that significant drag incrementsare attributable to wing surface irregularities, even when these irregularities are locatedProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-in the turbulent boundary layer. From the results presentedin table V it is rea
36、dily appar-ent that extreme care shouldbe exercised in wing construction to avoid the excessive highdrag penalties associatedwith surface irregularities. Furthermore, it shouldbenotedthat wing protuberances (for example, nonflushrivets) mayfix the point of transition fromlaminar to turbulent flow on
37、 the wing if the protuberance is located aheadof the naturaltransition point of the corresponding smoothwing. For example, ff transition for thesmoothwing occurs at 0.30_,then the addition of a row of nonflushrivets at 0.20_mayfix the boundary-layer transition at the 0.20_location. However, ff trans
38、ition for thesmoothwing normally occurs at 0.15_,then the addition of a row of rivets at 0.20_ shouldnot affect the location of the transition point. Whenthe transition point is movedforwardby the presence of the protuberances, a significant drag increment is causedby theincreased region of turbulen
39、t flow and a smaller drag increment is producedby the formdrag of the protuberance itself. Therefore, for configurations with surface irregulari-ties aheadof the boundary-layer transition point, the incremental values of drag wouldbeeven larger than those shownin table V. A detailed study of the eff
40、ects of surface irregu-larities onwing profile drag is presentedin reference 9.Landing-gear installation.- The drag increments associated with landing gear weredetermined from differences between the drag of the airplanes with the original retractedgears and that of the airplanes in a smooth conditi
41、on with gears retracted, all doors andcover plates sealed, and protruding portions faired. The results consistently indicatedthat considerable drag increments were produced by airflow disturbances caused byexposed components and air leakage. It should be noted that even in the completelyfaired condi
42、tion, inadequate sealing produced considerable drag due to leakage. Theresults obtained for specific landing-gear installations are discussed in appendix D.Cockpit canopies.- Sharp edges and short afterbodies on airplane canopies havebeen found to produce significant regions of flow separation, whic
43、h in turn leads toincreased drag. The results of tests conducted to reduce the drag increments producedby cockpit-canopy installations are discussed in appendix E.Control-surface gaps.- When seals and metal fairings were removed from the gapsassociated with control surfaces, significant drag increme
44、nts were measured. Suchcontrol-surface drag can result from several sources. Air can leak through unsealedgaps from the high-pressure side of the surface to the low-pressure side where it canexhaust normal to the stream and act as a jet spoiler. The blunt rear of the fixed finor stabilizer can also
45、cause considerable drag, both directly as profile drag and indi-rectly by inducing airflow through the airframe if there are lightening holes in the rearspar. Reference 10 indicates that such profile drag can be reduced markedly by reduc-ing the thickness of the airfoil at the blunt base of the fixe
46、d surface, so that it is thinnerthan the maximum thickness of the control surface.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-,; :;,t:;(_. _. (1:.: “:!-.,:I:A-_ ;.:_:,.1 “ “7_“.“. ! . .;. _;:;:; :7 b( : _+7L-.I.:_ ,L:j-.;:,.L_.i,I_;IS: hE,i ._c;j
47、: :.- 2-;:, OW:.) “ i .:;:“.:i_(.2.;1; L_;I(_.7;:_.: ,;:_-f-i “ ,:.:; i :7;=-:7:i,7,.; “.h77:h.iSpecific examples of drag-coefficient increments due to control-surface gaps are .presented in appendix F. iii?iiiii!):).;i.!Antenna installations.- The drag increment associated with antenna installation
48、s is ! :_f, / :=comprised of an increment due to the wires and an increment due to the mast. If exter- :h;:; :i:nal antennas are required, it is suggested that (1) the wires be positioned parallel to the :“flow and (2) the mast have a thin airfoil section. Specific examples of drag-coefficient : : -
49、:increments due to antenna installations are presented in appendix G. _iii.!ii:.CONCLUDING REMARKS _k:,:; : : S-j :, “Results of drag cleanup tests conducted in the Langley full-scale tunnel during the _L?_t_L:period from 1935 to 1945 have been summarized for potential application to current :i;:i:;:!:propeller-driven gener
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