1、Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1984Natural Laminar FlowExperiments on ModernAirplane SurfacesBruce J. HolmesLangley Research CenterHampton, VirginiaClifford J. ObaraKentron International, Inc.Hampton, VirginiaLong P. YipLangley Resea
2、rch CenterHampton, VirginiaNASANational Aeronauticsand Space AdministrationScientific and TechnicalInformation BranchProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Use of trademarks or names of manufacturers in this report does notconstitute an offi
3、cial endorsement of such products or manufacturers, eitherexpressed or implied, by the National Aeronautics and Space Administration.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-CONTENTS SUMMARY eeeeeeeeerrroeeee 1 INTRODUCTION .eee.eeeee.eeoe.a .
4、e 1 SYMBOLS AND ABBREVIATIONS ee.e*eeem.e. me 3 REVIEW OF PAST NATURAL LAMINAR FLOW RESEARCH . 5 . AIRPLANE DESCRIPTIONS AND CORRESPONDING EXPERIMENTS .e.m 7 Airplanes . 7 Rutan VariEze 8 Rutan Long-EZ . 8 Rutan aser Biplane Racer 9 Gates Learjet Model 28/29 Longhorn . 9 Cessna P-210 Centurion . 9 B
5、eech 24R Sierra . 9 Rellanca Skyrocket I1 . 9 Beech T-34C gloves 10 Testing Procedures . 10 Sublimating chemical detection of boundary-layer transition 10 Acoustic detection of boundary-layer transition 11 Other testing procedures 11 RESULTS I2 Wind-Tunnel VariEze Experiments 12 Transition locations
6、 . 12 Effect of fixed transition on canard . 12 Flight Experiments 13 Rutan VariEze 13 Rutan Long-EZ 14 Rutan Laser Biplane Racer 15 Gates Learjet Model 28/29 Longhorn . 16 Cessna P-210 Centurion . 16 . Beech 24R Sierra 17 Bellanca Skyrocket I1 17 Beech T-34C gloves . 19 DISCUSSION 20 rans sit ion o
7、cations . 20 Effects of Precipitation and Cloud Particles 21 Effects of Fixed Transition . 22 propeller Slipstream Effects 23 Waviness 24 Sweep Effects 24 Insect Debris contamination 25 CONCLUSIONS 26 APPENDIX . SURFACE WAVINESS ON RESEARCH MODELS . m 28 iii Provided by IHSNot for ResaleNo reproduct
8、ion or networking permitted without license from IHS-,-,-REFERENCES eeeeeeee.eeeooeeeeeeeeeeee 48 TABLES eeeeeeeeeeooeeoereeoeeeeeeeeee 52 FIGURES .r.e.eeeer.r.eoeeeeoeeeoeeeee 73 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SUMMARY Flight and win
9、d-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 X lo6 ft- and 3.08 x lo6 ft-I, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from O0 to 63O. The air
10、planes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak Locations for the test condit
11、ions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the mea- sured heights of surface waviness exceeded the empirically predicted allowable sur- face waviness. Experimental results consistent with spanwise contamination cri
12、teria were observed. Large changes in flight-measured performance and stability and con- trol resulted from loss of laminar flow by forced transition. Simulated rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on tra
13、nsition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth air- frames. The results taken as a whole indicate that significant regions of natural laminar flow
14、exist and that this boundary-layer behavior is more durable and persis- tent on certain modern practical production airplane surfaces than previously expected. INTRODUCTION In decades past, the achievement of extensive regions of natural laminar flow (NLF) was souqht as a means of increasinq airplan
15、e speed and range, However, early methods of wing manufacture and maintenance produced rough, wavy surfaces; therefore, the successful application of laminar-flow airfoils for increased performance on pro- duction aircraft was never achieved. In recent years, two major trends in airplane fabrication
16、 and operations have developed which are favorable to NLF, First, modern airframe construction materials and fabrication methods offer the potential for the production of aerodynamic sur- f aces without critical roughness and waviness. These modern techniques include com- posites, milled aluminum sk
17、ins, and bonded aluminum skins. The second modern trend favorable to NLF is the lower range of both chord and unit Reynolds numbers at which current hiqh-performance business airplanes operate. Most of these airplanes cruise at unit Reynolds numbers less than 1.5 x lo6 ft- and at chord Reynolds numb
18、ers less than 20 x lo6, Therefore, the achievement of NLF-compatible surface quality is rela- tively easy. These lower Reynolds numbers result from the shorter airfoil chord lengths (wing loadings and aspect ratios are larqer) and from the much hiqher cruise altitudes for modern airplanes. It is siq
19、nificant that NLF has been a practical reality for one category of aircraft - sailplanes. The achievement of laminar flow on sailplanes has been facil- itated by the lower chord Reynolds numbers ( 2 x 10 6 ft-1 , for the World War II high-performancefighters on which early NLF applications were atte
20、mpted; such free-stream conditionsmake the laminar boundary layer very sensitive to surface imperfections and insectcontamination.Even when the proper surface quality can be achieved, a concern which remainsthe subject of much research is the effect of operating environments on NLF maintain-ability.
21、 Past research has increased our understanding of some of the physical tran-sition phenomena resulting from exposure of laminar boundary layers to vibration,atmospheric particles (ice crystals), turbulence, and noise. Reference 28 is a sum-mary of much of this past work. The literature concludes tha
22、t airframe vibrationdoes not significantly influence boundary-layer transition for many important prac-tical applications (refs. 27 and 28). In flight, there have been no discernibleeffects observed of atmospheric turbulence on boundary-layer transition (refs. 2 to4, 8, and 28). Studies on the effec
23、ts of atmospheric particles (refs. 27 and 28)have identified the potential for significant loss of laminar flow on swept-winglaminar-flow-control airplanes during flight through high-altitude (stratospheric)ice-crystal clouds. At lower altitudes, where liquid-phase cloud particles exist,6Provided by
24、 IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-little research has been done to determine the influence of such cloud particles onlaminar flow of swept or unswept wings. Studies of the influence of noise onboundary-layer transition have shown the potential for
25、 loss of laminar flow due toturbine-engine and afterburner noise impingement on laminar surfaces (refs. 27and 28). Limited evidence exists that engine/propeller noise on piston-drivenairplanes may slightly affect transition position on NLF surfaces (ref. 10). Theliterature is not conclusive on the o
26、perational seriousness of insect contaminationand propeller slipstream disturbances to laminar flow.AIRPLANE DESCRIPTIONS AND CORRESPONDING EXPERIMENTSAirplanesEight airplanes were studied in these tests. Seven of the airplanes utilized inthe flight experiments were selected because of smooth skin s
27、urface conditions exist-ing on all or portions of the airframes. The eighth airplane utilized NLF gloves (asopposed to a production-quality wing surface). The Rutan VariEze, Long-EZ, and LaserBiplane Racer, and the Bellanca Skyrocket airplanes were constructed of compositefiberglass or carbon-fiber
28、skins over full-depth foam core or aluminum honeycombsandwich structures. The Gates Learjet Model 28/29, Cessna P-210 Centurian, andBeech 24R Sierra airplanes were constructed of aluminum structures with bonded,milled, or flush riveted skins. Waviness measurements were made on some of the sur-faces
29、of five of these airplanes. (See appendix.) The eighth airplane was a Beech-T-34C airplane fitted with laminar-flow airfoil gloves on the left wing; these glovedsections were used to develop boundary-layer transition measuring techniques and fortransition measurements in the propeller slipstream to
30、support related experimentalresults.A wind-tunnel investigation was conducted in the Langley 30- by 60-Foot Tunnelto study the aerodynamic characteristics of an advanced canard configuration air-plane, the VariEze (see ref. 29). The experiments specifically provided data on thefollowing: (1) Transit
31、ion locations on the wing, winglet, and canard; and (2) theeffect of fixed transition on canard aerodynamics caused by either artificial rough-ness or by water-spray simulated rain.Table 2 is a listing of descriptive photographs, drawings, unique airframe fea-tures and construction, experiments cond
32、ucted, and test conditions for each airplane.The flight experiments for all airplanes included, as a minimum, visual observationof transition locations for various airframe components. Other experiments includedstudies of the effects of fixed boundary-layer transition on the performance andmaximum l
33、ift of the Bellanca Skyrocket, Rutan VariEze, and Rutan Long-EZ airplanes;fixed-transition effects on stability and control were studied in the VariEze andLong-EZ. Some of the airplanes utilized more extensive flight-test instrumentationthan others. For example, chordwise pressure measurements and a
34、irfoil wake surveyson the Skyrocket provided section lift and drag data, respectively. Boundary-layerrakes provided measurements of laminar-flow behavior as affected by propeller slip-stream on the Skyrocket, and hot-film sensors provided similar information for theBeech T-34C.Rutan VariEze.- Flight
35、 and wind-tunnel experiments were conducted with a pusher-propeller, two-place airplane type with a high-aspect-ratio canard. (See fig. 1.)The airplane physical characteristics and design coordinates are presented intables 3 and 4. The flight-test airplane is shown in figure 2. The only significantd
36、ifference between the full-scale wind-tunnel model and the flight article was the7Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-installation of an outboard leading-edge droop on the flight-test airplane. Bothairframes were constructed using composi
37、te structures of full-depth foam core andfiberglass skins. The airfoil surfaces on the wind-tunnel model were filled andsanded to conform accurately to the airfoil design contours.Both the wind-tunnel and flight experiments with this configuration includedvisual determination of transition on the wi
38、ng, winglet, and canard surfaces, andmeasurement of the effect of fixed transition (using the method of ref. 30) of wing,winglets, and canard on airplane performance and stability and control. The flightexperiments included observation of the effect of flight through clouds on boundary-layer transit
39、ion (using acoustic transition detection). The calibrated airspeedrange of the flight tests was from 65 to 148 knots. Flight transition data using asublimation technique were taken at a unit Reynolds number of 1.4 x 106 ft-1.Static-force data and boundary-layer flow visualization data were collected
40、 withthe wind-tunnel model mounted on an external balance system in the Langley 30- by60-Foot Tunnel as shown in figure 3. The canard mount was isolated from the model byan internal strain-gage balance, and canard force data were collected simultaneouslywith model force data. Tests were conducted ov
41、er a range of angle of attack from-60 to 400 and a range of sideslip from -150 to 150. The nominal dynamic pres-sure of the tests was 10.5 psf which corresponds to a unit Reynolds number of0.625 x 106 ft-1.Chordwise pressure distribution data were recorded from four spanwise stationson the canard at
42、 T1 = 0.26, 0.53, 0.79, and 0.95. The effect of rain was simulatedin the wind tunnel by water spray from a horizontal airfoil-shaped boom located aheadof the canard as diagrammed in figure 4. Nozzles pointed downstream and located onthe boom sprayed water droplets of about 200-m volume mean diameter
43、 at a total flowrate of 1 gal/hr at 60 psi. The boom span of about 6 ft covered the right canardsemispan. The height of the boom was varied such that water spray enveloped thecanard throughout the angle-of-attack range.Rutan Long-EZ.- Flight experiments were also conducted on a two-place, pusher-pro
44、peller airplane type similar to the VariEze. The airplane configuration utilizeda high-aspect-ratio canard with different wings and winglets than the VariEze. Twodifferent Long-EZ airplanes were tested to verify the repeatability of the transitionresults. The only differences in these airplanes were
45、 the size of wheel fairing usedto aerodynamically fair the main wheels and the size and shape of the rudder sur-faces. Figure 5 contains a sketch of the geometry of these airplanes as designed,and table 5 is a list of the detailed geometric characteristics. Figure 6 is a pho-tograph of one of the tw
46、o Long-EZ airplanes tested. The design coordinates for theNLF airfoil on the wing and winglets are given in table 6. The canard airfoil isidentical to that of the VariEze (coordinates given in table 4). The composite air-frame was built using full-depth foam core with fiberglass skins.The experiment
47、s conducted with this airplane included visual observations oftransition on the wing, winglet, canard, fuselage nose, and wheel fairings. In addi-tion, the effect of fixed transition on airplane performance and stability and con-trol was determined. The indicated airspeed range for these tests was 6
48、5 to158 knots at density altitudes of 4700 to 7500 ft. The maximum unit Reynolds numberduring testing was 1.51 x 106 ft-1 . When only Vi was available for data reductionpurposes, it was assumed that the position error was zero.Rutan Laser Biplane Racer.- A single-place biplane with large negative-staggerand a tractor-propeller (figs. 7 and 8) was tested in flight. Detailed physical8Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-characteristics of the airplane are shown in table 7. The wing airfoil design coor-dinates are given in table 8. Th
