1、NASA TECHNICAL NOTEoONO13-1 (SSINASA TN D-6964woAN EVALUATION OF SOME UNBRAKED TIRECORNERING FORCE CHARACTERISTICSby Trafford J. W. IcelandLangley Research CenterHampton, Va. 23365NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. NOVEMBER 1972Provided by IHSNot for ResaleNo reproductio
2、n or networking permitted without license from IHS-,-,-1. Report No.NASA TN D-69644. Title and SubtitleAN EVALUATION OF SOMECORNERING FORCE CHARA2. Government Accession No.UNBRAKED TIRECTERISTICS7. Author(s)Trafford J. W. Leland9. Performing Organization Name and AddressNASA Langley Research CenterH
3、ampton, Va. 2336512. Sponsoring Agency Name and AddressNational Aeronautics and Space AdministrationWashington, D.C. 205463.5.6.8.10.11.13.14.Recipients Catalog No.Report DateNovember 1972Performing Organization CodePerforming Organization Report No.L-8351Work Unit No.501-38-12-02Contract or Grant N
4、o.Type of Report and Period CoveredTechnical NoteSponsoring Agency Code15. Supplementary Notes16. AbstractAn investigation to determine the effects of pavement surface condition on the cor-nering forces developed by a group of 6.50 x 13 automobile tires of different tread designwas conducted at the
5、Langley aircraft landing loads and traction facility. The tests weremade at fixed yaw angles of 3, 4.5, and 6 at forward speeds up to 80 knots on twoconcrete surfaces of different texture under dry, damp, and flooded conditions. Theresults showed that the cornering forces were extremely sensitive to
6、 tread pattern andrunway surface texture under all conditions and that under flooded conditions tire hydro-planing and complete loss of cornering force occurred at a forward velocity predictedfrom an existing formula based on tire inflation pressure. Further, tests on the dampconcrete with a smooth
7、tire and a four-groove tire showed higher cornering forces at ayaw angle of 3 than at 4.5; this indicated that maximum cornering forces are developedat extremely small steering angles under these conditions.17. Key Words (Suggested by Author(s)Automobile tiresTire cornering forcesTire hydroplaningSu
8、rface texture19. Security Classif. (of this report)Unclassified18. Distribution StatementUnclassified Unlimited20. Security Classif. (of this page) 21 . No. oUnclassified 36f Pages 22. Price*$3.00For sale by the National Technical Information Service, Springfield, Virginia 22151Provided by IHSNot fo
9、r ResaleNo reproduction or networking permitted without license from IHS-,-,-AN EVALUATION OF SOME UNBRAKED TIRECORNERING FORCE CHARACTERISTICSBy Trafford J. W. LelandLangley Research CenterSUMMARYAn investigation to-determine the effects of pavement surface condition on the cor-nering forces develo
10、ped by a group of 6.50 x 13 automobile tires of different tread designwas conducted at the Langley aircraft landing loads and traction facility. The tests weremade at fixed yaw angles of 3, 4.5, and 6 at forward speeds up to 80 knots on two con-crete surfaces of different texture under dry, damp, an
11、d flooded conditions. The resultsshowed that the cornering forces were extremely sensitive to tread pattern and runwaysurface texture under all conditions and that under flooded conditions tire hydroplaningand complete loss of cornering force occurred at a forward velocity predicted from anexisting
12、formula based on tire inflation pressure. Further, tests on the damp concretewith a smooth tire and a four-groove tire showed higher cornering forces at a yaw angleof 3 than at 4.5; this indicated that maximum cornering forces are developed atextremely small steering angles under these conditions.IN
13、TRODUCTIONUnder dry operating conditions, almost any tire and runway or roadway surfaceprovides adequate traction for vehicle stopping and for directional control at reasonableyaw angles. Under damp or wet operating conditions, however, unacceptable losses intraction may occur which depend upon comb
14、inations of speed of operation, tire tread pat-tern and inflation pressure, and runway water depth and surface texture. A great deal ofwork on wet runway braking traction loss, reported in references 1 and 2 for example,has identified at least two wet-surface phenomena which could cause serious loss
15、es incornering force as well. These phenomena are dynamic tire hydroplaning and viscoustire hydroplaning. Dynamic tire hydroplaning, as defined in reference 3, occurs whenhydrodynamic pressures built up by water trapped in the tire-ground contact area becomeof sufficient magnitude to lift the tire o
16、ff the runway; this results in complete tractionloss and wheel spin-down. Viscous tire hydroplaning generally occurs only when smoothtires are operated on smooth surfaces, and traction loss is due to the lubricating effectof a viscous film of water between tire and ground.Provided by IHSNot for Resa
17、leNo reproduction or networking permitted without license from IHS-,-,-The purpose of this paper is to present the results of an investigation conducted atthe Langley aircraft landing loads and traction facility to determine the effect of runwaysurface condition on the cornering forces developed by
18、tires having different tread pat-terns operating unbraked at fixed yaw angles. In this investigation 6.50 x 13 automobiletires were used since the rated load was compatible with equipment limitations, and therated tire inflation pressure resulted in an easily achievable hydroplaning speed. Thetests
19、were made at yaw angles of 3, 4.5, and 6 at forward speeds up to 80 knots ontwo concrete surfaces of different texture under dry, damp, and flooded conditions. Inaddition to cornering-force-coefficient data, tire footprint photographs for nearly all testconditions were obtained through a glass plate
20、 installed in the runway surface.SYMBOLSValues are given in both SI and U.S. Customary Units. The measurements andcalculations were made in U.S. Customary Units.d water depthFQ cornering force, measured normal to wheel planeFy vertical forcep tire inflation pressuresV forward velocitytire hydroplani
21、ng velocitycornering force coefficient, F/Fyi/ yaw angleco instantaneous wheel angular velocityco0 equivalent dry runway (synchronous) wheel angular velocityProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-APPARATUS AND PROCEDUREGeneral Description of
22、 Test FacilityThe investigation was conducted at the Langley aircraft landing loads and tractionfacility described in reference 1. The test facility was adapted for this program asshown schematically in figure 1. The facility employs a water-jet catapult that developsup to 1800 kN (400 000 Ib) thrus
23、t to accelerate the test carriage to the desired speed ina distance of about 120 m (400 ft). The carriage then coasts freely on steel rails for adistance of about 360 m (1200 ft) and is stopped at the end of the run by the arrestinggear shown in figure 1. The initial carriage velocity is determined
24、by controlling thetime duration of the water jet, and during the coasting period when the tire tests are per-formed, the velocity decay is very small owing to the large mass, up to 289 kN (65 000 Ib),of the test carriage. Paralleling the main test track is a concrete-lined channel 2.4 m(8 ft) wide a
25、nd 1.5m (5 ft) deep, which was formerly used as a water channel for high-speed hydrodynamic model testing; this channel and the small test carriage used to towthe hydrodynamic models were modified as described in the next section for use in thisinvestigation.Tire Test FixtureThe model towing staff o
26、f the test carriage is offset from the main carriage struc-ture and centered over the water channel. This staff was lengthened and a fixtureattached to enable the test tires to be operated on a runway surface installed in the floorof the channel. Figure 2 is an overall view of the test carriage with
27、 a fighter nose gearattached to the towing staff extension, and figure 3 is a closeup of the tire test fixtureused in this investigation. This fixture employed an aircraft main landing-gear shockstrut modified to hold the yoke and axle assembly depicted in figure 3 and schematicallyshown in figure 4
28、(a). The shock strut was pressurized hydraulically through an accumu-lator whose internal volume was much larger than that of the shock strut; thus, an essen-tially constant down force was supplied to the yoke. The upper support structure couldbe rotated with respect to the test carriage and fixed a
29、t yaw angles from 0 up to about 10.InstrumentationIn this report, cornering force is defined as the ground force developed normal tothe plane of the tire and was measured by means of the instrumentation shown in figure 4.The shock-strut assembly was attached to the staff extension at a pivot (fig. 4
30、(a) whichallowed motion in the lateral direction only. This motion was resisted by a load cell at thetop of the shock strut, located a distance A from the pivot. This load cell was orientednormal to the tire plane (fig. 4(b) to measure cornering force directly. Since the pivotwas located a distance
31、B from the runway surface, cornering forces developed by theProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-tire at the runway were mechanically multiplied by the value of B/A at the load cell; thisprovided very sensitive and accurate load measuremen
32、ts.Wheel angular velocity was measured by an axle-driven dc voltage generator. Axlevertical position was measured by a slide wire located between the upper part of the shockstrut and the yoke, and vertical loads were monitored by a pressure transducer located inthe hydraulic accumulator. Position of
33、 the test carriage along the track was indicated bya photocell interrupter system, with triggering provided by narrow white stripes paintedat 3.05-m (10 ft) intervals on the blackened track rail support wall. All measurementswere recorded as time histories on an oscillograph recorder carried on boar
34、d the testcarriage.Test Runway InstallationThe bottom of the water channel shown in figure 2 was judged unsuitable for tiretesting because of its relatively light construction and surface unevenness. A raised,reinforced concrete test surface was therefore installed and was carefully leveled withresp
35、ect to the track rail to provide minimum vertical motion of the test tire. The teststrip was about 61 m (200 ft) long by 0.46 m (1.5 ft) wide and was raised off the channelfloor a distance of about 10 cm (4 in.) in order to fair the concrete surface into theexisting glass plate (fig. 3). The test st
36、rip consisted of five different surfaces arrangedas shown schematically in figure 5. The first 15-m (50 ft) section of testing surfacewas covered by a steel plate 6.3 mm (0.25 in.) thick, which was coated with an antiskidcompound to provide positive wheel spin-up under all wetness conditions used du
37、ringthe test program. The second 15-m (50 ft) section of testing surface was the originaltest surface and had an extremely smooth, steel-troweled finish with a surface charac-ter not unlike that commonly found on hangar or shop floors. The third 15-m (50 ft)section of test surface was provided with
38、a fine-grained textured finish created by sand-blasting the original smooth surface. This surface, although significantly rougher thanthe preceding section, was still much smoother than would be acceptable for new run-way or roadway construction. The fourth 15-m (50 ft) section was again the origina
39、lsmooth concrete surface which was faired into the glass plate that formed the fifth test-ing surface. This glass plate, which was approximately 1.2 m (4 ft) long, 0.9 m (3 ft)wide, and 5 cm (2 in.) thick, formed the top of a camera pit which was used in this inves-tigation to obtain still photograp
40、hs of water action in the tire footprint.Test TiresThe tires used in this investigation were all 6.50 x 13, 4-ply-rating automobiletires having different tread patterns as shown in figure 6. The smooth tire of figure 6(a)was specially molded for this investigation and had a tread thickness equivalen
41、t to a newProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-tire, but had no tread pattern. The four-groove tire of figure 6(b) was also speciallymolded and had a tread pattern consisting of four straight, evenly spaced circumferentialgrooves about 4.6
42、 mm (0.18 in.) wide and 6.3 mm (0.25 in.) deep. The tire of figure 6(c)was a standard production tire having four evenly spaced zigzag circumferential groovesalso 6.3 mm (0.25 in.) deep and a regular arrangement of fine slits or sipes cut into thetread ribs. The tire of figure 6(d) was an early expe
43、rimental tire of radial-ply construc-tion, as opposed to the conventional bias-ply construction of the other test tires. Thetread pattern was similar to the production tire of figure 6(c), with the addition of largezigzag grooves cut transversely into the shoulder ribs. The tires shown in figures 6(
44、e)and (f) were similar in all respects to the four-groove tire of figure 6(b) but with themodifications shown. The four-groove dimpled tire of figure 6(e) had a series of regu-larly spaced 3.2-mm-diameter (0.125 in.) holes approximately 6.3 mm (0.25 in.) deepdrilled in the shoulder rib, whereas the
45、four-groove slotted tire of figure 6(f) had a seriesof straight slots cut into the shoulder rib at 2.5-cm (1 in.) intervals, each slot beingapproximately 3.2 mm (0.125 in.) wide and 6.3 mm (0.25 in.) deep.Testing ProceduresFor all phases of the test program, the tire inflation pressure was set at 18
46、.6 N/cm(27 Ib/in) and maintained at this level through periodic checks. The vertical load wasalso held constant, through the hydraulic loading system described previously, at 3.71 kN(835 Ib). The variable parameters for most test tires included forward velocity, yawangle, and test surface condition,
47、 although not all tires were tested at all conditions. Aset of five or six discrete, preselected forward velocities constituted one test series,with all other parameters held constant, and these velocities were in the range from 15to 80 knots. Three yaw angles, 3, 4.5, and 6, were investigated and t
48、hese angles werecarefully set and fixed for a.given series by using the track rail and the flat side of thesupport yoke as references. Three surface conditions were used in this investigation:namely, dry, damp, and flooded with water. In each case the entire 62-m (203 ft) lengthof the test strip was
49、 maintained at the same condition. Thus, for each surface conditionand forward velocity, cornering data were obtained on both smooth and rough concreteand a tire footprint photograph was obtained. For the damp runway tests, water wasapplied to the surface and allowed to run off. It was found that surface tension of thewater remaining created a water depth of about 1 mm (0.04 in.). This con
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