1、NASAt.f-t|Zt-ZTECHNICAL NOTE NASA TN D-2056PHENOMENA OF PNEUMATICTIRE HYDROPLANINGby Walter B. Horne and Robert C. DreherLangley Research CenterLangley Station, Hampton, VaNATIONAL AERONAUTICSAND SPACEADMINISTRATION WASHINGTON, D. C. NOVEMBER 1963Provided by IHSNot for ResaleNo reproduction or netwo
2、rking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TECHNICAL NOTE D-2056PHENOMENA OF PNEUMATIC TIRE HYDROPLANINGBy Walter B. Horne and Robert C. DreherLangley Research CenterLangley Station, Hampton, Va.NATIO
3、NAL AERONAUTICS AND SPACE ADMINISTRATIONProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-PHENOMENA OF PNEUMATIC TIRE HYDROPLANINGBy Walter B. Home and Ro
4、bert C. DreherSUMMARYRecent research on pneumatic tire hydroplaning has been collected and sum-marized with the aim of describing what is presently known about the phenomenaof tire hydroplaning. A physical description of tire hydroplaning is given alongwith formulae for estimating the ground speed a
5、t which it occurs. Eight manifes-tations of tire hydroplaning which have been experimentally observed are pre-sented and discussed. These manifestations are: detachment of tire footprint,hydrodynamic ground pressure, spin-down of wheel, suppression of tire bow wave,scouring action of escaping fluid
6、in tire-ground footprint region, peaking offluid displacement drag, loss in braking traction, and loss of tire directionalstability. The vehicle_ pavement, tire, and fluid parameters of importance totire hydroplaning are listed and described. Finally, the hazards of tire hydro-planing to ground and
7、air-vehicle-ground performance are listed, and proceduresare given to minimize these effects.INTRODUCTIONWhen runway or road surfaces become flooded or puddled with either slush orwater, both aircraft and ground vehicles such as automobiles can at some criticalground speed encounter the phenomenon o
8、f tire hydroplaning. The effects of hydro-planing can be serious to these vehicles since tires under hydroplaning conditionsbecome detached from the pavement surface and the ability of tires to developbraking or cornering traction for stopping or guiding vehicle motion is almostcompletely lost. Tire
9、 hydroplaning was first noticed and demonstrated experimen-tally about 1957 during a tire treadmill study. (See ref. i.) This investiga-tion had been prompted by the low values of tire-to-surface friction found duringwheel spin-up in landings of a large airplane on a wet runway (ref. 2) and by arash
10、 of military aircraft overrun landing accidents on wet runways. In this tiretreadmill study a small pneumatic tire riding under free rolling (unbraked) con-ditions on a water covered belt was observed to spin-down to a complete stop ata critical belt (ground) velocity. Later studies by the National
11、Aeronautics andSpace Administration on full-scale tires (refs. 3 to 9) along with actual opera-tional experience gained from aircraft take-offs and landings performed on verywet runways have further substantiated the fact that hydroplaning can create avery serious slipperiness problem to most pneuma
12、tic-tired vehicles.More recent hydroplaning research performed by the National Aeronautics andSpace Administration and the Federal Aviation Agency (refs. i0 to 17) in thisProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-country and by the Royal Aircra
13、ft Establishment (refs. 18 to 24) and others inEngland has enabled the phenomenonof tire hydroplaning to be more completelyunderstood. The purpose of this paper is to synthesize this work and previouswork with the aim of giving a physical description of tire hydroplaning alongwith definitions of the
14、 vehicle, pavementwetness, and tire conditions underwhich it can occur. Also included is a section that illustrates the various man-ifestations of hydroplaning in terms of vehicle or tire performance that havebeen uncovered to date. Finally, the hazards of tire hydroplaning to vehicleground performa
15、nce are listed and procedures are given to minimize these effects.SYMBOLSA,BAGCL,SDSdSFvFV,GFV,SgIMPfootprint regionsgross tire contact area, sq in.hydrodynamic lift coefficientdrag force due to tire rolling at peripheral speed less than groundspeed, _F, Gtire free rolling resistance, lbdrag due to
16、fluid displacement, lbfluid depth, in.vertical load on tire due to airplane or vehicle mass,Ibportion of FV supported by the runway (footprint region A infig. 3), lbvertical hydrodynamic pressure force (footprint region B infig. 5), ibacceleration due to gravity, 32 ft/sec 2tire and wheel moment of
17、inertia, slug-ft 2vehicle mass, slugsaverage ground hydrodynamic pressure, lb/sq in.tire inflation pressure, lb/sq in.FV, G + FV, S,Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-RrsIVCvGVpVSx e8PI_avlaeffP-maxskidhighway curve radius, ftunloaded ti
18、re radius, ftslip ratioposted speed limit on highway curves_ international statute milesper hourground speed, knotstire hydroplaning velocity, knots (airplanes), international statutemiles per hour (highway vehicles)vehicle sllde-out speed on highway curves, international statute milesper hourvertic
19、al load center-of-pressure displacementj ftwheel angular acceleration, radians/sec 2vertical tire deflection, ftfluid mass density, slugs/cu ftwheel angular velocity, radians/secinstantaneous tire-to-surface friction coefficientaverage friction coefficient between sllp ratios of O.10 and 0.90effecti
20、ve friction coefficient (average _ developed by aircraft asmodified by pilot braking or antl-skid system)maxlmumfriction coefficientskidding friction coefficient (friction coefficient at sllp ratioofI)PHYSICAL DESCRIPTION OF TIRE HYDROPLANINGConsider the case of an unbraked pneumatic tire rolling on
21、 a fluid coveredrunway as in an airplane take-off. As the moving tire contacts and displaces thestationary runway fluid 3 the resulting change in momentum of the fluid createshydrodynamic pressures that react on the runway and tire surfaces. In line withhydrodynamic theory, the resulting hydrodynami
22、c pressure force, acting on the tireas ground speed increases, tends to build up as the square of the ground speed,Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-as shownin figure I, for the fluid drag componentof this pressure force. Thisresult all
23、ows construction of the model of tire behavior under partial and totalhydroplaning conditions shownin figure 2.As ground speed increases, fluid inertia effects would tend to retard fluidescape in the tire-ground contact region and the fluid wedgeformed would tend todetach the tire from the ground. A
24、t somehigh ground speed the hydrodynamic liftdeveloped under the tire equals the partial weight of the vehicle acting on thetire and any further increase in ground speed beyond this critical speedmustforce the tire to lift completely off the runway surface. The critical groundspeed at which FV,S = F
25、V is termed the tire hydroplaning speed Vp. The tireis termed to be partially hydroplaning at ground speedsbelow Vp and totallyhydroplaning at ground speeds in excess of the tire hydroplaning speed Vp.DERIVATIONOFTIRE HYDROPLANINGSPEEDThe following derivation of tire hydroplaning speed is based on e
26、arlier der-ivations given in references l0 and 11. The net torques or moments acting on anunbraked wheel must, at any time, equal the inertia torque Is acting on thewheel. (See fig. 3.) Including hydrodynamic effects, the angular accelerationcan be expressed approximately as= FvCxc) - D R + DS + (F
27、V - FV_S)_(r - 5) (1)IWhen the vertical component of the hydrodynamic pressure force FV, S equals thevertical ground force FV, the tire-ground frictional moment (FV - FV,S)_(r - 5)reduces to zero, and since at this point the tire is entirely supported by thefluid on the runway, total tire hydroplani
28、ng must exist. To predict the groundvelocity VG at which this phenomenon will occur, it is assumed in line withhydrodynamic theory that the lift component of the hydrodynamic pressureforce FV, S is proportional to the tire-ground contact area AG, fluid den-sity p, and to the square of the ground spe
29、ed VG. If other possible variablessuch as the effects of tire tread design, fluid viscosity, and runway surfacetexture are ignored, and the fluid depth on the runway is assumed to be greaterthan tire tread groove depth, the following approximate expression for tirehydroplaning speed Vp may be obtain
30、ed:1Fv =Fv,s = CL,s %VP2 (2)Rearranging terms leads to the following equation which may be used to findVp in knots when AG is expressed in square inches:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Vp = 0.592(_ CL-_pj288-_I/2 (3)Recent research in
31、 the Langley landing loads track involving bogie and nose-gearstudies (refs. 12 and 13) indicates that equation (3) may be simplified toVp = 9_, knots (4)Vp = iO.35_, statute mph (5)where the tire inflation pressure p is expressed in pounds per square inch.This simplification is based on three main
32、assumptions: (i) The term Fv/A G(average tire-ground bearing pressure) in equation (3) may be approximated by thetire inflation pressure p, (2) Runway fluids which can collect in depths largeenough to produce tire hydorplaning have densities approaching that of water_ and(3) The hydrodynamic lift co
33、efficient CL, S developed by tires on a fluid coveredsurface is approximately 0.7. (See ref. ii.)It should be pointed out thatthe hydroplaning speeds obtained from equa-tions (3) and (4) are valid for smooth and closed pattern tread tires which donot allow escape paths for water, and for rib tread t
34、ires on fluid covered run-ways where the fluid depth exceeds the groove depths in the tread of these tires.Little quantitative data are yet available on the hydroplaning speeds for ribtread tires on fluid covered runways where the fluid depth is less than the groovedepth of the tread.Correlation of
35、hydroplaning speed, as determined by means of equation (4),with available experimental data is shown in figure 4. Note that the calculatedhydroplaning speeds of equation (4) are in reasonable agreement with the experi-mental hydroplaning speeds obtained for a variety of tire sizes having a verticall
36、oad range from 925 to 22,000 pounds and an inflation pressure range from 24to 150 pounds per square inch.EXPERIMENTAL OBSERVATIONS OF TIRE HYDROPLANINGSince tire hydroplaning was first demonstrated experimentally during theNACA tire treadmill tests of 1957, the following eight manifestations of hydr
37、o-planing in terms of tire or vehicle performance have been observed and aredescribed in this section of the paper: detachment of tire footprint, hydro-dynamic ground pressure, spin-down of wheel, suppression of tire bow wave,scouring action of escaping fluid in tire-ground footprint region, peaking
38、 offluid displacement drag, loss in braking traction, and loss of tire directionalProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-stability. Most of these manifestations are clearly shownin a documentary film.(See ref. 17.)Detachmentof Tire Footprint
39、In the explanation of tire hydroplaning given earlier in this paper, it wasassumedthat as ground speed increased, a wedgeof fluid progressively penetratesthe tire-ground contact region and a hydrodynamic pressure is developed betweenthe tire and the ground, the resulting hydrodynamic lift tending to
40、 detach thetire footprint from the runway surface. This effect is actually illustrated inphotographs in figures 5 and 6 for aircraft and automobile tires, respectively.these photographs were obtained during a recent hydroplaning study madeat theNASALangley landing loads track. (See ref. 13.)It is of
41、 interest to note that the portion of the footprint under the side_alls of the automobile tire (photograph (c) of fig. 6) is the last portion ofthe footprint to becomedetached as ground speed increases. This result indi-cates that higher tire-ground bearing pressures exist under the tire side wallst
42、han in other locations of the automobile tire footprint. The aircraft tirewhich was more circular in cross section and stiffer than the automobile tire didnot showthis sidewall effect (fig. 5) but a similar effect (fig. 7) appearspresent in the photograph of the small tire footprint obtained from re
43、ference 18.It is apparent from the photographs of figures 5 and 6 that as ground speedincreases, the _early dry“ contact patch developed between the rolling tire andthe ground is progressively reduced and then entirely eliminated whentotal hydro-planing is achieved.HydrodynamicGround PressureTire hy
44、droplaning speed, in an earlier section of this paper, was defined asthe ground speed required for the hydrodynamic lift acting on the tire to equalthe weight of the vehicle being supported by the tire or FV,S = FV. Stated inanother way, the tire hydroplaning speed is the ground speed required for t
45、heaverage hydrodynamic pressure acting in the tire footprint region to equal theaverage tire-ground bearing pressure or, in approximation, to equal the tireinflation pressure p. It has not been possible up to this time to measurethehydrodynamic pressure acting on the wetted surface of the tire, but
46、successfulmeasurementsof hydrodynamic pressure acting on the ground surface under the tirehave recently been madeat the Langley landing loads track. These measurementsof hydrodynamic ground pressure were accomplished with the aid of a recordingflush-dlaphragm-type pressure gage installed just below
47、the surface of the runwayat the center llne of the tire path. Typical hydrodynamic pressure signaturesobtained during tire passage over the fluid covered pressure gage are showninfigure 8. Several interesting points are suggested by the data shownin thisfigure: (1) The ground hydrodynamic pressure d
48、evelops ahead of the initial tire-ground contact point due to action of the tire bow wave, (2) The peak ground hydro-dynamic pressure is considerably in excess of the tire inflation pressure for the85-knot ground speed pressure signature, and (3) Apparently negligible hydro-dynamic ground pressures
49、are developed at the rear of the tire-ground footprintProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-at the higher ground speeds. The first and third points mentioned combinetoproduce a larger forward shift of center of pressure and consequently a l
