1、r; I + 4 U 4 I NASA TN D-405 3 /?/-ooc.cc TECHNICAL NOTE 0-405 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON June 1960 (NA SA-TN-D-40 5) IN VESTIG AT ION OF H89- 70906 TANDEM-WHEEL AND BIB-JET BPRANGEHENTS FOR IPPBOVXNG BRAKING FRICTION ON YET SURFACES NASA. Langley Research Center) 21 p
2、Unclas 00105 0199045 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-L . NATIONAL INVESTIGATION AERONAUTICS AND SPACE ADMINISTRATION TECHNICAL NOTE D-405 OF TANDEM-WHEEL AND AIR-JET ARRANGEMENTS FOR INPROVING BRAKING FRICTION ON WET SURFACES By Ezias
3、lav N. Harrin SUMMARY In an attempt to improve tire braking chasacteristics on wet sur- faces at high speeds, preliminary tests were made on a tire treadmill to determine the effectiveness of two methods of clearing away water ahead of a braking wheel. rolling or idling wheel ahead of a braking whee
4、l, and the other method consisted of directing an air jet on the water-covered surface ahead of a urakiiig xhcel. 3.0Q X 7 tires (about 12 inches in diameter) on the braking wneei ald a smooth 3.00 X 7 tire on the idling wheel. In tne blowing tests, two nozzles having different diameters were used w
5、ith air-jet pressures up to about 100 pounds per square inch. Measurements of tire friction coef- ficients were made with 0.09 inch of water on the belt of the treadmill over a range of speeds from 26 to 93 feet per second. One method consisted of mounting a free- Tests were made with smooth and dia
6、mond-treaded INTRODUCTION Several investigations (refs. 1 to 4) have been made by the National Aeronautics and Space Administration to determine the braking friction characteristics of tires on wet surfaces. Theresults of these studies indicated that the braking friction coefficient decreased rapidl
7、y with increase in speed. At sufficiently high speeds the maximum braking friction coefficient was of the order of 0.1 or less. In an attempt to improve braking friction on wet surfaces at high speeds, an exploratory investigation, reported herein, was undertaken on the tire treadmill of reference 1
8、 to determine the effectiveness of two methods of clearing away water ahead of a tire. 9ne me%hod con- sisted of mounting a free-rolling or idling wheel ahead of a braking wheel (referred to as the tandem-wheel arrangement), and the other method consisted of directing an air jet on the water-covered
9、 surface ahead of a braking wheel. treaded 3.00 X 7 tires (about 12 inches in diameter) on the braking wheel. 1;leasurements of free-roll friction, maximum braking friction, Tests were made with both smooth and diamond- Provided by IHSNot for ResaleNo reproduction or networking permitted without lic
10、ense from IHS-,-,-2 and full-skid (locked wheel) friction were made at speeds from 26 to 93 feet per second. The depth of the water was 0.09 inch for all tests. APPAFUTUS AND TESTS Tandem-Wheel Arrangement The tire treadmill used in the present tests was basically the same For the as that used in th
11、e investigation reported in reference 1. tandem-wheel arrangement the treadmill equipment was modified to allow an idling or free-rolling wheel to be mounted ahead of and independently of the braking wheel as shown in figures 1 and 2. Provision was made to permit the idling wheel to be raised off th
12、e belt for tests of the braking wheel alone. Smooth and diamond-treaded 3.00 X 7 tires (about 12 inches in diameter) were used on the braking wheel. The static vertical load on the braking wheel was 100 pounds and the tire inflation pressure was the recommended 13 pounds per square inch gage. The id
13、ling wheel had a 3.00 X 7 tire which was made smooth by grinding the tread material off a diamond-treaded tire. Measurements were made with static vertical loads on the idling wheel of 23, 63, and 1.03 pounds and the tire infla- tion pressure was 13 pounds per square inch gage. The tests were made w
14、ith a water depth of 0.09 inch over a range of speeds from 26 to 93 feet per second. urements of free-roll and braking friction were made, by using the strain- gage balance described in reference 1, with and without the idling wheel in place. At a given speed setting, meas- Air-Jet Arrangement For t
15、he tests with the air jets, the idling wheel was removed from the treadmill and two air supply tubes with inside diameters of 3/16 inch were installed. (See fig. 3.) The end of one of these tubes was fitted with about a 9- inch length of tubing having an inside diameter of 1/16 inch and the other wa
16、s fitted with about a 2-inch length of tubing having an inside diameter of 1/8 inch. The ends of these smaller tubes were bent about 45 from the vertical (fig. 3) and were cut off parallel to and 1/8 inch above the belt surface. The openings were located about 1 tire diameter ahead of the axle of th
17、e braking wheel. orifice with connecting tubing was used in each of the air supply tubes 2 . A static-pressure c L 6 2 9 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3 for measuring the static pressure. and vertical load on the braking wheel as we
18、re used for the tandem-wheel arrangement. Tire friction measurements were made for a 0.09-inch depth of water over a speed range of 30 to 87 feet per second with static pressures from 0 to 103 pounds per square inch gage for both the 1/16-inch-diameter and 1/8-inch-diameter tubes. blowing from one j
19、et only. Tests were made with the same tires Each test was made with RESULTS AND DISCUSSION L 6 2 9 b Tandem-Wheel Arrangement The results of the tests with the tandem-wheel arrangement are pre- sented in figure 4 for the smooth tire and in figure 5 for the diamond- treaded tire for vertical loads o
20、n the idling wheel of 23, 63, and lo3 pounds. same time with the braking wheel alone; that is, with the idling wheel raised off the belt. Maximum braking friction coefficients, full-skid braking friction coefficients, free-ruii friction coefficient, and free- roll wheel velocity are presented as fun
21、ctions of belt velocity. friction coefficients were evaluated as described in reference 1. Also shown in these figures are results obtained at the The With the idling wheel raised off the belt, the results are similar to those reported in reference 1 and show the rapid decrease in braking friction c
22、oefficient (maximum and fill-skid), the increase in free-roll friction coefficient with increase in speed, and also the tire-planing phenomenon in which the wheel stops rotsating at sufficiently high for- ward speeds. With the idling wheel ahead of the smooth tire (fig. k), the maximum and full-skid
23、 braking friction coefficients still decreased with increase in speed but at a much reduced rate, and tire planing was eliminated up to the highest test speeds. At speeds at which the smooth tire would plane when operating alone, the use of the idling wheel increased the maximum braking coefficient
24、by an increment of about 0.18 to 0.23, the amount of increase depending on the vertical load on the idling wheel. The full-skid braking friction coefficient, however, was increased only slightly at these speeds. With the idling wheel ahead of the diamond-treaded tire (fig. ), the maximum braking fri
25、ction coefficient decreased rather slowly with increase in speed, and tire plming was not encountered up to the highest speed of the tests. At speeds at which tire planing would occur with the diamond-treaded tire operating alone, the idling wheel increased the maximum braking friction coefficient b
26、y an increment of about 0.17 to 0.22, the amount of increase depending on the vertical load on the idling wheel. There was little difference in the full-skid braking friction coefficient with and without the idling wheel in place. Provided by IHSNot for ResaleNo reproduction or networking permitted
27、without license from IHS-,-,-4 For both the smooth and diamond-treaded tires, use of the idling wheel delayed the rise in free-roll friction coefficient with increase in speed and resulted in decrements in the free-roll friction coefficient of from 0.02 to 0.06, the amount of decrease depending on t
28、he tire and the vertical load on the wheel, at the highest test speeds. It should be pointed out that the assessment of the advantage of using the tandem-wheel arrangement requires the determination of an effective braking friction coefficient based on the distribution of weight on the forward and r
29、ear wheels, with the assumption that both wheels will be braked. If the forward wheel is considered to have the braking-friction capability of the single-wheel arrangement and the rear wheel to have the capability of the braked (rear) wheel of the tandem- wheel arrangement, for a bogie gear with equ
30、al loads carried on the front and rear wheels and both wheels braked, the effective maximum braking friction coefficient at the highest speeds would be about 0.19 for a gear with smooth tires and 0.28 for a gear with diamond-treaded tires (front-wheel load lo3 pounds, figs. 4 and 3). These values re
31、present increments of 0.075 and 0.11 over the single-wheel value or the mean of two single-wheel values. However, for a weight distribution involving only 23 percent of the weight on the front wheel (front-wheel load 23 pounds, figs. 4 and 5), the values of the effective maximum braking friction coe
32、fficient are increased to 0.23 and 0.32 for the smooth and diamond-treaded tires, respectively, which are increments of about 0.16 over the single-wheel value. Air-Jet Arrangement The results of the tests with the air-jet arrangement are presented for the 1/16- and 1/8-inch-diameter nozzles in figur
33、es 6 and 7 for the smooth tire and figures 8 and 9 for the diamond-treaded tire. Results are shown for air-jet tot$-pressure values of 0, 27, 48, 83, and lo3 pounds per square inch. The results are presented in the same form as for the tandem-wheel arrangement. Examination of the results in figures
34、6 to 9 indicates that for both the smooth and diamond-treaded tires, the use of blowing reduces the usual loss in maximum braking friction coefficient with increase in speed, and at the higher pressures used, the maximum braking friction coeffi- cient becomes either constant or increases with increa
35、se in speed. In addition, with one exception, use of blowing eliminated tire planing up to the highest speed tested. friction coefficient with increase in speed is improved only slightly by use of blowing. The rise in free-roll friction coefficient with increase in speed was delayed by blowing, and
36、decrements in the free-roll friction coefficient of from 0.02 to 0.06, the amount of reduction depending on the air-jet pressure and the nozzle size, were obtained at the highest test speeds. The usual loss in the full-skid braking (. . L 6 2 9 0 L Provided by IHSNot for ResaleNo reproduction or net
37、working permitted without license from IHS-,-,-5 L 6 2 9 L The effect of blowing on the maximum braking friction coefficient is summarized in figure 10, which gives the variation of maximum braking friction coefficient with air-jet pressure at belt speeds of 35, 60, and 80 feet per second for both t
38、he smooth and diamond-treaded tires and both 1/16- and 1/8-inch-diameter air nozzles. The results shown in fig- ure 10 indicate that little or no increase in the maximum braking fric- tion coefficient was obtained by means of blowing at the lowest speed, but an increment of about 0.07 was obtained a
39、t 60 feet per second and an increment of about 0.15 was obtained at 80 feet per second. eral, at the highest speed, the 1/8-inch-diameter nozzle gave somewhat larger increases in the maximum braking friction coefficient except at the highest air- jet pressure. peak value of maximum braking friction
40、coefficient for either tire was attained at air-jet pressures of approximately 50 pounds per square inch; further increases in pressure produced no significant increase in the friction coefficient. values generally occurred at about the highest air-jet pressure of the tests (100 pounds per square in
41、ch). In gen- For the 1/8-inch-diameter nozzle, the For the 1/16-inch-diameter nozzle, the peak CONCLUDING REWEE5 The results of an investigation of a tandem-wheel arrangement and an air-jet asrangement for improving braking friction on wet surfaces indicated that significant improvements were obtain
42、ed in alleviating the usual loss in the maximum braking friction coefficient with increase in speed by both methods invest.igated. In addition, both methods generally eliminated tire planing up to the highest test speeds. For the tandem- wheel arrangement, increases in maximum braking friction coeff
43、icient ranging from increments of 0.18 to 0.23, the amount of increase depending on the vertical load on the idling wheel, were obtained at usual tire- planing speeds. The increases in maximum braking friction coefficient for a diamond-treaded tire were somewhat higher on the average than those for
44、a smooth tire. For the air-jet configuration, an increment in maxi- mum braking friction coefficient of about 0.15 was obtained with the highest blowing pressure at usual planing speeds for both 1/16- and 1/8-inch-diameter nozzles and both the smooth and diamond-treaded tires. Results of braking fri
45、ction measurements with wheel locked showed only slight improvement in the value of the full-skid friction coefficient over the speed range investigated by either method. Decrements in the free-roll friction coefficient of 0.02 to 0.06 were obtained at the highest test speeds by both methods, the am
46、ount of reduction depending on the tread, vertical load, air-jet pressure, and nozzle size. Langley Reseasch Center, National Aeronautics and Space Administration, Langley Field, Va., March 24, 1960. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6
47、mCES 1. Harrin, Eziaslav N.: Wet Surface. Low Tire Friction and Cornering Forces on a NACA TN 4406, 1958. 2. Sawyer, Richard H., Batterson, Sidney A., and Harrin, Eziaslav N.: NASA Tire-to-Surface Friction Especially Under Wet Conditions. MEMO 2-23-591;, 1959. 3. Sawyer, Richard C., and KoInick, Jos
48、eph J.: Tire-to-Surface Friction- L Coefficient Measurements With a C-123B Airplane on Various Runway 6 Surfaces. NASA TR R-20, 1959. 2 9 4. Trant, James P., Jr.: NACA Research on Friction Measurements. hoc. First Int. Skid Prevention Conf., Pt. I, Virginia Council of High- way Invest. and Res. (Cha
49、rlottesville), Aug. 1959, pp. 297-308. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-7 I rl Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-8 L-58-44. 1 Figure 2.- Closeup view of tire treadmill with tandem-wheel arrangement. c Provided by IHSNot for ResaleNo
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