1、- - NASA TECHNICAL NOTE 0 00 ?d NASA TN D-03801 c, LOAN COPY: RETURN P,FWL (w LIL-2) iC !TI-AND AFB, N M STATISTICAL ANALYSIS OF LANDING CONTACT CONDITIONS OF THE X-15 AIRPLANE by Ronald J. Wilson Flight Research Center Edwards, Cali$ NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. J
2、ANUARY 1967 iI Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-STATISTICAL ANALYSIS OF LANDING CONTACT CONDITIONS OF THE X-15 AIRPLANE By Ronald J. Wilson Flight Research Center Edwards, Calif. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale b
3、y the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - Price $1.00 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-STATISTICAL ANALYSIS OF LANDING CONTACT CONDITIONS OF THE x-15 AIRPLANE By Ronald J. Wilson
4、 Flight Re search Center SUMMARY The landing contact conditions and slideout distances for 135 landings of the X-15 research airplane are discussed. The conditions are similar to those that might be experienced by future lifting-body reentry vehicles or other flight vehicles with low lift-drag ratio
5、s. Results are presented in the form of histograms for frequency distribu tions, and Pearson Type I11 probability curves for the landing contact condi tions of vertical velocity, calibrated airspeed, true ground speed, rolling velocity, roll angle, distance from intended touchdown point, and slideou
6、t distance. Additional statistical parameters presented for each of the de scribed conditJons are the mean, standard deviation, and the coefficient of skewness . INTRODUCTION Statistical studies of landing conditions just prior to ground contact for both military and commercial aircraft have been pr
7、esented in numerous reports, for example, references 1 to 3. These studies are useful to the designer in assessing landing-load requirements and in the design of runways. In recent years intensified studies have been made of the aerodynamic, structural, and operational characteristics of lifting bod
8、ies that may be used as piloted reentry vehicles. Advantages offered by this type of vehicle are low reentry heating rates and a large reentry footprint that would enable a pilot to select his landing site. Associated studies have been made of landing contact conditions for vehicles with low lift-dr
9、ag ratios (refs. 4 and 5) in order to assess landing-load requirements. These landing studies can best be supplemented by statistical analyses of actual landing experience with flight vehicles of this type. To provide such information, analyses were made of landings of the X-15 airplane, since the X
10、-15 is the only low lift drag-ratio, skid-equipped research vehicle with a sufficient number of recorded landings to permit statistical analyses of the data. The results of the analyses are presented in this paper in terms of vertical velocity, calibrated airspeed, true ground speed, rolling velocit
11、y, roll angle, touchdown distance from intended touchdown point, and slideout distance. The data were obtained Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-from 135 landings of the X-15 airplane following research flights from the NASA Flight Rese
12、arch Center at Edwards, Calif. Measurements were taken in,U. S. Customary Units; equivalent values in the International System of Units (Si) are added throughout the paper. Details on SI, together with physical constants and conversion factors, are given in reference 6. AIRPLAKE DESCRETION AXID LAXD
13、ING CONDLTIONS The X-15 airplane is described in detail in reference 4. Briefly, the vehicle (fig. 1) is a rocket-powered research aircraft capable of attaining a /Typical lifting bodies e P2+ c I I I I I 120 160 2oo 240Velocity, knots 280 320 Figure 2.- Variation of lift-drag ratio with velocity fo
14、r various X- 15 configurations and lifting bodies (adapted from ref. 7). used in the final flare. For this type of landing approach, the lift-drag ratio varied from 1.9 to 2.5. INSTRUMENTATION AND DATA REDUCTION Such pertinent quantities as air speed, roll angle, and roll velocity were recorded on N
15、ASA internal record ing instruments. Data for calibrated airspeed (for convenience, referred to hereafter as airspeed) were obtained from impact-pressure measurements on the flow-direction sensor in the nose of the aircraft and from static-Dressure. pic,kups on the aircraft fuselage.Roll rate and ro
16、ll angle were obtained by use of rate and attitude gyros, respec tively. The measured quantities were recorded on standard oscillographs, synchronized at 0.1-second intervals by a common timer. The natural frequency and damping ratio of the recording galvanometers were 20 cps and 0.64, respec tively
17、. Recordings were accurate within -+2percent of full-scale readings. Vertical velocity at touchdown was first obtained by phototheodolite cameras and by a velocity switch installed on the X-15 skid. As sufficient data became available, the imprint of the main-gear tread on the lakebed during the fir
18、st reaction (fig. 3) was correlated with the vertical velocity at touchdown. From the correlation it was determined that the vertical velocity could be predicted by the gear-tread measurements within A0.25 ft/sec(0.076 ,/see). After the first 38 landings, vertical velocity was determined by measurin
19、g main-gear tread. True ground speed at touchdown was calculated by dividing the measured distance between the main-gear and nose-gear touchdown points on the lakebed by the time interval between main-gear and nose-gear touchdown as obtained from oscillograph records. The data are accurate within +1
20、 knot. RESULTS AND DISCUSSION Landing contact conditions for the first 135 landings of the X-15 airplane are summarized in table I. Omissions in the table result from system failures, 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Slideout distanc
21、e, m 0 10 20 30 40 50 60 70 80 90 100 110 120 130 I I I I I I I I I I I r I -I2.0 6- Skids down solid Left skid leaves A 4-11 2 4.). Centerline of nose gear mL 0 c EO .- Hypothetical centerline1E First Second v) reaction reaction 4 I Right skid leaves grounF 1 / I I I 6O 100 200 300 400 Figure 3.- M
22、ain-gear-tread skid marks on lakebed for the touchdown phase. -1.5 -1.0 -*5 E v 0 -0 t” .-E .5 v)-1.0 -1.5 -2.0 instrumentation malfunctions, and emergency conditions. The four emergency landings are noted. The landing data were analyzed statistically by using the following pro cedure: Pearson Type
23、I11 curves were fitted to the data to provide a system atic fairing and a mathematical basis for extrapolation. The computed curves Vertical velocity, m/sec 0 .61 1.22 1.83 2.44 I I I I I l6 r h8 5 6 7 0 1 2 3 4 Vertical velocity, ft/sec Figure 4.- Histogram of vertical velocity at touchdown . were
24、then compared with the observed results. Values of the statistical parameters (mean value, standard deviation, and coefficient, of skewness) used in the determination of the Pearson curves are listed in table 11. Details of the computation process are given in the appendix. Results of the computatio
25、ns are presented in figures 4 to 17 as histo grams and probability curves. Vertical Velocity Figure 4 shows the frequency distribu tion of vertical velocity at touchdown in percent of landings occurring in class intervals of 0.5 ft/sec (0.15 ,/see). For the greatest number of landings, 14.2 per cent
26、, vertical velocity was in the interval of 2.0 ft/sec to 2.5 ft/sec (0.61m/sec to 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.- 0.76 m/sec); whereas, in only 0.8 percent of the landings a vertical velocity of 7.5 ft/sec to 8.0 ft/sec (2.29 m/s
27、ec to 2.44 ,/see) was attained. The mean vertical velocity for the 135 landings was 3.4 ft/sec (1.04 m/sec).l.o?hy 2.0m/sec 3.0Vertical velocity, 2.5 I I I Pearson Type 111 probability curve 0 Observed X-15 data -.1 -* -. n n e n -.01 .001 I l l Figure 5.- Probability of equaling or exceeding variou
28、s vertical velocities during landing contact. U E 41-Jl-ll0 150_. 170 Indicated airspeed, knots Figure 6.- Histogram of airspeed at contact. Figure 5 shows the probability of equaling or exceeding given values of vertical velocity. The vertical veloc ity at a probability of 0.01 is 7.4 ft/sec (2.27
29、m/sec), which is the rate of descent that will probably be equaled or exceeded once in every 100 landings. A probability of 0.01 was selected because it represented a fair ly low probability which, at the same time, required little extrapolation of the data in the sample. One landing (flight 2-3-9)
30、was made at a vertical velocity of 9.5 ft/sec (2.90 ,/see) under emergency conditions and, thus, was not considered a normal landing. Airspeed The frequency distribution of air speed at touchdown, in percent of landings, is presented in figure 6 in class intervals of 5 knots. The great est number of
31、 landings, 18.7 percent, occurred in the interval from 180 knots to 185 knots, while only 1.6 percent were made at airspeeds between 225 knots and 230 knots. Mean airspeed was 190.5 knots. The probability dis tribution of airspeed (fig. 7) shows that 1 landing in 100 would be likely to equal or exce
32、ed 228 knots. The emergency landing on flight 2-31-52 was made at a touchdown airspeed of 251 knots with flaps up and the air plane in an overweight condition and, therefore, was not considered a probable case for this analysis. True Ground Speed The frequency distribution of true ground speed at to
33、uchdown occurring in 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-+ .- 1.0 .1 .-. n n e n .01 .001 Pearson Type 111 probability curve o Observed X-15 data 1 1 170 190 210 230 250 Indicated airspeed, knots Figure 7.- Probability of equaling or ex
34、ceeding various indicated airspeeds at contact. class intervals of 5 knots (fig. 8) in dicates that the greatest percentage (12.2) of the landings occurred in the interval from 195 knots to 200 knots. The mean was 193.0 knots. The proba bility distribution of true ground speed (fig. 9) shows that 1l
35、anding in 100 would be likely to equal or exceed 234 knots. The landing for flight 2 31-52, described in the preceding dis cussion of airspeed, was made at a true ground speed of 256 knots but was not considered a probable case for this analysis. Aircraft Rolling Velocity Rolling velocities are pres
36、ented as rolling either toward or away from the first skid to touch the runway. The frequency distributions of fig ures lO(a) and 10(b) indicate that most of the rolling velocities were between C 2 4 V e U 2 0 140 160 180 200 220 240 True ground speed, knots Figure 8.- Histogram of true ground speed
37、 at contact. Pearson Type 111 probability curve 0 Observed X-15 data .001 I I I I True ground speed, knots Figure 9.- Probability of equaling or exceeding various ground speeds at contact. 6 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Rolling vel
38、ocity, rad/sec 0 .017 .035 .052 .070 .087 .lo5 I I 35Rolling velocity, rad/sec o .ow .035 .os2 .o70 .ow .io5 I I I I I I I 30 30 VI VI Y) 25 5 25.-c0 -0 -0 -8 20 ,“ 20 c r C8k 15 a 15 a 55 r a:10 = 10E0 Ue 1U 5 5 0 1 2 3 4 5 6 0 1 Rolling velocity, deg/sec Rolling velocity, deg/sec (a) Toward first
39、skid to contact. (b) Away from first skid to contact. Figure 10.- Histogram of rolling velocity at touchdown. 0 and 0.5 deg/sec (0.009 rad/sec), either toward or away from the first skid to contact. The highest percentage of rolling velocities (30.6) falls in the range of 0 to 0.5 deg/sec (0.009 rad
40、/sec) away from first contact. In the greatest number of landings (62) the rolling velocity was away from first contact; in 43 landings, rolling velocities were toward first contact. The mean rolling velocity was 1.77 deg/sec (0.031 rad/sec) toward the first skid to contact, and 1.47 deg/sec (0.026
41、rad/sec) away from the first skid to contact. The probability distributions (figs. 11( a) and ll(b) ) indicate that in 1 landing out of 100 rolling velocity would be expected to equal or exceed 6.6 deg/sec (0.114 rad/sec) toward the first skid to contact and 6.3 deg/sec (0.110 rad/sec) away from the
42、 first skid to contact. Roll Angle The frequency distribution of the absolute roll angle at touchdown (fig. 12) shows that the greatest percentage of landings (22.9) occurred in the interval from 1.0“to 1.5“ (0.017rad to 0.026 rad) . The mean roll angle was 1.4“ (0.024 rad). The probability distribu
43、tion of roll angle (fig. 13) indicates that 1landing in 100 would be likely to equal or exceed 3.92“ (0.068 rad). 7 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-c .- Pearson Type Ill 0 Observed X-15 data probability curve Rolling velocity, rad/sec
44、 0 .04 .08 .12 .16 .20 r - 1.- -1- - I Pearson Type 111 probability curve o Observed X-15 data I 2 4 6 8 1 0 Rolling velocity, deg/sec (a) Toward first skid to contact. Rolling velocity, rad/sec 0 .04 .08 .I2 .I6 .20 1-7- I I Pearson Type 111 probability curve o Observed X-15 data .oo 0 2 4 6 8 10 R
45、olling velocity, deg/sec (b) Away from first skid to contact. Figure 11.- Probability of equaling or exceeding various values of rolling velocity at touchdown. Roll angle, rad o .02 .04 .06 .oa .io I I I I I I 1.c Roll angle, rad 0 .017 .035 .052 .070 .087 I I I I I I 25 r .1 .-.-A 0 -0 e n .01 I 0
46、1 2 3 4 5 .001 I I I I I Roll angle, deg 0 1 2 3 4 5 6 Roll angle, des Figure 12.- Histogram of absolute roll angle at touchdown. Figure 13.- Probability of equaling or exceeding various roll angles at touchdown. 8 Provided by IHSNot for ResaleNo reproduction or networking permitted without license
47、from IHS-,-,-Distance to Touchdown Point The landings included in this analysis took place on the same runway, with the intended touchdown point at the 2-mile (3219-meter) marker. DuringX-15 landings, a smoke bomb is released at the 2-mile point to serve as a reference point for the pilot and as a w
48、indage indicator. For a number of landings, pilots were assigned the task of landing as near as possible to the 2-mile marker. For this analysis, the runway threshold is referenced from the 1-mile (1609-meter) marker to account for those landings that touched down short of the intended p0in.t. Figur
49、e 14 shows the frequency distribution of the distance from the 1-mile marker to the touchdown point for 94 landings. The greatest number of landings (20.2 percent) occurred in the interval from 5000 feet to 5500 feet (1524 meters to 1676 meters) from the 1-mile marker with the mean at 5447 feet (1660 meters
