THE UNIVERS I TY OF MI CHI GAN COLLEGE OF ENGINEERING Department of Mechanical Engineering Technical Report THE FLEXIBLE ENGINE AND ITS ACCELERATION PROBLEMS E. T. Vjinicent Kamalakar Rao ORA Proj ect 05847 under contract with: U. S. ARMY DETROIT PROCUREMENT DISTRICT CONTRACT NO. DA-20-018-AMC-0729-T DETROIT, MICHIGAN administered through: OFF:ICE OF RESEARCH ADMINISTRATION ANN ARBOR September 1965

TABLE OF CONTENTS Page LIST OF FIGURES v LIST OF TABLES vii ABSTRACT ix I. OBJECT 1 II. INTRODUCTION 2 III. METHOD OF CALCULATION 3 IV. RESULTS6 V. PERFORMANCE COMPARISON 10 VIL DISCUSSION 20 VII. CONCLUSIONS 21 VIII. APPENDIX 22 I. Engine Developments Required 22 A. Triumph 23 B. Chevrolet 23 C. M-151 Vehicle 23 II. Conclusions 23 REFERENCE 25 iii

LIST OF FIGURES Figure Page 1. Method of approximation. 5 2. Performance curves, standard vehicle on pavement. 11 3. Performance curves, flexible vehicle on pavement. 12 4. Performance curves, standard vehicle, 1.5 times pavement resistance.. 13 5. Performance curves, flexible vehicle, 1.5 times pavement resistance. 14 6. Performance curves, standard engine, 2.0 times pavement resistance. 15 7. Performance curves, flexible engine, 2.0 times pavement resistance. 16 8. Performance curves, standard engine, 3.0 times pavement resistance. 17 9. Performance curves, flexible engine, 3.0 times pavement resistance. 18 v

LIST OF TABLES Table Page I. HP Requirements on Pavement 6 II. Efficiency Employed in Different Gear Ratios 7 III. Engine BHP and Fuel Flow 7 IV. Flexible Engine Performance 8 V. Sample Machine Tabulation of Results 9 VI. Comparative Performance of Standard and Flexible Systems 19 VII. Relative Performance of Flexible System 19 VIII. M-151 Vehicle Performance at Low Speeds 24 vii

ABSTRACT This report presents the results of a study of the acceleration from zero to maximum speed of the M-151 vehicle, using the standard engine (1) coupled to the standard transmission, and (2) coupled to an ideal flexible engine transmission. The possibilities of using a flexible engine were investigated by operating three vehicles under conditions approximating Battlefield Day conditions. The slow-speed performance of the engine indicates that, if a successful flexible system is to be achieved, greater attention must be given to developments in the ignition system, carburetor, valve timing, manifolding, etc. ix

I. OBJECT The object of this study was to record the results obtained when estimating the acceleration of the M-151 vehicle fitted with the perfectly flexible engine.1 1

II. INTRODUCTION Reference 1 presented the results of an investigation of the fuel economies under Battlefield Day conditions of a perfectly flexible engine of the same performance characteristics as the L-141 engine. We demonstrated that operating the vehicle under terms of strict economy results in considerable loss of acceleration. In investigating the M-151 vehicle, the only change was that the transmission automatically accommodated the engine to the most desirable speed for minimum fuel consumption at all times. At full load and at high speed the F/A ratio was left unchanged so as not to impair the standard engine performance in the interests of economy. The results of these imposed limitations is that acceleration of the M-151 vehicle is poor, but that further fuel economies are possible by a small sacrifice in high-speed output by using a somewhat reduced F/A ratio instead of the rich F/A ratio used at full output. Such an adjustment would hardly affect the acceleration. This report presents the results of additional calculations with the perfectly flexible engine, and compares the acceleration characteristics of a vehicle with standard transmission with the acceleration characteristics of a vehicle with a perfectly flexible engine. 2

III. METHOD OF CALCULATION The relationship between time, velocity, and acceleration for small increments dt of time is given by Acceleration = change of velocity/time dv a =...Eq. (1) (1) dt a = acceleration, fps2 dv = increment of velocity, fps dt = time increment, sec. Force required for acceleration = a = F lb g F = force acting on mass w = weight accelerated, lb g = gravitational acceleration The power supplied by the engine is given by Power = work done/unit time dx dt dx = distance moved through, ft dt = time for dx, ft sec -= a dx 550 d(hp) ft lb/sec. g dt But, dx -- = velocity dt. = 550 d(hp) ft/sec...Eq. (2) (2) w v x - g d(hp) = increase in hp available for acceleration. 5

Using Equation (2), the acceleration a can be calculated at any instant when the velocity is v fps and a change d(hp) occurs in the engine output in excess of the road requirements. Equations (1) and (2) can be written in the finite difference form: At = AV (3) 17700 x A hp (4) vw Using finite differences, the time to accelerate from vl to v2 fps is given by ZAt or tvl+V = Zlv-v2 A The maximum performance of the vehicle can be calculated theoretically using Equations (3)-(5). Such calculations represent the actual acceleration from any steady speed to some higher desired speed which is achieved by suddenly applying full throttle and maintaining it until the desired speed is reached. The sequence of events is then a given hpv, at speed vl fps for the initial steady operation followed by the application of the maximum engine power hPvlmax the instant acceleration begins, which is the full-throttle output at the same rpm as the steady speed. This is followed by the gradual change in hpmax as engine speed increases as the vehicle accelerates until the desired velocity is reached. Of course, as vehicle speed increases the road resistance also increases; thus the available hp for acceleration is always given by Available hp = hmax - hProad. In Ref. 1, Fig. 1 records the ground hp at all speeds for the L-141 vehicle, and Fig. 10 is a plot of hPmax versus engine speed. It follows that the value of A hp for any initial condition is the difference between the engine hp under the desired steady road speed and the hpmax; as acceleration occurs the available hp changes with speed according to these two diagrams. This performance is then divided into suitable elements of At and the step-by-step calculation process repeated as necessary. One step of the calculation can be illustrated by Fig. 1, which shows the road resistance hp, i.e., the steady input of hp required to maintain constant velocity, and the maximum hp available at full throttle for all speeds. Divide the speed scale into a series of equal increments, say 2.5 mph; take as an example the element for 10-12.5 mph; then at point 10 mph, hpR 10 is the road resistance, while hpmax 10 is the maximum hp available. Similarly, at 12.5 mph we have hPR 12.5 and hpmax 12.5' Since it is assumed that during 4

FULL THROTTLE H.R P AVERAGE ENGINE H.P. AT FULL THROTTLE d H. P.R AVERAGE AH.P I-1 I bAHP, ROAD RESISTANCE H.P -, -n - ae- ---- AVERAGE ROAD H.R 0 5 10 12.5 15 SPEED IN MPH Fig. 1. Method of approximation. any elements of time At the A hp, etc., is also constant, the above values of output, etc., are averaged as shown in Fig. 1, and the elements are treated as being subjected to an average A hp, as shown for the time At from 10 to 12.5 mph. Equation (2) then gives the average acceleration for the element: the time At is given by vl12. = v10 + a At At v12.5-vl and the distance traveled by S = v0 At + 1 a(At)2 2 Thus acceleration, distance, and time for any range of speeds, loads, etc., can be determined by a series of calculations. 5

IV. RESULTS The data used in Calculations for the M-i51 vehicle are given in Tables I-IV, and the following conditions were investigated 1. Standard Vehicle on a. Pavement b. 1.5 x Pavement c. 2.0 x Pavement d. 530 x Pavement 2. Flexible Engine Operation of M-151 a, Pavement b. 1.5 x Pavement c. 2.0 x Pavement d. 3.0 x Pavement TABLE I HP REQUIREMENTS ON PAVEMENT hp to hp to mph Overcome mph Overcome Resistance Resistance 2.5 0.1 3550 12.5 5.0 0.3 37~5 14,7 7.5 0o5 40.0 17,3 10.0 0.96 42.5 20.5 12,5 1.30 45c0 23 9 15 0 1.90 47.5 28.0 17.5 2,70 50.0 32ol 20.0 3,550 52.5 56o6 22.5 4.80 55o0 41,0 25.0 6.oo 57o 5 46.5 27.5 7.50 60.0 51.0 50.0 8056 62.5 56.9 32,5 10o70 65.o 62.0 6

TABLE II EFFICIENCY EMPLOYED IN DIFFERENT GEAR RATIOS Gear Efficiency 1st 87.3 2nd 89.3 3rd 91.2 4th 93.1 TABLE III ENGINE BHP AND FUEL FLOW rpm bhhma iFuel Flow, lb/hr at max hp 250 4.5 5.0 500 7.3 6.0 1000 17.0 12.0 1400 28.4 16.5 1800 35.5 19.5 2200 45.0 24.0 2600 51.0 28.5 3000 54.0 30.0 5400 59.0 55.0 3800 60.0 37.5 4200 60.0 40.0 7

TABLE IV FLEXIBLE ENGINE PERFOR.MANCE Pavement Pavement Pasrement bhPmax: for Fuel Flow, bhPmax for Fuel Flow, Resistance, ^ ^ ib/hr Resistance, p/^ iesis anc nimilm Fel lb/hr nResistance,.nim'tm Fuel lb/hr hp hp 0 O 00 0.0 26.0 33.0 18.5 2.0 535 3.0 28.0 35.0 19.0 4.0 5.o 4.5 30,0 38.0 21l0 6.o 7m5 6,0 52o0 4.2.0 22.5 8.0 1.o 9.5 34.0 45.0 24.0 10o0 O150 10o5 36.0 47.0 25.5 12.0 17o0 12.0 358,0 48o0 26.0 14. 2 o 0 14.0 40,0 49.0 27.0 16.0 25o0 15.0 45.0 51 0 28.0 18o0 26,0 15o5 50.0 54.0 50.0 20.0 280 G16,5 55.0 59.0 55,0 220 50.0 17.0 o 60,0 60.0 575 24o0 32.0 18o0 Gear changes were made at appropriate points (see Table V) For example, at 10 mph on pavement the acceleration in 1st gear ends and the start of operation in 2nd gear begins. The data at 10 mph in 1st gear are used to evaluate the step just completed, and the 2nd gear speed is used for the beginning of the next step from 10 to 15 mph. The gear shift is considered to be instantaneous when the velocity reaches 10 mph. In this manner the time, acceleration, distance, fuel consumption, etco can be calculated, and the standard and flexible units comparedo The calculations were run on a ccmputer; a sample of the final machine tabulation is shown i:n Table V, which covers the speed:range from 175 to 55 mph c:on pavement with the standard vehicle in 2nd gear at 17.P5 mph, Ln 3rd at 20-52.5, and in )4th at 55,0 mph, as is indicated by the change in engine rpm, The data;used in evaluating this vehicle are tr.hose given in Ref. 1; data obtained from the present calculations are given in Table VI. 8

TABLE V SAMPLE MACHINE TABULATION OF RESULTS Fuel Total el Fuel Fuel Total Distance Total Vel., Vavg Road, Accel. G, Time, Rate, mph Vf fgs rpm dhp max ftseC2 avg sec Time, / Rate, Used, Fuel, Traveled, Distance, sec avg lb lb ft ft x 103 17.50 25.67 3366.69 2.65 55.94 11.99 1.71 9.61 9.78 32.14 27.50 3.51 1.04 3.06 3.19 32.55 20.00 29.33 2023.50 3.36 37.45 7.02 2.76 6.12 12.97 64.69 31.17 6.97.55 6.51 3.42 18.32 22.50 33.00 2276.44 4.60 41.54 6.92 3.28 6.91 16.39 83.00 34.83 6.78.54 7.30 3.95 20.84 25.00 36.67 2529.38 5.75 44.19 6.63 3.82 7.70 20.34 103.84 38.50 6.39.57 7.90 4.53 24.18 27.50 40.33 2782.32 7.19 45.17 6.16 4.40 8.11 24.88 128.02 ino 42.17 5.97.61 8.28 5.09 28.15 30.00 44.00 3035.26 8.21 46.23 5.78 5.01 8.46 29.96 156.18 45.83 5.62.65 8.89 5.80 32.29 32.50 47.67 3288.19 10.26 47.34 5.46 5.66 9.33 35.77 188.47 49.50 1.69 2.17 3.21 6.96 115.40 35.00 51.33 2119.45 11.55 31.54 3.38 7.84 6.41 42.73 303.87

V. PERFORMANCE COMPARISON Graphs of the two types of engines under each of the road conditions investigated are shown in Figs. 2-9: Standard Vehicle on Pavement Fig. 2 Flexible Vehicle on Pavement Fig. 3 Standard Vehicle o15 x Pavement Fig. 4 Flexible Vehicle 1.5 x Pavement Fig. 5 Standard Vehicle 2.0 x Pavement Fig. 6 Flexible Vehicle 2.0 x Pavement Fig. 7 Standard Vehicle 3.0 x Pavement Fig. 8 Flexible Vehicle 350 x Pavement Fig. 9 For comparative purposes the important data have been compiled in Tables VI and VII for acceleration up to the maximum speed possible under the assumed conditions. Some columns contain two sets of values: The first gives the same speed range as the standard unit; the second gives values up to the maximum possible vehicle speed. Exact maximum speed in each case is difficult to obtain, since it is a variable for the two conditions, standard drive and maximum economy power, because both engine rpm and hp vary at the limiting value. Table VII records the differences between time, distance, and fuel of the flexible system compared to the standard one. The flexible vehicle takes 3-4 times as long to accelerate, requires 1.5-4.0 times the distance, and uses 142.3 times as much fuel in the process. It is difficult to calculate accurately the initial acceleration, time, etc., because the slowest engine speed at which satisfactory performance can be secured with the L-141 engine is about 600 rpm (see Appendix, page 24), In the calculations it must be assumed that the engine rpm is not zero when the mph is zero, otherwise no power would be available. It was considered that the lowest engine speed that could be employed was 500 rpm and that 1.5 hp was developed to give the required traction plus slip of the clutch as necessary for a start. These assumptions prevent accurate determination cf the actual acceleration below the 2.5 mph, Fortunately the effect of these inaccuracies upon the total values is quite smallo 10

2000 / / / 1500 / / D 250 o0 1000 0 200 2LS 3150 FUEL FLOW/ W 10 w 500 u 100 DISPLACEMENT' v 500 I00 ~ 5a 3 50 ^ 30 30 s u s <^ 1ACCELERATION TOTAL TIME 20 20 I; W: 0o I O 1 0 00 10 20 30 40 50 VEHICLE SPEED IN MPH Fig. 2. Performance curves, standard vehicle on pavement. 11

8000 / C ~ D |^~~~~ / _ 6000 0.6 z Lw 0 I2 I / (JUW L I/ / -J 4000 w 0.4 - X)C'- DISPLACEMENT / aa 7/ 2000 o 0.2 / / FUEL FLOW / / 0 0 -111 4 140 3 120 100 TOTAL TIME z w 2 2 80 -J 60 u 0 I ~ 40 ACCELERATION Wo Q 20 0 10 20 30 40 50 60 VEHICLE SPEED IN MPH Fig. 3. Performance curves, flexible vehicle on pavement. 12

.0 0 Z o 72000 0 200 w 1500 150 / w C)0 0 // < 1000 J 100 a. I TOTAL FUEL FLOW,500 50... -- — TOTAL DISPLACEMENT 0-.0 I I N e 25 N 25 -, U; ACCELERATION -20 - 20 Z W TOTAL TIME 05 o ~ Ao 15 K 15- -- O 0 o5 5 0 10 20 30 40 50 VEHICLE SPEED IN MPH Fig. 4. Performance curves, standard vehicle, 1.5 times pavement resistance. 13

6000 / 3 // <.01: 4000 E 0.4 DISPLACEMENT/ 2000 0.2- -UEL FLOW o -J- I 1 1 4-> -. 120 u - / _.60 5 100 l J 2 40 0< I 20 ~0 0 0 10 20 30 40 50 VEHICLE SPEED IN MPH Fig. 5. Performance curves, flexible vehicle, 1.5 times pavement resistance. 14

0 0 0 = 1200 o 120 z 0 Jw U 80, 80 FUEL FLOW JI "/J 400 O 40 DISPLACEMENT 0 O 0 — 25 25 z 20 - 20 _ ACCELERATION z 20 20 - 0 0 < 15 1 5 O IJ — l 0 0 0 10 20 30 40 50 VEHICLE SPEED IN MPH Fig. 6. Performance curves, standard engine, 2.0 times pavement resistance. 15

.3 z O w 4000 uL 0.4 2 -J w w w 2000 _ 0.2 o 0 _H ^- ^ FFUEL FLOW' 5 _ 100 _. 4 80 z w 2\ TOTAL TIME 3 i 60 0 \ TTL X 2-JI ACCELERATION Y 2 40 w 0 O HI OI 20 0 10 20 30 40 50 VEHICLE SPEED IN MPH Fig. 7. Performance curves, flexible engine, 2.0 times pavement resistance.

0 0 0 1200 120 0 o - 2 800,,, 80 - // o5 o /H j5 400 0 40 - FUEL FLOW /DISPLACEMENT 0 0 -- %% 25 _ 25 ACCELERATION -s 25, 25 z I 20' 20 W I 1515 15 I0 I 10 0 TOTAL TIME 5 5 o 0 —-q —"'-" I- I - 0 10 20 30 40 Fig. 8. Performance curves, standard engine, 3.0 times pavement resistance. 17

. I- I. L g 4000 J 0.4 w O LL.J ) 2000 0.2 DISPLACEMENT, _ -. 0. FUEL FLOW o 0-_... o.... I —-' ——' - I u5 100 4 80 w ACCELERATION Z 2\ 0 3 60 <: p \ TOTAL TIME 2 2 40 20 U 20 0 0 0 10 20 30 40 VEHICLE SPEED IN MPH Fig. 9. Performance curves, flexible engine, 3.0 times pavement resistance. 18

TABLE VI COMPARATIVE PERF}ORMANCE OF STANDARD AND FLEXIBLE SYSTEMS ximtm Total Distance Fuel Flow Specific Fuel Speed Acceleration for Vehicl..e Road Surface Acceration Time Traveled for Flow, Range? Reached, Period sec ft Period ft/lb of Fuel mph fps2 lb Standard Pavement 25.0 28.0 1900 0.225 8450 0-60 Flexible Pavement 4 5 136.0 7600 0.52 14600 0-60 Standard 1. 5 x Pavement 25.0 22.5 1300 0.155 8400 0-50 91 4200 0.532 12900 0-55 H-lexible 1e5 x Pavement 4.5 lol 63oo oo 5o 126oo o-55 Standard 2.0 x Pavement 25.0 15.2 1120 0.136 8240 0-45 Flexible 2.0 x Pavement 4.5 72.0 3000 0.26 11550 0-45 Standard 3.0 x Pavement 25.0 15.5 990 0.109 9090 0-35 46.0 1430 0.15 9540 0-35 Flexible 3.0 x Pavement 45 46 1450 0.15 9540 0 57.0 2100 0.215 9770 0-40 TABLE VII RELATIVE PERFORMANCE OF FLEXIBLE SYSTEM Acceleration, mph Increase Relative to Standard Unit Resistance From To Time Distance Fuel 0 60 4.85 4.0 2.3 Pavement 0 50 4o05 3.23 2,1 1.5 x Pavement 0 45 4,73 2.68 1.9 2.0 x Pavement 0 35 2.97 1.45 1.38 3.0 x Pavement

VI. DISCUSSION To obtain a correct picture of the merits of a flexible engine as compared with the standard system, one would have to make a complete appraisal of the operating regime of the vehicle. Reference 1 analyzed the 48-hr Battlefield Day; based on fuel economy alone, the flexible unit scored approximately a 2:1 advantage over the standard system. In that analysis, however, the need for acceleration, etc., did not enter; so that, in fact, based on present results, the flexible system has some definite limitations not readily apparent from the earlier report. One would have to have a tape recording of a typical day's operation or an estimated program of events including starts, accelerations, stops, duration at certain speeds, etc., in order to obtain an accurate estimate of the relative merits of the two systems. Obviously, the situation depends a great deal upon the events that occur in any time interval: Periods of continued stops, starts, and accelerations could reduce the 2:1 advantage demonstrated in Ref. 1 to almost a 1:1 equality, as judged by the data of Table VII. We believe that under normal conditions the flexible system will have a definite advantage as far as fuel economy is concerned, but this advantage will be achieved only at a considerable sacrifice in pick-up ability. The data in this report suggest that the next step should be to examine the transmission possibilities to see if, by suitable design and gear changing, the higher acceleration factors can be re-established, while the economy of the flexible system is still preserved. Although such a step might result in reducing the fuel economy from 2:1 to a less ideal 1.5:1 approximately, an overall advantage may be secured in the process. It should be kept in mind that all studies to date on the flexible engine have included the same engine characteristics outlined in this report; no attempts have been made to eliminate the increased F/A ratio for vehicles under maximum load and at high speed which is wasteful of fuel for the small increase in power secured. Column 7, Table VI, gives a specific fuel flow: This is the distance traveled per pound of fuel burned during the acceleration period. Of course, the greater this distance is, the greater the overall economy will be; but, as we shall see, the acceleration time will also be greater. This time factor is greatest when the engine hp is the lowest (on pavement), and it is reduced as the engine hp is increased. This is to be expected, because it is at low resistance that the standard transmission utilizes the engine output in the least favorable manner. However, even at the 3.0:1 pavement resistance the flexible system has about a 7% advantage over the standard system so far as ft/lb are concerned. 20

VII. CONCLUSIONS The ideal flexible engine system, as applied to the M-151 vehicle without changing the engine characteristics, has the following advantages over the standard engine and transmission system: lo It reduces fuel consumption during the 48-hr Battlefield Day by as much as one-half. 2. It increases the time of acceleration from 0-60 mph on pavement in the ratio of 4.8:1i 3. It increases the distance traveled in reaching 60 mph by 4:1. 4, It increases the fuel burned during the acceleration period by 2.3:1. These conclusions suggest that a new appraisal of the system be made, in which acceleration, etc., are included in the 48-hr Battlefield Dayo 21

VIII. APPENDIX I. Engine Developments Required If the M-151 engine is to approach even closely the ideal of flexibility, certain improvements must be made. To ascertain some of these improvements, instrumentation was applied to three different vehicles for the purpose of obtaining various driver reactions under simulated flexible conditions. The main requirement for flexibility, as determined in Ref. 1, is that the engine operate at the lowest speed under all conditions of vehicle performance. As Fig. 12 and Table VII of Ref. 1 show, a large percentage of engine operating time, particularly on pavement, occurs at relatively low speeds when compared with the standard transmission. For example, in the 35 mph range the speed must be reduced from 1500-1800 rpm to about 500 rpm. The object of our experiments was to gather as much information as possible regarding low-speed operation of existing equipment. Since the M-151 vehicle can be considered a light one, we decided to experiment with vehicles in this same class: 1. Triumph Herald, a small, 4-cylinder engine of light weight and high speed, giving maximum hp at about 5000 rpm. 2. Chevrolet (1956 model with stick transmission) a 6-cylinder engine with a peak rpm of about 4000. 35. M-151 4-cylinder engine with stick transmission, with a peak rpm of 3600 approx. Of these three vehicles, (1) would be considered the most likely to show the greatest effects of slow speed; (2) and (3) would probably be about the same, although (2) would be expected to be somewhat better than (3) by virtue of the six cylinders. The standard carburator and ignition system of each vehicle was adjusted to the lowest speed at which the engine could idle smoothly without danger of stalling: Triumph, 500 rpm; Chevrolet, 500 rpm; M-151, 550 rpm. Then, equipped with an electronic tachometer, each vehicle was operated on the level road, on such hills as are locally available, and in all gear ratios in order to determine the slowest speed at which vehicle jerk became noticeable. All three vehicles were operated under the same conditions, and the results were recorded. 22

A. TRIUMPH On level road, on hills, and in all gears, the Triumph began to "buck" noticeably at speeds of 450-550 rpm; the lower speed could be approached only slowly if complete stall was not to occur. All tests indicated that the bucking occurred because either the ignition system failed to provide satisfactory ignition, or the carburetor failed to supply combustible mixture, or both, at speeds lower than the conventional idle speed. In other words, to achieve a satisfactorily low operating speed the engine's idling ability must be improved by changes in the ignition system, carburetor, valve-timing, manifolding, etc. B. CHEVROLET The same conclusions were reached for the Chevrolet as for the Triumph. Despite its 6-cylinder engine, the Chevrolet was able to idle at speeds only slightly, if at all, lower than the Triumph's idling speed. C. M-151 VEHICLE Fairly extensive tests were conducted on the M-151, since this is the vehicle under consideration. The results of these tests are presented on Table VIII. The lowest engine idling speed was 550 rpm. Observe that in this case substantially the same conclusions were reached as for the other two vehicles, the only exception being that on the steeper downhill runs higher speeds were recorded because of the driving component from the vehicle. II. Conclusions Before the flexible engine system can be completely effective, the engine's performance at low speeds must be improved. Since low-speed operation can occupy a considerable portion of the Battlefield Day, the possibilities for fuel economy are greatest under these conditions. Therefore some effort to reduce idling speed is justified. However, improvements to slow-speed performance usually affect the high-speed output adversely. This factor must be taken into account. Before any development work is undertaken, a hypothetical case should be examined,. The effect on the overall results of any improvements in acceleration and in low-speed operation should be calculated by the methods presented in this paper. to determine how far such efforts to improve low-speed operation should be carried before funds are expended. 23

TABLE VIII M-151 VEHICLE PERFORMANCE AT LOW SPEEDS Road Surface Year Lowest EngineComments Speed Level Blacktop 1st 675 2nd 700 3rd 650 4th 675 Level Gravel 1st 700 2nd 725 3rd 625 4th 675 Uphill 20~ Blacktop 1st 650 2nd 625 3rd 600 4th 625 Downhill 20~ Blacktop 1st 750 These results affected 2nd 750 by the vehicle driving by the vehicle driving 3rd 800 e engine~ 4th 825 Gravel 12~ Incline Uphill 1st 675 2nd 650 3rd 650 4th 600 Gravel 12~ Downhill 1st 675 2nd 675 3rd 650 4th 550 24

REFERENCE 1. Vincent, E, T., The Flexible Engine, ORA Report No. 05847-3-F, University of Michigan, May, 1964. 25

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