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MEMORANDUM REPORT NO. II80 DECEMBER 1958

DRAG AND STABILITY PROPERTIES OF

THE IOSMM SHELL, HE, T388 (U)

EUGENE D. BOYER

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BALLISTIC RESEARCH LABORATORIES

MEMORANDUM REPORT NO. Il80

DECEMBER I958

DRAG AND STABILITY PROPERTIES OF THE 105MM SHELL, HE, T588 (u)

Eugene D. Boyer

Reguests for additional copies of this report will be made direct to ASTIA.

Reproduction of this document in whole or in part is prohibited except with permission of the issuing office; however, ASTIA is authorized to reproduce this document for U. S. Government purposes.

Department of the Army Project No. 5BO3-O3-OOI Ordnance Research and Development Project No. TB3-OIO8

ABERDEEN PROVING GROUND, MARYLAND

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BALLISTIC RESEARCH LABORATORIES

MEMORANDUM REPORT NO. Il80

EDBoyer/sec Aberdeen Proving Ground, Md. December 1958

DRAG AND STABILITY PROPERTIES OF THE 105-MM SHELL, HE, T588 (U)

(UNCLASSIFIED) ABSTRACT

The drag and stability properties of the 105-mm, HE, T388 shell are

presented. These data were obtained from Transonic Range firings.

f

(UNCLASSIFIED) TABLE OF SYMBOLS

A Axial moment of inertia (lb - in )

2 B Transverse moment of inertia (lb - in )

d Diameter (in)

m Mass (lb)

IC Drag coefficient

K^ Overturning moment coefficient

K_ Lift force coefficient

K-j - K^ Damping moment coefficient

K„ Magnus moment coefficient

2 2 6 Mean squared yaw (deg )

_2 K^ 2 Yaw drag coefficient (rad )

6 3-1 A,, „ Yaw damping rates (ft x 10 )

s Gyroscopic stability factor

s Dynamic stability factor

N Number of yaw stations

N-, Number of timing stations

e Error in yaw fit (rad)

e Error in swerve fit (ft) s v '

K, 9 Sizes of yaw arms at mid range •*->'-

0' 0 Turning rates of yaw arms (deg/ft)

'

... - - ,

(CM—BBBft) INTRODUCTION

At the request of the Canadian Armament Research and Development

Establishment (CARDE), BRL fired, through the Transonic Range , four

versions of the 105-mm, HE, T388 shell, designed at CARDE (Figure l).

The four types varied only in body length and were designed to bracket

a stability factor of 1.8 at M = 1.1. These firings were suggested by the

Bi-partite Standardization Committee as a part of the development of improved

105-mm howitzer ammunition. The firings were to determine the drag properties

of these shell from M =0.6 to M =1.5 and the gyroscopic stability factors

at M = 1.1.

Early tests indicated that the drag of these shell was approximately 2 5

20$ lower than that of the standard Ml shell ' . The T388 shell has a long

hollow boattail and it was thought that the drag could be further reduced by

bleeding air into the base from the body of the shell. Three shell of each

type were available for stability firings at M = 1.1, and an additional ten

shell of Type 1 for base-bleed experiments.

The shell were launched from a 105-mm howitzer (l - 20 twist). A yaw

inducer was employed on the six rounds at M = 1.1. This was done in order

to obtain adequate yaw levels for a yaw reduction. The physical properties

of the shell are given in Figure 1.

PWnillirT ^ STABILITY

The stability factors and other aerodynamic properties of the shell are

given in Table I. The reduction parameters are given in Table II. The

stability factors, as determined at ^65 feet from the muzzle, at about M = 1.1,

vary from 1.66 for Type 1 to 1.95 for Type 2. All types are dynamically

stable at the velocity tested, M = 1.1. No yaw analysis was made at other

velocities fired. The yaw damping rates appear to be sensitive to yaw level

but the evidence, on this small sample, is rather weak.

(t DRAG COEFFICIENT

The drag force coefficient, IC, was obtained by fitting a cubic equation

to the time-distance data for each round. These data were then reduced to 2

zero-yaw by the relationship IC = IC + Krj p 5 • \\ 2' the yaw ^T&^ o 5 5

coefficient, was determined to be 2.0 (per square radian) at M = 1.1. This

value was used to reduce all drag values to zero yaw (Figure 2). A shadow-

graph of Type h at M = 1.086 is given in Figure 3- Three shell of Type 3

and one shell each of the other three types were fired at M = 1.1. When no

difference was noted in the drag for the different types, the six remaining

shell were fired over a range of Mach numbers to establish the drag curve.

In comparing drag values of the Ml with that of the T388 (Figure 2) it is

seen that in the subsonic region drags are the same for both shell while in

the supersonic region the T388 drag is 20$ less than that of the Ml.

To test base-bleed designs Picatinny Arsenal modified ten Type 1 T388

shell by drilling bleed-holes with a 0.25 inch diameter at 29 to the axis

of the shell. Five variations of vented areas varying from 6 to 48 holes,

located before and/or after the rotating band, were tested (Figures k and 5)«

Details and physical properties for each type are listed in Table III. These

designs showed no improvement in drag (Figure 2). In fact, for the two

rounds fired in the subsonic region there appears to be an increase in drag.

The 20$ drag increase at M>1.2, for modification 1, however, is due to the

removal of the boattail and not to the presence of the vent holes.

8

(4V0BRfflB9"»' CONCLUSION

The ballistic characteristics of these four types of shell differ

very little. At M = 1.1 the gyroscopic and dynamic stabilities are similar

and adequate. Therefore, because of the measured similarities of the

ballistic characteristics of all four types the selection of the final type

can not be made on the basis of these characteristics.

The hoped for further reduction in drag by bleeding air into the base

was not achieved. The intakes were located upstream of the boattail where

the surface pressures are higher. These locations, however, severely limit

the total intake area which can be achieved without jeopardizing the strength

of the projectile. Hence, only about one half of the optimum intake area

could be achieved even with kQ holes. This partially accounts for the

negative results, and perhaps inefficient ducting with l/l4-inch diameter

holes further reduces the amount of air bled into the base cavity. It is

rather doubtful that further experimentation with base-bleed with this design

would be fruitful.

EUGENE D. BOYER

(UNCLASSIFIED) REFERENCES

Rogers, W. K. The Transonic Free Flight Range. Ground: BRL R-1CM, June 1958.

Aberdeen Proving

Boyer, E. D. Some Aerodynamic Properties of Three 105-MM Shell, Ml, T57T, and T107. Aberdeen Proving Ground: BRL M-13M, April 1958.

Roecker, E. T. The Aerodynamic Properties of the 105-MM HE Shell, Ml, in Subsonic and Transonic Flight, Aberdeen Proving Ground: BRL M-929, September 1955.

10

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