Using figure 23 and the ordinate of the intersection of

pressure ratio 0.055 and the biaxial stress curve

(catapults are subjected to radical and tangential

Referring to sheet 1 of figure 23, the pressure ratio (P/Y)

stresses but not to longitudinal stresses), the wall ratio is

is found to be 0.066 and the minimum strength of the

found to be 1.059. Since wall ratio is the ratio of outside

material is calculated as follows:

diameter to inside diameter, the outside diameter is

From figure 23:

calculated as follows:

therefore,

OD = W X ID = 1.059 X 1.50=1.59 inches

Since the yield strength of 2024-T3 aluminum is 42,000

This is the diameter of the base of the machined groove

psi, the material provides more than the required safety

and the relieved section, not the outside diameter of the

factor of 1.15 and can be used for the outside tube.

inside tube. Since the groove must be at least 1/16 inch

deep, the diameter of the inside tube must be 1/8 inch

64. Trunnion.

larger than 1.59, or 1.72 inches (fig. 57). Referring to

tubing standards, it is found that 1.740-.005 is a

body which has two pivots, 180apart, perpendicular to

standard size tube.

the longitudinal axis of the catapult. The trunnion has

internal threads to accommodate the stop ring which

be made of aluminum. The tube size is determined in a

serves as one bearing surface for the latches. The

manner similar to that used for the inside tube. The

recess in the trunnion below these threads serves as the

inside diameter of the telescoping tube is 1.75 inches

other bearing surface for the latches. The stop ring-

and the outside diameter is 2.00 inches. Again, the

trunnion combination, for positioning the latches, is used

large outside diameter is not calculated from the wall

in most catapults and removers because of its ease of

ratio, but rather the diameter of the undercut at the end

assembly. The upper portion of the trunnion's large

of the tube is found. Using the wall ratio already found

bore is threaded to accommodate the outside tube. The

(1.059), the minimum diameter of the -undercut is found

small bore of the trunnion acts as a bearing surface for

to be 1.86 inches. The telescoping tube of the final

the telescoping tube. A spring (tortuous path) seal is

design is illustrated in figure 58. From the figure it can

provided in the trunnion to seal the telescoping tube.

be seen that although the standard 2-inch tube is

machined down over most of its length, the last 3 inches

trunnion. The diameter of these pivots is computed on

(near the shoulder) are tapered and the final 1 1/4

the basis of shear strength. The maximum static load

inches of the tube are 2.00 inches in diameter. This

applied to the pivots, according to the design

increase in diameter of the telescoping tube is designed

requirements, is 6,000 pounds. The maximum kinetic

to create an interference fit (0.000 to 0.007 inch)

load applied to the pivots, resulting from operation of the

between the telescoping tube and the trunnion bore, and

catapults, is computed by using Newton's law:

thus absorb some of the energy of the moving members

before the telescoping tube and its attached spacer

strike the stopping shoulder of the trunnion.

to have a 3-inch outside diameter and a 2 3/4-inch

Since the kinetic load is greater than the static load

inside diameter. A commercially available tube made of

specified (6,000 pounds) in the design requirements, the

2024-T3 aluminum (WW-T-785) has an outside

kinetic load is used in calculating the size of the trunnion

diameter of 3.0 inches and an inside diameter of 2.8

inches. The wall ratio of this tube is:

† Safety factor.

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