Special Equipment Considerations.

TM 38-400/NAVSUP PUB 572/AFMAN 23-210 MCO 4450.14/DLAM 4145.12

*These factors show the total grade resistance or

to or subtracted from that required for level movement.

rollback force in pounds per ton for a 5 percent grade.

Grade resistance amounts to 20 pounds per ton of gross

For this application, a tractor with a 2,600pound

weight of the tractor-trailer train and the combined load

drawbar pull would be satisfactory.

for each 1 percent of grade encountered. On upgrades,

the percent is added to the resistance; on down-grades,

the percent is subtracted.

Percent of grade is

4-22. Special Equipment Considerations.

determined by the feet of vertical rise per 100 horizontal

a. Truck, tiering, electric (straddle-type). This truck

feet.

eliminates the counterweight and the attendant increase

b. Estimating required drawbar pull. The estimated

in length by using outriggers which extend forward in a

drawbar pull in pounds and application of tractors used

plane at floor level parallel to the plane of the forks.

by the military are as follows:

The truck can operate in 6-foot aisles; the forklift truck

requires 10foot aisles. However, the outriggers must

Drawbar pull

Application

straddle the bottom tier when the truck is positioning a

2,600 pounds ...........................

Inside warehouse

pallet which necessitates the use of single-wing pallets

4,000 pounds ...........................

Inside and outside

(if double-opening racks are used, the bottom beam

7,500 pounds ............................

Outside work, heavy

must allow outrigger clearance when using standard

At times, it may be necessary to make a rapid,

pallets on the rack beams). Since it is not practicable to

reasonably accurate estimate of the drawbar pull

use single-wing pallets for the bottom tier only and

required of the motive power unit of a tractor for the

double-wing pallets for the upper tiers, this truck is used

handling of loads on a level surface and also on grades.

in pallet rack areas where single-wing pallets only can

The following example will illustrate a fairly accurate

be used. The tiering truck is lighter in weight than the

method for this estimate:

conventional forklift truck which permits its use on light

Step 1 What is the drawbar pull required for a tractor-

construction and in elevators of limited capacity. The

trailer for the following composition and conditions:

military services use a 3,000-pound capacity truck which

Weight of tractor ............................... 6,690 pounds

is available in both riding and walkie type. A variation of

Weight of driver ................................ 170 pounds

these trucks provides for the forks to extend by

Weight of 5 trailers at 500 tare each .. 2,500 pounds

mechanical means, thus eliminating the requirement to

Weight of net pay load ...................... 16,000 pounds

straddle the pallet.

TOTAL GROSS LOAD ...................... 25,360 pounds

Equals ............................................... 12.68 tons

b. Warehouse crane.

Step 2 If the surface is level poured concrete, the value

(1) Usually, the lifting and carrying capacity of

from the table to calculate drawbar pull is 53 pounds

the warehouse crane is stated as the maximum weights

resistance per ton moved. The calculation then would

which may be lifted at various boom angles. (If the

be as follows:

boom is telescopic, maximum capacity is obtained with

12.68

x 53

= 672 pounds

the boom at the shortest length.) As the boom is lowered

Total load tons

x Road resistance = drawbar pull

toward the horizontal position or as its length is

pounds per

required

extended, capacity decreases.

ton

(2) A load chart showing the capacity of the

Step 3 If the train is required to travel up a 5 percent

crane under all circumstances should be visible on the

grade, then the road resistance of 53 pounds per ton

crane. These charts furnished by the manufacturer will

would be increased by 20 pounds for each percent of

indicate clearly the safe load in pounds for maximum

grade. The calculation for this drawbar would be:

and minimum position of the boom and for at least two

12.68

x (53

+ (*20

x *5)

intermediate stations.

Total load

x Level

+ Grade re-

x Percent

(3) If the crane has a sluing boom and if the

tons

road

sist-

grade

load is to be moved only within the circumference of the

resist-

ance

slue, it is not necessary to move the crane. The boom

ance

pounds

is slued to the proper position and the load is ready for

pounds

per ton

placing.

per ton

per

(4) If the crane has a rigid boom or if the load is

percent

to be carried farther than the sluing boom can reach, it

grade

is necessary to move the crane. The crane should not

be moved until both the load and the

12.68

x 153

= 1,940 pounds

Total load tons

x total

= drawbar pull

resistance

required

pounds per

ton

4-61