76 BULLETIN 711, U. S. DEPARTMENT OF AGRICULTURE. 
cient grate area, most new logging engines are equipped with a fire 
box which is oblong or elliptical in shape and extends about 2 feet 
beyond the cylindrical portion of the boiler on the front side. This 
design increases the grate area considerably without correspondingly 
increasing the width of the engine frame. 
All of the engines are double — that is, have two cylinders. Ordi- 
narily, logging engines are classified by the size of the cylinders, the 
diameter being given first. A glance at Table 7 shows the range of 
sizes. The engines are of the heavy-duty type, the valves and valve 
gear differing with the make. 
Standard drum engines have two drums, placed either tandem or 
opposite, or nearly so. These rotate upon their shafts and are held 
fast when pulling by means of frictions. Several types of frictions 
are used. They are operated either by hand or steam, the steam 
friction being particularly desirable on the larger engines. The 
main, or hauling, drum is made of steel ; the trip drum, which car- 
ries the trip, or return line, is made of semisteel. These engines can 
be equipped with loading and straw-line drums, driven either by 
their own gear or pinions or by a chain drive. In the case of the 
simple-geared engine, the cut-steel gears of the main and trip drums 
are driven by a cut-steel pinion on the engine crank shaft. The trip 
drum of the compound-geared engine is driven in a similar way. The 
main drum in the latter type, however, is driven through a compound 
train of gears by an internal or external gear, a second pinion keyed 
on the trip-drum shaft driving the gear of the main-drum shaft. 
The standardization committee on logging engines of the Pacific 
Logging Congress recommended that the following definitions and 
formulas be adopted as standard : 
(a) Right and left hand sides of a logging engine. — When standing at the 
boiler end of the engine and facing out over the drum, that side of the machine 
to the right is termed the right-hand side and that to the left is termed the 
left-hand side. In general, the engine is operated from the right-hand side. 
This is frequently called the " engineer's side." 
(b) Main and trip drums. — The main drum is the drum which is used to 
haul in the load. This is sometimes called the forward or the lower drum. 
The drum which is used to return the main hauling line is the trip drum, also 
called the haul-back drum. 
(c) Rope capacity. — The rope capacity of the main drum and trip drum must 
bear a more or less definite relation. On road engines the trip-drum capacity 
should be not less than twice the capacity of the main drum, and so far as 
practicable there should be approximately six or seven hundred feet of addi- 
tional capacity on the trip drum. On yarding engines the capacity of the trip 
drum should be at least two and one-fourth times that of the main drum, and so 
far as practicable this ratio should be slightly increased. To find the drum 
capacity the following formula is used : 
Capacity=CXL X ^±dx^- 
