The Norden Bomb Sight manual

AB represents the spin axis in

the vertical

position

at the

start of the precession run.

hours later it

is represented by CD. CD

longer in the vertical. EF represents

the verti-

cal.

If the outer gimbal ring

is horizontal at

the beginning of

the run, it will naturally remain

that way two hours

later,

when

it is designated

as

G'H'.

FI represents the amount of apparent east-

erly precession.

in the bombsight,

the case and the cardan are

not stabilized for lateral tilt, i.e. roll. There-

fore,

they are

free, under any force to move in-

dependently of the gyro housing. Gravity is such

a force, and it will force the

right end of the

case

and cardan to move downward

as the earth

rotates (sight on North heading).

This means the

tilting will take place on the gyro gudgeon bear-

ings.

Since no bearing is absolutely friction-

less,

this

tilting will exert a slight force upon

trie

right

face of the gyro housing tending to de-

press the right face downward.

Under the laws of

precession,

the rear face will precess downward,

tbus

moving the

bottom

of the spin axis to the

north, i.e. north hook.

There are

Che dan in geon line front b

three flexible leads leading

from

the

left

end of the

cardan (two flexible leads in the M3) and three

more

leading from the front of the cardan to the

front of the gyro housing.

let the

The latter three only

Since nooneer

will be concerned with the tilting

this problem.

Since no lead is perfectly flexible, the tilting

of the

case and cardan

to the right

and downward

will tend

to exert a slight force upon

the right

face of the gyro housing. Thus, again we have

north hook.

If the

sight were placed upon a south head-

ing, the considerations would be the same as

the

above, except that the tilting of the case and the

cardan would take place in the opposite direction.

Here

the

right end

of the case

and the cardan

would

move

upward, and the left end downward.

If the sight were placed

upon either an east

or west heading, tilting would take place upon the

cardan

gudgeon

bearings,

since

both the gyro hous-

ing and cardan are stabilized in the fore and aft

against pitch.

planelt should now be obvlous why flexible lead

bearing drag, and pendulousness always, no

which heading, produce north hook. These

elements, no matter on what heading, always pro-