4. Translate the following text without a dictionary:
Standard Loran
Loran is a long-range navigational aid employing pulse transmitters sited 200 to 600 miles apart to provide Hyperbolic position lines as in Gee*. The stations operate in pairs of stations to obtain a fix. The stations radiate pulses of 50 micro-second duration with a peak power of 100 kw at a rate of 25 pulses per second. The radio frequency is about 2.0 Mc/sec and selection of chains is by change of recurrence frequency**. Sixteen recurrence rates and three radio frequencies are provided giving a total of 48 channels, which are sufficient for coverage extending over the whole world.
The whole of the North Atlantic Ocean and most of the Pacific Ocean are already covered.
The equipment provides position lines only. A single observation provides one position line; two observations taken successively may be combined, allowing for distance run, to obtain a fix.
Care must be taken*** during interpretation of the display, particularly at night, owing to the possibility of receiving multiple sky-wave signals. The training of operators must be thorough. Stations must be sited near the coast.
The sector coverage for each pair of stations consists of two sectors of about 120° centered on the right bisector of the base line.
Notes:
*Gee — навигационная система Джи
**recurrence frequency — частота повторения
***Care must be taken — следует быть внимательным /осторожным/
Lesson 7. The free gyrocompass
1. Read the following words:
spin slewing stability
symmetry suspension gravity
rotor immobile friction
perpendicular neutral apparent
intersect acquire peculiar
2. Grammar. Инфинитивный оборот “Complex Subject”.
1) The reliability is sure to be an essential feature of any vehicle.
2) The size of the structure seems to be rather large.
3) The problem of new generators is likely to be one of the most essential.
4) The losses because of metal fatigue appear to be great.
5) Radio is likely to be one of the most significant means of navigation.
6) The behavior of materials proved to depend of many factors.
7) Many of these systems are certain to be subjected to failures.
8) The device appears to be created by our engineers.
3. Read the following text: The free Gyroscope and its properties
The term "gyroscope" applies to a physical body that spins rapidly around its axis of symmetry and is suspended in such a way that the axis of rotation can occupy any position in space.
In the field of engineering, the gyroscope is usually a heavy disc; practically in all modern instruments the disc is the rotor of an electric motor. One of the ways of suspending the gyroscope is to mount it in gimbals . Being suspended in such a manner, the gyroscope is rendered the possibility to turn round any of the following three axes which are mutually perpendicular and intersect in one point:
(a) Axis AB — the axis of rotation of the gyroscope rotor called the main axis or spinning axis;
(to) Axis CD — the slewing axis of gimbal inner ring;
(c) Axis EF — the slewing axis of gimbal outer ring.
The three possible axes of rotation of the gyroscope are regarded its degrees of freedom; such a gyroscope possesses, therefore, three degrees of freedom.
The point 0 where the three axes intersect is known as the point of gyroscope suspension. It is the only immobile point when the gyroscope swings round any of its three axes.
A gyroscope possessing three degrees of freedom can be regarded a free or neutral gyroscope on condition 'that the centre of gravity of the whole system consisting of rotor and gimbal rings coincides with the point of suspension 0 and no external moments are applied to the gyroscope.
Due to fast spinning, the free gyroscope acquires a number of interesting features which are widely utilized in all kinds of gyroscopic instruments.
Here are the basic properties of a free gyroscope:
The main axis of the free gyroscope possesses stability, that is, it tends to maintain the direction it was given initially in relation to space.
The stability inherent to the main axis is the more pronounced, the more accurately the centre of gravity of the system coincides with the point of gyroscope suspension (that is, the better has the gyroscope been balanced out), the lesser is friction in the gimbal axes, and the greater is the weight of the gyroscope, its diameter and rate of spinning.
The stability of the main axis makes it possible to utilize the tree gyroscope as an instrument for detecting the rotation of the Earth, because the gyroscope axis performs an apparent (visible) motion in relation to earthly objects.
Under the action of an external force applied to the gimbals rings of the gyroscope its axis moves in a direction perpendicular to that of the force acting.
This peculiar feature of a free gyroscope is called processive movement or precession. Precession of the gyroscope takes place all the while the external force is present and ceases when the force stops acting.
There is a special rule of poles which is used for determining the direction of precession.
The gyroscope pole is that end of its main axis from the side of which the rotation is seen taking place counter-clockwise.
The pole of force is that end of a gyroscope axis from the side of which the force is seen acting counter-clockwise.
The rule of poles reads as follows: when a moment of external force is acting on a gyroscope, its pole moves towards the pole of force along the shortest way.
The product I Ω. of gyroscope inertia moment and its spinning rate is known as the kinetic moment of the gyroscope. It is usually depicted as a vector directed along the main axis pointing towards the pole of the gyroscope.
The rate of precession of the gyroscope axis can be estimated according to the following formula:
where
is the rate of precession;
M is the moment of external force.
Words to be learnt:
gimbal — универсальный шарнир
to intersect — пересекаться
slewing axis — вращающаяся ось
suspension — подвешивание, нить подвеса
to coincide — совпадать
inherent (in) — присущий
kinetic moment — кинетический момент
to depict — изображать, описывать
to estimate — оценить
EXERCISES