Text 3c. Compensated Roll Pendulum

Translate text 3C and put 3 special questions to its plot. Ask your

partner to answer them.

There is one variation of the rate gyro which looks something like the North seeking gyro compass. This is the compensated pendulum used to eliminate turn error in a vertical gyro. See Fig. 8. Instead of a spring restraint, the compensated pendulum uses a bottom heavy (pendulous) rotor. The spin axis is mounted along the aircraft pitch axis and the output axis is mounted along the aircraft roll axis. Therefore, the input axis is along the aircraft azimuth axis. When the plane is flying straight and level, the pendulous rotor acts like a plumb bob and lines up with the vertical. This provides the roll vertical reference for the vertical gyro.

Fig. 8.

When the plane goes into a turn, the pendulous rotor tries to fly to the outside of the plane. This produces a torque about the output (roll) axis of the compensated pendulum. But an angular velocity is produced about the compensated pendulum input (azimuth) axis. Since the pendulum acts like a rate gyro, the angular velocity about the input axis develops a torque about the output axis. The spin vector is in such a direction that the gyroscopic torque due to turning is in an opposite direction from the torque trying to make the pendulous mass fly to the outside of the turn.

In the simple system described, the two torques exactly balance for only one air speed and the pendulum stays lined-up with the vertical during the turn. It is possible to design a much more elaborate system wherein the torques balance out for all values of airspeed. The more simple system, however, provides good turn compensation over the range of speeds the aircraft is likely to fly.

Exercises

EX.1. Answer the following questions.

1. How does the change in temperature influence damping?

2. What mechanical means have been devised to reduce the damping variation with temperature?

3. What do these numbers in the text refer to: -5 deg F, 15 to 1, 5 per cent, +210 deg F, 4 to 1,10 to 1, +200 deg F, 4 times, 1.5 to 1.

4. How can one reduce the damping variation with temperature?

EX.2. Translate into English, using the verbs with prepositions:

компенсировать, быть направленным на, подвергаться чему-либо, другими словами, вместо, быть пропорциональным чему-либо, для сравнения, вращаться вокруг, быть похожим на, при помощи, наполняться чем-либо.

EX.3. Translate the following word combinations:

gyro – captive gyro, rate gyro, displacement gyro, gyro precision, single – degree of freedom gyro, rate gyro motor, rate gyro output, gyro output signal, rate gyro natural frequency, rate gyro damping, fluid filled rate gyro

angular – angular displacement, angular rate output (input), input (output) angular rate, angular velocity

damp – damping – damping factor, particular underdamped case, damping gap, damped oscillation, damping fluid, damping characteristics

torque – torque in – precession out relationship, various controlling torques, random torque, torque input (output), stall torque

axis – quadrature axis, gimbal axis, input axis, output axis, spin reference axis, axis alignment, aircraft azimuth axis

EX.4. a) translate the following connecting words and adverbs:

therefore, in other words, by means of, providing, conversely, instead of, basically, to my mind, for some comparison, although, in the end, note that, usually, let us look at, for example, imagine that, since, as far as I know, to sum it up, generally, as, here, however, while, in turn, similarly, just like, suppose, at the same time, as a matter of fact, in my opinion, moreover, despite, thus;

EX.5. Try to remember the information given in the texts of Unit 1, 2 and 3.

1. speak on displacement gyro and rate gyro in comparison. Try to use the expressions from exercise 7;

2. define the figure of merit;

3. speak on underdamped and overdamped systems;

4. tell how we can check the accuracy of rate measurement in rate gyros;

5. consider the statement: All fluid filled gyros compensate for the change in fluid volume with temperature. How can it be achieved?

EX.6. Translate the following sentences. Find infinitives and infinitive

constructions. Define their functions.

1. The wheel exerts no direction torque or force on the object to be stabilized. 2. The second method of stabilizing the antenna is to mount it on a stable platform. 3. Wheel speed must be kept constant to keep angular momentum constant.4. To get 100 percent flotation in a reasonable size, it is necessary to use a very dense fluid. 5. To keep this system operating properly, the gyro torques must be extremely accurate. 6. Many years ago, gyro compasses were built for the Navy that had to have drift rates in the order of 0.02 to 0.04 deg/hr. 7. Although the gyro appears to be mounted rigidly in the metal gimbals, any metal structure has some lack of rigidity. 8. Non-isoelectricity causes the wheel to deflect along the line which is not coincident with the line of acceleration. 9. According to an Archimedean principle the force on a floating body is known to be equal to the weight of the liquid displaced. 10. Gyros from recovered missiles have been found to be in good working order. 11. One of the difficult problems to be solved was how to detect the position of the spinning sphere without introducing frictions or torques. 12. The most popular alternate construction to the conventional ball-bearing supported gyro is likely to be the single axis floated gyro developed by the Mass. Institute of Technology many years ago. 13. We know the vertical and directional gyros to be commonly called displacement gyros. 14. In this example the antenna is unlikely to be used as a stabilization reference for other equipment. 15. A gyroscope is still considered to be a mysterious instrument.

EX.7. Translate the following sentences paying attention to the underlined

connecting words.

1. This problem becomes even more severe because of the particular damping fluids used with the integrating gyros. 2. Two integrating gyros are needed since each can stabilize about only 1 axis. 3. As long as the stabilized table is not rotating in inertial space, the gyro pickoff will have 0 outputs. 4. The integrating gyro cannot tell whether this torque about the output axis is coming from the torquer or from an angular velocity about the input axis. 5. Furthermore, the gimbal deflection of the spring restrained rate gyro will usually be less for a given input than the gimbal deflection of the integrating gyro. 6. Therefore, the inner gimbal and the rotor might be called stable platforms, stabilized about two axes. 7. But because the antenna is gimballed with the elevation axis connected to the airframe pitch axis the antenna elevation pickoff does measure the true aircraft pitch angle. At the same time, the antenna azimuth pickoff does not measure the true aircraft azimuth angle. 8. Since it is not easy, this kind of arrangements is avoided wherever possible. 9. Rather than have the roll gyro erect to the false vertical, a roll rate gyro is used to cut off the roll erection signal from the pendulum. 10. Compare this with the conventional autopilot displacement gyro which has a drift rate 300 times greater, even though H is 5 times larger. 11. With most radar antennas it does not make any difference if there is roll around the beam. 12. Whenever these pickoffs show a 0 signal the gimbal associated with that pickoff lies in the same plane as the vehicle carrying the platform.

SUPPLEMENTARY TEXTS FOR READING AND TRANSLATION

Text 1. The Earth is a Gyroscope

We have been concerned with the gyro as a transducer which provides an inertially stabilized reference line or plane for airborne stabilization applications. Let us note some other ways of applying the gyroscopic principle.

First, consider a really detailed situation. Did you know that you have been living on an enormous gyroscope? Our planet (some 8,000 mi in diameter and rotating once each 24 hours) is really a spinning rotor with an angular momentum of 0.53 times 10⁴⁰ gm-cm²/sec –a HIG-40, in other words. Because of this enormous H, the Earth for about as long as man knows, has maintained its axis pointing fairly well fixed in space within 1 deg of the North Star. The fact that the Earth's axis remains fixed in space, coupled with the rotation of the Earth about the Sun, explains the changes of season. Not only does the Earth keep its axis pointing in the same direction, it also exhibits typical gyroscopic precession. As a matter of fact, the word precession was derived from the motion of the Earth. A torque is applied to the Earth as a result of the gravitational pull of the Moon and, to a lesser extent, of the Sun. This torque tends to make the spinning axis of the Earth more perpendicular to its plane of motion around the Sun than it is. This produces a precession of the Earth's axis about an axis in quadrature to both the spin axis and the torque axis. The result is the Earth's axis has a conical motion – one complete cycle taking 26,000 years.