Gears and Transmission

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Questions and Answers

What are spur gears primarily used for?

Carrying heavier loads at high speeds

Changing drive directions

Transmitting power between intersecting shafts

Connecting parallel shafts (correct)

What is a characteristic of helical gears compared to spur gears?

They are noisier in operation.

They connect shafts at 90-degree angles.

They operate at lower speeds.

They can handle heavier loads. (correct)

What is the primary function of thrust bearings in a helical gear system?

To support the gear's weight

To increase rotational speed

To withstand end thrust produced during meshing (correct)

To eliminate sliding contact

What differentiates hypoid gears from spiral bevel gears?

They connect non-intersecting shafts. Signup and view all the answers

What is the design feature of double helical gears?

They eliminate end thrust. Signup and view all the answers

What is a notable characteristic of spiral bevel gears?

They are quieter and smoother in operation. Signup and view all the answers

What is the shape of the teeth in bevel gears formed on?

Conical blank Signup and view all the answers

Which type of gear is designed specifically to handle heavy sliding contact and usually requires special lubrication?

Hypoid gears Signup and view all the answers

What is the primary function of an idler sprocket in a chain system?

To support the chain run Signup and view all the answers

What is a significant advantage of belt drives compared to chain drives?

They do not require lubrication Signup and view all the answers

Which type of screw jack mechanism is specifically noted for its low-friction design?

Recirculating ball mechanism Signup and view all the answers

What is the role of a bellcrank in mechanical systems?

To transmit force or motion and change their direction Signup and view all the answers

What type of material are push-pull rods usually made of?

Aluminium alloy tubing Signup and view all the answers

In the context of screw jacks, what does the term 'high mechanical advantage' refer to?

Reducing the required effort to lift a load Signup and view all the answers

How is the adjustable feature in push-pull rods typically utilized?

To facilitate compliance with varying tension Signup and view all the answers

Which statement accurately describes a torque tube's function?

It converts linear motion into rotational motion Signup and view all the answers

What feature distinguishes the worm-and-nut mechanism from the recirculating ball mechanism in screw jacks?

The friction level during operation Signup and view all the answers

What characteristic of torque tubes can limit their functionality?

Fixed length, diameter, and angle Signup and view all the answers

What is the speed ratio of a gear train defined as?

The number of teeth on the driven gear divided by the number of teeth on the driving gear. Signup and view all the answers

What is a disadvantage of worm gears?

They produce a large sliding movement of their teeth, leading to inefficiency. Signup and view all the answers

In a single-reduction gear with a ratio of 2:1, how does the number of teeth on the driven gear compare to the driving pinion?

It is twice that of the driving pinion. Signup and view all the answers

What is the primary purpose of reduction gears in engines?

To allow the engine and propeller to operate at their most efficient rpm. Signup and view all the answers

Which type of gears are primarily used as reduction gearing in aircraft engines?

Epicyclic (planetary) gears Signup and view all the answers

How is a sector gear different from a complete circular gear?

It represents only part of the circular gear's full rotation. Signup and view all the answers

What does the gear ratio indicate?

The amount of torque on the driven shaft relative to the driving shaft. Signup and view all the answers

What effect do idler gears have on the speed ratio of a gear train?

They make no difference to the speed ratio. Signup and view all the answers

What is one arrangement that can be used in differential gearing?

Two inputs and one output. Signup and view all the answers

How is the speed ratio calculated for a pair of meshing gears?

By counting the number of teeth on each gear. Signup and view all the answers

Which type of gear system is known for keeping the propeller on the same axis as the engine output shaft?

Epicyclic Gear System Signup and view all the answers

What characterizes bevel epicyclic gears compared to spur planetary gears?

They are longer but have a smaller diameter. Signup and view all the answers

Which of the following describes the function of a rack-and-pinion gear system?

Transmitting motion between a rotating spur gear and a linear rack. Signup and view all the answers

In what way does the gear ratio relate to the speed ratio?

The gear ratio is the reciprocal of the speed ratio. Signup and view all the answers

What is the gear ratio when gear A is the input and gear C is the output with the output speed being three times less than input speed?

3:1 Signup and view all the answers

What role do idler gears play in a gear train arrangement?

To transfer drive without affecting gear ratio Signup and view all the answers

How can the direction of rotation be determined based on the number of gears between the input and output?

Even number results in opposite direction, odd in same direction Signup and view all the answers

What is required to allow for lubricant penetration and thermal expansion in meshing gears?

Backlash Signup and view all the answers

What can excessive backlash lead to in a gear assembly?

Increased gear noise and broken teeth Signup and view all the answers

In a planetary gear system, if the sun gear is fixed and the ring gear rotates, what happens to the output speed?

It turns more slowly than the sun gear speed Signup and view all the answers

Which component of a chain assembly helps prevent the chain from coming off the sprockets?

Chain keeper Signup and view all the answers

What materials are commonly used to manufacture sprockets in aircraft systems?

Steel and alloy Signup and view all the answers

How are control chains in aircraft systems typically sized?

By pitch, width, and roller diameter Signup and view all the answers

What type of backlash is typical for gears, as mentioned in general specifications?

0.003 to 0.004 inches Signup and view all the answers

What is the main function of sprockets in chain systems?

To convert rotating motion to linear motion Signup and view all the answers

If a chain is classified as non-reversible, how can it be connected?

Using end-fittings in one direction only Signup and view all the answers

What type of gear system arrangement is often used in gas turbine air-driven starter motors?

Planetary gear systems Signup and view all the answers

What happens if gears are set too far apart in an assembly?

Excessive backlash Signup and view all the answers

What type of gearing may be used to transmit high torque?

Helical gears Signup and view all the answers

Study Notes

Purpose of Gears

Gears transmit power, alter drive directions, and adjust rotational speeds when combined with bearings and shafts.

Spur Gears

Straight Cut: Common everyday gear with straight teeth; connects parallel shafts; noisy but easy to manufacture.
Helical Cut: Has angled teeth; allows for smoother operation and heavier loads; requires thrust bearings due to end thrust produced.

Special Types of Gears

Bevel Gears: Designed for intersecting shafts; can operate at various angles; spiral bevel gears are quieter and carry greater loads.
Hypoid Gears: Similar to spiral bevel gears but non-intersecting; used in automotive differentials; quieter than spiral bevel gears and require extreme pressure lubricants.
Worm Gears: Provide large speed reductions; quiet operation; vary in efficiency due to sliding movement; over 20:1 reductions prevent worm wheel from driving worm screw.
Rack and Pinion: Converts rotational motion to linear; common in automotive steering systems.
Sector Gear: Only part of a full circle is used; limited output shaft rotation.

Gear Reduction

Reduction Gears: Enable engines and propellers to operate optimally by lowering propeller speeds; single-reduction gears comprise small and large gears.
Epicyclic (Planetary) Gears: Comprises sun gear, planetary gears, and outer gear ring; suitable for reduction in aircraft engines; maintains alignment with engine output shaft.

Gear Ratio and Speed Ratio

Gear Ratio: Indicates torque on driven shaft compared to driving shaft; reciprocal of speed ratio.
Speed Ratio Formula: Ratio uses the number of teeth on driving and driven gears to determine speed differences.
Idler Gears: Intermediate gears that do not affect speed/gear ratios; can adjust rotation direction without altering ratios.

Direction of Rotation

Determined by counting gears between the driving gear and the gear in question; even numbers reverse direction, odd numbers maintain direction.

Backlash

Defines the clearance between meshing gears; some backlash is needed for lubrication and thermal expansion; excessive backlash can lead to gear damage or failure.

Chains, Belts, and Sprockets

Chains: Utilized in aircraft control systems for force transmission; made from multiple linked elements; high tolerance in manufacturing.
Sprockets: Convert rotary to linear motion; can be made from various materials; idler sprockets support chain run.
Belts: Used in systems like helicopter drives; quieter and smoother than chains but carry less load.

Screw Jacks

Types: Includes worm-and-nut and recirculating ball mechanisms; convert rotational into linear movement; common in aircraft for various applications.
Worm-and-Nut: Features Acme or square threads; utilizes shaft rotation to drive the nut.
Recirculating Ball Mechanism: Low friction design enhancing efficiency; frequently used in flap drive systems.

Control Rods and Linkages

Push-Pull Rods: Facilitate linear motion transmission; adjustable ends eliminate tension variability; made from aluminium alloy tubing.
Bellcranks: Change force direction; pivot on bearings with no inherent adjustment; allow force to be transmitted effectively.
Torque Tubes: Convert linear motion to rotary; transmit force over long distances; not adjustable in length or angle.

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