Hydraulic Systems: Accumulators Quiz

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Questions and Answers

What is one disadvantage of spherical type accumulators in hydraulic systems?

Failure can be sudden due to diaphragm rupturing. (correct)

They occupy more space compared to cylindrical accumulators.

They can store gas pre-charge for a shorter duration.

They tend to require more maintenance than cylindrical types.

Why are cylindrical accumulators more commonly used in modern aircraft hydraulic systems?

They provide better gas retention capabilities.

They can handle larger pressure differentials.

They are less expensive than spherical types.

They require less space than equivalent spherical accumulators. (correct)

What role does the diaphragm or bladder serve in a spherical type accumulator?

To increase the surface area for gas compression.

To control the fluid flow rate during operation.

To prevent fluid from escaping during pressurization.

To separate the gas and fluid chambers. (correct)

What indicates insufficient pre-load in a piston-type accumulator?

A loud hammering noise in the system. Signup and view all the answers

Which of the following statements about cylindrical accumulators is incorrect?

They usually experience gradual failure. Signup and view all the answers

What mechanism is used to hold the parking brakes in place in an aircraft?

A ratcheting system Signup and view all the answers

How does a brake debooster reduce pressure in an aircraft brake assembly?

By using a larger piston area at the output Signup and view all the answers

What does the anti-skid system primarily do to prevent wheel skidding during braking?

It automatically relieves pressure to brake pistons Signup and view all the answers

What is the primary purpose of the hydraulic power in an aircraft brakes system?

To provide effective braking force Signup and view all the answers

What factor contributes to the effectiveness of braking in aircraft that utilizes brake deboosters?

Lower pressure than the hydraulic system pressure Signup and view all the answers

Why is it important for pilots to monitor wheel rotation during braking?

To prevent tyre blowouts Signup and view all the answers

What occurs when the brake debooster valve is activated?

Pressure is relieved to prevent over-braking Signup and view all the answers

What is a primary challenge of operating the brakes on aircraft with multiple-wheel main landing gear?

Simultaneous braking of all wheels Signup and view all the answers

What is the primary purpose of the power brakes control valve in large aircraft?

To manage hydraulic fluid flow based on brake pedal pressure Signup and view all the answers

What role does the check valve play in the hydraulic brake system?

It prevents loss of brake system pressure during main hydraulic failure Signup and view all the answers

What is a key function of an accumulator in the hydraulic brake system?

To store power for hydraulic units when not powered Signup and view all the answers

In what situation would the pilot need to apply more force on the brake pedal?

When higher pressure at the brake assembly is required Signup and view all the answers

What happens within the accumulator when pressure surges occur?

It dampens the pressure surges in the hydraulic system Signup and view all the answers

Which of the following correctly describes the structure of a typical accumulator?

A sphere or cylinder divided into two chambers, each containing fluid Signup and view all the answers

What is NOT a function of the power brakes actuating system?

Preventing fluid from returning to the hydraulic reservoir Signup and view all the answers

How does the braking system manage higher demands of pressure and volume?

Through the presence of a power brakes control valve Signup and view all the answers

What is the formula used to calculate the working volume of an accumulator given isothermal conditions?

$VW = \left(\frac{P1}{P2}\right) V1 - \left(\frac{P1}{P3}\right) V1$ Signup and view all the answers

In an isentropic process, what is the expression for accumulator size, $V1$?

$V1 = \frac{VW}{P1 \cdot \gamma} \cdot (P2^{\gamma} - P3^{\gamma})$ Signup and view all the answers

Given the following pressures: $P1 = 70$ bar, $P2 = 114.18$ bar, and $P3 = 210$ bar, what is the working volume, $VW$, calculated as $V2 - V3$?

6.6 litres Signup and view all the answers

What units must the accumulator size, $V1$, be expressed in after calculations are complete?

Liters Signup and view all the answers

What type of gas is typically used for pre-charging the air side of a piston type accumulator?

Nitrogen Signup and view all the answers

What happens to the accumulator system in the event of total hydraulic failure in an aircraft?

The pilot can activate a pneumatic valve to use compressed nitrogen. Signup and view all the answers

What is the ratio used in the isentropic accumulator size formula involving the parameter gamma ($\gamma$)?

$\frac{P1}{P2}$ Signup and view all the answers

In hydraulic systems, the value of $\gamma$ is crucial when calculating the accumulator size. What does $\gamma$ typically represent?

Ratio of specific heats Signup and view all the answers

What is the volume of the accumulator, $V1$, under the conditions specified in the example with $VW = 6.6$ litres?

26.51 litres Signup and view all the answers

Which of the following pressures is not specified in the accumulator sizing calculations?

P4 Signup and view all the answers

What is the role of the squat switch in the aircraft brake system?

To prevent brake application when the aircraft is airborne Signup and view all the answers

What happens to the landing gear wheels' rotation when the brakes are applied during landing?

The wheels will not rotate if the brakes are applied while landing Signup and view all the answers

What is indicated on the brakes pressure gauge when the squat switch is closed?

Zero brake pressure Signup and view all the answers

What could be a potential malfunction in the aircraft brake system during landing?

Wheels do not rotate despite the pilot pressing the brake pedal Signup and view all the answers

What effect does the control valve have on the brake system after touchdown?

It allows brake fluid to flow back to the reservoir Signup and view all the answers

When is the locked-wheel detector activated in the aircraft brake system?

When the landing gear is extended but the aircraft is not moving Signup and view all the answers

What is indicated by the condition of the squat switch being in a closed position?

The aircraft is in flight with no potential for brake application Signup and view all the answers

What is the consequence of the squat switch being malfunctioning during landing?

Continuous brake pressure while airborne Signup and view all the answers

What is the primary function of the normal skid control?

To remove hydraulic pressure allowing wheel rotation during slowing down Signup and view all the answers

Under what circumstance does the locked wheel skid control activate?

When tyres fail to maintain friction with the runway Signup and view all the answers

What does the touchdown protection circuit prevent?

Activation of the full braking system before landing Signup and view all the answers

What condition must be met for skid control valves to allow brake application during landing?

The squat switch must indicate weight on the ground along with wheel speed over 20mph Signup and view all the answers

What is the function of the fail-safe protection in the anti-skid system?

To automatically return to full manual brakes in case of system failure Signup and view all the answers

How does the locked wheel skid control differ from normal skid control?

It bleeds pressure for a longer duration to allow wheel recovery Signup and view all the answers

Which of the following best describes the threshold for the locked wheel skid function to operate?

It is inoperative during aircraft speeds less than 20mph Signup and view all the answers

What happens when the normal skid control system engages?

It removes hydraulic pressure from the wheel to prevent sliding Signup and view all the answers

Study Notes

Aircraft Hydraulic and Pneumatic Power Systems

MM3531 Aircraft Systems covers hydraulic and pneumatic power systems.

Scope of Brake System

Aircraft brake systems include independent, booster, power, and emergency brake systems.
Anti-skid systems are vital for maintaining control during landing and taxiing.
Indication and warning systems provide crucial information during operation.
Auto brakes are designed for automatic operation.

Hydraulic Power: Operation of Bicycle Brakes

Images illustrate the mechanical operation of bicycle brakes.

Hydraulic Power: Aircraft Brakes System

Modern aircraft use brakes in main wheels for prompt stopping during landing and taxiing.
Pilots activate brakes by pushing rudder pedals.
Brake operation transforms kinetic energy into heat energy through friction.

Hydraulic Power: Types and Construction of Aircraft Brakes

Disc brakes are the common type, with multiple-disc designs used in combination with power brake control valves, or boost master cylinders.
Brake components include pressure cylinders, pistons, relines indicator, pressure plates, and rotors/stators.
Applying the rudder pedal extends the piston(s), compressing the stationary and rotating assemblies for braking.
This friction slows and stops the rotating wheel.

Hydraulic Power: Aircraft Brakes Actuating Systems

Three basic actuating systems exist: independent, booster, and power systems.
Independent systems function autonomously.
Booster systems use the aircraft hydraulic systems only when required.
Power brakes use the main aircraft hydraulic system for pressure.

Hydraulic Power: Aircraft Brakes Actuating Systems (Independent)

The independent system includes components such as a reservoir, brake pedals, brake assemblies, and master cylinders.
When the pilot pushes the rudder pedal, the piston inside the cylinder extends, pressurizing the hydraulic fluid that leads to the brake assembly.
When the pedal is released, the return spring retracts the piston to its original position.

Hydraulic Power: Aircraft Brakes Actuating Systems (Boosted)

Boosted systems are for medium-sized aircraft requiring greater braking force than independent systems can provide.
Pressure delivered to the brakes is proportional to the foot pressure on the rudder pedal.
The boosted master cylinder increases the pressure applied to the brakes.
This increased input pressure from the aircraft's main system leads to a greater force applied to the brakes.

Hydraulic Power: Aircraft Brakes Actuating Systems (Power/Master Cylinder)

Power brake systems use the main aircraft hydraulic system as their pressure source for larger aircraft.
The brakes power control valve receives braking pedal input, either directly or through linkages.
This valve meters hydraulic fluid to the brake assemblies.

Hydraulic Power: Accumulators

Accumulators are sphere or cylinder-type devices divided into two chambers.
One chamber holds fluid under system pressure; the other chamber is filled with nitrogen or air.
Accumulators dampen pressure surges, complement the power pump, provide power during pump downtime, and compensate for internal/external leaks.

Hydraulic Power: Accumulator Types

Spherical type has a rubber diaphragm or bladder inside.
Cylindrical type has an internal piston to separate fluid and gas/air chambers.

Hydraulic Power: Working Principle of an Accumulator

Diagrams illustrate pressure and volume changes in accumulators for isothermal and isentropic processes.

Hydraulic Power: Sizing of Accumulator: Sample Calculation

Mathematical formulas for sizing accumulator for given inputs (e.g., linear actuators, flow rates, forces).

Hydraulic Power: Emergency Brake System

In total hydraulic failure, pilots can use pneumatic systems to supply compressed nitrogen to the brakes.

Hydraulic Power: Parking Brake

The parking brake system is activated by engaging the mechanism.
The system holds the brakes in the set position.
Releasing the parking brake requires depressed pedals for complete disengagement.

Hydraulic Power: Brake Deboosters

Brake deboosters allow aircraft brakes to operate efficiently with lower pressures than aircraft hydraulic system pressures.
Deboosters use the principle of force application over different-sized pistons to reduce pressure.
Hydraulic pressure that inputs to a smaller piston translates to a reduction of force over a larger piston, resulting in lower outputs.

Hydraulic Power: Anti-skid System

Prevents wheel skid during braking.
Automatically reduces pressure on braking pistons of a specific wheel if skid is imminent.
An anti-skid system operates in conjunction with the main aircraft brakes system.

Hydraulic Power: Wheel Speed Sensors

Alternating current (AC) tachometer generators are mounted on the axle.
The sensors measures wheel rotational speed and changes.
Results are sent in DC voltage to a control box for subsequent operations.

Hydraulic Power: Control Box (Anti-Skid System)

Crucial for preventing brake application prior to touchdown.
Prevents skid during landing deceleration.
Circuit monitors the system operation and returns to manual operation in case of failure.
Warning lights indicate any malfunction.
Detects when wheel skid is imminent or occurring.

Hydraulic Power: Touch Down Protection

Protection measures during landing to prevent wheel skid or damage as the aircraft lands.
Wheels rotate without application of brakes when reaching landing speed.
Detects if wheels are not rotating, or are not rotating fast enough.

Hydraulic Power: Touch Down Protection (Malfunction)

System malfunctions/warnings indicate problems in the system.
Problems that occur when the system malfunctions can lead to potential issues with landing, especially landing gear and wheels

Hydraulic Power: Indication and Warning System (Anti-Skid)

The system uses a two-position switch to control its operation.
An anti-skid inoperative warning light alerts pilots when the system is off or faulty.

Hydraulic Power: Anti-Skid Control Valve (Anti-Skid System)

Valves are hydraulically located and serve as a conduit between the main brake system and the return manifold.
Valves work to direct fluid flow during normal braking operations.

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Description

Test your knowledge on different types of accumulators used in hydraulic systems. This quiz covers the advantages and disadvantages of spherical and cylindrical accumulators, their roles, and common misconceptions. Ideal for students studying hydraulic systems in engineering.