Questions tagged [hydraulic-system]

Hydraulic systems on aircraft use pressurized liquid to move components such as control surfaces and landing gear.

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2answers
730 views

Is the 737NG hydraulically controlled or electronically controlled?

I know that the 737NG is not fly-by-wire, but are the control surfaces controlled with hydraulic systems that transfer the input from the pilot to the control surfaces via fluid (hydraulics), or is ...
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1answer
143 views

Where is the control loop of the actuator closed?

When electro-hydraulic servo-actuators are used for the actuation of control surfaces in aircraft, linear variable differential transformers (LVDTs) are used for position or velocity feedback. There ...
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2answers
127 views

What does the isolation valve do in the landing gear extension/retraction system?

The isolation valve is an integral part of the landing gear extension/retraction systems on most larger aircraft. What is its funtion?
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3answers
8k views

Why is the most common hydraulic fluid so poisonous?

The usual hydraulic fluid, Skydrol, is poisonous. If it makes it to the air conditioning system, it causes fume events that may have adverse health effects up to and including at least one fatality. ...
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0answers
55 views

What factors should be considered to select jet-pipe or flapper-nozzle technology for a primary control surface?

How is the servovalve mechanism chosen between these two mechanisms? what are their advantages and drawbacks?
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2answers
160 views

How is the bandwidth of an actuator selected for a primary flight control surface?

How the bandwidth of an actuator is selected for a primary flight control surface? Is there any standard? Based on what factors this decision is made?
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3answers
3k views

Do jackscrews suffer from blowdown?

With hydraulic control surfaces, at high airspeeds, there is a point where aerodynamic loads exceed the capability of the actuators. This limits control authority and can result in the control surface ...
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4answers
14k views

What triggers the PTU (Power Transfer Unit)?

As highlighted by this answer and by this page the PTU (power transfer unit) is an hydraulic driven pump. It gets energy from one hydraulic system and uses it to pressurize another hydraulic system. ...
6
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1answer
575 views

How can the F-16 remain stable when there is a loss of hydraulic power?

Edit for justification: This question is different from If the EPU (Emergency Power Unit) on a modern fighter jet fails, will the aircraft drop out of the sky? for the following reasons: The ...
6
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1answer
322 views

Why does the B737NG need electrical power for aircraft towing?

I have read the AMM for towing and one of the mentioned steps is to supply electrical power. Is it because you need power to turn on the hydraulics in order to pressurize your brakes? For B737NG
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6answers
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Why do most commercial airplanes use hydraulics instead of electric/servo motors?

I'm sure it's possible to use servo motors to get precise control of the ailerons, elevators or the rudder. But still, hydraulics are widely used instead. Hydraulics do have a disadvantage that a ...
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2answers
746 views

What is the purpose of the shuttle valve in a Piper Arrow's landing gear system?

This is the PA-28R-201 landing gear hydraulic system diagram. I am wondering how this shuttle valve functions. Research I have done indicates that a shuttle valve blocks one attachment to the valve ...
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3answers
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How strong someone should be in order to fly without “power steering”?

Planes these days use fly by wire systems while older ones had a mix of hydraulics with electronic assistance like the MD-11 (And maybe 737-800?). But what would happen if you lost the electronic ...
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2answers
225 views

Why does only one hydraulic intake line from the reservoir have a filter on the Arrow II?

This is a portion of an Arrow II landing gear hydraulic system diagram. I noticed that there are two intake check valves, one located on each side of the pump, that would allow flow from the ...
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0answers
230 views

What is the difference between a pressure switch, high-pressure control, and low-pressure control in a landing gear hydraulic system?

This is an Arrow II landing gear diagram. In the diagram, the high and low pressure controls look like check valves. The pressure switch is unclear. What are these three items, and what purpose ...
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2answers
112 views

Surface deflection if loss of hydraulics on combat jet

In a typical combat jet from the 1970ties, at loss of hydraulic pressure, how does the deflection surfaces behave? If it happens on the runway, will the weight of the surfaces make them deflect ...
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4answers
10k views

What is the difference between MIL-H-5606 and MIL-PRF-5606 hydraulic fluid?

what is the meaning of PRF here and can you differentiate them visually ?
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1answer
116 views

Are hydraulic retractible landing gear possible

One of the impediments and drawbacks to extending landing gear in light of building larger engines are the larger space required for the taller gear. Would hydraulic retractable gear that works as a ...
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2answers
980 views

How many hydraulic systems does the Boeing 757 series have?

How many hydraulic systems does the B757 series have, does it have a Power Transfer Unit (PTU)? What is the operating pressure of the hydraulics in the Boeing 757? How big is the hydraulic reservoir?...
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4answers
9k views

Can the autopilot (or stall avoidance system?) of the B737 MAX 8 be overridden by sheer force?

A New York Times article from today about the Lion Air Flight 610 crash claims that in order to control the airplane the pilot could have braced his feet on the dashboard and yanked the yoke, or ...
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1answer
5k views

What happens if an aircraft's hydraulic system starts leaking during a flight?

What will happen if hydraulic fluid starts leaking during a flight? What will happen to the overall performance of the flight, and how will the pilot compensate for the loss of the system?
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1answer
728 views

Fly-by-wire vs hydraulic systems [closed]

So, the great old argument, flyer-by-wire systems vs conventional hydraulics. I was wondering which one was better and why. Which one is safer? Pros and cons in terms of safety? Basically, I just ...
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2answers
459 views

What is the average aerodynamic load on a control surface of a commuter-sized airplane?

I'm doing a study about aircraft hydraulic pump sizing. In order to do that, I need to know the size of a flight control actuator, then determine the maximum flow and pressure that the actuator needs. ...
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1answer
796 views

Why does the A320 right aileron float on dual engine failure?

On this question for the A320 after dual engine failure it says: When the hydraulic power is lost, the right aileron is lost, and is in the upfloat position. Why would this affect only the right ...
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1answer
147 views

Is it possible to 'retrofit' electric flight control actuators to replace existing hydraulic actuators on aircraft?

Read a bit about the potential cost savings of replacing existing hydraulic aileron actuators on large commercial aircraft such as the A350/380 with electrohydraulic/electromechanical actuators. ...
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1answer
236 views

How is the direction of the hydraulic fluid changed so that the cylinders and pistons can move backwards and forwards?

How is the direction of the hydraulic fluid changed, so that components and actuators (cylinders and pistons) can move backwards and forwards?
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1answer
161 views

How can I reduce the responsivness of my homebrew brake system?

I have a hydraulically actuated aircraft brake system. Each main landing gear are equipped with brake disk hydraulically operated. The actuation is realized independently for each wheels by means of ...
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1answer
531 views

Do Airbus aircraft have an “off” position for their landing gear?

I know some Boeing aircraft feature an up, down, and "off" position for their landing gear lever. I know that some Boeing wide-body jets do not have a 3rd lever position, but still have an "automatic" ...
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1answer
4k views

Why is fuel used as a hydraulic fluid?

Why is fuel used in some servo-systems as a hydraulic fluid (fueldraulic systems) of modern civil and military aircraft such as the Boeing 777-200/-300 (Pratt & Whitney PW4084) or the Lockheed ...
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3answers
4k views

Why is it called “STBY RUD” on a Boeing 737?

(Source: b737.org.uk) Anyone knows why "STBY RUD" is named "STBY RUD" when the selection of the switch position activates the standby hydraulic system as well as the standby rudder system (by opening ...
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2answers
2k views

How does hydraulic actuator servo valve feedback work?

The book Aircraft Systems uses the following diagram for a mechanically controlled hydraulic linear actuator (for moving a control surface e.g. an aileron): The following explanation is given about ...
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2answers
4k views

Why is 3000 psi the most common hydraulic pressure used in commercial aircraft?

As per the article on this website (from 2002), most of the aircraft use 3000 psi as hydraulic pressure: Since the 1970s, military aircraft have been using 5000 psi hydraulic systems, which use ...
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1answer
580 views

Have there been fully pneumatic aircraft?

Have there been any passenger aircraft that used pneumatics for all of their on board systems that required force actuation, such as: landing gear; wheel brakes; nose wheel steering; propeller ...
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84 views

What are the reasons for using hydraulic power on major aircraft systems? [duplicate]

What are the actual benefits or advantages of using Hydraulic energy in aircraft systems, compared to pneumatic and electrical systems.
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1answer
209 views

What would be the potential effects of not having an accumulator in the hydraulic system?

In an aircraft, what would be the potential effect of not having an accumulator in the hydraulic system?
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0answers
735 views

What is the noise that the A320 makes on the ground? [duplicate]

I've noticed that planes in the A320 family make a sawing noise on reaching the gate. The link below may give you an idea of what I mean (although the A320 in the video is still taxiing). Is this a ...
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1answer
1k views

What was the first airplane fitted with a hydraulic system?

What was the first airplane fitted with hydraulic system? Where was it used? What are the fundamental differences between the first systems and those that are used now?
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1answer
89 views

May someone please suggest EHA design procedures for AFS?

Are usual electro-hydraulic actuator designs for aileron control employable for aeroelastic flutter suppression? If not, where can I find design procedures for this specific case?
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2answers
464 views

Can the fluid from one hydraulic circuit go to another one (voluntarily or not) in flight?

Given the following facts for airliners: Fuel can be transferred in flight from one tank to another Hydraulic energy can be transferred without fluid transfer from one circuit to another in flight ...
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1answer
670 views

How much hydraulic fluid is in a jet airliner?

Hopefully the title is self-explanatory. I am wondering how much hydraulic fluid - in mass and volume - is carried in normal operations for a jet (the bigger the aircraft in your answer the better).
5
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1answer
838 views

What are hydraulically powered and electrically controlled actuators?

I thought that the actuators are hydraulically controlled when the hydraulic fluid changes their position, but some aircraft (Bombardier, for example) has hydraulically powered and electrically ...
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3answers
2k views

Is is possible to use non-hydraulic fluids in a hydraulic system in an emergency?

In this answer, Ralph wrote: Spare fluid is common enough to have on-board to replenish the resevoirs. After reading that, I recalled an incident I was told ...