Airframes & Systems

Pressure in an enclosed system exerted => transmitted in all directions throughout the fluid so that the pressure remains the same

In an enclosed system the pressure is transmitted equally and undiminished in all directions => total pressure: dynamic + static

p = F/A in N/m^2

100'000 N/m^2 = 1 Bar

1 bar = 15 PSI = 100'000 N/m^2

Hydraulic: the power derived from motion and pressure of a liquid medium such as oil => Power = Pressure_system x flow rate

up to 2000 big: 3000 PSI

viscosity of a fluid is a measure of its resistance against flowing => if an oil flows slowly it is of high viscosity => the viscosity of a hydraulic fluid should be the lowest practicable to minimize power consumption and resistance to flow

describes the process of vaporization, bubble generation and bubble implosion => result of increase in static pressure

a) Mineral based Hydraulic Fluid: small airplane => is red and flammable

b) Synthetic Fluids (Phosphate Ester Baster Fluids): Transport airplane => higher resistance against caviation and lower viscosity  => lower change of viscosity with temperature 

react aggressively and cause pain on contact with eye tissue

1. Fluid storage => reservoir and Hydraulic lines 

2. Power System => Pumps

3. Operating system => actuating units 

passive system:

active system: pressure is genrated by an engine or electric motordriven pump which runs continusously 

a) open centre system (small aircraft)

b) closed system (large aircrafts) 

pressure is only genrated when the hydraulic operating unit is used  z.B. brakes

pressure and fluid flow continusly generated by a hydraulic pump, it is called an active hydraulic system

=> the unit is below a specified value (es wird pressure benötigt), the unloading valve automatically connects an operating unit to the system pressure

=> no further flow of Hydraulic = result in an increase of the system pressure until a pressure-switching-valve of the unloading valve is reached 

allows free circulation of fluid when the operating unit is not in use => avoids system overload 

allows a free circulation of fluid when no operating unit is in use => conected to the return line

=> the system pressure is low, the flow rate is high

=> a selector valve allows teh pilot the hydraulic power to an operating unit and select its operation 

a) stores the hydraulic fluid of the system and cools the fluid down

b) supplies fluid to compensate for small leaks 

==> usually pressurised via a pressure regulator by air from the aircraft pneumatic system 

a) Gear-type or Vane-type 

b) Piston type pumps (larger aircrafts)

consists of a cylinder block and a piston-and-drive assembly contained in a housing  => the cylinder block with all the pistons is turned by the shaft 

a) Constant Delivery Pump: because of the fixed yoke angle between the cylinder block and the drive-shaft face

b) Variable-delivery Pumps: when actuating units are in operation and decreases the fluid flow when the actuating units are at rest

If the system pressure drops below 3000 PSI, the spring force is higher than the hydraulic pressure generated yoke actuator force  => the compensator spring increases the yoke angle as stated before  

=> no flow rate is required, the system pressure increases back up to 3000 PSI 

=> the electro-motor driven pumps or air => switched off by cutting the power source

=> engine driven pumps are switched off by cutting the pressure line

Immer von der grossen Fläche zur kleinen Flächen => so grössere Filterwirkung 

is simply a gear type or piston-type motor with hydraulic fluid introduced into the pressure port, so that the fluid backing up against the pistons or gears causes them to operate => rotary motion

A restrictor reduces the cross-sectional area of a hydraulic line => this limits the rate if fluid flow (one or both way) => limits the speed

permits free flow of the fluid in one direction and inhibits flow in the opposite direction

protect systems from excessive pressure generated by a pump or thermal pressure ( wenn auf ein Mal ein Überdruck entsteht) => similar to the check valve but the spring us stronger

The system with the higher pressure automatically supplies the operating unit. This is important if one supply system fails

if a blocked filter is bypassed with a bypass valve

provides constant flow rate to a hydraulic unit such as a flap drive => keeps the operating velocity constant

to allow high pressure fluid supply lines to be reduced to appropriate pressures for various application in operating units

a fuse blocks a hydraulic line, if a serious leak should occur

=> the flow rate is within normal operating range, there is not enough pressure loss between the inlet and outlet of the fuse to move the piston against the spring force

=> Broken hydraulic the pressure drops quite => the low pressure the piston is now forced to the right and shuts off the outlet