BS ISO 22072:2011 pdf download – Aerospace — Electrohydrostatic actuator (EHA) — Characteristics to be defined in procurement specifications
Allowable fluid loss, allowable refill interval, and life of fluid shall be specified.
4.7Strength and life
Static strength is defined by the following.
a) Limit load (without permanent deformation or leakage): maximum driving or resisting force capability of the unit,with account taken of any force limitation function possibly incorporated. In the case where ananti-back-driving device is included, the maximum holding force may define this limit load.
b)Ultimate load (without rupture): ×1,5 limit load.
c)Proof pressure (without permanent deformation or leakage): x1,5 maximum permanent pressure associated with the limit load or ×1,5 maximum operating pressure.For lines only submitted to the fluidcompensator pressure: ×1,5 maximum fluid compensator pressure.
d) Ultimate pressure(without rupture): ×2 maximum permanent pressure associated with the limit load or x2
maximum operating pressure.For lines only submitted to the fluid compensator pressure: x2 maximumfluid compensator pressure.
NOTE The above factors are recommended values. Other sizing cases, not specific to EHA and depending on thesystem configuration, may apply.
e) lf the actuator is connected to a hydraulic system, in order to avoid the need to service for example, the
usual hydraulic system sizing conditions shall apply to all parts exposed to the system pressures.
f)The EHA shall be able to withstand any bottoming loads corresponding to the design conditions of thecontrol system.
4.7.2 Fatigue and wear life
The fatigue life under external loads,acceleration， and pressure transients possibly generated by theoperation of the unit is associated with the absence of crack initiation.Generally the fatigue life of the actuatoris equivalent to the structural life of the vehicle.Appropriate scatter factors shall be used.
lf the actuator is connected to a hydraulic system, the usual hydraulic system pressure impulse requirements,SAE ARP1383B or specific requirements shall apply to all parts exposed to the system pressures.
The wear life under external loads, strokes, velocities, acceleration, and combinations thereof, is associatedwith the absence of component wear resulting in unacceptable degradation of performance.Generally, thewear life of the actuator is equivalent to the structural life of the vehicle. Appropriate scatter factors shall beused.
All components do not necessarily have the same life objective.4.8Protection against fire risk Special precautions against fire risk shall be specified, covering normal operation and failure conditions:
protection and monitoring functions;
4.9 Reliability and safety
The criticality level shall be defined.
Reliability shall be specified according to the application (mean time between failures).
Safety shall be expressed in terms of probability of loss of function, loss of control, runaway, etc.
Maximum resistance between any point of the EHA and the bonding connection shall be specified.
4.11 Lightning, electromagnetic compatibility
In accordance with ISO 7137,
or applicable specifications, requirements and/or levels shall be specified.
Direct lightning strike effects shall be specified.
4.12 Maintainability and servicing
Maintainability requirements shall include, where applicable,
4.13 Thermal requirements
Maximum heat rejection, maximal fluid and skin temperature shall be specified.
5 Installation and operating conditions
Data on the general environment and intended operating conditions for which the unit shall be designed are
specified in 5.2 to 5.8.
5.2 Mechanical data
The mechanical data shall include the following:
geometry and output load kinematics;
inertia of the load;
nature and characteristics of the load – aiding and/or resisting forces, constant or viscous frictions;
load attachment stiffness;
fixed structure attachment stiffness.