With the growing global air travel, the number of aircraft and pilot demand, aviation training centers are doing a great job trying to keep up with the aviation training equipment. According to the ainonline.com “only five years ago, 50 full flight simulators (FFSs) represented the historic total annual output for all producers. The simulator industry is now approaching a combined 100 new FFSs a year”.
In the modern simulator industry electromechanical actuators take the leading position, thus allowing to provide the market with full flight simulators driven on the electric motion system. However, there are plenty of older FFS in the market with the hydraulic motion systems, which continue operating successfully. So what is the actual difference between electric and hydraulic system?
System reliability depends on a proper operation of serial combination of components. When one fails, it causes all subsequent components in a functional chain to fail. Different systems require different maintenance.
Hydraulic motion systems need to be checked regularly and this procedure should be carried out after a number of estimated hours of operation which may vary according to recommendations of the FFS hydraulic motion system provider. It requires checking and replacing filters, general maintenance, taking fluid samples and running diagnostic tests to ensure proper work. Moreover, hydraulic oil has to be replaced after a manufacturer-indicated amount of operation hours.
On the other hand, electric systems typically require lubrication after a producer-indicated number of hours of operation as well as checking of power wiring and a multitude of limit switches, control logic verification and encoder or resolver operational checks.
Whether the motion system is electric or hydraulic type, they both use electric energy to perform and an uninterrupted supply is a must for their performance. Hydraulic motion system needs electricity for the motor, which drives the oil pump to create hydraulic oil pressure needed for the hydraulic actuators moves. Which motion system is more cost-effective considering the electric energy consumption? For example, new Boeing 737 NG FFS with electric motion system uses ~65 kvA electric and a 30-year-old Boeing 737 CL FFS needs 187,5 kvA. This example shows that new electric systems use much less electric energy that is important for training centers to plan their expenses.
Durability and reliability
Hydraulic systems have been operating for many decades (some of them count even 60 years of performance) with the same hardware in place. Although some parts made from rubber like gaskets and hoses have been changed, the main components are still original.
Electric motion systems are used for approximately 10-15 years. Over this time some parts have been changed, some parts have been replaced with hydraulic system components, some require generous amounts of oil for special moves.
Sometimes the unexpected power-cuts happen. Which motion system is safer for pilots training in the FFS cockpit?
Electric motion systems usually are designed to “lock” in position and it requires an additional procedure for “safe landing” to bring the training device back to a safe “park” position. For this procedure it needs power to bring the simulator back to the “park” position. The newest FFS have an additional battery as energy back-up in case of unexpected power-cut and it would be enough to bring the FFS to the safe “park” position.
What happens in a hydraulic motion system? In case of a power loss, hydraulic systems have reserve pressurized fluid that lets them return home to a “park” position for a safe exit by the crew or it can be easily designed to lock-in-place position.
For the engineers, who are responsible for the FFS maintenance, the electric motion system is considered to be safer. The reason lies in the construction of the hydraulic system, with its high pressure of 100 bars in the hydraulic hoses. There is a risk that the pipes may explode and the oils will be forced out.
Hydraulic power is environmentally less friendly because of oil leaks, spills, and the need to periodically dispose of used hydraulic fluids. In case of system malfunctions and breakdowns, it can cause local pollution due to one FFS motion system using 1,5 tons of oil which would be spilled out.
Electric motion system has no oil which would need to be spilled out or could leak. However, it faces another environmental issue of heat release. Both type systems generate heat while operating, but what is the difference? The answer is the amount of generated heat. Electrical motion system generates great heat and it needs to be air-cooled to work properly, so the generated heat migrates to the surrounding environment, probably a space with people. Hydraulic systems generate less heat, and that heat can be released in a remote mechanical room space.
Hydraulic motion system solutions are extremely quiet (the sound levels up to 50dbA) when the HPU is located remotely in the place with extremely good noise isolation. The noise created by hydraulic system is closely related to the HPU. This issue was solved locating it remoted from the motion platform. This decision has two positive results: a reduced noise level as well as controlled and reduced heat rejection.
Electric motion systems can be noisy because of their moving parts in the actuators. This happens because of a particular FFS design.
New developing technologies are taking the market segment over, however, the reliable old hydraulic motion systems haven’t retired yet and still operate successfully. Although, the hydraulic system has been used and developed for many years, most FFS providers choose to work with new technologies and offer FFS with electric system and becoming dominant in the market.