THE WHAT, WHEN AND WHY OF HELICOPTER ENGINE WASHES
To help optimize helicopter engine performance and reduce corrosion, you can do several types of washes in the field. Our helicopter engine expert explains what to do and why.
1. WHY ENGINE WASHES ARE NECESSARY
Over time, helicopter engines gradually become contaminated with particles such as dirt, oil, sand and salt. These get drawn into the compressor, where they form a coating on components that reduces their aerodynamic efficiency.
“To compensate for the loss of compressor efficiency, the engine will need to speed up,” explains Pat DiRico, P&WC Customer Engineering, Turboshaft Engines. “This can only be done by adding more fuel.”
With a dirty compressor, the engine will run faster and hotter, increasing fuel consumption and accelerating hot section deterioration.
For engines with automatic cycle counting, there will also be a higher than expected cycle count increase, since the electronic control system uses engine speed and temperature to calculate the number of cycles.
Washing is a simple, cost-effective way to restore compressor efficiency and lower fuel consumption—not to mention reducing corrosion due to sulfidation, enhancing time on wing, increasing the lifespan of hot section parts, restoring engine turbine temperature margins and reducing consumption of low cycle fatigue (LCF) components.
A helicopter engine being washed to restore performance and reduce the possibility of corrosion.
2. WHEN WASHING SHOULD BE DONE
To keep your engine in optimal condition, regular washing is advised. The applicable engine maintenance manuals provide the recommended intervals for all types of engine washes. However, Pat notes that these represent the minimum and may not always be enough.
P&WC recommends scheduling an interval based on your operational experience. You may want to increase the frequency, especially if engine performance deteriorates too much between your scheduled washes. When in doubt, it’s better to wash more often rather than not enough.
In the past, harsh detergents were used for engine cleaning. However, thanks to changes in health, safety and environmental standards, today’s soaps are milder. Cleaning often with soap is definitely better than waiting until the compressor becomes encrusted with dirt. “In short, it is easier to keep a compressor clean than it is to clean a dirty compressor,” says Pat.
3. WHAT KIND OF WASHES SHOULD BE DONE
There are four types of engine wash typically done in the field: engine desalination (rinse), engine compressor performance recovery wash, compressor turbine (CT) wash and external engine wash.
For engine desalination, a water solution is used to rinse off salt deposits and light dirt from the compressor and gas path area.
To minimize the impact on operation, P&WC has recently introduced the possibility of doing a desalination wash on a hot engine immediately after engine shutdown, as long as you use distilled or demineralized water.
An engine compressor performance recovery wash restores the efficiency of a dirty compressor by cleaning it with a soap solution.
A CT wash entails removing salt or contaminants from the compressor turbine with a water solution. A wash tool is typically used. This wash will help reduce the onset of CT blade sulfidation. This may also be done on a hot engine right after shutdown, provided that distilled or demineralized water is used.
If the outside of the engine is dirty, the same soap solution used for performance recovery washes may be used to perform an external engine wash. This will desalinate the exterior and remove any corrosive build-up.
Whatever kind of wash you do, don’t forget to do a drying ground run after it’s finished. This will prevent corrosion due to stagnant water inside the engine.
For more expert advice on optimizing helicopter engine performance, check out Protecting Your Turboshaft Engine from Particles.