I was seeing this image:

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The caption of this image says (source):

Here a Belgian NH90 NFH returning after a flight over sea. The helicopter is washed by the fire brigade to remove the salt water...

Should any helicopter be washed after any sea mission? Are those guys washing the engine? If so, should the engine of helicopters be washed after any sea mission?

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    $\begingroup$ This question is broadly related to my answer here where you can find more information on corrosion on aircrafts too. $\endgroup$ – ilias Jan 2 at 0:52

The helicopter shown is an Anti-Submarine Warfare Helicopter. ASW helicopters generally have the ability to detect submarines either Passively or Actively. Passively, sonar-buoys are dropped into the sea and act as ‘microphones’. The returns from these can be triangulated to track submarines.

To achieve this, the helicopters altitude will generally be 1500ft amsl in this role. Unless the winds are very strong salt accretion is minimal. In the active role, the helicopter hovers above the sea and lowers an active sonorhead into the water. The height for this is normally between 40-80ft. The aircraft will stay in this position as long as it takes to establish a 360deg sweep, which is typically less than 5 minutes, or if in contact could remain in the hover for 30 minutes or longer. This process is repeated for the duration of the sortie, which may be up to 2-3 hours.

During this time, the helicopter is experiencing recirculating sea spray. Depending upon the wind / sea state, will determine how much salt accrets (windscreen wipers are required on occasion). The engines experience salt ingestion, which accrets on inlet guidevanes and compressors. As the sortie progresses it is possible to see a reduction in engine performance (the advice for this used to be to find a rain cloud to fly through).

On completion of a days flying over water the engines receive a compressor wash or after a single flight if particularly bad. The airframe will also be washed on a regular basis, perhaps every couple of days. Many bases operating ASW helicopters have dedicated ‘drive thru’ washes. The helicopter will ground taxi over an area with water jets set into the ground and water will spray the airframe and underside of the rotor blades to remove the salt, sometimes known as a ‘bird bath’.

image of Anti-Submarine Warfare Helicopter being washes by an automated washing system

  • $\begingroup$ How is this achieved for ship-based ASW helicopters? It would use a lot of the available freshwater of the ship, no? $\endgroup$ – Roger Lipscombe Jan 3 at 10:43
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    $\begingroup$ You’re correct, however ships that operate aircraft allow for all water usage -the majority of which is taken on in port. The amount used for compressor washes is quite small. Engineers use a dedicated piece of equipment containing compressor wash fluid / water, sorry I don’t know quantities. Airframe washes wouldn’t use fire hoses when embarked for the very reasons you suggest. $\endgroup$ – Rob Wilkinson Jan 3 at 14:12
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    $\begingroup$ Operating aircraft at sea is a huge subject. As mentioned below, airframes are fully treated on all internal hidden surfaces with an inhibitor, compressor washing and airframe washing doesn’t happen on an ad-hoc basis, they are part of scheduled servicing or daily servicing just like refuelling or checking oil levels etc. $\endgroup$ – Rob Wilkinson Jan 3 at 14:13
  • $\begingroup$ As I recall (this is from 40 years and more ago though) we would wash the aircraft weekly and apply an all over coat of WD40; interim cleaning was done based on daily inspections (That was true for both fixed and rotary wing - a fast jet aircraft on the catapult can suck in significant amounts of spray). $\endgroup$ – Peter Smith Jan 4 at 11:38

Aluminum is corroded by salt when wet. Anodization and paint or coatings provide some corrosion resistance, but removing any salt is a big help. Also some components in sea water such as sodium sulfate can cause "hot corrosion" (a specialized high temperature relatively fast corrosion) in many turbine high alloys.


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