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I see helicopters which have air filters in their engine intakes, but jet fighters and commercial turbojet airliners don't seem to have any filters in their air intakes.

Isn't it true that even tiny particles can damage the turbofan's blades, especially since they rotate at such high speed?

What if the aircraft has to fly through a dusty area?

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  • $\begingroup$ Note that filters are not always the solution. For example, the Su-27 has closable vents on the top of its main two inlets where the main airflow entry can be closed and those two flaps opened in the case of a runway with excessive debris. $\endgroup$ – Jihyun Apr 30 '18 at 15:08
  • $\begingroup$ @Jihyun, MiG-29, not Su-27. $\endgroup$ – Zeus May 1 '18 at 1:05
  • $\begingroup$ @Zeus thanks, sorry about the misinfo. So similar I get them confused all the time. $\endgroup$ – Jihyun May 1 '18 at 2:16
  • $\begingroup$ In general, if you look at military tactical transports, they are all fitted with turboprops, because they are less prone to FOD / dust damage $\endgroup$ – BambOo May 1 '18 at 11:08
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Dust does damage the blades but the effect is like sand blasting; it takes some time to cause structural damage. The turbine engines of airliners can take some dust (by design) but also get extensive maintenance regularly. And if they do get caught in a dust storm they should get out ASAP and get the engines inspected.

The biggest danger dust-wise is volcanic ash as that will adhere to the turbine blades behind the combustion chamber and potentially shut the engine down due to compressor stall. This happened with British Airways Flight 9 where all 4 engines failed. This is why a volcano can shut down Europe airspace.

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    $\begingroup$ Also, jet airplanes spend most of their time above the haze line, where the air is fairly clean (not much dust or other particulates, volcanos excepted of course). Helicopters usually fly near the surface in much dirtier air. $\endgroup$ – TypeIA May 25 '14 at 13:07
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    $\begingroup$ Layman comment: On Aircraft the bulk of the thrust comes from airflow that would have to pass through the turbine/bypass ... i.e. the 'filter' would impede the thrust. In a Helicopter, the thrust comes from the rotors, not the turbine. To make the analogy complete, the helicopter would have to put a filter over the rotors as well as the turbine! $\endgroup$ – rolfl May 25 '14 at 18:35
  • $\begingroup$ The centripetal force in fan of a turbofan engine also causes larger debris to spun out and through the bypass duct. At least some engine also have another debris catcher after the low pressure turbine that ports debris that made it through the fan back to the bypass duct. Fine dust and sand can still make it through and can do a number to the HPT as the sand will melt and turn to glass then solidify in cooling passages. Cooling designers take this into account and try to design in pathways for the sand to get out of the cooling passage. $\endgroup$ – OSUZorba May 11 '16 at 2:13
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In addition to Rachet Freak answer I'll add that helicopter engines are subject to much dirtier air. Aircraft operate from runways which are relatively clean. Due to their speed, most dust and debris that is kicked up is behind the engine inlet so it is not sucked in.

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Helicopters hover and land vertically and therefore their engines ingest air contaminated with kicked up dust. Especially when operating outside paved surfaces this results in considerable pollution. A filter is much more useful here.

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    $\begingroup$ How about MV-22 Osprey? It kicks up a lot of dust when vertical landing, but it doesn't appear to be equipped with filters. $\endgroup$ – ashpool May 28 '14 at 17:17
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    $\begingroup$ @ashpool the MV-22 is equipped with Engine Air Particle Separators, fancy filters. $\endgroup$ – DeltaLima May 28 '14 at 20:06

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