Engine question

[sunshine40]

I flew Easyjet to Rome last week and a fine flight it was too. When we flew over the Alps we hit a little turbulence and the engine noise changed, sounded like they were grinding the air almost.

This happens on all the flights I go on and I know it's normal I would just like to ask if anyone knows why engine noise changes on flights when we're cruising? Does air get heavier and lighter?

Clearly I'm totally in the dark here!

cheers

[TightSlot]

When power is increased on modern engines, the engine fan noise becomes more noticeable (especially mid and front cabin), and this noise sounds and feels more like something spinning around and doing stuff than the normal jet roar (there'll be a more technical explanation Im sure ;)

Often, subject to various ATC and performance restrictions, pilots will attempt to climb out of turbulence, to a higher level, if they expect a smoother ride: This would require a power increase for the climb, and would account for the noise that you noticed.

I stand to be corrected, or even disproved by one who flies them - call this an educated guess?

[TotalBeginner]

I think it's also sometimes due to slight differences in the "thrust note" (for want of a better word) between the two engines. So you get changes in sound as the sound waves move in and out of phase, similar to turbo props when they are slightly out of sync.

[mutt]

Its also possible that the aircraft was slowing down to the Turbulent Air Penetration speed so you would have heard a difference in the engine noise.

Mutt

[Final 3 Greens]

If it was an Airbus (319), it could be that you heard the FADECs (Fully Automatic Digital Engine Controls?) continuously adjusting the power settings to maintain a target speed.

I'm not a airline pilot, but I understand from my neighbour (who is) that this is what might happen in turbulence, as the ''bumps'' that you feel are actually the reaction of the aircraft to gains or losses in airspeed.