What Are Engine Nacelles And Why Are Some Serrated?


An aircraft engine nacelle is the housing the protects the engine from the elements, and some of the designs have notches like the Boeing 787 Dreamliner. Why are they styled in such a way? Let’s find out.

787 engine
Why do some engines have little notches? Photo: Victor via Flickr

What is an aircraft engine nacelle?

An aircraft engine is a powerful piece of machinery that needs to be protected and contained within some casing. In early versions of aircraft, the engine was in the fuselage with a propeller sticking out the front of the aircraft, or in the case of the first commercial jet aircraft (the de Havilland <Comet), designers chose to embed the engine into the wing.

However, when engines became bigger, they would no longer fit inside the wings of planes. Plus, airlines wanted the ability to swap out an engine if it was offline with a working version to keep the plane flying. Thus engine nacelles were born!

However, nacelles are not just limited to engines and can include anything housed outside the plane. Some designs like the B-52 Stratofortress have two engines in a single nacelle, and radar planes insert radar dishes inside their top-mounted nacelle.

And for those wondering, nacelles is a french word for a small boat, which you may agree is rather fitting.

Lufthansa 747-400
Typically engines are stored in nacelles in all modern airliners. Photo: Getty Images

Why do some have notches?

You may have noticed that some engine nacelles have a bit more of a creative finish, like notches. This is not just a cosmetic reason but is to reduce noise.


For the Boeing 787, the planemaker worked with its engine supplier, GE Aviation, and NASA to change the way noise from the engine travels during takeoff and landings at airports. This was in order to future proof the design for upcoming noise laws.

Some of these changes included adding serrated edges to the engine nacelle called chevrons. These chevrons reduce the noise from the blast of the engines by changing the way the air mixes after passing through and around the engine. Hot air passed through the engine meeting the cold air from around it creates turbulence that carries the sound further.

The Boeing 787 engines have notches. Photo: Eric Prado via Wikimedia

This design change is so effective that a few hundred kilos of sound insulation has been removed from the design.

“This program achieved or exceeded all our expectations,” said Walt Gillette,
Boeing Commercial Airplanes vice president for 787 Engineering, Manufacturing, and Partner Alignment.

“What we learned from QTD2 (Quiet Technology Demonstrator 2) will help make the 787 better for people—better for the passengers inside the airplane, and better for the people who live in the communities around airports.”

Less noise also means that the Boeing 787 can operate early in the morning or late at night – typically reserved for quiet aircraft or at a time when airports typically close due to nearby residences.

Boeing gave the technology to other engines that fly on its aircraft, like the Rolls-Royce Trent 1000 and others, including the 747-8 and Boeing 737 MAX.

“We see this technology making a big difference on the 787, the 747 Advanced, the next-generation single-aisle airplane, and all-new generations of aircraft from here forward,”

What do you think? Let us know in the comments.