The Purpose Of Jet Engine Spirals

You may have noticed those spinning white spirals in a jet engine at one point or another. But have you ever stopped to think about why they’re there? As cute and as comical as they look, those spirals on the spinner cones are more than just for aesthetics – they are an important safety measure for ground crew and even for birds. This article will attempt to enlighten you on this matter!

Advertisements

Ground Crew Warning

The reason for painting designs on engine spinners is for the safety of ground personnel. Working near a running jet engine is extraordinarily dangerous. A Boeing 737 engine, running at idle power, has a hazard zone of 9 feet to the front and sides of the engine. This means that, even at idle thrust, a human that walks in the hazard area runs the risk of being sucked inside and consumed by the engine. When the engine is above idle thrust, the hazard zone increases to 14 feet or more. Engines on larger jets, like the 777 have much larger hazard zones. It is absolutely critical that ground crews can identify a running engine and stay away from it.

Advertisements
hazard-placards Aircraft Engine Spirals
Hazard placards on a 737 engine. If you can read these – YOU’RE TOO CLOSE!
credit: Boeing Aero
Advertisements

Even though jet engines make incredibly loud, whining noises, a running engine may not be obvious to ground crews. Airport aprons often have several airplanes in close proximity with engines screaming. Ground crews wear hearing protection to suppress the deafening noise. Making matters worse, it can be hard to see that an engine is running.

Engine Spinner - Aircraft Engine Spirals
Spinner Spiral on a 767 CF6 Engine
credit: aerosavvy.com

Just like the blades on a window fan, engine fan blades become translucent when they are spinning, especially in the dark. Aircraft engine spirals make it easy to identify a running engine. A quick glance is all it takes.

Advertisements

Working around running jet engines can be very dangerous if one is unaware that it is running. Just take a look at this video of a ground crew who got sucked into a Grumman A6 Intruder and lived:

Advertisements
credit: youtube.com/dark footage
Advertisements

Effect On Birds

Bird ingestion and impacts cause expensive damage to engines. For years, it has been speculated that spinner spirals might startle or frighten birds away from engines during taxi, takeoff, and landing.

Advertisements
Bird strikes severely damage an engine’s components and can cost thousands of dollars in repair costs
credit: sciencephoto.com
Advertisements

However, the spinning spiral effect on birds is highly controversial. A few studies on the effectiveness of spinner spirals for deterring bird impacts have been done. None of them come to a conclusion one way or the other. One study, by the University of Oslo, was conducted on a very small scale with inconclusive results.

Advertisements

Japan’s All Nippon Airways (ANA) completed a well known, year-long study in 1986. The airline painted “Wobbly Ball” styled “eyes” on the engine spinners of several aircraft. The airline found a small reduction in bird impacts on the airplanes with the “engine eyes.” Soon after, ANA added the markings to all their aircraft spinners.

Advertisements
Other spiral variations can be used on aircraft, including the “Wobbly Ball” that was added on Japan’s ANA aircraft engines.
credit: wikimedia
Advertisements

Engineers at Boeing have taken the position that engine spinner spirals do not reduce bird strikes. Boeing’s safety newsletter, Aero, states it is a misconception that airplane colors and jet engine spinner markings help to scare away birds. In addition, a representative from engine manufacturer Rolls-Royce stated: “The nose cone (both in terms of strength and angle) is designed to reduced bird impact damage to the engine and reduce ice build-up. The spirals are there as a warning to ground crew when taxiing. In flight, the spirals could not be seen by birds as the rotation of the engine would be too fast.”

Advertisements

Are Engine Spinner Spirals Being Done Away?

Aircraft Engine Spirals
Embraer 190: No spiral.
credit: JohnMurphy

Not every jet engine has spinner markings. Airplanes are popping up here and there without spirals. The Embraer E-Jets (170, 175, 190, 195) have naked spinners. A few Boeing 757, 787 Dreamliners and 747-8 aircraft have been spotted without the swirls. Manufacturers and operators are questioning the value of the markings.

Advertisements

There you have it! Regardless of their value as a safety enhancement or bird repellent, the spinning swirls are nonetheless a part of aviation history and tradition among Avgeeks alike.

Advertisements

Sources:

Cover Photo: https://aerosavvy.com/aircraft-engine-spirals/?doing_wp_cron=1619728885.7868139743804931640625

https://isaaclow.medium.com/what-is-the-objective-of-the-spirals-drawn-on-jet-engines-c144ef659d16

https://www.google.com/amp/s/amp.interestingengineering.com/heres-why-airplane-engines-have-white-spiral-marks-on-them

https://www.sciencephoto.com/media/852379/view/jet-engine-bird-strike-illustration

Advertisements
%d bloggers like this: