Blue note (aviation)
Encyclopedia
In the context of aviation, a blue note is the distinctive whine produced by some jet aircraft
Jet aircraft
A jet aircraft is an aircraft propelled by jet engines. Jet aircraft generally fly much faster than propeller-powered aircraft and at higher altitudes – as high as . At these altitudes, jet engines achieve maximum efficiency over long distances. The engines in propeller-powered aircraft...

, over and above the sound of their engines and airframe noise.

Considered by some aircraft aficionados as an attractive aural signature of military jets of a particular era, blue notes are often associated with turbojet powered military aircraft from the 1950s and '60s, such as the Gloster Meteor
Gloster Meteor
The Gloster Meteor was the first British jet fighter and the Allies' first operational jet. It first flew in 1943 and commenced operations on 27 July 1944 with 616 Squadron of the Royal Air Force...

 and Hawker Hunter
Hawker Hunter
The Hawker Hunter is a subsonic British jet aircraft developed in the 1950s. The single-seat Hunter entered service as a manoeuvrable fighter aircraft, and later operated in fighter-bomber and reconnaissance roles in numerous conflicts. Two-seat variants remained in use for training and secondary...

.

The jet blue note was used as a sound effect in many of Gerry Anderson
Gerry Anderson
Gerry Anderson MBE is a British publisher, producer, director and writer, famous for his futuristic television programmes, particularly those involving specially modified marionettes, a process called "Supermarionation"....

's productions.

More recently, the Eurofighter Typhoon
Eurofighter Typhoon
The Eurofighter Typhoon is a twin-engine, canard-delta wing, multirole combat aircraft, designed and built by a consortium of three companies: EADS, Alenia Aeronautica and BAE Systems; working through a holding company, Eurofighter GmbH, which was formed in 1986...

 has been cited by some observers as creating a distinctive blue note audible by observers as it flies overhead; the phenomenon is thought to be attributed to its large air intakes.
In the case of the Hunter, its blue note is purportedly produced by interference drag produced by its gun ports, situated under the nose.
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