Strange UFO Effect

Prandtl-Glauert singularity is an effect which presents itself as a cone of vapor over airplane fusellage. For its formation high speed and high air humidity are needed. The effect makes an impression that a plane flies out of the other dimension. Let's study this breathtaking phenomenon.

One can easily take the effect for an UFO.

Despite the common opinion that the effect is created when a plane breaks the sound barrier is not right. The engines with extrahigh turn can create it when taking off as the very engine has got low pressure and the blades work at near-sonic speed.

The thing is that a plane creates a high-pressure area in front of it and low-pressure area behind. The low-pressure area starts to get filled with air masses from adjoining areas.

The effect can appear when a plane flies at the sonic speed or a bit lower. The sound barrier gets broken at 1235 km/hr and the near-sonic speed is 965-1448 km/hr.

The sonic element is however crucial here. The cone form is created by the sonic power which moves faster than the waves it creates.

If to take a plane as a crest we can imagine that these ultrasound crests overlay one another and the cone forms. Its end is the very source of sound.

To become visible for the human eye one more component is needed - humidity. When it is quite high the air condenses and forms a cloud that we see. The effect almost always appears around planes that fly over an ocean at summer - the combination of heat and water gives the proper level of humidity.

Some also think that Prandtl-Glauert singularity gets created as a result of fuel combustion.

Those people take the effect we are talking about for the inversion layer, that is an unnatural flower that appears from condensed vapor produced by the plane engines. But that's not the same thing - the vapor is already there, before a plane flies through it.

It is also needed to say about air pressure. When a plane flies at near-sonic speed the air pressure around it is called N-wave since when the pressure depends on time the result looks like letter "N".

The effect is named after two outstanding scientists who discovered this phenomenon - Ludwig Prandtl and Hermann Glauert.

Believe it or not, you can create this effect outdoors yourselves. You will need two things: a whip and high air humidity day. If you lash a whip strongly you will observe the very Prandtl-Glauert effect.

via felbert