Shock Wave Formation in Transonic Flight

Formation of a shock wave around the engine cowl of a Boeing 767 at high speed.

The aircraft itself isn't going supersonic, but it's going fast enough (probably around Mach 0.8) that the local airflow around the engine cowl is supersonic, in a small area. This is called "transonic," and results in the formation of a shock wave at a right angle to the surface of the plane. The air in front of the shock is supersonic, and the air behind it is subsonic.

The shock wave is visible because of the abrupt change in the density of the air. The change in density causes a change in the refractive index of the air, and so the scenery behind it is optically distorted. This is similar to how a spoon in a glass of water looks "bent" at the water's surface, due to the difference between the refractive indices of water and air. It helps that this is seen nearly edge-on... if I had been a couple of rows further forward or back, it might not have been visible.

Further information for the curious:

[haljohnson]

The faster you go, the further aft the spike shifts. On the p-38 when the spike reached the far aft of the wing, it would lift the tail up causing transonic dives that ripped the tail off. On the x-1 Chuck Yeager watched the spike shift back into his ailerons and could barely hold control at mach .88. At mach .94 the spike hit the elevator and made it completely uncontrollable. The secret was to make the entire elevator movable with no tabs or hinges to get caught in the spike. Solving the ailerons was done by making the movable elevator work as elevons so that ailerons werent needed in transonic. Once you go fast enough (past mach 1) the spike is completely behind the aircraft and it flies smoothly again.

[theroskyyyy]

Nice one, that a perpendicular presure wave, it seems to be learning forward but its perpendiculsr to the surface at its point of origion, looks awsome

[billmceachern]

A very good aircraft to see this phenomena on is a Folker F28 - the shock happens just aft of the wing leading edge and is visible down most the span. Best observed if the sun is in front of the aircraft.

[stringmanagmaildcom]

I observed similar on the wing of a 737 one time. Took videos of it on my phone and showed to a friend of mine who is an aero engineer. He said the same thing. Density change, trans-sonic region, very cool!

[josephastier]

I need to start paying closer attention when I have a window seat. That was cool, and I have probably seen it before, but never knew it.

[darkdelta]

Well, today I was made aware of this phenomenon, thanks for posting. There's a science to everything.

[joeschmoe]

When I flew the MD80, we could feel buffeting from transonic flow at the engine pylons at around M.82 all the way up in the cockpit.
Back it off to M.78 or so and it would stop.

Thanks for posting this, what a cool video!

[compressor_stall]

Seeing shockwaves form in transonic fight is absolutely awesome

[SternLX]

Friend: "You can't 'see' compressed air!"
Me: Shows him Pressure Waves caught on video.

[BillPalmer]

I remember being able to see that on the upper wing surface of a 727, there would be a light shadow as well.

[Pguy]

Thank you for posting! I’ve seen this on the wing before too. Most folks never notice this stuff.

[Rocket-hbjh]

Thankyou……. I saw this phenomenon on a Qantas 747-238B about 40-45 years ago and I could only describe it as looking like a thin jet of heat wobble or like a thin strip of cellophane protruding up from the engine nacelle and no one, not even engineers could tell from my description what it was, the closest they came was to say perhaps it was a form of St Elmo’s fire but I’ve seen that and that’s not what it was……. You have solved a 45 year old mystery for me 😊
By the way, my Dad worked for Qantas and so did I and I moved on to other companies but spent 37 years in aviation and this old mystery gets solved by a YouTube video LOL

[hueyrosayaga]

I love non-clickbait stuff like this. Keep it up man! And nice observation. I would’ve missed that.

[jimmcmahon]

Pretty common to see along the span of any aircraft flying at high-subsonic Mach and with the light at your back. There, it appears as a thin, linear shadow near the surface and along the span at or near mid-chord, dancing fore-and-aft somewhat. Pretty cool...thanks for posting!

[lawrencemartin]

That is a great spot and really cool. A good visual demonstration of the phenomena.

[sky]

That looks more like a warp in the fabric of the time-space continuum, but that's just me. :)

[dickdickenson]

WOOW! That is amazing video! I have never tought that it's possible to see it by naked eye...!

[cde]

Captain was probably a commuter and had a flight home to catch! That’s a nice shockwave, it forms because the air forced over the engine lip is accelerated.

[hook]

Call me silly but I've been a jet engine mechanical engineer for almost three decades. The aluminum leading-edge ring on the jet engine, nacelle, that happens to be a Pratt Whitney, has anti-ice, which is engine bleed air.
You can't pump bleed air into the nacelle without having a place for it to go.
You're simply seeing engine bleed air dumping out of one of several ports, or holes, located in different sections of the nacelle. While the air being dumped overboard may be transonic, the aircraft, especially on initial descent, is nowhere near transonic.
The 767 has a cruise of between Mach .82 and Mach .84.
It definitely doesn't accelerate above those numbers on decent as the autopilot/autothrottle is pulled back damn near to the stops. Decent is in the mid Mach .70's

[TeemarkConvair]

nice! with all the flying i had done(707, CV990, DC-10 ) i had never seen this effect.