Standing Shock-Wave on Subsonic Commercial Aircraft

[SuperLadiesman5]

what am i supposed to look for????

[aardvark2zz]

Only the very recent ones which are copied from a discussion already talked about somewhere else ! :-)

[shadowhunter45s]

how does this happen?

[aardvark2zz]

Similar to a mirage, the air density over the wing is less; but in this case, due to the high speeds, a sudden abrupt barrier (shock-wave) abruptly bends light. 

We don't see this as much today since planes fly slower to save fuel. Therefore, the shock-wave is less intense and abrupt.

[aardvark2zz]

Also, see the links in the attached notes in the upper-right.

[megagues]

i like shock waves, they go boom!!

[314159fritz]

Yeah, I use to see that in the older days. Too bad it's rarer today. I also saw smaller ones near the engine cowlings and mounts.

[aardvark2zz]

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I wish the naysayers would at least prove their point with ANY logic. But, most have one liners that are not even remotely substantiated with any minimal logic.

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[aardvark2zz]

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(see pic link in description) The distortion is in focus as good as an air refraction can be. Look at the very clean vertical edges.

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[aardvark2zz]

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For those scratch believers, (see pic link in description) please do explain how come the "scratch" is in focus !! Only large military super cameras with massive signal processing are capable of using a depth of view of around 1500:1 !!!

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[aardvark2zz]

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Also, there is quite a bit of zoom. This seriously limits the depth of focus. Certainly in a situation like here where, up to, 1500:1 it would be rarely possible with personal cameras. If it's a distortion on the outer window then we're talking about a few cm.

Look at the video; especially freezeframe.

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[aardvark2zz]

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Anyone who still believes it's a window distortion then they'll have to explain why the detailed thin vertical lines are in focus even though the inner window is almost touching* the camera (a cm) and the wing tip is (approx 1500) cm away.

Note* : that's intentional to seriously minimize distortions from the window.

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[aardvark2zz]

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The optical path looking towards the trailing edge passes through the boundary at a point close to the trailing edge; which also explains the lack of parallax when the camera moves. If it was a defect in the window there would be a lot of parallax wrt the camera. Some horizontal movement of the vertical "lines" occur due to the movement of the boundary which is due the movement of the wing as it flexes and passes through a bit of turbulence and due to a bit of roll.

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[aardvark2zz]

see figure. do google wiki FAA-8083-3A_Fig_15-9.png

Look at the image, more specifically, for e.g. M=0.77, at the blue area and it's boundaries/perimeter. The camera is approximately located in the center of the blue area and is looking at the leading and trailing edges; in other words looking through the boundaries which are the shock-wave boundaries, this is where the light bends (at the boundaries). The boundaries are where the air flow changes drastically.

[aardvark2zz]

General comments:

If it was a deformity in the window, explain how the "lines" don't move relative to the wing during bumps in the flight. See the Parallax principle due to near and far objects. Come-on, do the basic science.

We both use to see those on many flights, in the past, today it's much harder due to the lower speeds.

see wikipedia Parallax

[LTF85199]

I didn't believe this was actually present on an airline jet until i read it on an Fundamentals of Aerodynamics from John Anderson Book, I just thought it was the result of the plastic passenger window!

[bwalt822]

It is amazing how people assume that they know about transonic and supersonic airflow with no education on it. I'm an aeronautical engineer and can bet my degree that this is 100% a standing normal shock wave. See the vids that I just took on a 757 nearly the same effect.

[73aussie1]

what ???

[alvaroe16]

To all those users who think they know because they are pilots or frequent flyers, I recomend you to read "Modern Compressible Flow by John D. Anderson.

Once you understand Normal Shocks, we can talk and see if this is real or not.

HOWEVER:

aardvark2zz, the tittle of the video is not completely accurate as what you recorded is not exactly a standing/stationary wave.... it is a Recompression shock and not a wave.

[alvaroe16]

As an Aerospace Engineer and pilot, I have to say that this is very likely. In fact, when designing an airplane, it is important to understand the location of this Normal shock because after this point you will get unfavorable conditions( turbulent flow, separation etc.)

I must say that this is something you will only be able to see in older airplanes since newer designs have supercritical airfoil which will prevent this from occurring.

[Jetflir]

As a pilot for a major airline I have heard and seen this many times. The "local" mach number over the wing does indeed go sonic. Due to the wing curvature, the air molecules are forced to accelerate faster than the aircraft speed, creating a lower pressure and therefore lift.

On the 747, the big hump creates a very low pressure at cruise speeds, especially around and above the cockpit. The noise above .83m (cruise is .85-.86norm)is so loud that we wear noise canceling headsets.

[SpinBoldak]

I saw this very effect today on a 757. I thought there was something on the window, too. But the wave moved and you could also see the shadow of the prismatic effect.

I'm say I'm a fair judge as I have a major in aviation and I fly jets for a living.

[doomsmash123]

i'm sorry i'm not sure whats happening all i see is a airplane wing with a white line on it, can someone explain please

[228Ghost228]

shockwaves are "invisable" so you cant really see them only a bit. like you see heatwaves on roads.

[LTF85199]

No, don't look at the white line, look along that center line (border between dark grey and silver paint). It is very hard to distinguish a vertical optical wavy thing dancing up and down, it is the called the "normal" shock wave. The wave is comprised of just air so it is transparent to see but rare occasion like this when the sun it at the right position you can kind of detect it.

[Pyrotrons]

aardvark2zz, thanks for sharing the video. This is REALLY cool. Too bad that most people will ignore perfectly good science and call it window effects. I usually such general disregard for scientific explanation on my vid's...had to disable commenting it got so stupid.

[skotlogan]

this is a warp in the window. a shock wave would be very apparent and appear as mist or vapor or a fuzziness. these are obviously warps in the window. no question. i am a commercial pilot and instructor. if people "ignore good science" and have "general disregard for scientific explanitions(s)" then just be happy you know everything

[krisstrigos]

If this is due to warp of the window then the motion of this effect has to correlate to the motion of the camera. We can see the camera move with respect to the wing, the motion of the "warp" is not syncronous in any way.

[andyroo22]

wow so its flying at the speed of sound?

[aardvark2zz]

The plane flies at M 0.85 but the air on top of the wing M 1.0

[kinsley2108]

clearly a warp in the window

[yank2z0025]

Nope, because the spacings between vertical lines are changing quite a bit (note, other parts of the wing are not distorted). Airplane windows are too strong to warp. I've seen these shock waves many times in the past. Nowadays, it's very rare because of fuel savings.

[Coffeeeggsbacon]

thats just a warp in the plastic.

[aardvark2zz]

Nope, for many reasons: "warp" would have unchanging spacings between vertical lines, focus, camera motion, etc....

[largefallingicicles]

The maximum operational speed for the 747 is mach 0.88 which is not even close to a high enough speed to create transonic shock waves. To put it into perspective, going from .88 to .98 is a 70 mph difference. In a steep decent its probably possible to go from a tailwind in the jetstream to neutral winds or a headwind which could do it for a minute. The aircraft stress load would be dangerous.

[aardvark2zz]

No, transonics can start as low as M 0.7 . See wikipedia references in info window.

[LTF85199]

Video no longer avaliable? please re upload...

[tauren224]

Good to know that one, Gypsykingg knows a little about airplanes ;)

[gypsykingg]

no. thats condensation in the air flowing over the wings

[aardvark2zz]

Nope. There's extremely little water content at 39,000 ft. In other words the dew-point is less than -75 C. Even if you had condensation it would be effectively transparent !

[gypsykingg]

not condensation i mean water vapor. my bad on that part. a shock wave will start to appear on the plane when its about to reach super sonic. airliners do not go this fast. they cruse at about 525-565mph determining an what type of plane it is.

[aardvark2zz]

There's no worthwhile water at 39000 ft ! Although these planes don't go above M 0.9, the air over this wing does go over M 1.0. That's why we see the "mirage" on the video.

[gypsykingg]

your ground speed might be that fast but your air speed wont. and if the air over the wing was that fast it would break the sound barrier and the shock wave would rip the wings apart

[gypsykingg]

and also airliners do not go .9 mach cause that is 684 mph. the fastest airliner is a 747 with a max cruising speed of 600. and your ground speed might have been that fast cause maby you had a 100 mph tail wind but your air speed was def not that fast

[aardvark2zz]

see supersonic flow images at address:

en. wikipedia. org..wiki..Transonic

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[gypsykingg]

that is not transonic either. transonic is about .98 mach- mach. when you hit transonic is when you get the shock wave around the plane. airliners go subsonic which means under the speed of sound

[aardvark2zz]

Look clearly at the figure at wiki and you'll note the wing at M >= 0.77 and the airflow over a part of the upper surface going M >= 1.0.

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[gypsykingg]

and you believe that site?

[aardvark2zz]

Very funny !! Just do a search for yourself on the web ! There are many very similar diagrams and explanations. Check out several universities that have aerodynamic engineering depts. This explanation is not rare !

[HiWetcam]

I saw similar on a 777 at normal cruise speed and also on a 747-300 which was trying to make up time. On the 747 there were 2 overlapping waves, one straight out from the wing root and one following the sweep of the wing, about 35 degrees. They did not appear outboard where the wing was thinner and the air did not also have to flow around the fuselage and (on a 747) fat wing root. I was sitting abeam of the waves, does that mean my head and trunk were supersonic and my legs subsonic?

[lushusone]

WAY DOOD, everytime i see the shuttle launch i see that during period prior to breaking the sound barrier, so that really is shock wave? wow kewl, if your in a jet flying faster then sound, can you hear your jets engines? your own voice? your co pilot puking ?

[pmxc]

Yes it is a shock wave. I captured similar stuff in photos once. At high subsonic mach there will be regions over the wing where the accelerated air will have local supersonic flow. Very cool to see as someone trained in aerodynamics. It helps to be looking almost straight along the shock, so that the slight refraction of the light due to density changes become apparent. When I saw it, the sun was also shining along the shock and cast shadows of the shock wave onto the wing.

[kikikeywest1]

Dudes, not a shock wave! Sorry. Looks like the laminar flow across the wing is separating; most likely caused by the "white Horiz piece" near the trailing edge of the wing.

[aardvark2zz]

Nope, the mirages are vertical and not horizontal. The white-horiz-piece is way beyond the mid-wing shock-wave.

[POPWELLMAN]

amazing

[galpir]

@ hbomb1970

Wearing glasses can be useful.

[hbomb1970]

I see nothing

[galpir]

Wearing glasses can be useful.

[phildawe]

either that, or its an angel!, but im sure an angel would look more amazing!

[aardvark2zz]

I'll give a million bucks if you film a shock wave; especially these days with slowed down planes.

[aardvark2zz]

Look at the tall vertical streaks moving in the middle of the video frame, that bend light like a mirage. Those locations are boundaries where the airspeed decreases from above Mach 1. Remember this plane was going Mach 0.85 or below M 1.0 . Today in 2007, this is rarer due to the planes that fly a bit slower or around Mach 0.8 to conserve fuel; then it was gas guzzling time. Also, the pilot might of wanted to arrive early.

[rusak24]

Can commercial airliners handle those kinds of forces.

[aardvark2zz]

No problem as long as the pilot flies within the normal envelope.

[PWN3GE]

oh, i thought those were scratches in the window!

[aardvark2zz]

Yep, I forgot to mention that those are NOT window scratches !! The vertical mirages move horizontally a lot as the wing bends a bit.

[JiggyHolland]

what am i looking at

[LTF85199]

yea those are not shock waves lol. most or all modern airlines have swept wings to avoid shock waves. What you are seeing is the sun rays reflecting of the wing and its appearance through the plastic windows.

[aardvark2zz]

Nope, for many reasons: "defomation" would have unchanging spacings between vertical lines.

[LTF85199]

Sorry you are right, they are indeed shock waves: just read it on Anderson Fundamentals of Aerodynamics and I observed the video more closely this time too. Very interesting thanks for posting.

[lostinthetriangle]

I have seen this before, but can not remember which flight or aircraft it was on.

[aardvark2zz]

Not this exact one since this is from personal stock and is published for the 1st time.

[lostinthetriangle]

Sorry, I meant to say I have seen this same effect before on a previous flight of my own. Either that or it was a bad case of "Deja-Vu".

[JaanAir]

i think its an Boeing 767