The Mysteries of the B2
January 17, 2003 –
Updated December 8, 2005
Page 7
A video shows the B2's MHD system in action.
When trying to keep a secret, one must be extremely vigilant. Sometimes, certain clues inevitably leak out. By entering:
http://www.is.northropgrumman.com/videos/b2_tx.wmv
into your browser, you can view a one-minute sixteen-second downloadable video (1.9 megabytes). It displays a series of aerial shots of the B2—this is the actual B2, not the hypersonic bomber.
Here is the key short excerpt:
The B2 passing through transonic flight above the sea. Migration of the electrical discharge (MHD)
into the water vapor environment. Isolated sequence converted into an animated GIF by Christophe Tardy.
Note that the glow of the discharge affects only the upper part of the aircraft.
The B2 is equipped with a plasma generation system using the surrounding airflow as an MHD generator, enabling it to be enveloped in plasma even in subsonic configuration. This plasma is not visible during daylight. It is this plasma that renders the aircraft stealthy by absorbing and scattering radar waves. If this "demonstration B2" weren't so obviously not stealthy, people might wonder, since it is generally believed to be undetectable. In the video, this minimal MHD system is activated. Normally, the electrical discharge would not be visible. However, when the aircraft flies over the sea—a region saturated with humidity—it passes through transonic flight. Below is a wing profile in transonic regime. As the aircraft approaches the speed of sound, "compressibility effects" appear near the thickest part of the profile (indicated by a dashed line).
Airplane wing and fuselage in transonic regime.
This is precisely where water vapor condensation occurs, usually fleeting because aircraft are not designed for prolonged transonic flight, where they are also unstable. When an aircraft breaks the sound barrier, it passes through a speed range where it doesn't tend to linger. The same applies when slowing down. Below is a photo of an F-18 flying over the sea in transonic flight. A variable cloud-like formation appears, obviously white, since it is... water vapor.
F-18 performing a transonic passage in humid air.
(Photo provided and transmitted by J. Costagliola)
Other photos of the same phenomenon, reported by Gérard Chenu:
This link leads to a video showing an aircraft passing through transonic flight. It's not a "crazy plane," but a classic example in fluid mechanics:
http://www.incroyablement.com/images/videos/asf/avionfou.wmv
In the video showing the B2, however, we see something entirely different. See the two images below:
The electrical discharge fills the transonic region where water vapor condenses.
Notice the reflection of the glow on the wing's upper surface.
Second image extracted from the film: the vapor bubble is at its maximum extension.
The same applies to the electrical discharge.
What do we observe? On the upper part of the aircraft—where the MHD system is located, primarily at the engine air intakes and exhaust nozzle—the vapor bubble is strongly luminous. This is normal: air filled with tiny water droplets is more electrically conductive. The electrical discharge therefore tends to spread throughout this region. Clearly, this vapor bubble emits light, due to the radiative de-excitation of gas molecules excited by collisions with free electrons in the discharge. This luminosity is greatly attenuated, or even absent, on the underside of the aircraft.
How did the Air Force allow such images to be released? In our opinion, because no one paid attention. Under normal conditions (matching all other footage in the video), the electrical discharge is invisible. It became visible only for a brief moment because the water vapor condensation associated with transonic flight suddenly increased the air’s electrical conductivity. These images were handed over to a company tasked with editing this one-minute video. No one noticed the abnormal coloration and luminosity of the vapor bubble during this very short sequence. Only a specialist’s eye could detect this anomaly.
Moral: Even when great care is taken to conceal things, clues always remain.
The image below shows the same halo phenomenon around the B2, but with the MHD system deactivated.
Halo of micro water droplets from condensation around a B2 passing through transonic flight
MHD system deactivated. (Photo provided and transmitted by J. Costagliola)
Another image, transmitted by Eric Dezoête
The background clouds indicate the air's humidity
Submitted by reader Laurent Molieras, found on an Air Force website:
An odd image
We see again the theme of a vapor cloud forming near the main wing section of an aircraft in transonic flight. The reader then poses two questions, to which I cannot immediately provide answers.
- Why does this phenomenon not occur on both escort fighters as well?
- Why is it limited to the upper surface of the aircraft?
Some observations: The aircraft are flying through humid air (over the sea). We know this transonic phenomenon is quite sharp and fleeting, corresponding to a relatively narrow speed range. It reflects a localized "compressibility" effect just before shockwave formation around an object. To be complete, one should mention a regime where air density can vary, not just pressure (hence "compressibility" and "decompressibility"). One might also consider that the three aircraft may not be flying at exactly the same speed. The B2 might be catching up to the two fighters. But this hypothesis seems unlikely. Finally, the B2, being more compact than the escort fighters, might experience this phenomenon before the others. Thus, the condensation could occur on the B2 before appearing near the two slimmer aircraft. Furthermore, fluid mechanics experts might offer insights into why this phenomenon occurs only on the upper surface. Still, something remains strange. Let's examine the attitudes of the different aircraft:
The B2 is presented as an aircraft expected to operate near (the lower limit of) the speed of sound. In such a flight regime, it should fly at low angles of attack—see the image provided earlier by Dezoëte. Yet here, its angle of attack appears relatively high. If it is flying horizontally, its speed would be significantly below transonic. But nothing indicates it is flying this way. It might instead be in ascending flight, transonic, with the pilot just pulling back on the stick. This observation would also apply to the second aircraft in the background, but not to the third, which wouldn't...