The History of Stealth in Aviation III

The idea of creating stealthy aircraft capable of avoiding detection is as old as the idea of using aircraft in war. All the way back in World War I the Germans created the Linke-Hofmann R.1. This was an attempt to create an aircraft that the enemy would see straight through, and they did so by replacing much of the canvas on its body with cellophane. This ended up having the opposite effect, however, as it would catch the sun's rays and reflect them brightly into the enemies' eyes. Despite its failure though, it shows forward thinking on their part and represented a first step towards stealthy aircraft.

Linke-Hofmann R.1 image from the Ray Wagner Collection

These days stealth is generally referred to as L.O, or Low Observable. This description has five major elements to it:

1. Radar Cross Section (R.C.S.)

2. Acoustic Signature

3. Infrared (I.R.) Signature

4. Visibility

Today we tackle the topic of Infrared (I.R.) signature. I will also be referring to it as thermal signature, as infrared light is used to look for heat which in turn can be used to locate humans and their vehicles.

Infrared tracking basically uses sensors that are extremely sensitive to energy in the infrared wavelength, and are used to track objects which emit any sort of heat. Infrared is a kind of light which is at too short of a wavelength for human eyes to detect, but that can be used to measure the heat an object gives off. At short ranges this could mean detecting troop positions, missile sites, or night-vision. At longer ranges though, this can be extremely useful to detect and track aircraft. Infrared is often used for the navigation of missiles to strike a moving target (these missiles are called "heat-seekers").

Image of a Sidewinder "Heat Seeking" Missile courtesy of the US Department of Defense

Since aircraft, like any fast-moving machine, produce a ton of heat this makes infrared especially useful against them. The exhaust created by jet engines especially can act like a homing beacon of heat that leads directly to the plane. Because of this, the first and most important part of reducing a plane's I.R. signature is reducing the visibility of this exhaust.

Since IR tracking is a relatively new technology as far as early warning and detection of aircraft is concerned there are only a few examples of aircraft really designing their stealth around minimizing their thermal signature. That being said, we once again have to mention the B-2 and its exceptional design. As mentioned in the last part, the B-2's engine placement gives it a big advantage when it comes to thermal stealth. The placement inside the body not only dampens the sound but also helps insulate the engine itself. This makes it much harder to detect by using infrared sensors. The stealth bomber also deals with the extremely hot gas that exits its engines by directing a lot of air from its surroundings behind the engine in order to cool the exhaust down extremely quickly. It also leaves a long path behind the engines covered by special heat-absorbing tiles. These help cool the air down further before it becomes visible from the ground.

Diagram of B-2 from USAF and Northrop Grumman Corp.

#B2 #Warbirds