The History of Stealth in Aviation IV

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

This time we'll tackle the fourth and final of these elements: Visibility. Visibility is probably the easiest of the elements to understand. It's just how easy or hard the plane is to see.

As stated before, the Linke-Hofmann R.1 was one of the first attempts at this type of stealth. Failure though it was, it - along with other Nazi designs - inspired generations of designers to pursue aircraft that the enemy could never so much as detect, forget shoot down.

Nowadays a plane's visibility is reduced in a few key ways. The first is to use non-reflective paints. If you've ever seen a bare metal plane before you will know exactly why this is done. The more a plane reflects the sun's light, the more visible it is from far away. A plane that might otherwise pass as a bird could radiate telltale light back to the ground giving away its position. A lot of bright paints have this same issue, reflecting too much light back to the ground. For this reason dark paints are typically used: gray for day operations where a super dark plane may contrast too brightly with the sky, and black for night operations where it doubles up as an effective camouflage.

Image of the SR-71 Spy-plane by Judson Brohmer of the USAF

In addition to this, stealth aircraft often fly at altitudes where contrails won't form behind them. Contrails are trails of water vapor that form behind a plane due to the hot exhaust that it ejects in flight. These can create a visible trail of what look like long white clouds behind a plane and reveal it. During stealth operations, routes are meticulously charted and can even take into account the likelihoods of contrails forming at various altitudes when other factors aren't taking priority.

Image of an A380 and its contrails by Stiopa via Wikimedia