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A brief history of LO

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Old December 29th, 2010   #1
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A brief history of LO

All the following content provided by gf0012-aust, recommended reading for anyone interested in the subject.


Stealth is currently a buzzword typically thrown around in debate, and usually (and most commonly) with reference to platforms like the F-22 and F-35. The whole basis of stealth is one of "low observability". very few people in industry use the term "stealth" as it's incorrect - it leads to follow on arguments by the more enthusiastic but less technically astute to also mumble about "invisibility" - when its clearly not.

So, LO platforms have been around for a while and need to be considered in the construct of an ability of a sensor system to correctly identify and respond defensively. The history of LO aerial management is important to look at as it shows why LO adapts and evolves and why itís a moving feast that can't be pigeonholed as an obsolescent capability. I.e. itís evolved over the last 90 years and will continue to evolve.

E.g. the first stealth aircraft was in 1912 - it was a Taube biplane that had clear cellophane type skin named Emaillit to make it transparent vis a vis it's "bulk". LO was regarded as a visibility issue.

The second stealth aircraft was in 1913, (it was a monoplane) - the Germans decided to take it one step further and decided to retain the cellophane surface but to also paint the frame the same colour as the sky, i.e. blue/grey.

The third iteration of this was when the Germans fielded modified Fokker E111's in 1916; Emaillit was replaced with "Cellon". They then tried the same tech on a variety of different aircraft including an Albatross, Aviatik, Rumpler and even a few bombers (VGO-1 and an R-1) so, as can be seen nice idea in principle, but ignored the fact that the engine, fuel tank and pilot were sitting up in the air for everyone to see, but it did show lateral thinking.

LO was regarded as an extension of the previous management of visibility issue. Both concepts failed as the cellophane material actually behaved like a reflector, and the pilots spent most of their time "snow blind" due to reflections. On top of that, Cellon was a material developed for the automobile industry and was applied by soaking it in water, and then stretching it over the airframe. The problem here was that when it rained, the Cellon started to expand, and thus become loose. Not exactly the best thing for an aircraft skin to do...

The next LO aircraft (in relation to enemy sensor systems being able to identify it and respond) was when the British used to run what was called "ferret missions" into the Soviet Union in the late 1940's and 1950's. The British used modified EE Canberraís. When the Soviets developed more persistently competent missiles, radar systems and procedures to intercept, the west coast hi-speed low level ferret missions were reduced and eventually stopped. LO was regarded as low level and high speed as the Soviets did not have radar systems that could deal with low level hi speed entry, and their method of controlling gave the advantage to the ingressing aircraft. At one point the English also went high altitude as the lightened Canberras couldn't be intercepted by the Soviets (this changed once decent SAMs were bought into play). The Canberra by the way was used as initially the RAF were badging USAF B-45 Tornados (which were flying lemons)

As a legacy of the success and superiority of the EE Canberraís, the US then developed their own solution which emerged as the U2 and family. The U2 was considered LO due to a number of reasons, primarily the fact that for a short window of time the Soviets were unable to reach out and touch it. This changed with the arrival of the SA-2.

So the absolute advantage of high altitude to escape SAMs changed the LO requirement immediately. The requirement for LO management then turned to high speed high altitude aircraft.

The first purpose built LO aircraft was the A-12. It was considered LO as the Soviets could not and did not have any system capable of intercepting it. Even though it was "hot" and radar visible, the Soviets had no system capable of catching it - even when they volleyed intercepts. The LO management was high speed, high altitude where the enemy had no meaningful and managed capability to intercept even though the aircraft traffic was identified (not the plane though).

The follow on to the A-12 was the RS/SR-71 Blackbird. What's significant about the RS/SR-71 was that it was the bigger cousin to the A-12. What's even more significant was that it was a much harder beast to see and intercept. The fundamental reason was that not only was it finished in signature managing technologies, but when the impact of chineís around the nose cone area was discovered, its frontal aspect radar emitting footprint was reduced by 90%. The LO management was high speed, high altitude, on-board ELINT and shape management.

At the same time that the SR-71 was in play, the US had also started to use unmanned aircraft for subsonic, low altitude recce. Again, the environment the unmanned aircraft were used in gave the US advantages. Although a number of platforms were lost, it was regarded as a success as it acted as the development vehicle for UAV's, RAM management, signature management, and it involved the enemy reacting to the threat and thus providing USAF escorting aircraft with harvesting opportunities. The Firebees/Lightning bugs were used in various guises, not just low level, so the platforms were adaptive.

The LO management was subsonic, low, medium, high altitude, surface management (RAM "blankets" were actually used) and in some cases, the use of escorting aircraft as emission benefactors (such as Wild Weasels). ELINT versions of these platforms were also developed (147TE). The final product development would have been a low footprint high altitude model to be used over China referred to as the 154.

The next series of LO aircraft basically were from the "Senior xxxx", "Have xxxx" and "Tacit xxxx" series of platforms. These were completely different in LO management, and this was due to a number of reasons. One was the final comprehension of some study done by Bahret (US, and radar cross sections), Wright (US and RAM development)

The real breakthrough though was due to some Lockheed staff (Schroeder and Overholser). They came up with the concept of faceting. The original equations for faceting were done by a Scotsman named Maxwell.

These were then modified by a German electromagnetic expert named Sommerfield who developed signature management equations for simple shapes. This was followed up by some discoveries by a Russian named Ufmitsev who came up with an approach that could be applied to more complex shapes such as discs. The Russian is often touted as being the key to the development of "Stealth" - he is not, but he is one individual along a long line of others who contributed to the comprehension of LO management in its infancy.

What bought Maxwell, Sommerfield and Ufmitsev's calculations and mathematical assumptions to fruition were the improvements made in Computing. Schroder and Overholser were able to marry all of the previous work into a computer model and then made their own breakthroughs.

So, why the long winded history lesson?

Well, thatís because "Stealth" or more correctly LO platforms are a moving feast, a moving technological development where the capability evolves against the response. What was regarded as "Stealthy" even 25 years ago is now obsolete and replaced with new technology concepts.

It's a mistake to look at Stealth as a single technology entity - itís not, and that why when people state that bi-static radar, or OTHR or sympathetically merged commercial solutions such as mobile phone towers hooked into the sensor grid make it redundant, one then ignores the fact that the technology is not static. It ignores things such as the fact that sensor systems find it very hard to discriminate between nature and manufacture, e.g. there is a reason why the West chose subsonic cruise missiles over supersonics - and itís tied into the history of stealth/LO development. The classic example of that is HALSOL (as a concept)

e.g., the F-22 can literally be LO managed due to its design.
Something simple like sensor arrays along the wings are able to be upgraded or improved via software. The F-22 will continue to have a role as the capability to identify it and commit to it is "not easy". The plane is not "invincible" and itís not "invisible" - but itís not meant to be - itís meant to be able to be used as part of a package to exploit a weakness in the defenders grid so that other assets can bring their own "additional" sympathetic violence or electronic "wedge" to bear.

The danger is that some amateurs only consider single platforms, they don't understand, comprehend or appreciate that response is about packages and systems. Itís also why this forum doesn't allow "this vs. that" threads as it just dumbs down the debate to a meaningless cycle of "mines bigger than yours"

As an observation, the next LO platform in real terms will be hypersonics, as it is the next leap forward where existing sensor systems struggle to cope with intercepting it in time. It will then adapt to MIRVed responses on top of that hypersonic vehicle, and it will include (as the Russians have hinted at) controlled flight MIRV's.

In a weapons management sense, miniaturisation of the previous weapons into carriers such as the F-22 make it even more relevant, when one considers that the F-22 will operate as part of a package with Compass and Rivet support, Prowler/Growler, an ability to hook into ForceNET etc etc... One can start to understand that LO participation in future wars is here to stay.

There will always be evolving counter solutions to any effective capability, but LO has been in play now for over 95 years, and we're already onto 6th and 7th generation solutions at the UAV level

By the way, LO management for ships and subs has not been touched upon - and that is a topic in its own right as well.
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