to the B2 bomber to the F-35 but what about  helicopters. They are an integral part of the  

military but the majority of them are hardly what  you would call stealthy and ever since the advent  

of radar-guided and heat-seeking missiles they  have been more vulnerable than their faster-fixed  

wing cousins. Although we've had hints of a  black ops stealthy helicopter with the raid  

on bin Ladins compound in 2011, there isn't  the rotary equivalent of the F-35 in service. 

But one was developed over 20 years ago and its  mission was to do then for helicopters what the  

F-35 has done now for fixed-wing aircraft with  stealth, sophisticated digital battlefield field  

electronics, advanced networked sensors,  high performance and firepower. Even though  

it was praised by the military, just two  prototypes were ever built. This is the  

story of America's first and so far last stealth  helicopter, the Boeing–Sikorsky RAH-66 Comanche. 

This video is sponsored by Brilliant The story of the Comanche starts  

back in the early 1980's with the US  Army looking at replacing the OH-58  

Kiowa and OH-6 Cayuse scout helicopters with  something more survivable but also capable  

of attacking lightly defended targets. Attack helicopters had come about during  

the Vietnam war when gun platforms had been  fitted the Bell UH-1 Iroquois or the Huey  

to give them some form of protection when  flying troops into battle but it soon became  

apparent that a dedicated platform would be  required to make a true attack Helicopter. 

The first attempt was the 1962 Bell Model 207  Sioux Scout, this introduced the key features of  

the modern attack helicopter, the tandem cockpit,  chin-mounted gun and stub wings for weapons.  

Whilst the US Army liked it they thought it was  too small and underpowered. Bell replied with the  

Model 209 AH-1 Cobra which used the same engine,  transmission and rotor systems as the Huey. 

The AH-1 Cobra was light, manoeuvrable  and effective but lightly armoured and was  

susceptible to enemy fire which in the mid-1970s  led to the development of the McDonnell Douglas  

Apache AH-64 as a replacement for the Cobra.  This was more like an airborne tank, very well  

armoured with a wide array of weapons but this  lacked the light manoeuvrability of the Corba. 

By the early 80s the US Army was looking for  a light attack and reconnaissance helicopter  

but one which would be heavily armoured and use  stealth technology to defeat more sophisticated  

radar and heat-seeking missiles allowing  to not only act as a forward scout for  

the more heavily armed Apaches but also  attack smaller targets when it found them. 

This resulted in the LHX or light  helicopter experimental program  

but as a portent of things to come this  took nearly a decade to come to a conclusion  

and award the contract to build the advanced armed  reconnaissance and attack helicopter prototypes  

to Boeing-Sikorsky in 1991 with a development  budget of $2.6 Billion. 1200 were to be built  

at a cost of $28 million per helicopter. The program was going be the next  

generation helicopter and would introduce  advanced new and untried design features.  

This would take the stealth knowledge gained  from previous programs like the F-117 night hawk  

as well as introducing the concept of the digital  battlefield using networked sensors to instantly  

transmit the location and strength of the enemy  back to mobile headquarters directing the battle. 

To do this many new technologies would have to  be developed. The fuselage for example was a  

composite made up of 350 parts, a big reduction  compared to the 6000+ parts for a normal  

metal helicopter of a similar size. It used the flat faceted construction first seen  

on the F-117 to reflect radar signals away and was  coated in radar and infra-red absorbent materials  

which reduced the Comanches radar cross-section to  360 times less than that of the Apache AH-64 and  

half that of a hellfire missile allowing it to get  five times closer than an Apache before detection. 

To help reduce the radar cross-section the wheels  and weapons including the chin-mounted Gatling gun  

retracted into the body which also had the  benefit of making it more aerodynamic and faster. 

It was constructed with Kevlar and graphite  armour that could withstand heavy machinegun  

fire from up to 23mm shells and it  would also be more crash-resistant. 

As helicopters operate close to the ground and at  slower speeds than attack aircraft the first thing  

that most people know when one is approaching is  the loud chop, chop, chop sound from the rotors.  

This is caused by the interaction of the  airflows from the main rotor and the tail rotor.  

So on the Comanche, the tail rotor was  an enclosed ducted fan to reduce airflow  

interaction and help reduce the sound, this was  also tilted over to be less radar reflective. 

The tail ducted fan was also very powerful  and along with sophisticated control systems  

allowed the helicopter to change its angle of  direction whilst it was travelling in a straight  

line. The effect of this was that it could fly  sideways at speed or even backwards and aim its  

weapons without having to change course. It also had the benefit in that the tail  

fan blades would be protected during low-level  manoeuvres at night and when flying at treetop  

level, a time when it's difficult for the pilot to  see obstacles like tree branches, something that  

could damage normal tail rotors and bring down  the helicopter. The composite tail fan blades  

could also withstand hits from 12.7mm rounds. To further reduce the sound, the main rotor had  

five composite blades downward-canted which had  less of a regular beating sound and more of a hum  

that was half the noise of a regular helicopter  and could blend into the background better. 

To defeat heat-seeking missiles the engine exhaust  from the twin T800 turboshaft engines would be  

channelled along the tail to exit by the fan where  it would be cooled by the fresh air from the fan. 

The powerful engines and streamlined body made  the Comanche very fast at 324km/h, 201mph. 

The Comanche had extensive electronic  countermeasures and fire control systems including  

a 2nd generation long-range Forward-Looking  Infrared Sensor to spot targets which could then  

be illuminated with a laser to guide missiles. It  could be fitted with the longbow millimetre radar  

based on that of the Apache above the  rotor to look over hill crests and trees. 

Data from these could fed the automatic  target identification and tracking system  

and forward it to others in the force  a bit like the F-35 does now to provide  

near real-time intelligence. The crew had  helmet-mounted displays and a night vision  

system and the separate crew cabins which were  sealed again chemical and biological attack. 

The triple-redundant fly-by-wire flight  control electronics were fault-tolerant  

so that if part of it was damaged in an attack,  backup systems could instantly over take over. 

The first prototype started flying in  1996 with a second joining it in 1999  

but as development and tests went by, more  and more problems started to crop up. The  

sheer number of new systems and technologies  being brought together in one aircraft meant  

that Boeing–Sikorsky were playing an increasing  costly game of whack-a-mole to iron out problems  

which weren't helped by the Army shifting the  goalposts and adding new feature requests. 

The Army want more weapons so stub wings were  added with hard points for more missile but this  

then made it hundreds of kilos heavier and  less aerodynamic but no one at the time had  

figured this out until it was loaded with weapons. The Comanche was far more reliant on software for  

all its systems but this was proving to be buggy,  sensors were unreliable and the radar absorbing  

body was susceptible to corrosion from rain.  All of this, the changing requirements and poor  

management slowed the project causing cost overuns  which ended up tripling the development costs. 

One example was the Army's request that the range  of the helicopter which was designed to be a scout  

be raised so that it could be flown across  the Atlantic and yet it was designed with a  

narrow body so that it could be more  easily transported by plane or ship. 

As the cost went up, budget cuts from the  so-called peace dividend after the fall of  

the Soviet Union put more pressure on the  program which was designed to fight a war  

against an enemy which no longer existed, so  large numbers of reconnaissance helicopters  

were seen as no longer necessary. Afghanistan and the war on terror  

moved the focus away from cold war era  design goals even though other stealth  

and UAV programs were given more money but the  stealth helicopter was seen as a niche project. 

Over the lifetime of the program, the total  number on order was gradually cut more and more  

which meant the unit cost of each went up and up  which emboldened the project critics to push for  

even more cuts saying they were now too expensive. In 2002 it was estimated that by 2008 the Comanche  

would be taking 40% of the army's  aviation budget, money that could  

be put to better use funding development and  renovation of the existing helicopter fleet. 

But in 2004 the Comanche project  was abruptly cancelled by the Army,  

the development cost had risen to $6.5 billion  

and the cancellation fees to Boeing and Sikorski  added another $500 million to the final bill. 

So like many other forward-thinking programs, the  RAH-66 Comanche ended up as another museum piece  

with both the prototypes now located at the US  Army Aviation Museum at Fort Rucker, Alabama. 

Time will tell if a future stealth helicopter  will see the light of day in the US  

or maybe other countries might be looking  to take on the challenge and create the  

worlds first operational stealth helicopter. One of the feature requests was for the Comanche  

to control UAV reconnaissance drones which  ironically helped hastened it's cancellation  

because it was realized that they didn't need the  Comanche to act as sort a data middleman and as  

drone technology advanced they could be controlled  more directly from regional headquarters. 

The future of UVA's and helicopter drones  will need skilled people to design,  

build and operate these new aircraft and  our sponsors for this video Brilliant  

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