Stealth HELICOPTERS???

Since the successful raid on Bin Laden’s compound in Abbottabad, Pakistan in early May of this year, much has been made of the mysterious “stealth helicopter” which reportedly crashed during the initial phase of the raid.  Due to the loss of one helicopter and a section of its modified tail boom falling outside the walled compound, there was plenty of news fodder that brought out numerous self-appointed aviation experts, and speculation that ranged from wild guesses to opinions that defied both physics and the physical evidence at the crash site.  With only the tail boom of the new design to look at, it appears that the regular four bladed tail rotor was replaced with a five bladed design, and a hubcap-like cover was mounted over normally exposed tail rotor linkages, which would make at least the tail rotor both quieter and stealthier.

But like “jumbo shrimp” and “military intelligence”, “stealth helicopter” is a awkward concept at best.  While it is possible to make a helicopter quieter and while its huge radar-reflecting cross section might be made smaller, helicopters in this class are still a twenty thousand pound whirling mass of rotating and vibrating parts.  All of this does not add up to a package that “can be hovering right next to you, and you wouldn’t know it”. With all apologies to Blue Thunder, Airwolf and even the Romulans, it just cannot be done.  Ditto for the claim that the helicopter “can be coming towards you, but it sounds like its moving away” and “can’t be heard until its right on top of you”.   No, no, and NO!

So what can be done to make a helicopter more stealthy?  Several things.

Quieter rotor blades, such as this “Blue Edge” blade developed by Eurocopter significantly cut down on rotor noise (listen to the noise comparison in the above link).  Low noise designs such as this are not new technology, they have been operationally employed since Vietnam. 

Both the hot exhaust and noise of engines can be suppressed somewhat through creative ducting around the intakes and exhausts. 

Sikorsky builds both the UH-60 Blackhawk series of helicopters and the now canceled RAH-66 Comanche scout helicopter, designed from the ground up to be a more stealthy design.  It is not in the economic or business interests of either the DoD or the contractor to reinvent the wheel, so you can bet that the easiest, cheapest, and quickest way to modify a UH-60 was with bolt-on panels that were remarkably similar to what was developed for the Comanche program.  In fact, in 1991 at the Paris Air Show, the Sikorsky “Fantail” design built for the Comanche was first demonstrated to the public on a S-76B, another Sikorsky helicopter, which was itself a derivative of the UH-60.  Therefore, the safest guess is that the helicopter that crashed during the raid was a modified UH-60 which would look more like a Comanche. 

UNMODIFIED UH-60 BLACKHAWK

RAH-66 COMANCHE

"STEALTH" UH-60 BLACKHAWK (ARTIST CONCEPTION)

Would these modifications make the helicopter more difficult to control, and cause the crash, as some have proposed?  Maybe.  

There is very little correlation between fixed wing aerodynamics and rotary wing aerodynamics in a hover, so comparisons between the flight characteristics of a high flying stealth airplane and a modified helicopter are mostly meaningless.  

Adding weight and changing the shape of the airframe can definitely affect flight characteristics and controllability, but its not as if this mission was not rehearsed and flown in simulators many times.  High altitude may also have been a factor, but Denver is higher than Abbottabad, and helicopters routinely operate in Afghanistan at much higher altitudes.  At the end of the day, when you are sneaking in low, in close formation, in the middle of the night, on what is possibly the biggest clandestine raid of the war, there are about five hundred ways to crash a helicopter that have nothing to do with airframe design and high altitude.  

As for the leaked explanation that the helicopter crashed because the temperature was different inside the compound, so the helicopter “couldn’t hold the hover”... I cannot locate anybody who has been flying helicopters for any length of time who has any idea what the congressman is talking about.  Perhaps it’s a aerodynamic phenomenon unique to Pakistan?

Stealth helicopter or not, was stealth really a must-have requirement for this mission?  Probably not. 

First up, Pakistan is not noted for their impenetrable air defense network.  We give their equipment and their operators far too much credit, and our own people far too little.  If Mathias Rust could land a Cessna in Red Square, having flown in from Finland, how do you like the odds of the Pakistanis vs. Task Force 160?  Backed up by the US Air Force and Navy?

Secondly, the US did not just Hail Mary two helicopters into Pakistan and hope things went well.  This was likely one of the most overplanned operations in modern warfare, with all manner of diversions, electronic jamming, and reinforcements on call for every contingency imaginable.  The fact that they were able to lose a helicopter and still execute the mission and extract in around forty minutes is testimony to the professionalism and the preparedness of the team on the mission. 

Thirdly, THE PAKISTANIS KNEW BIN LADEN WAS THERE and any Pakistani forces able to respond to an attack on the compound were either smart enough to stay away, slow enough to not make a difference, or dumb enough to not even notice. 

And lastly, the number one reason why this mission did not need a stealth helicopter… the task force extracted on Chinooks!  About as stealthy as a Greyhound bus… though not as quiet.