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  • Hold The Tumbrils, People
    Posted by Bill Sweetman 2:22 PM on May 05, 2011

    I now have a couple of emails accusing me of compromising national security by publishing an analysis of a few not-very-clear pictures of the back end of a helicopter.

    Which is amusing, considering how frequently I and others are taken to task by JSF fans, who point out that any analysis of a military system based on imagery, without access to the classified data, is rubbish.

    Can you guys get your act together? Or can I put you all in a cage armed with rusty knives, screwdrivers and cudgels and let you work it out like real men, on pay-per-view?

    Most likely, the most secret thing about the stealth-modified helicopters used in the Osama raid was that they existed. That in itself is no big surprise. Those in charge, up to the President, knew that there was a risk that the secret would be compromised if anything went wrong, and accepted it.  And the cat was out of the bag the moment the team departed without demolishing the tail section (the right tactical decision) regardless of what we did here.

    Former counterterrorism official and general-purpose worrywart Richard Clarke has been fretting about the pieces ending up in China. They may well do, but it does not concern me unduly, for a number of reasons.

    There is nothing particularly secret about quiet-helo technology. As we have noted, the CIA was developing and using quiet helicopters in Vietnam. I was briefed on the quieting and other features designed into the Boeing 360 experimental helicopter in 1987 (in particular, the ability to slow the rotor down in low-speed forward flight) and wrote a lot about the stealth technology in the Comanche.

    blog post photo

    At Heli-Expo in 2000, I even flew in a quietened helicopter -- the Whisper Jet S-55QT, a modified version of an ancient Sikorsky that was designed for tour flights over the Grand Canyon.

    Neither would I expect the radar cross-section reduction to use the best of what's out there. The main reason is that reducing a helicopter's RCS is like reducing the RCS of a warship -- you are starting with huge and trying to make it normal, and the target will be in clutter. So fairly crude measures, like bolting a dishpan to the rotor hub, retracting the landing gear, and suppressing the antennas, hinges, grab rails and other warts that festoon the average military transport helicopter will do a lot.

    There's also a reason that the very not-classified NH90 has canted body sides -- although every operational example I have seen is covered with knobs and bumps that throw any RCS benefits of the body shaping out of the window.

    blog post photo

    Another point: I'm not aware of any RCS measurement facility, at least in the US, that has a support system robust enough to take a full-scale helicopter model with spinning rotors. (EADS' Ra-Sigma 3 range at Manching might be able to.) That in itself sets a pretty hard limit on the ability to engineer massive RCS reductions on a helicopter -- because in the signature world, what you can't measure, you can't do.

    Tags: ar99, osama, stealth

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