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  • Bomber On A Bar Napkin
    Posted by Bill Sweetman 11:00 AM on Mar 23, 2009

    Northrop Grumman’s NGB design to some extent resembles, and to some extent looks unlike a bigger version of the X-47B UCAV-D unveiled late last year. However, assuming that the patent drawing is reasonably accurate, there are a few first-order conclusions to be drawn.

    blog post photo
    Northrop Grumman

    Northrop Grumman and the USAF have both talked about weapon loads in the 20-25,000-pound class for the new bomber. That’s just about half the payload of the B-2, which has two equal-size weapon bays. Moreover, Northrop Grumman and the USAF are planning to invest more money in the B-2’s rotary weapons launcher, allowing each launcher to carry a mixed load of weapons.

     

    blog post photo
    Northrop Grumman 

     

     

    It would therefore make sense to design the new bomber around a single B-2-sized bay. In fact, that works out pretty well. An advantage of the cranked-kite planform used on the NGB and UCAV-D is that the center-section can be made longer and deeper, while the aerodynamic center can be adjusted separately by changing the sweep and size of the outer wing sections.

    Dropping a B-2-like bomb bay into the NGB, behind the cockpit and ahead of the point where the lower mold line starts to sweep up, scales into an airplane about 70 feet long – a bit longer than the B-2 – but with a smaller wingspan, around 120 feet. (The B-2 spans 172 feet.) If that’s correct, either a wing-loading or span-loading calculation points to a demi-B-2, with a 2500 sq ft wing area and a 160,000+ pound normal take-off weight. 

    The NGB has a higher aspect ratio than the X-47B, not surprisingly since it does not have to fit on a carrier:

    blog post photo
    At a minimum, that 160,000-pound-class weight would call for about 9,500 pounds of thrust from each of the four engines. For the demonstrator, non-afterburning General Electric F404s would be close to ideal.

    Exactly how much thrust, and what bypass ratio, you’d want in a production NGB engine depends in large measure on the desired altitude. A Vulcan-like 60,000-foot service ceiling would call for more power (adding weight and sacrificing range) but it’s a good approach to the visual-detection problem.

    Ultimately, range depends on propulsion efficiency, comprising not only the engines themselves but stealth-compatible inlets and exhausts, and on the details of aerodynamic efficiency. But a 2000 nm unrefueled radius should be easily attainable.

    Stealth? There are no tails and the smallest external features of this aircraft are well over a meter across, and there’s room for deep-section, wideband edge treatments. Result: the NGB should be a wideband, all-aspect design, protected against VHF radars that can cause conventional stealth aircraft problems.

    USAF Lt.Gen. Dave Deptula’s comments to Danger Room – “I wouldn't call it a bomber, because that creates a perception based on historical uses of bombers that this platform is going to be well beyond” – are important. First, the program’s backers have to make the case that the airplane is not the next B-2 – with its associated price tag and operational limits.

    For example, a lot of things that cost a vast amount of money to invent for the B-2 – low-probability of intercept, Ku-band active array radar; stealth-compatible satcoms; automated threat detection, tracking and avoidance; and composite primary structure – are available off the shelf, or will be by 2018. A lot of this work is planned under B-2 upgrade programs, together with other capabilities like moving-target attack.

    The NGB represents advances in aerodynamics and signatures, and a flight-test and pole-model program goes a long way towards closing those risks.

    The NGB should also be adaptable for many missions (and relatively speaking, affordable enough to fill them). The option should exist of making the Block 20 or Block 30 airplane unmanned. With low probability of intercept satcoms – using the same kind of hardware being developed for the B-2 – it becomes an intelligence, surveillance and reconnaissance platform (think, someone comments, of the RB-47s and ERB-47s of the 1950s), a communications node, and electronic attack aircraft. Fit an infra-red sensor and load the weapons bay with modified THAAD missiles, and you have a persistent, survivable boost-phase interceptor.

    And whether one is a pessimist or an optimist regarding the maturity of tactical directed-energy weapons, be they lasers or high-powered microwave devices, they’re going to fit on a bomber long before they fit on a fighter.

    Ultimately, a lot of the value of this program will depend on the degree to which the designers have managed to combine breakthroughs in aerodynamics and signatures – and what’s interesting is that Northrop Grumman seems to have been pulling together newcomers, seasoned leaders (like aerodynamics guru Barnaby Wainfan) and retired experts into the design process. But the future will also depend on how well the USAF and Northrop Grumman communicate with dollar-focused leaders in Congress and the administration.

    Tags: ar99, ngb, northrop grumman

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