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Northrop YRB-94A

by Phil Brandt

 

Lockheed YRB-94A

 


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Background

 

The YRB-49A, Last of Jack Northrop's Wings

The frail, eighty-four year old man had tears in his eyes as a small box was opened at a highly classified 1980 ceremony in Southern California. No matter that the emotional event was over thirty years late; it was vindication of John K. Northrop's lifelong dream of a viable flying wing, for in the box was a model of what would shortly become the B-2 Stealth Bomber. Mr. Northrop died the following year, and it is difficult to imagine anyone in aviation history who contributed such an eclectic list of engineering innovations. Donald Douglas Sr., himself no small figure in world aviation, was quoted as saying that every major airplane in the world had a piece of Jack Northrop in it.

The large Northrop flying wings were developed in the mid-to-late Forties amidst the most feverish developmental burst in world aviation history. One day's cutting edge technology would be quickly surpassed by a blizzard of new discoveries and events. Compounding this technological whirlwind, Air Force weapon system requirements seemed to change monthly as Cold War reality engulfed the West.

Northrop was being pushed very hard in the marketplace; Boeing's B-47 and B-52 possessed superior overall performance, and Convair's slower B-36 had range and impressive weightlifting ability. Unfortunately, the many aerodynamic advantages of the flying wing concept were offset by powerplant material failures. Developmental ceilings in piston engine technology and propeller gearbox metallurgy had been reached, posing a show-stopping impasse. Enter the jet engine.

Eight-jet powered YB-49s were converted from the propeller-driven XB-35s, ushering in a new era of power and smoothness. But, flight instability in all three axes remained a serious obstacle to accurate bombing, and autopilot technology of the time was inadequate to the unique requirements of the big wings. Additionally, the Air Force ratcheted up flight test rigors, which alarmed veteran Northrop test pilots. These increased demands apparently culminated in the 1948 inflight disintegration and crash of the second YB-49 and the deaths of Air Force test pilots Captain Glen Edwards and Major Daniel Forbes. The final blow to the flying wing program came in 1950 when an unrecoverable nosewheel shimmy led to the destruction of the remaining YB-49 in a highspeed runway test.

Northrop's last glimmer of salvation was a one-off, six-engined reconnaissance airframe, the YRB-49A. Although generally resembling previous wings, it reflected lessons learned. The pilot and copilot now sat in tandem, with a jettisonable canopy, and two of the six engines were suspended on large pylons beneath the wing, allowing more fuel space and providing needed directional stability. Flight test of this final design ended in 1951 although the 'ballgame' had really been over for the Northrop wings for a year. In 1952 a bitter, sick and disillusioned Jack Northrop left the company which bore his name, and soon his flying wings were gone, too. The last-of-the-line YRB-49A was scrapped at Ontario Airport in 1953.

Conventional airframe design ruled for the next thirty years, until Northrop designers Irv Waaland and John Cashen started with a clean slate and the benefits of the Computer Age, not to mention that Jack Northrop had already proven the feasibility of an all-wing design. When the stealth requirements of modern day air warfare were factored in, the advantages of a flying wing design resurfaced, with the traditional instabilities inherent in the design now neatly solved by computers. Amazingly, Waaland and Cashen independently arrived at a pure wing configuration--minus stealth-destroying fins and fences--having the exact wingspan of Jack Northrop's earlier design!

Jack Northrop has been deceased for over two decades at this writing, but the sinister fleet of B-2 bombers at Whiteman AFB is a constant reminder of this aviation pioneer's genius and foresight.

 

 

The Conversion

 

Although essentially having departed today's plastic model aircraft market, AMT/Ertl's big plane releases were welcomed by modelers for their risk-taking subjects. To date, it is the only company who has done an injected 1/72 line of KC-135s and early flying wings.

I had acquired the prop-driven XB-35 kit, but desired the one-off, last-of-the-line YRB-49A. Execuform to the rescue! Mike Herrill's three-versions-in-one (XB-35/YB-49/YRB-49A) vacuform release predates the AMT/Ertl kit by a few years but, of course, has all the labor intensiveness of the vac genre, though, as Bondo has noted in an earlier article, lack of engraving can be a plus. And, as far as I'm concerned, the wonderful eighteen legal-sized pages of flying wing line drawings are easily worth more than the plastic. These contain more information than you'll ever need. All versions of the early wings are covered, with cockpit and engine details not seen anywhere else by this modeler.

 

 

Background

 

The plan was to convert the prop-driven XB-35--the YB-49 kit version was not yet a reality--into the six-engined YRB, just as in real life. From the Execuform vac I scavenged the radar/photo empennage from the central pod , the jet intake trunks, the suspended J-35s/pylons, the fin/fence assemblies and the tandem canopy.

 

Re-Engining's Got to be the Hardest Thing...

All four engine nacelles and associated underwing turbocharger intakes were cut out of the Ertl wing, and the openings filled with sheet plastic and epoxy putty. Then, new twin jet exhausts were scratchbuilt from Evergreen tubing and faired in to the wing trailing edge, accompanied by lotsa Bondo's favorite 3M Blue Acryl lacquer putty.

 

 

As the project moved ahead, Ertl released the eight jet YB-49, and I elected to use the injected fin/fence assemblies from this kit instead of the vacformed ones. An added plus was that the fin/fence assemblies would exactly match the XB-35 wing contour.

All four vertical fins and wing fences were removed from the new Ertl YB-49 wing and relocated on either side of the YRB's twin jet exhausts in the following manner: a Number 24 blade was used in multiple passes to score around the fin/fence assemblies. Then, with needle nose pliers, the assemblies were gently wiggled back and forth sideways until they popped off the wing surface. After sanding the bottom surfaces the assemblies were ready to glue onto the wing in their revised positions.




Intakes...Big Suckers!

The Ertl intakes are represented with a shallow (1/4") blocked off depression in the wing leading edge. I decreased the width of the intakes to that required for just two engines by filling in the ends of the four-jet intake with A&B epoxy putty. When it cured, I Dremmeled out the two-engine opening slot and adapted the vacuform halves of the correct depth (2") Execuform intake trunks. The hardest part was fairing in the interior trunk surfaces with puddled CA and accelerator. Compressor blade faces were 'cannonballed' from the parts pile.




Radar/Photo Pod

First the bulged, teardrop fairing adjacent to the XB's aft pod was cut out and the resulting hole sheeted in. The entire aft portion of the Execuform pod was separated from the vacuform wing. Then the forward one inch of the surface to be joined to the injected Ertl pod was scarfed, that is, thinned to a knife edge. The vacuform aft pod was then slipped over the existing injected pod and glued. And, as before, appropriate Blue Acryl blah, blah...

 

 




Jet Pods

These were used in toto from the Execuform kit with spares box compressor and turbine faces added.

 

 


 

Cockpit and Canopy

Here the Execuform detail drawings were invaluable. The side-by-side pilot seating was reconfigured to tandem, sticks substituted for control columns and a scratchbuilt navigator position added, with periscopic sight and forward oblique camera station.

 

 

The Execuform canopy, thin and clear, was used as is.




Flaps and Rudders

Inner flaps were dropped and details scratchbuilt per the Execuform drawings; ditto for the opened wingtip rudders.

 

 

 

 

Painting and Finishing

 

After even more Blue Acryl and lacquer primer, I wet-sanded with 1000 grit, and started shooting four shades of original acetone formula Alclad (Alclad II did not yet exist). The flying wings were minimally marked, and I went to the spare decal repository to locate the correct large and small serial numbers. The most time-consuming task was applying the long black wingwalk stripes from a Superscale sheet.

 

 

Conclusion

 

Once again, Mike Herrill's Execuform kits have come to Bondo's rescue, saving untold hours of intensive 'practice bleeding' labor in scratchbuilding conversion components. And, the huge sheaf of superior line and detail drawings is in itself a valuable reference 'work' not to be missed.


 

Additional Images

 

Click the thumbnails below to view larger images:


Model, Images and Article Copyright 2002 by Phil Brandt
Page Created 24 June, 2002
Last updated 04 June, 2007

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