Skeleton Alleged in the

Stealth Bomber's Closet

'A 40-year-old dispute over the range of '!flying wing" aircrafthas been resurrected in a critique of the B-2

A MATHEMATICAL ERROR in an appendix toa secret report completed 43 years ago hascome back to haunt its author-and, per-haps, the Air Force's controversial B-2"Stealth bomber program.

Joseph V. Foa, an emeritus professor ofengineering at George Washington Univer-sity, has charged in a memorandum hecirculated recently among scientific organi-zations and members of Congress that therehas been "an unrelenting cffort to concealthe facts and to obfiuscate the record" aboutwhat he daims is the inferior range of jet-powered "flying wing" aicraft such as theB-2.

Foa, whose 40-year research career in-duded a decade as chainnan of the depart-ment of aeronautical engineering and astro-nautics at Rensselaer Polytechnic Institute,traces what he labels a "cover-up" of theflying wing's alleged deficiency to an embar-rassing error in research performed for theAir Force in 1945 by two Northrop Corpo-ration aerodynamicists. Northrop at thetime was the prime contractor for an all-wing bomber that is generally viewed as aprecursor of the B-2, which is also beingbuilt by Northrop.The paper by William R. Sears and Irving

L. Ashkenas was part of a secret assessmentof promising military technologies under-taken in the immediate aftermath of WorldWar II. A team of prominent scientist andengineers directed by Theodore Von Kar-man surveyed such fields as aviation, rocket-ry, electronics, and psychology to identifythe most fertle areas for future develop-ment. Sears, a former student of the illustri-ous Von Karman, was Northrop's chief ofaerodynamics and Ashkenas was his assis-tant. Von Kanran and Sears are widelycredited as the guiding lights behind theNorthrop XB-35 and YB49 flying-wingbombers ofthe 1940s, which were appedby the Air Force after the production of 15airframes.

In their paper, which was delivered toGeneral Henry H. "Hap" Arnold at thebegnning of 1946 and then circulatedamong top Air Force officials, Sears andAshkenas made fiequent reference to thepromise of all-wing aircraft. Only two tech-

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nical appendices were at to the gener-al dicussion, one that analyzed sonm of thesdll-novel flight characteristics of rocketsand anothcr that daimned to prove mathe-matically that, for best range, an airplane'svolume should be contined almost entirelyin the wing. At the itme, Nortirop was in afierce competition for a contract to build astrategic bomber for the Air Force. It wasdeveloping the exotic XB-35-a visuallystunning tailless span of 172 feet, poweredby four 3000-horsepower propeller engines.The XB-35's test program turned out to

be plagued by mechanical problems with theprop engine assemblies, as well as questionsabout stability. In the early months of 1947,while Northrop was converting the XB-35to a turbojet version taed YB49, Foaheaded a research group at the CornellAeronautical Laboratory in Buffalo, NewYork, that was studying the range and aero-dynamics of an unmanned jet-propelled air-craft called Hermes. Sears had recently leftNortirop to become chairman of Cornell'sgraduate school of aeronautical engineeringin Ithaca. During his theoretical work, Foacame upon what he thought was a remark-able contradiction of conventional wisdom,namely that-based on aerodynamic consid-erations alone-the range ofHermes wouldbe considerably lower with an all-wing con-figuration than with a traditional wing-fiLselage shape. As he looked into the prob-lem further, he convinced himself that theresult was universally true for jet-propelledaircraft: an all-wing shape would alwayshave range inferior to a wing-fiselage shape,with other specifications being equal.

In April 1947, Foa brought this findingto the attention of Sears and suggested in aletter to the Laboratory's hierarchy that theysubmit a proposal to the Air Force for moreresearch into its implications- "especially inview of the brge sums of money that arenow being spcnt to maintn leadership in arace which is apparently rnning on thewrong track [i.e., the Nortlrop YB-49 proj-ect]," he wrote.Foa does not recall encountering a well-

spring of enthusiasm. "Sears responded bystating, in effect, that what I was claimingwas absurd, that he and Irving Ashkenas had

William Sears. "Of course we were embar-rassed by [the error]," but "we never agreed withFoa about his conclusions."

rigorously proven in a Northrop report (ofwhich he could not provide me a copy) thatthe optimum configuration for range in thecase of the YB-49 was indeed a flying wing,and that we should definitely not proceedwith the submission of the proposal I hadsuggested," Foa writes in his current memo-randum. "It was not until 3 months laterthat I was able to see the Sears-Ashkenasreport," which turned out to be the appen-dix to the secret 1945 Air Force study.

In that mathematical exercise, Sears andAshkenas had written formulas involvingsuch standard parameters as weight, flyingspeed, thrust, fuel consumption, drag, lift,and air density that could be manipulated toreveal how an aircrafts volume should beproportoned between wing and fuselage forbest range. The formulas were valid, Foafound, but when Sears and Ashkenas calcu-lated the maximum and minimum valucs forthe ratio of total volume to wing volume,they reversed the correct answers.

In the jargon of calculus, the vanishing ofthe first derivative of range with respect tovolume had given two solutions, one wherethe total volume was almost all in the wingand another where the wing volume wasmuch less than the total. Sears and Ashkenasthen simply stated that "it can be ascertainedthat the former gives a maxumum range.while the latter gives a minimum." But withhis own contrary research in the back of hismind, Foa examined the calculations andfound that the Sears-Ashkenas "maximum"was in fact a minimum. "In other words, theflying wing was the aerodynamically worstpossible choice of configuration for the YB-49," Foa writes in his recent memo.On 15 July 1947, Foa sent a letter to

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Sears pointing out the error. Sears repliedon 17 July, saying "As you can imagine theerror is embarrassing to Irv and me-al-though I hardly suppose anyone has takenserious action as a result." It certainly ap-

peared that the optimum configuration was

not a flying wing, Sears admitted. Nonethe-less, he ended his letter by stating his opin-ion that the Laboratory should not under-take further study ofthe problem for the AirForce. "I suspect you will find that they haveenough studies from airplane manufacturersso that they wouldn't be particularly excitedabout the proposal," Sears wrote.

"I found his response shocking," Foarecalls, but he says he felt "that the onlyresponsible and honorable way out of it wasfor Sears himself to disclose the truth." Foasays he asked the Laboratory's director to

tell Sears that ifhe or Ashkenas would do so,

"I would not find it necessary to make any

public statement on the matter of my own,and would agree to remain silent." Mean-while, the YB-49 began test flights in Octo-ber 1947.The reaction to Foa's ultimatum was a

paper written by Ashkenas titled "Range

performance of turbojet airplanes" pub-lished in the February 1948 issue of theJournal of the Aeronautical Sciences. In it, Ash-kenas engaged in a far more abstruse para-

metric study than the one appended to the1945 Air Force report. A crucial graphshowed that for certain values of a dimen-sionless factor he called the "geometricshape parameter," the all-wing configura-tion gave best range. Foa's interpretation ofthe text indicated, however, that these valueswould produce a wing impractically thick.Foa sent a critique of Ashkenas's paper to

the Journal on 13 December 1948. It was

published in the magazine's April 1949 edi-tion along with a contentious reply fromAshkenas, with no further debate on therecord.A month after Foa's critique was sent in-

on 11 January 1949, to be precise-the AirForce canceled Northrop's YB-49 contract.

The official reason was budget limitations,but aviation historians still argue about thetechnical and political aspects of the deci-sion. According to Northrop publications,the YB-49 achieved a range of 3155 mileswith a 16,000-pound bomb load. In VonKarman's introduction to the secret 1945Air Force study, he had stated the range goalas 3500 miles with 20,000 pounds ofbombs.Later in 1949, the Air Force told the HouseArmed Services Committee that "the YB-49showed considerable promise in speed andaltitude but had inadequate range."

There the matter rested until it was re-

vealed that the B-2 would be a flying winglike the YB-49.

Sears and Ashkenas, while acknowledgingtheir old error, do not take Foa's underlyingconcerns seriously. Today, Sears is emeritusprofessor of aerospace and mechanical engi-neering at the University of Arizona, wherehe moved in 1974 after a distinguishedcareer at Cornell that spanned nearly threedecades. Reached by telephone in Tucson,he declined an opportunity to respond indetail to Foa's memorandum. "Of course we

were embarrassed by it," he said of the 1945

Northrop's YB-49. A precursor ofthe B-2, it was canceled in 1949 ostensiblyfor budget reasons. AirForce officials later testified that its range was inadequate.

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error, but "we never agreed with Foa abouthis conclusions." Engineers "make these pa-rameter studies to get general trends," henoted, and they are of limited value in thereal world of aircraft construction. "It neverseemed very important," he added. "Itdidn't change anything."

Irving Ashkenas, now vice president ofSystems Technology Inc.-a consulting firmin Northrop Corp.'s hometown of Haw-thorne, California-remembers the appen-dix to the 1945 Air Force report as "just alittle simple exercise that I thought was cute,and that backfired on me." He says that nocorrection was ever issued (the report wasnot declassified until 1977). "It was a smallpart of my contribution and I don't recallworrying about it."Both Sears and Ashkenas contend that

other advantages to the all-wing design havebeen established in recent years that shouldmore than make up for the aerodynamicpenalty on range expounded by Foa. Chiefamong these is a theory called "span-load-ing," whereby the airplane's weight is dis-tributed along the wing, resulting in rela-tively small bending moments and thereforea lighter structure. In a 1987 Aerospace Amer-ica article, Sears went so far as to refer to theYB-49 project as "the world's first seriouseffort to prove or disprove the span-loadtheory for designing big airplanes."

If weight saving was hoped for in the B-2design, then there are indications that Nor-throp has had difficulty obtaining it. In1984, the B-2 underwent a major redesigncosting at least $1 billion that changed theaircraft's wing structure and decreased itsweight. The Air Force's publicly stated rea-son for such massive rework was to give theB-2 a capability to fly low-altitude earthhugger missions, in addition to the high-altitude attacks initially posited for thebomber. But terrain-following flight, whichrequires continuous use of radar altimetersto maintain proper distance above ground,would negate some of the stealthiness thatwas the primary reason for selecting a flying-wing design in the first place.

Resolution of the Foa-Sears debate awaitsthe B-2 flight test program, which has yet torecord its first hop, though the bomber wasrolled out last November. Anyone outsidethe tight Air Force security circle can onlyspeculate about related technical issues, butlast week, House Armed Services Commit-tee chairman Les Aspin (D-WI) noted thatthe aircraft is "new technology with perhapsfundamental problems."

* WAYNE BIDDLE

Wayne Biddle is a Washington, D. C.-basedjournalist who is writing a book about the aero-space weapons industry.

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