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The Flying Wing

The Flying Wing. Idea : To achieve the highest possible L/D in a transport or a bomber, eliminate everything but the wing itself! Pioneers : Northrop, DeHavilland, Handley Page, Lippisch. Northrop XB-35 (nothing but a wing) Design driven by PL – R requirements.

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The Flying Wing

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  1. The Flying Wing • Idea: To achieve the highest possible L/D in a transport or a bomber, eliminate everything but the wing itself! • Pioneers: Northrop, DeHavilland, Handley Page, Lippisch

  2. Northrop XB-35 (nothing but a wing)Design driven by PL – R requirements

  3. Northrop YB-49 (tail-feathers allowed)Design driven by V – PL – R requirements

  4. The Flying Wing Pros: • No other components to create D • Very low CD0 : comparing a FW w. a CW of equal volume and PL density, both have roughly the same Swet but FW has greater span + buried engines, hence lower D • flying wing ac: 0.008 – 0.011 • conventional ac: 0.015 – 0.02 • Very high L / D [ L / D is inversely proportional to CD0 ] For a given A, L / D may be increased by 40%, resulting in a 40% increase in R for similar WF, TOW, and V. OR gain in fc reduction, engine P and TOW for a specified PL and R. • Wwing is lower [ favorable mass distribution within the wing, reduced BM @ wing root ]

  5. The Flying Wing Pros: • Higher PL weight fractions • Stealth advantage: FW is difficult to detect visually or by radar (Ho IX, B2, F-117) Cons: • Ingress / egress. • Shape of FW is far from ideal for a pressure vessel; W penalty to pressurize the cabin. • Difficult to integrate a pressurized passenger compartment, a cargo compartment and fuel bays. • For small FW, the size of the human body dictates the inclusion of a fuselage, unless pilot sits in supine position. • For large FW the size and type of PL determines whether or not a FW is a suitable configuration.

  6. Horten IX: An early stealth fighter

  7. Northrop B2 stealth Bomber

  8. Lockheed F-117 stealth fighter

  9. The Flying Wing Cons: • Not very good loading flexibility, especially in the case of low density PL. Loading restrictions are necessary both in longitudinal and lateral position. • Nil stretch potential (cannot increase PL). • S of a FW tends to be larger than S of conventional ac (defeats part of the L/D advantage). • Incapable of producing high CLmax (flaps @ TE cause nose-down PM, which cannot be trimmed; must use low W/S for TO and LND, which results in low cruise efficiency). • High load factors in turbulent air result in uncomfortable ride + heavy workload for the pilot. FW response to control surface deflections and bumps is accompanied by a poorly damped phugoid and an oscillatory short period motion. • Difficult to achieve good W & B + S & C characteristics: • Lack of moment arm • Difficult to have cg ahead of ac (entire PL must be in the forward part of the wing). Solutions: Reflex airfoils, wing sweep, tip-mounted fins. Problem: reduced L/D. • Good news: for high-performance ac can use SAS (Stability Augmentation System); w. enough power to drive the SAS a FW can be made to behave quite nicely!

  10. Span-Loader

  11. Span-Loader Idea: PL is distributed along the wing span (Lockheed concept: TOW = 2,354,000 lbs). Pros: • Reduced wing structural W. Cons: • Need to support PL throughout the wing span to the tips. Requires very large taxiways, not available at current airports. Solution: air-cushion LND system @ each wing tip and @ centerbody. • Adverse ground effects result in low flap effectiveness.

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