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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,

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Presentation on theme: "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,"— Presentation transcript:

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 C D0 : comparing a FW w. a CW of equal volume and PL density, both have roughly the same S wet but FW has greater span + buried engines, hence lower D flying wing ac: – flying wing ac: – conventional ac: – 0.02 conventional ac: – 0.02  Very high L / D [ L / D is inversely proportional to C D0 ] For a given A, L / D may be increased by 40%, resulting in a 40% increase in R for similar W F, TOW, and V. OR gain in fc reduction, engine P and TOW for a specified PL and R.  W wing is lower [ favorable mass distribution within the wing, reduced 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 C Lmax 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 each wing tip centerbody.  Adverse ground effects result in low flap effectiveness.


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