The Flying Wing

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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, DeHavilland, Handley Page,
  Lippisch

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Northrop XB-35 (nothing but a wing)Design driven
by PL R requirements
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Northrop YB-49 (tail-feathers allowed)Design
driven by V PL R requirements
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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 _at_ wing root

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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.

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Horten IX An early stealth fighter
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Northrop B2 stealth Bomber
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Lockheed F-117 stealth fighter
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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 _at_ 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!

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Span-Loader
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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 _at_ each wing tip and _at_
  centerbody.
• Adverse ground effects result in low flap
  effectiveness.