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:
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
Northrop YB-49 (tail-feathers allowed) Design driven by V – PL – R requirements
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: 0.008 – 0.011 flying wing ac: 0.008 – 0.011 conventional ac: 0.015 – 0.02 conventional ac: 0.015 – 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 BM @ wing root ]
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.
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 (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!
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.