The Flying WingThe Flying WingIdeaIdea: To achieve the highest possible L/D in : To achieve the highest possible L/D in

a transport or a bomber, eliminate everything a transport or a bomber, eliminate everything but the wing itself!but the wing itself!

PioneersPioneers: Northrop, DeHavilland, Handley : Northrop, DeHavilland, Handley Page, LippischPage, Lippisch

Northrop XB-35 (nothing but a Northrop XB-35 (nothing but a wing)wing)

Design driven by PL – R Design driven by PL – R requirementsrequirements

Northrop YB-49 (tail-feathers Northrop YB-49 (tail-feathers allowed)allowed)

Design driven by V – PL – R Design driven by V – PL – R requirementsrequirements

The Flying WingThe Flying WingProsPros::No other components to create DNo other components to create D

Very low CVery low CD0D0 : comparing a FW w. a CW of equal volume : comparing a FW w. a CW of equal volume and PL density, both have roughly the same Sand PL density, both have roughly the same Swetwet but FW has but FW has greater span + buried engines, hence lower D 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 / DVery high L / D [ L / D is inversely proportional to C [ L / D is inversely proportional to CD0D0 ] For a ] For a given A, L / D may be increased by 40%, resulting in a 40% given A, L / D may be increased by 40%, resulting in a 40% increase in R for similar Wincrease in R for similar WFF, TOW, and V. OR gain in fc , TOW, and V. OR gain in fc reduction, engine P and TOW for a specified PL and R.reduction, engine P and TOW for a specified PL and R.

WWwingwing is lower is lower [ favorable mass distribution [ favorable mass distribution within the wing, reduced BM @ wing root ]within the wing, reduced BM @ wing root ]

The Flying WingThe Flying WingProsPros:: Higher PL weight fractionsHigher PL weight fractions Stealth advantageStealth advantage: FW is difficult to detect visually or by : FW is difficult to detect visually or by

radar (Ho IX, B2, F-117)radar (Ho IX, B2, F-117)ConsCons:: Ingress / egress.Ingress / egress. Shape of FW is far from ideal for a pressure vessel; W Shape of FW is far from ideal for a pressure vessel; W

penalty to pressurize the cabin.penalty to pressurize the cabin. Difficult to integrate a pressurized passenger compartment, Difficult to integrate a pressurized passenger compartment,

a cargo compartment and fuel bays.a cargo compartment and fuel bays. For small FW, the size of the human body dictates the For small FW, the size of the human body dictates the

inclusion of a fuselage, unless pilot sits in supine position.inclusion of a fuselage, unless pilot sits in supine position. For large FW the size and type of PL determines whether or For large FW the size and type of PL determines whether or

not a FW is a suitable configuration.not a FW is a suitable configuration.

Horten IXHorten IX: An early : An early stealth fighterstealth fighter

Northrop B2 stealth BomberNorthrop B2 stealth Bomber

Lockheed F-117 stealth Lockheed F-117 stealth fighterfighter

The Flying WingThe Flying WingConsCons:: Not very good loading flexibility, especially in the case of low density PL. Not very good loading flexibility, especially in the case of low density PL.

Loading restrictions are necessary both in longitudinal and lateral Loading restrictions are necessary both in longitudinal and lateral position.position.

Nil stretch potential (cannot increase PL).Nil stretch potential (cannot increase PL). S of a FW tends to be larger than S of conventional ac (defeats part of S of a FW tends to be larger than S of conventional ac (defeats part of

the L/D advantage).the L/D advantage). Incapable of producing high CIncapable of producing high CLmaxLmax (flaps @ TE cause nose-down PM, (flaps @ TE cause nose-down PM,

which cannot be trimmed; must use low W/S for TO and LND, which which cannot be trimmed; must use low W/S for TO and LND, which results in low cruise efficiency).results in low cruise efficiency).

High load factors in turbulent air result in uncomfortable ride + heavy High load factors in turbulent air result in uncomfortable ride + heavy workload for the pilot. FW response to control surface deflections and workload for the pilot. FW response to control surface deflections and bumps is accompanied by a poorly damped phugoid and an oscillatory bumps is accompanied by a poorly damped phugoid and an oscillatory short period motion.short period motion.

Difficult to achieve good W & B + S & C characteristics:Difficult to achieve good W & B + S & C characteristics: Lack of moment armLack of moment arm Difficult to have cg ahead of ac (entire PL must be in the forward part of the wing). Difficult to have cg ahead of ac (entire PL must be in the forward part of the wing).

SolutionsSolutions: Reflex airfoils, wing sweep, tip-mounted fins. : Reflex airfoils, wing sweep, tip-mounted fins. ProblemProblem: reduced L/D.: reduced L/D. Good news: for high-performance ac can use SAS (Stability Augmentation System); 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!w. enough power to drive the SAS a FW can be made to behave quite nicely!

Span-LoaderSpan-Loader

Span-LoaderSpan-LoaderIdeaIdea: PL is distributed along the wing span : PL is distributed along the wing span

(Lockheed concept: TOW = 2,354,000 lbs).(Lockheed concept: TOW = 2,354,000 lbs).ProsPros::Reduced wing structural W.Reduced wing structural W.ConsCons::Need to support PL throughout the wing span to Need to support PL throughout the wing span to

the tips. Requires very large taxiways, not the tips. Requires very large taxiways, not available at current airports. available at current airports. SolutionSolution: air-: air-cushion LND system @ each wing tip and @ cushion LND system @ each wing tip and @ centerbody.centerbody.

Adverse ground effects result in low flap Adverse ground effects result in low flap effectiveness.effectiveness.