Design Flying wing

1 design

1.1 engineering design
1.2 directional stability
1.3 yaw control

design

a northrop n-1m on display @ national air , space museum s steven f. udvar-hazy center

a clean flying wing presented theoretically aerodynamically efficient (lowest drag) design configuration fixed wing aircraft. offer high structural efficiency given wing depth, leading light weight , high fuel efficiency.

because lacks conventional stabilizing surfaces , associated control surfaces, in purest form flying wing suffers inherent disadvantages of being unstable , difficult control. these compromises difficult reconcile, , efforts can reduce or negate expected advantages of flying wing design, such reductions in weight , drag. moreover, solutions may produce final design still unsafe uses, such commercial aviation.

further difficulties arise problem of fitting pilot, engines, flight equipment, , payload within depth of wing section.

other known problems flying wing design relate pitch , yaw. pitch issues discussed in article on tailless aircraft. problems of yaw discussed below.

engineering design

a wing made deep enough contain pilot, engines, fuel, undercarriage , other necessary equipment have increased frontal area, when compared conventional wing , long-thin fuselage. can result in higher drag , lower efficiency conventional design. typically solution adopted in case keep wing reasonably thin, , aircraft fitted assortment of blisters, pods, nacelles, fins, , forth accommodate needs of practical aircraft.

the problem becomes more acute @ supersonic speeds, drag of thick wing rises sharply , essential wing made thin. no supersonic flying wing has ever been built.

directional stability

for aircraft fly without constant correction must have directional stability in yaw.

flying wings lack anywhere attach efficient vertical stabilizer or fin. fin must attach directly on rear part of wing, giving small moment arm aerodynamic center, in turn means fin inefficient , effective fin area must large. such large fin has weight , drag penalties, , can negate advantages of flying wing. problem can minimized increasing wing sweepback , placing twin fins outboard near tips, example in low-aspect-ratio delta wing, many flying wings have gentler sweepback , consequently have, @ best, marginal stability.

another solution angle or crank wing tip sections downward significant anhedral, increasing area @ rear of aircraft when viewed side.

the frontal area of swept wing seen in direction of airflow depends on yaw angle relative airflow. yaw increases drag of leading wing , reduces of trailing one. enough sweep-back, differential drag sufficient naturally re-align aircraft. stabilization scheme used in northrop flying wings, in combination vertical engine nacelles (yb-35) or diminutive stabilizers (yb-49).

a complementary approach uses differential twist or wash out, swept-back wing planform , suitable airfoil section. prandtl, pankonin , others discovered washout fundamental yaw stability in turn of horten brothers flying wings of 1930s , 1940s. due necessity elevons located near wingtips, 1 on upward-moving wing causes drag impedes turning deflects high-pressure airflow under wing. hortens described bell shaped lift distribution across span of wing, more lift in center section , less @ tips due reduced angle of incidence, or washing out. restoration of outer lift elevon creates slight thrust rear (outer) section of wing during turn. when displaced, vector pulls trailing wing forward compensate adverse yaw caused elevon. did not work in practice.

yaw control

in flying wing designs, stabilizing fins , associated control rudders far forward have effect, alternative means yaw control provided.

one solution control problem differential drag: drag near 1 wing tip artificially increased, causing aircraft yaw in direction of wing. typical methods include:

split ailerons. top surface moves while lower surface moves down. splitting aileron on 1 side induces yaw creating differential air brake effect.
spoilers. spoiler surface in upper wing skin raised, disrupt airflow , increase drag. effect accompanied loss of lift, must compensated either pilot or complex design features.
spoilerons. upper surface spoiler acts reduce lift (equivalent deflecting aileron upwards), causing aircraft bank in direction of turn—the angle of roll causes wing lift act in direction of turn, reducing amount of drag required turn aircraft s longitudinal axis.

a consequence of differential drag method if aircraft maneuvers frequently create drag. flying wings @ best when cruising in still air: in turbulent air or when changing course, aircraft may less efficient conventional design.