The principal aerodynamic benefit of sweeping a wing on a high-subsonic transport is that it
Answer: A
Sweep reduces the velocity component the section actually responds to, so local supersonic flow and the shock that closes it are delayed to a higher free-stream Mach number. That postponement of drag rise is what makes cruise near Mach 0.85 practical, and it is why every jet transport has a swept wing.
Please log in or register to report this question.
Sweeping a wing back carries which of the following penalties?
Answer: B
Sweep drives the boundary layer outboard along the span, thickening it near the tip and encouraging the tip to stall first, which costs both maximum lift and roll control. Swept wings therefore need washout, fences, vortilons or leading-edge devices to restore acceptable stalling behaviour.
Please log in or register to report this question.
A supercritical aerofoil differs from a conventional section principally in having
Answer: C
Flattening the crest keeps the local supersonic region at a modest Mach number over a long run, so the shock closing it is weak and both wave drag and shock-induced separation are reduced. The aft camber restores the lift that flattening the crest gave away, at the cost of a more nose-down pitching moment.
Please log in or register to report this question.
The Whitcomb area rule states that transonic wave drag depends chiefly on
Answer: D
Whitcomb showed that the whole aircraft behaves, at transonic speeds, like a body of revolution with the same streamwise area distribution. Making that distribution smooth is what matters, which is why fuselages were waisted at the wing junction to give the characteristic Coke-bottle shape.
Please log in or register to report this question.
Applying the area rule to an aircraft typically involves
Answer: A
The wing adds cross-sectional area over its own length, so the fuselage is narrowed there to keep the total distribution smooth. The F-102 is the classic case: it could not exceed Mach one until its fuselage was waisted, after which it could.
Please log in or register to report this question.
A wing's leading edge is described as subsonic when
Answer: B
What matters is the velocity component normal to the leading edge. If the edge is swept far enough to lie inside the Mach cone, that component is below sonic speed and the edge behaves in a subsonic manner, permitting a rounded nose and leading-edge suction even though the aircraft is supersonic.
Please log in or register to report this question.
A supersonic leading edge is one that
Answer: C
If the edge is not swept far enough to hide inside the Mach cone, the flow meets it supersonically and an attached shock forms along it. Such an edge must be sharp, and it recovers no leading-edge suction, so the drag due to lift is higher than for a subsonic edge.
Please log in or register to report this question.
A rounded leading edge is aerodynamically acceptable on a supersonic aircraft only where the edge is
Answer: D
Behind the Mach cone the normal component is subsonic, so a rounded nose behaves as it would in subsonic flow and develops useful leading-edge suction without forcing a detached shock. Ahead of the cone the edge must be sharp, or a strong bow shock and heavy wave drag follow.
Please log in or register to report this question.
The wave drag of a supersonic wing is conventionally divided into contributions due to
Answer: A
Linearised supersonic theory separates the drag into a part depending on the thickness distribution, the volume-dependent wave drag, and a part depending on the loading, the wave drag due to lift. Both are pressure drags present in inviscid flow, and both are quite distinct from induced drag and skin friction.
Please log in or register to report this question.
Wave drag due to volume is reduced most effectively by
Answer: B
Volume-dependent wave drag scales with the square of the thickness ratio, so halving the thickness cuts it to a quarter. This is why supersonic wings are so conspicuously thin, typically three to five per cent, and why fitting fuel and structure inside them is such a difficult design problem.
Please log in or register to report this question.
