What are the advantages and disadvantages of a delta wing compared to a swept wing?

Question

What advantage does a delta wing have over a swept wing with high AR for supersonic flight? And what disadvantage does a delta wing have over a swept wing with high AR for transonic flight?

The Concorde is made to cruise at supersonic speed--delta wings.

Most commercial airliner--swept wing with high AR.

Would you design a supersonic airplane with the conventional airliner swept wings? On the other hand, would you design a transonic flight with delta wings?

Answer 1

Benefits of a delta wing:

• Due to the large root chord, a delta wing combines low relative wing thickness with a sufficiently thick wing spar for a lightweight structure. Since a low relative thickness keeps wave drag down (a drag component which occurs only in supersonic flow), this makes delta wings especially attractive for supersonic aircraft.
• The large root chord gives the delta wing a high internal fuel volume even at a low relative thickness.
• The large root chord also provides it with a large surface area which helps to bring the minimum speed of the aircraft down.
• With sufficient leading edge sweep, a delta wing produces vortex lift, so flow separation can be turned into a means of increasing lift.
• A delta wing is naturally stable in pitch, therefore it does not require a separate tail surface.

Drawbacks of a delta wing:

• The large wing area causes more viscous drag for the same amount of lift compared to a high aspect ratio wing. Swept wings have a better lift-to-drag ratio (L/D) than delta wings.
• High-lift devices like fowler flaps are hard to integrate into delta wings. The higher relative thickness of regular airliner wings allows to integrate large flaps more easily, and the rearward location of the trailing edge of a delta wing will produce intolerable pitching moments if such flaps would be deflected.
• Vortex lift at high angle of attack produces considerably more drag than a comparatively sized conventional wing, so a delta wing airplane will bleed off speed in tight turns more than a conventional airplane.

Generally, the moderately swept high aspect ratio wings of subsonic airliners are ideal for flight at high subsonic Mach numbers. Delta wings are superior only in supersonic flight, and due to their good low speed characteristics they offer the best overall compromise for supersonic aircraft.

North American XB-70 in flight, a classical delta wing design (picture source). Note the canard wing, which has little sweep and a low aspect ratio: This kind of wing is ideal for supersonic flight, provided it has a low relative thickness. The main wing of the XB-70 is a delta wing to keep the take-off and landing speeds relatively low and offers the best compromise of low and high speed characteristics. Also, the wing tips could be deflected downwards to improve directional stability at supersonic speed and to improve L/D by using the waverider effect.

The wings of both the Boeing 787 (top, picture source) and the Airbus A350 (bottom, picture source) show their powerful high-lift devices in these pictures, which allow them to fly with less than half the wing area of a comparable delta wing aircraft. Also, the lower surface area translates into lower drag at high flight speed, and the higher possible wing span helps to reduce induced drag, making those wings far superior for efficient flight at high subsonic speed.

Answer 2

Delta wing advantages

• Can fly at high angles of attack, which that's why fighter jets use a delta wing to fly at very high angles of attack

• Provides good amount of drag for landing. On landing you need drag and that's the purpose of flaps is to increase drag and lift and you can make the flaps a little bit smaller

Delta wing disadvantages

• Lots of drag, which is caused by vortex lift that a delta wing uses instead of conventional lift. Instead of just suffering drag from a wing tip vortex you suffer even more with 2 extra vortices that form on a delta wing.

With a swept wing you reduce drag by decreasing the lift. The problem with that type of wing at supersonic speeds is that you surfer from wave shock drag. Wave shock drag forms when air on top of the wing exceeds the speed of sound. Even at subsonic speeds that a 787 travels at you suffer from wave shock drag. Air is moving so fast on top of the wing at subsonic speeds that it causes the air to break the sound barrier. If you try to fly a swept wing at supersonic speeds your aircraft is really going to suffer from wave shock drag and any faster speeds could result in the whole plane splitting apart and is very serious. A delta wing doesn't have a slope on top of the wing like a swept wing does so the air doesn't travel any faster than the aircraft does. The reason airliners use swept wings is to reduce the lift to reduce the amount of high pressure air that can rotate around the wingtip. The swept wings reduce wake vortex and wake vortex can actually decrease an aircrafts lift and you want as much lift as possible. The major companies that build airliners main focus is to decrease drag. With a supersonic aircraft your main focus is to reach supersonic speeds and aren't designed to reduce drag. So you wouldn't design a supersonic aircraft that has swept wings, but you would design it with delta wings.