Do all supersonic airliners have a high angle of attack when landing?

Question

The Concorde had a famously high angle of attack (and pitch angle) when landing. This led to its famous droop nose:

The Concorde's Russia counterpart, the Tupolev Tu-144, had the same issue.

These are the only two supersonic airliners to have been built, so there is, admittedly, a small sample size. The Tu-144 has also been derisively called "the Concordski", as some claim that its designers stole plans from the Concorde. So there are clear similarities.

However, there are some supersonic airliners on the drawing board. Will they, too, have high angles of attack when landing? As a follow-up question: Will they, too, be fitted with droop noses?

Answer 1

The basic problem is that a wing that works well in supersonic flight does not work well in low speed flight. The principles of how higher pressure is created below the wing relative to above the wing is quite different between the two flight regimes. Aircraft intended for supersonic cruise have to have wings that work well in supersonic flight. However, these aircraft have to eventually land, which will be done at well below supersonic speed.

Some compromises have to be made somewhere. Note that this discrepancy between efficient cruise and not falling out of the sky at low landing speed is already a issue even with subsonic aircraft. Allowing some reconfiguration of the wing by the use of flaps is a common solution.

It gets trickier with a delta wing. Part of the solution used in the Concorde was high angle of attack on landing, which required the famous droop nose so that the pilots could see the ground. Other planes that are superosonic-capable have other mechanisms. For example, the F-14 and F-111 have variable wings that reconfigure themselves between delta shape for supersonic flight, and more traditional wings for subsonic fight. Particularly the F-111 was known for problems in this area, and this concept doesn't scale well to airliner size.

All these mechanisms are expensive, add weight, and complexity, so I'm sure creative engineers will continue to come up with new ways of dealing with this problem. None of the solutions so far are optimum, so there is room for alternatives.

Answer 2

The high angle of attack is required because the landing speed must be reduced to a value comparable to that of subsonic aircraft, mainly so that the SST can use the same runways. If the SST could have a longer runway for slowing down, it could land at a higher speed, with a more "normal" angle of attack.

But to answer your question about the droop noses, I would say that there's no longer a need for this. Instead, the pilots will use a video system, similar to those already used on UAVs (unmanned aerial vehicles).

Answer 3

There are two main considerations here which causes the supersonic designs you mention to differ from more conventional, subsonic aircraft:

1. the supersonic aircraft employ delta wings to generate their lift. Delta wings are particularly thin wings with little shape to them, but rely on generating strong vorticies to produce lift. The thin profile makes them excellent at producing little drag, however strong vorticies are difficult to produce at slow speeds as viscous forces dominate.
2. in order to reduce the drag contribution of shockwaves produced by the wings at high speeds, the designers have made the span narrow with a long chord, resulting in a very low aspect ratio. Low aspect ratios produce an awful lot of induced drag.

So, given these considerations, the angle of attack must be large to produce enough lift at speeds slow enough to land at, and the design of the wings means that stall is less of a design consideration so these AoAs are viable; the drag penalty for flying at such high AoA makes up a smaller proportion of the total drag, so there is a smaller penalty for accepting the additional drag if it reduces landing speed and allows your aircraft to operate out of more airports around the globe.

Also of note: these aircraft fly at significantly higher speeds and somewhere between cruising and pulling up to a terminal gate you have to lose all that speed - using your wings as a giant air brake is a pretty good way of doing that without requiring any heavy braking system, indeed flaring is the primary mechanism of braking for most supersonic aircraft.

Edit: I didn't see your follow up question; almost certainly not, the droop nose is phenomanally heavy and complex to make it a desireable design feature, it was included out of necessity. These days I would almost guarantee a electronic HUD system which allows the pilots to "see" through the floor using cameras and a battery of other sensors to aid them. Such a system would require multiple failsafes in the event of a power outage, however even considering this it would be substantially simpler, cheaper and lighter - quite possibly safer also since the droop mechanism could fail, just as a camera could, and there is a limit to how many failsafes you could feasibly include on such a mechanism. By contrast, having an array of multiple cameras on independant circuits, each with an isolated backup power supply makes for a simple, easily expandable and very effective failsafe.

Answer 4

A long trapezoidal wing grows significantly in lift coefficient and area through flaps/slats and Fowler flaps, respectively. Delta wings, especially those using elevons, essentially have no capability to employ high-lift devices. A confluent design driver for delta wings is that they stall only at very high angles of attack; a vortex sheet rolls up in front of both edges and makes the wing have a high effective camber after the rest of the airflow goes over the sheet.

The drawback of using vortex lift is the longer landing gear and very bad lift-to-drag ratio, approximately 3. This additional drag is what made losing two engines on the Concorde unrecoverable at the takeoff speed.

As far as nose-droop on future designs, I would expect to see the use of cameras and monitors instead. Triple redundant, battery-backed electronics are likely lighter weight than a mechanical hinge.

Fun fact: it's impossible to generate lift at supersonic speeds without emitting external shockwaves, some towards the ground. Because we know that any aircraft will generate lift and that the creation of shockwaves is a source of aerodynamic (non-isentropic compression/expansion) drag, a low lift co-efficient given by a large wing implies some aerodynamic savings at cruise.