FSW

For years the primary purpose for developing forward-swept wings was structural—to allow the wings to be mounted farther back on the fuselage so that their connecting structure did not interfere with anything inside the fuselage (like bombs or people). Wind tunnel tests made it clear that there were many problems with forward-swept wings and few aerodynamic advantages. One major problem was that the wingtips tended to bend upwards and cause the plane to stall—inevitable for metal wings. But in the mid-1970s, a U.S. Air Force officer noted that new composite materials then becoming available for aviation could be incorporated into the wings of a modern jet and eliminate the tendency of the wingtips to bend upward and cause the plane to stall. At the same time, several U.S. aviation companies were exploring ways to make planes that were highly maneuverable at transonic speeds

Aircraft with forward-swept wings are highly maneuverable at transonic speeds because air flows over a forward-swept wing and toward the fuselage, rather than away from it.

X-29

The X-29 used the fuselage from the Northrop F-5A, the main undercarriage and other equipment from the F-16, and an engine from the F/A-18. Its wings were made of advanced composites and it was equipped with small wings called canards mounted on the forward fuselage rather than on the tail where horizontal stabilizers are usually located. These helped increase the plane's maneuverability. The reverse airflow inward from the wing tip toward the root of the wing did not allow the wing tips and their ailerons to stall at high angles of attack. The Grumman X-29 first flew in 1984. It had a strange appearance, with the wings mounted well back on the fuselage, and almost looked like it was flying backward. The aircraft could only be flown with the help of an advanced computer control system. In numerous tests over the next several years, the X-29 demonstrated that the forward-swept wing design produced a 15 percent better ratio of lift to drag in the transonic speed region.

Su-47

MANOEUVRABILITY

The Su-47 has extremely high agility at subsonic speeds enabling the aircraft to alter its angle of attack and its flight path very quickly, and it also retains manoeuvrability in supersonic flight. Maximum turn rates and the upper and lower limits on air speed for weapon launch are important criteria in terms of combat superiority. The Su-47 aircraft has very high levels of manoeuvrability with maintained stability and controllability at all angles of attack. Maximum turn rates are important in close combat and also at medium and long range, when the mission may involve engaging consecutive targets in different sectors of the airspace. A high turn rate of the Su-47 allows the pilot to turn the fighter aircraft quickly towards the next target to initiate the weapon launch.

The swept-forward wing, compared to a swept-back wing of the same area, provides a number of advantages:

higher lift to drag ratio; higher capacity in dogfight manoeuvres; higher range at subsonic speed; improved stall resistance and anti-spin characteristics; improved stability at high angles of attack; a lower minimum flight speed; a shorter take-off and landing distance.

FUSELAGE

The Su-47 fuselage is oval in cross section and the airframe is constructed mainly of aluminium and titanium alloys and 13 per cent by weight of composite materials. The nose radome is slightly flattened at the fore section and has a horizontal edge to optimize the aircraft's anti-spin characteristics

Dimensions  Length 22.60 mWingspan 16.70 mTake-off weight 24,000 kgPerformance  Maximum speed 1.6 MachMaximum g-force higher than 9g quoted for Su-27Construction  Airframe aluminium and titanium alloysComposites 13 per cent by weight

Properties

Properties of the forward swept wing at low speeds have been known for some time (Weissinger, 1947; Multhopp, 1950). They include an uneven spanwise distribution of lift and excessive root bending moment.

The largest loads occur at the root, while an aft swept wing has a more gradual loading with a maximum lift around mid-span. Fast calculations can be performed with a linearized lifting surface theory.

Figure 1: foward and backward swept wings

Features of Forward Swept Wings

At transonic speeds the sweep is needed to reduce and post-pone the drag rise. Research performed in recent years (Wachli, 1993), showed that for at constant shock location, shock wave sweep, taper ratio, aspect-ratio and area, a forward swept wing has a lower leading-edge sweep that an aft swept wing. This produces a lower profile drag and a lower root bending moment.

At constant root bending moment, the wing with forward sweep has a slightly higher aspect-ratio, which leads to a further reduction of the profile drag.

Wing Stall

Wing stall starts at the root and proceeds outwards, while on a wing with aft sweep stall unusually starts at the tip and proceeds inwards. Root stall provides better control capabilities at high speed, although lifting and stability capabilities may be enhanced by appropriate canards.

Wing Divergence

Another problem of the wing is the critical wing divergence (e.g. the operation point at which irreversible aeroelastic effects take place, with catastrophic consequences). This difficulty would require a much heavier wing than the corresponding backward swept wing. The problem could be partially solved with the use of advanced composite materials.

Current Applications

The use of this wing is mostly confined to experimental fighter aircraft (Grumman X-29A, Sukhoi S 37). These research airplanes feature tapered wings with leading edge root extension (LERX), foreplanes, slightly canted fins, and extreme agility at angles of attack above 90 degs !

One production aircraft with swept back wings, the German business jet HFB 320 Hansa, was moderately successful in the 1960s.

Canard

Canard foreplanes act in a similar way to conventional tailplane and elevators, but due to swap in position about the centre of gravity control surface actions have the opposite effect.[citation needed]

Advantages

A canard arrangement produces more lift than a conventional set-up when total lift produced is considered. During manoeuvres the canard control surfaces mirror those of the main wing adding to the lift to climb and decreasing the lift to descend. This means that the aircraft can move tighter and faster than with a conventional set-up

Because the canard generates upward lift, unlike with a tail plane which produces downward or negative lift, there is a reduction in the lift required from the main wing. This reduction in the required lift generation by the wing to over come the weight of the aircraft a reduction in lift-induced drag by the wing. As well as removal of the negative lift generated by the tailplane and the associated lift-induced drag. Overall drag and lift requirements of the aircraft is reduced

The canard is, sometimes, designed to stall prior to the main wing. This means that once the canard stalls, the nose tends to pitch down, thus reducing the angle of attack of the main wing. However, that is not to say that the main wing cannot stall: a vertical gust that causes a sufficiently high angle of attack on the main wing will cause both the canard and the main wing to stall

In a propeller aircraft, a canard normally uses a pusher configuration. This reduces fuselage drag, because the fuselage is not operating in the increased flow induced by the propeller

Disadvantages

The wing root operates in the downwash from the canard surface, which reduces its efficiency, although the effect of the downwash does not cause as large of a problem as the tailplane would experience in a conventional set-up

The wing tips operate in the upwash from the canard surface, which increases the angle of attack on the tips and promotes premature separation of the air flowing over the wing tip. This premature separation at one tip or the other would promote wing-drop at the approach to the stall, leading to a spin. This must be avoided by precautions in the design of the wing, and may require extra weight in the wing structure outboard of the wing root

Because the canard must be designed to stall before the main wing, the main wing never stalls and so never achieves its maximum lift coefficient. This may require a larger wing to provide extra wing area in order for the airplane to achieve the desired takeoff and landing distance performance

It is often difficult to apply flaps to the wing in a canard design. Deploying flaps causes a large nose-down pitching moment, but in a conventional aeroplane this effect is considerably reduced by the increased downwash on the tailplane which produces a restoring nose-up pitching moment. With a canard design, there is no tailplane to alleviate this effect. The Beechcraft Starship attempted to overcome this problem with a swing-wing canard surface which swept forwards to counteract the effect of deploying flaps, but usually, many canard designs have no flaps at all

In order to achieve longitudinal stability, most canard designs feature a small canard surface operating at a high lift coefficient (CL), while the main wing, although much larger, operates at a much smaller CL and never achieves its full lift potential. Because the maximum lift potential of the wing is typically unavailable, and flaps are absent or difficult to use, takeoff and landing distances and speeds are often higher than for similar conventional aircraft

In the case of a pusher propeller, the propeller operates in the wake of the canard, fuselage, wing and landing gear. Also, the propeller diameter is often smaller than optimum, because of ground clearance considerations at rotation. A smaller propeller operating in a large wake will result in reduced propulsive efficiency

Although some of the advantages and disadvantages above apply to all situation a few of the disadvantages can be, and have been used in the design of high performance military aircraft

were aerodynamic instability can allow for a large improvement in the maneuverability of the aircraft

Though in the civil aviation industry the disadvantages are seen to far outweigh the advantages and few canard design civil aircraft have been successful though with exception of a range of light aircraft produced by Burt Rutan

Examples of canard aircraft

Aircraft that have successfully employed this configuration include:

AEA Silver Dart Atlas Cheetah B-1 Lancer (small canards help negotiate low-level flying)

Beech Starship Berkut 360 Chengdu J-9 Chengdu J-10 Cozy MK IV Curtiss-Wright CW-24B Curtiss-Wright XP-55 Ascender

Dassault Rafale Eurofighter Typhoon

Freedom Aviation Phoenix Grumman X-29A IAI Kfir IAI Lavi Kyūshū J7W1 Shinden McDonnell Douglas (now

Boeing) F-15 S/MTD MiG-8 Utka Miles Libellula North American SM-64

Navaho North American X-10 Peterson 260SE (a Cessna 182

with an added canard for STOL operations)

Piaggio P180 Avanti (3 surfaces aircraft with flapped canard for pitch trim)

Pterodactyl Ascender Rockwell-MBB X-31 Rutan Defiant Rutan Long-EZ Rutan Quickie (more a tandem

than a canard) Rutan VariEze

Rutan VariViggen Rutan Voyager Santos-Dumont 14-bis Saab Viggen Saab Gripen Steve Wright Stagger-Ez Sukhoi Su-30 MKI Sukhoi Su-33 Sukhoi Su-34 Sukhoi Su-35 Sukhoi Su-37 Sukhoi Su-47 Sukhoi T-4 Tupolev Tu-144 Velocity SE Velocity XL Wright Flyer XB-70 Valkyrie