Tiltrotor Concepts

Tiltrotor aircraft combine the traits of aeroplanes and helicopters. Most have a pair of large propellers housed in swivelling nacelles on the tips of short fixed wings. Tilting the nacelles allows these aircraft to take off and land vertically, hover and turn on the spot, or achieve high forward speeds.

Most early tiltrotor designs were obvious aeroplane/helicopter hybrids, but the latest would be best described as a new class of aeroplane with VTOL capabilities. They need no fixed landing strips, but are much faster than helicopters and can fly at higher altitudes. They can be based almost anywhere and reach more remote locations in a shorter space of time.

While they give their users options they would not have otherwise, tiltrotors have some obvious drawbacks. Being more mechanically complex than aeroplanes or helicopters, they cost more to build and maintain. Their airframes are usually heavier, reducing their efficiency. Their wings reduce the speed at which they climb vertically and can cause the rotor blades to stall during rapid vertical descents. In forward flight the large rotor arcs place limits on wing armament and increase radar signature. Tiltrotors are also harder to fly, as crews have to master more controls and different handling characteristics during hovering and level flight.

Given improved construction techniques, fly-by-wire control systems, more intensive pilot training and experience gained from past mistakes, these drawbacks are now less apparent. Tiltrotors are best used in roles that call for fast deployment irrespective of terrain, such as emergency response, troop insertion and extraction, or providing ground forces with locally based air support.

Concept Aircraft:

1. Djinn

The Djinn is a light transport that draws on the lessons learned from older tiltrotor designs. The short wings are built in one piece for more strength and have reinforcing spars that run straight from tip to tip. They have no dihedral, but are mounted high on the fuselage to increase stability. This also helps to simplify the internal transmission shafts that keep both rotors spinning if one of the engines fails. The extreme taper of the inner wing offers further reinforcement and greater lift in level flight without interfering with the rotor thrust while hovering.

The T-tail keeps the tailplanes and elevators out of the rotor vortices, so handling is more consistent as the rotor angles change. The rudder is not needed for turns, which can be made through changing rotor pitch, but it offers more control in event of total engine failure. The Djinn’s rotors can autorotate if need be, but owing to its weight, small wings and relatively short rotor blades its gliding characteristics are poor.

The rest of the airframe follows a more conventional layout. The short nose and large canopy offers good ground visibility and the two pilots sit side by side to aid communication and safety. Two hull crew are normally carried to help with loading and unloading and ensure proper cargo placement.

As tiltrotors can fly much higher and faster than helicopters, they are less vulnerable to ground fire except when taking off or landing. When they are used in combat zones, Djinns are armed with machine guns in nose and tail turrets well outside the rotor arcs. The hull crew are trained to operate these while the pilots concentrate on flying.

2. Banshee

The Banshee was developed at the same time as the Djinn. It uses the same powerplant and many of the same components, reducing construction and maintenance costs. The Banshee’s most obvious difference is its smaller, sleeker fuselage which substantially reduces drag, increases fuel efficiency and presents a harder target. Though more of its potential payload is given to armour and armament, it can reach much higher speeds and handles more responsively.

The V-tail is lighter and more streamlined, producing two tip vortices instead of the usual three. It is also mechanically simpler, as its two control surfaces act as rudders and elevators. The small crossbar provides reinforcement, and though the V-tail is more prone to yaw, skilled pilots can use this trait for more extreme manoeuvring.

The cockpit seats two pilots in tandem, reducing frontal area. A long bubble canopy gives good all-round visibility, though the engine nacelles create large blind spots. One pilot normally acts as a gunner while the other flies the Banshee, though they have identical controls and can swap roles if need be.

Due to their large rotor arcs, armed tiltrotors’ weapons are usually carried in the nose or round the hull. Banshees typically carry two pods filled with small unguided rockets and up to six larger missiles with more sophisticated warheads and/or internal guidance systems. A nose-mounted autocannon is used for close range engagements or low level strafing runs.

3. Gargoyle

This brutal-looking tiltrotor is designed for surface strikes. Its well-armoured fuselage contains two large jet turbine engines that drive the wingtip-mounted rotors via long transmission shafts. This reduces the size and weight of the rotor nacelles and tilting mechanisms. The smaller, more aerodynamic nacelles also create less drag, present smaller targets, and interfere less with rotor thrust. The engines can be built more simply as they do not have to tilt, while their placement gives them more protection and shortens fuel and control lines. As the engines’ weight is carried closer to the Gargoyle’s central axis, its controls are more responsive especially during turns and rolls.

This layout also has its drawbacks. Transmission systems are more complex; internal space is much reduced; and more stress is placed on the wings during vertical takeoff and landing, necessitating stronger construction.

Instead of one large canopy, the Gargoyle has two smaller ones that give its pilots adequate headroom while providing more protection. The short sloped nose, triangular hull, and smaller rotor nacelles offer good ground visibility, though the air intakes comprise a blind spot. Two armoured cameras and machine guns are mounted in a tail turret, allowing either occupant to locate and engage pursuers or targets that survive a pass. Tubes in the lower fuselage can also deploy chaff and flares against incoming missiles.

Multiple hardpoints on the hull allow the Gargoyle to carry a variety of weapons that can be easily replaced or changed depending on mission requirements. Small unguided rockets are used to saturate wide swathes of ground; larger guided missiles deal with tougher armoured targets; heat seekers can take down enemy aircraft; and nose-mounted autocannons provide high-volume, short-ranged fire. As they need no landing strips, Gargoyles can be based close to the front and relocate more easily as battlefield conditions change.

4. Griffon

The Griffon is a large four-engined transport. It is slower than the Djinn but can carry larger payloads. The Griffon helps to speed deployment in regions that lack infrastructure and can avoid the bottlenecks that form around seaports and airfields.

The Griffon’s raised cabin, external undercarriage pods, and wing-mounted engines help provide more cargo space. The jet turbines are fixed in place for more strength, but drive short camshafts that spin rotors on the ends of tilting masts. Side vents can direct the engine exhaust to adjust trim or aid manoeuvring.

The Griffon’s rotor vortices can pose a hazard to ground crew, and its side doors are best used when the machine has landed and its rotors have stopped turning. Paratroops and cargo can be safely dropped from the large rear hatch while the Griffon is in flight, and the hatch acts as an access ramp when the machine is on the ground.

The cabin is high off the ground but the sloped nose aids visibility. One pilot can fly if need be, but this task is usually shared with the help of dual controls. Griffons also normally carry a navigator, flight engineer, and four or more hull crew who move cargo, assist passengers and fire weapons if required.

The Griffon’s cost and complexity make it a high value target, and it normally only operates in secure territory. Where this is not possible it is given fighter escorts. Most Griffons are only lightly armoured to increase their range and payload, but their size lets them absorb some damage. Defensive armament includes paired chainguns in nose and tail turrets, though many Griffon crews make additions of their own.

The Griffon approaches the maximum practical size for a twin-rotor aircraft. Plans exist for larger transports with four or six tilting rotors, but no prototypes have yet been built due to the projected cost.