VTOL

VTOL means vertical take-off and landing. The A-4, E-10, E-11 and W-6 use main-engine thrust for atmospheric VTOL. Reaction control (RCS) supplies attitude control and a small amount of vertical translation. The P-13 uses its separate TGD drive; the T-19 has no VTOL system.

Controls

The default F9 binding requests upward translation and F8 requests downward translation. Equivalent requests can be assigned to a game controller. Main-engine throttle and forward/reverse selection continue to request longitudinal acceleration. Autoflyte requests use the same propulsion limits as manual controls.

With TVM engaged against a ground reference in BCL, the E-10, E-11, A-4 and Manx use F9 for maximum upward demand, F8 for a height-scheduled descent, and key release to request hover. This does not select a fixed altitude, steer to the reference's position or guarantee sufficient lift. See TVM vertical landings for the descent schedule and limitations.

No separate nozzle or VTOL-door control is required. The propulsion system combines the vertical and longitudinal requests automatically. Requesting lift can increase main-engine output even with the longitudinal throttle at idle. Allow for engine thrust buildup before attempting to leave the ground; nozzle or door travel alone does not provide full lift.

Engine arrangements

E-10, E-11 and A-4

The front and rear outlets on the two side engines tilt down through 54 degrees. Full nozzle travel takes about 1.5 seconds. Each engine can supply its full rated thrust through each opposing outlet. At 54 degrees, about 80.9% of each outlet's thrust acts vertically and 58.8% acts longitudinally. Equal opposing flows cancel longitudinal force while adding lift; both flows consume fuel. Unequal flows permit braking or acceleration while producing lift.

The side-engine nozzles can move while the engines are firing. While airborne, applying or releasing lift starts nozzle travel immediately; thrust buildup and rundown still take time. Forward or reverse thrust can develop during the transition, without waiting for both wing engines to extinguish.

When grounded and idle within the atmospheric operating limits, the side-engine nozzles automatically park at 54 degrees downward, including during shutdown. This provides an inspection position and removes the tilt delay from a subsequent VTOL request; it does not produce thrust or remove engine spool-up time. Forward or reverse thrust requests return the nozzles toward axial unless lift is also requested. After taxi thrust is released, remaining axial flow runs down before the nozzles park. Releasing lift while still grounded leaves fully tilted nozzles down as thrust runs down.

The E-10 and E-11 aft engine remains axial during VTOL and supplies approximately one third of the three-engine axial rating. With AUG on and the wing nozzles stowed for axial flight, it can vector in pitch through up to 15° at 5°/s to help balance main-engine torque. This assistance also works in manual flight and reverse thrust; RCS retains residual attitude control. The vector returns toward neutral with AUG off, during VTOL/hover and at ground idle. The A-4 has two engines and no aft engine.

W-6 Manx

The Manx routes thrust through protected downward outlets. Its underside doors take about 0.6 seconds to open. Downward exhaust is inhibited until the doors are fully open, and the downward flow is shut off before they close.

Each engine shares one thrust budget between its forward, reverse and downward outlets. Full downward thrust leaves no thrust available for longitudinal acceleration. Partial lift can be combined with forward or reverse thrust. The engine rating is unchanged: a heavy Manx may be unable to hover.

Atmospheric operating envelope

The E-10, E-11, A-4 and Manx enable or re-enable main-engine VTOL below 18 km MSL. Once enabled, it remains available up to 20 km MSL. Power, engine condition and the available force and balance limits still apply.

On the E-10, E-11 and A-4, hold F9 during forward flight to request upward thrust while continuing to command forward or reverse thrust. The tilting nozzles do not use the Manx door airspeed interlock. This is not an exemption from the aircraft's operating-speed, heating or control limits; allow for nozzle travel and engine spool response.

The W-6 Manx additionally requires air-relative speed below 90 m/s and dynamic pressure below 3.2 kPa to enable its doors. Above 100 m/s or 4 kPa, downward flow is cut off and the doors close. Air-relative speed includes airflow in any direction, not just indicated forward airspeed. Dynamic pressure depends on local mass density and the square of air-relative speed; in Vieneo's dense surface atmosphere its limit can be reached well below 100 m/s.

Above the atmospheric VTOL envelope, including high-altitude suborbital coast and orbit, vertical translation uses RCS only. Main engines remain available for forward and reverse thrust; Manx VTOL doors remain closed. Returning below the re-enable limits permits atmospheric VTOL again.

Hover capability and balance

Available lift depends on loaded mass, engine condition, power, atmospheric performance and the torque that can be balanced about the centre of gravity. The allocator varies front/rear and left/right output, with RCS supplying the remaining attitude correction. It reduces thrust when the requested combination cannot be balanced. Maximum gross weight is not a guarantee of VTOL capability.

Vertical RCS on these four vehicle types provides approximately 0.5 m/s² at maximum gross weight at full power and condition. Its acceleration increases at lower mass and decreases with power or wear. It is a small supplement to atmospheric main-engine lift and the source of vertical translation in space. The P-13's TGD operation is separate.

Aircraft-specific nominal-CG, hover-capacity and powered-ascent references are available under E-10 operating envelope and E-11 operating envelope.

Near-surface effects

Main-engine exhaust can raise dust or spray wherever its spreading plume reaches nearby ground or water around your own A-4, E-10, E-11 or W-6. Ground wash follows actual engine output and nozzle direction in manual flight and with Autoflyte; it does not require VTOL operation. For example, an E-11 pitched steeply nose-up can blow the ground with its aft engine. Wash can extend beyond the visible exhaust glow, becoming broader and weaker with distance. Parked nozzles alone do not produce wash.

Dry loose sand produces more dust than roads or hard ground. Wet ground produces less dust and some mist; open water produces spray. Snow-covered ground can produce pale airborne snow. Surface wetness uses accumulated weather when available; low cloud by itself does not mean wet ground. The mist represents blown droplets, not boiling water.

Dust, mist and spray can obscure the surface during low-altitude operations. Their appearance is not an indication of available lift or altered handling. They fade after thrust ends and are absent in the flight simulator. Distant terrain, intervening structures and shoreline transitions are approximate.

See also TVM, Autoflyte, Airspeed and Vieneo.