GB2088521A - Inducing lift on a stationary wing - Google Patents

Abstract

To induce lift on a conventional aircraft wing during vertical take-off, landing, or hover, rearward flow is induced over the inboard half of the wing by blowing air at 2 through slots at the rear of a leading edge flap, and forward flow is induced over the outboard half of the wing by blowing air at 6 through slots at the front end of trailing edge flaps, with boundary layer suction at 3 ahead of the trailing edge flap of the inboard half and at 7 behind the leading edge flap of the outboard half to reduce flow separation over said flaps. Large fins between the inboard and outboard using halves are reduced in area for normal flight, e.g. by sliding some sections into others (Figs 6,7, not shown). <IMAGE>

Description

SPECIFICATION Air flow control for a vertical take-off aircraft Patent application number 8031223 shows the in board and outboard chordwise airflow distribution for an aircraft with fixed wings and vertical take-off capability with the engine thrust appreciably less than the aircraft weight.

Patent application number 8034661 shows a radial flow engine for such an aircraft.

This application shows how the efficiency of such an aircraft can be considerably improved by the use of airflow control.

Laminar boundary layer control was invented more than 35 years ago but no military or civil aircraft uses laminar boundary layer control because of its high weight, high manufacturing cost, high maintenance cost and low serviceability. The fine holes in the wing skin were subjected to clogging by flies in hot weather and icing in freezing conditions.

The method was only used during the cruise phase of the flight.

With this proposed design the ducts and slots are already there. Immediately after the engines are started there is a hot airflow to de-ice all the ducts in the combustion chamber. There are no small holes to be clogged. All the relatively large ducts will be periodically cleaned to remove the dead flies and maintan the aircraft's performance.

Figure 1 shows a cross section through the inboard wing at take-off and cruise.

Figure2 shows a cross-section through the outboard wing at take-off.

Figure 3 shows a cross-section through the outboard wing at cruise.

Figure 4 shows a vertical air flow control valve.

Figure 5 shows a lateral spanwise airflow control and duct distribution to the engines.

Figure 6showsthe wing-fin at take off.

Figure 7 shows the wing-fin at cruise.

To obtain the maximum efficiency for a vertical take-off aircraft at take-off and hover the inboard trailing edge flap and outboard leading edge flap must be given the maximum possible deflection.

Unfortunately if the boundary layer is laminar over the fiat central wing box region there would normally be separation of the laminar boundary layer at very low deflection angles of the flaps. Even if the boundary layer is turbulent there is a limit to the maximum allowable flap deflection angle. The solution is to remove the boundary layer (laminar or turbulent) in order to obtain the maximum possible flap angle.

Figure 1 shows the air entering the inboard wing intake (1 ) with a very large vertically upwards motion. The engine then discharges the air in the aft direction with a large velocity through nozzle (2) over the flat main wing box region. By the time the air reaches the end of the main wing box it will have either a laminar or turbulent boundary layer, depending on the Reynolds Number. The boundary layer on the upper wing surface is sucked away through slot (3). The free stream air then turns through a large angle and is given a large vertically downwards velocity at the trailing edge (4) by the flap. This large flap angle is mainly used during the take-off phase of the flight.

Figure 2 shows the air entering the outboard wing intake (5) at take-off. It is discharged forward through nozzles (6). A laminar or turbulent boundary layer is then built up over the flat main wing box region. The boundary layer on the upper surface is sucked away through slot (7) so that the free stream air can be given a large vertically downwards deflection (8) by the flap.

At cruise the direction of chordwise air flow over the outboard wing region is reversed. Figure 3 shows the air entering the engine intake (9) with the flaps having almost zero deflection. The air is discharged through exit flaps (11) in the aft direction.

As the trailing edge flap is set at almost zero deflection angle during the cruise, then the free stream airflow can accommodate any adverse pressure gradient due to the jet (11).

It will be noted that the direction of the jet airflow reverses from Figure 2 to Figure 3 by the angle of the exit flap (6 and 11). Similarly the velocity is reduced to zero for ducts (5 and 12) and (7 and 10) and the velocity is increased from zero for duct (9). This is accomplished by the use of control valves in the engine ducts of the outboard wing.

Depending on the position of the aircraft wing relative to the ground at take-off and hover from air fields at different altitudes and temperatures it is desirable that the aircraft pilot has some control of the air flow to the upper and lower surfaces of the wing. It is not possible to exceed a pure vacuum on the upper wing surface, and the amount of air which lies below the wing lower surface may be limited. A simple vertical air control valve (13) in the exist ducts (2,6 & 11) can control the relative air flow to the upper and lower wing surfaces as shown in Figure 4.

This air control can also give the wing a nose up or a nose down pitching moment and hence can replace the tailplane and elevator, and also to some extent the flaps, for longitudinal aircraft control.

At take-off and hover it is required to have a mid-semi-wing-span fin as large as possible in order to obtain the maximum amount of air entrainment which changes direction at the wing, but prevents the outboard wing air flow opposing the inboard wing airflow.

At cruise it is required to have a fin as far aft as possible and with a size only sufficient to give aircraft stability, and control of the aircraft if the power plant fails, or during air manoeuvres. Thus a well designed aircraft requires a variable fin area.

One obvious method is to have a fin which can fold to a smaller size. Another obvious method is to have the extra fin area capable of sliding into the minimum basic fin area. This latter method give the minimum adverse aerodynamic effect when the fin area is being altered at some small aircraft speed. A possible fin which can be varied in area by a sliding action is shown in Figures 6 and 7.

The procedure for fin contraction is as follows.

Area (14) slides into area (15) at the same time as area (16) slides into area (17). Area (17 and 18) slides into area (19) and then area (15) slides into area (19).

In order to accomplish this, the fin surfaces must be verystiffand strong bythe use of high modulus sandwiches. Care must also be taken with equipment such as rudder jacks and fin jacks so as not to impede the sliding action of the fin components.

Any power plant failure could be controlled if there were valves (20) in the duct which connects the different power plants or nozzles, so that air can be ducted in the spanwise direction to an air deficient region as shown in Figure 5. Thus each nozzle would still function, but at a reduced airflow, unless the remaining operating engines were overloaded for the period of the emergency.

In order to keep the engine depth as small as possible so that it can fit into thin wings then the intake and exist air ducts in the wing need not be a singie duct with a large cross sectional area, but could be a number of ducts, say five, each of which has a smaller cross sectional area, say 1/5th of the larger duct's area. The intake ducts are all in the same wing horizontal plane and the exit ducts are all in a parallel plane as shown in patent application 8034661. The intake ducts feed into the periphery of the engine and the exit ducts feed out from the other periphery of the engine as shown in Figure 5 for the outboard port and starboard engines.

The safety of engines and compressor blades is considerably improved by the use of intake ducts as bird ingestation is no longer a serious problem.

At the tips of the wing, winglets, as shown on Figure 5, are an advantage. They help to prevent any appreciable detrimental spanwise airflow. However an inflow of free stream air into the outer wing region is beneficial and this may be assisted by having a rudder at the aft end of the wing let as shown on Figure 7. If port and starboard rudder are turned outwards at hover then air outside the wing tip region is inducted to flow over the wing, and the mass flow, which affects the lift generated by the wing, is thereby increased.

Claims (6)

CLAIMS It is claimed that for a vertical take-off aircraft the invention:

1. Gives the maximum wing flap deflection because of wing boundary layer suction control.

2. Gives control of the relative air flow to the upper and lower wing surfaces by use of a valve in the vertical air flow duct.

3. Gives control of the wing airflow at take-off and hover by the use of a variable area fin attached to the wing at its mid semi-span.

4. Gives control of the aircraft when an engine fails by ducting air spanwise along the wing from the remaining operating engines.

5. Keeps the wing and engine depth as small as possible by replacing one large diameter duct by several small diameter ducts all lying in the plane of the wing.

6. Induces additional air flow over the wing by the use of a tip wing let with a rudder attached to it at its aft end.