Background of the Invention In all jet engines, air is drawn into the engine. In the case of the ram jet engine, air enters the engine intake at atmospheric pressure at the speed at which the aircraft is flying if the air is stationary, or at a velocity dependent on wind speed and direction and aircraft speed. Turbo jet and turbo fan engines can draw air into the engine at high velocity due to the pressure drop created at the intake by the operation of the compressor fan (s) or turbo fan even when the aircraft is stationary. Engine air intake velocity during flight is dependent on wind speed and direction, aircraft speed and fan speed. If debris is drawn or forced in with the air, the debris impacts on the engine and may cause damage. In particular, if a large piece of debris such as a bird strikes the outer part of an engine near the air intake, most or all of the bird may be sucked into the engine, frequently causing severe damage and/or clogging the engine. At best, this damage is expensive to repair; at worst, the damage may be life-threatening.

It is known to protect air intakes of jet engines with a mesh over the outside of the intake, but such a mesh easily can become clogged, restricting or cutting off the air supply to the engine. It is of course impossible to clean the mesh in flight.

Obiect of the Invention It is therefore an object of the present invention to provide a guard for an engine air intake which resists clogging and which tends to be self-cleaning in flight.

Disclosure of the Invention The present invention provides an air intake guard for an engine (which term shall include turbochargers and superchargers for engines), said guard being securable over an engine air intake so as to extend outwards therefrom, said guard being closed at its outer end and having a plurality of spaced apertures formed in the sides thereof, the total surface area of said apertures being at least as great as the surface area of the intake over which the guard is to be fitted.

Preferably, the guard is dimensioned to cover all of the air intake and the total surface area of the apertures is greater than the surface area of the intake-typically, at least 130% of the surface area of the intake.

The guard may be symmetrical or asymmetrical in shape but preferably has a cross sectional shape to match that of the air intake to which it is to be fitted. For example, the outer surface of the guard may be cylindrical or conical or a concavely curved cone or a convexly curved cone or pyramidal in shape for a square air intake.

Preferably, the apertures are in the form of slots ; these may be of uniform width or tapered and may be straight or angled or curved or formed as a spiral around the guard.

The guard may be rigidly secured to the air intake or arranged to rotate relative thereto.

The guard may be used in combination with a cowl, as hereinafter described.

Brief Description of the Drawings By way of example only, preferred embodiment of the present invention are described in detail with reference to the accompanying drawings, in which:-

Fig. 1 is a side view of a guard in accordance with the present invention; Fig. 1a is a section on line A-A of Fig. 1; Fig. 1 b is in the end view of the guard of Fig. 1 in the direction of Arrow B; Fig. 2 is a plan view of engine intake on the same scale as the guard of Fig. 1, for purposes of comparison; Fig. 3 is a diagrammatic sectional side view showing a guard in accordance with the present invention fitted to a turbo jet engine; Fig. 4 is a diagrammatic sectional side view showing another type of guard in accordance with the present invention fitted to a turbo fan engine; Fig. 5a-d are a series of sections equivalent to Fig. 1a, but showing possible variations of cross-sectional shape; Fig. s 6a and b-9a and b inclusive are sets of end views and corresponding longitudinal sections of four other possible variations of the guard shown in Fig. 1/1 a/1 b.

Fig. 10a and b are end views of two other types of guard, showing different slots patterns; Fig. 11 is a diagrammatic sectional side view showing another type of guard in accordance with the present invention, combined with a shroud, fitted to turbo fan engine; Fig. 12 is a diagrammatic sectional side view showing another type of guard in accordance with the present invention, combined with a different type of shroud, fitted to a turbo fan engine; Fig. 13 is a diagrammatic sectional side view showing another type of guard accordance with the present invention, combined with a different type of shroud, fitted to a turbo fan engine; Fig. 14a-c are a series of diagrammatic sectional side views showing a guard in accordance with the present invention fitted to a turbo fan engine and combined with a movable shroud; Fig. 15 shows a diagrammatic part-sectional side view of a guard of the present invention fitted to a turbocharger intake; and Fig. 16a and b are plan view of further guard shapes.

Best Modes for Carrying Out the Invention Referring to Fig. s 1 and 2, a guard 2 in accordance with a first embodiment of the present invention comprises a regular cone having a base 3 the diameter of which is equal to the diameter of the air intake 4 (Fig. 2), so that when the guard is secured over the intake, the intake is completely covered by the guard. The tip 5 of the cone, and the sides of the cone immediately adjacent the tip, are solid. The sides of the cone are slotted with a series of spaced longitudinally extending slots 6a, 6b. The slots 6a alternate with the slots 6b and extend from close to the base 3 of the cone to adjacent the tip of the cone; the slots 6b are shorter. The slots 6 are shown as continuous, but it will be appreciated that some or all of the slots could be formed as intermittent slots.

In the embodiment shown in Fig. 1, the total area of the slots is approximately 130% of the area of the intake 4. The total area of the slots may of course be varied, but is at least equal to the area of the intake 4, and preferably is greater than the area of the intake 4. Thus, if parts of the slots are blocked by debris e. g. a bird strike as shown in outline in Fig. 1, although the air supply to the engine inevitably is reduced, the remaining unobstructed area of slots is still greater than the minimum area of air intake required for the engine. In the example shown in Fig. 1, when the area of the slots obstructed by the bird strike is deducted from the total area of the slots, the remaining unobstructed area is still approximately 115 % of the area of the air intake 4 to the engine.

The smooth elongated shape of the slots gives good air flow characteristics into the guard and tends to reduce turbulence in the air supply to the engine.

A further advantage is that the shape of the guard, being sloped, tends to shed debris :- there is a natural tendency for debris to slide off the guard and the force of air passing over the guard tends to pull debris off. In contrast, with currently used flat mesh guards over the air intakes of engines, external air pressure tends to press any debris caught on the guard firmly on to the guard.

Fig. s 3 and 4 show two variations of the basic shape of the guard fitted to turbo jet and turbo fan engines respectively. In each case, the guard 2 completely covers the air

intake 4 of the corresponding engine, i. e. all air supplied to the engine passes through the slots in the guard. The guard 2 is secured to the engine by any suitable means.

The guard 2 may be secured rigidly over the air intake of the engine or may be rotatable. A rotatable guard could be either free-spinning or driven, e. g. by the exhaust turbine of the engine. A free-spinning guard would have to be one of the variants described below in which the slots are angled or curved, so the slots catch the incoming air to give the necessary rotation to the guard.

Fig. 5 shows four different possible cross-sections of variant guard designs. Fig. 5a shows a variant in which the guard is formed as a double skinned structure, with a passage 7 between the two skins, in communication with an outlet 8. In use, engine exhaust gases are passed down the passages 7, emerging through the outlets 8; this has the dual function of warming of the guard and warming the inlet air, to prevent or reduce icing.

Fig. 5b shows a variant in which the slots 9 are angled to give the incoming air a swirl ; this improves air flow characteristics and also can be used to rotate the guard if a rotatable guard is required.

Fig. 5c shows a variant in which the edges 10 of each slot are raised; it is believed that this may be of assistance in getting air flow underneath any debris stuck on the outside of the guard. Fig. 5c also shows the interior of the guard lined with a sound insulation material 11, to reduce noise and vibration.

Fig. 5d shows a guard made out of a series of spaced pipes 12 with plates 13 secured over the pipes; the slots 14 are formed by the gaps between adjacent pipes. If it is necessary to heat the guard, exhaust gases may be ducted through some or all of the pipes.

Fig. 6a and b show another embodiment of the guard, in which the guard is in the shape of a concavely curved cone 15 with alternating longer and shorter slots 16,16a around its periphery. It is believed that the pointed shape of this guard will create a shock wave in front of it, so that air passes into the engine at a lower velocity.

Fig. 7a and b show a guard in the shape of a cone with a rounded apex 17; cone is

slotted with straight slots 18 of equal length.

Fig. 8a and b shows a guard in the form of a cone with a convex flare 19; cone is slotted with alternating longer and shorter straight slots 20.

Fig. 9a and b shows a guard which is a virtually a cylinder 21 with a rounded top 22; the sides of the cylinder are formed with equidistantly spaced slots 23 of equal length.

Fig. 10a and b illustrates two further possible slot styles :- in Fig. 10a, the slots are tapered outward towards the base of the cone so the width of the slots increases towards the base.

In Fig. 10b, each slot is formed as a part spiral around the cone.

All of the guards illustrated above are symmetrical and are circular in cross-section.

However, the guards will be shaped to fit the engine air intake, e. g. an engine which has a square air intake would have a guard with a correspondingly sized square base and thus would be approximately pyramid shaped. Fig. 16a shows a plan view of this design of guard. Further, it is believed that the guards do not need to be symmetrical, but may be any of a range of asymmetrical shapes, to suit particular applications. For example, Fig. 16b shows a half-cone shaped guard, in plan view.

The guards may be of solid material or, as described above, may be double skinned with two spaced layers.

It is envisaged that the use of a cowl surrounding the guard will protect the guard, improve air flow into the engine and also increase the ram effect at high speed. Three different designs of cowl are shown in Fig. s 11,12 and 13. In Fig. 11, the cowl is in the form of a cylinder 25 which is slightly longer than the guard 26. One end of the cylinder 25 secured around the air intake 27 of an engine; the other end 28 of the cowl is tapered inwards to give a streamlined shape to the exterior of the cowl. The cowl 25 is fixed in position; this has the advantage that the cowl is stable and easy to secure, but has drawback that debris may be trapped between the exterior of the guard 26 and the interior of the cowl, as indicated by reference 29.

In Fig. 12, a cowl 30 is shown secured around the air inlet 31 of an engine by an intermittent bracket 32 which leaves gaps 33 between adjacent sections of the bracket. Debris entering the cowl therefore can escape through the gaps 33.

In Fig. 13, a cowl 34 is shown secured around an intake 35 of engine by means of an outwardly convex bracket 36 which, like the bracket 32 of Fig. 12, is intermittent; the shape of the bracket 36 leaves large gaps 37 through which debris entering the cowl can escape.

Fig. 14 shows a more complex type of cowl which can be altered in position in flight.

In this design, the position of a cowl 40 can be adjusted e. g. by hydraulic cylinders 41 mounted in the cowl housing. It is envisaged that the cowl position could be continuously variable or could be movable between predetermined positions. Fig. 14a shows the cowl 40 in the retracted position in which the guard 42 is self-cleaning but the cowl has no effect. Fig. 14b shows the cowl 40 in the partly advanced position, which is a compromise between the advantages of the cowl and the risk of debris lodging between the cowl and the guard.

Fig. 14c shows the cowl 40 fully advanced; this maximizes the advantages of the cowl but increases the risk of debris lodging between the cowl and the guard.

Fig. 15 shows a guard 50 of the present invention fitted over the air inlet 51 of a turbocharger for a petrol or diesel engine 52. Turbochargers of the type usually fitted to engines have many similarities to a jet engine :- both have a multi bladed turbine 53 driven by engine exhaust gases which drives, by means of connecting shaft, an inlet air compressor fan 54. A supercharger is of similar structure to a turbocharger, except that it is driven from the engine fan belt rather than by engine exhaust gases.

As shown in Fig. 15, a guard 50 is secured over the air intake 51 of a turbocharger 53 with the guard 50 located within the ducting 55 between the air cleaner filter element 56 and the inlet to the compressor fan 54 of the turbocharger.

The guard 50 is shown as a smooth sided slotted cone of the type described in detail with reference to Fig. 1. However, it will be appreciated that the guard 50 may in fact be any of the above described types of guard, although the guard 50 would be stationary rather than rotating.

The object of fitting a guard to a turbocharger or supercharger primarily would be to obtain an improvement in engine performance, since the air filter preceding the guard would protect the engine against dust and debris in the usual way. However, the guard would still be useful as a guard by protecting the turbocharger or supercharger from the entry of such items as parts or tools that might be left in the air intake ducting after engine repairs.