Airborne apparatus for ground erosion reduction

Abstract: Apparatus for reducing ground erosion caused by impinging hot jets (2) such as the lifting jets of VSTOL aircraft or rockets, said jets emanating from a hot jet nozzle (1) such as a lift engine nozzle or a lift/propulsion engine nozzle, comprising means for introducing a coolant fluid (7) to an impingement surface immediately beneath the turning zone.

Description: This invention relates to means for reducing ground erosion caused by impinging hot jets, such as the jets from the propulsion and lifting gas turbine engines of Vertical/Short Take-Off and Landing (VSTOL) aircraft or the hot gases in the exhaust of vertically launched rockets. The impingement of a lifting jet from an exhaust nozzle of a gas-turbine engine or rocket motor on a horizontal or almost horizontal surface is characterised by three distinct zones: 1. A free jet issuing from the nozzle; 2. A stagnation region surmounted by a turning zone where the jet is deflected laterally and radially outward from the point of impingement; 3. A wall jet zone where the jet moves predominantly parallel with the impingement surface. Erosion of the most commonly used surfacing materials by an impinging jet is confined almost entirely to the region beneath the turning zone. This is because it is here that most of the heat transfer from jet to surface takes place. Apart from ground erosion, in the case of gas-turbine powered VSTOL aircraft, the hot impinging jets produce other problems, such as hot gas ingestion and debris and dust ingestion into air intakes. These problems will be further exacerbated by the introduction of improved performance VSTOL aircraft with high temperature, high pressure lifting jets. To counter the problems mentioned above it is known to use prefabricated aluminium sheeting or portable ground environment mats to protect the ground surface during VSTOL aircraft operations. These known protective measures can only be taken in situations where the aircraft will be landing or taking off from a pre-designated area which can then be covered with one of the known protective surfaces. Another approach to solving the problem of ground erosion in VSTOL aircraft operations is described in French patent No. 1,300,094 (M.A.N. - Turbomotoren GmbH). The solution proposed in that patent is to incorporate an ejector in the exhaust nozzle of a VSTOL aicraft's main lift gas-turbine engine. The ejector uses the hot jet efflux of the engine to entrain air at ambient temperature and pressure via holes in the walls of the nozzle and an ejector orifice located below the nozzle in a low pressure zone in the efflux. The entrained air is delivered as a coolant to the ground impingement zone. The idea has never been adopted in a practical embodiment due to the fact that large volumes of ambient air have to be entrained otherwise there is no appreciable ground cooling effect. Heat transfer between the hot jet efflux and the entrained air as they mix downstream of the nozzle is rapid and in a very short distance from the nozzle the temperature of the mixed gases is too high to provide the desired cool barrier at the ground surface. It is an object of the present invention to provide a means for reducing ground erosion, and thereby related problems, by providing apparatus to be carried on a VSTOL aircraft or any other type of vehicle, such as a vertically launched rocket, which necessitates the use of hot ground impinging jets thus allowing the aircraft or other vehicle to operate in areas other than those which have been pre-designated. According to the present invention there is provided apparatus for avoiding ground erosion caused by impinging hot jets such as lifting jets of VSTOL aircraft or rockets, said jets emanating from a hot jet nozzle such as a lift engine nozzle or a lift/propulsion engine nozzle, comprising means mountable on the hot jet nozzle for introducing coolant fluid to an impingement surface immediately beneath the turning zone characterised in that the apparatus may alternatively be mounted on the airframe of the aircraft and that the coolant fluid is delivered into the hot jets at a pressure in excess of the prevailing static ambient pressure. Preferably, said means comprises means for directing a high pressure jet of fluid at relatively low temperature at the impingement surface, with the objective of providing an insulating film of fluid on the impingement surface, thereby reducing the heat transfer to it. The fluid may be a gas such as air, or a liquid such as water, or a mixture thereof, but is preferably a fluid with a higher thermal capacity than air allowing a lower rate of flow to achieve a given cooling effect. The primary objective of the invention is to supply coolant fluid to the centre of jet impingement so that the fluid spreads radially over the impingement surface as uniformly as possible. In one form of the invention, therefore, the fluid is introduced coaxially with the hot jets. In alternative forms of the invention, where jets that are splayed (at an angle to the vertical) or of non-circular cross-section emanate from the engine in use, the coolant is introduced into the hot jets in a direction that does not initially correspond to the jet axis. Preferably the coolant fluid is arranged to enter the jet as far downstream from the hot jet nozzle and as close to the impingement surface as possible, in order to minimise the coolant flow rate. In a practical aircraft installation the fluid supply may be obtained from an on-board tank via a high pressure pump, and may enter the hot jet by means of a coolant nozzle fixed to, or downstream of, a lift/propulsion or lift nozzle of an engine of the aircraft. The coolant delivery nozzle may be supported and protected by a fairing. Both the coolant nozzle and fairing may be adapted or mounted so as to be able to swing into and out of the hot jet as required. Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings of which; Figures 1a and 1b are schematic side elevation views of a known VSTOL jet and of a VSTOL jet according to the invention respectively operating in a ground environment illustrating the principles of the invention; Figure 1a shows a conventional jet/ground interaction and; Figure 1b shows a jet/ground interaction with a cooling fluid being employed. Figures 2a to 2f illustrate alternative applications of the invention; Figure 2a is a side elevation view of a lift engine nozzle with a coolant nozzle fixed to it; Figure 2b is a side elevation view of a vectorable propulsion/lift engine nozzle with a coolant nozzle fixed to it; Figure 2c is a side elevation view of a vectorable propulsion/lift engine nozzle with a coolant nozzle fixed downstream of the engine nozzle; Figure 2d is a side elevation view of a lift engine nozzle with a mixed fluid coolant nozzle fixed to the engine nozzle; Figure 2e is a side elevation view of a vectorable propulsion/lift engine nozzle with a mixed fluid coolant nozzle fixed to it: and, Figure 2f is a side elevation view of a vectorable propulsion/lift engine nozzle with a mixed fluid coolant nozzle fixed downstream of the engine nozzle. For ease of reference, similar elements in the various drawings have been given identical reference numbers. In Figure 1a, a downwardly-directed exhaust nozzle 1 of a gas turbine engine or fan of a VSTOL aircraft (not shown) directs the gas turbine engine or fan exhaust efflux, or jet, 2 towards a ground surface 5 during vertical take-off or landing operations. Upon impact with the ground 5 the jet 2 is diverted into a radially expanding ground jet 12. Between the downwardly-directed jet 2 and the radially expanding jet 12 the engine jet goes through a turning zone 4. In this zone 4 the engine jet is deflected laterally and radially outward from an impingement surface 6, which is directly beneath the jet 2. A cusp shaped quasi stagnation region 3 is developed beneath the jet 2 as shown. Almost all ground erosion takes place on the surface encompassed by the turning zone 4, because it is here that most of the heat transfer from jet to surface takes place. Figure 1b illustrates the principle of providing an insulating film of fluid to the impingement surface 6 as employed by the invention. A jet of coolant such as water 7 is introduced coaxially to the engine jet flow 2 as far downstream of the engine nozzle 1 as possible. This water jet hits the impingement surface 6 and spreads outward radially as shown at 8, thus providing an insulating film of fluid on the impingement surface 6 thereby reducing the heat transfer to it. Figure 2a illustrates a coolant nozzle 10 fitted to a lift engine nozzle 1. The coolant nozzle 10 is coaxial with the lift engine nozzle 1 allowing a water jet 7 to flow coaxially with engine jet 2 emanating from the nozzle 1. A fairing 9 supports the coolant nozzle 10 and protects it from the engine jet 2. The coolant nozzle 10 is fed with water from a reservoir tank (not shown) via a pipe which passes through a side wall of the nozzle 1 and the fairing 9. Figure 2b illustrates a coolant nozzle 10 fitted to a vectorable propulsion/lift engine nozzle 1. The coolant nozzle 10 is again coaxial with the propulsion/lift engine nozzle 1 allowing a water jet 7 to flow coaxially with the engine jet 2 emanating from the nozzle 1. A fairing 9 supports the coolant nozzle 10 and protects it from the engine jet 2. The coolant nozzle 10 is fed as before from a reservoir tank (not shown). Figure 2c illustrates a coolant nozzle 10 fixed downstream of a vectorable propulsion/lift engine nozzle 1. The coolant nozzle 10 is coaxial with the propulsion/lift engine nozzle 1, allowing a water jet 7 to flow coaxially with engine jet 2 emanating from nozzle 1. A fairing 9 supports the coolant nozzle 10 within an assembly 11 and protects it from the engine jet 2. The nozzle and fairing assembly 11 is pivotally mounted to the aircraft (not shown) so that it can be swung into and out of the engine jet flow as required. Figure 2d illustrates a mixed fluid coolant nozzle 10 fitted to a lift engine nozzle 1. A first coolant feeder tube 13 for feeding the nozzle 10 is supported and protected by a fairing 9. Air is bled from a compressor stage of the engine (not shown) along the first coolant feeder tube 13 and a second coolant, such as water, is introduced to the coolant tube 13 at any point 14 between the compressor and the coolant nozzle 10. The coolant nozzle 10 is coaxial with the lift engine nozzle 1 allowing the air/water vapour jet 7 to flow coaxially with the engine jet 2. Figure 2e illustrates a mixed fluid coolant nozzle 10 fitted to a vectorable propulsion/lift engine nozzle 1. A first coolant feeder tube 13 for feeding the nozzle 10 is supported and protected by a fairing 9. Air is bled from a compressor stage of the engine (not shown) along the first coolant feeder tube 13 and a second coolant, such as water, is introduced to the coolant tube 13 at any point 14 between the compressor (not shown) and the coolant nozzle 10. The coolant nozzle 10 is coaxial with the propulsion/lift engine nozzle 1 allowing the air/water vapour jet 7 to flow coaxially with the engine jet 2. Figure 2f illustrates a mixed fluid coolant nozzle 10 fixed downstream of a vectorable propulsion/lift engine nozzle 1. The coolant nozzle 10 is coaxial with the propulsion/lift engine nozzle 1, allowing a water jet 7 to flow coaxially with engine jet 2 emanating from nozzle 1. A fairing 9 supports the coolant nozzle 10 within an assembly 11 and protects it from the engine jet 2. The nozzle and fairing assembly 11 is pivotally mounted to the aircraft (not shown) so that it can be swung into and out of the engine jet flow as required. Many modifications and improvements to the invention described above will now suggest themselves to those skilled in the art. Taking by way of example the case of a recently projected VSTOL aircraft which was required to perform vertical landings on an Ordinary Portland Cement Paving Quality Concrete (OPCPQC) surface at a vertical rate of descent of 1.37 metres/second (4.5 feet/second). It was predicted that the minimum permissible vertical speed to avoid erosion of the OPCPQC surface was 3.57 metres/second (11.7 feet/second), i.e. the desired rate of descent was less than half the "safe" rate of descent. However, fitment of the invention described above to the aircraft would enable it to operate safely at the desired rate of descent on OPCPQC surfaces. Furthermore, it is known that most of the heat transfer to the impingement surface in a vertical landing occurs in the last ten diameters of nozzle travel, thus the invention in the case cited would need to operate for only about 3.6 seconds (lifting jet nozzle diameter = 0.5 metres (1.64 feet)). Clearly, the control of coolant fluid could be linked to signals from the aircraft's altimeter such that coolant fluid is introduced into the lifting jet(s) only as the aircraft descends through a pre-determined height above the ground and at a rate of descent that is less than the minimum permissible (for an aircraft not equipped with the invention) for a particular type of surface. In the case cited the coolant fluid would need to be introduced into the lifting jet at, and below, an altitude of 5 metres (16.4 feet) when the aircraft was descending at less than 3.5 metres/second (11.7 feet/second).

Claims: Apparatus for reducing ground erosion caused by impinging hot jets such as the lifting jets (2) of VSTOL aircraft or rockets, said jets (2) emanating from a hot jet nozzle (1) such as a lift engine nozzle or a lift/propulsion engine nozzle, comprising means (9, 10) mountable on the hot jet nozzle (1) for introducing a coolant fluid (7) to an impingement surface (5) immediately beneath the turning zone (4) characterised in that the apparatus may alternatively be mounted on the airframe of the aircraft and that the coolant fluid (7) is delivered into the hot jets (2) at a pressure in excess of the prevailing static ambient pressure. Apparatus for reducing ground erosion as claimed in Claim 1 characterised in that the coolant fluid (7) is introduced coaxially with the hot jets (2). Apparatus for reducing ground erosion as claimed in Claim 1 characterised in that the coolant fluid (7) is introduced into the hot jets (2) in a direction that does not initially correspond to the jet axis. Apparatus for reducing ground erosion as claimed in any one of the preceding claims characterised in that the coolant fluid (7) is delivered through a coolant nozzle (10) to be located downstream of or within the hot jet nozzle (1). Apparatus for reducing ground erosion as claimed in Claim 4 characterised in that the coolant nozzle (10) is protected and supported by a fairing (9). Apparatus for reducing ground erosion as claimed in Claim 5 characterised in that the coolant nozzle (10) and fairing (9) are to be fitted to the hot jet nozzle (1). Apparatus for reducing ground erosion as claimed in Claim 5 characterised in that the coolant nozzle (10) and fairing (9) are to be fitted to an airframe of the VSTOL aircraft or structure of the rocket downstream of the hot jet nozzle (1). Apparatus for reducing ground erosion as claimed in Claim 5, 6 or 7 characterised in that the coolant nozzle (10) and fairing (9) can be swung into and out of the coaxial position with the hot jet (2) as required. Apparatus for reducing ground erosion as claimed in any preceding claim characterised in that compressed air is tapped off at a tapping point in an early stage of compression from the lift/propulsion engine(s) and used as cooling fluid (7). Apparatus for reducing ground erosion as claimed in Claim 9 characterised in that water or any other fluid is introduced into the air between the tapping point and the coolant nozzle. Apparatus for reducing ground erosion as claimed in any of Claims 1 to 8 characterised in that a fluid with a thermal capacity higher than that or air is used as a coolant (7). Apparatus for reducing ground erosion as claimed in Claims 1 to 8 characterised in that water is used as a coolant (7). Apparatus for reducing ground erosion as claimed in any preceding claim characterised in that the fluid is stored in an on-board tank and pumped to the coolant nozzle (10) by means of a pumping system.

Inventors: ANGEL ROBERT GEORGE ANDREW, ANGEL, ROBERT GEORGE ANDREW, Angel, Robert George Andrew, British Aero Def Ltd
Applicants: BRITISH AEROSPACE, BRITISH AEROSPACE PUBLIC LIMITED COMPANY
Application year: 1996
Main classification: B64C29
IPC codes: B64C29, F02K1