US3424384A - Adjustable plug type jet propulsion nozzle - Google Patents

Description

Jan. 28, 1969 H. M. A. R- LAcoMBE 3,424,384

ADJUSTABLE PLUG TYPE JET PROPULSION NOZZLE Filed Sept. 19, 1 966 United States Patent 3,424,384 ADJUSTABLE PLUG TYPE JET PROPULSION NOZZLE Henry Marie Andr Ren Lacombe, Bois-le-Roi, France, assignor to Societe Nationale dEtude et de Construction de Moteurs dAviation, Paris, France, a company of France Filed Sept. 19, 1966, Ser. No. 580,538 Claims priority, application France, Sept. 21, 1965,

US. Cl. 239-26539 Int. Cl. B64c 15/06; B05b 1/30 2 Claims ABSTRACT OF THE DISCLOSURE conjunction with the tapered portion of said tail cone, a

divergent jet pipe section having a mean flow direction which converges with respect to the axis of said nozzle.

The present invention relates to jet propulsion nozzles of the so-called plug type having a tail cone which tapers rearwardly from a part of maximum cross-section to a tail end and which forms the inner wall of an annular jet pipe of convergent or convergent-divergent configuration with its zone of minimum area or throat being at the level of said tail cone part of maximum crosssection.

It has already been proposed to adjust the throat area of such nozzles by means of flaps extending from an end pivoted on an outer wall at a location upstream of said part of maximum cross-section to a free trailing edge positioned opposite said part.

Theoretical studies, which have moreover been corroborated in practice, have revealed two drawbacks of this solution:

(1) The ejection is defective at the level of the flaps. In fact, as these flaps extend wholly upstream of the above-mentioned part of maximum cross-section the mean direction of ejection diverges from the longitudinal axis of the nozzle. The jet must consequently undergo over the convex profile of the central body a considerable deflection which brings it back towards the axis and which excessively intensifies the effect of the Prandtl-Meyer expansion originating from the ends of the flaps. Moreover, at certain speeds, the Mach waves, after reflection on the jet line, form a recompression bundle or beem which focuses in a violet shock producing losses.

(2) Irnmersing the flaps into the motive gaseous flow creates a drag zone at low pressure behind the flaps and usually secondary air from a surrounding casing is fed into said drag zone to raise the pressure level thereof in an attempt to reduce drag losses. However such satisfactory operative conditions are not attainable at all flight runnings for lack of reaching the appropriate pressure level. In fact, if this level is too high, the jet bursts out at a small angle on leaving the flaps and there subsists in the plane of ejection, between the jet boundary line and the end of the casing, a considerable pocket which is difficult to ventilate and is always the cause of 3,424,384 Patented Jan. 28, 1969 losses. If the level is too low, the jet bursts out very strongly and encounters the casing at a considerable angle, so that on impact there is created a shock which produces losses and there is a risk of the hot gases being driven back. This is frequently the case in highspeed flight.

It is one object of the present invention to provide a jet propulsion nozzle which does not exhibit the faults hereinbefore described.

One embodiment of the invention will now be described by way of example with reference to the single figure of the accompanying drawing which is a diagrammatic view in axial half-section of a jet propulsion nozzle embodying the invention.

The nozzle comprises a fixed profiled plug or central body 1 having an upstream portion 2 which is of increasing cross-section in the direction of flow and which is connected, through a part 3 of maximum cross-section, with a downstream portion 4 of decreasing crosssection. The nozzle is defined externally by a fixed wall 5 to which a number of inner flaps 6 are hinged at a location 7 upstream of part 3; these flaps extend to a free trailing edge positioned downstream of part 3 and so override the latter. They cooperate with a number of outer flaps 8 which are pivoted at 9 at the rear end of a casing having ports 10 for the inlet of ambient air.

In the drawing the lines of the jet boundary are indicated as follows: at A1 and A2 are shown the jet boundary lines corresponding respectively to take-off without afterburning (flaps 6 in position 6 and with afterburning (flaps 6 in position 6 the flaps 8 being in position shown in dashes; at B is shown the jet boundary line corresponding to transonic speed (flaps 8 in the position shown in chain-dotted lines); and at C is shown the jet boundary line for supersonic cruising speed (flaps 8 in the position shown in solid lines).

It will be noted that the throat adjusting flaps 6 extend downstream of part 3, thus eliminating the drawback mentioned above in respect to the initial deviation. Moreover, the central body 1 is designed so as to form with these flaps a primary convergent-divergent jet pipe section, the nominal expansion ratio of which at the ends of the flaps always remains close to the minimum expansion ratio of the engine under take-01f conditions, so that in this case the performances of a correctly designed and well adapted nozzle can be expected. The jet boundary line A1 or A2 is therefore almost parallel to the downstream portion 4 of the central body 1.

Whatever the expansion ratio, the terminal flaps 8, which are free or controlled, can be directed tangentially to the corresponding jet boundary line, thus preventing inner drag zones of low pressure to build up in the highvelocity motive jet and transferring them from behind the inner flaps 6 to behind the outer flaps 8 which are bathed in ambient air. This is the case in low-speed flight and in transonic flight (positions shown in dashes and chain-dotted lines, respectively).

At high expansion ratios, the flaps 8, which are in the position of maximum opening (solid lines), form with the central body 1 a secondary divergent structure, the pressures and ventilating flow-rates of which remain low, in spite of the practicaldisappearance of any inner drag zone. As a matter of fact, the pre-expansion oflered by the inner flaps 6 greatly reduces the bursting angle of the jet and still permits the tangential pick-up thereof on the terminal flaps 8.

Whatever the circumstances, the inner flaps 6 are always substantially convergent. Their downstream portion bounds a divergent section adapted to the expansion ratio.

Moreover, there is generally a slight flow of secondary air induced by the jet.

What is claimed is:

1. An adjustable jet propulsion nozzle comprising a stationary plug member which tapers rearwardly from a part thereof of maximum cross-section to a tail end, and movable flaps outwardly spaced with respect to said plug member and pivoted at a location spaced upstream of said part of maximum cross-section, said flaps ending with a free trailing edge at a location spaced downstream of said part of maximum cross-section but upstream of said tail end, thereby overriding said part of maximum cross-section and defining with said plug member a convergent-divergent nozzle element with a throat in the zone of said part of maximum cross-section, said flaps being adjustably inclinahle inwardly to define, in conjunction with the tapered portion of said plug member, a divergent nozzle section having a mean flow direction which converges with respect to the nozzle axis.

2. Jet propulsion nozzle as claimed in claim 1, further comprising a fairing outwardly spaced from said flaps,

and pivotal wall elements'hingedly connected to said fairing and forming a downstream extension thereof, said wall elements extending downstream of the free trailing edge of said flaps.

References Cited UNITED STATES PATENTS WALTER SOBIN, Primary Examiner.

US. Cl. X.R. 239127.3

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