AN IMPROVEMENT IN RAM AIR TURBINES

Abstract: An improvement in ram air turbines, especially for missiles comprising a device for limitation of the range of the velocity of rotation of the turbine, the turbine comprising a ram air inlet (10) for first and second passages or ducts (30, 31) respectively, the first passage (30) conducting air to the turbine runner (15) for driving the latter. According to the invention the second passage is connected to a common outlet (17) for the two passages (30, 31) via a device (20) comprising at least one member or portion (23), e.g. flaps or tongues. The member (23) is adapted to exert a variable resistance to the air flowing through the second passage (31), whereby the air resistance coefficient of the member (23) decreases upon increasing missile velocity.

Description: An improvement in ram air turbines The invention relates to an improvement in ram air turbines, especially for missiles, comprising a device for limitation of the range of the veocity of rotation of the turbine, the turbine comprising a ram air inlet for first and second passages or ducts respectively, the first passage conducting air to the turbine runner for driving the latter. In known ram air turbines the outlet is arranged to let the pressure at this point increase with increasing speed of the object, e.g. a missile and hereafter denominated missile, which carries the turbine. It is, consequently possible to prevent the r.p.m. of the turbine from getting to high when the missile speed is at maximum, but in case of low missile speed the turbine r.p.m. may become too low for the turbine to drive, e.g. an electric generator. Alternatively, it may occur that the lowermost r.p.m. of the turbine is high enough, whereas the maximum r.p.m. will excede a permitted value. It is an object of the invention to provide a ram air turbine of the above kind, in which the mentioned disadvantages are eliminated. It is, thus, desirable for the turbine to achieve a minimum operational r.p.m. as soon as possible upon launching of the missile, and that maximum permitted r.p.m is not exceded at the highest achievable speed of the missile. The invention is disclosed in more detail below with reference to the drawing which shows an embodiment of an arrangement in ram air turbines according to the invention. Figure 1 is a longigudiήal section along line I-I through the front portion of a missile; Figure 2 is a view of the missile shown in Figure 1, as seen in the direction of arrow A; Figure 3 is a plan view of a plate. As will appear from Figure 1, in the front portion, e.g. of a missile 1, a hole 2 is designed to extend coaxially with the latter and to open forwards. It comprises a first cylindrical portion 3 extending rearwards to a bottom 4 having a convex spherical front surface, and a second cylindrical portion 5 of hole 2 having a smaller diameter than the first portion 3 and extending centrally from bottom 4 and to a third cylindrical portion 6 having a larger diameter than second portion 5. In the hole 2 a cylindrical air intake tube 10 is indicated as comprising an external tube 11, the length of which is slightly less than the length of the first cylindrical portion 3 of hole 2, and an internal tube 12, the external diameter of the external tube 11 and the internal tube 12 being adapted to the internal diameter of the first, and the second cylindrical portion, 3 and 5, respectively of the hole 2, and the front end of the cylindrical portion 3 of the hole 2 and the external tube 11 being arranged substantially at the same place, as seen in the longitudinal direction. The rear portion of the external tube 11 and the front portion of the internal tube 12 are firmly connected with each other, via a series of radially extending ribs 13 which, together with the tubes 11, 12 limit a series of axially extending apertures 14. The external tube 11, thus, ends at a distance from the bottom 4 of the hole 2 , and in the portion of the missile forming the external wall of the hole 2 there is provided a series of through orifices 17 substantially between said bottom 4 and the rear end of the external tube 11. In radially external portions of the bottom 4 axial orifices 18 are provided to form passages which connect the third portion 6 of the hole 2 with the orifices 17 in the wall of the missile. The outlet orifices 17 open mainly forward in a manner known per se. In the third, expanded portion 6 of the hole 2 a turbine runner 15 is provided and is mounted on a shaft 16 extending coaxially relative to the hole 2. Between the bottom 4 and the ribs 13 of the air inlet tube an annular, circular plate 20 is provided. It has a concentric through hole 21 the diameter of which is slightly smaller than the external diameter of the internal tube 12 of air inlet tube 10, and the external diameter of the plate is slightly smaller than the diameter of the first cylindrical portion 3 og hole 2. Furthermore, in plate 20 there is formed a series of radially extending slots 22, which open radially outwards and define a series of tongue-shaped plate portions 23. The inner portion of the tongues 23, but preferably the entire plate, is manufactured from a resilient material, e.g. stainless steel, so that it is possible to bend tongues out in a direction away from the plane of the plate. When the plate 20 is mounted in missile 1, it is firmly held along its inner peripheral portion between the ribs 13 and the bottom 4 of the hole 2. By this arrangement an air intake with two passages 30, 31, indicated by arrows in Figure 1, is provided. The first passage 30 comprises a central portion of the external tube 11, the internal tube 12, the third cylindrical portion 6 of hole 2, and orifices 18 in bottom 4. The second passage 31 comprises a radially external portion in the external tube 11 and the apertures 14 between the ribs 13, both passages opening in the common orifices 17 forming outlet openings in the missile wall. The function of said arrangement is as follows: When the missile is at the rest plate 20 extends along the rear side of the ribs 13 and substantially closes the apertures 14 between said ribs and, thus, the second passage 31. Immediately upon launching the missile receives its highest speed. During missile movement the pressure on the air in the air inlet tube 10 approximately corresponds to the stagnation pressure, and due to the provided orifice 17 in the missile wall the pressure on the air in the common outlet of first and second passage will be less than said stagnation pressure. Without the arrangement according to the invention there would be danger of too high r.p.m. of the turbine during launching, even though the increased pressure in outlet orifices 17 to some degree contributes to limit the pressure difference in intake and outlet. Due to this pressure difference, however, tongues 23 and plate 20 will be bent rearwards and contact the uniformly curved bottom 4 of hole 2 which supports the plate to prevent it from becoming overstrained, and open the second passage 31 to permit air flow through said passage. The outlet 17 being common to both passages and limiting the total air flow from them, the volume of air flowing through the first passage 30 will be comparatively small, so that the r.p.m. of the turbine does not exceed its maximum value. When the missile speed decreases, said pressure difference will also decrease. Due to their resiliency the tongues 23 will consequently be moved forward correspondingly, away from the bottom 4. The resistance which they exert against the air flow in the second passage 31 will, thus, cause an increase of the portion of the air flowing in the first passage 30, so that the r.p.m. of the turbine is substantially maintained in spite of this reduced pressure difference. The r.p.m. of the turbine may thus be substantially constant in a large range of velocities of the missile. The plate 20 is advantageously biased in such a manner that the tongues project obliquely one way away from the paper plane in Figure 3. It may thus be achieved that the plate does not open the second passage until the missile has reached a predetermined velocity. Even though it is stated above that the front surface of bottom 4 is shaped like a spherical plate, it may in stead be, e.g. conical or pyramidal, and in stead of the tongues 23 of plate 20 being resiliently springy all over their length, only the radially inner tongue portions may be resilient, so that the radially external portion of the tongues will maintain its plane shape and contact the bottom 4 substantially level when the missile has reached its highest velocity. Furthermore, air intake tube may only comprise the internal tube, which has then an upper, radially outwards projecting flange which may be designed to urge the radially internal portion of plate 20 towards the bottom 4.

Claims: CLAIMS : 1. An improvement in ram air turbines, especially for missiles, comprising a device for limitation of the range of the velocity of rotation of the turbine, the turbine comprising a ram air inlet (10) for first and second passages or ducts (30, 31) respectively, the first passage (30) conducting air to the turbine runner (15) for driving the latter, c h a r a c t e r i z e d i n that the second passage (31) is connected to a common outlet (17) for the two passages (30, 31) via a device (20) adapted to exert a variable resistance to the air flowing through the second passage (31) whereby the air resistance coefficient of this device (20) decreases upon increasing missile velocity. 2. An improvement in ram air turbines according to claim 1, c h a r a c t e r i z e d i n that the opening of the outlet (17) is facing forwards. 3. An improvement in ram air turbines according to claim 1 or 2, c h a r a c t e r i z e d i n that the device for exerting a resistance against the air flow in the second passage consists of at least one member (20) which is designed to be moved by the air flowing in the second passage (31) between a first position, in which it exerts high resistance against the air flow, and a second position, in which it only exerts a slight resistance against the air flow. 4. An improvement in ram air turbines according to claim 3, c h a r a c t e r i z e d i n that member (20) is a plate which is provided in second passage (31) and the shape of which is adapted to the shape of the cross section of second passage (31) , whereby the plate (20) is adapted to be moved between a first position in which the plane of the plate extends substantially across the second passage (31) , this thereby being closed and to a second position in which the plane of the plate extends obliquely relative to the transversal direction of the second passage (31) , this thereby being open. 5. An improvement in ram air turbines according to claim 4, c h a r a c t e r i z e d i n that the plate (20) is mounted to protrude from a wall portion of the second passage (31) , and that at least the portion of the plate which is close to the point of attachment is resiliently flexible. 6. An improvement in ram air turbines according to claims 2 and 5, c h a r a c t e r i z e d i n that the forward position of the first passage is circular in cross section, and that the forward portion of the second passage (31) extends substantially ring shaped around this forward portion of the first passage (30) , and the plate has a series of radially extending slots which open outwards, and is designed to be fastened to the radially inner wall of the second passage (31) . 7. An improvement in ram air turbines according to claim 6, c h a r a c t e r i z e d i n that the radially inner wall portion of the second passage extends approximately convexely immediately downstreams of the annular.plate, and that said plate is flexible and designed to be gradually made to contact the convex surface, the plate being increasingly bent down due to increasing air velocity.

Inventors: ODDEN VIDAR, OLSEN STEN OVE, ODDEN, VIDAR, OLSEN, STEN, OVE
Applicants: NORSK FORSVARSTEKNOLOGI, NORSK FORSVARSTEKNOLOGI A/S
Application year: 1991
Main classification: F42C15
IPC codes: F42C15