US2098565A - Engine cooling and cowling - Google Patents

Description

NOV. 9, 1937. c o 2,098,565

ENGINE COOLING AND COWLING Filed April 12, 1934 2 Sheets-Sheet l Fig.1.

Prior iii INVENTOR Q LHND CHILTON ATTORNEY Nov. 9, 1937. R. CHILTON ENGINE COOLING AND COWLING Filed April 12, 1934 2 Sheets-Sheet 2 INVENTOR Rom CHILTON ATTORNEY Patented Nov. 9, a 1937 ENGINE COOLING AND COWLING Roland Chilton, Ridgewood, N. J., assignor, by mesne assignments, to The Reed Propeller 00.,

1110., York Garden City, N. Y., a corporation of New Application April 12, 1934, Serial No. 720,283 7 Claims. '(01. 123-171) This invention relates to means for improving cooling air flow and the specific showing of the drawings relates to air flow over the finned cylinders of radial air-cooled aircraft engines.

The cowling for these engines usually comprises the so-called N. A. C. A. cowl surrounding the engine from an air entrance immediately back of the propeller to an annular exit slot around the nose cowling of the airplane. The

air flow is further confined to the finned periphery of the cylinders by means of baflles which prevent waste of air through the inter-cylinder spaces. -In such an installation it is possible to accurately measure the cooling effectiveness by 5 observing the difference in air pressure in front of and behind the engine cylinders, this measurement being known as the baflle difierential. Little cooling trouble is experienced in level flight in modern high speed airplanes because the high'air speed then gives a baiiie differential of the order of 12" water pressure. This high cooling pressure is lost, however, in climb conditions, where in many cases, with conventional cowling, the pressure falls below 4" water pressure,

whereupon the cooling is inadequate.

To obtain the optimum rate of climb, the air speed will be about one half of normal, which a should correspond to one fourth of the normal baille differential. In many cases, however, the pressure differential under climb conditions has been observed to fall to one eighth of the high speed condition, indicating an inconsistent behavior in the air fiow, which will now be explained by reference to the drawings, in which:

Fig. 1 is a fragmentary diagram illustrating the re-circulation which occurs with the conventional cowling;

Fig. 2 shows the provisions of the present invention which overcomes this deficiency;

Fig. 3-shows a rotary form of the invention; and A Fig. 4, illustrates the vanes 01' Fig. 3.

In the figures, the engine crankcase is indicated at I 0 and a typical air-cooled cylinder at I I2. The lines l4 show the outline of the engine cowling, while cylinder head baffles are indicated at l6. Other baffles are used to blank off the spaces between the cylinders. The propeller, indicated at I8, is of the current metal type which has a relatively bulky hub with round sockets to take the propeller blades which, unfortunately, have very little effective airfoil section or pitch within the radius of the cowling entry. The resuit is that the center part of the propeller acts 5 as a centrifugal rather than as a pitched fan and accordingly tends to displace the air radially over the outside of the cowl instead of axially as is necessary to force air into the conventional cowl entrance and overthe cylinders.

The area for flow past the bafliesis only a small fraction of the entrance area into the cowl,

wherefore the axial velocities at the entrance are relatively low, which again tends to augment the centrifugal displacement due to the unpitched center part of the propeller. These effects get worse' as the air speed is reduced in climb, and actual air flow observations have indicated a re-circulation of air as indicated by the arrows, 20, in Fig. l, and it is this re-circulation which results in the abnormal reduction in the baille diiferential pressure which prevents adequate cooling under climbing conditions.

Fig. 2 illustrates the provisions of the present invention whereby this re-circul'ation is prevented and the centrifugal action of the propeller is taken advantage of to augment the air flow. This provision consists of a plate 22, which may be secured to the no's'e of the engine and which extends within the cowl entrance to define a slot giving radial rather than axial flow. The cowl forwardly overlaps the nose plate or blame and so collects the air which is radially displaced by the propeller. The area of the slot is preferably in conformity with the area for flow past the baflles, whereby the air enters at high velocity.

In actual tests with this simple provision, the cooling pressure difi'erential, at 100. mi./hr. climbing speed, was increased from 1%" of water to 3 of water, which improvement changes the installation from one having definitely unsatisfactory cooling to one that is adequate. It will be obvious that re-ciroulation, as indicated in'Fig. l, is prevented by the radial fiow nose baflle of this invention.

This beneficial effect may be enhanced as shown in Figs. 3 and 4'by securing the plate 22' to rotate with the propeller and by adding fan blades 24' to augment the radial displacement from the propeller, which displacement has now become an advantage instead of a detriment.

The direction of the resultant air fiow due to the combination of radial and axial movement thereof tends more in a radial direction than in an axial direction whereby, the path taken by the cooling air upon entering the cowling is at an angle of more than 45 to the propeller and cowl axis. This is plainly shown in Figs. 1, 2 and 3 by the arrows designating air flow directiQn. Thus, in designing the cowling and bailie 45. The term element above used, and used in the claims in connection with the cone, is

used in the geometrical sense wherein the element of a cone is a line along the surface extending from the apex to the base. Likewise,'th leadingedge of the ring cowling I4 is inturned to such an extent that a tangent to the leading edge curve, passing through the propeller and cowling axis, also makes an angle of greater than 45 with said axis. Thus, one of the said tangents and lies in the same axial planewith said tangent, lie substantially parallel to one another, both making an. angle with the propeller and cowl axis of more than 45. when the fixed type of baiile, such as is shown in Fig. 2, is utilized, itsdiameter is preferably somewhat less than the entrance opening diameter of the cowling II, but still, is of suiiicient magnitude so that thebaiiie diameter is more than 70%.of the cowl entrance 7 opening diameter. This effectively prevents the recirculation of cooling air entering the cowling as described in connection with Fig. l.

I am aware that nose cowls having shutters which could be opened and closed have been used in the prior art, although not in connection with an over-lapping external cowl. The intention of such controllable shutters was that the cylinder temperatures could be increased in cold weather by closing the shutters, but they have been abandoned because it was found in practice that they did not function as expected. I believe that this disclosure contains the first explanation of the reason for the ineffectiveness of these old shutter type nose cowls.

with the very high output engines now in vogue, it is very doubtful if any provisions for increasing the cylinder head temperatures are necessary, even in the coldest weather, but should this be desired, it could be achieved by providing controllable openings in the nose plate 22. However, the action. would be the-precise inverse of that supposed to apply to the. old nose cowls. That is to say, the opening of the shutters would tend to permit re-circulation through the open- -ings as indicated in Fig. l and would increase the cylinder temperatures in opposition to the operating instructions issued with the old shutter typ'e nose cowls. It should be emphasized that such nose cowls were not effective in utilizing the centrifugal displacement from the propeller because they were still predicated on an axial air entrance and did not have the forwardly over-lapping outer cowl nor suflicient diameter to utilize radial flow at the entrance. While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modifications and changes.

What is claimed is:

i. In combination with an engine having a propeller apt to induce a greater degree of radial than axial air fiow rearward thereof; a substantially conical imperforate disc coaxial with said propeller and mounted rearward thereof, said disc being so formed that the elements thereof are substantially parallel to the combined an element of said coned plate which,

edge of saidring cowl aoeases I radial and axial air fiow and make an angle greater than 45 with the propeller axis; and a fixed ring cowl having an inturned leading edge terminating forwardly of the disc edge in annularly spafied 4 relation thereto to provide an air entranc annulus.

2. In' combination with an engine ,having a propeller apt to induce a greater degree of radial than axial air flow rearward thereof; a substantially conical disc rotatable on the propeller axis and mounted rearward of the propeller, said disc being so formed that the elements thereof are substantially parallel to the combined radial and axial air flow and make an angle greater than 45 with the propeller'axis; fan blades carried on the forward side of said disc toward the edge thereof; and a ring cowl encircling said disc and the outer cylinder ends, the leading edge of said ring cowl being between the propeller and the engine and being inturned to define with said disc edge an annular air entrance opening.

3. In combination with a radial cylinder enginehaving a propeller and a fixed ring cowl encircling the outer cylinder ends, the leading being inturned so that a tangent to said cowl at theleading edge, in the plane of the cowl axis, makes an angle of more than 45 withthe cowl axis; -means defining a relatively narrow annular air entrance opening beneath the leading edge of said ring cowl comprising a coned disc having its elements respectively substantially-parallel to the coplanar cowl leading edge tangents;

4. In combination with a radial cylinder engine having a propeller and a fixed ring cowl encircling the outer cylinder ends, the leading edge of said ring cowl being inturned so that a tangent to said cowl at the leading edge, in a plane containing'the cowl axis, makes an angle of more 5. In combination with a radial cylinder engine having a propeller and a fixed ring cowl encircling-the outer cylinder ends, the leading edge of said ring cowl being inturned so that a tangent to said cowl at the leading edge, in a plane containing the cowl axis, makes an angle of more than 45 with the cowl axis; means defining a relatively narrow annular air entrance opening beneath theleading edge of said ring cowl, com-' prising a coned disc having each element substantially parallel to respectively coplanar cowl leading edge tangents at the same side of the cowl axis, said disc being rotatable on the propeller axis; and fan blades carried by said coned disc extending across said annular air entrance opening.

6. In combination with a radial cylinder engine having a propeller forward thereof and a fixed ring cowl encircling the outer cylinder ends and having an inturned leading edge terminating in a transverse plane between the engine and the propeller; a coned disc coaxial with said cowl, said disc slanting rearwardly from its center toward its edge, the disc edge lying rearwardly of said cowl leading edge to define with said cowl edge a substantially radial air entrance annulus, the edge of said cowl being so proportioned that a tangent to said cowl at the leading edge there-- '75 of, man axial plane, makes an angle of more than 45 with the cowl axis, said coned disc having such a form that an element thereof coplanar with said tangent and on the same side of the cowl axis, is substantially parallel to said tangent.

7. In combination with a radial cylinder engine having a propeller; a ring cowl encircling the engine cylinders and having an inwardly 10 curved leading edge portion between the propeller and engine, the curve of said cowl adjacent said leading edge being such that a tangent to said curve intersects the cowl axis, and makes an angle of more than 45 therewith; and a coned disc having its edge within said cowl so shaped that elements thereof coplanar with respective cowl tangents and on the same side of the cowl axis lie in substantially parallel relationship therewith.

ROLAND CHILTON.

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