Convexly curved deflector for elevated jet engines blasts

March 7, 1967 b. s. lynn 3,307,809

CONVEXLY CURVED DEFLECTOR FOR ELEVATED JET ENGINES BLASTS

<img file="US3307809A_D0001.tif" />

his Attorney

March 7, 1967

B. S. LYNN

3,307,809

CONVEXLY CURVED DEFLECTOR FOR ELEVATED JET ENGINES BLASTS

Filed June 1, 1965

Sheets-Sheet 2

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FIG. 2

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FIG. 3

Inventor: Bernard Stanley Lynn By'i t .

his Attorney

United States Patent Office

3,307,809

Patented Mar. 7, 1967

307 809

CONVEXLY CURVED DEFLECTOR FOR ELEVATED JET ENGINES BLASTS

Bernard Stanley Lynn, 19451 Black Road, Los Gatos, Calif. 95030

Filed June 1,1965, Ser. No. 460,083 6 Claims. (Cl. 244—114)

This invention relates to blast deflector fences, particularly to such fences as are required to deflect the blast of aircraft jet engines where the jet nozzles are so high above ground level that present day deflectors are no longer adequate. The principal object of the invention is to produce a deflector fence that will effectively and safely deflect the blasts of elevated jet engines.

Another object of the invention is to produce a blast fence in which the loads and stresses on same caused by elevated jet engine blasts are reduced, thereby lowering the cost of the deflectors.

A further object of the invention is to provide a blast deflector fence in which the higher the blast strikes the fence, the lower the overturning moment.

Other objects of the invention are covered in the claims.

Deflectors such as described in my U.S. Patents Nos. 2,974,910 and 3,126,176 while excellent for jet blasts which are low to the ground or which intersect the deflector at or near the base or leading edge are not structurally adequate for elevated jet blasts because if the centerline of the blast intersects a concave deflector at or near its upper edge, serious vibration problems resu’t from the pulsating unbalanced load. Also the projection of the resultant of the blast load will intersect the ground far behind the deflector and this will cause an unduly large overturning moment. The higher the resultant on a concave fence, the farther away it intersects the pavement, the larger the overturning moment. An unusually large, expensive slab of reinforced concrete to adequately counterbalance the overturning moment is therefore required. In addition it has been found that the vibration caused by this pulsating overturning moment will cause fatigue failures and the loosening of anchor bolts and nuts. The higher the jets are located above the pavement, the worse this problem becomes. .

Conventional concave deflectors are aerodynamically inadequate if the blast hits near the upper edge because instead of being deflected upward and to the rear, much of the blast is deflected downward and forward along the concave surface, and back toward the source of the blast. In addition to the unwanted back pressure, there is the danger of dirt and debris being blown forward and ingested into the engine. In case of a concave deflector these high blasts will hit the curve of the deflector where the chord line approaches the vertical, this greatly increasing the dynamic impact loading by acting as a nearly vertical splash-plate. That portion of the blast which hits such near-vertical area is not deflected upward, but bounces backward in swirls and eddies, thus causing violent turbulence.

Economically concave deflectors are undesirable for elevated blasts because the cost increases markedly with the height. For an equal blast loading and working stress, a ten foot high concave deflector would weigh about twice as much (and therefore cost about twice as much) as a seven foot deflector. Thus a high concave deflector becomes very expensive.

In the drawings:

FIGURE 1 is a side view;

FIGURE 2 is a front elevation;

FIGURE 3 illustrates a higher fence; and

FIGURE 4 illustrates a modified rear base anchor clip.

Referring to FIGURE 1 the surface facing the blast, instead of being concave, is convex and is of corrugated metal with the ribs and valleys horizontal. This metal surface 10 is bolted to a curved rib 11 which with the chord brace 12 and the auxiliary truss braces such as 14, 15, and 16, all of structural shapes, form a solid statically determinate rigid truss. The rib 11 is shown as an arc but the curve need not be of uniform radius and may be curved to suit special conditions. A radius of .14 feet will give an ideal curvature for deflectors from 10 to 12 feet high, the radius increasing with increased height of deflectors.

Each rigid truss is removably secured at its lower or leading edge to a curb type concrete foundation for example 20 wide and 24 deep to transmit the blast load to the ground. The connection includes an anchor , clip 24 held by an anchor bolt 25 of suitable length and the truss may be pivoted as at 26 so that the entire series of trusses may be uniformly rotated forwardly and upwardly from about 45° to 60°, thus providing a convenient variable height feature of considerable utility. For example, at the 45° position, the angle of impact of blast is reduced and for given thrust, load is reduced; thus this configuration will withstand the heavier loads with •afterburner as encountered, for example, on SR-71 aircraft. When rotated to 60°, it will be seen the deflector height is increased from about 10 feet to 12 feet, which makes it suitable for use with Boeing 727, DC-9, and BAC-111 aircraft with higher engines but without afterburners, and consequently lighter loads. The trms is supported by a strut 20 pivoted as at 21 to the chord brace 12 and its lower end is secured to the anchor clip 22 or to the clip shown in FIGURE 4 which allows variation in the slope of the corrugated metal surface on the truss.

Experience and experiment have shown that the jet blast will tend to follow a concave surface and to exit about tangent to the trailing edge. It is thus inadvisable and undesirable to slope the chord line of my convex deflector of this invention at less than 45°, as the blast will' tend to sweep downward toward the ground behind the deflector by following the downward sloping tangent line. Conversely, and optionally, deflection may be improved and the blast diverted in a more nearly vertical direction by installing a relatively narrow nearly vertical extension 31 at or near the trailing edge. This consists of a channel member 33 bolted to the end of the chord brace 12 and carrying a foot or more of corrugated metal 34, preferably with an optional gap 35 of slight dimension between it and the surface 10.

The rib trusses are held together by the corrugated panels 36 which may be 6, 8, or 12 feet long, bolted together preferably 24 center to center where afterburners are expected but otherwise may be 36 or more center to· center, and may be as much as 60 center to center if 1 x 3 corrugated metal is used. The height of the fence illustrated is nominally 11 feet high but with the extension 31 runs to approximately 12 feet. The distance between anchors 25 of FIGURE 1 should be about equal to fence height, the length of the strut 20 determining the height, for a given chord truss design.

FIGURE 3 shows a 22 foot high fence, this requiring extra auxiliary truss braces 27 and two struts 29 and 30 in place of the single strut 20 of FIGURE 1, and this type may be considered to be of fixed height.

In FIGURE 4 the truss may be positioned between 45° and more than 60° by securing the strut bolt 37 in the proper hole 38 of the horizontal row in the angle iron rear base clip 39, the bolt being a pivot in this case