Flares

Abstract

A flare is produced which by incremental configuration provides a more or less constant level of illumination on the ground.

Description

The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me of any royalties thereon.

Standard airdropped flares in the past have consisted of a cylindrical flare pellet enclosed by a metallic or non-metallic jacket with an igniter. This flare assembly was placed into position over the target to be illuminated by artillery, mortar or aircraft and employed some gravitational retarding means, such as a parachute, wings or vanes, to elongate its suspension over the target area. These flares were designed to burn with a constant candle-power output and, since, even with retarding means, the flare descended a considerable distance, the illumination on the ground, which is proportional to the inverse square of the distance of the flare to the ground, continually increased. As a result if the target area below the flare was adequately illuminated at the initiation of burning, upon descent of the flare the target was illuminated far in excess of what was required. More commonly however, the illumination at initiation was inadequate and only after descent of the flare did the illumination become adequate.

It is therefore an object of this invention to provide a flare which will provide a nearly constant illumination on the ground while in descent.

Yet another object is to provide an equally effective flare which is lighter in weight than standard flares in present use.

A still further object of this invention is to provide an incremental flare which is more efficient and economical than standard flares in present use.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following description.

This invention relates to the design of a flare such that the flare provides constant, adequate illumination on the ground throughout its descent.

A preferred method of effecting the above consists of a standard flare system wherein the flare pellet is made up of increments of a standard flare composition, e.g. Mg/NaNO.sub.3 /laminac, and each increment is varied by Mg particle size.

An illustrated example of a flare system utilizing an incremental flare pellet can be seen in FIG. 1. In this Figure a flare container 1 with standard igniting means 2 is incorporated with an incremental flare pellet. A three increment type of pellet was chosen as an example in this case. The first increment 3 may contain as a fuel Mg with a particle size of 125 .+-. 25 microns, the second increment 4, Mg of 200 .+-. 25 micron size and the third increment 5, Mg of 350 .+-. 25 micron size.

By varying the particle size of the metallic fuel, the ratio of fuel to oxidizer, the types of fuels and oxidizers, the burning rate and candlepower may also be changed as the flare burns through each increment while still maintaining its approximate luminous efficiency in terms of candle-seconds per unit weight or volume. Since the flare will be designed to ignite at a particular altitude and descend at a known rate, the candlepower may be varied such that the product of the candlepower divided by the square of the distance of the flare from the ground is a constant. This constant represents the illumination level on the ground.

Lastly, as a gravitational retarding means, a parachute 6 is shown in FIG. 1.

Further, it has been found that when successive layers or zones of illuminant composition are placed in the flare container in parallel zones slanted to the vertical axis, a smoother change in light intensity occurs as the flare burns from one increment to another. Examples of a flare pellet embodying such slanted increment design can be seen in FIGS. II and III. This type of slanted loading is accomplished by means of punches whose faces are slanted with reference to the vertical axis, i.e., a conical or somewhat canted cylindrical punch.

Although it is not intended that the invention be limited thereto, there is set forth herein below for the purposes of illustration examples of how an incremental flare may be produced.

EXAMPLE I

THREE INCREMENT FLARE SYSTEM

Percent Metallic Fuel Nominal MATERIALS by weight particle size Candlepower 100/200 mesh 1st Inc. Mg/NaNo.sub.3 / Laminac 4116* 65/35/6 125 .+-. 25 microns 500,000 50/100 mesh 2nd Inc. Mg/NaNO.sub.3 / Laminac 4116 70/30/6 200 .+-. 25 microns 275,000 30/50 mesh 3rd Inc. Mg/NaNo.sub.3 / Laminac 4116 60/40/6 350.+-. 50 microns 100,000 *Polyester-Styrene resin (30% solution in styrene) 98.0% Methyl Ethyl Ketone in Dimethyl Phthalate 1.5% cobalt Naphthenate 0.5%

The burn times chosen were based upon a 60 second total burn time and a relatively constant descent velocity of the flare system. The first increment has a nominal burn time of 16 seconds, the second increment 19 seconds and the third increment 25 seconds. The illumination on the ground produced by the above example may be found by dividing the nominal candlepower of the particular increment by the square of the height of the burning flare from the ground.

EXAMPLE II

TWO INCREMENT FLARE SYSTEM

Percent Metallic Fuel Nominal MATERIALS by weight particle size Candlepower 100/200 mesh 1st Inc. MgNaNO.sub.3 / Laminac 4116 65/35/6 125 .+-. 25 microns 500,000 20 parts 50/100 mesh 2nd Inc. MgNaNO.sub.3 / Laminac 4116 60/40/6 200 .+-. 25 microns 165,000 20 parts 30/50 mesh 350 .+-. 25 microns

The burn times chosen were based upon a 60 second total burn time and a relatively constant descent velocity. The first increment has a nominal burn time of 25 seconds and the second increment, a nominal burn time of 35 seconds.

A similar calculation to find the ground illumination may be made as recited in Example I.

Various fuels, oxidizing agents, and binding agents known to the art may be substituted for their analogues in Examples I and II.

Fuels which may be used to advantage in place of the magnesium are aluminum (and alloys thereof), titanium, charcoal, sulfur, silicon, zirconium, calcium silicide, and metallic hydrides.

Oxidizing agents which may be selected include the nitrates of barium, strontium, sodium and potassium, the perchlorates of ammonium and potassium and the peroxides of barium, strontium and lead.

Binding agents which may be substituted include polyvinyl chloride, ethyl cellulose, metallic resinates, oils, waxes and asphaltum. Found to be particularly effective were binding agents of polyester and sulfur plastics which are polymerized in the pressed flare candle and vinyl alcohol acetate resin.

The aforelisted illuminate type compositions are placed in any well known type of flare container in order of highest light intensity to lowest light intensity. The composition layer of highest intensity is placed in the flare case such that it is in contact with igniting means and will therefore burn first.

The successive layers or zones of illuminant composition are then placed in the flare container in parallel zones slanted to the vertical axis. This slanting effectuates a smoother change in light intensity as the flare burns from one illuminant composition to another. An example of this type of loading would be the use of a cylindrical punch with a conical point to obtain conical mating surfaces of the zones of various illuminant compositions incrementally loaded into a cylindrical flare container.

The proportion of the volumes and compositions of the incremental layers is selected in accordance with the burning time, illumination level (ground), initial height and rate of descent desired for the flare system.

Both igniting means and gravitational retarding means known to the art may be used in the present invention.

I wish it to be understood that I do not desire to be limited to the exact details and compositions described in this specification for obvious modification will occur to a person skilled in the art.

Claims

I claim:

1. A flare adapted to provide a substantially constant ground illumination during descent comprising:

A. a flare container

B. a plurality of light illuminating pyrotechnic compositions of differing illumination levels arranged in three transverse zones in said container so that the composition providing the highest light illumination is placed at a terminal end and successive zones of illuminant compositions are disposed thereafter in decreasing order of light illumination

C. igniting means located adjacent to the composition having the highest light illumination, and

D. gravitational retarding means attached to the flare container, wherein the first zone adjacent to the igniting means is a pyrotechnic composition of 65 percent Mg (125 .+-. 25 microns), 35 percent NaNO.sub.3 and 6 percent laminac 4116; the second zone is a pyrotechnic composition of 70 percent Mg (200 .+-. 25 microns), 30 percent NaNO.sub.3 and 6 percent laminac 4116; and the third zone is a pyrotechnic composition of 60 percent Mg (350 .+-. 50 microns) 40 percent NaNO.sub.3 and 6 percent laminac 4116.