Werle, Donald K. (Hillside, IL)
Kasparas, Romas (Riverside, IL)
Katz, Sidney (Chicago, IL)
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The United States of America as represented by the Secretary of the
Navy (Washington, DC)
241/5, 116/214, 40/213
B64D1/16; B64D1/00; B64D1/16
Field of Search:
244/136 40/213 241/5,29 222/3,4 239/171
Blix, Trygve M.
Kelmachter, Barry L.
Attorney, Agent or Firm:
Sciascia St., Richard Amand Joseph S. M.
What is claim is
1. Contrail generation apparatus for producing a powder contrail having
maximum radiation scattering ability for a given weight material,
2. Apparatus as in claim 1 wherein said jet tube means is a ram air jet
3. Apparatus as in claim 1 wherein an upstream deflector baffle is
provided at the output of said deagglomeration means into said jet tube
means to produce a venturi effect for minimizing back pressure on said
powder feeding means.
4. Apparatus as in claim 1 wherein said deagglomerator means comprises:
5. Apparatus as in claim 4 wherein pressurized gas means is provided
for operating said deagglomeration means.
6. Apparatus as in claim 1 wherein said radiation scattering powder
particles are titanium dioxide pigment having a median particle size of
about 0.3 microns.
7. Apparatus as in claim 1 wherein said radiation scattering powder
particles have a coating of extremely fine hydrophobic colloidal silica
thereon to minimize interparticle cohesive forces.
8. Apparatus as in claim 1 wherein the formulation of said powder
consists of 85% by weight of TiO2 pigment of approximately 0.3 micron
media particle size, 10% by weight of colloidal silica of 0.007 micron
primary particle size, and 5% by weight of silica gel having an average
particle size of 4.5 microns.
9. The method of producing a light radiation scattering contrail,
10. A method as in claim 9 wherein said light scattering powder
particles is titanium dioxide pigment.
11. A method as in claim 9 wherein said powder particles are treated
with a coating of extremely fine hydrophobic colloidal silica to
minimize interparticle cohesive forces.
12. A method as in claim 11 wherein said treated powder particles are
further protected with a silica gel powder.
The present invention relates to method and apparatus for contrail
generation and the like.
An earlier known method in use for contrail generation involves oil
smoke trails produced by injecting liquid oil directly into the hot jet
exhaust of an aircraft target vehicle. The oil vaporizes and
recondenses being the aircraft producing a brilliant white trail. Oil
smoke trail production requires a minimum of equipment; and, the
material is low in cost and readily available. However, oil smoke
requires a heat source to vaporize the liquid oil and not all aircraft
target vehicles, notably towed targets, have such a heat source. Also,
at altitudes above about 25,000 feet oil smoke visibility degrades
The present invention is for a powder generator requiring no heat
source to emit a "contrail" with sufficient visibility to aid in visual
acquisition of an aircraft target vehicle and the like. The term
"contrail" was adopted for convenience in identifying the visible
powder trail of this invention. Aircraft target vehicles are used to
simulate aerial threats for missile tests and often fly at altitudes
between 5,000 and 20,000 feet at speeds of 300 and 400 knots or more.
The present invention is also suitable for use in other aircraft
vehicles to generate contrails or reflective screens for any desired
The powder contail generator is normally carried on an aircraft in a
pod containing a ram air tube and powder feed hopper. Powder particles,
surface treated to minimize interparticle cohesive forces are fed from
the hopper to a deagglomerator and then to the ram air tube for
dispensing as separate single particles to produce a contrail having
maximum visibility for a given weight material.
Other object, advantages and novel features of the invention will
become apparent from the following detailed description of the
invention when considered in conjunction with the accompanying drawing.
DESCRIPTION OF DRAWING
FIG. 1 is a schematic sectional side-view of a powder contrail
generator of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENT
The powder contail generator in pod 10, shown in FIG. 1, is provided
with a powder feed hopper 12 positioned in the center section of the
pod and which feeds a powder 13 to a deagglomerator 14 by means of
screw conveyors 16 across the bottom of the hopper. The deagglomerator
14 produces two stages of action. In the first stage of
deagglomeration, a shaft 18 having projecting radial rods 19 in
compartment 20 is rotated by an air motor 21, or other suitable drive
means. The shaft 18 is rotated at about 10,000 rpm, for example. As
powder 13 descends through the first stage compartment 20 of the
deagglomeration chamber, the hammering action of rotating rods 19
serves to aerate and precondition the powder before the second stage of
deagglomeration takes place in the jet mill section 22. In the jet mill
22, a plurality of radial jets 24 (e.g., six 0.050 inch diamter radial
jets) direct nitrogen gas (at e.g., 120 psig) inward to provide energy
for further deagglomeration of the powder. The N 2 , or other suitable
gas, is provided from storage tanks 25 and 26, for example, in the pod.
The jet mill 22 operates in a similar manner to commercial fluid energy
mills except that there is no provision for recirculation of oversize
particles. Tests with the deagglomerator show that at a feed rate of
approximately 11/2 lb/min, treated titanium dioxide powder pigment is
effectively dispersed as single particles with very few agglomerates
The nitrogen gas stored in cylinder tanks 25 and 26 is charged to 1800
psig, for example. Two stages of pressure reduction, for example, by
pressure reduction valves 28 and 29, bring the final delivery pressure
at the radial jets 24 and to the air motor 21 to approximately 120
psig. A solenoid valve 30 on the 120 psig line is connected in parallel
with the electric motor 32 which operates the powder feeder screws 16
for simultaneous starting and running of the powder feed, the air motor
and the jet mill deagglomerator.
Air enters ram air tube 34 at its entrance 35 and the exhaust from the
jet mill deagglomerator passes directly into the ram air tube. At the
deagglomerator exhaust 36 into ram air tube 34, an upstream deflector
baffle 38 produces a venturi effect which minimizes back pressure on
the powder feed system. The powder is then jetted from the exhaust end
40 of the ram air tube to produce a contrail. A pressure equalization
tube, not shown, can be used to connect the top of the closed hopper 12
to the deagglomeration chamber 14. A butterfly valve could be provided
at the powder hopper outlet 39 to completely isolate and seal off the
powder supply when not in use. Powder 13 could then be stored in hopper
12 for several weeks, without danger of picking up excessive moisture,
and still be adequately dispensed.
Preparation of the light scatter powder 13 is of a critical importance
to production of a powder "contrail" having maximum visibility for a
given weight of material. It is essential that the pigment powder
particles be dispensed as separate single particles rather than as
agglomerates of two or more particles. The powder treatment produces
the most easily dispersed powder through the use of surface treatments
which minimize interparticle cohesive forces.
Titanium dioxide pigment was selected as the primary light scattering
material because of its highly efficient light scattering ability and
commercially available pigment grades. Titanium dioxide pigment (e.g.,
DuPont R--931) with a median particle size of about 0.3μ has a high
bulk density and is not readily aerosolizable as a submicron cloud
without the consumption of a large amount of deagglomeration energy. In
order to reduce the energy requirement for deagglomeration, the TiO 2
powder is specially treated with a hydrophobic colloidal silica which
coats and separates the individual TiO 2 pigment particles. The
extremely fine particulate nature (0.007μ primary particle size) of
Cobot S--101 Silanox grade, for example, of colloidal silica minimizes
the amount needed to coat and separate the TiO 2 particles, and the
hydrophobic surface minimizes the affinity of the powder for absorbtion
of moisture from the atmosphere. Adsorbed moisture in powders causes
liquid bridges at interparticle contacts and it then becomes necessary
to overcome the adsorbed-liquid surface tension forces as well as the
weaker Van der Waals' forces before the particles can be separated.
The Silanox treated titanium dioxide pigment is further protected from
the deleterious effects of adsorbed moisture by incorporation of silica
gel. The silica gel preferentially adsorbs water vapor that the powder
may be exposed to after drying and before use. The silica gel used is a
powder product, such as Syloid 65 from the W. R Grace and Co., Davison
Chemical Division, and has an average particle size about 4.5μ and a
large capacity for moisture at low humidities.
A typical powder composition used is shown in Table 1. This formulation
was blended intimately with a Patterson-Kelley Co. twin shell dry
LB-model LB--2161 with intensifier. Batches of 1500 g were blended for
15 min. each and packaged in 5-lb cans. The bulk density of the blended
powder is 0.22 g/cc. Since deagglomeration is facilitated by having the
powder bone dry, the powder should be predried before sealing the cans.
In view of long periods (e.g., about 4 months) between powder
preparation and use it is found preferable to spread the powder in a
thin layer in an open container and place in a 400°F over two days
before planned usage. The powder is removed and placed in the hopper
about 2 hours before use.
Table 1 ______________________________________ CONTRAIL POWDER
FORMULATION Ingredient % by Weight
______________________________________ TiO 2 (e.g., DuPont R-931) 85
median particle size 0.3μ Colloidal Silica (e.g., Cabot S-101
Silanox) 10 primary particle size 0.007μ Silica gel (e.g., Syloid
65) 5 average particle size 4.5μ
Other type powder compositions can also be used with the apparatus
described herein. For example, various powder particles which reflect
electromagnetic radiation can be dispensed as a chaff or the like from
the contrail generator.
Obviously many modifications and variations of the present invention
are possible in the light of the above teachings. It is therefore to be
understood that within the scope of the appended claims the invention
may be practiced otherwise than as specifically described.