US2268320A - Formation of thermal air currents - Google Patents

Description

lDec. 30, 19.41. R. l.. BRANDT 2,268,320

FORMATION OF THERMAL AIR GURRENTS Filed May 5, 1938 2 sheets-sheet 1 Dec. 30, 1`941. R. L. BRANDT FORMATION OF THERMAL AIR CURRENTS Filed May 5, 1938 2 SheetsfSheet 2 Patented Dec. 30, 1941 UNITED STATES PATENT OFFICE FORMATION F THERMAL AIR CURRENTS Robert L. Brandt, New York, N. Y.

Application May 5, 1938, Serial No. 206,282

4 Claims.

This invention relates to a method and means for the artificial formation of atmospheric thermal currents. More particularly, this invention is concerned with the production of atmospheric or thermal air currents that are to be utilized in connection with that branch of aeronautics known as soaring or gliding flight.

The art of soaring or gliding ilight wherein a heavier-than-air machine maintains itself in flight without the use of a motor and propeller or other mechanical means depends on the pilots finding up-draughts or vertical currents whose velocity is such that while keeping the air-speed of the sail plane above its stalling speed, the ship actually rises at a velocity equal to or greater than the speed it would naturally descend because of the gravitational forces acting upon it.

There are several kinds of natural currents or up-draughts that are generally found useful for soaring flight. One is a slope current that is created when a horizontally moving air mass or wind strikes the sides of a hill or mountain range and is deilected upward. If the velocity of the wind is great enough, these currents -or updraughts permit a pilot to gain a higher altitude. Another type of up-draught is the thermal air current that is formed by the heating of the earths surfaces by the sun.

One difficult problem in soaring ight hasv been caused by the fact that the pilot must rely solely on mechanical means to get the craft; into the air usually without the aid of up-draughts, such as a slope current. The greater the altitude initially reached by the craft by mechanical means of launching, the better are the possibilities for the pilot finding natural up-draughts to aid him in sustaining his night. By means of an airplane tow, the craft usually is launched at an altitude of from between 1,500 and 2,000 feet. By means of a winch tow, under the best of conditions and with' the best of facilities, the craft will be raised only to an altitude of around 1000 feet.

It is therefore an object of the present inven- I tion to artificially create thermal air currents to be used in connection with launching and with the soaring of the craft, whereby the initial alti-- tude that can be attained will be greatly above that now possible by purely mechanical means and whereby the pilot can regain altitude naturally lost by gravitational eects.

It is an object of this invention to create these Lip-draughts essential to guiding Hight by heating large volumes of air either by solar or artificial means.

It is an object of the present invention to create thermal air currents in the immediate vicinity of the airport so that the craft may be mechanically launched to a relatively low altitude and the pilot may then spiral upward in the thermal air currents until he has attained the desired altitude.

The method of and apparatus for attaining the foregoing objects is described in the following specific description and illustrated in the accompanying drawings wherein:

Fig. 1 is a view of a glider launching field arranged with ground cover according to a preferred form of the invention;

Fig. 2 is a detail view showing the ground cover of Fig. l in section;

Fig. 3 is a detail view showing a modified form of ground cover in section;

Fig. 4 is a detail view showing an alternative modification in section;

Fig. 5 is a sectional view showing the dark colored material located in a pit;

Fig. 6 illustrates schematically an arrangement for heating by steam; and

Fig. 7 shows a schematic arrangement for heating by electricity.

The degree of heating of a substance by insolation depends on many factors, such as the color, mass, the condition of the surface exposed, the specific heat and thermal conductivity of the substance, and the location of the substance on the surface of the earth in relation to other nearby objects. It is a well-known law of physics that surface color plays a very prominent part in the phenomena of radiant heat absorption and emission. 'I'hus, a black body will under the same conditions emit a greater amount of sensible heat than a White body per unit surface.

To set up ideal conditions for the formation of thermal currents in accordance with the invention, it is desirable to have a hot body surrounded by a colder body. Under this circumstance, cool air will continually flow over the hot area, be raised in temperature, expand, decrease in specific gravity, and therefore rise.

Fig. l illustrates one arrangement for producing thermal air currents. A substantially continuous white or light-colored body I3 having concentrically disposed thereon a substantially continuous black or dark-colored body II is placed on the surface l2 of the earth forming a part of the airport or glider launching eld. In order that this black or dark-colored heat-absorptive material resting on the layer of lightcolored material I3 may produce up-draughts that are of substantial assistance to the pilot in raising the craft, a considerable surface of the earth should be covered by the light-colored body I3 and the dark-colored body II should cover a large part of the center area of said light-colored or non-heat absorptive material as shown in Fig, 1. The amount of h'eat energy obtained per unit area exposed to solar radiation depends on the efficiency of the black body. The surface of black body II should be porous in order to aid in a rapid rate of heat transfer between the hot body and the surrounding air. Preferably, the more porous or sponge-like the material of body I I, the more efficiently will thermal currents be produced thereby as will be explained later.

A specific example of one type of material that may be used as a heat absorptive or black body is a composition of petroleum coke (specific heat 2.0) or coal coke intimately bonded with a thick mass of material of high heat capacity and high thermal conductivity. However, any black or dark-colored body may be utilized to produce the thermal currents, but those which possess high heat capacity and conductivity and are of a porous nature are preferable.

The portion of the light-colored or white body I3 surrounding the black body Il serves as a reflecting surface. This reflecting surface is preferably white, because a white surface will absorb radiant energy less than any other colored surface, although any other light color may be used. The area i3, is thus cooler than the A' tends to augment the force and effect of the thermal currents produced to a greater degree than thail effected under similar conditions if only the earths surface I2 surrounded the black heat absorptive surface II. The White or lightcolored body I3 is placed under the black body II as Well as around it to prevent loss of the heat absorbed by the black body from solar sources by absorption by the earth as the case would be if the black body rested directly on the earths surface I2. The light-colored or white body I3 kbeing between the black body II and the earths surface I2 reflects the heat passing through the dark material which would otherwise be absorbed by the earth but for the presence of the light-colored body. However, if conditions or circumstances do not permit, the black or dark-colored absorptive material may rest directly on the earth with the white or lightcolored body surrounding the black body.

The radiant energy transferred to sensible heat by the black body heats the air in contact withthe latter by conduction. On the contrary, the air in contact with the lighter colored surface is not raised to an appreciable extent in temperature because the suns energy is reflected rather than absorbed by the white surface. 'I'he gases composing the atmosphere, with the exception of water vapor and carbon dioxide, absorb but little heat. Thus cold air flows over the white surface, makes contact with the warm black body and is raised in temperature, expands and rises as indicated by the arrows in Fig. 2, to provide a steady vertical draught (thermal) of air.

The white body may be composed of any white or off-white color.v It should preferably be a thermal insulator as well. Practical considerationsV are that the material should be water insoluble so that it will remain in place during wet seasons. For example, water insoluble salts like chalk, crystallized gypsum,v magnesium oxide, etc. may be employed as the white body. Water films also are useful and may be so used, as for example a small island that is covered with a black body, the water surrounding the island being of sufficient depth to effect the necessary temperature difference.

Where conditions are such that it would be impracticable to employ the layer of light-colored material described above, adequate results can be obtained by eliminating the such material and allowing the dark-colored body to rest directly on the earths surface. Being more absorptive than the earth, the black body will emit more sensible heat than the earths surface surrounding it, hence there will be a flow of air from the area above the bare earth across to the area above the dark-colored surface. There said air will be heated to cause the production of rising thermal air currents. Fig. 3 shows this form.

Another improvement is illustrated in Fig. 4. The black body II or dark-colored absorptive surface is supported above the surface I2 of the ground. It is well known that the rate of heat. transfer between a solid and a gas, inthis case the heat sponge II and the air in contact with it, respectively, is among other things a function of the velocity of the gas. In this embodiment, the optimum condition for producing thermal air currents is realized by utilizing a thin layer of porous black material II intimately bonded to a porous mass of material of high heat conductivity such as iron shavings or brass turnings.

The interstices should be large to permit flow of air throughout the mass with lowpressure drop. Instead of the black body or large mass merely contacting a relatively stagnant film of air, its elevated position permits theV free vcirculation of the air through it with the resultant creation of a much more powerful up-draught. In this case also. the efficiency is increased by surrounding the sponge or absorptive body I I by the lightcolored reflecting surface I3 which rests on the earths surface and extends under the black body as shown in Fig. 4.

The black porous body II may also be located in a pit Il with the walls and bottom I5 of the pit Il so arranged that they reflect the radiant solar rays onto the surface of the body II. Such an arrangement will minimize the effect of natural winds and thereby permit a better directional control of the thermal air currents as they are inthe process of artificial formation. The walls and bottom-of the pit are preferably white in color. 'I'he black body in this case is raised above the bottom of the pit wlth'space left bei tween the outer edge of the black body and the walls of the pit so that the air currents may freely circulate around and under the dark-colored or black body. Fig. 5 shows this variation.

The heat absorptive material II or black or dark-colored porous body may be artificially heated and so produce substantially the same results as those effected when the energy derived from the suns rays is utilized to produce rising thermal air currents or up-draughts. The heat absorption material may be artificially heated by means of steam and/or waste flue gases, either directly or indirectly. Direct heating, for example with steam, offers the advantages of i 1) reducing the density of the air because ci the lower molecular weight of water relative to that of air; (2) obtaining better heat exchange; (3) giving greater heat absorption because the water vapor is one of the few gases normally occurring in air that will absorb heat from the sun by direct radiation.

Hence, as shown in Fig. 6, steam pipes I6 may be embedded in a porous or heat retentive sheet I 1 covering the-surface of the earth in the vicinity of the airport. The heat absorptive material I1 is thus heated by the steam in the pipes I., and as the area over this surface I1 is warmer than that over the surface of the earth surrounding it, the thermal air currents are produced on the same principle as that involved in the case of solar heating of the black or disk-colored body I l of high absorptive capacity.

As shown in Fig. 7, absorptive or porous sheet I8 may be heated by any suitable electrical arrangement such as encased resistors I9, and ris ing thermal currents produced from heat effected thereby.

From the foregoing it will be observed that a thermal current may be formed in the immediate vicinity of the airport so that getting into the air at suillcient altitude is no problem. All that is necessary is to be winch or auto-towed to a relatively low altitude into the thermal current. At this point the pilot releases the tow rope and may then spiral upward in the thermal current to gain the required altitude. Ideally the location of the black body would be in a small valley. A wind blowing the heated air against the sides of the surrounding hills would give the effect of both thermal and up-draught and this is of great advantage to the soaring pilot.

I claim:

1. In combination, a field for the launching of gliders, said field having a predetermined area, a layer of porous heat retentive material covering a portion of said field, pipes horizontally incorporated with said material, and means for passing steam through said pipes to heat said heat retentive material and cause rising thermal air currents to be produced.

2. In a glider launching field, means for the artificial production of rising thermal air currents comprising a circular layer of absorptive material covering an area of the earths surface of at least three acres. and means for heating said material.

3. An arrangement for producing rising or vertical thermal air currents that comprises a substantially continuous and circular dark-colored heat-absorptive surface surrounded by and resting on a light-colored surface, said light-colored surface disposed over the surface of the earth and covering an area of at least several acres. the said dark-colored surface absorbing radiant energy from the sun's rays while the lightcolored surface largely reflects said energy. thereby creating a now of the cooler -air over the light-colored surface to the warmer dark-colored surface. where said cooler air is heated, expands, and

then rises. Y

4. An arrangement for producing rising thermal air currents that comprises a circular layer. of dark-colred porous 4heat-absorptive material exposed to the action of the suns rays, surrounded by and resting on a circular layer of light-colored material, said light-colored material being disposed over the surface of the earth and covering an area of the earths surface of at least several acres, the porous material absorbing the heat from the suns rays more efficiently than the light-colored material, whereby a flow of the air is effected over the light-colored material toward the area over the porous material where the air becomes heated, expands, and rises.

ROBERT L. BRANDT.

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