Te15 26
4RAV
UT AIRORAJW RANGiNG DEVICE
by
SCAlPAlI
WILLIAM SCOKVILIE,
Graduate,
COAST ARTILLERY CORPS, U. S. ARMY
United States, Military Academy
1917
and
LIE
N
JO
E.
OLIBIES, PHILPPI E SCOU
Graiuate, United. State
, U.
AM\
AMR
N~aval Academy
19W5
Submitted in Partial Fualfillment of the, Requirement
for the degree of
in
from the
LSSE'GEliTrES RiZINTM'
OF TECHNOLOGY
1986
Signature of Authors.
OC=i1OCAION BY TIEDE2ABIWMa
OFi1O
tALy 1"a.I1
lING
Professor in Charge of Researcho
Chairman of Departmenta1
Committee on Graduate Stude
+)
+
I .-
......................
8''+ ,+-a
.,
.+. ..
. '.,
TABILE OF COEMMeTS
Page
liroQduction.............................•.......
Acanewledgment ..............
o.* ....
Sttemsent of the Problem .........
I
.....
I
...
2
................
3
Requrements of the Ideal Instrument.........
II Possible
.
3
eMeas of Detection and Location........
4
By Sound
Waves
......
**...............*.
By Radio Wveso... .....
O.....00
-
a....
By Li&ht Waves*............•.............
By Heat 1vess.*..*4..***
...
6
7
*...*..........
7
III Instruments for Detecting Heat Wvea........ ... lb
The Radimeter...-.
......
...... . ....
The iRadiomicrometer ................
,
The Bolometer
10
l................
10
The Thermopile...... .....................
11
The Photo-electric Cell..................
12
IV .The Problem
V
... ,,...
O
f Rage...........
.......
13
Products of Combustion of Exhaust Gas ...
1Z
The
14
irror...................
Bibliography...................................
16
INTRODUCT ION
The subfect of locating: aireraft at night by means
of the heat radiation of the exhaust was suggested to us by
Professors V. Bush and J. W. Barker.
Realizing that one of
the greatest problems of the Coast Artillery Corps at the
present time is the location of aircraft at night,
and believ-
ing that the present method based on sound does not fully
ftulfill the requirements ot a good aircraft, detector, we at
once saw possibilities in the idea which warranted, its being
tried out.
&-1-
In this work. not enough thanks can be given to Profoesor J.
W.. Barker whose constructive suggstions and untir-
ing effbrts in our behalf were a great factor in making it
poasible to carry on the work in the face of mayr ~-iMtt
lties.
Due thanks should also be given to Dr. G. L. Clark,
Professor A.
C. Hardy, Mr. F. V. Cunningham, Professor G. W.
Pierce, Mr. T. i.
Case, Dr. V. WV Coblentz and Professor H. B.
Phillips whose timely suggestions were of great aid.
Ve take. this occasion, to e~press our appreiation
to the Electrical Engineering Department of the Massachnsetts
Institute of ~acEbnology, The Mar Department, The, Bell Telewphone Laboratories and The General Electric Company for the
equipment which they were good enough to place in
i[-2
;I
our hands.
TER PROBIll
?bhe problem is to devise a means by which a plane
may be detected and its position located at night.
I
BEQUIREMENTS Or AN
UMIZUlT
AICRBMA
UR DETECTIMG AND LO=APING
-AMI XIG
In any definite problem there is always an ideal
which we should strive to attain. Human nature however, is
so inadequate that this ideal can not always be reached,
consequently, the solution that can best appioach
the
optimm mst of necessity be the end to strive for. To our
mind the ideal instrment for locating aircraft at night
must fulfill the following requirements:
It must be instantaneous in action, that is, the
disturbance caused by the plane which actuates the detecting instrument should not take any appreciable length of
time to travel from the plane to the detector. The signal
produced by the detecting instrument should activate the
detecting tense to a maximm degree. The instrument must be
accurate in-its location of the plane position and capable
of following it.
-1i-
iC
;.2~x
The range at which it is able to detect
.
must be a maximum. It
should be sensitiver to the disturbance
crested by the plane only and insems4tve to all outside &isaturbiMagentsf. The instrument
meist be able to distinguish
times so that there may be
between planes of a group at all
a means by which the Battery Commander can "check" on the
plane being tracked. It should elimilmate the use of the,
seachlight so as to gain the advantage of surprise on the
enemye Finally, it mnst be portable and of rugged construction
in order to withstand service conditions, and mest have a
minimum of adjustments so that it
may be operated by the
average enlisted man.
II
POSSIBIE MEHODS BY WHICH A PIAEL
ALY BE LOCA~D AV, NIfIG
Assuming that we have a plane in the air at night,
the question is,
what means have we available for locating
its-position? First there is
the disturbance in
the air
cteated by the propeller and the detonations of the exhaust
which produce sound waves which may be used as a means for
detection.
Then there is
the electric disturbance in the
ether created by the ignition system of the engine which
causes electric waves to be propagated through spaceand thus
become an agent for detection.
Also,
there is
the power
dissipated throtgh the exhaust in the form of"light or visible
rays and infsrared or heat rsqv These rays may also be used
asE a mUans for detecttig the-pxaeeaee of the plane.
Sound waves as a means for detecting airplanes at
night is the basis of the method now in use.
tage of great volume,
truction.
It has the advan-
and simplicity and ruggedness of consg-
Against these however, may be urged the following
disadvantages:
Sound travels at the rate of 1100 feet per
second, consequently,
it
takes an appreciable time to reach
the receiving apparatus so that the wave front actually received startedC at a point wh t i h is
a
- considerable distance from
the present position of the plane. This is
Iutrthermore,
called time lag ,
the velocity of the wind affects the speed of
both the sound waves and the plane causing a fUrther deviation in the located position. This is
called wind lag. These
deviations which are not susceptible of accurate prediction
and correction make it
impossible to accurately locate the
plane. Moreover, dne to the fact that there is
no means of
knowing that two receiving apparatus are on the same plane
of a group, firing data can be obtained only through the use
of searchlights. This is
a decided disadvantage as it
to the enemy our own position.
reveals
It is a well known fact that the ignition system of
a gas engine acts as a spark gap transmitter producing radio
waves which are propagated through space by the leads from the
distributot to the spark plugs acting as antenna. The action
is as follows: The condenser across the breaker points in conjunction with the breaker points and the primary of the induction coil produce radio frequency oscillations in the primary
circuit. This action induces radio frequency oscillations in
the secondary coil which is in series with the spark gap and
the leads to the spark plug. In effect, we have a radio transmitting set which radiates energy through space as explained
above. Dr. G. L. Pickard states that during his experiments
on the polarization of short radio waves, he experienced
ference from passing airplanes.
inter-
He estimated that the signals
from an airplane engine could be received at a maximum distance
of one mile. By using the directional properties of coil antennas it
however,
is possible to obtain the azimuth of the plane,
since its
unidirectional property depends on the
symmetry of the coil capacity to ground, the location of the
.plane in elevation would be difficult of attainment. This
method has the advantages of (1)
the speed of the radio wave
which would eliminate time and wind lag, (2) ease of detection
under unfavorable weather conditions and (3) comparative
S-8-
simplicity and ruggedness of constraction. The disavantages
are, the interference from other radio signals due to the
fact that the wave lengths emitted are in the banlincluded
n
between twenty and forty meters- a d its
inability to locate
Farthexmore, the greatest disa&vantage
the plane accurately.
is the facility of shielding the leads so that the energy
- be such as to limit the range to a minimum
emitted would
which would be eatirely inadequate as a means for defense.
Vision used as a means for detecting adrla ea
is the method par excellance.
If it were possible to use the
method of vision at night., the problem would literally
itself.'
There is
a possibility of using this ifetho
solve
as the
exhaust actually emits a flame visible at night which is
due
to the presence of incandescent carbon particles therein.
The range at which the flame is
using a telescope it
visible is
may be increased.
limited, but by
However, this stream
of flame, being limited in length, may easily be obscrired
from viewr by shielding.
The beat waves emitted from the ezhbust of the
p;'ane would be a convenient means of detecting and locating
its
position if
.ensitiave
a sufficiently
device were available
for this purpose. These heat waves have the speed of light;
hence time lag, which is so objectionable in the present
method based on. sound, would be eliminated. The wave- being
electro-magnetic,
it
isen6Vtdeflected by the wind, consequent-_
ly, there is no wind lag. The above being true, the plane may
be accurately- located and by employing twoe. detecting instrwments aefither
end of a base line, f"ring data may be obtain-
ed without the use of searchlights. Moreover, by the use-of
selective detectors which make use, of the periodicity of
impilse of the exhaust, a means is
available to ascerta
i
Swhether or not the two instruments are on the same plane.
One disadvantage of this methad' lies in
is
the fact tht
there
a certain amount. orfabsorption of the heat energy in the
atmosphere which would tend to reduce the range
Alsoe, the
exhaust may be shielded to acertain degree, but this shield"
ing is
limited by the loss of officiency of the engine. CoQn-
sidering- the, fact that the defense is
primarily against bomb-
ing planes with heavy loads, the engine efficiency can not
be greatly reduced without materially limiting their offensive
value.
Of the four methods described above,
those by vision
and radio waves may at once be eliminated as proper shielding
'would reduce the range obtainable to such a degree that the
defensive value would be negligible. The problem therefore
reduces itself
to a choice between sound and heat waves as a
-8.-
means of detection. From a consideration of the previous dis-
cussion of these two methods, the follwoAng points may be
evolved:
Sound will locate the approximate position of the
plane only while the heat method would give an accurate
location. Moreover, the heat method has the advantage of
selectivity mentioned above, whereas sound does net. Under
these considerations it would be possible, using the heat
Smethod to make an accurate track of the plane- and obtain
ifiring data without the use of searchlights,
thus gaining
the advantage of surprise on the enemy. A comparison of the
maximum ranges of the two methods, which is of primary importance,
can not. at present be made. However, granting that
sound would give the greater range, the combination of the
two methods would still allow the searchlight to be eliminated as the heat method would take i~
ass iged mission of
tracking the plane. For the above reasons and the fact that
the sound method has not been a complete success, the method
using the heat radiation from the exhaust has been selected
for the-solution of this problem.
-9
!
Lh
t
-
III
INSMMlENMS WHICH MAY BE USED FOR DETECING EAT 1LVES
Heat energy, being invisible, requires the use of
instruments which transform this invisible radiation into
some other form of energy, the effects of which can then be
detected. Various instruments of this kind have been devised,
most important of which are the radiometer, radiomicrometer,
bolometer,
thermopile and photo6-electric cells.
The radiometer which is extensively used in infra-
red investigations, is
a very sensitive instrument, but due
to its suseeptibility t/ the slightest vibration, it is neo.
cessary to isolate it
f=rm all possible mechanical vibrations
during the progress of an investigation. This makes it
licate an instrument that its
useif
so de-
restiibted toPtbhe labora4
tory.
The raiomicrometer whih is in effect a moving coil
galvanometer is aS sensitive as the radiometer,
same disa4dvantage in that it
i
but it has the
too delicate an instrument to
be used under service conditions.
The bolometer is a more rugged instrument than the
two previously mentioned, but it requires a very elaborate
installation and is difficult to keep in adjustment. It is
not thearefore an entirely satisfactory instrument for field
-10-
use.
The the
thermoile is
for detecting heat waves.
the saimplest type of instrument
It
zQdte rugged and may b-e made
is
as se sitive as any of the aeabve instrumentsi
It has already
been employed for the detection of heat energy from the exi
haust of an airplane. In 1919,~~ael 0. Hof man used a croasehair thermopile the separate elements of which (vertical and
horizontal) were separate piles of thirty-two couplea each,
electrically insulated from each other and connected to
separate galvanometers.
The thermopiles were placed at the
focus of a twenty-four inch mirror provided with slow screw
movements in azinth'and elevation. With the plane developing
fifty horsepower at a range of two thousand yards, an average
galvanometer deflection of ten centimeters was otained. No
difficulty was experienced in
picking up" and tracking the
plane. However the slighteat whiff of cloud drifting across
the field produced deflections in the galvanometer of the
same order as those of the plane, but without the abrupt
jUmp
which chracterized the start of the deflection produced
by the plane. The- amount- of deflection seemed to depend. more
on the angle of presentation of the exhaust rather than on
the range.
The disadvantage of using delicate instrumenta- such
-11-
as galvanometers when a thermopile is used may be overcome
if
a tride valve and telephone were substituted for the
galvanometer. By placing an interruptor in
series with the
thermopile and primary of a step-up transformer,
the palsa-
ing voltage induced in the secondary may be impressed on the
grid of the, first tube of an amplifier , thus making it
posaib-
ble to detect the thermopile current by means of a telephone.
This arrangement would give the further advantage of greater
sensitivity. The chief disadvantage of the thermopiie, how-.
ever, is its non-selectivity as it does not distinguish
between the heat radiation from the exhaust of a plane and
any other source in so far as concerns detection. If a ther&'
mopile could be constructed such that it would be sensitive
to, a definite band of wave lengths only, this disadvantage
would be minimized and the method would be of extreme value.
It is an open question, however, Whether or not such a thermopile could be constructed.
The extreme selectivity of photo-electric cells
g-ive them a decided advantage over any other type of instruw
met that may be used for detecting the heat radiation from
the exhaust of an airplane. If the cell used has a maximum
sensitivity in the region where the energy distribution curve
of the exhaust gases is
,-l
a maximum, W
,-
IIX
would have-an apparatus
that would be very sensitive to the heat radiation from the
plane.
In addition, any other source emitting rdiatio
of
wave lengths greater or less than those emanating from the
exhaunt would not be detected by the cell. Moreover,, since
the heat is&taiated in periodic trains corresponding in
frequency to the periodicity of impulse of the exhaust,
the cell could recover its
if
resistance between these periodic
trains, the output of the cell would have the same frequency
as the number of impulses of the exhaust and the advantage,
previouly mentioned,
of having a means to ascertain whether
or not two instruments are on the same plane,
would be gained.
IV
TM PRBsI=
OP RAEGB
The products of combustion in the exhaust of an
airplane consists of water vapor, carbon dioxide,
carbon
monoxide and ineandescent carbon particles. lkter vapor, carbon dioxide and carbon monoxide produce radiations which are
readily absorbed by the -atmosphere. This abnormal dissipation
reduces the range obtainable from their radiations to a minimm. The incandescenat
carbon particles produce most of the
visible flame emitted from the exhaust and at the same time
'are
sources of black body radiation. The emission spectrum
tl
-
of this radiation which is a maximum at about 1.28.to l.- U
(U m 10-4cm.),
is supposed to be smooth and continpous, hence
it is not so readily absorbed as in the case of the gases.
We ,mat
therefore depend upon this black body radiation in
order to obtain maximum range, for detection.
Due to the dissipation of energy in black body
radiation which is believed to be inversely as the square
of the distance, the range obtainable is limited. By employing a collecting apparatus for concentrating the rays, such
as arparabolic mirror, this limited range may be increased
considerably. The collected rays or amount of energy received would then vary as the area.or, in
other words,
directly
as the square of the diameter of the mirror. The choice of
dimensions of the mirror is governed by the sensitivity of
the detecting instrument placed at its focus and also the
mission assigned. After the ultimate sensitivity of the
detector has been attained,, the only means of increasing the
range is by increasing the size of the mirror. On the other
hand, its portability must be taken into account. If
it is
to be used for fixed defense, the mirror may be made as
large as desired consistent with ease of operation, but if
it is for field use, its portability must necessarily limit
its size. The material of the mirror must also be considered.
- 14-
The surface mat have a minimum of absorption for the wave
lengths. of the rays to be reflected. Measurements of the
reflectivity to infra-red r diation by various metals have
aided
the choice of suitable materials to be employed. Highly
polished metallic mirrors give good reflection for wave
lengths in the neighborhood of 1.
electr -deposited
U. Platinum or silver
on a glass surface, on account of their
high resistance to the corrosive action of the atmosphere
and their high reflective: power,
-^
are also suitable for this
purpose.
NOTE:
The remainder of this thesas, being of a confidential
nature, is not included ii this:paper. It is, on file7 at the
Department in Wshington, D.
C.
-15-
r
B-IBLIOGAPHY
"Cantor Lectures--Instruments for Measuring
Jour. Soc. Arts Vol. 37,
Radiant Heat"
Boys, C. V.
1889 p816
Case, T.
"Notes on the Changos-of Resistance of Certain
bhys. Re~a. 1917.
Substances in Ligit"
.
Case, T:. We
Coblentz,
"Thalof ide, a LNew Photo-electric Substance"
Phys. Rev. 1920.
W. 7.
"Instrument
B.
I
B.
II
Ii B.
s and Methods Used in.,Radiometrey
of S. Bul. Vol. 4, 1907 pZ91
of S. Bul. Vol. 9, 1912 p7
Of S.- Bul. Vol14,, 1917 p507
Coblentz, W. W.
" he Reflecting Powers of Various BEtals"
B. of S. Bul Vol. 7, 1911 p197
Coblentz, V. V.
"A Vaacuum Radiomicrometer"
Vol. 2, 1906
B. of S. Bul.
Coblentz, W. W.
o. n.
Coblentz,
Coblentz, T. T.
p4r79
!Radiometric Invest igat ions of Infrarred Absorptia
and Reflection Spectra# B. of S. Bul. 2, 1906,
"Selective Radiation From Various Substances"
B. of S. Sci. Paper # I61, 1909.
II
III B. of S. Sci. Paper #156, 1910.
"A aomparison of Stellar Radiometers and Radio~metric Measurements of 110 Stars"
B. of S. Bul. Vol. 11, 1915 p615
Coblentz, W. W.
.
~
Cohlentz, Y.
Coblentz, W. V.
"The Spectrophotoelectric Sensitivity of Thalofide*
B. of S. Sci. Paper # 360, 1980.
"Spectral Energy Distribution in Acetylene Flame"
B. of S. Sci. Paper # 279, 1916.
"A Portable Vacuum Thermopile"
B. of S. Sci. Paper # 415, 1921.
"Invisible Signaling"
B. of S. Misc. Pub. # 46, 1921
Hoffman,
S.
0.
pl30
" Detection of Invisible Objecta by Heat Radiation"
Phys. Rev.
-16-
Vol. 14 (2),
1919 pl6Z
-Hoffamn, S. 0.
"Ranging dn Aircraft by Thermal Radiation*
Phys. Rev. Vol. 14 (2), 1919 p 165
Houston, R. A.
*A Treatise on Light"
Book Chap. XVII p2 9 5-305
Nichols, RE F.
"Radiometer Described"
Ann. Phys.
Vol. 60, 1897
Preston, T.
"Theory of Heat" Book Chap.
Randall, H. M.
"Infra-red Spectra"
Am. Phil. Soc. Proc.
Taylor, H. S.
Weber, H. F.
p40'-417
IV
Vol.
"Physical Chemistryf
Book Vol. II
Chap. XI
62,
1923
p326
pl2 5Z
"The Radiomicrometer"
Archiv. Sci. Phys. et Nat.
-17-
p569
Vol.
18,
1887