Friedensburg, Walter

Miner, D M

English

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NATIONAL jDV3RY COITTEE FOR ARONSVTICS. 
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	 (2?-D. 21. 
DISTANT - COMPASS.
By
Walter Friedensburg. 
Translated from 
t'Zeitschrift fIr Flugtechnik und Motorluftschiffahrt, 
Vol. 11, No.15.
4 
1
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https://ntrs.nasa.gov/search.jsp?R=19930080746 2020-03-17T04:52:27+00:00Z
DISTANT QOMPASS.
By
Walter Friederisburg. 
For a long time, small fluid compasses were almost exclus-
ively used on aircraft. Suth a compass. consists essentially of 
a number of comparatively weak magnets which, supported by a hol-
low float, turn on a needle point in a vessel f.illed with alco-
hol and water. This would answer for ordinary use, if there were 
on the aircraft no iron parts and no other magnets, like starters, 
magnetos, dynamos, etc. 
The compensation of these disturbances by small magnets is 
only a makehift and by no means frees the .compass, readings from 
error. The many neighboring movable iron parts, like steering 
devices, weapons, tools, bombs, etc., even key-rings, knives and 
the like in the pockets of the occupants, exert, according to 
their size and proximity, a varying influence on the compass 
readings which, on the aircraft, are 2iardly controllable and can 
not be corrected, any more than the constantly varying influ-
ence of the above mentioned magnets. 
Every deviation of the aircraft from the.horizontal posi-
tion, in either a lateral or longitudinal direction, likewise 
exerts an influence on the compass readings. Thus there are gen-
erated, especially by sudden changes of position in curved flight, 
oscillations of the card which may even increase to the complete 
* From "Zeitschrift fiar Vlugtechnik und.Motorluftschiffabrt," 
August 15, 1920.
I
revolutions dreaded  by every aviator. 
The oscillations of the compass card, due to those magneti' 
and mechanical influences, are indeed deadened by the compass 
liQuid, but this friction is operative not only in the indicated 
instances, when the card, with the magnets, oscillates with ref-
- - erence to the comtass vessel, but also when the system is at 
rest and only the vessel turns, as in every curving flight. In 
the latter case, the card is also carried along and indeed just 
so much more the weaker the magnet system arid, accordin gly, its 
directive power. On the other hand, the greater the di'reotive 
power of a magnet system, the greater are its errors of deflec-
tion from neighboring masses of iron. These errors call for 
stronger compensation magnets which, the stronger they are, the 
more they weaken the directive power of the syem. Out of this 
endless circle there was yet on an aircraft only the unsatisfac-
tory compromise. The employment of a reliable magnetic compass, 
free from objections, was impossible and one was compelled to 
make the best of inaccurate and unsatisfactory compasses. 
An improvement of the properties of the air-plane compass to 
real serviceableness in aerial navigation is only possible then, 
when the disturbing causes are eliminated. The Navy prescribes 
for every compass on shipboard a minimum distance within which 
there must be no iron. This is impossible on an airplane, since 
there is no such amount of room free from iron within view of the 
pilot or observer. . It is difficult to install a compass-, on an 
airplane at all, on account of the limited space.
On the other hand, the remedy by placing the compasses in 
magnetically somewhat more favorable position, for instance, on 
the upper or lower supporting deck, presents many other disad-
vantages: inconvenient reading of the compass, difficilt and in-
accurate steering by such a distant instrument, compulsory ces-
sat ion of the ,possibility of taking bearings, as also the impos-
sibility of using adjustable indicators and other accessories, 
mistake sin reading in oblique and side views, insufficient pro-
tection of cnpasa against cold, and wet, as also against, the 
force of the air current which, in auth a location, often tilts 
the oornpasa or even upsets it. Moreover, only small compasses 
with weak magnets can be used, since a higher directive power 
cannot be employed, for reasons already giv1, and the still un-
avoidable prox. imity of iron and because the limited, space pre-
vents the installation of larger compasses. 
Against the use 'of the ordinary compass on an airplane there 
are various further practical considerations. Steering by a ref-
erence mark and the general use and complete utilization of such 
a compasm req.Ures too much experience on the part of the pilot, 
especially of one with little or no knowledge of navigation, 
while even an experienoedi and educated pilot finds it too stren-
uous to watch the card, with its finely diidd.i scale, arid, at 
the same time, attend to the numerous details of managing the 
airplane, observing, fighting and keeping constant watch of the 
ever increasing number of instruments. The increasing demands 
on the pilot emphasize the need of direct communication between 
-4.-
him and his observer, in order to do away with time-robbing at-
tempts at Epeech, signals and makeshifts. 
For solving all these problems, there is now a new device?. 
the "distant-compass" constructed by Carl Bamberg, Friedenau, 
and improved in 1918 by the Seaplane Division and practical ly 
tested in comprehensive experiments and use at the front. 
Since this compass dLoesnot need to be in sight of the aviators 
and can be located far from all iron parts, it can be aspcwer-.. 
ful as those used on ships. This compass is free from error 
down to the fraction of a degree and at lea a,sreliable as those 
on large ships. The most favorable location on the ordinary 
type of airplane is from one to one and a half meters behind the 
rear seat in the fuselage, where the compass, enclosed in a 
wooden case (see Fig. 1 at end of article), is protected from 
the wind and weather. The magnet system is the Caine as demon-
strated-its stability in-the submarines. Its use on airplanes 
has greatly increased the accuracy of steering in oomparison with 
the compasses formerly used, and., even vhile flying in clouds 
and bad weather, there were no harmful oscilla.tt one nor revolu-
tions. Not much compensation is u1y necessary, since in ev-
ery type of machine it is posai'ble to find a location entirely 
free from magnetic disturbances. The improvement thus obtained. 
consista first in eliminating the cDmpensation, which always. re-
Quires an expert, and further, in the fact that the directive 
power of the compass is not weakened by compensation magnets.
-5-
 The magnet system of this conass is supported in the usual 
manner in a compass-vessel filled with alcohol and water. In the 
bottom of the vessel there are two lighting devioes . (eaoh con-
sisting of a small electric bulb and "condenser"), which throw 
two conea of light, sharply defined by the condensers, up through 
the compassliquid (Fig. 2). Both light-cones fall on two-selen-
ium, cells (Fig. 3) which are applied in an air- and water-tight 
cap to the vessel (Fig. 4). The electric resistance of the se-
lenium is lessene& by the illumination, so thst, for instance, 
an electric current pas.ng through it can cause the pointer of 
an indicator. to move. For the distant-compasa, a special pre-
cision galvanometer with suitable scale serves as course-indicator 
(Kurszeiger), with radiurnized. marks and pointer (Fig. 5). 
The magnet system carries a. diaphragm which, in a certain 
position, simultaneously intercepts both light-cones and leaves; 
both selenium cells dark. If now the compass vessel (Kompass-
kessel) is rotated about its vertical axis, whereby the magnet 
system remains constantly in the north-south ciiret ion, one or 
the other cell passes out of the diaphragm shadow into one of the 
light-cones and the pointer moves to one side or the others. In 
this way, every swing of the compasvessel can be 'reak on the 
course-indicator and, indeed, so that the amplitude of the os-
cillation of the pointer is proportional to the deviation from 
the course. This result is obtained by givingthe proper oblique 
shape to the diaphragm, so as\to cause a gradual strengthening 
- 
or weakening of the illumination and therewith a proportional de-
crease or increase of electrical resistance' in the selenium cells. ce ls.
This method of transmitting the compass indications differs from 
most otherknown methods in that it is aoomplished without in-
uluenoing the compass card or weakening its directive power, 
Any seaplane or airplane provided with this device, can be 
steered exactly in the desired direction, since every deviation 
from this direction causes a rotation of the compass vessel 
with reference to the magnet system, which is immediately indi-
cated. The pilot only needs to turn the rudder right or left 
according to whether the pointer moves to the left or right.. 
This device has two fundamental advantages over the ordinary.com-
pass. First, the pointer moves a relatively longer distance- 
than the card of an ordinary compass, a deviation of 150 from 
the course causing a motion of about 5 cm. in the former case to 
only 1 cm. in the latter case, making the accuracy of the reading 
about five times as 'great for the former. Second,' this compass, 
like all the other instruments on the airplane, is read on a 
fixed scale by means of a mobile pointe.r and thus spares the avi-
ator the special thought required, on all other instruments for 
reading the mobile card scale with reference to a fixed'. steering 
mark.
If the compass vessel is rotated a certain an..e, say 650, 
with reference to the longitudinal axis of the airplane, then 
the new course, if flown according to the course-indicator, will 
evidently deviate 650 from the original direction, since one of
-7-
the selenium cells receives the light and thereby brings the 
course-indicator to one side ., until, by the turning of the air- 
plane itself 65°, it comes again into the shade of the diaphragm. 
At any time during flight, any desired new course can be estab-
lished by turning the compass vessel the desired angle with ref-
erence to the longitudinal axis of the airplane. The compass 
vessel had for this purpose a suspension device which can be 
readily rotated by means of a worn gear (Fig. 4). 
For this purpose, the compass isplaced in the rear part of 
the fuselage or other iron-free. location. The turning of the 
compass vessel, and with it the establith inent of the course, is 
then effected..by means of a flexible shaft (Fig. 7) which is 
within reach of the aviators and is turned by a crank. By this 
shaft a compass card near the crank is simultaneously turned 
exactly the same angle as the compass vessel, so that on this 
course-giver (Kuregeber) (Fig. 8) the angle and thus the compass 
course can be read. Naturally, in such a system with 8- flexible 
shaft, several course-givers and course-indicators can be in-
stalled, for the pilot and observer and any other persons in any 
part of the airplane, who are thus enabledL to observe and assist 
in the navigating. 
• The heat generated by the electric lamps prevents the freez-
ing of the compass liquid, even in very cold weather. The mini-
mum current required for the compasa installation is about 10 
watts, This current can be obtained by connecting the system 
with a source of electric current already on the airplane, but
is usually supplied by a small airscrew double generator of es-
pecial reliability (Fig. 9), specially constructed for this pur--
pose, with an output of 40 volts, 6 milliamperes for the indi-
cator circuit, which f1cs through the selenium cells, and 8 
volts, 2 amperes for the electric lenips, and weighs only 18 kg. 
(4 lbs.). The tension of the generator is kept ccrLtarit between 
3700 and 7500 r.p.m. by an automatic regulator according to the 
Sumner principle. The beat location for the generator is in the 
air current from the propeller. The number of r.p.m. reQuired.. 
for the work of the compass system wa6 found in a test to be 
about half the r,p.m, of the engine. 
The weight of a complete distant-compass set, with two 
course-givers., course-indicators, generators, cables, shaft, etc., 
was about 9 kg. (20 lbs.) 
•	 Practical Application of the Distant-Compass. 
The course to be steered. (for example, 130 0 ) is set by the 
pilot or observer, --while the crank of one of the course-givers 
is turned so that this degree number of the compass card comea 
opposite the steering mark of the course-giver. Thereby the 
whole system is adjusted.. to the 1300 course and the pointer of 
the course-indicator oscillates until the airplane is brought 
exactly on this course. If, for instance, the previous course 
was 450 N.E., then, after setting it at 130 0 , the pointer lies 
hard to the left. The pilot then turns the rudder continuously 
to the right, in order to bring the pointer to the middle. When 
the airplane, in turning to the right, reaches course 100, then
-9-
the pointer, with the further turning of the airplane, 	 inning tc 
move slowly, lies at 1300 , it stands on the.middle point. If the 
a.irplane turns too far, say to 135 0, then the course-indicator 
moves correspondingly to the right until, by steering to the left, 
the airplane is brought back to the course and the pointer: to its 
middle position. Further holding to the course is accomplished 
in the same manner, since, on the slightest deviation of the air-
plane from itscourse, the pointer moves to the corresponding 
side and indee&proportiotially to the deviation, so that the avi-
ator is always givah the measure for the degree of correction in 
steering. Up to 300 on either side, the motion of the pointer 
is proportional to the deviation from the course. Above 30 0 the 
pointer remains in the same position, This angle of 300 has been 
found suitable in praQtice for an ordinary airplane, but it can 
be varied at will, according to the size and corresponding sen-
sitiveness of the airplane (or airship), by resistance, from 50 
to 4)0  
Every change of course during flight is accomplished in the 
manner indicated by setting one of the course-givers for the new 
course and steering according to the course-indicators, without 
the necesaity of any communication between the occupants by signs, 
notes, etc. Also the observer or any other occupant can, with-
out any closer understanding, call the attention of the pilot to 
an object that the latter has not noticed, or accurately mdi-
cate..a target, since the pilot hasnly to steer according to the 
pointer, the accuracy of which makes it possible to steer for the 
smallesb goal.
- iO -	 I 
If it should happen, in curved flight or great changes of 
the course, that the course set on the course-indicator should 
be exactly opposite to that followed by the airplane at the time 
(for example, set on the course-giver: East 900, airplane flying 
west = 2700 ), the course-indicator in this special case, when 
the difference is just 1800, stands in its middle position, 
whi ch results from the two selenium cells being located, at 1800 
apart. This position, however, hides no possibility of error, 
because it is immediately evident that (likewise following from 
the construction) the course-indicator swings in the opposite 
direction than when the airplane is flying on the course set. 
If the airplane, as assumed in the example, is flying west and 
turns only one degree to the right of this course, the pointer 
swings to the left and the pilot must therefore steer to the 
right. Thereby he continually goes further to the. right from 
his false west course, for the pointer remains on the left un-
til the airplane is again on the east course t r which the 
course-giver is set. Only then is the pointer again in its cor-
rect middle position. The second and opposite middle position 
of the course-indicator mae'it possible therefore for an air-
plane that haa deviated by a large angle, (around 1800) from 
its correct course, to be always shown the smaller angle and 
therefore the shorter way back to its correct course. Every 
aviator must therefore become accustomed to following the course-
indicator blindly, then, whether in clouds or fog, even in bat-
tie, after completely losing his bearings, he will immediately
'U 
return to his-	 "ect course, without danger of the ompasa 
whirling, even from the most violent motions of the airplane. 
The sensitiveness. of the pointer, whid indicates devia-
tions of fractions of a degree from the direct course, enables 
the aviator to fly straight ahead and horizontally in clouds 
and at night. Only this condition enables the use of airplanes 
for photogrammetria surveying which requires the holding of a 
straight line and further. imparts genuine accuracy to observa-
tions from an airplane and from the earth, which uncoridition-
ally- require straight lines, like speed measurements, etc.. 
True, there already exists, in the Drexler Gyroscope Indicator 
(Icreiselssueranzeiger) a highly sensitive instrument for facil-
itating direct flight, but its value-is confined exclusively-to 
the aerornamic field, since it only shows whether, for the time 
being, the airplane is flying straight ahead or in a curve, and 
does not enable the holding of a single definite course, like 
the distant-compass course-indicator. 
Furthermore, the distant-compass not only makes possible 
the general control of one's bearings, but also the accurate de-
termination of compass directions and variations, even without 
seeing the compass itself, because the card of the course-giver, 
as long athe airplane continues on the course set for it, al-
ways corresponds to the true magnetic compass card, since the 
oourse-givers are always mounted parallel to the longitudinal 
axis of the airplane. A variation device attached to a course-
giver is more convenient and utilizable for compass variations 
than when attached to the sensitive and mobile compass itself.
- 12 - 
The advantages. and possible applications of the distant-
conpass are 60 numerous that it has become one of the most im-
portant- instruments for aircraft. This was alsD demonstrated 
by its adoption in 1918 for all former naval seaplanes, with the 
exception of combat  airplanes, as well asfor certain types of 
army airplanes. This device is a very important aid for oommer-
cial, as well as military aviation. By its advantages it in-
drea.ses both the safety and economy of avIation. The accuracy 
of course-steering, which the distant-compass has made many times 
greater than that hitherto attainable, lessens fuel consumption, 
facilitates unconditional reaching of one's goal even under-the 
most trying circumstances, and diminishes the intellectual and 
nervous tension of the pilot, which is of especial irnportance 
in long distance commercial aviation. 
It is not the purpose of this article to disousa the appli-
cation of this invention to sea ships. The parallels ara readi1y 
drawn. Even the farthest evolution posaibilities open up favor-
able vistas. Thue, on a ship, there habeen successfully sub-
stituted fcr the indicating instrument a relay enabling thecom-
pass to operate the rudder directly. Such a device, which has 
already been uinishe& and tested, demonstrate the possibility of 
dispensing with the pilot and replacing him by an automatia, and 
considerably more accurate steering-compass. The lateral steer-
ing of an unriiaxined airplane rests on the same principle. 
Translation from the German by D. M. Miner.

Figs 
Fig. 8


Distant-compass

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