96 SURVEY NAVIGATION, DISCUSSION
vertical error of a maximum of three sexagesi-
mal minutes of arc. The system must be turned
on before take-off for a period of about half an
hour to three-quarters of an hour. During this
period, the system goes through a sequence of
switching operations which ensures that the
proper initial conditions are inserted into each
of the integrations, and that the gyros have the
proper initial orientations. After this period the
system automatically switches into an operating
mode and the aircraft may take off. Thereafter,
the maximum system error is retained.
Two such systems have been completed and
have undergone environmental and simulated
flight testing successfully. Unfortunately, the
actual flight test has not yet occurred, but within
the next few months this is expected to be com-
pleted.
Mr. F. L. CORTEN: lt is a pity that these
flight test are not yet ready. Mr Lófstróm yes-
terday had some results on the horizon camera.
Perhaps he can tell us in a few words what were
the final results.
Herr LôFSTRÔM: Ich möchte nur kurz auf
folgendes aufmerksam machen. Die Neigungs-
variationen der Aufnahmekammer werden, um
grössere Genauigkeit zu erhalten, durch die
Vertikalunterschiede der Horizontlinie und
nicht der Neigung der Horizontlinie bestimmt.
Durch Horizontregistrierung in vier Richtun-
gen hat man eine Überbestimmung. So können
z B die Omega-Variationen der Aufnahmekam-
mer getrennt sowohl aus der linken als aus der
rechten Horizontregistrierung erhalten werden.
Eine unmittelbare Beurteilung der Genauigkeit
der relativen Neigungsvariationen ist also mög-
lich. In diesem Falle war der mittlere Fehler der
relativen Horizontangaben, also der Neigungs-
winkel, plus/minus zwei neue Minuten für die
monokuläre Horizontvermessung und 1,3 Neu-
minuten für die stereoskopische Horizontver-
messung. Der Vergleich zwischen absoluter und
negativer Neigungswertung — die Tabelle bitte —
geht aus der Tabelle hervor. Die absolute Orien-
tierung jedes Modells der Bildreihe wurde auf
Grund terrestrischen Messungen ausgeführt.
Die Öffnungen 1 bis 3 zeigen die Differenzen
von entsprechenden absoluten Neigungen und
den relativen Horizontneigungen. In der Notie-
rung 1, Omega, in Neuminuten, und vier Mi-
nuten zeigt die Differenz an, wenn man bekann-
te Punkte im ersten Modell und in dem letzten
Modell hat. Also im Abstand von 50 Kilome-
tern. Da kann man also jedes Modell mit dieser
Genauigkeit in Minuten übersehen und mit
einem mittleren Fehler von etwa 3 Minuten ho-
rizontieren, auf Grund der Horizontangaben
Danke.
Mr F. L. CoRTEN: May we have a discus-
sion on the general aspects?
Mr B. ATTWELL: I have a very brief com-
ment to make on Mr Corten's paper which is a
remarkably comprehensive catalogue of the
methods and apparatus available to the aircraft
operator. I would say that in planning any sur-
vey operations one must obviously be guided by
the practical and economic considerations, and
that delightful as it would be to equip an air-
craft with all the devices and systems listed in
Mr Corten's paper, this is obviously impossible.
When it comes to the survey of areas devoid of
a clear feature — such as a desert or a thick for-
est — it is obviously an advantage if the naviga-
tional system can be completely contained
within the aircraft. In this respect, a Doppler is
already offering a considerable advantage but
it has, as Mr Corten has pointed out, the defect
of a lower accuracy in azimuth. However, in
distance runs one has a very high accuracy, but
as it is referred to in general as one of the forms
of compass heading indications, the azimuth
direction is poor for normal survey purposes
and unless it is coupled to an inertial naviga-
tion system this is a weakness. I would very
quickly like just to bring to your notice a new
development in radar equipment which may
have some applications in this respect, prima-
rily in flying a block of photography in desert
or thick forest area without the necessity of in-
stalling ground transmitter stations. There is al-
ready available to the commercial aircraft a
very compact form of forward-looking radar
which is used by airlines for cloud and collision
warning, and by depressing the antenna it can
be used as a navigational device for picking up
coastlines or clearly-reflecting detail. The de-
velopment to which I refer is the practical pro-
duction of a Luneberg lens as a reflecting sur-
face and I would quickly like to show you this
model. This is a radar reflector which has these
60? response, and the six inch sphere has a
reflecting area equivalent to four square metres.
The reflecting areas go up with the diameter and
a sphere of ten inches diameter would have a re-
flecting area equivalent to 36 square metres. A
Luneberg lens of this type would produce a very
ready response on the normal type of forward-
looking radar, and suitably ballasted so that it
always erected itself in the right direction it
could be parachuted down — a number of these
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