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Manual

Compass 46--MFK--1

BOHLI MAGNETTECHNIK AG

Edition 01.2007

Page 13 of 16

By this comparatively simple levelling procedure (which must be done accurately, however)
the compass has been adjusted for zero bank and for a pitch angle of the fuselage correspon-
ding to a flying speed of 100 to 110 km/h (62 to 70 mph). By the same procedure all stray ma-
gnetic fields within the glider have been compensated. A check may be done by taking other
compass readings on different headings, e.g. from 30

to 30

. In most cases there will be no

noticeable deviation. A special deviation or correction table is consequently superfluous. In
an exceptional case only, when strong and uneven magnetic fields are influencing the com-
pass, such a table may become necessary.

Due to the compensated stray magnetic fields the compass is not necessarily aligned with
the vertical or cross axis of the plane. The mirror must now be adjusted, so that the N--S axis
of the scale appears vertical on the image, and the E--W axis horizontal. Thus, when circling,
the image of the E--W axis may always be set parallel to the horizon. The bank angle scale
shall be visible along the top edge of the mirror, but it need not regularly be observed in flight.
If the compensation area is aligned with the geographic (true) North, the local variation must
be added or subtracted (if the red mark would be adjusted to the true North, the error when
facing South would be twice the local variation).

If no calibration area is available, the compass may be levelled and compensated by lifting
the tail to the proper height and, with the wings held level, rotating the whole plane around
360

several times in a row. By adjusting the upper center screw (ZS) and turning the knob,

the compass is adjusted until the red mark describes a circle around the center point of the
dial (and concentrical to the circles marked thereon). Obviously, this must be done way out
on a field, away from constructions, steel, cars, etc. The compass can then be checked in
flight by flying parallel to known tracks, such as roads, railway lines, etc. The local variation
and possible deviations must accurately be accounted for when using this last method of com-
pensation.

Maintenance and care

The compass requires little maintenance. The maximum permissible shock acceleration is
approx. 25 g. Care must be taken to avoid hitting the instrument against hard objects or letting
it drop. A dusty or dirty mirror shall be cleaned by breathing against and using cotton--wool.
The same applies for the two dials. Make sure never to come close to the compass with a
strong magnet. When adjusting the screws with the screw--driver, turn gently and avoid swin-
ging the needle against the stop with a jerk. If treated with care, the compass will function pro-
perly for years.

Technical data

Operating area:

Northern hemisphere in areas with approx. 75

-- 45

inclination; this corresponds to latitudes between
approx. 65

-- 30

North.

Inclination on scale:

inner circle = 72,5

, center circle = 65

, outer circle = 57,5

Scale division: