TM 55-4920-390-13&P
SECTION IV
OPERATION INSTRUCTIONS
4-1. GENERAL. This section contains:
a) Required "equipping" of the helicopter.
b) Operation and use of the Strobex 135M-9.
c) Aids in interpretation of results.
4-2. EQUIPPING THE HELICOPTER.
4-3. DC POWER. Means must be provided (a suitable connector) to furnish 28 VDC from the aircraft's supply. 28 VDC
is universally available, and suitable connectors generally exist. The Strobex has a 40', 2 conductor power cable with an
MS-3106-E16-11P connector (P 101) on the free end. The helicopter should have a suitable mating connector or an
adaptor can be devised for whatever connector exists in the helicopter. Refer to circuit diagram (Fig. 1-8) for polarity.
4-4. SIGNAL FROM ROTOR HEAD . The helicopter rotor head must be fitted to deliver a one-per-rev pulse as follows -
a) The rotating swash plate must be fitted with a soft iron (magnetic material, but not a magnet) wiper which
will pass close by a magnetic pickup secured to the fixed swash plate. (4-4, b).
b) A suitable magnetic pickup (Electro Products 3030AN or equal) must be secured to the fixed swash plate
so that the wiper (4-4, a) will pass in close proximity to it once per rev, thus generating one electrical pulse
per rev. The gap should be adjusted to about .020" to .040". This is approximately equal to the thickness
of a matchbook cover.
WARNING
The aforementioned parts are in a very sensitive area of the helicopter mechanism and they
must be absolutely secured so they cannot loosen and interfere with the "machinery".
NOTE 1
Many helicopter types are equipped to receive the wiper and pickup as above, and many
others can be so equipped quickly and easily. In many cases the airframe manufacturers have
suitable bracketry already designed and may be in a position to help.
4-1