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TM 1-6625-724-13&P
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The UH-1H/M Flight Plans are listed below with a brief description of their purpose. The selectable Flight Plans (see
table 1) are listed in order of appearance in the menu on the CADU and not in the order in which they are to be
performed. The UH1 script file is for aircraft with metal blades and the UH1CRB script file is for aircraft with
composite blades.
FLIGHT
This test is primarily designed to reduce the in-flight vertical vibrations using pitch links, sweep, tab, and weights. It is
to be used after the GNDTRK and INITIAL flight plans when smoothing an aircraft after component change, or for
"tuning up” an aircraft that is already in service.
GNDTRK
This flight plan is designed to get the rotor into a flyable track prior to hovering. It consists of two measurements, and
will adjust pitch links and tabs only. It should be the first test that is performed after any component change or major
rework on the rotor.
INITIAL
This flight plan is performed after the GNDTRK, and will balance the rotor prior to flight. It will adjust pitch links,
weights, tabs, and sweep to perform this goal. This test should be performed after any component change or major
rework on the rotor.
PROBES
This flight plan is designed to acquire data from up to four accelerometers to assist in isolating irregular or unusual
vibrations. The flight plan will measure data one channel at a time on DAU ACC1 through ACC4. These
accelerometers may be installed anywhere on the airframe and will measure a 0 to 500 Hz spectrum (0 to 30,000
RPM).
tail
This flight plan is designed to balance the UH-1H/M tail rotor. It uses the optical RPM sensor on TACHO 2 and one
accelerometer on ACC4. It should be performed after any rework on the tail rotor or anytime a medium to high
frequency vibration is felt in the aircraft.
ROTOR SMOOTHING OVERVIEW
The UH-1H/M is smoothed in two steps: a ground or initial tracking and an in-flight final smoothing of the rotor.
Properly conducting the ground or initial step greatly reduces the amount of effort required to smooth the rotor in flight
and yields a good ride.
The recommended ground/initial method to smooth the UH-1H/M uses these basic steps:
a. Use GNDTRK to adjust pitch links to flat track the rotor at 226 rpm rotor speed and trim tabs for a flat track at
324 rpm rotor speed. This flight plan will not balance the rotor while on the ground and is used to obtain a flat
track condition prior to hover.
b. Use INITIAL flight plan the same as GNDTRK except that the software now includes the Hover test condition
where the rotor will be balanced by including the sweep and span weight adjustments. If GNDTRK flight plan
has been previously accomplished it is still recommended that all test conditions be recorded even though the
idle and 100FPG were previously recorded.
It should take approximately three initial runs to get the rotor in track. If after three runs the rotor track is not within
the 0.1-0.2 inch range, review the adjustment procedures to make sure the correct adjustments are being made and
re-orient the aircraft to make sure that the tracker is not looking at the sun or that the sun is at the left front of the
aircraft. As long as the 226 rpm and 324 rpm track are in the 0.1-inch range (2-3 mm) and hover balance is below 0.2
ips, it is acceptable to discontinue the initial mode and press into flight.
NOTE
The better the ground track is the less vibration will be
encountered in the first flight and the rotor will be closer
to finished levels.
Once the ground tracking or initial phase has been conducted and the aircraft is taken to forward flight at least one forward
flight condition must be taken on every run to insure that the program specifies correct adjustments. The only criteria for
successfully completing the in flight smoothing of the rotor is the vibration levels, the final track does not matter.
