Alpha Unmanned Systems ALPHA 800, Aircraft Maintenance Manual, Page: 49 / 143

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DEV ‐ M ‐ MM A800 V1.7
MAINTENANCE MANUAL
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Sheet # 010 Title CARBURETOR ADJUSTMENT
Applies to UAVs ALPHA 800
Special Tools Required Infrared temperature gauge
Time 30 min
Introduction
All Alpha UAVs with a gasoline engine (010172341) leave the factory with their carburetor WT ‐ 990
(010172780) (carb) correctly set for optimum performance, economy and emissions; however, if the UAV
is to be used in a different climate, or at a different altitude, then adjustment to the carb settings may be
necessary. Adjustment is achieved by rotating either one, two or three needles on the carb body. This
Maintenance Sheet shows the procedure for a two needle carb, although the principles can be applied to
any carb.
Once correctly adjusted, the engine must start easily and idle reliably at minimum throttle. During a flight
the engine must not produce excessive smoke and must smoothly produce enough power across the
operating revolutions and for all flight modes. For fixed wing aircraft engine performance can be tested as
part of pre ‐ flight checks on the ground. For helicopters a good test of engine performance is the vertical
climb out at maximum positive pitch from hover (in manual mode); the helicopter must climb smoothly,
with adequate power to maintain tail authority. After climb test is performed operator must engage hover
mode and check that the GOVERNOR RPMs are reached and maintain easily without excessive variation of
the percentage of engine used.
Normally the percentage of engine used to hover is between 30% to 55% depending on weight, altitude
and ambient temperature, when hovering in auto mode the maximum variation considered as normal in
the engine percentage is +/ ‐ 10%. If the autopilot when governor is engaged (any auto ‐ mode) commands
an increase higher than 10% and the rpms are not maintain the internal operator must ask the external
operator to LAND manually and to check engine temperature, after temperature is checked carburetor
setting must be repeated until both in manual and auto mode rpms are maintained.
Typical values:
Empty weight RPMs % of
throttle for
hover
Ambient
temperature
Engine
temperature
9.5 – 10.5 Kg 1175 ‐ 1250 30 ‐ 45 % 5ºC ‐ 15ºC 85 ‐ 95ºC
10.5 – 11.5 Kg 1225 ‐ 1300 35 ‐ 50% 15 ‐ 25ºC 95 ‐ 105ºC
11.5 ‐ 12 Kg 1250 ‐ 1350 40 ‐ 55% 25 ‐ 35ºC 105 ‐ 115ºC
Step by Step Procedure