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guidelines during the various phases of ground and
flight operations:
• Make sure the proper grade of fuel is being
used. Drain and refuel if the fuel is old.
• Develop a habit of monitoring the engine
instruments to verify proper operation according
to procedures established by the manufacturer.
Preignition occurs when the fuel-air mixture ignites
prior to the engine’s normal ignition event. Premature
burning is usually caused by a residual hot spot in the
combustion chamber, often created by a small carbon
deposit on a spark plug, a cracked spark plug insulator,
or other damage in the cylinder that causes a part
to heat sufficiently to ignite the fuel-air charge. Preignition
causes the engine to lose power, and produces
high operating temperature. As with detonation, preignition
may also cause severe engine damage, because
the expanding gases exert excessive pressure on
the piston while still on its compression stroke.
Detonation and preignition often occur simultaneously
and one may cause the other. Since either condition
causes high engine temperature accompanied by a
decrease in engine performance, it is often difficult to
distinguish between the two. Using the recommended
grade of fuel and operating the engine within its proper
temperature and RPM ranges reduce the chance of
detonation or preignition.
Fuel Systems
The fuel system is designed to provide an uninterrupted
flow of clean fuel from the fuel tank to the engine.
See Chapter 3 for more information on fuel tanks. The
fuel must be available to the engine under all conditions
of engine power, altitude, attitude, and during all
approved flight maneuvers. [Figure 4-12]
Fuel Pumps
Powered parachutes have fuel pump systems. The
main pump system is engine-driven and sometimes an
electrically-driven auxiliary pump is provided for use
in engine starting and in the event the engine pump
fails. The auxiliary pump, also known as a boost
pump, provides added reliability to the fuel system.
The electrically-driven auxiliary pump is controlled
by a switch in the cockpit.
A diaphragm pump is the primary pump in the fuel
system for two-stroke engines. Air pulses in the
crankcase actuate a diaphragm and provide fuel under
pressure to the carburetor. Four-stroke engines have a
mechanical pump driven directly off the engine.
Fuel Plunger Primer
The fuel plunger primer is used to draw fuel from the
tanks to supply it directly into the cylinders prior to
starting the engine. This is particularly helpful during
cold weather when engines are hard to start because
there is not enough heat available to vaporize the fuel
in the carburetor. For some powered parachutes, it is
the only way to deliver fuel to the engine when first
starting. After the engine starts and is running, the
fuel pump pushes fuel to the carburetors and begins
Figure 4-12. Fuel pump system.
4-11
normal fuel delivery. To avoid overpriming, read the
priming instructions in your POH for your powered
parachute.
Choke
A choke or fuel enrichening system is an alternate
method to provide additional fuel to the engine for
initial cold starting. Actuating the choke control allows
more fuel to flow into the carburetor.
Fuel Bulb Primer
The fuel bulb primer is manually actuated by squeezing
the bulb to draw fuel from the tanks. This charges
the fuel lines and carburetor float bowls before starting
the engine the first time on a given day. After the
engine starts, the fuel pump is able to deliver the fuel
to the fuel bowls.
Fuel Gauges
The fuel quantity gauge indicates the amount of fuel
measured by a sensing unit in each fuel tank and is
displayed in gallons. Do not depend solely on the accuracy
of the fuel quantity gauge. Always visually
check the fuel level in the tank during the preflight inspection,
and then compare it with the corresponding
fuel quantity indication. It is also important to track
your inflight fuel consumption. Be sure to consult the
POH for your powered parachute and know the approximate
consumption rate to ensure sufficient fuel
for your flight.
If an auxiliary electric fuel pump is installed in the
fuel system, a fuel pressure gauge is sometimes included.
This gauge indicates the pressure in the fuel
lines. The normal operating pressure can be found in
the POH.
Fuel Filter
After leaving the fuel tank, the fuel passes through a
filter before it enters the fuel pump or carburetor. This
filter removes sediments that might be in the fuel.
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Powered Parachute Flying Handbook动力伞飞行手册(34)
