What is a delta-3 hinge?

Diagram explaining helicopter delta 3 hingeA delta-3 hinge is a hinge that is not at a 90-degree angle, it is offset to some degree.

When a delta-3 hinge is used in a rotor blade, the blade angle is changed as the blade flaps.  This change in angle is because the hinge is offset.  The delta 3-hinge is commonly used in tail rotors to reduce the degree of flapping that is required.  This practice allows for the tail rotor to be closer to the tailboom, ultimately reducing vibration.  This type of hinge is used in some main rotors to a lesser degree.  The primary deterrent for the use of the delta-3 hinge is the increased stress imposed on the hinge.

Reference(s):

Principles of Helicopter Flight, 2nd Edition, pg. 96

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What is pitot static system?

The pitot static system consists of the instruments used for determining aircraft’s speed, altitude, and altitude trend (or change in altitude).

These instruments generally consist of the altimeter, airspeed indicator and vertical speed indicator.  The system utilizes air pressure differences to provide the pilot specific information.  The static air pressure port provides baseline air pressure.  This pressure is used for the altimeter.  A pitot tube outside the aircraft receives air pressure due to forward flight, or ram air.  This pressure is compared to the static pressure and the difference is displayed as airspeed.  The vertical speed instrument uses the static pressure and a calibrated leak.  The rate of change is indicated as climb or decent.

Reference(s):

FAA-H-8083-25B Pilots Handbook of Aeronautical Knowledge pg. 8-1

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What instrument would fail if the pitot tube is clogged?

If the pitot tube is clogged, the airspeed indicator will no longer work properly.

If the ram air portion of the pitot tube is clogged, but the drain hole is open, the airspeed will indicate zero airspeed. Basically, the system would be displaying the same static pressure. However, if the ram air inlet and the drain hole of the pitot tube are clogged, the airspeed would increase when climbing and decrease when descending. This odd behavior is because the pressure in the tube is constant, but the static pressure would be changing. As such, the differences received would be inverse from what was expected.

Reference(s):

FAA-H-8083-25B Pilots Handbook of Aeronautical Knowledge pg. 8-10

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What instrument would fail if the static port is clogged?

If the static port is clogged, all pitot static instruments will provide incorrect readings.

Many aircraft will have an alternate static port to provide an alternate source of static pressure. If the static port becomes clogged, the airspeed indicator will under report speed when climbing and an over report speed when descending. This error is the opposite when the pitot tube is clogged. The vertical speed indicator will show zero rate of change with a clogged static port. The altimeter will remain constant at the altitude reading when the blockage occurred.

Reference(s):

FAA-H-8083-25A Pilots Handbook of Aeronautical Knowledge pg. 8-10

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Why does a piston-powered helicopter have dual magnetos?

Most piston-powered helicopters have dual magnetos so that if one magneto fails in flight, the engine will still operate.

Magnetos provide the spark needed for the ignition system by generating their own electricity.  Magnetos do not need the electrical system active to work. For safety, there is built in redundancy.  During the preflight, one magneto should be turned off and the engine should still run.  Then, the other magneto should be tested. Both magnetos should be operational and on during flight.  In addition to safety, the dual magnetos provide some additional performance benefits. When one magneto is disabled, the RPMs will decline some.

In addition to checking before flight, magnetos operation should be confirmed before maximum performance takeoffs, where an engine failure would be extremely hazardous.

There are some helicopters that have one or more electronic ignition system instead of a magneto.  However, the redundancy principle still remains.

Reference(s):

FAA-H-8083-25B Pilot’s Handbook of Aeronautical Knowledge pg. 7-15

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What are types of aviation fuel?

The most common types of aviation fuel are 100LL [low lead] and Jet A.

Aviation fuel or AVGAS is color coded blue to help distinguish it from other types of fuel. Jet A is straw colored or colorless. Most reciprocating piston engines use 100LL while turbine-powered aircraft use Jet A.

Reference(s):

FAA-H-8083-25B Pilot’s Handbook of Aeronautical Knowledge pg. 7-27

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