Rotor Trim

Aviator168-aircraft

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How are your rotor trims implemented? I heard a lot about the term "trim spring", but I can't wrap my head around how a single spring can implement an inflight trim system. The working mechanism of RAF's aerodynamic trim is the only trim system I know. Can someone shed some light on a simple spring trim system? A picture or two can help a lot. Thanks.
 

Vance

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How are your rotor trims implemented? I heard a lot about the term "trim spring", but I can't wrap my head around how a single spring can implement an inflight trim system. The working mechanism of RAF's aerodynamic trim is the only trim system I know. Can someone shed some light on a simple spring trim system? A picture or two can help a lot. Thanks.
An offset gimble rotorhead will have a built in trim speed.

In some gyroplanes to trim for a lower speed a spring is used to counteract some of the effect of the offset gimble.

More pull on the spring trims for a lower indicated air speed.

Some gyroplanes do this with a linier actuator and some with a simple screw to pull on the spring.

Some gyroplanes use a pneumatic cylinder to trim for a lower indicated air speed.

Pictured on The Predator there is a straight cable at the back of the rotor head that is attached to a spring and linier actuator for trim.
 

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Abid

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To be clear effective offset should be considered which also means or takes into account height of the teeter bolt. The bigger the effective offset, the bigger spring needed.
 

Aviator168-aircraft

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Got you. The greater the effective offset, the higher the spring load needed to achieve the desired trim. That also means harder to put the stick forward. So the design of the rotor head has a direct impact on the feel of the gyroplane.
 

Vance

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Got you. The greater the effective offset, the higher the spring load needed to achieve the desired trim. That also means harder to put the stick forward. So the design of the rotor head has a direct impact on the feel of the gyroplane.
In my experience everything on the gyroplane affects the feel of the gyroplane.
Rotor head
Rotor blades
Rotor control ratio
Center of gravity
Center of pressure
Horizontal Stabilizer volume
Vertical stabilizer volume
Rudder volume
Weight and Balance
Rotor size
Rotor blade weight
Mast height
 

MikeBoyette

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Got you. The greater the effective offset, the higher the spring load needed to achieve the desired trim. That also means harder to put the stick forward. So the design of the rotor head has a direct impact on the feel of the gyroplane.
You are correct a Bensen style can be altered so you need almost no spring. This is done by changing the offset in the torque tube.
 

MikeBoyette

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That just means he matched the offset of any to the particular blades he’s flying. I’m pretty sure they were McCutchen’s they need very little trim because of the airfoil being tail heavy already. Most who fly them report a very light stick,like it has power steering. Dad had much smaller off set on his but still required a light trim spring. Bensen Standard is what others base theirs on.
 

gyrojake

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My gimbal has a different pivot point than the standard rotor head.My torque tube is not the center of pitch it is in a pitch and roll block 1 1/2" lower similar to the sport copter . The pivot hole is placed according to the results of the center stick hang test.
Plus I always try to keep the spindle center of mast101_0001 (1).JPG
 
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