How to choose shock/bungy cord?

[skippydiesel]

I am trying to design a bungee cord, one way trim system for aileron & rudder.

 

The cord will need to be:

• Strong enough to maintain desired adjustment
• Weak enough to be easily overcome by pilot inputs ie not impede normal use of stick/peddles
• Durable -   consistent  elasticity over time 
• Prefer two diffrent colours, so as to easily ID the two separate systems
• Able to be used with directional pulleys eg aileron direction of pull, will be away from pilot input direction

 

I could do with some help;

• Selecting likly cord - guessing 8-10 mm 
• Source of reliable product
• Finding lightweight pulleys suitable for cord diameter

 

Marine hardware stores would seem to be a likly supplier however pulleys (single) come in a bewildering array of shapes, sizes & cost - max rope size seems to be 5mm - online perusal leads to confusion in the aged mind.

 

 😈