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.

 

 😈

[Moneybox]

I would try someone like Sling Rig. They are the best I've found for ropes, chain, shackles etc. They may also have the shock cord you're looking for?

[Moneybox]

On 19/10/2025 at 5:46 PM, skippydiesel said:

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.

 

 😈

https://sydneyropesupplies.com.au/product-category/shock-cord-bungee-cord/page/

 

https://www.camscords.com.au/collections/shockcord?srsltid=AfmBOoq9cNam-PgQ-bHMGPuSW7C47Bjsw80bo-kbi4bHCqMNF4uCGUmS

 

https://www.theoriginalshockloc.com.au/products/100-australian-made-marine-grade-shock-cord?srsltid=AfmBOorJe8dhe1NkT5cxKIzhHV5BvGby-FoCI5yzSRcgx49qY9X44NWm 

 

I'd start with these places. Search SHOCK CORD.

[skippydiesel]

Thanks Moneybox - Have contacted the above and asked for performance specifications for 4-5-6-8-10 mm shock cord.😈

[skippydiesel]

From SRS (Sydney Rope Supplies);

 

 

I think I may be able to get away with a 4-6 mm cord. One Black & one White to differentiate which surface is being trimmed.😈

Edited October 21 by skippydiesel

[skippydiesel]

Donaghys of Australia make shock cord - Surprisingly no force extension specifications. They make rope/cordage that has all the spec.s you could ask for.

 

Will send me a short length of 5mm to assessed for myself.

 

https://www.donaghys.com.au/file_uploads/fact-sheets/Shock_Cord_NZ_Fact_Sheet_Feb2018.pdf

 

😈