y harness vs single strand for motor mount

[The_Quacken]

Hey, im starting to plan a new project which is a 3" MAC villain I've been looking at the motor mount on It and I had some questions. MAC uses just a single piece of webbing that's attached by a pin and while it seems to fly well as per some of the other build threads I also see most high-power airframes being built with y harnesses on the motor mounts. Is there any reason that the as-built would be inadequate and I should upgrade or is the Y harness mostly just a mix of redundancy and anti-zipper?

 

[fyrwrxz]

Redundacy, stress load sharing and anti zip. We've all seen shock loaded ply bulkheads fail. They are usually found about the middle layers of the archeological dig in the crater....

 

[bobbyg23]

No need for a y harness. The Mac cr's are plenty strong being made of 3/8” material.

 

[cerving]

It depends on the webbing, and the materials. If it's a 3" fiberglass rocket, a single piece of 7/16" Kevlar attached to the motor mount is fine, or a 3/8" Kevlar Y-harness attached to the fiberglass centering ring. If it's cardboard, you can go lighter because the momentum of the pieces at ejection will be much less due to their lower masses. If you're in doubt, beef up both the harness and its mount; a strong harness with a weak mount is no better than a weak harness and a strong mount.

 

[krislhull]

I have built two MAC rockets with his standard single strap design, and it has worked perfectly on both rockets with no issues. On my latest MAC build, I went with a Y harness partially due to it being a heavier fin can, but mostly just to try something new. Both will work just fine.