3" vs 4"

[Jack Mulinix]

So, looking at plans for the magnum, it has a 3" bellcrank. Alot of talk about about 4" bellcranks. What's the plus'es for a 4". What's the drawback to the 3". And no, the wing's not sheeted yet. Just curios, is this like the flavor of the month, or is there a real differance. I know it's been discussed, but could'nt find.

[Brett Buck]

So, looking at plans for the magnum, it has a 3" bellcrank. Alot of talk about about 4" bellcranks. What's the plus'es for a 4". What's the drawback to the 3". And no, the wing's not sheeted yet. Just curios, is this like the flavor of the month, or is there a real differance. I know it's been discussed, but could'nt find.

   If it's the "flavor of the month" it has been one exceptionally long month - like 20 years!

    The advantage is that it's easier to slow the control rates with usual handle sizes, and you get better mechanical advantage for a given amount of line tension.

    Brett

[Jack Mulinix]

thanks brett

[Andrew Hathaway]

When the Magnum was introduced, the control system was state of the art.  Now it's starting to show it's age.  Sig's 4" bellcrank would be an affordable, effective, upgrade.  I'd probably also inspect the kit control horns carefully, and make sure the joints are solid.  I bought a bunch of the Magnum kit horns several years ago and some of the joints were really questionable.  From a modern standpoint they're probably too short anyway.  The provided pushrods will get the job done, but ball links and Central Hobbies pushrods are easier to setup and would probably be a worthwhile upgrade.

[Jim Thomerson]

Brett has explained why I use 4 in bellcranks in 1/2A and 09 airplanes.