CAD Drawing for Infinity Bellcrank

[Brett Buck]

Here is the original drawing for the Infinity bellcrank. Note that it specifies the materials clearly, including cross-grain balsa and a spacer where the ball link connects, and .025 6061T6 aluminum sheet. The only thing I do differently, and only for convenience, is make it 1/8" instead of 3/32 between the faces, and then use  1/8x1/4 circuit board standoffs for the spools instead of 3/32x3/16. I have tested this to destruction and it greatly exceeds the strength and durability of 1/4" phenolic or delrin.

   I am sorry Chris' failed but it appears to not be constructed according to the drawing, wherever it came from.

    Brett

[bill bischoff]

I understand "end grain" balsa as mentioned in the other thread, but what is "cross-grain" balsa. To me it would mean two or more plies of balsa glued together with the grain staggered 90 degrees.

[Brett Buck]

I understand "end grain" balsa as mentioned in the other thread, but what is "cross-grain" balsa. To me it would mean two or more plies of balsa glued together with the grain staggered 90 degrees.

  End grain= cross grain.  The grain goes across from top to bottom, like Mallite.

   Brett

[Tim Wescott]

  End grain= cross grain.  The grain goes across from top to bottom, like Mallite.

My rule of thumb is that if someone asks, then I need to make the directions more clear -- I believe that end-grain is the more common term, but a double-headed arrow on the drawing with a comment "run the grain this way" would remove as much ambiguity as can be humanly done.

[Brett Buck]

My rule of thumb is that if someone asks, then I need to make the directions more clear -- I believe that end-grain is the more common term, but a double-headed arrow on the drawing with a comment "run the grain this way" would remove as much ambiguity as can be humanly done.

   This was never intended to be distributed and these are not instructions on how to build one. The original description is perfectly clear, as were the directions I provided to Tom Morris.

    Brett

[Allan Perret]

Hey Brett, curious why you chose the 6061 aluminum for this,  isn't 2024 stronger ?

[Brett Buck]

Hey Brett, curious why you chose the 6061 aluminum for this,  isn't 2024 stronger ?

  Because 6061 was more than adequate. I cannot emphasize how much effort it took to break my test articles, it would have rendered a standard flat bell crank  into a U-crank at half the load. There's some other issue here.

     Brett

[Allan Perret]

One other thing I don't understand.  What is reason for the pushrod attachment hole displaced 1/16" aft of center ?

[Brett Buck]

One other thing I don't understand.  What is reason for the pushrod attachment hole displaced 1/16" aft of center ?

  To correct the geometry for the leadout sweep and pushrod angles. It's not the same for every airplane.

    Brett

[Perry Rose]

Did it hurt when you broke your testarticles?

[Carl Cisneros]

Perry

OMG   

good one tho,,,,,,,,,,,

[Steve Helmick]

Am I correct in thinking that this BC is intended to be installed "normal" and not "reversed"? I.e., "up" leadout will be the rear one. 

Vertical grain would be the only way to go with this design. It would allow much better epoxy penetration, pretty close to 100%. The balsa would not fail in this configuration, tho the epoxy/aluminum bond most certainly could, if the aluminum wasn't properly prepped. Anybody with a 10" table saw (and a decent blade) could slice off 3/32" slabs of hard balsa that would be perfect for the core.     Steve

[Brett Buck]

Am I correct in thinking that this BC is intended to be installed "normal" and not "reversed"? I.e., "up" leadout will be the rear one. 

     Yes. You could easily design it to go the other way around, and it has some advantages in terms of pushrod clearance over some of the other leadout termination methods, but I don't think there's any good reason to put it in backwards, and I haven't seen many reverse systems used recently.

     Brett