Flap weldment tension

[wirejock]

How much is too much?
I searched but the threads don't answer my problem.
It's a 7a but I suspect this is an issue with other models.
I spent all day trying to get the weldment to rotate smoothly in the bearing blocks.
The weldment rotates but not bearing smooth. It's takes a little force to move it.

The weldment was not round and the blocks were too close in tolerance.
A little squeezing got the weldment reasonably round within a couple thousandths.
A little sanding got the blocks to rotate without binding.
It's not the center block. In or out, it's about the same. I do have washers between the center blocks. One on each bolt.
The outboard blocks are the black predrilled type. They are not split and the hole does not go all the way through.
I got the blocks to rotate freely on the ends of the weldment but the weldment gets tighter when the block bolts are torqued. AN3 bolts torqued to 20 inch/pounds. The bolt holes were drilled on a press and perfectly square through the blocks.
I don't want to go too far and end up with the weldment breaking in sloppy.
Any advise is appreciated.

[rv7charlie]

All the UHMW bearing blocks in my -7 kit were very tight on the tubes. I had little to no luck trying to sand for clearance; I think I even tried a flat nosed carbide burr at one point. I ended up dressing the ends of the tubes with fine sandpaper/emery cloth.

Note that as long as the flap tube isn't actually binding, it probably isn't that big a deal since the air loads on the flaps will be far greater. But... I really fought the rudder pedal blocks. I worry that friction there will affect rudder trim and centering due to higher breakout forces.

FWIW...

Charlie

[wirejock]

Originally Posted by rv7charlie

All the UHMW bearing blocks in my -7 kit were very tight on the tubes. I had little to no luck trying to sand for clearance; I think I even tried a flat nosed carbide burr at one point. I ended up dressing the ends of the tubes with fine sandpaper/emery cloth.

Note that as long as the flap tube isn't actually binding, it probably isn't that big a deal since the air loads on the flaps will be far greater. But... I really fought the rudder pedal blocks. I worry that friction there will affect rudder trim and centering due to higher breakout forces.

FWIW...

Charlie

I suspected as much. I even polished the pipe bearing surfaces.
After some thought, maybe the bolts are distorting the block a little when they get tightened.
The rudder blocks are pretty smooth but haven't been torqued yet. Guess another day will be spent tomorrow on rudder weldments.

[wjb]

Hey Larry,

Mine are a bit tight, too. No "ball bearing" feel here. However, the flap motor seems plenty strong to extend the flaps. Like other posters have said, the air loads will be much higher. I did put washers between the bearing block halves to minimize the friction. Mine are tight but not too worrisome.

[Billythekid]

Pictures please to help me understand. Thanks

[JanRV6UK]

Hi Larry,

Might be a good idea to use a spring balance so you can see what force you need to move the flap mechanism. Everyone have different opinions about what is a 'bit tight' .. nice to have some numbers ... Just hook the spring balance in place of the flap actuator. Then keep the angle between the spring balance and the flap tube at 90 deg as you pull.. note the stick friction .. and what force you need to move the arm... Always good to have number :-)

[-goose]

Originally Posted by wirejock

After some thought, maybe the bolts are distorting the block a little when they get tightened.

I found this to be the case and backed off the bolts a little so that they are snug, but not so tight that they are distorting the plastic to the point that the flap tube won't move reasonably freely. I'd be cautious about overloading the flap motor, I seem to remember reading some accounts of them burning out prematurely.

I also found that a shim was required under the lower block to keep the flap tube aligned. Without it, tightening the centre block bolts pulled a bow into the flap tube. And I put an additional thin washer between the block halves, but my saw cut was a bit thick.

[bret]

tightening that plastic is tricky, just don't distort, and mine is tight, but that linear actuator is so strong I don't thing you can hold it and stall it, I tried, very strong ;-)

[wirejock]

I'm pretty sure the blocks are distorting a tiny bit as the nuts are brought to the correct value. Has anyone opted for drilled bolts, castle nut and cotter pin? Seems like a much better solution.

[rv7charlie]

You could, but as long as the nyloc is making full contact it shouldn't move. Remember, the whole point of a locknut is that it won't back off on its own.

Keyed nuts are usually used on assemblies that can rotate around the bolt, which could drive the nut off the bolt.

Charlie