Flap weldment tension

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.

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

Thanks

rv7charlie said:

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

Click to expand...

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.

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.

Pictures please to help me understand. Thanks

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

wirejock said:

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

Click to expand...

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.

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 ;-)

Distorted block

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.

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

Thanks

Thanks. And thank you all for the information.
I hate spending days i. The shop with little or nothing to show for it.
Now I can go back in and hopefully get these blocks to cooperate.

wirejock said:

I'm pretty sure the blocks are distorting a tiny bit as the nuts are brought to the correct value.

Click to expand...

Can you determine which way they're deforming? Maybe a shim or a little shaping of the top or bottom surface of the block could compensate for that and make them line up correctly when the bolts are tightened.

It seems like there's only one plane in which the block would be rotating as the bolts are tightened, at least enough to cause the binding you're seeing. It should be fairly simple to slip some thin shim stock, just a few thousandths at a time (like a strip of paper), under the inboard or outboard edge and see if that makes things better or worse.

Or maybe just a little more work on the weldment ends with emery cloth.

Shims

DaleB said:

Can you determine which way they're deforming? Maybe a shim or a little shaping of the top or bottom surface of the block could compensate for that and make them line up correctly when the bolts are tightened.

It seems like there's only one plane in which the block would be rotating as the bolts are tightened, at least enough to cause the binding you're seeing. It should be fairly simple to slip some thin shim stock, just a few thousandths at a time (like a strip of paper), under the inboard or outboard edge and see if that makes things better or worse.

Or maybe just a little more work on the weldment ends with emery cloth.

Click to expand...

They rotate smoothly when the bolts are finger tight.
However, now that you mention it, I recall seeing the blocks move when the weldment is rotated. This implies, as you describe, something is out of alignment. I'll try it today.

Same problem....flap tube tight when tightening AN3 bolts

Great thread, and thanks for the ideas.....

I see this is a fairly old post, but I have exactly the same issue when torquing the nylon flap blocks.

Weldments sanded/ polished.... nylon blocks drilled square, no centre block even installed...and yet still the flap tube goes from 'ball-bearing' friction, to requiring a firm yank to move with bolts tightened.

I do like the idea of -A bolts and castle nuts....

Wondering if this is this a common issue... and how guys have solved it..?:confused

Stay safe one and all..

Chris

I did mine yesterday and posted the results on Facebook RV-14 site.

https://www.facebook.com/photo.php?fbid=10217715897871585&set=p.10217715897871585&type=3&theater

https://scontent-yyz1-1.xx.fbcdn.ne...=7dcb485a31b5bc474c437956cad5671f&oe=5EDF6B31 (sorry the video is not working here but does on facebook)


I polished the flap torque tubes a fair bit then used a brake hone in the blocks. The blocks are not to be overtightened. I then got it to move with one finger very freely. After tightening the bolts that connect the tubes together it got a bit tighter but still very acceptable.

The link above is after everything is bolted to proper specs.

Sorry but not sure how to post pics & video.

Do- polish the ends of the torque tube with emery cloth (or similar) till it turns easily in the plastic blocks.
Do not- try to sand out the plastic blocks as it will leave surface rough (collects dust & binds)
Do not- lubricate plastic blocks as it attracts dirt, stiffen & bind with age.

Ralph Inkster said:

Do- polish the ends of the torque tube with emery cloth (or similar) till it turns easily in the plastic blocks.
Do not- try to sand out the plastic blocks as it will leave surface rough (collects dust & binds)
Do not- lubricate plastic blocks as it attracts dirt, stiffen & bind with age.

Click to expand...

The hone I used on the blocks actually "polished" the surface smoother than it was prior.

Also on the -14 plans section 34-03 step 4 says:

Step 4: Apply wheel bearing grease to the CS-0010-L & -R Torque Arm tubes in the areas that are not powder coated. See Figure 2.

After blocks are cut in two pieces, bolt them together and re drill the hole with a spade bit on slow speed. No need to use spacers.