Flap Torque Tubes won’t fit

[TASEsq]

Has anyone had any issues installing the flap torque tubes into the uhmw blocks?

The plans have you bolt on the blocks then install the torque tubes later on, but I did a test fit of the blocks onto the tubes and can’t get them to go on.

I can get the raw (un powder coated) end into the outboard block with some force, and it will turn but with extreme friction. I can’t turn it with just a finger - needs a good wrenching to make it turn. It will not slide on past the power coating - I’ve sanded the ends of the powder coat transition as per the plans.

If I sand the holes in the blocks to get it to slide past the powder coat, I think the fit will be very loose on the bearing surfaces.

I have measured the UHMW blocks, as well as the CS-00010 flap arm in two dimensions, 90 degrees apart and called them Horizontal and Vertical. I used a set of calipers, so there is likely a bit of error, but I gives an idea of what is going on.

As you can see, the section of the part which is unpowder coated (raw) is 0.0015-0.0030 larger! than the hole in the blocks – it goes in, but with force. The powder coated section is 0.015ish bigger than the hole! I would have to sand all the powder coating off to have any chance of getting these in? OR use total brute force? Is this the correct approach?

UHMW Blocks Hoz Dia Vert Dia
L Outboard 0.9955 0.9970
R Outboard 0.9955 1.0005
L Inboard 0.9990 0.9920
R Inboard 0.9940 0.9940

Flap Arm Raw 0.9985 0.9985
Flap Arm PC 1.0115 1.0075

Does anyone have a set of UHMW blocks / flap torque arms we can compare measurements?

Before taking these measurements I emailed support and had the following response. I have not had a response yet after emailing them the measurements above. I can’t imagine with the above dimensions how any of the below is going to make them fit:

I don’t have a CS-00010-PC in stock here to verify dimensions.
The formation (by you) of a lead-in radius, chamfer, taper, and
The smoothing/polishing of the weldment and
The liberal use of grease and/or wax (can be cleaned up later)
Has been used by many builders before successfully.

 

[mc607]

I called Vans when I ran in to the same issue. Same reply you got. They were right. I tapered the bare end with a light sanding just to get it started. I also tapered the powder coat. I used plenty of grease and my knee against them and a twisting motion when I installed them. I didn’t have to, but if they’re not going you could put them in the freezer overnight. Read through section 54 if you’re gonna install the flap position sensor. Actually, you should drill that #30 hole in the WD1013A even if you’re not gonna, in case you change your mind. If you think installing them is a chore, try sliding them back out a bit if you forget to drill that stupid hole.

 

[PeteT]

Trent-
I had the same scenario- the UHMW would scarcely fit over the bare steel ends, let alone the powder coating area of the torque tube. I ended up reaming by hand using a 1.00 or so reamer. With the dimensions you have listed, that size could work. This took out a small amount of material which made for a nice fit over the bare ends- but not loose. Still no luck with the powder coating fit- so removed all of it. Primed the bare steel, greased it up and all good.

Cheers
Pete

 

[TASEsq]

Thanks for the replies.

I think I might go ahead and do the flap torque tube drilling, the try all your suggestions to put the outboard block on the tube before the block is installed in the airframe.

The only problem is this would be a big roadblock for me - turns out I only received one flap torque tube and missed it in my inventory.

So doing it this way would mean I can’t proceed with any steps to close out the baggage area.

 

[PaulvS]

An option is to make your own blocks, it is very easy to do. The UHMW sheet is available from specialist plastic suppliers. I bought some 20mm sheet and cut it up with a circular saw and band saw and drilled the holes with a woodworking spade bit. I made new blocks for the rudder bars as well as for the flap centre block because the blocks that came in the kit were not a good fit, particularly the rudder block which had the holes too far apart.

 

[PhatRV]

The formation (by you) of a lead-in radius, chamfer, taper, and
The smoothing/polishing of the weldment and
The liberal use of grease and/or wax (can be cleaned up later)
Has been used by many builders before successfully.

I remembered doing something very similar when fitting the torque tube on my RV8. I think the hole in the block is very slightly undersized to ensure a very tight fit, and less chance of flutter. I lightly removed the powder coat with 320grit sandpaper until it fitted.

 

[TASEsq]

I lightly removed the powder coat with 320grit sandpaper until it fitted.

Thanks for all the assistance.

I ended up sanding the whole powder coated surface with 320 grit, and focused on smoothing out the transitions a bit more between the powder coat and the steel.

I lubed the whole torque arm up and it slid in with only moderate force. It is tight on the raw steel rotational surface - more than I imagine it should be, but the flap motor is good for 450lbs so I’m sure it will be fine!

Thanks for the support.

 

[mc607]

It is tight on the raw steel rotational surface - more than I imagine it should be

I had the same concern so I ran the motor through a couple cycles once it was installed. Except for the motor sounding a little different between extending and retracting it was all good.


Trent,
Did you have the block mounted in your vice when you tried the first dry fit? Like in the 3rd picture. If so, that would have worked against you by compressing the block and not allowing it to “stretch”. When you get your other torque tube try mounting the block to a piece of plywood with a through hole. I’m sure it’ll go with no powder coat removal.