Elevator foam trailing edge rib tips

stigaro · #1 01-05-2021, 08:06 AM

While I didn't make this mistake, I could see how it could occur. I have access to a 11x17" printer and was able to make a printout of the foam cutout templates from the digital .pdf files on Van's website. After making sure the templates were the correct size (be sure to print "Actual Size"), I noticed that the paper plans provided by Van's were printed about 95% scale. So, had I used the actual page 09-29 templates as supplied (or a photocopy), the ribs would be too small. So don't assume the paper plans you receive from Van's to have the correct page scaling. Maybe some do, mine didn't.

On another note, in my empennage kit, I was provided 5 PVC foam blocks, 4 were 5.25" long and the 5th was only 4" long. I'm not sure if this is how Van's is supplying these blocks now or if was just unlucky, but after some repositioning, I did manage to get all 3 ribs to fit the 4" block, but it's pretty tight. I used a hot wire to cut these out as I'm not sure a bandsaw would have worked.

rvbuilder2002 · #2 01-05-2021, 10:08 AM

There are a lot of reasons that a paper drawing can be out of scale.

A major one that people are not typically aware of is shrinkage or expansion of the paper due to changes in temp and humidity.
The amount of change can be significant depending on the conditions delta compared to when it was originally printed.
That is one of the reasons for the scaling reference being present on all drawings that are have full scale templates printed. It should always be cross checked before using as a template for any critical fit parts.

All of the processes described in the manual have been (test kitchen) tested in our shop, so I can assure you that the foam cuts very nicely on a band saw, assuming it is performing reasonably (no weird tracking on the blade, etc.).

stigaro · #3 01-05-2021, 12:05 PM

Perhaps this is true, but in this case it was really more of how the page was printed. Van's print on the left, my print on the right (with top template cut out). Note the difference in page margins while the paper size is identical. I know because I initially printed it using the default "Scale to Page Size" in Adobe before printing it "Actual Size" and the scale was about the same. At any rate, the instructions say to confirm the size and I did, so no problems, but I could see how someone COULD have issues.

As for the bandsaw, sure, if the blocks were 5.25" long, the 3 trim tab ribs could be cut with a bandsaw. But, my block was only 4" long and I had to adjust the middle block to squeeze in between the other two and shift those ones closer to the edge. There was not enough room between the ribs at that point to get a saw blade in between, at least not my bandsaw.

Not complaining, just providing information on what I recently found when doing my elevators in the hope it might save others some frustration.

Ron B. · #4 01-05-2021, 02:09 PM

I had to reprint to get the proper scale as mine were way off . I also had zero issue cutting them out with the band saw. Plenty of margin also.

stigaro · #5 01-05-2021, 05:01 PM

Were your foam blocks all 5.25" long? My 5th one was only 4" so necessitated creatively fitting the ribs into the available space and hence the reason I wasn't able to use the band saw. Plus I wanted to see how the foam cutter would work with PVC foam. Basically, it worked but it takes a lot more heat than polystyrene.

Ron B. · #6 01-05-2021, 07:16 PM

If I remember correctly one was shorter but it was for the trim tab. That was two months ago or more.

TASEsq · #7 01-06-2021, 05:12 AM

Quote:

Originally Posted by Ron B.

If I remember correctly one was shorter but it was for the trim tab. That was two months ago or more.

Same experience here:
https://2.bp.blogspot.com/-lxkCTjIpf...0/IMG_3177.JPG

AndyWAUS · #8 01-14-2021, 11:34 PM

Oh ****, I completely overlooked the warning on the page! I cut out from the Vans provided plans thinking this was to scale. They were fitting pretty tight, so I thought they were okay. I just went and measured the page, and the long size that is supposed to be 16" measured to 15 1/2"

This is a whole 3% difference. Is my elevator ruined?

rvbuilder2002 · #9 01-15-2021, 09:38 AM

Quote:

Originally Posted by AndyWAUS

Oh ****, I completely overlooked the warning on the page! I cut out from the Vans provided plans thinking this was to scale. They were fitting pretty tight, so I thought they were okay. I just went and measured the page, and the long size that is supposed to be 16" measured to 15 1/2"

This is a whole 3% difference. Is my elevator ruined?

With the page scale 1/2" short it should have produced ribs that are smaller than nominal, which would have made them fit looser, not tighter.

At this point I would evaluate based on how the elevator looks. If you lay a straight edge cord wise on the elevator over each rib location, does the skin appear flat? If it does, and the ribs appear to be fully bonded on both sides to the skins, then it is probably fine.

Ron B. · #10 01-15-2021, 09:58 AM

Quote:

Originally Posted by rvbuilder2002

With the page scale 1/2" short it should have produced ribs that are smaller than nominal, which would have made them fit looser, not tighter.

At this point I would evaluate based on how the elevator looks. If you lay a straight edge cord wise on the elevator over each rib location, does the skin appear flat? If it does, and the ribs appear to be fully bonded on both sides to the skins, then it is probably fine.

Scott, I think he might have been referring to being tight as using up most of the block of foam?