Tipper canopy latch

PaulR · #1 12-16-2008, 06:06 PM

I put the WD-617 canopy latch bar back into the fuselage for hopefully, the last time. When I finished torqueing the bolts down that hold the bushing in, it seems to be pretty hard to rotate. At least harder than I think it should. I haven't hooked up the canopy release lever yet, but before I go any further I thought I would see if anyone else had this problem. I assume I can take some really fine emory cloth or sandpaper and polish the ends of the rod where they go into the bushings. It just seems like it should rotate more freely.

Merry Christmas to all!

roee · #2 12-16-2008, 06:37 PM

...this issue applies to all UHMW plastic bushings in the airplane.

Look carefully at the UHMW plastic bushings and you will notice that they significantly deform if you tighten the bolts to their specified torque values. One consequence of this is that the bushing will go out of round and put excessive pressure on the tube, causing the excessive resistance that you describe. I've also wondered if this amount of stress/strain on the UHMW part might accelerate its total failure, i.e. does it increase the risk that the plastic will eventually break.

So I don't have an answer to your question, but I will pose a related and more general question: Should the bolts that secure UHMW bushings be torqued to the full specified value of the bolt, or should they only be snugged up by feel to prevent excessive deformation of the UHMW? Has anyone ever asked Van's this question? If not, I will.

Rupester · #3 12-16-2008, 09:20 PM

Mine was too snug at first, but I buffed the non-painted ends of the tube on a 6" Scotchbrite wheel and wiped just a teeny bit of LPS2 on them. After I exercised the whole latch assembly a few times, the resistance is quite acceptable now. I have not noticed a problem torquing down UHMW blocks, either on the flap rod or the canopy latch.

Greg Arehart · #4 12-16-2008, 09:30 PM

I'm not sure about torquing these down - when I tried putting full torque values on any bolts in this plastic, it deformed too much for my liking, so I backed them off.

Related is that my canopy latch was a very tight fit in the blocks (I mean impossible to turn initially without a wrench). I sanded the blocks down as well as the latch bar. Still very tight but it loosened up sufficiently after moving it back and forth a bunch. A bit of lubricant would probably have helped as well.

greg

roee · #5 12-17-2008, 12:49 AM

Quote:

Originally Posted by roee

...So I don't have an answer to your question, but I will pose a related and more general question: Should the bolts that secure UHMW bushings be torqued to the full specified value of the bolt, or should they only be snugged up by feel to prevent excessive deformation of the UHMW? Has anyone ever asked Van's this question? If not, I will.

I sent off an email to Van's. I'll post when I hear back from them.

PaulR · #6 12-17-2008, 06:52 AM

Thanks for the replies guys. My flap rod is really tight as well. After posting this, I took the canopy rod back out and found a SLIGHT burr on the tube ends that are unpainted so I took that off, but haven't done anything to the diameter yet. I reinstalled it with a little lubriplate and it is marginally better. I didn't notice the UHMW deforming at all. I will await the reply from Van's.

noelf · #7 12-17-2008, 07:53 AM

My RV-6A tipper uses the same WD-617. I remember that it was also "tight" in the UHMW (C-611) blocks. I could not rotate the Latch Bar by hand when installed.

After installing all of the canopy links, idler, push-rod, latch and handle hardware, the mechanical advantage provided made the activation and rotation of the WD-617 extremely easy.

roee · #8 12-17-2008, 05:03 PM

Quote:

Originally Posted by roee

I sent off an email to Van's. I'll post when I hear back from them.

Got a reply from Van's:

"Never thought about it, really. We've always used the std torque values and
haven't had any problems."

jsharkey · #9 12-17-2008, 05:16 PM

Quote:

Originally Posted by roee

Got a reply from Van's:

"Never thought about it, really. We've always used the std torque values and
haven't had any problems."

Sounds like Gus

roee · #10 12-17-2008, 06:21 PM

Quote:

Originally Posted by jsharkey

Sounds like Gus

No, this was from Ken Scott. All nice folks over there, but they do have somewhat of a standard response to design issues raised by builders: [paraphrased by me]: "We haven't lost one of our planes because of this issue [yet], so it's not a problem." I find that frustrating.