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-   -   Landing light lens questions (http://www.vansairforce.com/community/showthread.php?t=106165)

propsync 11-03-2013 03:56 PM

Landing light lens questions
 
Hi Group,

I've read a few threads re landing light lens's but still have a few questions.

First, page 15-08 would have me attach the leading edge of the wing to the spar before page 15-09 has me install the landing light lens. I'm guessing its probably best to do the lens before attaching the leading edge to the spar, do you agree? Is there a reason I should attach the LE to the spar first??:confused:

Next, as far as installing the lens is concerned, Step 1 basically says the following- "Be aware of curled edges on the lens". What are they driving at here?

Then it goes on to say to place the lens on the outside of the leading edge (over the leading edge). I notice right off the bat that it fits over the outside of the LE better one way than it does the other way. I presume I should use the better fit correct? Here are two pics.





And final question, the directions essentially say to trace a line 3/4 inch. What about where the rivets will be, it seems that 3/4" is not an exact enough measurement to take the rib into account? See pic.



As always, thanks for you help!

YellowJacket RV9 11-04-2013 11:38 AM

Work slow and you can trim away more plexi as needed if it doesn't quite fit. It does fit one way better than the other, so use that orientation. Also, use a plexi bit or a dulled drill bit to drill the holes or you risk a crack. I went through 4 lenses before I was happy with the fit; the shape and thickness of the plexi is such that it is REALLY hard to get a snug fit at the very leading edge. Pull the lens in super tight while drilling. I settled for a bit of a gap between lens and the very tip of the LE, but would like them to make a thinner, more flexible lens that would conform to the shape better. The lens on the 172 I fly is about half the thickness, so I know strength isn't an issue. When you're done, don't overtighten the mounting screws or you risk cracking the lens as well (ask me how I know); I probably should have countersunk the plexi a bit more but was concerned about widening the hole and loosening the fit even more. I have no idea what they mean about curled edges, maybe just the way the plexi curls up when cut.

propsync 11-04-2013 12:19 PM

Quote:

Originally Posted by YellowJacket RV9 (Post 822903)
Work slow and you can trim away more plexi as needed if it doesn't quite fit. It does fit one way better than the other, so use that orientation. Also, use a plexi bit or a dulled drill bit to drill the holes or you risk a crack. I went through 4 lenses before I was happy with the fit; the shape and thickness of the plexi is such that it is REALLY hard to get a snug fit at the very leading edge. Pull the lens in super tight while drilling. I settled for a bit of a gap between lens and the very tip of the LE, but would like them to make a thinner, more flexible lens that would conform to the shape better. The lens on the 172 I fly is about half the thickness, so I know strength isn't an issue. When you're done, don't overtighten the mounting screws or you risk cracking the lens as well (ask me how I know); I probably should have countersunk the plexi a bit more but was concerned about widening the hole and loosening the fit even more. I have no idea what they mean about curled edges, maybe just the way the plexi curls up when cut.

Do you know if there is such a bit for dremmels?

Tom023 11-04-2013 02:04 PM

Quote:

Originally Posted by YellowJacket RV9 (Post 822903)
I went through 4 lenses before I was happy with the fit; the shape and thickness of the plexi is such that it is REALLY hard to get a snug fit at the very leading edge. Pull the lens in super tight while drilling. I settled for a bit of a gap between lens and the very tip of the LE, but would like them to make a thinner, more flexible lens that would conform to the shape better.

I'm not at this step so I don't know, but would it be possible to heat the plexiglass with a heat gun while pulling it in to get a good fit? Or perhaps would that damage or make the pleixiglass too brittle?

YellowJacket RV9 11-04-2013 03:47 PM

Quote:

Originally Posted by Tom023 (Post 822953)
I'm not at this step so I don't know, but would it be possible to heat the plexiglass with a heat gun while pulling it in to get a good fit? Or perhaps would that damage or make the pleixiglass too brittle?

That may be a good idea, I may try that. For now the wings are sitting in the cradle mostly done, so I may wait until near the end of the build. For all I know the one for the -14 may fit much better, but I was never 100% satisfied with the fit in the -9.

propsync 11-14-2013 04:55 PM

Hi group,

One of the RV9 builders commented on my log that his duckworth lenses came with a gasket type material to fit between the lense and leading edge. I don't see any mention of this in the plans or inventory that I'm aware of.

I have to believe that even if you get a perfect fit, 200mph water is going to make its way in there without some kind of gasket.

Thoughts?:confused:

rvbuilder2002 11-14-2013 06:18 PM

Quote:

Originally Posted by propsync (Post 822578)
Hi Group,

I've read a few threads re landing light lens's but still have a few questions.

First, page 15-08 would have me attach the leading edge of the wing to the spar before page 15-09 has me install the landing light lens. I'm guessing its probably best to do the lens before attaching the leading edge to the spar, do you agree? Is there a reason I should attach the LE to the spar first??:confused:

Next, as far as installing the lens is concerned, Step 1 basically says the following- "Be aware of curled edges on the lens". What are they driving at here?

Then it goes on to say to place the lens on the outside of the leading edge (over the leading edge). I notice right off the bat that it fits over the outside of the LE better one way than it does the other way. I presume I should use the better fit correct? Here are two pics.





And final question, the directions essentially say to trace a line 3/4 inch. What about where the rivets will be, it seems that 3/4" is not an exact enough measurement to take the rib into account? See pic.



As always, thanks for you help!

Pick up your L.E. assembly and note that it can be twisted along its length. If it is twisted while you fit/drill the lens, the lens wont fit once the L.E. is attached (rigidly) to the spar.

The curl is referring to the left and right edges of the lens, that can get a curl on it during the forming process. Some are worse than others. Lay a straight edge on the surface span wise in a few places and you may be able to see it.

Look at the airfoil shape from the wing tip end. It is not a symmetrical shape, so the lens will only fit properly one way.

Read through the entire process first (highly recommended for the entire airplane build). I think the 3/4 is an initial rough cut that will be finished to a closer fit near the end.

rvbuilder2002 11-14-2013 06:25 PM

Quote:

Originally Posted by YellowJacket RV9 (Post 822903)
I settled for a bit of a gap between lens and the very tip of the LE, but would like them to make a thinner, more flexible lens that would conform to the shape better. The lens on the 172 I fly is about half the thickness, so I know strength isn't an issue. When you're done, don't overtighten the mounting screws or you risk cracking the lens as well (ask me how I know); I probably should have countersunk the plexi a bit more but was concerned about widening the hole and loosening the fit even more. I have no idea what they mean about curled edges, maybe just the way the plexi curls up when cut.

1/16 thick material has been tried. It is much more fragile. Cracks much easier while drilling and machine countersinking. Cracks much easier if screws are over tightened. The only way to have a more flexible lens is to use a different material. The more flexible material would require a lot more screws to keep it laying tight, and it would scratch more easily.

BillL 11-14-2013 07:07 PM

Now might be a good time to invest in some plexi drill bits. I found the grinding instructions to make a plexi bit from a standard one, but decided to buy them from Avery's. They worked great!. I have cracked many pieces of plexi in the past with standard drill bits.

I can send the grinding instructions if you want them. edit: Go to sport aviation.org and the april 2013 issue. there is a picture of the bit, but "original" and "modified" are labeled backwards.

Happy Building!

http://www.bertram31.com/proj/tips/drill_acrylic.htm

propsync 11-14-2013 08:52 PM

Quote:

Originally Posted by propsync (Post 826161)
Hi group,

One of the RV9 builders commented on my log that his duckworth lenses came with a gasket type material to fit between the lense and leading edge. I don't see any mention of this in the plans or inventory that I'm aware of.

I have to believe that even if you get a perfect fit, 200mph water is going to make its way in there without some kind of gasket.

Thoughts?:confused:

Any comments on a gasket? That's why I revived the thread.


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