rkcruit

I have a question re: the SIg 1/5 scale J-3 cub's wing assembly. I am having trouble determining the correct orientation of the balsa leading edge.
This is the piece that is sort of triangular shaped with a rounded front edge and is glued to the front of the ribs. The documentation says it is not symmetrical and to compare it to the cross section diagram on the plans. For the life of me (and my old eyes don't help much either) I can't see any difference. Any good ideas on the proper alignment?

Thanks in advance for any help.
Robert

Zor

Hello Robert,

You can use some hard material like 1/16" or 1/8" thick solid plastic and cut it to the shape of the drawing outline of the wing or rib. Make it so that it can sit on the bottom surface of the wing long enough to be consistent (may be 2" to 4" depending on the length of the wing chord).

That becomes a gauge you can use to finish shaping the leading edge.

Note that the leading edge shape is not terribly important becasuse air separation takes place ahead of the leading edge.

Zor

KitBuilder

I think he's not sure which side is up and which is down.. but not sure about that ...

The LE when looking at the cross section should show an angle down from the top curving around the front to a flat bottom for the cub.

If you hold the front of rib to to the backside of the shaped LE piece..... you will clearly see which way its supposed to go. The balsa LE should transition from the top of the rib smoothly as well as the bottom of the rib. If the LE is upside down you will probably notice the very front of the LE angled up from the bottom moving forward to the very front of it.

rkcruit

Thanks Zor and Mike for the tips. Mike, based on your description (and some new glasses), I can see the correct way the leading edge needs to fit.

Robert
Winter Haven, FL

Zor

It now appears that what you referred to as sort of triangular is really a pre-shaped leading edge.

Glad you got it sorted out.

Zor

KitBuilder

If you can... maybe you can post a pic to be sure we're all on the same page...

rkcruit

After looking at my wing again this moring (re: the pre-shapped leading edge), I am still having 2nd thoughts concerning correct orientation. I am including pics of the piece of balsa and the fit to the front of the rib. I'm not trying to be picky, but the SIG instruction manual clearly states that the builder should be completely sure that the piece is right side up. My guess is that it may affect the alignment of the top and bottomsheeting which is installed next.
Thanks.

SunDevilPilot

I built the same plane many years ago and vaguely remember that step. If I recall correctly the part is installed with the more aggressive rounding at the bottom, which appears to be the way you have it. Remember, the wing is flat bottom so the bottom edge of the leading edge needs to be slightly rounder than the top.SunDevilPilot

Zor

rkcruit,

Another example that a picture is worth one thousand words.

We now see why you referred to this leading edge as being trianglular.

Now take the following for whatever you feel it is worth to you.

The front of that leading edge appears to be an arc of a circle and does not have any variation in the radius of the curve. It means that there is no up or down. It does not matter in which orientation it is installed.
After the sheeting is on you will have to sand anyway to match (smooth) the ouside surface and perhaps fill tiny fissures beween the sheeting and leading edge piece.

Sometime the leading edge piece has a variable radius in its cross section and orientation is important.
What I think has happened in this case is that manuals are written by different people and often many paragraph are just copied over to a new manual and their insructions migh not be appropiate for the new manual to the model.

I would simply disregard the manual instructions in this case.

Zor

bikerbc

If you have two pieces ,( one for each wing) put them end to end to see if there is in fact any difference in the shape depending on orentaion.....you could figure out which way is up that way..or draw the end pattern on a piece of paper and turn it over ...It is hard to tell from the pics but it dosent look like it would matter which way it went .

Zor

I reached the same conclusion looking at the pictures as I mentioned in the previous posting.

Zor

rkcruit

My thanks to everyone for their comments re: my problem. As was suggested,I mounted the leading edge (assuming thatthe orientation didn't really matter)as well as the top and bottomsheeting and it looks exactly right according to the plans.

Great support on this forum!

Robert

Zor

All together now ___\
HIP ...HIP ... Hoorah .... nice job Robert

Zor

Zor

Pictures Robert ?

Zor

rkcruit

I've finally been able to make some progress on my plane, specifically the right wing, aileron, and wingtip. This build has been a bit more tedious than the small balsa models I made as a kid. I have read numerous posts on this forum from people concerned with the level of skill/expertise needed to successfully build this model. One tip that I can pass on is to read the Sig instruction booklet in its entirety. Don't skip paragraphs, dont skip sentences, and don't skip any words. Read and fully understand each step. Everyone's heard the phrase, "Measure twice and cut once."These are wisewords to follow because after you hit your joint with CA, it ain't comin' off. Also, when it's late at night and I'm getting tired, mental mistakes start creeping in, no matter how carefulI try to be. Give it up for the night and go watch television.And yes, Iam actually admittingthat I haveglued two of my fingers together (it happened LATE last night). I guess I'm part of the club now.

Tomorrow I plan on attaching the wing tip. I triedfor a short whilethis evening but itkept getting the best of me. Just looks so darn crooked.

Imade thedecisiontobuildthe clip wing versionso I can do something other thanstraight and level flying.I understand the limitations of this model, so every bit helps. I'm also mounting a Saito .72 up front so I should have a nice power reserve in case I need to get out of a tight spot. I think I read a post somewhere herethat said rolls in a cub can be measured with a calender. Maybe I can do a little better than that.