Hi there everyone

I've just taken over a Himax build which is about 90% complete but needs one of the wings to be finished off.

I'm at the stage of putting the leading edge plywood on and was after some advice on getting good even contact along the nose ribs. In the photo's you can see there is some gaps around the nose rib with the ply held in place.

What have you guys used?

Thanks in advance

Mick

Hi
Just this week I did the three pieces of leading edge on a Max wing so my experience is quite recent.  If you were reasonably comfortable with all of the nose pieces being the same when someone made them, I would not lose too much sleep at this point.  Focus instead on getting the leading edge piece to lie properly on the two end nose ribs, with those two nose ribs, you can glue and then staple sequentially from one spar around to the other spar, and in doing it in sequence, you will see that you can make a lot of the "gap" you are concerned about, go away, it is gap that can be hard to just pull away with bungees.  Along the way, a fair amount of effort has to be brought to bear with bungees or some other method to pull the leading edge sheet as tight as is possible, but get that all figured out ahead of the glueing and stapling and it should go along well.  A quick down and dirty series of steps could be as follows:
1. clamp leading edge sheet to either of the spars as close as you can to what will be its final position
2. do the bungee thing to get the sheet fully curved to the point it sits on the other spar in pretty nearly the correct spot
3. pencil mark a line along the first spar showing where the sheet is to lie, then remove the sheet and apply glue
4. clamp and then staple the first edge of the sheet on the pencil line
5. you can either wait overnight for this glue line to dry or not, the staples, every inch or so, will hold a ton of pulling so I would not worry about it letting go
6. do the bungee thing as tightly as you can, and then mark where the glue line should be on the other spar
7. release the bungees, and glue appropriately, for both the nose ribs and the other spar line
8. do the bungee thing shooting at the pencil line, but just temporarily clamp that line
9. then start at the first spar line and staple around the nose ribs at each end of the sheet you are installing, and while doing, make sure one edge butts nicely against the sheet you had already installed and the other edge of the sheet stays on the doubled nose rib for gluing purposes.
10. I think you will find that doing it this way eliminates the gap problem you were inquiring about.  As  you are stapling the nose ribs, you might find that the temporary clamping you had put in place on the second spar needs to be tightened/adjusted, as you have actually gained a small part of an inch, maybe an eighth or so.  It won't be much but it won't be much to get rid of that small gap(s) in your photos.
Hope this helped.
Kim Brown
New Hampshire

I am almost at the stage you are in my build. I plan on wetting the plywood and prebending it, then simply stapling it to the ribs at the 1/4" doublers. If you were to "take apart" a typical max, this would probally be a typically issue of getting a good joint at the 1/8" nose ribs. most of the wing twisting is takin up by the struts. skypup had a leading edge d cell made of 1/32" plywood to resist twisting, luckily the center of lift landed right on the spar.  

Gaps can also arise if the ply has not been pre-bent adequately.
Pre-bending the ply’s leading edge a bit more could help. ( ie bending it slightly more acutely at the front edge )

For the wrapping process, I used gorilla tape instead of rubber bands.
After gluing /stapling the ply to top spar cap ( make sure ply is square before stapling ) I stuck gorilla tape to top spar cap along each nose-rib, and used the tape, which is plenty strong, to pull and wrap the ply to the bottom spar cap.
After you are sure there are no gaps, staple the ply to bottom spar cap, and then staple along all other glue joints.

There are many ways to do this, so I guess any technique is right if you are satisfied with the end result.

The plans take up almost half.a page discussing how to glue the leading edge ply to the nose ribs, my guess is people have trouble with this step

  Don't worry about a few gaps. I went and looked at my wings, and I have gaps. Not as bad as  your picture, but if you follow the above recommendations you should be fine. The primary purpose of the nose ribs is to give the proper shape to the leading edge. The purpose of the plywood is to makes a smooth transition from the leading edge to the front spar. The strength of the "D" tube comes from the plywood being attached to the spar caps. My Max has several hundred hours over 20+ years and it's OK. My Max is home in the garage, and the wings are off, so I was able to look in the root with a flashlight. In a perfect world (airplane) we would like to have 100% contact, and glue, over every rib, but it's not necessary.
  Now I expect that someone is going to suggest that my assessment of the problem is all wrong, and I'm OK with that. It's just my opinion.

Greg, I feel  you are absolutely right. A few tiny gaps along the nose ribs, should not cause concern, as long as the ply is properly glued to to top and bottom spar caps and also to the RS4 stringer in front. Also the nose rib’s primary job may be to hold the RS4 in place to prevent compressive loads from buckling the plywood.

Thanks for all the reply's. The picture I showed was just after I had bent the ply around the ribs. I had soaked the ply in our bath for a hour or so prior to bending and after it has dried out the gaps have reduced slightly.

I appreciate the comments about gluing and stapling to the top spar cap first as I hadn't realized that. The cable ties worked ok during the pre bending stage but I'm thinking of using small ratchet straps just to get some more control.

I'll post up how I go.

Cheers, Mick

If I recall correctly from about 5 years ago. I soaked and pre-bent the ply as suggested. I test fitted the pieces and made reference lines to line the wrap up with the stringer at the nose of the ribs. (The photo in the post(s) below with the white straps and blue clamps is the test fit) I used a combination of sticks and rubber bands to get initial tension when doing the final assembly, but also employed ratchet straps near each rib going to the rear spar. I was careful to not go overboard when tightening the ratchet straps since getting ham-fisted with the ratchets could quickly crush the wing!!!! The straps were run over thin plastic strips to keep any glue squeeze-out from gluing the straps to the leading edge and spar caps. (The photo in the post(s) below with the rubberbands and red straps is final gluing assembly) The first thing stapled was the leading edge/stringer lining it up with the previously made reference/line-up marks. Then the rubberbands and ratchet straps were tightened to pull the leading edge into place. Stapling was done from the center out in all locations to prevent bulges and low spots in the leading edge contact points as well as assuring a smooth, consistent radius on the leading edge.

Thought I'd just throw out my best recollection of what I did. I hope it offers some useable ideas. I won't pretend my leading edges turned out perfect, but I was pleased with the results.

Lynn

Test Fit.

Final Assembly

Another - Final Assembly

Quoted from lake_harley

Stapling was done from the center out in all locations to prevent bulges and low spots in the leading edge contact points as well as assuring a smooth, consistent radius on the leading edge.
Lynn

Very good advice.  Also, one might let the epoxy go a little green, there will be less squeezed out, less mess and better gap filling.

Go ahead and spill the beans, how did you know I was gonna use ratchet straps.to glue my leadin  edge. What are you a weirdo or something?

Thanks for the info and photos Lynn. My thoughts were also to use the tie downs at the points where the ribs are as well.

One more question, what varnish have people used for the inside of the leading edge ply (plus the rest of the wing). I saw a post from gyrojeffro showing what looked like a fairly general purpose spray on Polyurethane Varnish. I was looking at a Marine Polyurethane Varnish from our local hardware shop.

Cheers, Mick

Nice looking assembly. Is there anything between (connecting) the nose ribs and leading edge skin (epoxy or other glue) or do they support in a free manner?  What are you using between the ratchet straps to pull on the leading edge (rubber bands or just pulled/tightened string)?

Nice looking assembly. Is there anything between (connecting) the nose ribs and leading edge skin (epoxy or other glue) or do they support in a free manner?  What are you using between the ratchet straps to pull on the leading edge (rubber bands or just pulled/tightened string)?

Opinion on coating (varnish) will vary, but I used exterior, marine spar varnish. I marked out the contact pattern of all structural members, ribs, spars and stringer on the "inside" of the leading edge plywood. I allowed about 1/4" extra clearance of non-varnished area on either side of contact to be on the safe side. When the T-88 was applied I made sure the entire non-varnished area was coated with epoxy to be sure all surfaces were sealed.

Lynn

The last 2 days I've been busy with the leading edge work. I went ahead a got some ratchet straps which have made some difference to getting the ply to contact the ribs more evenly.

Santa got me some nice Dremmel accessories which have been a great help in trimming the ply for final fitment.

I finished second coat of varnish today so will be looking at final install and gluing in the next day or so.

Cheers, Mick

Finished fitting the leading edge sections. I'm happy with the final result.

Thanks for all the input and advise.

Offshore for work for the next couple of weeks then back into it.

Cheers, Mick