Dimples in leading edge

[CHARLES DEBOER]

Any help on fixing dimples on the leading edge.  First wing no dimples.  Second wing five dimples as big as my palm.  Uggly!!

[rfeenstra]

I had no dimples when I built.  Some minor dimples after I covered.  Major dimples all along the wing after it set out in high humidity for awhile even though the wood was sealed with 2 coats of sealer. I guess it is what it is.

Rob

[Jerry Carter]

I have the same issue.  I may try to glue in some additional nose ribs, like those made of lexan that Sam did, going through the lightening holds to try to push the dimples out. Maybe somebody has a better idea.....

[Sam Buchanan]

I have the same issue.  I may try to glue in some additional nose ribs, like those made of lexan that Sam did, going through the lightening holds to try to push the dimples out. Maybe somebody has a better idea.....

Not lexan.......luan mahagoney ply (doorskins).

[Jerry Carter]

Not lexan.......luan mahagoney ply (doorskins).

Ah, thanks.

[CHARLES DEBOER]

Thanks guys, I do have some laun laying around.  I'll give it a try.

[Tom H]

We had the same problem on our LEU wings after our Ohio Valley humidity went to work.  I made some false nose ribs with 2" thick blue foam, then cut the false ribs into three pieces, the center piece a wedge shape, each small enough to fit through the lightening holes in the spar.   Then applied some quick set epoxy and assembled the pieces where they needed to go, and forced the wedge shaped piece to push the other two pieces to eliminate the dimples.  Held in place until epoxy set. 

It worked OK, but would not be useable in the sections with no lightening holes.

Later, when we built the DE, we put in one false nose rib (thin luaun plywood) between the plans located nose ribs.  This helped a bunch, but we still got some slight dimpling in a couple spots.  If I ever built another wing, I think I would go with two false ribs in each bay, maybe made of 1/2" blue foam.  Strong enough, but as light as possible.

[hawkaleuge]

I built 3 leading edges, 2 original and 1 rebuild after a prop strike.  I never had dimples.  Leonard never had dimples either.  We both live near Houston - translates to high humidity all the time.  I rolled my leading edge ply and stored it in a 4 in pvc pipe open ends until I used it.  Maybe you could put the ply in a humidor of sorts to get the moisture content up before you glue it on.  This makes the wood at maximum expansion when it's locked down if it dries from there is shrinks.  
I have heard of riveting al skins on at elevated temps and this made a tighter skin after installation.  Seems it would be the same for wood.

Anyone else in high humidity places have dimples,  Rockydog, Judge?

Ed L.

[CHARLES DEBOER]

I believe you are correct.  The first wing I built which had no dimples was completed in the month of February.  Here in California that is the wettest month of the year and most humid (by calif. standards)  no dimples and the second was completed in July (very dry month) five dimps as large as the palm of my hand.  I am trying a repair method suggested by Tom H. below.  see pics attached.  So far I have had a fair amount of success.

[Sparetime]

Tom,
Could you estimate the total amount of added weight of the two false ribs made of blue foam for the entire wing?

Thanks,
Jim


We had the same problem on our LEU wings after our Ohio Valley humidity went to work.  I made some false nose ribs with 2" thick blue foam, then cut the false ribs into three pieces, the center piece a wedge shape, each small enough to fit through the lightening holes in the spar.   Then applied some quick set epoxy and assembled the pieces where they needed to go, and forced the wedge shaped piece to push the other two pieces to eliminate the dimples.  Held in place until epoxy set.  

It worked OK, but would not be useable in the sections with no lightening holes.

Later, when we built the DE, we put in one false nose rib (thin luaun plywood) between the plans located nose ribs.  This helped a bunch, but we still got some slight dimpling in a couple spots.  If I ever built another wing, I think I would go with two false ribs in each bay, maybe made of 1/2" blue foam.  Strong enough, but as light as possible.

[Tom H]

Sparetime, the DE plans show a false rib of plywood in the nose between each real rib to support the leading edge.  This did a pretty good job, but we still have some shallow dimples.  If two false ribs made of 1/2" blue foam were used in place of the plywood false rib, the weight would not change much, I don't think.  But, the leading edge would be better supported to resist dimpling.  The DE has 11 bays.

The LE has 9 bays between ribs, but plans do not call for any false ribs.  If one added some false foam ribs between the real ribs in the nose, then that would be added weight.  I found a density number of about 1.5 pounds/cu ft (1.5 lbs/1728 cu in) for the insulating type foam sheets.  If using two false ribs per bay, the LE would need 36 false ribs.  A real rough estimation is each rib, with a center lightening hole, would have about 20 sq inches of area, and 1/2" thick would be 10 cu in per rib, times 36 = 360 cu inches of false ribs.  Multiplying all of this: 1.5 cu in/1728 cu in X 360 cu in = 0.3 lbs total weight for the ribs, maybe 0.5 lbs by the time you glue them in.

Is this weight gain too much to pay for no dimples?  Your call.

I don't know about the LEXL construction, false ribs, # of bays, so can't estimate.

[Bob S.]

Removing dimples start with pre-curling and the way you put the ply on the ribs/spars...

I cut my ply to length and width +/- and put in a 6" PVC pipe when I started the wing....then when I needed it for the wing it had a real good curl built in... As Leonard described, I put small nails in the spar and removed the heads to hold one side (top) and pulled the ply over to the bottom. used a number of bungies, rubber bands, and cargo-ratchet straps to pull and hold the ply to the wing assy. Rub and stretch the ply down continuously smoothing out the dimples as you go while the glue drys...I didn't put nails on the bottom only the top.... SOME places you may have to put strips of 1/4" between the bungie/rubber bands and the ply to help hold it down too...

Some dimples won't be any issues in the fly-ability of the Eagles....

[Dan_]

Do like Leonard and Bob said, but unless you live in Houston or San Antonio, add moisture to the plywood with wet paper towels before you epoxy it on.  


T-88 is not affected by it...  Google it.  


West Epoxy was designed for boats.  Google it.  


The point being, if you attach the plywood when it is as damp as it will ever be, it can only tighten when the wood dries out thus no dimples, and no added weight...

[Dan_]

Here is a post from the Flitzer builders Yahoo group from August 2011 on pre-soaking leading edge plywood before attaching it to the wing ribs...

If one were really anal about it you could fit the piece and mark the inside where the glue line will be for each nose rib, then apply a coat of epoxy there and let it set up before wetting the wood with the water.
This will assure deep penetration of the epoxy, then you would soak it and sand said glue line before adding the bonding coat of epoxy.  You must sand and flush the pre-applied area with distilled water.  The sanding activates the already bonded epoxy and the distilled water flushes the unwanted sanding particles.

 
 
  

•   morrisoff@aol.com  
• Aug 28, 2011

 To

• Flitzer-Builders@yahoogroups.com

 
 
 
 
 Ronnie - That could look fabulous!


But before going full-speed ahead one should realize that even 1mm ply is not completely malleable, and it doesn't like compound curves. You might find a few in that fin.



So first, I would "cover" one side with art card and see if it will do it without wrinkling. If it wrinkles, see how much, and then explore whether the plywood can be formed accordingly. I suspect it can, much as I made my plywood wingtip leading edges. Sometimes a heat gun can be used judiciously as a persuader. I will look up the photos and post them.



You can apply T--88 to wet plywood. I applied all mine wet, and covered it with hot, steaming towels as the glue initially set. I even laid the plywood on the bench on hot steaming towels while gluing, to minimize evaporation. The only stipulation from System Three is that the glue be well worked into the wet gluing area with more energy than otherwise needed.



And yes, I presealed the interior areas between the glue lines. This shouldn't be too exact, as one can also use the glue for sealing the bits you missed. In other words, if you are too exact, you risk getting sealant instead of glue in the join.



When the plywood goes on wet, it should dry as tight as a drum no matter what the outside weather or humidity. To wet it, I soaked it in hot water in the bath for a couple of hours. Even preformed plywood can be wetted again without unshaping.



I would be inclined to do both sides of the fin in at least the same day or so. A lot depends on whether you are using stapling strips - I can just imagine trying to wrestle two sides of slippery, sliding plywood that won't stay put while you're trying to get clamps on! You could use the staple strips just along just finpost - that would locate the ply positively enough for clamping. But can you keep the clamps on that shaped leading edge? Might it be easier to do the sides separately, starting with one side, glue just the leading edge and let it set up before glueing the rest of that side?



The appearance of the feathering of that leading edge will be crucial to the finished look of the airplane. That's why I might glue it first, stapling the ply to the leading edge to keep it flat and conforming. The staple holes hardly show at all after the staples are removed. (I used a total of 9,000 staples in the Morrisov machine!)



At Miles Aircraft, they said you could tell a summer-built from a winter-built aircraft. The summer ones were invariably more wrinkled, because the winter ones had the wood go on damper and moister (the company couldn't afford climate control, or even proper heating, for the factory, so the moisture content of the plywood varied according to season).



There is a wonderful thread on building Albatri on the Airdrome forum (www.theairdrome.com), but you have to join to see the photos. If you do, then check out



http://www.theaerodrome.com/forum/replica-aircraft/35610-albatros-d-ii-d-iii-news.html



to see how the masters make Albatros fuselages and plywood covered fins. I found it very inspiring!



I'll get to those photos later.



Prost! - Ivan



Baron Ivan Morrisov

Connecticut Flitzer Werke

[Bob S.]

Do like Leonard and Bob said, but unless you live in Houston or San Antonio, add moisture to the plywood with wet paper towels before you epoxy it on.  


T-88 is not affected by it...  Google it.  


West Epoxy was designed for boats.  Google it.  


The point being, if you attach the plywood when it is as damp as it will ever be, it can only tighten when the wood dries out thus no dimples, and no added weight...

I would agree here, that you can put some hot/wet towels where you have a possible dimple and help stretch the ply around the curve.. why not? Wetting the outside makes it swell a bit and the outside IS the longer dimension of the parabola's circumference... That would only help bending around the LE.... But I didn't need to on LE 64H/Got 'er Done!