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Lowrider LSA

As scary as it may sound, but...perhaps my little pea brain was hearing your thoughts...First thing this morning I measured, marked and was getting ready to cut skin and it became apparent that I didn't have very much left in the piece after I cut out the access holes. I soon realized this was a bad idea so I made a command decision and grabbed a broom and swept up a bit of the shop. When I got done I looked at the layout of holes in the skin and it was clear that this was wrong so I'm going with one piece of 0.032 with no holes.

Thanks for the thoughts wherever they came from...and people think it's wrong to listen to the voices.

I have a light weight bar and that's just as bad...#2 son is coming over this afternoon so he can buck these rivets.
 
That first bay does a lot structurally. As nice as it would be to have access there for fuel fittings, I don't think it's a good idea structurally to install those access panels. Opinion.

As scary as it may sound, but...perhaps my little pea brain was hearing your thoughts...First thing this morning I measured, marked and was getting ready to cut skin and it became apparent that I didn't have very much left in the piece after I cut out the access holes. I soon realized this was a bad idea so I made a command decision and grabbed a broom and swept up a bit of the shop. When I got done I looked at the layout of holes in the skin and it was clear that this was wrong so I'm going with one piece of 0.032 with no holes.
While it may not be suitable in this application, it is permissible to make structural access panels. Some may only be a small round opening while others could be a long narrow panel with a gazillion screws. It does require the proper reinforcement, fastener type and spacing.
 
Thanks Sky!

I can access the area from above if need be or from inside...just thought it would be nice to have holes on the bottom too.

How'sthe weather back East? I have about 11" and counting.
 
My little side-by-side 80hp Carlson winged lsa will do 130mph with pulled rivets and 8.00's. That's as fast as I want to go with flat unbalanced tail surfaces. It's only got 20 degrees of flap, but that's enough to get the landing below 40. Doesn't flush riveting require heavier skins? With real extruded spar these are more like "metallized" wings to use a term from the 1950's. The rivets aren't loaded anything like an RV. Wing loading is less, too. An Avex won't shear as the steel shank stays in place. I don't think brownbear's test is valid, sort of ripping,not pure shear. The only place where the rivets have any pull on them would be going thru the skins into the ribs, and there the thickness of the rib flange would be the limiting factor. If you're nervous there, closing up the spacing a little probably wouldn't weigh more than the skin savings.
 
Thanks Sky!

I can access the area from above if need be or from inside...just thought it would be nice to have holes on the bottom too.

How'sthe weather back East? I have about 11" and counting.
We had a nice freeze early then it thawed with open patches of water. Never was enough to walk on. Only one storm of about 10" which is all gone with a forecast of 56* next Wednesday. Unless we get a good freeze in the next few weeks, there will be no flying until spring.

Doesn't flush riveting require heavier skins?
Generally countersink for flush rivets with .040" or greater. Below that thickness the holes are dimpled for flush riveting. The shear strength is actually a bit greater with the dimples.
 
Spent the afternoon shoveling snow and running the tractor...no riveting. I'm seriously considering doing the prop blast area (first 4') with 426 - 3 at 1.5" and the rest of the wing with pulled rivets at 1". Skin is upgraded one size from drawings and I really don't think it'll be an issue. There are a bunch of aerobatic planes being built with pulled rivets...the Panther for one that cruises at 150+ and they seem to stay together just fine.

Thoughts please.
 
Winter is still here...12" more snow and an 11 hour power outage which is very rare. Shop dropped to 47F and was dark until 1100 Local.

Question for you metal wing experts...Trying to remember how I did this for my RV4 build but that was almost 20 years ago. Starting at the wing root working outward I believe the laps on the skin are made by slipping the next outboard skin under the one closest to the root, and so on. Sound correct? I'm doing a 1.5 inch overlap with 2 rows of 426 rivets with the 0.025 2924T3 dimpled.
 
On the Bearhawk, Bob prefers the other order but says either is fine. He specifies one inch overlap with two rows of 426-4 rivets except single row with 5/8" overlap at the outer skin.
 
Starting at the wing root working outward I believe the laps on the skin are made by slipping the next outboard skin under the one closest to the root, and so on. Sound correct? I'm doing a 1.5 inch overlap with 2 rows of 426 rivets with the 0.025 2924T3 dimpled.
On the Bearhawk, Bob prefers the other order but says either is fine. He specifies one inch overlap with two rows of 426-4 rivets except single row with 5/8" overlap at the outer skin.
How do you get both rows on the rib or does that matter?
Low, You will get a better fit since you are starting at the root end by placing your first sheet down tight first. Then the next sheet over the first and so on. If you try to slide your next sheet under the first your fit will likely not be tight with the possibility of some small puckers in the metal when it is riveted. Sheet metal is not nearly as flexible as fabric when covering. ;-)

As I understand it your wing has one lift strut. That means that the wing skins must assume all of the structural torsion loads.

Since he suggests two rows of rivets at each sheet joint, that implies that the two sheets are being structurally joined and not just a covering for the wing. The rib would not need both rows, just one to hold it in place. Since the last sheet would have minimal torsion loads, one row of rivets would suffice.

Take a look in AC 43.13 for some skin splice pictures.
 
Sky,

That makes sense to lap over top. I was going to check the RV site and refresh my memory but 43.13 is a better source for sure. I did the RV wing set between 2 post standing up and not flat on a table...seems like a better way from an ease of access standpoint. I'm having some issues getting square with no twist. Once I get things right I will put the bottom skin on. I'm using a laser level so it is easy to get it set up but clamping in place is not simple.

I'll follow 43.13 for laps. Dimpling a 48" sheet is a bear.

Average Feb snow is 8.7" in La Nina years and we have 41" so far. Come on Spring!!
 
Wing Skins

Low,
Are you buying prebent skins or bending your own?

There are two very important things for you to keep in mind when assembling the wings. Make absolutely certain that the twist in each wing is exactly the same.
The other is that the leading edge radius is correct for the airfoil and is accurate on all of the skins. AND that it is the same on both wings.

A trick. After the leading edge radius is formed accurately, form a slight curve in the opposite direction (away from the wing rib curve) in the remainder of the sheet. This will force the skin to sit tight against the rib when you drill and fasten it, thus eliminating puckers between the rivets. Work from the leading edge aft.

IF both leading edges are not exactly the same and to the proper airfoil contour, the performance will not be what you expect. It could be better or more likely it could be worse. One wing may fall off in a stall or the other wing may drop first. It may have a benign stall or it may be abrupt and scary. I flew many different versions of the same model production airplane with a tapered wing. Some of them would stall to the left, some would stall to the right. Some were superb low speed short takeoff performers, others were outright dogs. It was later learned that the cause was a production error. The radius of the leading edge varied from wing to wing. Once the manufacturer started verifying the leading edge with special tooling, the irregularities disappeared.

Dimple with light taps of the rivet gun after all holes are drilled. Not a big deal.
 
Bending my own. I understand the need for matching wings and will do my best to make it so.

Last sentence...does that mean "dimple with the rivet"...never done that. I'll practice on some scrap. Is there a trick?
 
No not dimple with a rivet. That's possible but tedious and can get away from you. A tool such as these:
http://www.aircraft-tool.com/shop/search.aspx
I have the top round one. You also need a dimple/die set for each size rivet which you expect to use. These dimple/dies also fit in a hand squeezer. It just takes a light tap to accomplish the mission. Don't over do it.

Make sure that the rivet gun is held perpendicular to the skin in order to prevent smiley faces. Practice on scrap.
 
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Your link didn't work but I think I have what you're talking about. A heavy round thing with the female die that goes under the sheet and a smaller one that takes the male die. Whack the small one and it sets the dimple. I also have the long arm one that is table mounted but won't reach more than maybe 18".
 
Yes Sir...same ones I have. They work well but are slow and they must be exactly perpendicular to the sheet for good results. Thanks for reminding me!!
 
Alright, frustration set in today with trying to set up my wing on the table. If I get the front spar right the there is a twist somewhere and I can't find it....I give up after hours of fooling with it. I took off for Home Depot (with a not so quick stop for fried indian bread, a bowl of clam chowder and giant (1lb) pastrami on fried sour dough sandwich) and picked up two 4x4x8', six 2x4x8' and piece of 1 1/2" PVC to suck down the nose bends. I'm going to stand up the wing between the 4x's and plumb and square it so I can get the damn thing correct. I used this method for my RV 4 wings and they turned out just fine. After all, how hard can a straight wing be to skin anyway! I think by using the 3 direction at once laser level it should be pretty much a simple process setting it up properly and locking it in place. We'll see...suggestions?
 
I got my frame work up to suspend the wing. It's cross braced and very solid. just waiting for a couple little things to get done before hang the wing. Ihave painting to do on steel parts before I start skinning.

I did use the "vacuum bend" method to get the nose bend done on the first piece of skin. It worked great and I learned that my 5 hp shop vac is just a little too much suck for this method. It took about 12 nano seconds for it to go from the "looped" skin to the skin hugging the 1.5" PVC tightly. My first thought was oooops, I ruined the skin but when I removed all the tape and plastic and the PVC the 0.025 2024T3 sprang back to an appropriate bend and no indication of being any worse for the experience. I have a 1.5hp vacuum that I'll try on the next piece...the big one scared me! Just a word to the wise.
 
I have my tank straps primed and ready for paint. I planned to use anti-chafe tape between the straps and the tank but what I have is 1" and the straps are 1" and I wanted an overlap on the straps so it they shifted in turbulence or another reason the edge of the strap would not be in contact with the aluminum tank. I suppose most anything that would isolate the strap like inner tube rubber would suffice. Anybody have any ideas?
 
Sky,

That was the plan but I am concerned that the edge of the strap could rub on the tank.

Marcus,

That looks like a better solution than the cloth tape. I searched ACS but I think I was looking for anti-chafe and didn't see the rubber strap material...gotta be specific on searches! Thanks!
 
I just used a strip of thin felt glued to the straps. It won't move and it's unlikely that there will be movement between the tank and straps. Emphasis on unlikely, not impossible.
 
Maybe I'm over thinking this again, but I was interested in having a soft "skid proof" material between the tank and the straps. That's why I was thinking inner tube rubber or something similar. I would have thought felt would wear thru quickly, but I guess if the tank can't move it won't matter so much.
 
We got the wing hung on the posts and it is Straight, square and plumb and the whole thing is rock solid. I'll start tomorrow to get the first piece of skin set up and ready to start drilling holes. I'm going to use the same straps that I used on my RV-4 wings and see how that works out. The wing contour is way different but it should work with a little tweaking or whatever it takes. Feels really good to get to this point if only with one wing...it's progress...now we'll see if I can buck rivets.
 
Today's progress:

wing hung 005.jpg
Now, to take it apart and dimple. I did get assistance from my wife...she cleco'd and I drilled...went much faster but it didn't come without a price...lunch tomorrow at Mick Duffs...oh well...they have the best calamari in town!


wing hung 005.jpg
 

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Looking good Low, Do you have a mushroom rivet set? http://www.cleavelandtool.com/1-Mushroom-Set/productinfo/RSM10/#.WK7L3tJViko
You should use one for your flush rivets on the skins. Some of the rivets on the nose ribs look as though you used too much pressure with the set in relation to the rib. There are some dimples around the rivets. Look at the second and fourth nose ribs outboard of the leading edge skin. You don't want this on your nice smooth skins.
 
Thanks Sky!

There are no rivets in there yet. It may be some clecos I put in from the back that makes it look that way. That's 0.025 2024-T3 and it is hard to make that nose rib bend even with it pre-bent with the vacuum. The rest of the skin will be 0.020 so it should be a little easier but also easier to put "smiles" on the skin.

I do have a mushroom set with the rubber around the edges. I'm planning to back-rivet in those areas where I can. I made a 2" round brass bucking bar that works really well for that. It gets beat up some but I just put it in the lathe and "freshen it up" a bit.
 
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