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Wings, metal leading edge or no

60 posts in this topic

Posted

The alternative to aluminum is Larch marine ply. Here's a quote from a previous post in this thread:

As for the aluminum leading edge top skins, sure there are aerodynamic benefits but, at HH speeds, does it really matter? I've read sooo many disgruntled owners wishing they hadn't done it, certainly many more than opined they wish they had. Once the aluminum is dented you are s-c-r-e-w-e-d until you re-cover the wings. I suppose you could always cut in an inspection ring below and have a go at it, but I question if you would ever be able to get it to be un-noticable again. I would surely go with the assumption that it's a 'when, not if' proposition that the aluminum would get dented somehow.

For the most part, I tend to listen to those that have the experience so I am using 1/32" thick epoxy varnished larch marine ply on my current long spar Avid+ Speed wing build. A local builder here did that on her Avid C model Speed wing and not only does it look great, it definitely will a good knock without a problem. And, I'm talking about a -HARD!- knock, the kind that'll hurt your knuckle. She also used one thin layer of PolyFiber polyester padding over the ply and also the wing tanks, for both chaff protection and to avoid having to Bondo, Super-Fil and sand the f/g wrapping around the tanks smooth. Sure seems superior to me.

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Posted (edited)

The alternative to aluminum is Larch marine ply. Here's a quote from a previous post in this thread:

As for the aluminum leading edge top skins, sure there are aerodynamic benefits but, at HH speeds, does it really matter? I've read sooo many disgruntled owners wishing they hadn't done it, certainly many more than opined they wish they had. Once the aluminum is dented you are s-c-r-e-w-e-d until you re-cover the wings. I suppose you could always cut in an inspection ring below and have a go at it, but I question if you would ever be able to get it to be un-noticable again. I would surely go with the assumption that it's a 'when, not if' proposition that the aluminum would get dented somehow.

For the most part, I tend to listen to those that have the experience so I am using 1/32" thick epoxy varnished larch marine ply on my current long spar Avid+ Speed wing build. A local builder here did that on her Avid C model Speed wing and not only does it look great, it definitely will a good knock without a problem. And, I'm talking about a -HARD!- knock, the kind that'll hurt your knuckle. She also used one thin layer of PolyFiber polyester padding over the ply and also the wing tanks, for both chaff protection and to avoid having to Bondo, Super-Fil and sand the f/g wrapping around the tanks smooth. Sure seems superior to me.

About the same as my 1mm (,040") Finland plywood from Spruce - Came packaged in 2' x 4' sheets, and I cut it to 1' for top and bottom of  4" extended leading edges.

EDMO

Edited by EDMO

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Posted

Where are you guys getting the plywood from. Also is this something you wrap all the way around the leading edge and also attach to the bottom of the rib Or does it stop at the plastic leading edge.

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Posted (edited)

I got mine from Spruce.  It stops near the top of the spar - I put it on top and bottom to extend leading edge.

You could probably get by with Three 8" pieces out of each 2'x4' sheet.

EDMO

 

Edited by EDMO

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Posted

I got mine from the local lumber yard, same place I got my floorboards. They tend to stock specialty stuff the big box stores won't have. Just make sure you get a marine quality ply that has no voids in the plies. The sheeting is applied on top of the wing only, from the front spar aft. It is important that the leading edge of the ply is smoothly faired to the spar, you should not be able to feel the transition. There was an Avid or Kitfox SB (can't remember which) that warned of loss of lift from disrupted airflow over the wing due to a bump in that transition area. Again, this is not intended to take the place of the PVC leading edge extrusion from Kitfox or change the airfoil appreciably.

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Posted

Doug - do you fair the plywood into the spar by sanding it down at the attach point, or do you build it up with hysol to make the smooth transition? The thought of the plywood is interesting as I would think it would provide additional structural integrity. How about oil-canning - seems at 1/32 it's thin enough and wouldn't be an issue, but wonder what you've seen/heard regarding that aspect of using wood?

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Posted (edited)

Chamfer underside of sheeting where it butts to spar, you will still have to sand the top edge flat. Do that before you glue sheeting down to prevent scratching the spar. Smooth transition with SuperFil or Hysol. I've not seen or heard complaints of oil canning with the wood top leading edge. IMHO it does add some structural integrity, a factor for me as I wanted a few wing mods to justify a higher MTOW on my A+, without a crazy increase in empty weight.

Edited by dholly

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Posted

Thanks!

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Posted (edited)

Well we've made some progress and have removed the aluminum leading edge (that was not properly installed) and replaced it with plywood. Not ready for fabric yet but before I begin that work I wanted to confirm that the rib stitching would begin just aft of the plywood. And the fabric would be glued to the entire span of the plywood.

 

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Edited by RobS

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Posted

Just curious, why are you rib stitching? With the speeds you'll get out of this bird it certainly doesn't need it. If it's just something you want to do that's different. 

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Posted (edited)

That's a lot of glue to put on if you glue to all the plywood - I have about the same amount (top & bottom) even over the tank, and only planned to glue to a few inches of front of plywood and a 1" stripe of glue lining up with ribcaps - I would also like to hear some comments about that.  Yes, if you are ribstitching, it would begin at end of plywood.   I don't plan on ribstitching, as the glue holds the fabric just fine.   I would put some chaf tape at the end of the plywood before covering.   EDMO

Edited by EDMO

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Posted

The last set of Avid wings I covered had the aluminum sheet on top of the ribs.  I had the materials on hand, so I rib stiched the wings.  Started right after the aluminum.  Might have been 1" back of the aluminum to the first stich.  JImChuk

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Posted

I chose to rib stitch basically because I could.  It is an added safety factor, needed or not, it's done and I would do it again.

My question is:  With that much of a wood leading edge, how does the wing flex?  These wings are designed to flex up and down quite a bit.  Making a rigid leading edge like that is begging for a structural failure, IMO.

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Posted (edited)

Even though it's not required, I believe the rib stitching is worth doing because of the undercambered wing.

Thanks Ed, your ideas make sense - I'll be interested to see what others say.

Edited by RobS

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Posted

Even though it's not required, I believe the rib stitching is worth doing because of the undercambered wing.

Thanks Ed, your ideas make sense - I'll be interested to see what others say.

Rob,  I modified my ribs to the Riblett  (late Kitfox) type and got rid of the undercamber when I extended my leading edge 4" and added plywood.   Comments from others would really make me feel better, or wrong?    EDMO

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Posted

When you go over a solid surface (at least with polyfiber system) you coat the area with poly brush before you cover it.  Then when you brush the poly brush through the fabric, it gets glued down to the plywood, or in my case, aluminum.   JImChuk

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Posted (edited)

When you go over a solid surface (at least with polyfiber system) you coat the area with poly brush before you cover it.  Then when you brush the poly brush through the fabric, it gets glued down to the plywood, or in my case, aluminum.   JImChuk

So, how much of the leading edge of the plywood would you use Polytak on first?

I don't know what is suggested with Stewarts or Oratex - guess if that is used, then ask their experts?  Thanks, Jim.   EDMO

Edited by EDMO

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Posted

When you go over a solid surface (at least with polyfiber system) you coat the area with poly brush before you cover it.  Then when you brush the poly brush through the fabric, it gets glued down to the plywood, or in my case, aluminum.   JImChuk

So, how much of the leading edge of the plywood would you use Polytak on first?

I don't know what is suggested with Stewarts or Oratex - guess if that is used, then ask their experts?  Thanks, Jim.   EDMO

You would only poly-tac the spars and or the 2" overlap along with the ribs, But all Plywood surfaces bigger than 1 inch get Poly-Brush

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Posted (edited)

When you go over a solid surface (at least with polyfiber system) you coat the area with poly brush before you cover it.  Then when you brush the poly brush through the fabric, it gets glued down to the plywood, or in my case, aluminum.   JImChuk

So, how much of the leading edge of the plywood would you use Polytak on first?

I don't know what is suggested with Stewarts or Oratex - guess if that is used, then ask their experts?  Thanks, Jim.   EDMO

You would only poly-tac the spars and or the 2" overlap along with the ribs, But all Plywood surfaces bigger than 1 inch get Poly-Brush

Thanks TJay.   Rob,  I put spar varnish on my plywood exterior, after taping off the 1" strip lining up with my ribcaps, and sprayed the poly-whatever? by Minwax or some brand? on the inside after it was glued.   I planned to go back and sand the front area where the fabric will be glued.   EDMO

Edited by EDMO
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Posted

Larry - the plywood is 3 ply birch from Wicks and only .8mm, slightly less than 1/32 thick, so I have no concern with the wing flexing like it should. In fact, it's even more flexible than the original aluminum that came with the kit. The aluminum wasn't  placed properly by the guy who started the plane so I decided to replace it with the plywood. I liked the concept of the "solid" leading edge and the plywood will bounce back rather than permanently dent like the aluminum.

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Posted (edited)

Larry - the plywood is 3 ply birch from Wicks and only .8mm, slightly less than 1/32 thick, so I have no concern with the wing flexing like it should. In fact, it's even more flexible than the original aluminum that came with the kit. The aluminum wasn't  placed properly by the guy who started the plane so I decided to replace it with the plywood. I liked the concept of the "solid" leading edge and the plywood will bounce back rather than permanently dent like the aluminum.

I went with 1mm (.040") 3-ply birch plywood from Spruce, top and bottom - I don't think there will be much bend in my wings - I have the spars with the full-length web plus another tube in the extended leading edge, and 2 tanks in each wing should stiffen them.   My flap and aileron pivot tubes are very stiff too, and there is another tube in the leading edges of them.   EDMO

Edited by EDMO

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Posted (edited)

Larry - the plywood is 3 ply birch from Wicks and only .8mm, slightly less than 1/32 thick, so I have no concern with the wing flexing like it should. In fact, it's even more flexible than the original aluminum that came with the kit. The aluminum wasn't  placed properly by the guy who started the plane so I decided to replace it with the plywood. I liked the concept of the "solid" leading edge and the plywood will bounce back rather than permanently dent like the aluminum.

I went with 1mm (.040") 3-ply birch plywood from Spruce, top and bottom - I don't think there will be much bend in my wings - I have the spars with the full-length web plus another tube in the extended leading edge, and 2 tanks in each wing should stiffen them.   My flap and aileron pivot tubes are very stiff too, and there is another tube in the leading edges of them.   EDMO

you got a name for that bird yet, Maybe Lead sled ha ha :P

Edited by TJay

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Posted (edited)

Larry - the plywood is 3 ply birch from Wicks and only .8mm, slightly less than 1/32 thick, so I have no concern with the wing flexing like it should. In fact, it's even more flexible than the original aluminum that came with the kit. The aluminum wasn't  placed properly by the guy who started the plane so I decided to replace it with the plywood. I liked the concept of the "solid" leading edge and the plywood will bounce back rather than permanently dent like the aluminum.

I went with 1mm (.040") 3-ply birch plywood from Spruce, top and bottom - I don't think there will be much bend in my wings - I have the spars with the full-length web plus another tube in the extended leading edge, and 2 tanks in each wing should stiffen them.   My flap and aileron pivot tubes are very stiff too, and there is another tube in the leading edges of them.   EDMO

you got a name for that bird yet, Maybe Lead sled ha ha :P

Big Bird?  DoDo Bird?  :lol:  AvidFox Tanker?  "I bring fuel"! ,  LRO "Long Runways Only"?   EDMO

Edited by EDMO
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Posted (edited)

Larry - the plywood is 3 ply birch from Wicks and only .8mm, slightly less than 1/32 thick, so I have no concern with the wing flexing like it should. In fact, it's even more flexible than the original aluminum that came with the kit. The aluminum wasn't  placed properly by the guy who started the plane so I decided to replace it with the plywood. I liked the concept of the "solid" leading edge and the plywood will bounce back rather than permanently dent like the aluminum.

I went with 1mm (.040") 3-ply birch plywood from Spruce, top and bottom - I don't think there will be much bend in my wings - I have the spars with the full-length web plus another tube in the extended leading edge, and 2 tanks in each wing should stiffen them.   My flap and aileron pivot tubes are very stiff too, and there is another tube in the leading edges of them.   EDMO

you got a name for that bird yet, Maybe Lead sled ha ha :P

Big Bird?  DoDo Bird?  :lol:  AvidFox Tanker?  "I bring fuel"! ,  LRO "Long Runways Only"?   EDMO

Maybe I should remind you TJay, that I will have about 160 square feet of wing surface - Now compare yours to mine, or a Kitfox with 1200 lbs GW to mine: 

1200 lbs / 136 SF = 8.8 lbs SF Wing Loading,  and mine is 1200 lbs / 160 SF = 7.5 lbs SF Wing Loading:  Which is Lighter?  

I could put mine up to 1320 lbs GW and still have a lighter, 8.25 lbs Wing Loading. (l have a 1500 lb landing gear.)

I would have to load up to 1400 lbs to have your 8.8 lbs Wing Loading. - still less loading than an Airdale.     EDMO

Edited by EDMO
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Posted

Rob,

The wing looks great!

The Magnum came with the option of a fiberglass leading edge, so the concern for limiting flex most not have been an issue.

Im going to explain how I covered my wings, but this was my first shot at it, so there might be a better way.  I used Super flight, but the glueing process is the same as the Poly stuff.

The superflite glue is blue/green and is like poly tac.  Look at the first pic and you will see glue on the fuel tank, the trailing edge, wing tips, and the entire leading edge.  When you get the fabric on the wing, you will brush glue along the trailing edge and the bottom of the spar.  Once it dries then you can start shrinking the fabric.  After you get everything ironed and all wrinkles gone it is time to brush glue on the entire fuel tank and leading edge plywood. This coat of poly tack is very thin...mostly MEK.

Rib stitching can be done a lot of ways, or evidently not at all.  I actually started rib stitching on the bottom right behind the front spar.  I took the string through the lightening holes in the ribs until I made it past the leading edge material...then I did it the normal way to the trailing edge.  I came up with that system on my own, so I'm not saying it is right or the only way, but I like how it turned out.

I hope that made sense, if not, pics are worth a thousand words!

 

Ron

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