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Wings, metal leading edge or no

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Posted

I purchased a unfinished Mark IV Heavy Haulerkit last year and it had the wings in pink but it was not well done. I wanted to see what was under the fabric to determine the condition of the construction. It had two broken flaperon tabs, a broken small rib, no varnish on the wood and a couple of missing small corner braces. The overeall construction was sound. The repaiars have been made. The leasing leading edge was not covered in metal. I am ready to recover the wings so the question is, metal or no metal. I asked C5Engineer and he said it was not needed but said to ask all of you for an opinion. The wing does have the 4 mini ribs between the primary ribs.

Thanks,

Jon

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Posted

Welcome Jon and congrats on the new project! Sounds like you're not totally unfamiliar with building, is this your first Avid?

 

Very good call on opening up the wings for an inspection. No varnish, yikes! Curious when you say "a couple of missing small corner braces", are you talking about gussets epoxied in between the spar and drag tubes? I don't think the step was in the manual but it's so easy and beneficial most builders have added them. (see pic)

 

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.

 

Personally, unless the aesthetics of a smooth top wing are important to you, I wouldn't bother with either as the extra false ribs between each wing rib on the HH prevents most oil canning already. I guess it would also boil down to how fast you want to get back in the air. Whether aluminum or ply, the L.E. skins really are an unnecessary, time intensive extra step with a lot of fussy work getting everything faired in nicely. It is critical that the leading edge transition is smooth to the spar to prevent disturbing airflow over the top of the wing.

 

Welcome to the circus, post up some pics for the rest of the clowns when you get a chance!

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Posted

Mine has the aluminum leading edge wrap.. I think it probably adds more weight and thats about it.  Steve Winder tried to talk me into ripping it off when I was rebuilding the wings but I left it on.  So far, they have taken some pretty good knocks and are not dented.  If I had it to do again, I would probably leave them off.

 

 

:BC:

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Posted

I would leave them off if I had it to do again.

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Posted (edited)

Depends on whether you are talking about just covering the leading edge with aluminum, or adding the aluminum leading edge extensions.

With my short fuselage, and heavy Soob engine and nose gear, I extended my leading edges 4 inches, but used plywood ribs and 1mm plywood cover like Doug talked about.

EDMO

Edited by Ed In Missouri

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Posted

I realize that the leading edge probably doesn't need this, but from my viewpoint of using it in the backcountry and flying tight into trees at times I think the little added protection wouldn't hurt. Not that I'd try to test it against a tree but I've seen some strange things that people have done over the years. I once saw an ag-wagon leading edge that had a dent about 4" into the leading edge. The pilot just kind of turned his eyes to the ground and said, "yeah, didn't see that tree on my approach", when I asked about it. He told me later that it was just a sapling but it took about a 2' wide section patch to fix it! Good thing those ag-wagons are built fairly tough.

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Posted

you do that in a kitfox or avid and your looking at a new spar.. the spar is the leading edge so whacking trees that leave dents will dent your flying for awhile.

 

:BC:

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Posted (edited)

I think the plastic leading edge trim that Kitfox sells is good protection for the front spar for normal mis-handling - but tree-hacking is a little much!

EDMO

Edited by Ed In Missouri
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Posted

I didn't mean to sound like I would go tree whacking just because I had a leading edge wrap on a wing, simply that things happen. The example was an extreme case, but like Ed said, just a little protection from rough handling more than anything.

 

I understand that just about any airplane would be down for the count for a while if tree whacking were involved! :hammerhead: Now if that there just a tree instead of another smiley! lol

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Posted

Thanks for the input, I will go with no metal.  The missing braces are for the inboard and outboard ribs from the corner of  the rib (near the trailing edge) to the rear spar, about a 12" brace.

 

 Has any one reinforced the wood rib flaperon tabs with metal?  They seem to be a week point. I am considering laminating .030 Alum. on each side. They still fit the slot on the flaperon bracket as the tab seems to be thin.  

 

This is my first Avid, I did start a Fly Baby some years ago but sold it when I thought I had a medical problem (it turned out I did not) and I was also moving from Idaho back to Colorado for retirement.

 

As it show I am new to the forum I have lots of question, do I need to open a new topic for each one?

 

Thanks Jon

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Posted

No sir, you dont need to open a new topic for each question, but if it is something totally unrelated then it may help for guys doing searches of the forums to find answers on a specific topic.

 

Something you could do, is start a build thread under the MK IV section and post all your questions and build progress under that one thread so it will all stay in one place for you.  If you would like, I can move this thread to its own topic under the MK IV section and you can just keep adding onto this one.

 

:BC:

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Posted

I think the plastic leading edge trim that Kitfox sells is good protection for the front spar for normal mis-handling - but tree-hacking is a little much!

EDMO

 

I agree with Ed on this one.  The plastic leading edge will help if you take a little excursion through the willows or tall weeds etc.. but dont help with a full on tree. 

 

I have whacked 1" alders and willows with my aluminum leading edge wrap and didn't leave any permanent marks other than the streak / stain in the paint :lol:

 

:BC:

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Posted

Akflyer, I'm not sure what a thread is but sounds OK to me.  How will I find this thread, will it be under the Avid Flyer General Hanger?

Jon

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Posted (edited)

Jon,

     The UK did not like the strength of the rib ends that support the flaperons, therefore they made Kitfox add some .025 aluminum angles to each side of them to pass certain tests.   There should be a post about this somewhere in this site which shows the installation process.   Others have cracked or broken rib ends, and there are posts about how to repair them.  Maybe Leni "Akflyer" or Joey "C5E", Doug "DHolly" or someone can direct you to the proper posts for the info you need.  I do well to turn on the puter and type.

EDMO 

Edited by Ed In Missouri

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Posted

Thanks for the input, I found the information on adding metal.  As I checked the thickness for the tab they were all over the place.  I had replaced an aft rib where the tab was brokenn and it was .240 others were .220, .20 or just under.  I am using .30 material so can not put it on both sides except for one or two tabs. I am forming an angle on the bottom of the full plate and will make a partial plate on the other side with the angle on top.  The partial will go around the flalperon mounting plate.  It will still support the weak point.   

 

I will let you know it it works.

 

Jon

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Posted

Hey Jon,

I'm building an Avid Magnum and I live in Pueblo West too! Small world! I'd love to see your aircraft. I'll send you a pm with my info.

I have the plastic leading edge on my uncovered wings if you want to see what it looks like. I also have a fiberglass top leading edge that comes back about a foot on my wings, I think it adds a lot of unwanted weight and the fiberglass was a bit wavy too.

I saved a pic of someone else's aluminum flapperon horn covers. I will post it here for you, but I don't know much about it, it just looked like a good idea.

See ya,

Ron

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Posted

Small world, eh? Now you guys have an excuse to get out of the house every week 'cause your new building buddy needs a hand, hehe.

 

BTW, those were the rib tail reinforcements I made for my Avid Mk-IV. At the time, I did not extend the metal through the cap strip onto the interior rib web. Honestly, after seeing just how easy it is to snap a rib tail off, I probably would make the extra effort and do it today. Certainly would make it a much stronger structure overall.

 

Obviously, the KF4 rib tails and flaperon hangers are completely different. I've attached the Service Bulletin from Denny showing their solution and a pic of my old KF3 showing the root rib with retrofitted reinforcement in place.

 

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Posted

I thought I'd use this original thread regarding the metal leading edge to ask a couple of related questions and see if anyone has changed their opinion about the benefits or draw backs of the metal leading edge. The MK IV HH partially completed kit I purchased included wings with the metal leading edge. I decided to pull the metal off because the bonding between the false ribs and metal was not good, the joints between the pieces rough, and a number of the false ribs has broken loose due to poor bonding/adhesion.

I've attached a picture of he wings as purchased and a couple of pictures that show the current state of the wing. As you can see there is a fair amount of hyssop to clean up. Here are a few of my questions:

1. Will a heat gun soften the Hyksol and make it easier to remove.

2. Is there a place where I can purchase new false ribs (if I can clean them up).

3. Is the metal leading edge worth it?

4. Why was the original leading edge multiple pieces of metal and can it be a done with a single piece?

5. I see the Kitfox LLE comes in two pieces per wing - is it to minimize oil-canning when the wing flexes?

Thanks for your help!

 

 

 

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Posted

yes a heat gun will make the structural epoxy soften up and a putty knife will take it right off.  I like the aluminum on mine but Steve Winder told me that he would take it off if it was his plane due to the oil canning.  I wanted to leave it on so he sent me a bunch or short pieces to redo the wings so the shipping would be less... I just went to the local metal supply place and got 8' strips from them sheared off to the correct width and used those instead to replace my buggered up sections.  If you wanted new false ribs cut, you could check around your area and  see if anyone is doing laser cutting.. I made a few model boat kits and some other parts using a local guy and the parts came out great and he was able to cut the 1/4" aircraft ply with ease!

 

:BC:

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Posted (edited)

Rob,

       I would be very wary about using a heat gun on the spar - aluminum must not be heated over 250 degrees or it will change.  On the wood support, it might be OK.

       The Kitfox leading edge I had was just a plastic bumper to protect the spar - It may have helped a little with the airflow?

       When I extended my leading edges, I used 1mm finland plywood, which don't dent like aluminum.

       Avid made a fiberglass leading edge covering at one time.

       Kitfox sells false ribs, but not sure how they compare to yours.

EDMO

Edited by EDMO

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Posted

Rob,

       I would be very wary about using a heat gun on the spar - aluminum must not be heated over 250 degrees or it will change.  On the wood support, it might be OK.

       The Kitfox leading edge I had was just a plastic bumper to protect the spar - It may have helped a little with the airflow?

       When I extended my leading edges, I used 1mm finland plywood, which don't dent like aluminum.

       Avid made a fiberglass leading edge covering at one time.

EDMO

If the aluminum changes at 250 then you would never be able to weld it... The transition temperature for aluminum is much higher than 250.  A normal heat gun will get the glue soft LONG before the aluminum gets too hot to tough... at least mine did.  It really did not take too much heat at all for the glue to soften up and scrape right off.

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Posted (edited)

Rob,

       I would be very wary about using a heat gun on the spar - aluminum must not be heated over 250 degrees or it will change.  On the wood support, it might be OK.

       The Kitfox leading edge I had was just a plastic bumper to protect the spar - It may have helped a little with the airflow?

       When I extended my leading edges, I used 1mm finland plywood, which don't dent like aluminum.

       Avid made a fiberglass leading edge covering at one time.

EDMO

If the aluminum changes at 250 then you would never be able to weld it... The transition temperature for aluminum is much higher than 250.  A normal heat gun will get the glue soft LONG before the aluminum gets too hot to tough... at least mine did.  It really did not take too much heat at all for the glue to soften up and scrape right off.

I think that depends on the aluminum - I was told that 6061 should not be heated over 250F - ???  I don't even know if you can weld it...

I'm sure you know more about welding than I do - my only experience/schooling in metalurgy has been with steel alloys.

EDMO

Edited by EDMO

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Posted

I'm sure Aircraft Spruce in their catalog list 6061 as being weldable.  Just looked and all the 6061 alloys they show are listed as  'Generally weldable by all commercial procedures and methods.    As far as the aluminum on the wing, I've had 2 Mk IVs with it and I liked it.  I think it makes for a bit of a stronger wing.  It probably does oilcan a bit, but it's main purpose as I understand it was to keep the fabric from bowing down between the false ribs, and it does that.  I don't think short pieces will oil can less, if you have it glued on right, it shouldn't move at the joints between the pieces.  I think it is probably a lot easier to install and ship in small pieces.  Jim Chuk

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Posted

Heating the spar with a heat gun to remove the adhesive will be just fine.  There isn't enough heat from a gun to heat more than a small localized area on the spar and the heat will quickly sync away.  To loose the T6 temper the aluminum would need to be heated for a period of over 8 hours at 325º F or more.

The plastic Kitfox plastic leading edge extrusion is to produce the sharper leading edge of the Riblett airfoil and is not what Rob is referring to.  He is talking about the aluminum leading edge wrap that extends along the top of the wing.  Two totally different things.

Kitfox now offers a Laker leading edge which is similar to the old Avid aluminum sheets, only it is a composite sheet.  The design of the newer Kitfox wings do not flex as much due to longer reinforcing I-beams, therefore oil-canning of the Laker leading edge is less likely.

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Posted

Thanks guys, I appreciate the feedback . . . especially for clarifying the amount of heat the spars can take. I tend to agree with Jim on shorter metal pieces not doing much to minimize any oil-canning (if the individual sheets are tightly secured/glued down), so I think I'm going to go with one long piece of sheeting and see how that works out. As you can see I have a bit of work to do cleaning things up before that work begins. I'll post something when I get to laying down the metal leading edge . . . .

 

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