MK IV Aerobat speedwing spar gouge/repair


43 posts in this topic

Posted

Well one thing is for sure, you can't do to good a job on an airplane, but it certainly is possible to do to poor of one.  Therefore erring on the side of caution is never likely to bite you.  While the opposite is.  If you are going to change out the spar, I would cut it in lengths that would work on your wing extentions before you remove it.  That will make it much easier to separate from the ribs.  The epoxy used to glue the ribs to the spar should soften with heat to help you remove it.  Hysol or scotchweld both should soften with heat, just don't get the wood ribs to hot.  JImChuk

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Posted

Interesting. Did he say what program he was running the simulations with? If your an EAA member you can download a full working version for free. It's got some great analysis tools. Was he simulating fatigue with the original spar design or a sleeved design? How many hours to failure? Etc.

Since the wing is a composite structure it will be tough and expensive to rebuild it. As far as the glue goes; I have not seen a glue yet that won't break down from heat. The problem is the wood might catch on fire before the glue fails. An extreme example of glue against heat would be the tiles on the space shuttle. Each flight experienced some failing.

Cutting out each section in pieces and then grinding/sanding away the metal fragments and old glue sounds like more like punishment than fun but it would be cheaper than starting from scratch.

Another idea would be to build a D-cell spar out of wood between the two ribs containing the damaged section. Plenty of aircraft flying with wood D-cell spars. Either design it to include the damaged spar or start it just behind the leading edge spar as a separate component. Wood is cheap and easy to work with. You could still patch the original in addition to the D-cell add on. Any designers see anything wrong with that?

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Posted

What a bunch of Gobbledy Gook. I cant tell you what to do but I can give an example to think about. Take a 5 inch thick slab of concrete you put a saw cut 1/2 inch deep in it that's 10 percent of its original thickness. The first time that slab moves it cracks in that cut every time. Now you need to think about how much that spar bounces up and down right in that thin spot. Just something to think about the next time you go fly. ;)

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Posted

No spar needs a "control joint".  Tile and glass are much the same, a thin scratch, and that's where they crack.  Obviously harder material than aluminum, but still.....   Also, the more I worry about the plane while flying it, the less fun I have.  Even when nothing goes wrong.  JImChuk

 

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Posted

A wing is designed so that stress flows thru the whole wing and no one section has it concentrated at a certain point. But it will build up at a repair or strengthened area and possibly fail at that point. Even though it has been sleeved or patched, it IS a weak spot. An example is to watch a 747 or a glider wing in flight. It bends and flexes throughout the full length of the wing not just a certain section. Even a relatively short wing still flexes some even though you might not see it. Repair or replace? Not a question you want to ask after it fails in a gust or rough air flight.  A fuselage has other tubes and paths for the stress to flow around, A wing spar does not, it is the load carrying member. Bite the bullet and replace it!

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Posted

What a bunch of Gobbledy Gook. I cant tell you what to do but I can give an example to think about. Take a 5 inch thick slab of concrete you put a saw cut 1/2 inch deep in it that's 10 percent of its original thickness. The first time that slab moves it cracks in that cut every time. Now you need to think about how much that spar bounces up and down right in that thin spot. Just something to think about the next time you go fly. ;)

There's a hole in that spar that's about 1/4" in diameter already. It has a tiny little fastener dropped through it to hold the entire wing to the side of the airplane. Ever hold your hand out the window of a car at 80 mph? Now imagine your hand stuck out over 15 feet instead of 2 feet with all that additional surface to hold against the wind. Now imagine that hole being flexed back and forth with each direction change and gust of wind. Why aren't you worried about that hole?

If I take a five inch diameter tree and cut a 1/2" saw cut in one side of it, what do you think will happen to it on a windy day? Nothing!  I guess a plywood prop should just fly apart at the glue joints because the way you see things; if it isn't one piece it's less than full strength no matter how you patch it? You do realize most wood propellers are plywood right? I hope you understand those those composite props are made of different materials laminated together? Why don't they just use one material?

That concrete example you mentioned brings up another point, did you put any steel in that concrete? Under every saw crack on the Interstate are rows of steel bars that are designed to expand and contract with the weather. That saw mark has no effect on the steel under the same saw mark. Mixing steel with concrete is another form of a composite structure. 

There's a huge difference between Gobbledy Gook as you call it and sound scientific principals based on various material properties and proven methods to create composites out of those materials.

It won't matter what I say; your mind is made up. Reminds me of an old farmer that used to come into my bar everyday back in the early 80's. A typical rainy day here in Iowa brought a lot of farmers to town to pick up a few things. We were watching a space shuttle launch on TV. The farmer turned to me and said "That's why were getting all this rainy weather." "All those dammed shuttles blowing holes in the atmosphere!" This old guy was dead serious. I made the mistake of pointing out he was crazy. I said what about all those shooting stars that burn through our atmosphere every day and night from outer space? A couple of holes more from the shuttles isn't going to change anything! He got pissed off and left. I didn't see him for six months.

I'm not trying to start a flame war but everyone has a right to their own opinion and with different backgrounds we obviously have developed different opinions.

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Posted

A wing is designed so that stress flows thru the whole wing and no one section has it concentrated at a certain point. But it will build up at a repair or strengthened area and possibly fail at that point. Even though it has been sleeved or patched, it IS a weak spot. An example is to watch a 747 or a glider wing in flight. It bends and flexes throughout the full length of the wing not just a certain section. Even a relatively short wing still flexes some even though you might not see it. Repair or replace? Not a question you want to ask after it fails in a gust or rough air flight.  A fuselage has other tubes and paths for the stress to flow around, A wing spar does not, it is the load carrying member. Bite the bullet and replace it!

I'm reminded that almost all my fishing poles are two piece and while I've broke a few in my life; I've never broke one at the joint. Same goes for the 2 piece sleeved mast on a sailboard which is in effect the leading edge spar of a wing.

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Posted

A wing is designed so that stress flows thru the whole wing and no one section has it concentrated at a certain point. But it will build up at a repair or strengthened area and possibly fail at that point. Even though it has been sleeved or patched, it IS a weak spot. An example is to watch a 747 or a glider wing in flight. It bends and flexes throughout the full length of the wing not just a certain section. Even a relatively short wing still flexes some even though you might not see it. Repair or replace? Not a question you want to ask after it fails in a gust or rough air flight.  A fuselage has other tubes and paths for the stress to flow around, A wing spar does not, it is the load carrying member. Bite the bullet and replace it!

I'm reminded that almost all my fishing poles are two piece and while I've broke a few in my life; I've never broke one at the joint. Same goes for the 2 piece sleeved mast on a sailboard which is in effect the leading edge spar of a wing.

But losing a fish, or the mast of a sail boat won't result in you falling to earth and splatting like a ripe melon. ;)

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Posted (edited)

A wing is designed so that stress flows thru the whole wing and no one section has it concentrated at a certain point. But it will build up at a repair or strengthened area and possibly fail at that point. Even though it has been sleeved or patched, it IS a weak spot. An example is to watch a 747 or a glider wing in flight. It bends and flexes throughout the full length of the wing not just a certain section. Even a relatively short wing still flexes some even though you might not see it. Repair or replace? Not a question you want to ask after it fails in a gust or rough air flight.  A fuselage has other tubes and paths for the stress to flow around, A wing spar does not, it is the load carrying member. Bite the bullet and replace it!

I'm reminded that almost all my fishing poles are two piece and while I've broke a few in my life; I've never broke one at the joint. Same goes for the 2 piece sleeved mast on a sailboard which is in effect the leading edge spar of a wing.

Question is, would you buy that aircraft, put your family member in it and go flying with a repair on the wing spar? I don't think many of us would. Its easy for us to armchair a repair like that and give advice knowing we aren't responsible for the outcome. The only 100% safe way is to replace the spar. I always try to consider if it was my tail in the aircraft and answer accordingly.  Besides, wood, alum and fiberglass all have different stress qualities. And from what little I know about sailing here in the mountains, mast are usually cable or rope braced in several locations. And a sailboard isn't in a high stress situation unless you are being chased by a shark and I bet you would be praying the mast doesn't break.

Edited by Allen Sutphin

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Posted

Question is, would you buy that aircraft, put your family member in it and go flying with a repair on the wing spar? I don't think many of us would. Its easy for us to armchair a repair like that and give advice knowing we aren't responsible for the outcome. The only 100% safe way is to replace the spar. I always try to consider if it was my tail in the aircraft and answer accordingly.  Besides, wood, alum and fiberglass all have different stress qualities. And from what little I know about sailing here in the mountains, mast are usually cable or rope braced in several locations. And a sailboard isn't in a high stress situation unless you are being chased by a shark and I bet you would be praying the mast doesn't break.

Yes, I would put my family member in it and go flying with a repair on that wing spar. When I got done with it, the repaired section would be stronger than original spar and I would have ordered a couple of extra feet of tubing to build up a sample joint and tested that to failure to verify it was stronger. I don't give out advice I offer suggestions that I would feel 100 percent comfortable with if I were in the same situation. I've designed and built and tested an airplane; have you? I build within my knowledge and comfort levels. When I'm outside those limits I ether gain the additional knowledge and skills needed to complete a task or find an expert. 

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Posted

 

Well to me I guess there is only one way to fix this problem right.

And your right My mind has been made up about that from day one.

If you wanna go out to your plane and chop your spar in half at the  29 inch mark tonight  then splice it back together and fly it all winter  I will listen to your suggestions but for now this will be my last post about this. 

Sure would love to see you start another thread on this plane you designed and built?

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Posted (edited)

 

Well to me I guess there is only one way to fix this problem right.

And your right My mind has been made up about that from day one.

If you wanna go out to your plane and chop your spar in half at the  29 inch mark tonight  then splice it back together and fly it all winter  I will listen to your suggestions but for now this will be my last post about this. 

Sure would love to see you start another thread on this plane you designed and built?

My last comment on it, too. No sense beating a dead horse. Being an A&P/IA for 38 yrs + probably doesn't count for much. I wouldn't sign off on a repair like that!

Edited by Allen Sutphin
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Posted

 

Well to me I guess there is only one way to fix this problem right.

And your right My mind has been made up about that from day one.

If you wanna go out to your plane and chop your spar in half at the  29 inch mark tonight  then splice it back together and fly it all winter  I will listen to your suggestions but for now this will be my last post about this. 

Sure would love to see you start another thread on this plane you designed and built?

My last comment on it, too. No sense beating a dead horse. Being an A&P/IA for 38 yrs + probably doesn't count for much. I wouldn't sign off on a repair like that!

Building practices and repair practices for certified aircraft are just that; for certified aircraft, the same standards do not apply to experimental aircraft. While most A&P mechanics may be certified to work on metal structures many lack the credentials to work on wooden structure aircraft. Even those with the additional certification may not be qualified to work on composite structures. I've read AC 43.13-1B and it says nothing about repairs to composite structures made of wood and aluminum so I don't know what you are basing your refusal to sign off on all repair suggestions other than complete leading edge replacement for a non certified experimental airplane.

For those wondering; AC 43.13-1B does contain great information on tubing repair using sleeved methods from rivet structures to welded structures and a combination of the aforementioned.

Link here for AC 43.13-1B: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43.13-1B_w-chg1.pdf

 

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Posted

Interesting. Did he say what program he was running the simulations with? If your an EAA member you can download a full working version for free. It's got some great

Cloud Dancer,  he didn't elaborate on either the program or parameters.  It certainly isn't in his interest to suggest nonstandard repairs from a financial or legal standpoint, so I don't blame him.  

I appreciate all of the suggestions, and I've gone back and forth quite a bit.  I purchased some 2.5" ID 6061 aluminum to make a patch and fly by myself while working on a new wing.  I don't have any extra spar material to test a repair, so pulling and reinstalling a spar would probably take about the same effort.  I wouldn't mind overbuilding a patch and flying solo, but I wouldn't feel comfortable taking up others who can't consent or attest to the unknown quality of my repair job.  I'd also like to be able to present a "clean" repair if I decide to sell it at some point. 

The more I think about it, I'd like a little more performance up here than my 1.5" washout speedwing will be capable of providing.  I considered buying a single speed wing and using the old spar parts to extend it, but I think the built-in washout will make for a negligible performance gain.  I'll either replace the single wing or toss the pair and go with a modified HH set.

Again, a sincere thank you to everyone who weighed in.  Considering the odd nature of the damage and kit planes in general, it is great to be able to hear a lot of differing viewpoints.  I've learned a LOT the past couple weeks from this discussion, and everything I've been told has been insightful and enlightening.  

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Posted

I appreciate all of the suggestions, and I've gone back and forth quite a bit.  I purchased some 2.5" ID 6061 aluminum to make a patch and fly by myself while working on a new wing.  I don't have any extra spar material to test a repair, so pulling and reinstalling a spar would probably take about the same effort.  I wouldn't mind overbuilding a patch and flying solo, but I wouldn't feel comfortable taking up others who can't consent or attest to the unknown quality of my repair job.  I'd also like to be able to present a "clean" repair if I decide to sell it at some point. 

The more I think about it, I'd like a little more performance up here than my 1.5" washout speedwing will be capable of providing.  I considered buying a single speed wing and using the old spar parts to extend it, but I think the built-in washout will make for a negligible performance gain.  I'll either replace the single wing or toss the pair and go with a modified HH set.

Again, a sincere thank you to everyone who weighed in.  Considering the odd nature of the damage and kit planes in general, it is great to be able to hear a lot of differing viewpoints.  I've learned a LOT the past couple weeks from this discussion, and everything I've been told has been insightful and enlightening.  

Another option would be to chop the old wings and have the shortest wings on the group. Just on the group I'm afraid, as people have been cutting wings off for decades to make clipped wing Cubs and other tiny wonders. One of the best at it was Ray Stits; the same guy that invented the covering process used on many of our airplanes. Ray took the wing chopping theme to another whole level. An interesting fact; Ray was not an engineer! He was a self taught designer. Here's a little link describing one of his clipped wing designs:

https://www.flyingmag.com/aircraft/perspectives-homebuilding/ray-stits-early-homebuilt-designer

I'm not saying chop it to improve it; because it won't. I'm saying there are those on this group that don't realize that without guys like Ray Stits they would still be flying Wright Flyers covered with canvas covering. Hang those old wings up in the rafters. Ten or twenty years from now you may see them in a new light and build something out of them. Maybe a biplane Avid Flyer is in your future. If so, please make it into a stagger wing enclosed cabin model. Getting the wings to fold would be interesting if not impossible but you got time.

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Posted (edited)

I must admit that I did not see the location of the decimal point on the caliper as a depth gauge.  Screen too small, I guess.  Gotta agree with JimChuk here in that too good is vastly preferable to too bad.  This certainly makes the splice approach look good.  My bad.  Nobody is going to do a stress analysis of the spar in its current condition, so we could go around and around and ultimately never reach any meaningful conclusion.  

Edited by Turbo

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Posted (edited)

 A lot of strong opinions based on an improper measurement method. Anyone who has used a set of calipers for a living knows this is an inaccurate way to measure a tube hence a total misrepresentation of the actual damage.

Edited by NorthIdahoAvidflyer

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Posted

Agreed; it was meant as a quick-and-dirty visual for suggestions, certainly not for any kind of stress analysis or engineering purposes.  

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