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Fluting HS Ribs question

sumitku

Active Member
Folks hoping for some guidance here. I've read section 5.13 of the construction manual a few times and also read a bunch of posts on fluting and watched some of the referenced youtube videos.

I just can't seem to visualize what needs to be achieved from fluting. If you look at the below pic, when I lay the HS rib web flat on the bench it sits significantly raised up on both sides. To me this looks like it's due to the center of the web being bent a bit which I could reverse by bending at mid web in the opposite direction.

Or is the goal just to get each section of flange fluted so the web underlying just that particular flange lays flat, and not necessarily the whole rib web laying flat all at once.

Really confused here so thanks so much for any help!

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I would think that the newer kit parts with the relief-cuts in the flanges wouldn't need to be fluted. I'd cleco the parts together and as long as all the parts line up straight, no fluting required. --- Is that not correct?

On ribs that don't have the relief cuts in the flanges, you need to flute the flanges in order to get the ribs to lay flat so that pre-punched holes will line up in the center of the flanges.
 
You want to flute until the web of the rib is basically flat along its entire length.

When I look at your picture, I see the bend you are talking about at midpoint, but also see lesser curvature in other segments of the rib. The goal is to eliminate all of it (the midpoint bend and the curvature in the segments).
 
Your picture appears to show the spar attachment end of the rib. You do not want to flute that end, only the rounded parts of a rib.
 
Here is what made this part bend: You start with a flat sheet of metal cut out the notches, corner pieces etc. Just visualize what that part would look like if it was flattened out.
You will notice a couple of small holes on the flat area, web of the part. These are tooling holes. You would place the part on your wooden forming blocks on these pins. This is done so that you can make a bunch off similar parts.
Another wooden block is clamped on top of the pins. The "flanges" are sticking out. These are bent down, or hammered down. This bending, either in an expensive press or with a hammer, stretches the flange. This now longer flange is what curves the part.
Now you can shorten that flange by putting a crimp, or flute, in it. This gathers the metal and shortens the flange.
Simply put the web of the part on a flat piece of material, get down at eye level and put your fluting pliers in the middle of the holes and crimp it until the part lays flat.
Sometimes a couple of small flutes are better then one large one. Make sure none of the flutes will interfere with subsequent dimpling. Too much fluting will shorten the flange and cause the part to curve the other way!
This is one of what I call satisfying jobs in the project. You get to make something "right" with a little squeeze and a look!
 
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If it were me I'd cleco it together and see if the holes line up with the skin. If I remember correctly they lined up perfectly in my kit without the need to flute. From what I understand the older kits with the solid flanges required significantly more fluting than the newer kits.

Dave
 
First off, thanks to all of you for taking time out to provide insight. Very appreciated.

Ken, Dave, yes I've heard that a few times that the newer relief cut kits may not need any fluting whatsoever. What makes me wonder is that the manual still says flute if necessary the curved flanges of the HS-1004 ribs on page 8-7. Also, the web certainly doesn't lay flat even though it does look like the holes on the flanges are in a straight line, at least on each flange section between the relief cuts.

Mark, not sure if I follow, my pic is looking at the side of the HS-1004 rib which indeed is curved and is going to rivet directly to the skin over it.

Tom, thank you for explaining the forming process that leads to the curvature. I had seen videos of scratch building but never put it together until now how the flanges elongate through the process. I definitely will be satisfied when I figure this one out!

Kyle, agreed I can see that curvature, though less, is still there on the flange segments themselves and would certainly aim for those with fluting. It's the middle of the web bend that still throws me. I've tried flexing it a bit with my fingers and that doesn't seem to be effective enough, so it feels as though I'd have to get more aggressive to take that bend out by reverse bending the web in the middle. Neither the manual or any posts that I've been able to find talk about doing this, so I continue to wonder if I'm doing something wrong in trying to bend that out.

Think I should give Van's a shout or is it clear that I should reverse that mid web bend in addition to fluting the flanges?
 
Oops. Looking again I see that. Those are I guess the short nose ribs.
Where they cleco in or not they should be fluted to lay flat. If you were to put a straight edge down the row of rivets you will find that they don't line up well. It is a short rib so it may not be too bad but it only takes a second to flute a rib once you get the hang of it. You will be amazed at how flat you can get them to lay when fluted correctly.

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Flute a small amount at the red lines and all around the rib on the curved sides. Not the flat spar flange. The more curved the flange the more fluting it will need. Start very slowly and work all the way around to all the flanges before adding more or less fluting. Quit when it sits flat.
 
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Mark,

Thanks for clarifying and for the diagram! This statement seems to be definitive to me "whether they cleco in or not they should be fluted to lay flat."

Not sure why I'm so stuck on that bend in the middle of the web as being the main culprit, it just looks like the main cause of each side of the rib sticking up from the bench. For instance, I can rock the rib back on forth with the lever point being right at the midpoint of the web there.

I think I'll give the fluting a go and see what happens?
 
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There are a couple videos on the EAA website that show a real person fluting a real rib and showing how to figure where to flute. I'm not sure whether the videos are available to non-members but while logged into the EAA website, this URL shows a bunch of their videos.
 
Jerry, thanks for the tip and noted. The videos work for non-members. In reviewing them now it's very helpful. The one thing I'm noting is that most of the rib warps I'm seeing in the videos that are corrected by fluting seem to start in the opposite way to what mine look like untouched.

I think I'm probably deep into the over thinking category here.
 
The one thing I'm noting is that most of the rib warps I'm seeing in the videos that are corrected by fluting seem to start in the opposite way to what mine look like untouched.

I think I'm probably deep into the over thinking category here.


This is one of those topics that is difficult to describe on the internet, but could be grasped very easily in person if there is a fellow builder near by. Excuse my crude drawing, but I'm travelling and had to use paint, so the lines aren't the best, but I think they will explain the scenario. You said your flange is bent in the opposite direction as the one in the video - not really. It is if you're looking at the lower blue line. To fix that you could probably just bend it slightly by hand as there is a large break in the flange in the middle. The part you are trying to correct are the two upper red lines that are, in fact, bent in the same direction as the flange in the video - just not as much. You want the rib to lay flat, but more so, you want the holes - the rivet line - to be straight, so you're not forcing clecos into the work with undo pressures. Think about what's happening when you flute that flange - the slight divet you make in the flange is effectively shortening it's length, which will pull up both ends (red arrows) and align the rivet holes in the flange. As a previous poster mentioned, easy does it. A little bit of fluting goes a long way.


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Jon,

Really grateful for time taken to explain at length and draw something for me. Hope I can pay this all forward someday!

Yes you hit it spot on. I wasn't doing a great job with words, but indeed the red upper lines are bowed in the same direction as the videos showing the fluting will correct those, and the blue line is the opposite overall trend in the rib which looks like it's all caused by the web right at the midpoint.

So I will (1) try to bend out the blue line curve by hand, probably against the edge of a bench where I'll be bending the actual web of the rib to reverse the blue line, and then (2) lightly flute to aim for the red line curves.

I need to deburr that rib first and will give it a go and then post my results.

Thanks again,

Sumit
 
Guys,

Here's where I ended up. I did ping Van's and they said I can straighten the web in the middle and then flute or just flute and let the clecos straighten that inverse bend.

I did try a bit of work on the web, but got to diminishing returns on that being able to totally correct the blue profile which I'm now not convinced isn't just twist or something else. I didn't want to go too far so left them and focused on the red profiles correctable by fluting.

What do you guys think?

Thanks!

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Get a mentor!!!

I started my RV-12 build a year ago. Progress was slowwwww. Primarily because I was somewhat afraid to 'just do it'.

Found a person who was willing to tutor me at home in my garage where I am building my 12.

Fluting is just about the simplest skill to learn during your build. There are much greater challenges ahead - I consider a mentor to be absolutely necessary for me and recommend the idea to all beginner kit builders. You will finish faster and the aircraft will be better built. You will ruin fewer pieces of aluminum and consequently, not have to send Van's $$$ for replacement parts.

Recently, I became aware of a partial kit that was 'put together' by someone who either did not know better or (did not give a d**n) - the riveting was pathetic. Those parts were ugly and obviously not airworthy. Can't help but think that a mentor would have helped this guy a lot. As it was, he had about $20 of scrap aluminum in what he was calling a wing and empennage parts - really pathetic and sad.
 
For me, I find that a steel ruler will show if the holes along a flange are in a straight line. The forming process usually causes an arc and the holes sweep away from the web. Fluting makes the outside edge shorter, bringing the holes back toward the web. Flute carefully so the holes are in a good straight line. Overfluting will be seen as a hole too close to the web. Ultimately if all the holes are lined up with the piece they mate too it is done right.

Most of my pieces don't lie flat on the table after fluting - that isn't the goal really. Straight lines for the holes is the main goal. The web can be flexed one way or the other and in assembly that gets straightened out; it won't lay flat because of that sometimes.
 
E.D. thanks for the advice and noted. I did give that some thought to this point and have struggled to find someone local. We don't have an EAA chapter anywhere nearby. I think I'll reinvigorate that effort the next time I find myself stumped.

JDA, thanks for the explanation and yes I think I've reached the conclusion also that the web may not lay flat and keeping the flange holes straight is the only goal. With that said, from the pics do you think I've achieved that? To my eye, and with a straight edge laid across, they look fairly well aligned.
 
Fluting is just about the simplest skill to learn during your build. There are much greater challenges ahead - I consider a mentor to be absolutely necessary for me and recommend the idea to all beginner kit builders. You will finish faster and the aircraft will be better built. You will ruin fewer pieces of aluminum and consequently, not have to send Van's $$$ for replacement parts.
Ditto this advice, but I would go a step further. You're going to spend at least $60K to build an airplane, why not invest one weekend (or even one day) and one or two hundred bucks on a basic build course. Yes, you may have to drive a couple hours to get to one, and maybe spring for one night in a hotel, but I would argue the amount you are going to save in parts that you will not have to replace will more than make up for it. Moreover, you'll also be then able to build a better (and safer) airplane. Good luck, and have fun.
 
Mentor & basics class

Excellent advice on getting to a basics class. This will be cost effective because you will have a better idea of which tools to purchase (and from which vendors), your confidence will be up, and your 'product' will be much better.

You gotta find a mentor. Doesn't have to be an RV-10 builder - just someone who has built an aluminum airplane - preferably and RV. There must be more than a few RV builders there in BC. Search this blog - go to the nearby airports and look for someone who is flying an RV. EAA has been of no help to me but there are really good chapters out there.

Find someone to help you at least into the empennage/tail cone finish. I have built a lot of stuff in my lifetime but have found that building an RV-12 has offered new challenges and new skills to learn.

My mentor has helped me immeasurably. Make this some kind of priority.

A few years from now, you will look back on this building experience as one of the highlights of your life - you will learn an unbelievable amount of 'stuff'.
 
After you are satisfied that the fluting has straitened the holes lay the rib flat on the table and run a set square along the table and against the flange and adjust the flange so there is no gap between the set square and the flange. It's important you get the skin and flange to lay flat against each other prior to riveting. If you don't a buckle in the skin will be evident especially with the thinner skins.
 
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