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  #271  
Old 09-05-2016, 08:03 PM
David Paule David Paule is offline
 
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Lately I've been working on my replacements for the F-312 ribs. These run from the firewall center engine mount bolts to the main spar bulkhead, a lot like on the RV-4. The RV-3B plans calls for a rib that doesn't quite get to the spar bulkhead. It's slanted and terminates on the belly skin just forward of the wing spar splice fittings.

First I had to lay out the part and cut it to shape. You should be able to see the layout. I have a borrowed air nibbler that leaves a spiral kerf. In this case there was a narrow edge that was attached so I had a rare two-stage squiggly.



Once the end fittings were made an a plan of construction developed, I made and clecoed in the pieces. Here's the left one from the bottom left. You can see the two spar bulkhead attach points. Right now they are lined up on 1/4" shims. These fittings get drilled to the ribs and installed after the splice plates are in place on the spars



Here is the front flange of the right rib and its engine mount bolt attachment fitting. This section is much like the RV-3B plans.



This shows the inside. The upper 3/4 angles are on the inside like on the RV-3B version. The spar bulkhead end is slightly narrower than the forward end to give me slightly more leg room. When I sat in an RV-3, I felt this was worth having -- and I'm neither tall nor excessively fat. I do have wide thighs, though, and that's where this extra room should help.

And yes, you can see that my roughly-bend flanges left the ribs curved; I'll flute those flanges later.



When I was lining the rib up and figuring out its shape and dimensions, I used a skin simulator to locate the rib flange. The simulator was just a piece of 3/4 angle from the firewall area to the spar bulkhead splice F-303F.

These photos are also available on this other server in case Tinypic goes away. Here, they have more pixels.

Here,
here,
here,
here.

Dave
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  #272  
Old 09-05-2016, 10:01 PM
rockwoodrv9 rockwoodrv9 is offline
 
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Dave, you are really pulling it all together. Nice. I remember when you started!
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  #273  
Old 09-09-2016, 08:27 PM
David Paule David Paule is offline
 
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On the RV-3B, the bottom forward lower longerons are riveted to the F-303 spar bulkhead. You can see this on drawing 21 pretty well, with the lower longeron riveted pair inboard of the F-303E side plate. For the plate and the spar bulkhead, see drawing 11.

The side plate means that the lower longerons attach inboard of the skin by .063. No concern, though, as SK-45 shows how to deal with that:



That seemed a bit of a kluge, frankly. I thought perhaps that I might be able to joggle these longerons at that intersection. Yes, the lower one was 1" x 1" and they were both 1/8" thick, but even so.

If you'll go back, back to post #240 or so, you'll see a longeron bending tool. Look closely. Notice how this is not a hydraulic press? And how there aren't any tool steel forms standing by? I noticed that, too. Both of these, I might add, would have increased my confidence considerably.

This has been a week that's just been too full of non-RV stuff. Here and there, I've had some time to play, though. And my scrap bin had a number of 6061-T6 angle extrusion cut-offs that were the right size and the right material and which I didn't seem to actually need at this moment. So I played.

After I ruined most of my 1" angle scrap, I'd learned the techniques.

1. Start at the bend farthest from the end and clamp the end in a vice with soft jaws.

2. Allow 1" for any compressive bend on the upstanding flange, and 3/4" for any tension bend on that flange. Allow 2 3/4" between bends.

3. Bend it a bit. Reposition the tool and correct any out-of-plane errors.

4. Move to the bend closest to the end.

5. Remember which way to bend it. Bend it a bit. Reposition the tool and correct any out-of-plane errors.

6. Go to the fuselage and see how far off it is.

7. Take it back to the vice and items 3 through 6 as needed.

Here's my successful trial piece. I've clamped it to a piece of straight angle so I could see the joggle. The bend on the left is marked 3/4" and it's from this piece, correcting errors, that I learned to make it 1".



Since I took that photo, I've joggled all four of the lower forward longerons and have yet to do the ones on the F-315 seat ribs. It's slow going but it is possible.

The pictures are also here and here.

One small thing worth mentioning. You might ask, well, structurally, which approach is better? And the answer is that I think Van's method shown in SK-45 is better. It's slightly lighter, slightly stronger, and doesn't need a tapered shim on the transition section like my joggles do. However, the strength is only better if you make a careful fillet radius at the change of section. If you leave it sharp-edged, then the joggle is probably less likely to have issues in the distant future.

Or maybe not. The bending, after all, does introduce its own cold-working changes to the material. Want to see an extreme example of that?



In this bit of scrap, I was still using a negligible length to absorb the bend. And I positioned it at a #40 hole. You can clearly see the over-stress as the bend put the hole and the area at the edge in tension. And the hole has elongated, too. Scary, isn't it? That's why I changed the process to include 3/4" to absorb the bends. What did I do right? The mark to show which way to make the bend is a good thing. It's easy otherwise to bend it the wrong way.

This was scrap, remember.

Dave

Last edited by David Paule : 09-09-2016 at 08:32 PM.
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  #274  
Old 09-10-2016, 01:49 PM
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longranger longranger is offline
 
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David, with a bend that long, it looks to me like you might end up with a wavy skin fit like what you are trying to avoid. On the bottom of the seat backs on the RV-7 the 3/4x3/4x1/8 6061 stiffener angles get notched identically to your illustration above to fit around the hinge. Not having a milling machine, and after a failed attempt free handing it with a scotchbrite wheel I hit upon a technique that, while very tedious, worked quite well:

Mark the area to be notched with dye-chem or sharpie and use the vixen file to just file off the ink. Use a scrap angle clamped crosswise to keep the notch square. Lather rinse and repeat a few dozen times until the notch gets to the desired depth. It took about a half hour per notch. See my build log here for photos of my setup and results.
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  #275  
Old 09-10-2016, 03:55 PM
David Paule David Paule is offline
 
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Miles, I'll fill the gap with a tapered shim. Not real happy about that but it'll be necessary.

Dave

Last edited by David Paule : 09-11-2016 at 12:57 PM. Reason: spelling
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  #276  
Old 09-10-2016, 09:16 PM
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longranger longranger is offline
 
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It would take me longer to make the tapered shim than it did to file the notch.
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SB Fuselage Just Past QB Stage


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Picasa: Empennage Album, Wings Album, Fuselage Album


1955 Cessna 170B flying since 1982


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  #277  
Old 09-11-2016, 12:56 PM
David Paule David Paule is offline
 
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It might for me, too... I've been thinking of how I'm going to do that and so far the best idea might just follow David Howe's concept of using an aluminum-filled epoxy shim that has gaps at the rivet locations for a local aluminum spacer.

I don't want anyone to think that the joggled lower longerons are optimum; they aren't. But it's how I did it. And I should say that the non-optimal aspects are relatively minor in this case. You know when you get an idea and want to follow it through? That's what happened.

The best way to do it, I think, would be to use a mill. If the angle is oriented correctly, that would leave a generous fillet radius at the change of contour. The axis of the cutter's rotation would be parallel to the width of the flange.

Dave

Last edited by David Paule : 09-11-2016 at 12:59 PM.
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  #278  
Old 09-14-2016, 04:48 PM
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ppilotmike ppilotmike is online now
 
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Quote:
Originally Posted by David Paule View Post
Miles, I'll fill the gap with a tapered shim. Not real happy about that but it'll be necessary.

Dave
I looked at mine and that's exactly what was done (tapered shim).
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  #279  
Old 09-15-2016, 09:38 AM
jliltd jliltd is offline
 
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Quote:
Originally Posted by David Paule View Post
Getting ready to install the tailwheel mount to the fuselage and encountered a bit of an issue. The tailwheel assembly, the part that bolts to the aft end of the tail spring, is loose on the tail spring. There's a couple degrees of free-play in the roll axis, even with the AN3 bolts all the way seated.

Dave,

The original RV-3 tailwheel spring rods are a smaller diameter than the follow-on aircraft. So they fit loose in the standard tailwheel mounting socket. The RV4+ tailwheel springs fit tighter in the socket. I don't know which of the two diameter spring rods you have but it looks from the photo to be a later version.




My RV3B has the original smaller diameter rod and a non-swiveling tailwheel assembly consisting of a 90 degree bend in the spring used as a pivot (common to early RVs). So I contacted flyboyaccessories (Vince/Blake Frazier) back in June and provided them measurements of the smaller diameter RV3 spring and implored them to provide a modified mounting socket for the smaller RV3 spring. Yesterday I talked with Blake on the phone and they not only complied with my request they have added it to their lineup as a stocked option. So while I had him on the phone I ordered an new full swivel Screaming Eagle tailwheel assembly and new lightweight wheel with the RV3-optioned mounting socket and steering arm with tiedown ring. I will remove my tail spring rod, cut off the original bent end and machine lathe it to the new 33/64" diameter mounting socket per the instructions included.

I would encourage you to call Blake or Vince and talk to them on the phone. They know as much as anybody about RV tailwheel installations.

I too had a Cessna 180 that had been previously converted to an Alaskan Bushwheel and looking at the original Scott casting showed that whoever did the swap used a sledge hammer to "gently" nudge the Scott off the spring. The old assembly was a total.

Jim
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  #280  
Old 09-15-2016, 12:15 PM
David Paule David Paule is offline
 
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Mine is the current version.

The issue here is oversized bolt holes, not the fit of the assembly on the tail spring itself.

Dave
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