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  #1  
Old 04-30-2014, 11:26 AM
CATPart CATPart is offline
 
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Default A spliced former - is this common in an RV-4?

It looks like the former is split and spliced back together. Is this a common thing that builders do to this airframe?

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  #2  
Old 04-30-2014, 11:56 AM
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Kahuna Kahuna is offline
 
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No this is not common on the 4.
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Old 04-30-2014, 12:02 PM
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Haven't seen that but what is fairly common is to see the top flange cut off the fuselage formers and a new and repositioned on riveted in its place. The fit between the fuselage formers and the top skin not being all that great in the early kits (and as far as I know the latest ones, either). The build manual actually called out that solution to the problem and had nice sketches drawn by Van hisself documenting the procedure.

That may have been what is going on here. The top of the former didn't align well with the top skin and the solution chosen was to split the former and move the top up and to splice the resulting joints.

The formers are basically just there to hold the skin in shape (well they do a bit more than that but for structural load calculations I'd assume they were ignored. The skin is sized to carry the shear and the longerons sized and spaced to carry the bending moments of the tail, IMHO. That is another way of saying that I don't think the modification in question is all that big a deal. Only question might be the number and spacing of rivets used to make the splice. You would want the strength of the combined rivets to be equal to the former metal strength in shear in both directions, etc.

A call to Van's might make one sleep better at night?.
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Old 04-30-2014, 12:32 PM
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Those of us that have done the fastback conversion have all the rear formers spliced. If it was a problem then it would have surfaced by now.
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Old 04-30-2014, 12:45 PM
CATPart CATPart is offline
 
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Quote:
Originally Posted by acam37 View Post
Those of us that have done the fastback conversion have all the rear formers spliced. If it was a problem then it would have surfaced by now.
Is it a similar splice, just using a flat plate? Do you have a picture you could share?
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Old 04-30-2014, 12:50 PM
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Common the RV-3....
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Old 04-30-2014, 01:05 PM
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Similar situation is required on many RV-6's. Here is how I spliced a bulkhead on N399SB fifteen years ago:



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Last edited by Sam Buchanan : 04-30-2014 at 01:08 PM.
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  #8  
Old 04-30-2014, 01:17 PM
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az_gila az_gila is offline
 
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I bet it is common.

The formers were not sized well, so if the height was made to fit, the width would probably be wrong.

One fix was to reposition the formers fore and aft a bit to get the height correct, and then to adjust the overlap of the left and right halves of the formers to fit the width. However, if you followed the plans and riveted the halves together first, then the height needed to be fixed by a splice as shown.

There were several lists of variations of revised spacing of the formers floating around for the -4 and -6 fuselages to compensate.
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Old 04-30-2014, 02:37 PM
Christopher Murphy Christopher Murphy is offline
 
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I haven't looked at a lot of -4s but I am sure it is common. Not sure I like how it was done but as previously mentioned, it is called out in the manual.

Mine has at least one bulkhead former spit and re joined at the top.

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Old 04-30-2014, 02:57 PM
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Quote:
Originally Posted by Sam Buchanan View Post
Similar situation is required on many RV-6's. Here is how I spliced a bulkhead on N399SB fifteen years ago:



Yes it is common in the 3, 4, and 6 airframe. The bulkheads would be cut and spliced to make the tail cone look nice, straight, and smooth. That was a faster way than moving the bulkhead forward and aft to get the same end results.

I did my -6 similar to the above more than 18-years ago.
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