Help with RV-4 Plans.

[MS1095]

I am in the process of replacing both F-405 and F-406 bulkheads on my project. One side was 1 1/2" forward of the other so I have nothing to go off of. The plans are hard to read at best.

It appears to me that the top of both bulkheads meet on the top longeron 49" back from the firewall. I am having trouble reading the measurements for the location of the bottom of the bulkheads. F-405 looks like 41 5/15 ??? and F-406 looks like 55 1/32. Setting F-406 is no problem since you set if off of the bracket bent at 18? that attaches to F-406B. I don't know where to set the bottom of F-405. it attaches to F-405B the 3/4 angle that forms the support for the front seat floor. No where in the plans to I see a measurement for how far back F-405B should be from the aft face of F-404 (spar carry through bulkhead) Am I missing something?

[Dean Pichon]

I completed my -4 quite a few years ago, so keep that in mind as you read this post.

The F-406 bulkhead is the rear spar carry thru. First and foremost is to locate this so it fits your wing. I agree that F-405 appears to be located 41-5/15" aft of the datum, but believe that dimension is 5/16.

I believe the F-405B angles should be located 41-5/16" aft of the datum. There is no (direct) reference from the F-406 bulkhead.

All bulkheads should be located to provide a fair surface for the skin. This is more important than any dimension in the plans.

The RV-4 plans were drawing before sophisticated 3-D CAD tools were available (to Van's). As a result, not all dimensions are perfect. It was quite the norm for -4 builders to build the fuselage to be fair rather than compliant with the drawings.

Good luck,

Dean

[Ricksrv4]

F-405 41 and 5/16 from the firewall, F-406 55 and 11/32 from firewall.

[MS1095]

Originally Posted by Dean Pichon

I completed my -4 quite a few years ago, so keep that in mind as you read this post.

The F-406 bulkhead is the rear spar carry thru. First and foremost is to locate this so it fits your wing. I agree that F-405 appears to be located 41-5/15" aft of the datum, but believe that dimension is 5/16.

I believe the F-405B angles should be located 41-5/16" aft of the datum. There is no (direct) reference from the F-406 bulkhead.

All bulkheads should be located to provide a fair surface for the skin. This is more important than any dimension in the plans.

The RV-4 plans were drawing before sophisticated 3-D CAD tools were available (to Van's). As a result, not all dimensions are perfect. It was quite the norm for -4 builders to build the fuselage to be fair rather than compliant with the drawings.

Good luck,

Dean

Dean,

Thanks for the reply. I should have been more specific when referring to the parts. I am talking about F-405AR-L and F-406AR-L.