Finally back to work - Fixing mistakes on my belly skin.

I am finally back to having time to work on my project! Please take notes from this entry so you do not make the mistakes I made on my belly skin installation!

My 1st mistake was not cutting my belly skin with the extension at the forward edge that overlaps onto the bottom of the center section. I simply forgot to review the plans carefully and when I laid out my bottom skin, I just forgot to include it. The plan was to put a splice that would overlap both the center section and the belly skin and rivet it into place. But then came my 2nd mistake which has caused me to re cut the forward section, so now I have included this extension.

So I cut my belly skin out in one long piece as shown on the cookie cutter sheet (sheet #7) in the plans. Reading the posts on the Yahoo Groups email list about how best to install the belly skin, most people agree that it is too difficult to install a single piece of skin. Most builders agree that 3 pieces is the way to go. I chose to cut my skin into lengths that would span between F6 and F8, F8 to F9 and then F9 to F12. But wait a minute!!! It's not that simple.

I measured the distance at the center line from the bottom of F8 to the bottom of F9 and cut my forward skin piece using this measurement. This was my mistake. This piece needs to be about 1.5" longer than this measurement because of the geometry involved at the F9 bulkhead. As you can see in the photo below, my 1st attempt was not long enough so that when I rolled the skin around the bottom of F9, my bottom skin edge did not mate up with the F9 bulkhead flange.

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After a conversation with Dave Thatcher and a trial fit of the other two pieces, I came to the conclusion that I just needed to re cut the forward section bottom skin.

One other thing that I would like to mention is that the forward edge of this forward section of the bottom skin will need some trimming to fit around the F6 bulkhead as well. I can't find where the Instruction Manual or the plans tell you this. Again this is because of the geometry of the F6 bulkhead which leans rearward at the top. You must trim the outer forward edge so as to fit nicely around the flange of the F6 bulkhead. This trimming also eliminates any interferance from the rear spar of the center section gives you when you try to roll the skin up around the F6 bulkhead flange. I found that the trimming starts where the F6 bulkhead flange begins to curve upward. Take your time trimming, so as not to remove too much material. I used some poster paper to get to shape and transferred this shape to the metal before I began cutting. Below is a photo of both the before and after forward skin pieces.

The re cut piece is on the right and is 2" longer, has the forward overlap extension and does not yet have the side flanges bent. I'll get the flanges bent this week and attempt to install the bottom skins again next weekend.

Bending up the fuel tank "box"

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I haven't done much lately but I did bend up my fuel tank "box" today. I used an 18" table top metal break that I bought at Harbor Freight a while back. This took ten minutes to complete. I bent the 1st two sides and then turned the piece around. I then bent the "joint" flange and then the final side. Again, I do not have any flanges for the top and bottom attach points because I decided to put them on the top and bottom pieces themselves.

Fuel Tank Construction Begins

I haven't worked a lot on my project lately as I have been managing my son's Little League baseball team, but I found some time this past weekend to start on the fuel tank. Actually, I have been in the planning stages for a while now. In one of my conversations with Dave Thatcher about how to proceed with the fuel tank construction, he mentioned that he had drawn up a new design for the tank which eliminates the mounting angles that are attached directly to the tank and instead incorporates straps from which the tank hangs from. This sounded good to me, so I had Dave send me the yet to be published drawings. In these drawings was a new 10.5 gallon tank design which works well with the floor mounted rudder pedals, but not the hanging pedals. So, I'm sticking with the demensions of the original 10.5 gallon tank, but I will be using the straps to hold it in place.

Here is a photo of what I have cut out so far. I used an air cut off disk to trim close to my lines and then filed up to them. I'll be cutting out the top and bottom pieces next. Another thing I am doing different from the plans is putting all the flanges on the top and bottom pieces instead of this piece (which I call "the box"). I discussed this with Dave as well and he seemed to think this was a good idea.

Finished work on rudder pedals and brakes

Painted and mounted the master brake cylinders on the rudder pedals.

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More work on my rudder pedals

I just kept wondering how I was going to lubricate my rudder pedals. After some thought I drilled a couple of #40 holes in the tubing that the pedals hang from so I can put drops of oil in them.

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I did the same on the back side of the foot pedal itself.

Not shown in the photo is another change I made to the assembly that I bought from Dave Thatcher. He used a rivet in the sleeve he used to hold the foot pedal in place. I drilled this hole clean through to the other side so I could hold the sleeve in place with a cotter pin. This way I could easily remove the sleeve if there was ever a need to without having to drill a rivet out.

Reinforcing my hanging rudder pedals

I came full circle on which rudder pedal setup to use. I had bought hanging rudder pedals from Dave early on in my build process. Then came the discussion of why they wouldn't be approved in Europe. The concern is that being attached to the hanging mechanism from only one side at the top and bottom is weak due to the twisting forces introduced when using them. I discussed this issue with my local EAA Chapter 80 Tech Counselor and he agreed that over time there might be a problem of the weld breaking due to the design. He related a story about another local Chapter 80 member and his RV6. The early RV6's had a similar hanging design. The twisting side loads from using the pedals eventually broke the weld and near disaster happened. Our fellow chapter member was on take off roll when the pedal broke. He did manage to stay on the ground, but did significant damaged his aircraft. Van's actually changed the rudder pedal design because of this incident. They added another vertical tube to the other side of the rudder pedal to make a "box" frame that evenly distributed the loads when using the pedal.

So, after I heard this story I went about trying to "fix" my hanging pedals in the same way. However, after a conversation with Dave Thatcher, it was determined that I could not use the "box" design because the additional vertical tube would interfere with the fuel tank that sits just in front of the pedals in the CX4. Darn!

By this time Dave had come up with his floor mounted rudder pedal setup and I was headed in that direction. But I’m a little hard headed when it hits my pocket book and I kept coming back to the hanging pedals I had already had purchased. Why throw away good hard money when some of the early builders who have the hanging pedals say they like them and don’t intend to switch. So, after further discussion with my Tech Counselor, we came up with a plan to reinforce my hanging pedals.

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You can see in the photo’s that we welded a couple of triangles to both sides of the upper joint and welded a strap to the lower joint to help take the twisting forces that will be applied when using these pedals.

Are these necessary? Maybe not, but now I personally have more confidence in them. As they say; “It’s my butt in there”. Be assured, checking these welds will still be on my annual inspection list!

 

That took longer than I thought it would!

I finally finished my forward access panels. It took longer than I thought it would. Mainly because it is tedious work.

Once I got the flange made and shaped the way I wanted it, I then needed to rivet it to the forward side skin. I postioned it on my workbench near the edge and clamped it in place. I marked the position of the holes and drilled through both the skin and the flange at the same time. After drilling the first hole I used a cleco as another way to hold everything in position. I used a 2nd cleco in the second hole and then drilled the rest of the holes.

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I used a similar method for drilling the holes for the cover panel and the flange. For instance, after the first hole was drilled, I used a screw and a nut to hold the position of this hole while I drilled the second hole and used another screw and nut while I drilled the remaining holes.

The nut plates were way to tight, so after a call to my friend and technical counselor, I used a tap and carefully opened them up slightly. If you over do it and make the nut plate too loose, just simply use pliers to squeeze it back to the tightness needed.

I took everything over to my friend's house and used his dimple die and rivet squeezer to put everything together.

I was not pleased with the gap around my cover plate, so I made them over again. My second attempt is better, but I won't be winning any Lindy awards with them either. It certainly looks hand made to me.

I'm glad I made these access panels and I'm glad the work is done.