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Instrument access in fuselage
I am considering making three entry access points on the top of the forward fuselage, in order to gain an easier way to install wiring and instruments.
I need to know exactly how to do this and also a way to waterproof so water does not leak into the fuselage. Does anyone know of a video or instructions? Thanks Dave |
Not really needed with standard EFIS installs. Pull the EFIS display and you have a lot of access. Put a few connectors on the rest of the panel and just pull it when needed. I can have the whole panel out and on the bench in 15 minutes.
Carl |
Several have done that, including me, and
so glad I did it! I have done many panel upgrades to my -6A, tip up, and have never had to get on my back, under the panel. I can't post pics, but if you will send me an email, I can provide a few. FYI, I seal mine with heavy silicon GREASE, like that used for swimming pool O-rings, and such.
Several others have done the access panels --- search the forum. Ron |
Access panels.
I put three access panels in the front skin of my 9 tip up. It’s time consuming to do it. I asked a friend that put them in his 7 if he would do it again and he said yes. So I went for it. They made it very easy for riveting the skin. I’m assuming you have not installed the skin. Important. When laying out the holes,the two that are on the sides run parallel to the longeron. They are trapezoids not rectangles.
Layout the locations on the skin and carefully cut them out, file and clean the edges. Layout and drill #40 holes around the perimeter using proper edge distance. I used a rivet fan to space the holes. Cleco on the skin to the airframe to fit the backer plate. Rough cut the plate oversize as it will change as it curves. Match drill the backer plate and cleco all around. Trace with a sharpie around the hole onto the backer plate. Remove the backer plate and create an outside line 5/8” from traced line, then do the same 5/8” inside the traced line. Cut both inside and outside line, clean and polish edges. You now have your backer plate. Next make the cover plates. These must be made with the skin cleco’d to the fuse. Rough cut larger than needed. Match drill and cleco. You will need a helper to climb in and push the plate to conform while you match drill. Trace and cut 1/8” outside the line. The plate now needs to be finely tuned to fit the hole. Cut and file to fit. Cleco on the backer plate for support while fitting. When your happy with the fit, if not make another one, layout #40 holes, match drill cover plate into backer plate. The rest is straight forward. Dimples for rivets and #6 screws in cover plate. Install nut plates in backer plate. Last is to rivet the backer plate if your satisfied with the fit and finish. Otherwise do it all again. It’s only a small amount of 032 sheet skin. ![]() ![]() |
One solution
Here is one solution. I used these on my RV-7, it was faster than fabricating my own.
http://www.mykitairplane.com/product...rvak/index.htm |
Keep in mind that the skin of the aircraft is part of the primary structure, cutting big holes in it without sufficient reinforcement may lead to problems.
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Look at Paul K's picture site, he has some in process pictures, very clean work.
http://www.vansairforce.com/communit...35&postcount=1 |
I did it, but wouldn't today!
I did it on my 7a because there was so much stuff that I needed to mount fwd of the sub panel. That was back in 2007 when we were still installing analog gages. I have gotten back in there a few times but now that my plane is painted I'm trying to not have to open them up.
With the new glass panel stuff, it is a lot easier to mount that stuff between the sub panel and the instrument panel. If I was building today I would be doing that and not cutting the holes. But one thing I did and would do again is use a modular panel, mine is called the "affordable panel" But no longer being sold, I think. That way you can remove just the side you need to work on or behind. You can see my panel and my upgrades on my web site listed in my tag line. |
Danger Will Robinson! Danger!
Quote:
Aircraft structure is semi-monocoque, which means the skin is loaded as well as stringers and frames. The skin takes shear load which allows this type of structure to be very light for its load capability. If you cut a portion of the skin away, that load has to go somewhere else. Generally that means going into the stringers and frames/bulkheads. I'm sure there is some extra margin built into said structure, but without knowing the loads you're rolling the dice a bit. I doubt Van's will share this information with you. If you don't know the loads, a way around this issue is to do a capability analysis of the existing structure to determine how much load carrying capability is there. Then you design a reinforcing doubler that can take at least as much or preferably a little more load than the existing structure. Do not count on the access panel to take any load. Removable fasteners by design have loose tolerances so they can't be counted on to load up the panel. If the cutout reinforcement is undersized, you most likely will see cracking around the panel and surrounding structure. Worst case scenario is you could buckle or cripple the stringers and/or frames. |
No argument on the idea that skins are involved in load carrying in a semi-monocoque a/c structure. Having said that, follow the load paths (or get an engineer friend to do it for you). What loads does the skin above the top longerons carry? Bonus questions: What loads does the stainless firewall carry? What loads does the (screwed-on) boot cowl on an RV-4 carry?
(Hint: Look at the boot cowl skin on an RV-8.) Disclaimer: I'm definitely NOT suggesting doing something potentially structurally stupid without properly evaluating (or having a qualified person evaluate) what you're considering. Charlie edit: If one does elect to do this kind of mod (I did it), then I'd consider using #8 screws if you expect to actually remove/replace the panel. IIRC, most, if not all of the access panels that are designed-in use #8 screws. I've found the #6s to be a bit less than durable, especially when used with nut plates. Hard to get enough 'bite' with the screwdriver, especially if the skin can flex a bit while you're driving or removing the screw. |
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