Forward skin access panels Vs. 8 front baggage door

Cfrisella · #1 08-13-2009, 10:30 PM

Just wondering if the 8's are designed/reinforced differently to allow the large front Baggage door. I'm building a 7A and want to put a large access opening on the front top skin. Van's doesn't recomend it and other's say it will weaken the fuse. Seems to me if they can design the 8 with that massive "access opening" then my idea shouldn't be an issue. Maybe someone who's built a 7 and 8 can give their opinon.

rvbuilder2002 · #2 08-14-2009, 08:36 PM

Quote:

Originally Posted by Cfrisella

Just wondering if the 8's are designed/reinforced differently to allow the large front Baggage door. I'm building a 7A and want to put a large access opening on the front top skin. Van's doesn't recomend it and other's say it will weaken the fuse. Seems to me if they can design the 8 with that massive "access opening" then my idea shouldn't be an issue. Maybe someone who's built a 7 and 8 can give their opinon.

One consideration might be that the 8 is tandem seating and more of a narrow tubular fuselage. The seven is much wider and not as torsionally stiff on its own.

scsmith · #3 08-15-2009, 03:02 AM

In the RV-8, there is a baggage floor and vertical partition that ties the structure together in a way that regains most all the torsional stiffness lost by having the door. Its all about closing out bays. If you were to put a floor under your instrument bay, you could probably have an access panel, Or it would probably be ok if the panel was retained with screws around the perimeter, not just quarter-turns or something. Then, it is still acting as a structural skin when all the screws are in.

billdianne · #4 08-15-2009, 07:37 AM

Quote:

Originally Posted by scsmith

In the RV-8, there is a baggage floor and vertical partition that ties the structure together in a way that regains most all the torsional stiffness lost by having the door. Its all about closing out bays. If you were to put a floor under your instrument bay, you could probably have an access panel, Or it would probably be ok if the panel was retained with screws around the perimeter, not just quarter-turns or something. Then, it is still acting as a structural skin when all the screws are in.

This brings up the question of the instrument access doors cut into the the back of the RV8 baggage wall. I've seen the door retained by screws and in others by Camlocs. All of them had a doubler added around the perimeter of the opening. What is the thinking on using Camlocs ( for easier opening) vs screws?

n2prise · #5 08-15-2009, 09:46 AM

I did all those things you guys are discussing. I put the access panels in the forward top skin of my RV-9A as you can see starting on this web page when I was under construction. I did not change anything about the three ribs between the firewall and the instrument panel. Riveting the front skin on was easy, and I did it without any help. I have opened only ONE of those two panels since the airplane was painted when I was adding a serial bus connection to my Garmin SL-30 NAV/COM radio. http://www.n2prise.org/rv9a095.htm

I mentored a first-time RV-8 builder friend of mine. The access door to the avionics area was one feature we had seen on another RV-8. Here is how that installation went. It begins on this web page: http://www.n2prise.org/wfrv8016.htm

Here is the finished door after painting and installation seen in the second photo on this page:
http://www.n2prise.org/wfrv8079.htm

rvbuilder2002 · #6 08-15-2009, 10:31 AM

Quote:

Originally Posted by scsmith

In the RV-8, there is a baggage floor and vertical partition that ties the structure together in a way that regains most all the torsional stiffness lost by having the door. Its all about closing out bays. If you were to put a floor under your instrument bay, you could probably have an access panel, Or it would probably be ok if the panel was retained with screws around the perimeter, not just quarter-turns or something. Then, it is still acting as a structural skin when all the screws are in.

On a (semi) monocock structure like the RV-8 I would agree that would be true if the fwd baggage floor truly boxed the fuselage, but it does not. It does not carry all the way a crossed the fuselage to the right side skin. That is not to say that is is not helping at all (It probably is), but it does not box the fwd fuselage in a manner that you can assume it is what allows for the baggage door opening. Particularly since the baggage door is on the same side of the fuselage as the point where the is no connection between the fwd baggage floor and the fuselage side.

Cfrisella · #7 08-17-2009, 07:43 AM

Thanks for the replys. I'll post some pictures today of what I've done. Nothing is set in stone yet so I'd like some opinions.

Cfrisella · #8 08-17-2009, 04:09 PM

Here's a picture of what I'd like to do. I realize it's a big opening and may not be possible. If that's the case I'll just get a new skin and go from there. At the moment the panel is molded with carbon fiber, although aluminum can still be use. Is it just too crazy?

L.Adamson · #9 08-17-2009, 06:07 PM

Quote:

Originally Posted by Cfrisella

Here's a picture of what I'd like to do. I realize it's a big opening and may not be possible. If that's the case I'll just get a new skin and go from there. At the moment the panel is molded with carbon fiber, although aluminum can still be use. Is it just too crazy?

I don't design airplanes, but I build sheet metal boxes for a living. I can take flimsy sheet metal; form four sides, and then put a top & bottom on. At that point, that flimsy metal becomes torsionally stiff, and can support a lot of weight.

If I remove most of one side, or the top or bottom; the box looses most of it's strength. Our planes use the sheet aluminum in these box structures to support weight and become a rigid structure.

IMO, taking out a big chunck for access, isn't a good idea. It would have to be engineered, and require a lot of fasteners. I don't like some pics I've seen of putting doors in the rear baggage bulkhead either. Once again, the builder is removing part of the structure that stiffens everything up, and holds it in place.

That front top skin is part of a structure that's holding a lot of weight....... the engine. Then we add the prop, and all the gyroscopic forces!

L.Adamson --- RV6A

DanH · #10 08-17-2009, 06:48 PM

Chris, the issue seems to be "Is the fuselage strong/stiff enough with a big hole cut in it, or does the cover need to be structural?" If you're going to do this, obviously the safer bet is a structural hatch cover.

As a first cut at the problem, I'd suggest looking at an aluminum hatch cover, as structural fasteners in composites do not work quite the same way and can be tricky (isotropic vs orthotropic materials). I'd consider a hatch panel which overlaps the opening, with flush structural-grade screws in nested dimples and matching nutplates. The trick is determining the number, size and placement of the fasteners. Doing so is a wonderful opportunity to exercise the "education" aspect of "for education and recreation". You sound like a sharp guy, so go for it. When you think you have it worked out, have your results looked at by a pro.