Carbon Fiber Baggage Door Project

I am not happy with my baggage door (sits up 3/32" in front) and have decided to attempt fabrication of a carbon fiber replacement. Why not just buy the parts from Vans and remake the door? Because they're all matched hole now and my kit is an early version. The probability of those parts fitting without a lot of cutting, patching etc are nil. Besides, I haven't worked with carbon fiber and this will be a fun learning experience I hope.

So, I wanted to outline my "plan" and get the feedback from the more experienced (read everyone else out there) composite gurus.

In terms of making a "mold", my plan is to use some thin plastic (an old "for rent" sign) cut to size and shape, and use it to cover the baggage door opening using packing tape, etc. I may use a couple of aluminum stiffeners taped to the back of the plastic to add strength and stiffness. The goal here is to provide a backing for making the mold from fiberglass that will be used for laying up the carbon fiber off the plane.

I figure that I'll lay up 3 plies of glass on the plastic backing, let it cure, remove it from the fuselage, sand, smooth, and seal with neat resin. Then after all that, I'll layup two plies of carbon fiber on the fiberglass mold using wax and PVA mold release. Once that's done, cutting, sanding, adding additional reinforcement, and provision for the lock and pins...detail work.

From high level point of view, does this sound like it has a chance of working?

Just curious if you have asked Van's about producing parts without holes for ya...

Unless you're just looking for a bigger project. LOL

MercFE said:

Just curious if you have asked Van's about producing parts without holes for ya...

Unless you're just looking for a bigger project. LOL

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I have to admit that part of this is wanting to see if I can do it. The supplies are cheaper than buying the parts from Vans as well. Also, I just don't believe that the parts from Vans are going to fit, holes or no holes. My current baggage door was modified significantly to make it fit as well as it did. If I had tried to use the parts as they came, there was no way they were even close. If I have a choice between buying more parts from Vans and having to hack them up to make them work, or trying something new, I'll opt for new.

Mark, I'm 100% for the idea of trying new construction methods, but...

First, carbon and aluminum don't mix, a corrosion issue. That includes the steel and aluminum fasteners, the lock, etc. Everything needs to be insulated to live long term.

Second, you're talking about a two ply layup as structure. Even in carbon, it won't have good stiffness, because it lacks what engineers call "moment of inertia" or "second moment of area"...it has no distance between its neutral axis (center of the thickness) and the outer surfaces. That's why your cowl has a honeycomb core.

A cored carbon or glass door is probably heavier than an aluminum door. It will unquestionably be heavier if filler is required to finish it. That brings us to the mold, which has to be near perfect if the finished part is to have little filler. The fiberglass shell mold you propose will pick up every detail of the plastic sheet and tape, so it will need a lot of finishing.

I like glass work, but there is so little merit here that I wouldn't do it. And for what it's worth, I built my aluminum baggage door from a blank sheet (the top skin cutout) because I was too dumb to look for the prepunched door sheet in the parts box.

DanH said:

Mark, I'm 100% for the idea of trying new construction methods, but...

First, carbon and aluminum don't mix, a corrosion issue. That includes the steel and aluminum fasteners, the lock, etc. Everything needs to be insulated to live long term.

Second, you're talking about a two ply layup as structure. Even in carbon, it won't have good stiffness, because it lacks what engineers call "moment of inertia" or "second moment of area"...it has no distance between its neutral axis (center of the thickness) and the outer surfaces. That's why your cowl has a honeycomb core.

A cored carbon or glass door is probably heavier than an aluminum door. It will unquestionably be heavier if filler is required to finish it. That brings us to the mold, which has to be near perfect if the finished part is to have little filler. The fiberglass shell mold you propose will pick up every detail of the plastic sheet and tape, so it will need a lot of finishing.

I like glass work, but there is so little merit here that I wouldn't do it. And for what it's worth, I built my aluminum baggage door from a blank sheet (the top skin cutout) because I was too dumb to look for the prepunched door sheet in the parts box.

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OK, since I have no idea what a "motion of inertia" or "second moment of area" is, I can see that carbon fiber is not for me on this. I guess I will very reluctantly buy more expensive, ill-fitting Vans parts and try again. Thank for warning me off this!

Have you thought about getting the newer prepunched door parts?

We have an old fuselage QB-8 in work at the moment, and we bought the new door parts out of curiosity - cleco'd together, they seem like they will work very well.

EdH said:

Have you thought about getting the newer prepunched door parts?

We have an old fuselage QB-8 in work at the moment, and we bought the new door parts out of curiosity - cleco'd together, they seem like they will work very well.

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That's what I will end up doing. The thing I am skeptical about is those parts, which are made for the matched hole fuse, working with my pre-matched hole, hand built fuselage. But, I have no choice but to give it a try.

Don't give up...

Mark Dickens said:

OK, since I have no idea what a "motion of inertia" or "second moment of area" is, I can see that carbon fiber is not for me on this.

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Don't give up so easily. I've nearly finished building a whole plane from composites, and you're throwing in the towel on a door?! The project you're describing can be done in two work sessions, maybe 4 hours total work. It would be much less if you were doing this on a regular basis and had all of the materials at hand.

You just need some thickness to the part when it is done. 2 layers of carbon, especially if it is flat and doesn't have curvature in a couple directions, will be pretty floppy. You can add thickness in the form of hex core or foam core.

Do just as you said, making a new door from plastic, tape, whatever you like. Cover it with packing tape as a mold release, and spend some time getting it right so the tape is smooth and doesn't overlap. Do a layup of fiberglass over this area, and do yourself a favor and put some soda straws into the back of it in an X pattern. Cover the straws with a layer of glass too. Let this cure and then pop it off. Sand, micro fill, and sand the face of that mold.

Mold release the face with either more packing tape, or preferably spray PVA. Layup a sandwich of 2 layers of carbon, one layer of Lantor Soric that is cut ~1/2 - 1" smaller in each direction so that you have a carbon-carbon bond on the edge, then a final layer of carbon. Peel ply the back with Dacron, and let it set up. If you're after a nicer part, vacuum bag it, or Lo-Vac it. When it is cured, pop it out, sand the face, and prime and paint as usual.

You could also use the soda straw X instead of the Soric, but it is tougher to get the carbon over the straws to lay nicely. The Soric will make you have a finished door that is ~0.150" thick, and very stiff. DanH is correct, anywhere you have a metal fastener you should add a patch of fiberglass to electrically separate the carbon and the metal.

Watch out for those carbon slivers. They hurt!

Stiff panel from carbon fiber

Dan is the undisputed resident expert for good reason ! That said, here is some general experince FWIW. I was amazed at how stiff you can make parts from 1/4" foam sheet sandwiched between single layers of glass or carbon. I used it to replace the canopy frame and skirt on my RV-3. Plan ahead on the final finish you desire. Carbon is a coarse weave. You will need micro if you desire a smooth surface.

Why CF?

Why use carbon fiber? The finished part will not gain a lot of weight if you are doing a std layup (no vacuum) if you use thin glass to start with; if you are going to use vacuum, then I can see a very slight gain with CF.

Yes, you will need to use a core material to get the door just so, and expect it to survive. I used 1/8" foam in the F1 cowlings, and some other parts - those came out very stiff. Seems to me that this easy process would work for your door too.

I see the largest problem in this whole process as getting the mold shape correct. My guess is you will spend more time getting that part right.

I say give it a shot! This is experimental aviation!

krwalsh has some great tips there!

Carry on!
Mark

Thanks all for the comments and encouragement! I think I'll give it a shot and see what happens. Either way, I'll learn something new in the bargain! What's the worst that can happen? Waste of time and money? Not like that's a new phenomenon for me!

Mark Dickens said:

T . . . Waste of time and money? Not like that's a new phenomenon for me!

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Yes, but WE always learn something. I enjoy learning more about build techniques. It would be more fun if I was flying by now, but that will come soon.

Keep us posted on trials and successes!

I have considered doing this on an -8. I'd suggest that you lay a stiff card over the door area as others suggest, but well oversize. Make it some non stick material and PVA or wax it, then using fiberglass mat and polyester, just splash the whole area. You are not worried about weight here, so make the mold thick and stiff. As for the door itself, as others have suggested, carbon will not buy you any benefit here over fiberglass. You will need to do a sandwich anyway, so save the money and do glass. Much easier to work with too.

For reference, a carbon Lancair IV door is 3 ply outer laminate, 1/4" nomex core, and 1 ply inner laminate. These are made from prepreg and vac bagged, obviously.
As others have mentioned, I think the key will be creating a mold surface the is perfect. Any substantial bodywork will negate the weight savings.

Regards,

Brad Simmons
Airframes Inc.
Milan, TN
[email protected]

Not a new idea!

Back in '05-'07 these were available! I actually gave one away at an RV fly-in in KY as a door prize. They were made by Charles ? (senior moment here) and were carbon fiber. They fit perfectly and I know there were at least a couple that were sold. IIRC he used 1/4" foam for the core and beveled the edges so the fabric didn't have to go around a sharp corner. I believe he vacuum bagged them, but I never saw the parts being built. Shortly after he went out of business, I would suspect for good reason. He is the same guy that built the carbon fiber canopy frame for my RV-9A and several other planes, one belonging to a member of VAF. His work was beautiful, and it was an excellent productat a good price. I would think there is a market for these, if you develop a good mold.

Bob

Carbon Baggage Door

I bought one of these back in 2003, it fit excellent and had a nice locking latch mechanism. Perhaps the original supplier still has the mold. I had one extra door that someone could pull a mold off if I can locate it.

Frank

Toobuilder said:

I have considered doing this on an -8. I'd suggest that you lay a stiff card over the door area as others suggest, but well oversize. Make it some non stick material and PVA or wax it, then using fiberglass mat and polyester, just splash the whole area. You are not worried about weight here, so make the mold thick and stiff. As for the door itself, as others have suggested, carbon will not buy you any benefit here over fiberglass. You will need to do a sandwich anyway, so save the money and do glass. Much easier to work with too.

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I am obviously not knowledgeable about carbon fiber, but the reason I was planning to use that is that I wanted the outer skin to be as thin and stiff as possible so it didn't sit up proud of the surrounding skin. My thinking was that fiberglass (8oz harness would be the plan if I went this way) would be thicker and not as stiff. Is this incorrect?

Hello Mark
I had problems with the door fit also on my pre prepunched kit. The door for these older kits is still available from Vans. Call them and ask for it specifically. I found the key to getting a good fit after several attempts. On my kit# 80660, I found the fore and aft door ribs had a different curvature than the curvature of the firewall and top skin. I used a sheet metal hammer and dolly to reshape the curvature of both the fore and aft door ribs to get them to match the curvature of the top skin bulkhead and the firewall. I now have a very tight fit. This may be easier than trying to create a composite door.
If you must create a composite door, you may want to use the door skin and build a composite support structure for it. This worked for me, but I rejected this option because of the weight of the composite door. But I admit to not doing well with composites anyway.

Mark Dickens said:

I am obviously not knowledgeable about carbon fiber, but the reason I was planning to use that is that I wanted the outer skin to be as thin and stiff as possible so it didn't sit up proud of the surrounding skin. My thinking was that fiberglass (8oz harness would be the plan if I went this way) would be thicker and not as stiff. Is this incorrect?

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I would suggest two layers of 4oz compared to a single 8oz layer - use #1522 fabric for this. Lay one later at 0 and the next at +45. Same with the bottom layer(s).

Too builder's idea of a splash is spot on, and pretty easy to do.

You can do this!

BTW I need a splash of an SF-260 tip tank (only the outer sfc, thank you), if anyone feels like supplying one.

Carry on!
Mark

When does carbon pay off ?

F1Boss has a good point! I used carbon and glass because I just wanted to play with carbon. Setting cost aside, there are trade offs in weight, conform ability and finish that should be understood to make informed use.

Does anyone know of a source of info ( for layman's consumption ) that conveys the features , benefits , proper process etc of glass compared to carbon ?

Mark Dickens said:

I am obviously not knowledgeable about carbon fiber, but the reason I was planning to use that is that I wanted the outer skin to be as thin and stiff as possible so it didn't sit up proud of the surrounding skin. My thinking was that fiberglass (8oz harness would be the plan if I went this way) would be thicker and not as stiff. Is this incorrect?

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In this case, I retract my statement. This is exactly where carbon shines, and is the reason I use it in places. The top windshield frame on the -8 is carbon and razor thin. I'm also doing gear leg intersection fairings on the Rocket in carbon. All that said, the edge of a glass baggage door could be disguised to be nearly invisible on an -8. Even the glass layup is going to be pretty thin around the perimeter.

broken1234 said:

....the key will be creating a mold surface the is perfect. Any substantial bodywork will negate the weight savings.

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Thanks Brad.

Well, if you insist on re-inventing a perfectly good aluminum door, sidestep the whole mold finishing process by fastening a clean aluminum sheet over the door opening, then flox some plywood ribs to the backside to fixate the curvature. Now you have a slick mold surface ready for wax and PVA.

Here's an example, a replacement for a lost Falco gear door.



The problem was that the underside of the wing had curvature, just like your baggage door. So, clamp a sheet firmly to the surface:



Blob flox on a plywood backup board...



...then gently smoosh the floxed board against the sheet and fixate for cure...



....which locks the curvature into the aluminum sheet. No mold surface finishing is necessary. Just add wax and PVA...



...then do the cored layup and bag it. Here I just bagged the whole mold sheet and plywood backup.



The resulting foam cored door conforms to the surface curvature of the wing.



Ok, so go do it!

DanH said:

if you insist on re-inventing

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Now we are getting somewhere!!! great demonstration there Dan!!!

Nifty Dan!

Dan,
Great illustration!

Brad

Gentlemen don't try to do coal(carbon) details, without vacuum, as the carbon works only on the strength with good formability.
And without carbon fiberglass in the attachment is not working.