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Originally posted by spinningwrench
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Boeing, Airbus, and GA OEMs disagree. Though I imagine they're wrong somehow too. -
sexy and light aren't the only requirements/drivers for choosing a material.
durability, repair-ability, cost, mounting, cost to make a design change, etc. all come into the mix. The Carbon Cub guys are looking for light, but also sexy, but I wonder about durability and the hazards associated with fabrication, damage and repair. Large Aircraft do a lot of things we can't build into ours, but show me a 737 that has a cost/flight hour under $2500 bucks and can land in 350 feet and then we can compare approaches to system function, design and materials.
I have some cub time flying in Wyoming and I'm sure the Carbon Cubs are great aircraft, but cracks in fuselages are a lot easier to identify in good ol' 4130 than they are with any composites. Floorboard take a lot of abuse, can a sheet of composite take it, if you core it can the core handle the damage, how do you identify it? how easy is it to fix and what does that do to the weight?
Also a big carbon plate between your upper antenna's and lower antennas (GPS, COM/NAV) can cause problems with interference? Corrosion...Carbon is the natural enemy of aluminum and other metals we routinely use to build with...Large aircraft spend a lot of energy to paint, seal, coat etc.
Carbon, Kevlar have their place in aircraft construction, but builders have to understand the pro's and con's...and if you're gonna use it, know that you will get a splinter and you may never get it out! The nice thing about experimental you can make it then way you want...if you want comp floor boards, go for it!
AndyComment
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Pretty sure commercial aircraft that use composite panels for the floor see a lot more abuse than anything in GA, though they are usually covered with carpet or floor pans. The 1/2" 3-ply 9lb core stuff we usually use is different than the 1/4" 2-ply 3lb I'm using for the Bearhawk, I will need to take efforts for additional protection in the baggage and foot areas. Also pretty sure carbon cubs still use 4130 tube fuselages. Not sure how a carbon plate between antennas can cause interference. CF does block RF so you don't want to surround an antenna with it, like a wingtip VOR, but floorboards made of the stuff wouldn't be an issue, or any more of an issue than the steel cage we're fixing these antennas to. Corrosion is always something to keep in mind when designing and building airplanes...
If you're worried about splinters in an apparently inevitable crash, don't make your instrument panel out of CF.
Don't discount entire material groups because of an impression, understand there are reasons they're used everywhere by nearly everyone...Comment
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I hear ya Dave, worked in the industry for 27 years (manufacturing/design/maintenance and operations) and extremely familiar with carbon, etc. I just throwing out some data for those that are trying to decide if they want to go down the composite rabbit hole. It's not a simple replace the .025-.032 aluminum with a carbon sheet or even sandwich.
I ran depot level maintenance on business jets and Boeings (737/4/5/6/7). They use comp floor panels to save weight on the passenger birds and the cargo handling systems for the freighters don't actually touch the floor boards, but are locked into rails. Chubby girls in high heels are the bane of comp floor boards...in fact we had an issue with the 767 Tanker as several areas we had to design new floorboards because the aircraft wouldn't have carpet or the dime mat.
I guess the point I was trying to make was when you add up the cost, hazmat, durability, special mounting considerations...sometimes aluminum with some rhino liner on it makes more sense!
The time we beat this horse we could have made a set of floorboards!
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Sure, but as someone who has actually fabricated and installed composite sandwich panels floorboards on my Bearhawk I'm saying it is nearly a direct replacement for the aluminum panels, aside from having to raise your controls that is. If you have the opportunity I highly recommend it. -
what was your final weight and fastener configuration? got any pics? -
Weight equivalent to the aluminum floors, slightly less since they were measured against untrimmed floor boards. Fastening is just through holes with larger nylon washers, seems to obviate the need for potted inserts.
ETA: Also, cutting sandwich panel is far easier than trimming large aluminum sheets, surprisingly less messy too.Last edited by Archer39J; 03-21-2019, 06:10 PM.
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We have a light weight marine carpet on our floors. If a person is going to coat the aluminum with truck box liner then consider doing it on the topside so it does double duty for sound and wear. if a person is truly worried about the floor drumming then they could use a Harbour Freight metal roller to roll some stiffening into the panels similar to the car guys fabbing their floors. Could roll simple x's in that fid between the fuselage tubing. It does not have to be a sophisticated as this but it give the idea.
Last edited by Glenn Patterson; 03-21-2019, 01:23 PM.Comment
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