Carbon Landing Gear Molding
02-23-2021, 05:58 PM
#1
Carbon Landing Gear Molding
Are there any good threads or articles on the techniques to mold carbon fiber landing gear? There are plenty for cowls/canopies but I haven't seen much for landing gear. I'm interested in some with a little bit of form, not just a stack of carbon.
I found a couple posts within other build threads, but they don't have much detail (can't link because I don't have enough posts, but they're in the 'Pattern Biplane' and 'Zeus' threads). For example, doing the two piece mold presumably with a parting plane, how do you do a parting plane on a thin piece, how you deal with the fabric around the edges (do you wrap it around?), do you use a core material?
If there are posts or articles I've missed I'd appreciate any pointers. Thank you.
I found a couple posts within other build threads, but they don't have much detail (can't link because I don't have enough posts, but they're in the 'Pattern Biplane' and 'Zeus' threads). For example, doing the two piece mold presumably with a parting plane, how do you do a parting plane on a thin piece, how you deal with the fabric around the edges (do you wrap it around?), do you use a core material?
If there are posts or articles I've missed I'd appreciate any pointers. Thank you.
02-23-2021, 07:35 PM
#2
Make a strong (at least 1/2" wood) FORM 6 to 10 inches long. The idea is that you are going to make a "rack" of
landing gear. Think of it like a rack of ribs. Lay up the carbon on a wax paper, or poly film, so you can be certain
the cloth is fully wetted out, then transfer it to the form. Put it in a vacuum bag, and pull at least 20" of vacuum.
Once cured you will need something like a table saw to chop off individual landing gear. The FORM needs to
have parting film (PVA) applied to it, and then the surface that is toward the vacuum bag will have "peel ply" over
the layup. Lots of people also use "bleeder felt" around the edges. The form can be made as an "inside" form,
which looks a little like a house gutter, or outside form similar to a step stool. The difference is that the "gutter"
form will make a landing gear with the shiny side up, where as the "stool" form will have the shiny side down.
This is only a brief outline of what's involved. The intended purpose of the landing gear will dictate how many
layers of cloth you use. Carbon is expensive, and has some handling challenges. I tape the edges where I cut out
the individual layers. I also alternate layers of carbon, and glass. I make several landing gear for 3 to 5 pound
airplanes. They consist of 9 layers of approximately 9oz. per sq. yd. glass and carbon. (5 layers of carbon, and 4
layers of glass). There are lots of resins to chose from, and some are better then others. I use West Systems
epoxy with great success. Of course if you only want a single landing gear your layup will only be slightly larger
then the final landing gear. I glass, prime, and paint my landing gear forms to make them as smooth as possible.
landing gear. Think of it like a rack of ribs. Lay up the carbon on a wax paper, or poly film, so you can be certain
the cloth is fully wetted out, then transfer it to the form. Put it in a vacuum bag, and pull at least 20" of vacuum.
Once cured you will need something like a table saw to chop off individual landing gear. The FORM needs to
have parting film (PVA) applied to it, and then the surface that is toward the vacuum bag will have "peel ply" over
the layup. Lots of people also use "bleeder felt" around the edges. The form can be made as an "inside" form,
which looks a little like a house gutter, or outside form similar to a step stool. The difference is that the "gutter"
form will make a landing gear with the shiny side up, where as the "stool" form will have the shiny side down.
This is only a brief outline of what's involved. The intended purpose of the landing gear will dictate how many
layers of cloth you use. Carbon is expensive, and has some handling challenges. I tape the edges where I cut out
the individual layers. I also alternate layers of carbon, and glass. I make several landing gear for 3 to 5 pound
airplanes. They consist of 9 layers of approximately 9oz. per sq. yd. glass and carbon. (5 layers of carbon, and 4
layers of glass). There are lots of resins to chose from, and some are better then others. I use West Systems
epoxy with great success. Of course if you only want a single landing gear your layup will only be slightly larger
then the final landing gear. I glass, prime, and paint my landing gear forms to make them as smooth as possible.
02-23-2021, 07:37 PM
#3
I'm the author of the Pattern Biplane thread. I did make molds for the landing gear but since then found a source that was less expensive then I could make them. For a landing gear you would simply make the mold the same as any other mold with a parting flange. The difference is you want to completly fill the mold when making the gear. You really need to compress the fibers together to make a gear that won't delaminate. You basically overfill both halves and then clamp them together. Yes some of the fibers will work their way between the two flanges. With some practice you will get a feel for how much fiber you put into each half. Typically I just pack the molds with 50K tow but if you are after a nice CF cloth look you would need to bag the CF cloth into the mold first then once the shells are formed you can fill them with tow and clamp the molds together. Hope this helps.
02-23-2021, 08:15 PM
#4
Okay, great, thank you both for the information.
speedracerntrixie, in your method, is it safe to assume then you will end up with a rough edge where the two mold halves meet that you cleanup/sand after pulling the part? I'm not worried about looks much because it would likely be painted, but it seems like there would be a real art to laying the fabric for nice seams if you wanted the raw look.
speedracerntrixie, in your method, is it safe to assume then you will end up with a rough edge where the two mold halves meet that you cleanup/sand after pulling the part? I'm not worried about looks much because it would likely be painted, but it seems like there would be a real art to laying the fabric for nice seams if you wanted the raw look.
02-23-2021, 08:23 PM
#5
Yes there will be some flashing that will need to get trimmed. The amount will depend on practice/skill level. If you remove most of it with a file and then finish with fine sandpaper you could then go back and apply a very thin application of laminating resin to the tooled edge and it almost disappears. Good quality epoxy laminating resin actually polishes up really well.
