ColinB

oh yes the pattern and mold making can be hideously expensive if you paid full price for the pattern machining and making of the molds

i know what you mean about the expense of structural adhesives, they can certainly cost quite a lot, a smallish (i think 1L) tin of 3M 9323 is around 60-70 pounds, fortunately it goes quite a long way if you dont waste it

also you dont need to use autoclaves, i have made prepreg parts just using oven cure under vac, but you do get a far far better result if you can apply pressure to the bag as well in a clave

You cagey rascal.

maybe hes just toying with the viewers.

i thought that at first but there are other pics with them being glassed onto the aircraft

Found this in the photo gallery over on the ezjets page

quite an interesting looking mod, anyone know much about this?

I'm relatively green to composite construction and the term prepreg was completely new to me. This thread and some additional research have piqued my interest in prepreg construction. I'm interested in what ColinB is building. Are many others using prepreg materials and methods for canard-aircraft construction? Is this an acceptable alternative to the materials and methods used in the Cozy aircraft?

Pre-preg and autoclaves arnt really something that has been used in home building before

you have to understand that this is the latest technology in composites and is usually only used in high end motorsport and aerospace

the costs for this kinda thing are normally huge (autoclaves cost a LOT of money)

to make use of prepreg you need to have high quality molds that can withstand the temperature and pressures inside the clave

as well as this you need to start looking at the materials, in this process you need to use cores that can withstand the t&p's of the process, either honeycombs or high temp foams such as rohacell

im sure it will become more clear as my project progresses and you will see how these methods are utilised

Hi, no i have the full version of delcam powershape and powermill at work

but i do know if you were to type powershape into the search on a torrent site such as thepiratebay you would find a copy on there also

That might get your epoxy percentage down to 40%

I think the 40% figure is an optimistic one just using the lowvac approach

your getting into the realms of prepreg ratios at 35-40% and i doubt people are getting that close with wetlay in most circumstances

I have a better way to seal the bags (and it even works on the hightemp bags used for prepreg and claving)

the heat sealers you use for packaging (and infact the clear packaging tubes also work well as vac bags and are ultra cheap)

seal one end a few times

place part and valve inside

then use heat sealer to seal the end up

creates one of the best vac bags iv used, iv never had a leak to find as with bag tapes and other than the cost of the sealer it costs next to nothing

you can get the hand held sealers that are best as they dont have anything at the sides limiting the width of the bag so you can even seal the really big bags by moving it along and zapping it

something like this

Whereabouts are you thinking of making camp?

Thanks for the links

iv just been reading the SAAA pages, apparently you can fit any engine and do any modifications you like (even fit a jet which i wanted to do here but was not allowed by the LAA)

making the move sound even more tempting

i think ill probably end up somewhere around Melbourne but my options and mind is open

side view of initial canard work

started work on the canard

front view

added the f10

Hi, Im currently in the UK, but i may have a job offer out Oz

now im curious how your homebuilding setup works over there?

over here the LAA that governs home built are very strict and put a lot of limitations on what you can and cant do and power restrictions as well

how do you guys over there find it?

how does it compare to the USA's EAA as they seem very permissive of modifications and engine choices

Thanks

Colin

Colin, I am a little confused about the autoclave process.

 

What am I missing???

Im not entirely sure what your asking, but ill try to explain best i can

inside the clave the part is put inside in a vacuum bag and is vacuum is applied

then pressure is applied to the clave

its the differential pressure between the part inside the vacuum bag and the outside pressure that creates a lot of force pushing the laminate into the mold

yeah the great thing about working with pre-pregs is that you can do it in a nice cool clean room (air conditioned) and it doesn't make a huge mess everywhere

its the consolidation from the extra pressure that really gives the components the better quality and increased performance

so you can still get benefits using a pressure vessel even if the cure of the parts is only at room temperature (you can use an extra slow hardener then use a slightly elevated temp to send it off giving you a bit of extra time to lay up and bag)

Hmmmmm ....... well above my pay grade as far as projects go.

That king of pressure would result in damage to our foam core method of building but I can see where it would be applicable in prepreg applications.

 

I ran into some problems earlier in the year dealing with foam cores at the joints where they were glued together (3M 78) just using regular VB technique.

 

Cool stuff all around though.

well the idea of this post is to show that its not actually above anyones paygrade

you can still use wetlay in a clave and use the extra pressure for consolidation, you just adjust the temperature accordingly (or use a higher temp curing resin)

well dont forget the foams i use are capable of 350f so that isnt an issue for me

the reason for the extra pressure is consolidation

if you can imagine the force pressed onto the laminate at 14psi (atmospheric pressure with vacuum) then if you pressurize the cylinder to 90 psi, you end up with a huge amount of force pushing the lamination into the mold and compressing the layers or even if you have a 2 part closed mold, by time you take into consideration the surface area of the mold you have several tons of force compressing the mold shut (and squeezing the laminate onto the core)

this pressure is especially relevant when using prepreg materials to achieve good consolidation

Ok, First off what im about to describe to you i neither endorse nor recommend, this device is a pressurized vessel and as such if poorly constructed can cause death and mayhem so consider this article a work of fiction and do not ever attempt to recreate this yourself, all information here was conducted by a highly trained stunt man in a controlled environment. so DONT TRY IT AT HOME! and if you do dont blame me if it goes badly

ok so now i have abolished any blame for anyones stupidly let me explain to you the fun bits

The autoclave was constructed out of a 1 meter long propane cylinder with roughly a 370mm dia.

the flanges were sent to a water cutting company and came back as nice metal objects (i will include the dxf for the flanges incase they are of interest) the thickness is 12mm in mild steel with a grove machined into one flange for the seal to sit in, and then smeared with a high temp silicone grease to create a tight seal (superlube)

the heater element and fan are just domestic oven parts very cheap to get hold of (i got mine on fleabay) and are controlled using a PID temperature controller (also a fleabay item)

there are 2 air fittings as seen in the picture, 1 is for the vacuum line into the clave to the part and the other is for the airline to connect too, the normal valve on the tank is used as an air release

if you do decide to ignore what i said about not building one of these then please make sure on the pressure test you fit the cylinder with water as much as you can, this way the uncompressable water reduces the amount of compressed air inside the cylinder and if there is a burst the amount of energy is significantly reduced

ring.dxf

not completly sure yet

but it will be of the twin opening style

i think im probably going to have my own shape to suit my fuselage

I will have my canopy and engine mounts in cad soon

TMan,

I'd like to see someone go edit or troubleshoot g-code generated by a high end CAM program, you can't. You have to run the code through a graphic interface to see each block then in most cases use the CAM software to generate new blocks to paste in. Learn to write the simple code and annotate heavily and you can go back and fix anything quickly.

Iv heard this argument before and tbh it doesn't really mean a lot

if you have a decent CAM system with a well setup post proccessor there is never a need a manually edit the code, and any alterations can be done in the CAM system itself very very quickly

I use the Delcam CAD/CAM systems of Powermill and Powershape

i find it an extremly easy sytem to create surfaces and solids (and convert from one to the other)

sometimes i find with the large PLM softwares such as NX and catia that you spend more time learning the systems than using them and they just have so much in them that it often takes longer to do what you want

i think you need to know what you expect to get out of CAD and ask yourself why are you trying to achieve? what is your reason to spend so much time building an aircraft in CAD detracting from your time building

CAD/CAM can make the build process much quicker if your using CNC, but at the same time it can be a bit of a time waster if you then have to repeat all that work to make the physical parts by hand

nothing new yet, mostly been reading and studying manuals and plans gotta get things right

ultimately the most important thing to get right is to ensure the positioning of the bulkheads are absolutely perfect

if i make a mistake here then all other work based from them will be rendered useless

i have also been a little busy rewiring my autoclave with new fan assisted element and PID temperature controller

im not a member of the EAA, as im not a US resident

I am part of the LAA that covers the UK market

unfortunately we are a lot more restricted over here, so because of this i will be limited on certain things

the main one being engine choice as we have a power limit, (we also have sky high fuel prices too) so because of this the most likely choice is going to be the Wilsch diesel engine

on the upside, i did speak with the chief engineer for the LAA today, and he doesnt seem to have any issues at all with my proposed change in materials as long as they meet the required spec (and they do)

i am considering looking into the effects of honeycomb core for a molded/ribbed wing but this could be quite a lot of work, i will need to consult with some people on that at the LAA

Having supported CAD systems for 20 years and taught classes in their usage, I know what a workplane is. I'm not talking about the workplane coordinate system - I'm talking about the Global Coordinate System. Do you understand the difference?

of course i understand the difference, and i realize you know what a work plane is, however other people reading this may not quite be so familiar with CAD systems, hence i tried to explain it slightly

anyway all im trying to say is dont read anything into the coordinate or work planes that are shown in the pictures

anyway this is really just splitting hairs as im currently the only person who is working on these cad files so whatever i find easiest to work with is the method ill use