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build composite aircraft - 3/25/2006 4:41:11 PM   
cncfoam


 

Posts: 34
Joined: 11/21/2002
From: MN
Status: offline 		Hi List,
I am looking for help in all areas of composite aircraft construction. I have two weapons at my disposal. I have a large cnc foam cutter and a cnc router. I made them both, and Im looking for a project to utilize these machines.

I would really like to produce female molds with the cnc router. I have a cutting area of 42"x22" , so it is possible to cut out wing molds of each side and have a wingspan of about 80".

I would like this thread to be like a build log and have much input as possible from everyone. I have never done any composites. I have a basic idea of how to, but never have done it.
I can navigate fairly well in Solidworks, 3D modeler. Autocad. So I have pretty much all the tools to do this project.

Hear are some pictures of my machines and some other projects that I have cut.
My foam cutter, my cnc router, foam parts to the Hurley Extra 300, 26 foot ice boat wing.

I would like to build a 60 -90 size plane, all composite.
So, I need some plans for a plane and lots of imput.

Lets start with imput.

Eric Z



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       Post #: 1

RE: build composite aircraft - 3/26/2006 2:41:57 PM   
ramagu


 

Posts: 5
Joined: 3/26/2006
From: Bristol, UNITED KINGDOM
Status: offline 		Hello ...I´m planning to build an all carbon fiber wing, my idea is to have it manufactured by a professional since I don´t have all the necessary equipment to do it properly.
The plan is to build a hollow wing, the carbon fiber would give the external airfoil geometry and I would reinforce it by myself later on by adding some spars and ribs near the wing root.
Do you have any experience in cabon fiber part manufacturing?

Thanks
looking forward for your reply

(in reply to cncfoam)
       Post #: 2

RE: build composite aircraft - 3/26/2006 3:15:14 PM   
cncfoam


 

Posts: 34
Joined: 11/21/2002
From: MN
Status: offline 		No experience on carbon fibre. I would be willing to cut out your molds. At this point I want to learn the processes involved in manufacturing parts and or kits, for composites. With the cnc router , I have the ability to cut out the female molds, no plugs to make, and I can cut out formers, all with great precision.
That is why Im doing this post, hopefully the experts will chime in and educate me/you/others on this type of construction.
I am looking to build a pattern like plane, I have a MVVS .60 with a tuned pipe that I would like to use.
Again, I can navigate fairly well in Solidworks, a 3D modeling program and Autocad. So I have pretty much all the tools to do this project.


EZ

(in reply to ramagu)
       Post #: 3

RE: build composite aircraft - 3/27/2006 3:09:22 PM   
SCALECRAFT


 

Posts: 1357
Joined: 1/7/2002
From: MONTEBELLO, CA, USA
Status: offline 		Thats a great way to save a lot of time on the plug work.

These models plugs were made by hand. Needless to say, they took a lot of time.

Is there a material that can be cut by your router that will need less finish work than foam? Some thing that can be primed right off the router table without the need to put a glass finish on??. Just a thought.

The foam wing is good, it can be covered by many materials if it is to be a plug.

My buddy suggested we learn cnc.

Steve

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RE: build composite aircraft - 3/27/2006 4:20:58 PM   
daven



Posts: 6766
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		Eric,

What kind of materials can your CNC router cut?

_____________________________

Dave Norman

klasskote.com
supertrc.com

(in reply to SCALECRAFT)
       Post #: 5

RE: build composite aircraft - 3/27/2006 7:39:54 PM   
Rikard Levenstam


 

Posts: 41
Joined: 3/11/2006
From: Stockholmwww.modellbyggeriet.se/sukhoi, SWEDEN
Status: offline 		Hi!

I almost finished with my mouldmaking period og mu Sukhoi! I hope soon to be in air and get payback of time at the cnc machine! I have a 3 axis homebuild cnc and have machined masters in wood and then made glasfibre moulds.

Anyone having experience in dimension carbonspar for a aerobatic model in 1.9meter size? I have machined a mould in Perspex(?) Plexiglas(?) Plastic!!

Please look at www.modellbyggeriet.se/sukhoi

Best regards

Rikard

(in reply to daven)
       Post #: 6

RE: build composite aircraft - 3/27/2006 8:02:28 PM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline
quote:

ORIGINAL: cncfoam Hi List, I am looking for help in all areas of composite aircraft construction. I have two weapons at my disposal. I have a large cnc foam cutter and a cnc router. I made them both, and Im looking for a project to utilize these machines. I would really like to produce female molds with the cnc router.


Wow, you have built some impressive machines there, congrats! You are in an enviable position, most guys have the 'sticky stuff' (compositess) experience & dream of having the machines & cad skills to help with teh tooling . In terms of your plan of attack, there are a couple ways to go depending on a few things like, the robustness & accurracy of your cnc, how much time & money you want to invest in the composites tooling, how many layup parts you intend to make, the quality & dimensional accuracy you are seeking etc. Heres some thoughts to get you going.

CNC MILLING MALE PLUGS, maybe more popular & established as a method in europe, typically:
- cnc each male plug half out of typical tooling material like renboard or other varieties of high density urethane
- a center splitter datum is integrated into the surface file as well as features like alignment detents & clamping datums
- the plug surface get surface prepped, usually final finishing with tough high end auto paints, then polished etc
- an epoxyglass female mold is made from that male plug
- the layup then occurs in the female mold (just like any conventional mold made from non-cnc plugs inbedded into profile boards)
Pros
- the original cnc plug can be utilized to make more molds. In fact this is what certain euro teams do specifically seeking to recoup their investment by renting out the plugs to end users for a licence fee.
- its a time/cost compromise of both handwork to acheive a high quality finish & bullwork for the cnc to acheive very close to the desired shape.
- I am aware of individuals who have done essentially this procedure but using low cost MDF wood (well 'H'DF) laminated, sanded, epoxy/primed etc & have produced dimensionally stable tough plugs in the same way
- ability to laminate up thickness from dimensionally thinner stock
Cons
- cost, the tooling board material itself is not cheap & can approach the cost of say aluminum female molds
- the lighter the density tooling board, the more surface prep work is required & higher degree of distortion
- you are still left with the task of making female molds & all that that entails, material cost, tooling gel, reinforcement backing, maintaining rigidity, a certain life, edge degradation etc
- depending on the actual material, distortion can still be an issue. Its not uncommon to see the plugs mounted (epoxy grouted actually) onto a steel tube frame.

Here are some links to give you a feel for the tools & methodology of this option:
http://www.rcgroups.com/forums/showthread.php?t=229462
http://www.rcgroups.com/forums/showthread.php?t=141255
http://www.rcgroups.com/forums/showthread.php?t=270446&highlight=jibe


CNC MILLING FEMALE MOLDS

- start with a sold blank of 'finish' material & mill the female finished mold cavity from which the layup occurs in. Aluminum comes to mind & it is used in certain applications,
Pros
- easier milling than say steel, but still spends a lot more time on the mill (this may not be an issue with the machine residing in your garage!)
- long lasting tool, super high quality finish
- if done right, dimesnionally stable & can integrate alignment & clamping methods
Cons
- more demanding of the mill, clamping, horsepower, duration of milling
- if the step resolution is too course, the blocking & polishing process can be painfully long, it still involves handwork
is one of the softer materials for milling & can acheive a high finish
- sometimes very difficult to get into sharp nooks & crannies (think of the nose ring area or flaring wing fillets, or wing saddles on a fuse for example). The limitation may be the diameter of the ball cutter, or just getting the cutting tool in there.
- weight of the mold can be very clunky dpending on the size of the project, not bad for skinny racing wings or other high performance applications, probably prohibitive with larger projects. This becomes an even bigger pain when vac bagging.

Here is a project I was involved with for a friend, check the pics & videos showing this kind of tool (Q500 wing).
http://www.hmracinginc.com/


My suggestion is to start with a small test projet, hopefully something useful to you like a cowl or something & go through the procedure from start to finish. You will be in a much better position from a knowledge & experience standpoint to take on a larger project & avoid the pitfalls. Good luck & looking forward to your rojects!

- Peter



< Message edited by ptxman -- 3/27/2006 8:08:49 PM >

(in reply to cncfoam)
       Post #: 7

RE: build composite aircraft - 3/27/2006 8:14:18 PM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline
quote:

ORIGINAL: Rikard Levenstam I almost finished with my mouldmaking period og mu Sukhoi! I hope soon to be in air and get payback of time at the cnc machine! I have a 3 axis homebuild cnc and have machined masters in wood and then made glasfibre moulds.Rikard


Very nice work! I was just mentioning others using laminated wood for plugs (as opposed to more expensive materials) & see (I think) that is what you have done. Maybe you would like to elaborate on your choice of materials & methods?

(in reply to Rikard Levenstam)
       Post #: 8

RE: build composite aircraft - 3/28/2006 1:13:41 AM   
cncfoam


 

Posts: 34
Joined: 11/21/2002
From: MN
Status: offline 		ptxman,

thanks for all the info. I will look at those links and learn some new things.

I do have a friend that makes plugs for a modeling company. One of the projects he told me about was the male plug of a hood for a full size catapiller tractor. I will talk to him. I believe he said they use MDF and they coat it with an automotive primer, I looked at a couple of threads and saw the name Duratec, I would assume that is some sort of primer. I guess MDF is what I was thinking on using. I could probably get some tooling material from my buddy. what they call scrap is probably gold to me.

I think that my machine will cut aluminum, I havent tried yet. very sturdy machine.

nice work Rikard and Scalecraft!

I am going to draw up a wing in SW and upload picture and maybe try to cut that as practice.

thats it for now.
Again, I want to make this post as a build log of a project that is yet to be determined. I will take suggestions. A qickie might be a good place to start, wings and fuse will fit on my machine, or even something simular to the Great Planes Ultra Sport. 40-60 size.

EZ


(in reply to ptxman)
       Post #: 9

RE: build composite aircraft - 3/28/2006 1:47:18 AM   
cncfoam


 

Posts: 34
Joined: 11/21/2002
From: MN
Status: offline 		Here is a wing that I made in solidworks. this was just a wing I made to test and see what I could do. It sweeps back, and up and all around, LE edge and TE edge sweep forward and back. Just did this to see what I could get away with.
I did this a while back, it does have a real airfoil.

EZ

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RE: build composite aircraft - 3/28/2006 4:22:52 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		Duratec I believe is a polyester based primer surfacing material. I used it in my polyester days both on plugs & molds. When I switched to (much more odor freindly) epoxy gels & resins I didnt use it much after that. Ive also heard of it being used on MDF however, but havent seen the results first hand.

One of the things to be aware of with any laminations, but particularly with wood, is likely tear-out problems when milling shallow angled surfaces as the intersect laminations. For example visualize a 3" thick plug block made of 6 lams of 1/2" material. The typical wing (when viewed from the LE) will have a shallow angle as ittapers from from root to tip. As the endmill approaches the glue joint it can rip it out a bit along that transition line. I guess thats what filler is for, but if you can stagger the laminations or set your datum to avoid this better yet. The better the surface, the less handwork & corrections.

MDF has some peculiarities in itself to be aware of. When its pressed during manufacturing it passes through rollers under high pressure. The result of that is the outside 'skin' is much denser than the inside core. When you mill this, the material can stress relieve (ie distort) & you can also get different quality of finish accross teh surface even though the mill is stepping the same amount. The thicker the stock, the more the density difference. Somebody told me as much as 50% softer core vs skin on 3/4" stock but I havent found a reference yet to verify. One might be inclined to laminate up 3 pieces of 1" & get it over with, but what might be a better option is say 6 lams of 1/2" to equal the same thickness. That way you get more consistant density & probably more rigidity too with more glue joints.

Avoid water & moisture like the plague on MDF or you will have mismatched plugs & parts that dont fit. A small % distortion over a long plug can add up to something to fret about. So after the milling, get going after the finishing which essentially seals it & mitigates this problem. Despite what you read, i would avoid any water based priming material for this reason & also because you want something very tough to withstand the pressures of releasing the mold. I have also heard of water resistant MDF's (cant recall the name) used for outdoor construction. Might be a good thing to consider.

All in all, the stuff is cheap enough & readily available. Might take a bit of learning but Im confident it can be used to make decent plugs at least, molds might be pushing things a bit. Depending on the thickness of your car hood analogy, he may have not have had any such issues because relatively speaking he had a lot more bulk material there. But smaller/thinner model plugs may be different again. Plus, modelers can tend to be a very exacting bunch. 20 thou may be perfectly acceptable to a car hood which is bolted to a frame & will see primer & paint, but your eye can certainly see 20 thou of waviness or thickness variation along a paint-in-mold trailing edge of a wing for example! Good luck!

(in reply to cncfoam)
       Post #: 11

RE: build composite aircraft - 3/28/2006 4:32:47 AM   
ptxman


 

Posts: 351
Joined: 7/31/2002
From: Calgary, AB, CANADA
Status: offline 		Geez, I guess I officially have to call my hand made plugs 'old school' now, huh? Just out of curiosity, what kind of $ do you think is typically invested in a home built cnc router/mill & what sort of accuracy would you say is achievable?

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