Composite Spec'ing

[steveinindy]

Does anyone know a good introductory to intermediate-level source of information on how to choose particular composite materials (as in the specific brand and model of fabric, epoxy, etc) for specific applications?

[spungey]

AviationSpruce or Wicke's?

[steveinindy]

I am looking for stuff more technically oriented than what they have to offer or more so how to interpret things that are more technically oriented than what they have to offer since the decision is coming down not "Do I use Kevlar or E-Glass here?" but to "What grade/type/etc of carbon fiber do I want for this particular application?". I have a lot of the technical specs for things but I have little specific experience in these particular aspects (my area of knowledge is injury biomechanics, not materials science at this level).

[Mike Switzer]

Steve - take the Sportair composite workshop at IUPUI (or Versailles or whatever they are calling it now, on the north side of the big airport) next time they have it

I took it several years ago, it was taught by an engineer that worked for Rutan (cant remember his name off the top of my head) & Troy Grover from Danville / Avon helped out some, pretty good, I learned a lot & it convinced me I did NOT want to use fiberglass composite construction for the structure on my project...

My project will look a lot like a Long EZ but it will be tube & fabric......

[steveinindy]

Steve - take the Sportair composite workshop at IUPUI (or Versailles or whatever they are calling it now, on the north side of the big airport) next time they have it

Oh, the Vincennes University "campus" up here? LOL


I took it several years ago, it was taught by an engineer that worked for Rutan (cant remember his name off the top of my head) & Troy Grover from Danville / Avon helped out some

Ah....OK. I think I have met Troy before.


pretty good, I learned a lot & it convinced me I did NOT want to use fiberglass composite construction for the structure on my project...


Why is that? Granted, I want to stay away from the standard foam core composite technique that a lot of homebuilders use since it's not the best thing for occupant protection but I would be interested in hearing your reasoning for choosing a more traditional method of construction.


My project will look a lot like a Long EZ but it will be tube & fabric...

Very interesting. Mine will look like a traditional aircraft. After a conversation with Rutan, I decided to ditch the idea of a pusher configuration although I might come back to it in a later design just for the challenges involved.

[Mike Switzer]

Why is that? Granted, I want to stay away from the standard foam core composite technique that a lot of homebuilders use since it's not the best thing for occupant protection but I would be interested in hearing your reasoning for choosing a more traditional method of construction.

While i wanted to be a design engineer for Ford, I couldn't because 1) my grades weren't real great & 2)the year I graduated they laid off 6000 engineers

So I went to work for ADM, got lots of training as a maintenance engineer & went on to do that as a consultant for a lot of similar companies.

Foam core composite is easy to build in your garage, but it is a real pain to ever fix in the future. It is also pretty much impossible to determine if it was constructed properly without doing destructive tests.

With Tube & fabric, I can design all the structural elements, then add all the controls BEFORE I cover it, makes it real easy to work on, plus the guy that taught the composite class told me tube & fabric was the lightest construction method out there.

And if it ever gets screwed up. get out the carpenter's knife, cut off the fabric, fix it & re-cover it.


Edit - plus I'm scared of fire & I know what a foam core does when it gets hot....

[steveinindy]

Edit - plus I'm scared of fire & I know what a foam core does when it gets hot....

Well....two things:

1. Ever seen a Piper Cub burn? Fabric isn't exactly something I would want to be riding to the ground on with a fire on board. Then again, there's a reason why parachutes would work
2. It depends on what you're using for the core. There are core materials available that are pretty resistant to burning or melting. They aren't as inexpensive as the glorified Styrofoam a lot of folks use so they aren't common, but they are available if someone is building with safety in mind.

Taking that into account with my design. Welcome to the wonderful world of building a fire suppression system into the cowling as well as the landing gear wells.


Foam core composite is easy to build in your garage, but it is a real pain to ever fix in the future.

Yeah, it might be useful for skin panels (which could be designed in such a way to be replaceable; such a design would also make other forms of maintenance as well as the later stages of construction easier) but not for anything structural.


plus the guy that taught the composite class told me tube & fabric was the lightest construction method out there

It is....but there are some trade-offs just as with any other method. Personally, I love Piper Cubs, Aeroncas, etc but at the same time, I think I'm better suited to something a little more sporty. That said, my next design will be an LSA. It'll be a good way to figure out how scale down the things developed from a safety aspect for the first design to something to help protect a broader audience.

[martymayes]

1. Ever seen a Piper Cub burn? Fabric isn't exactly something I would want to be riding to the ground on with a fire on board.

Fabric coatings and finishes have come along way since the days of Grade A cotton and nitrate dope.

[steveinindy]

I know but unless they've started making the stuff out of Nomex, P84 or something similar, I'm still not fond of the idea. Actually, regardless, if I were in something small enough to be made out of fabric the first sign of a serious fire, I'm bailing. There are three things that scare the crap out of me when it comes to flying:
1. Fire
2. Drowning after a ditching
3. In-flight breakup

[flyingriki]

Yeah, maybe Boeing should go back in time to caveman construction and use tube and fabric. I'll point out to them they are really off base with that composite stuff....... Maybe someone should tell Burt too?
PS: foam core composite is the easiest structure out there to repair. Really easy.

[steveinindy]

Yeah, maybe Boeing should go back in time to caveman construction and use tube and fabric. I'll point out to them they are really off base with that composite stuff

I'm not really sold on the degree of composite use in the 787. I guess time will tell if they overstepped the limits of the technology.


Maybe someone should tell Burt too?

If you ever get to actually talk to him about it on a technical level, he's very open about it's limitations and drawbacks. He's an engineer and designer, not a zealot.

[flyingriki]

Well Steve, I'm not sure how much credibility you hope to achieve when you think you're a better engineer than several hundred at Boeing, resort to calling people names when they disagree with you and pretend to know Burt and his technical theories on aircraft design then suggest the system he has been using successfully for almost 40 years and continues to do so to this day is bested by tube and fabric. I know I'm not impressed.....
I fly a Rutan design and have talked to the Rutans, Mike and a couple of their engineers all of which, by the way, fly composite foam core aircraft. So let's stop the insults and move on. Your "opinons" have been noted. :rollseyes:

The industry has spoken and the results are obvious.

[Mike Switzer]

Umm... The Scaled Composites engineer that taught the class I attended flys an RV. We had a detailed conversation about the pros & cons of the different construction methods.

Unless you have an autoclave in your garage (like Scaled Composites & the other Boeing contractors do) your composite aircraft will probably be heavier than you planned.

And Boeing's engineers had very little to do with any of the composite design of their newest product, like every other major manufacturer in this country they are "Engineering Managers" and the work is done by outside contractors. I went to school with a few of their project managers, I have a pretty good idea how much engineering vs project management they actually do now.

[flyingriki]

Umm... The Scaled Composites engineer that taught the class I attended flys an RV. We had a detailed conversation about the pros & cons of the different construction methods.

Unless you have an autoclave in your garage (like Scaled Composites & the other Boeing contractors do) your composite aircraft will probably be heavier than you planned.

And Boeing's engineers had very little to do with any of the composite design of their newest product, like every other major manufacturer in this country they are "Engineering Managers" and the work is done by outside contractors. I went to school with a few of their project managers, I have a pretty good idea how much engineering vs project management they actually do now.

OK, since you know it all - let's take this one apart:

1.Scaled guy fly's an RV - how many do vs. composite? 1.....2....? What does Mike fly? What does Dick fly? What did Burt fly for 40 years?

2. Mine came out just fine on weight. They were never designed to be built with an autoclave and the weights expected are routinely hit without any issues. A Boeing Engineer that built his own Vari came in at around 600 lbs. ....! No autoclave. Point is your knowledge of composite construction is extremely limited and commenting with such authority is foolish and embarrassing, but I'll never convince you of that, nor care to.

3. So what if some "other" engineers did the design....you still profess to know better than them, which was the point you avoided with that off-topic diversion to avoid the point. Reminds me of the techniques we get from the White House so often these days.........

I'm done Mike, believe what you want. Tube and rag, give me a break! :rollseyes:

[Mike Switzer]

Huh?? I'm not here to argue with you about what you want to build, I simply told Steve what I decided I was going to do.

And for the record, I have a Mechanical Engineering degree from Rose-Hulman & I am a licensed Professional Engineer, so I think I am qualified to discuss the subject.

Use whatever method of construction you want, I don't care. For what I want to build I have chosen the most suitable construction method.

Besides, the smell of fiberglass gives my sinuses fits.

[spungey]

With Tube & fabric, I can design all the structural elements, then add all the controls BEFORE I cover it, makes it real easy to work on, plus the guy that taught the composite class told me tube & fabric was the lightest construction method out there.

And if it ever gets screwed up. get out the carpenter's knife, cut off the fabric, fix it & re-cover it.


My main concern with this idea is stiffness. Composites are extremely rigid in those frequencies that cause flutter. I don't really know for sure about fabrics, but I don't see many 200 mph ragwings. Your mission might not call for flying fast with your hair on fire, but if you do want to go lickety-split you might want to keep an eye out for things to do with your control surfaces to make them less susceptible to "the demon."

[Mike Switzer]

you might want to keep an eye out for things to do with your control surfaces to make them less susceptible to "the demon."

Control surfaces are way down the road in the design process, but they probably wont be fabric covered. Fiberglass may be a good solution there, but all wood (thin plywood covering) would be also, as well as aluminum, they need to fairly rigid.

[Matt Gonitzke]

If I'm not mistaken, the B-29, DC-6, and DC-7 all had at least some fabric-covered control surfaces, and all were 300+mph aircraft.

[Mike Switzer]

Matt, you are correct, a lot of the WWII aircraft had fabric covered control surfaces. I know at least some models of the P40 did also.

[Matt Gonitzke]

Heck, I saw a picture of Strega from Reno today, and it sure looks like it has a fabric-covered rudder (and went a touch over 499mph!)

[spungey]

This is probably wandering off the original topic, but I'd like to see a tube and fabric pusher. Please let us know what it looks like when you get that far.

[steveinindy]

This is probably wandering off the original topic, but I'd like to see a tube and fabric pusher. Please let us know what it looks like when you get that far.
Likewise. I'm definitely intrigued but then again I'm a generalized airplane geek so I tend to have at least some interest in anything that flies.

[Mike Switzer]

Well, I believe Geoffrey de Havilland built a few tube & fabric pushers a long time ago, but they probably didn't go as fast as what I hope to build

Y'all want to guess what kind of engine I was planning on, the N Number I have reserved is 350GT, what do you think that goes with...

But in the last 6 months I have seen an engine with the same displacement (from the same company) that I might use instead if I can figure a way to get it to run on 100LL without a lot of computer gyrations....

[David J. Gall]

steveinindy, in answer to your question about composite spec'ing: I found Jim Marske's excellent but terse Composite Design Manual (http://marskeaircraft.com/) to be very helpful, and Andy Marshall's book which is available from EAA and all the usual sources. You can also try Martin Hollmann's books, but they're kind of simplistic for my tastes, although they cover things like fabric weaves and core materials fairly well, as well as manufacturing methods (vacuum bagging, etc.). Marske touches on that, too, as well as fitting design and tooling and joggles. I have more "Engineer-y" references if you want them. Try searching the web for Mil HDBK-17, NASA CR-4750, NASA RP-1351, and the General Plastics and Hexcel websites (and others) for core material product data sheets. You might also like the Structural Analysis Reference Library website: http://euler9.tripod.com/.

[corsair82pilot]

Here is a link to the "Reference" section of my website. I did a lot of composite research and testing while developing my composite Corsair.


http://corsair82.com/corsair/reference/reference.html

(http://corsair82.com/corsair/reference/reference.html)Most of these books are in the EAA Book Store. Some can be found on Amazon.

[flyingriki]

This is probably wandering off the original topic, but I'd like to see a tube and fabric pusher. Please let us know what it looks like when you get that far.

I think the Wright Brothers had one. After that designers got a lot better - at least most did.....

[WLIU]

Composite design is one of those topics where finding the reference materials is part of the aptitude test. The manufacturers of the core materials and fabrics that you buy at places like Aircraft Spruce have almost all of their materials properties data on the web. And guys like Martin Holmann have published descent books on the topic of designing with composites.

Your problem is that a composite structure is composite, not homogeneous like Aluminum, so the math gets a lot harder. And you have to learn about weaves and analyzing the directions that you will apply stress on the part(s).

Go build some simple stuff, like a flat panel, with carbon fiber on either side of say 1/4" H45 core, and load it up with sandbags to see what it does and get some data on how your construction techniques hold up. You might find it very interesting. Very strong stuff, but harder to figure out.

Boeing, and Scaled know what they are doing.

Best of luck,

Wes

[steveinindy]

Composite design is one of those topics where finding the reference materials is part of the aptitude test. The manufacturers of the core materials and fabrics that you buy at places like Aircraft Spruce have almost all of their materials properties data on the web. And guys like Martin Holmann have published descent books on the topic of designing with composites.

Your problem is that a composite structure is composite, not homogeneous like Aluminum, so the math gets a lot harder. And you have to learn about weaves and analyzing the directions that you will apply stress on the part(s).


Thanks for the input Wes (and everyone else for that matter).


Boeing, and Scaled know what they are doing.

I'll agreed with Scaled but there's a big difference between designing and building a one-off or kit design and figuring out how to build an airliner that will be used and abused. I suggest we sit back and see if the Boeing's predictions pan out or if the "Dreamliner" is more of a nightmare.

[Barrett]

Isn't this kinda like a CHEVY vs. FORD thing? :-) Each to his own.

[David Darnell]

Tube and Fabric Canard- You mean like a MIG-8?