Is carbon fiber / kevlar fabric of any benefit?

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RSD

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We add a ply of similar stuff into the inside of our glider cockpits; the stuff we use intersperses aramid and carbon on both the warp and the weft. Primarily it's there for splinter mitigation when everything else starts breaking.
That's certainly a possible benefit in answer to the question that I posed at the start of the thread.
 

RSD

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German Akaflieg research projects in the 1980s and 1990s showed that there is actually quite a lot that can be done with composite cockpit design to protect pilots. As a result, the gliders of the late 1980s onward are much safer than earlier ones, with a substantially lower incidence of debilitating injuries.

--Bob K.
Bob do you have any links to those research projects or pdf's that you can post? I saw an idea recently that had been installed in gliders that made me wonder whether there were safety ideas that we could learn from the glider community that we could incorporate into our composite homebuilts - this particular idea was an airbag in the seat that when activated would raise the occupant to the cockpit rim which then made bailing out much easier.
 

BoKu

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Bob do you have any links to those research projects or pdf's that you can post? I saw an idea recently that had been installed in gliders that made me wonder whether there were safety ideas that we could learn from the glider community that we could incorporate into our composite homebuilts - this particular idea was an airbag in the seat that when activated would raise the occupant to the cockpit rim which then made bailing out much easier.
If you google "sailplane safety cockpit," you'll find most of what there is. The big leap in crashworthiness came with the ASW-24, it was the first commercially-available sailplane with a cockpit specifically designed around crash protection.
 

RSD

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If you google "sailplane safety cockpit," you'll find most of what there is. The big leap in crashworthiness came with the ASW-24, it was the first commercially-available sailplane with a cockpit specifically designed around crash protection.
Cheers - will do!
 

RSD

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Many thanks Scheny - as I had started to suspect there is a lot we can learn from the glider crowd!
 

Scheny

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Then you will definitely like my Beast One. It incorporates this and a little bit more.

I have not been happy about a few cornerstones, so I got help from formula racing guys. They convinced me to change to a (literally) bullet proof center tank instead of a wet wing tank between two fail safe spars (they will stay nonetheless) and I also made some changes to the nose, to incorporate the latest lessons learned from small overlap testing with cars.

BR, Andreas
 

RSD

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Then you will definitely like my Beast One. It incorporates this and a little bit more.

I have not been happy about a few cornerstones, so I got help from formula racing guys. They convinced me to change to a (literally) bullet proof center tank instead of a wet wing tank between two fail safe spars (they will stay nonetheless) and I also made some changes to the nose, to incorporate the latest lessons learned from small overlap testing with cars.

BR, Andreas
Hi Andreas,

It sounds like you are on a similar track to my thinking - because I'm designing my plane around a Mazda rotary that everyone says will chew through fuel like there's no tomorrow I've incorporated two wing tanks feeding into a fuselage header tank. I need to find a few of those formula racing guys too!
 

Yellowhammer

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A mix of metals and fibers can result in improved properties. There was an article in Sport Aviation (1970’s) by a company that did tests on carbon wrapped aluminum tubes for ultralights.

I plan on doing just as you mentioned on the nose gear of my Pulsar, which notorious for it's fragility.
 

Royal

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I work in the automotive industry and the whole idea in cars is directing the energy around the cabin. The cabin should be as stiff as possible. Usually anything absorbing energy absorbing parts are cone shaped.
If you want to see a factory chassis done right check out Volvos. 5 Amazing Safety Features Of The Volvo S60 That Probably Make It The Safest Sedan Ever @ Top Speed
Every time I work on a Volvo its fun to look at how they make the energy transfer around the occupant even down to the seat. In a side impact there are honeycomb plastic inserts in the door and metal posts protruding from the seat base into the rocker all the way to the tunnel.
 

nestofdragons

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If a panel with only carbon breaks open, it makes sharp edges which can hurt you when you slide over them. Kevlar does not break open, If you slide over it, you are less hurt.
 

Scheny

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I recently changed my mind about the usage of Carbon/Kevlar hybrid composites. I initially wanted to have Kevlar interior in my aircraft, but then one of our composite specialists (who builds formula cars) said that "If the safety cell breaks at over 26G, you would already be dead. And if you could survive, it would not break. Period."

He pointed out, that these hybrids (Carbon/Kevlar) are very unpredictable and they have to be treated like having two independent composites as the fibers are unequally stiff. So Carbon would take most of the load and fail quite early, as only 50% is carbon.

The material has its best use for ship bows or kayaks, where you have a short impact and then again normal load. Carbon would break, and the Kevlar keeps integrity of the hull (watertight).

BR, Andreas
 

Vigilant1

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I recently changed my mind about the usage of Carbon/Kevlar hybrid composites. I initially wanted to have Kevlar interior in my aircraft, but then one of our composite specialists (who builds formula cars) said that "If the safety cell breaks at over 26G, you would already be dead. And if you could survive, it would not break. Period."

He pointed out, that these hybrids (Carbon/Kevlar) are very unpredictable and they have to be treated like having two independent composites as the fibers are unequally stiff. So Carbon would take most of the load and fail quite early, as only 50% is carbon.

The material has its best use for ship bows or kayaks, where you have a short impact and then again normal load. Carbon would break, and the Kevlar keeps integrity of the hull (watertight).
I think it is useful to consider the problem in somewhat more detail. The "safety cell" can remain largely intact in a big crash, the passenger restraints remain in place, etc. Still, point loading could cause a local failure (the bottom of the firewall/footwell area collapses when a rock is struck, etc). In these cases, it >could< be useful to keep the laminate together (so it keeps absorbing energy after the fracture and cracks propagate less/absorb more energy as they propagate.) and also reduce the presence of very sharp shards in the passenger spaces.
I suspect that Kevlar/aramid is no longer king of the hill in this respect, the available UHMWPP and UHMWPE fibers have better properties and lower weight. Dyneema, Spectra, etc. Unfortunately, they don't bond very well to epoxy, so incorporation of another material in the fabric layer is usually good practice. It could be carbon, but maybe for this purpose fiberglass would do.
Many armored vehicles use a spall layer/spall liner. It doesn't make the tank's hull stronger, but it significantly reduces injury from all the fast moving, hot debris that enters the crew area if the hull is breached.
 
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BJC

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Many thanks Scheny - as I had started to suspect there is a lot we can learn from the glider crowd!
Yup. They may wear funny little hats, but they have had significant success in designing and building light (made heavy on demand) aerodynamic structures to significant deflection limits, without flutter. Plus, they have some nice control linkage couplings and wing-to-fuselage connections. Plus some neat canopy jettisoning systems. Their airplanes are trailerable, too.

You do need, however, to get close to the idling tow plane to enjoy the aroma of partially burned 100LL.


BJC
 

Gregory Perkins

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I recently became aware of some very advanced new concepts and practices being used
in bicycles resulting in some unbelievably lightweight bikes. New records are being broken in the strength to weight ratios and designs. Google something like lightweight carbon bicycles or latest composite bicycles .... Some are costing tens of thousands of dollars using methods that no doubt would be too expensive for planes. One I saw I think was using 3D printing using continuous filament CF and other fibers.
 
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