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Gorn
2014-Mar-11, 09:47 AM
Hello. I know 'certain' modern airplanes use 'composites' in their structures. (ie. just as strong or strong enough as metals)

I think modern rockets do not.

Question: Why not? (ie. I think they only use metals like aluminum etc)

SC

Jens
2014-Mar-11, 10:36 AM
My guess is that aluminum is good for getting the job done, and it isn't worth the cost of using expensive materials for a small saving in fuel.

NEOWatcher
2014-Mar-11, 12:09 PM
Falcon 9 (http://www.spacex.com/falcon9)

Composite Fairing 13.1m (43 ft) height, 5.2m (17.1 ft) diameter
[...]
The interstage is a composite structure that connects the first and second stages and holds the release and separation system.

NEOWatcher
2014-Mar-11, 12:15 PM
Delta IV (http://en.wikipedia.org/wiki/Delta_IV)

The RS-68 engine is mounted to the lower thrust structure of the vehicle by a four-legged (quadrapod) thrust frame, and enclosed in a protective composite conical thermal shield.
[...]a composite cylinder called the centerbody,
[...]Both interstages are built from composites
[...]4-meter composite payload fairing
[...]5-meter composite fairing

Glom
2014-Mar-11, 12:18 PM
My guess is that aluminum is good for getting the job done, and it isn't worth the cost of using expensive materials for a small saving in fuel.

Especially when you consider that the rocket is expended.

Falcon 9 is designed for recovery.

profloater
2014-Mar-11, 12:26 PM
this question contains a false premise so it begs a different question. You can say composites have different properties from typical engineering metals but just to say they are stronger is not factual. Composites using fibres in resin is one class. Here the tensile strength, say, is dominated by the fibres but the matrix provides crack resistance and toughness, even graceful failure, which usually means some strength is retained as the failure progresses. There are also production effectiveness factors. Engineers then like to make ratios such as tensile strength divided by density. That one is useful for flying, you want high strength per unit weight. However stiffness is also very important. Carbon fibre composites are very strong and light but they are relatively elastic, they deflect under load. Many plastic resins have glass beads or fibres added to improve one particular weakness, creep. Plastics can be strong, stiff and tough but as a generallsation they all creep under sustained load whereas metals are crystaline and hold load without ever creeping. That key difference is one important reason why resins are not used to replace metals. Rolls Royce tried to replace metal turbine blades with carbon fibre composites, it bankrupted the company is 1972 IIRC.

Swift
2014-Mar-11, 02:33 PM
Just to add to the excellent comparison that profloater gave - carbon fiber composites will have very different thermal properties than metals such as aluminium. I don't design rockets, but I suspect that will enter into the considerations.

profloater
2014-Mar-11, 02:57 PM
One point about aluminium (aluminum) in particular, it has very good strength to weight especially in age hardening alloys used in aircraft, can be machined easily with excellent recycling of scrap and when anodised becomes both hard and corrosion resistant. One major design factor learned in tragic crashes (Comet) is fatigue, which is cracks from repeated stress reversals. Al has no lower limit for fatigue, eventually it will always break so it has a life to be monitored in aircraft use. Single use rockets have much less fatigue problems. Glass fibre composites, carbon too, might creep, see earlier post but their fatigue life is excellent, towards infinity.

Trebuchet
2014-Mar-11, 03:03 PM
The Lockheed-Martin X-33 (http://en.wikipedia.org/wiki/Lockheed_Martin_X-33) spaceplane failed because of their inability to construct the oddly shaped composite fuel/oxidizer tanks. The technology is continually advancing and they might have better luck if they tried to do it today.

Boeing has discovered that the learning curve in constructing the composite 787 was steeper than expected. One of the problems was lack of electrical conductivity, which required a whole grounding system to be developed where previously there'd just have been "chassis" grounds. They've fairly recently completed repair of a 787 that suffered a moderately serious fire. There'd been concern that it couldn't be done, but it has been. That clears one major hurdle for wider acceptance.

Profloater:

Carbon fibre composites are very strong and light but they are relatively elastic, they deflect under load.

I believe that's incorrect. One of the great advantages I always hear for carbon fiber is that it is much stiffer than metals.

profloater
2014-Mar-11, 03:15 PM
Profloater:


I believe that's incorrect. One of the great advantages I always hear for carbon fiber is that it is much stiffer than metals.
No it is less stiff, good for making springs such as the carbon fibre reinforced fishing rods and tent poles. Stiffness to weight ratio is different again here carbon is much lighter than metals. It is interesting that stiffness to weight of most engineering metals is a near constant. So for a given beam say, fixed dimensions, steel is stronger and stiffer but carbon will be much lighter, nearly as strong and much more flexible. Energy at rupture steel will win again, it absorbs a lot of energy in plastic deformation, while the composite breaks up. Iron crystal fibres have the highest stiffness of all but we cannot yet get macro materials to use its potential.

profloater
2014-Mar-11, 03:45 PM
Using Giga pascals the stiffness of steel is around 200 while CRP is around 30 to 50 rising to 180 when all the fibres are along the grain. Now I see very high values for carbon nanotubes like 1000 but I have questions about the way this is calculated, these exotics are single atomic layers and the value used for the thickness is not , I maintain, comparible with conventional cross section areas. When you divide by density Carbon will win, which is why we see it used when weight is important.

Squink
2014-Mar-11, 04:17 PM
Rolls Royce tried to replace metal turbine blades with carbon fibre composites, it bankrupted the company is 1972 IIRC.

The situation deteriorated further when in May 1970 the new Hyfil (a Carbon (fiber) composite) fan stage, after passing every other test, shattered into pieces when a chicken was fired into it at high speed.[8] Rolls had been developing a titanium blade as an insurance against difficulties with Hyfil, but this meant extra cost and more weight.Rolls-Royce RB211 (http://en.wikipedia.org/wiki/Rolls-Royce_RB211)

Looks like graphene is currently being touted for wind turbines, but I don't see anything on jet engines yet.

Van Rijn
2014-Mar-11, 06:50 PM
The Lockheed-Martin X-33 (http://en.wikipedia.org/wiki/Lockheed_Martin_X-33) spaceplane failed because of their inability to construct the oddly shaped composite fuel/oxidizer tanks. The technology is continually advancing and they might have better luck if they tried to do it today.


I was going to mention that one. X-33 was to be a single stage to orbit spacecraft, so it was important to have light tanks, and the odd shape also was to help minimize weight in that design. The real problem was with the hydrogen tank. Hydrogen can leak through very small holes. The tank would work fine holding the fuel until it was warmed back up. The hydrogen was getting between fibers, and when it warmed up it expanded and destroyed the tank wall.

There's a light aluminum-lithium alloy that has turned out to be very good for tanks. It was used in the ET for later Shuttle flights, and on the Falcon and probably other rockets today.

Trebuchet
2014-Mar-11, 07:12 PM
Rolls Royce tried to replace metal turbine blades with carbon fibre composites, it bankrupted the company is 1972 IIRC. That should be fan blades, not turbines. Turbine blades are hot. </nitpick>
Interestingly, the latest edition of Aviation Week magazine has an article about RR developing composite fans for their next generation of engines. Their competitor, GE, is already using composite fan blades on the GEnx engine for the Boeing 787 and 747-8.

profloater
2014-Mar-11, 07:20 PM
yes you are right it was compressor blades, sorry to be inaccurate. Creep however is a often ignored problem, just as fatigue was before the crashes.

profloater
2014-Mar-11, 07:23 PM
Rolls-Royce RB211 (http://en.wikipedia.org/wiki/Rolls-Royce_RB211)

Looks like graphene is currently being touted for wind turbines, but I don't see anything on jet engines yet.I was in BAC at the time and there was a disastrous chicken firing test where the chicken was not defrosted from frozen.! It wrecked a whole engine. defrosted chickens would not damage the Olympus engine normally.

profloater
2014-Mar-11, 07:26 PM
I was going to mention that one. X-33 was to be a single stage to orbit spacecraft, so it was important to have light tanks, and the odd shape also was to help minimize weight in that design. The real problem was with the hydrogen tank. Hydrogen can leak through very small holes. The tank would work fine holding the fuel until it was warmed back up. The hydrogen was getting between fibers, and when it warmed up it expanded and destroyed the tank wall.

There's a light aluminum-lithium alloy that has turned out to be very good for tanks. It was used in the ET for later Shuttle flights, and on the Falcon and probably other rockets today.

Interesting that we knew in 1970 that GRP etc was porous to hydrogen and Helium and aluminium foil was the preferred method. Indeed water molecules will pass through grp and crp, to hold vacuum you need glass or metal skins.

Garrison
2014-Mar-11, 08:22 PM
I was going to mention that one. X-33 was to be a single stage to orbit spacecraft, so it was important to have light tanks, and the odd shape also was to help minimize weight in that design. The real problem was with the hydrogen tank. Hydrogen can leak through very small holes. The tank would work fine holding the fuel until it was warmed back up. The hydrogen was getting between fibers, and when it warmed up it expanded and destroyed the tank wall.

There's a light aluminum-lithium alloy that has turned out to be very good for tanks. It was used in the ET for later Shuttle flights, and on the Falcon and probably other rockets today.

According to the Wikipedia entry on the X-33 they did crack the problem a couple of years later:


On September 7, 2004, Northrop Grumman and NASA engineers unveiled a liquid hydrogen tank made of carbon fiber composite material that had demonstrated the ability for repeated fuelings and simulated launch cycles. Northrop Grumman concluded that these successful tests have enabled the development and refinement of new manufacturing processes that will allow the company to build large composite tanks without an autoclave; and design and engineering development of conformal fuel tanks appropriate for use on a single-stage-to-orbit vehicle

cjl
2014-Mar-11, 08:58 PM
Using Giga pascals the stiffness of steel is around 200 while CRP is around 30 to 50 rising to 180 when all the fibres are along the grain. Now I see very high values for carbon nanotubes like 1000 but I have questions about the way this is calculated, these exotics are single atomic layers and the value used for the thickness is not , I maintain, comparible with conventional cross section areas. When you divide by density Carbon will win, which is why we see it used when weight is important.

Extremely high modulus carbon fibers can definitely achieve an elastic modulus of >200GPa. The fiber itself (for example, this one (http://www.toraycfa.com/pdfs/M60JDataSheet.pdf)) can have an elastic modulus approaching 600GPa, and when used in a composite structure, can easily be over half that value (in the neighborhood of 300GPa, depending on manufacturing technique).

selvaarchi
2014-Mar-11, 09:31 PM
I was going to mention that one. X-33 was to be a single stage to orbit spacecraft, so it was important to have light tanks, and the odd shape also was to help minimize weight in that design. The real problem was with the hydrogen tank. Hydrogen can leak through very small holes. The tank would work fine holding the fuel until it was warmed back up. The hydrogen was getting between fibers, and when it warmed up it expanded and destroyed the tank wall.

There's a light aluminum-lithium alloy that has turned out to be very good for tanks. It was used in the ET for later Shuttle flights, and on the Falcon and probably other rockets today.

Interesting article on India's journey in handling hydrogen

http://articles.economictimes.indiatimes.com/2014-01-09/news/46030395_1_cryogenic-engine-mahendragiri-isro


"Why do you need a high-pressure hydrogen facility?" he asked. "We are using it to launch rockets," came the answer. "You cannot just fill an engine tank with high-pressure hydrogen," he told the ISRO team. "It will evaporate in no time." The ISRO engineers, thus, learned a thing or two about dealing with hydrogen at high pressure.

swampyankee
2014-Mar-11, 09:50 PM
I was in BAC at the time and there was a disastrous chicken firing test where the chicken was not defrosted from frozen.! It wrecked a whole engine. defrosted chickens would not damage the Olympus engine normally.

I suspect that that is not true: the FARs and JARs are very similar, and the FARs required freshly killed birds at least into the mid-1980s.

John Mendenhall
2014-Mar-11, 11:05 PM
I was in BAC at the time and there was a disastrous chicken firing test where the chicken was not defrosted from frozen.! It wrecked a whole engine. defrosted chickens would not damage the Olympus engine normally.

Hm. Properly stuffed, I see potential as a HEAT round. Then the tank crew could eat the munitions for dinner in a pinch.

selvaarchi
2014-Mar-11, 11:38 PM
My guess is that aluminum is good for getting the job done, and it isn't worth the cost of using expensive materials for a small saving in fuel.

Unfortunately using any aluminum is not a option as India found out

http://www.thespacereview.com/article/2428/1


Still, these efforts proved to be inadequate. After the scrub of the August launch attempt, engineers found that the fuel tank, made of aluminum alloy called Afnor 702, had developed cracks. This time a new aluminum alloy, 2219, was used.

Garrison
2014-Mar-12, 12:11 AM
Hm. Properly stuffed, I see potential as a HEAT round. Then the tank crew could eat the munitions for dinner in a pinch.

It was also the incident that took the Mythbusters 3 separate tries to confirm...

NEOWatcher
2014-Mar-12, 12:05 PM
Unfortunately using any aluminum is not a option as India found out

Are you saying "any" as in "no aluminum is an option" or as in "not just any normal aluminum is an option"?
The article seems to be the latter.

profloater
2014-Mar-12, 12:11 PM
Extremely high modulus carbon fibers can definitely achieve an elastic modulus of >200GPa. The fiber itself (for example, this one (http://www.toraycfa.com/pdfs/M60JDataSheet.pdf)) can have an elastic modulus approaching 600GPa, and when used in a composite structure, can easily be over half that value (in the neighborhood of 300GPa, depending on manufacturing technique).
Ok I stand corrected high modulus fibres are stiffer than steel, good to know.

selvaarchi
2014-Mar-12, 12:13 PM
Are you saying "any" as in "no aluminum is an option" or as in "not just any normal aluminum is an option"?
The article seems to be the latter.

They need to use the right aluminum alloy. It cost them a 5 month delay at least and lots of $$$ to get it right.

JohnD
2014-Mar-12, 06:19 PM
Point I would make about "composites" is that they have variable properties. As mentioned by profloater, the nature of the fabric, the direction and nature of the weave, the resin and any fillers can make a single composite assembly have different properties and qualities in different places. Material made from a single substance can't approach this versatility.
JOhn

Jerry
2014-Mar-18, 09:01 PM
Composite are the primary components of the Peacekeeper, Castor, and Trident missile systems; as well as the Star and Pam DII satellite launch systems. The primary reason they are not used in other launch systems is cost - mostly in the additional quality control steps that are necessary to verify integrity. These programs (and others) do use metal stiffening rings and at the assembly points, but most of the trident system rockets, including the ignitors, are composite.

Boeing has been very conservative in shifting to composites - the 777 has composite components in the tail and control services. The trade-off for commercial air is weight verses processing costs and the added potential for catastrophic failure.

Liquid systems have so many internal stress points and farings that it would be difficult to design a composite case until after all the internal loads are well understood; but you could see that happen.

swampyankee
2014-Mar-18, 09:25 PM
A lot of missiles, especially ICBMs, use beryllium. A number of years ago, there was a paper in the Journal of Aircraft comparing graphite-reinforced plastics ("composites"), aluminum, and beryllium as construction materials for aircraft. Beryllium gave the best overall performance, and would be much more widely used if it weren't for two problems: it's expensive and it's toxic.

Trebuchet
2014-Mar-18, 11:45 PM
Composite are the primary components of the Peacekeeper, Castor, and Trident missile systems; as well as the Star and Pam DII satellite launch systems. The primary reason they are not used in other launch systems is cost - mostly in the additional quality control steps that are necessary to verify integrity. These programs (and others) do use metal stiffening rings and at the assembly points, but most of the trident system rockets, including the ignitors, are composite.

Boeing has been very conservative in shifting to composites - the 777 has composite components in the tail and control services. The trade-off for commercial air is weight verses processing costs and the added potential for catastrophic failure.

Liquid systems have so many internal stress points and farings that it would be difficult to design a composite case until after all the internal loads are well understood; but you could see that happen.

I wouldn't say Boeing has been all that conservative, given that they are ahead of any other manufacturer in use of composites. The 787 has had its problems, oh my yes, but the composite structure hasn't really been one of them, once the grounding and lightning issues were addressed. Legend at Boeing had it that the composite body was inexpensive to build, but not particularly light, while the wing was very light but also very expensive. I didn't work on it and have no idea how true that is.


A lot of missiles, especially ICBMs, use beryllium. A number of years ago, there was a paper in the Journal of Aircraft comparing graphite-reinforced plastics ("composites"), aluminum, and beryllium as construction materials for aircraft. Beryllium gave the best overall performance, and would be much more widely used if it weren't for two problems: it's expensive and it's toxic.

I actually used beryllium-copper alloys for a couple of parts at Boeing, not for weight (they were very small) but for strength. After a while the materials folks decided those alloys didn't produce toxic dust and started calling them copper-beryllium!

swampyankee
2014-Mar-19, 09:11 AM
My father was a toolmaker who worked at one of the contractors (United Technologies, when it was still United Aircraft) for the Apollo program. Just about all the processing of beryllium parts was done in glove boxes.

litespeed
2014-Mar-19, 10:00 AM
Hello. I know 'certain' modern airplanes use 'composites' in their structures. (ie. just as strong or strong enough as metals)

I think modern rockets do not.

Question: Why not? (ie. I think they only use metals like aluminum etc)

SC

Dude called Burt Rutan used them a lot..ie wood-foam-fibre structures.

Foam is just 20-40 kg/m3 as aluminium is 2450 kg/m3.

swampyankee
2014-Mar-19, 10:09 AM
Of course, the first aircraft were made with naturally occurring composites. Sandwich construction was used on the Mosquito, the XF5U, and the F6U, among others. It's actually common, although the core is often honeycomb. In WWII-era aircraft it was frequently balsa.

jrkeller
2014-Mar-19, 11:17 AM
Composite overwrapped pressure vessels (COPV) are used frequently for aerospace applications.

jrkeller
2014-Mar-19, 11:32 AM
Here is a press release http://www.prnewswire.com/news-releases/atk-provides-propulsion-and-composite-structures-for-successful-launch-of-pegasus-rocket-213438371.html from ATK about the composites they use on their rockets.

Trebuchet
2014-Mar-19, 02:56 PM
Of course, the first aircraft were made with naturally occurring composites. Sandwich construction was used on the Mosquito, the XF5U, and the F6U, among others. It's actually common, although the core is often honeycomb. In WWII-era aircraft it was frequently balsa.

As well as the "Spruce Goose", which IIRC was really birch plywood impregnated with resin.

litespeed
2014-Mar-20, 06:57 AM
As well as the "Spruce Goose", which IIRC was really birch plywood impregnated with resin.


No it was laminated birch...there is a big difference.

http://en.wikipedia.org/wiki/Hughes_H-4_Hercules

There was a 4 piece Hercules interview video made in 1980 or so with remaining project managers being interviewed...but it vanished from the web ( YouTube ).

http://www.youtube.com/watch?v=8indPzIoH_U

JohnD
2014-Mar-20, 06:31 PM
Beryllium toxicity didn't stop so many F1 racing teams making brake callipers out of copper/beryllium alloys that FIA had to ban them in 2006!
They can only be made in aluminium alloys today.
John

NEOWatcher
2014-Mar-20, 06:40 PM
Beryllium toxicity can cause some nasty effects (http://hamm0ndeggs.files.wordpress.com/2012/05/gq_miners.png) after long exposure.