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Quick Question
03-20-2010, 09:43 AM
Post: #31
Hi everyone,as we know aluminium oxidize faster than ferrous(steel),why we still use Al as aircraft main structure?
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03-20-2010, 10:18 AM
Post: #32
... err because its light and strong? therefore less lift is required to achieve flight - oxidization is just a small price to pay compared otherwise? plus all u need to do is the proper coating D:

this isnt a text book answer so u might wanna look further into detail.

u might wanna look up <!-- m --><a class="postlink" href="http://www.kastenmarine.com/alumVSsteel.htm">http://www.kastenmarine.com/alumVSsteel.htm</a><!-- m -->

The Bottom Line:

Aluminium is structurally more efficient at the costs of less fatigue and abrasion resistance
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03-20-2010, 12:19 PM
Post: #33
If you were to talk about generic aluminium yes.

The ones that are used for aviation are alloys and basically we have 9 different classification of aluminium alloys alone that is used for aircraft construction.

Pure aluminium will react and corrode itself to produce an oxide layer which is resistance to further corrosion. This is termed as 'sacrificial corrosion. Other forms of protection that is employed to enhance corrosion resistance on aluminium alloys are 'cladding'. Cladding is a process whereby pure aluminium is used on aluminium alloys at a depth of 2.5% of the thickness per side based on the properties of pure aluminium corrosion characrteristics mentioned earlier. This greatly enhance the corrosion resistance properties and is extensively used for aircraft skin construction.
Painting is another way to protect them aluminium!

There is a detail subject dealing with aluminium and aluminium alloys including corrosion.

If we were to use steel instead, then we're be operating sealiners.... :><.:

khye89 Wrote:Hi everyone,as we know aluminium oxidize faster than ferrous(steel),why we still use Al as aircraft main structure?

Real planes have propellers!
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03-24-2010, 02:46 PM
Post: #34
As torx said, even though Al alloys are prone to corrosion, there are many protection for them.
Such as cladding the Al alloys, and anodized other parts like bolts and nuts before installing to Al structures.
In some part where the Al alloys interfaying with steel and titanium alloys, zinc spray method is used to protect the Al structures.
Even the paint system is specially designed to protect the structure from corrosion. All Al parts will be primed, to create a protective layer before the paint applied.
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03-24-2010, 03:09 PM
Post: #35
sepeng Wrote:As torx said, even though Al alloys are prone to corrosion, there are many protection for them.
Such as cladding the Al alloys, and anodized other parts like bolts and nuts before installing to Al structures.
In some part where the Al alloys interfaying with steel and titanium alloys, zinc spray method is used to protect the Al structures.
Even the paint system is specially designed to protect the structure from corrosion. All Al parts will be primed, to create a protective layer before the paint applied.

Question, is Zinc coating also used in the aviation industry - particularly over surfaces on planes? From what i know in other industries, its used coz its the cheapest BUT it is also among the heaviest coating materials; so would it still be good to coat a wide surface area with Zinc? Or is the weight for Zinc coating is insignificant. Just wondering.
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03-24-2010, 04:13 PM
Post: #36
Strictly zinc coating, not that I have come across. Anything that increases the weight unnecessarily is a no-no in aviation. The existing protection treatments available for aluminium is good enough without incurring additional weight by putting zinc coat. Honestly I don't see the need to.

Real planes have propellers!
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03-24-2010, 04:42 PM
Post: #37
yeah i would assume so. anyway thanks for the clarification Smile
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03-24-2010, 04:51 PM
Post: #38
Not at all.. this is what foruming is all about! :^^:<br /><br />-- Thu Mar 25, 2010 8:38 am --<br /><br />Moving on.
A trainee text me this and I thought why not we all chip in and discuss this in this thread.

Describe a typical fuel cooled oil cooler (FCOC) operation in the engine oil lubrication system.

Real planes have propellers!
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03-27-2010, 01:34 AM
Post: #39
FCOC. the name suggests it's operation.

First of all it is a Heat Exchanger.

An engine (lets assume a gas turbine for this) needs a method of reducing friction for a proper operation and slower wears rate that haunting the engine. On top of that friction creates heat, a lot of heat.

Lubrication system - oil is used to reduce friction and dissipate heat and also removes debris.

The oil lubrication system is to provide lubrication basically between two moving surfaces (ex: bearings and shafts) and to carry some unnecessary heat in the engine. The last job is- it has to remove the unwanted products. Remember it also removes metal chips(this is always be monitored time to time) and dirts. Then it continues to circulate within the oil lubrication system as long as the engine is running.

as for metal chips, dirts - it throws them in the oil filter associated in the oil lubrication system. actually for metal chip the MCD will catch it first.
as for heat- it transfers it to another medium- for this case it is the COLD/COOL fuel.

The fuel is said to be COOL at lower altitude and COLD at higher altitude due to low temperature.
The idea is to transfer/ remove the heat from the hot oil to the cooled fuel.

why they transfer heat to the fuel instead of dissipating it to the atmosphere?

The reason is to prevent fuel in the pipelines that is going to the fuel system from freezing. fuel also contains water and freezing fuel is not a good thing for the fuel system. It can kill the engine almost instantly due to fuel starvation.

The best reason is: don't waste an energy. Because we pay for energies : FUEL- BURNT - get thrust, shaft horsepower , electrical power, hydraulic power, pneumatic, heat & etc. we pay for all these sort of energies.

so the FCOC is winning both on FUEL and OIL. you need heat, i give you some.

Remember a car radiator, it works similar (same principal) to this FCOC. it transfers heat.

The oil flowing thru the FCOC in it's own piping and so does the fuel. They are not mixing each other. Oil transfers heat to the fuel thru 'a wall' between it and fuel.

Talking about the efficiency of the FCOC, it is all about the design - the type of materials, the areas expose, the piping length and etc.

Usually to control the amount of heat being removed, the pipings under discussion have provisions to avoid their path to the heat exchanger - they are allowed to by-pass. This is done by heat sensors that senses a temperature rise (ex: the fuel is too hot after passing the FCOC), and then send a signal to open a valve that allows the fuel to by pass the FCOC.

If the FCOC alone cannot reduce the heat from the engine oil, there will be another extra cooling system for the oil - uses ram air to removes heat. Again a Heat Exchanger will do this job.

-- Sat Mar 27, 2010 1:53 am --

Remember for aviation's sake : HOT means HIGH PRESSURE. COLD means LOW PRESSURE. Heat flows from high to low pressure. everything is like this.

just bare a waterfall in mind.<br /><br />-- Sat Mar 27, 2010 1:57 am --<br /><br />*bear - not bare. Tongue

“A friend cannot be considered a friend until he is tested in three occasions: in time of need, behind your back, and after your death.”
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03-27-2010, 10:07 PM
Post: #40
Pretty good! :^^:

Real planes have propellers!
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