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Why In Aerospace Everybody Wants To Switch To Aluminum Instead Of Steel Turnlocks?

Why is weight reduction so important in aerospace? Is aluminium which has half the weight of steel, the answer?

Is aluminum a big saver in costs? 

To know the answer we need to make a calculation. 

What are now the costs for an airplane? Here is a rule of thumb that let you calculate the involved costs:

In a 10 hours flight = the cost of the fuel to transport any weight in an aircraft.

So imagine you have 1kg on board, this means that the pilot needs to fuel 1kg of fuel in order to transport that little weight over the ocean. Every time again and again when it takes of for that flight (I'm just curious when the airlines will start to request you to stand on a scale and request you to pay extra since your BMI is not good :-) that's anyway something for the future).

Quarter turns Boeing 747

In a case of a 10 hour flight this is what it means: 

1 kg of fuel is more then 1 liter of fuel, since the weight is less: the density of kerosine = 0.82g/cm³, while the density of water is 0.997 g/cm³

So: 1 x 0.997 / 0.82 means you require 1.215 liter of fuel

The average fuel cost = 0.99 euro per liter ; which means it costs 1.2 euro to transport your 1kg for 10 hours on an aeroplane.

A typical Boeing 747 flies for 30 years before it is retired, which means it flies between 135000 and 165000 hours.

For an average of 150000 hours, this means 1.215 x 150000 / 10 = it will cost the airplane company 18225 euro for each kilo they transport in those 30 years. 

In the case of aluminium: this is half the weight of steel, so you're saving half of that money: roughly 9000 euro per kg.


In the case of Turnlocks, they do not weigh a lot, so one could say, why bother...

Well: the typical weight of a Turnlock is 0.006kg per piece.

Imagine you install 100 pieces in steel on one aircraft: 9000 x 0.006 * 100 = 5400 euro extra cost, which is the cost that can be equal or less for an aluminum specially produced part for you.

If it's only 10 pieces, then 540 euro difference in pricing can be accepted. Of course, as soon we talk about 50 pieces or more, aluminium should be considered.

In conclusion, yes, aluminium parts can be a big saver in costs for the aerospace industry. 


One of the technical issues one would say, is that aluminium quarter turns are less strong, but this is not the case, since the critical part of the quarter turn is the cross pin, which is still made of stainless steel.