I was looking through the Aircraft Description for Airport Planning documents on the A350 and I noticed something interesting.

Each wing has seven LE slats, one inboard of the engine pylon and six outboard. If we number them 1-7 starting from inboard, then slats 1,3,4, and 5 are made of an aluminum alloy, as is the airplane skin surrounding the flight deck. (https://www.airbus.com/content/dam/corp ... 0-1000.pdf, Section 10-0-0, pg. 12-13)

Why are these slats made of AL alloy when the others are not? What's special about those specific locations? Also, why is the nose made of aluminum?

From what I recall, the nose section was made from aluminium due to damage tolerance from impact, such as birdstrikes and the likes. Composites can have complicated damage behaviour from impact strikes when compared to metallic structures. I believe a similar constraint is at play for leading edge devices (A380 has some interesting materials from LE devices too I think, but could be wrong), however I can't comment on why different materials are used for different slats.

Could be a number of reasons. Could just be that they were supplied by different suppliers who sourced and bid different pricing etc. Could be the contours make it easier in different spots. Could be icing considerations - would be beneficial to have two different material systems which will respond differently in icing conditions so you still have half of your slats available.

Leading edge is aluminum because of the radome and easier to repair if hail strike or bird strike. (A copper mesh imbedded in composite layup for lightning strike does not bode well for radomes - can cause a faraday cage problem if i recall correctly)

trpmb6 wrote:

Leading edge is aluminum because of the radome and easier to repair if hail strike or bird strike.

What ever the radome over the weather radar is made of : it most definitely is not made from Al

WIederling wrote:

trpmb6 wrote:

Leading edge is aluminum because of the radome and easier to repair if hail strike or bird strike.

What ever the radome over the weather radar is made of : it most definitely is not made from Al

Fiberglass

DocLightning wrote:

I was looking through the Aircraft Description for Airport Planning documents on the A350 and I noticed something interesting.

Each wing has seven LE slats, one inboard of the engine pylon and six outboard. If we number them 1-7 starting from inboard, then slats 1,3,4, and 5 are made of an aluminum alloy, as is the airplane skin surrounding the flight deck. (https://www.airbus.com/content/dam/corp ... 0-1000.pdf, Section 10-0-0, pg. 12-13)

Why are these slats made of AL alloy when the others are not? What's special about those specific locations? Also, why is the nose made of aluminum?

Most likely because those slats are heated to prevent/abate icing. Also, heated L/E's are not painted either. If you mean the radome, it is made out of fiberglass. On an aluminum airplane, the aluminum structure ends just forward of the cockpit and the fiberglass radome is attached to the aluminum structure.

stratclub wrote:

Most likely because those slats are heated to prevent/abate icing.

And four of the seven are not?

DocLightning wrote:

stratclub wrote:

Most likely because those slats are heated to prevent/abate icing.

And four of the seven are not?

That would be my guess. The leading edges of the horizontal and vertical stabilizers on Boeing aircraft are aluminum and they are not heated. I think that polished clad aluminum just might be a better material for critical aerodynamic areas than composite because it is less likely to degrade from airflow erosion than painted composite. Perhaps those two slats per wing are not considered to be in an aerodynamic critical area so they are composite to save weight.

On the A350, slats 3, 4 and 5 can be heated, The rest cannot be heated. Slatsare counted from outboard.

Thus, starting from the outside, the first two slats are not heated, then the next three are, then the next one is not. The last one, inboard of the pylon, is not

DocLightning wrote:

I was looking through the Aircraft Description for Airport Planning documents on the A350 and I noticed something interesting.

Each wing has seven LE slats, one inboard of the engine pylon and six outboard. If we number them 1-7 starting from inboard, then slats 1,3,4, and 5 are made of an aluminum alloy, as is the airplane skin surrounding the flight deck. (https://www.airbus.com/content/dam/corp ... 0-1000.pdf, Section 10-0-0, pg. 12-13)

Why are these slats made of AL alloy when the others are not? What's special about those specific locations? Also, why is the nose made of aluminum?

I would think for both the leading edge and nose the reason for the use of AL is for bird strike certification. While composite could be used it would require titanium reinforcement to meet bird strike requirements, making it uncompetitive on cost.

Part of the design requirements for a wing is that systems need to be protected against damage of a bird strike.

zeke wrote:

DocLightning wrote:

I was looking through the Aircraft Description for Airport Planning documents on the A350 and I noticed something interesting.

Each wing has seven LE slats, one inboard of the engine pylon and six outboard. If we number them 1-7 starting from inboard, then slats 1,3,4, and 5 are made of an aluminum alloy, as is the airplane skin surrounding the flight deck. (https://www.airbus.com/content/dam/corp ... 0-1000.pdf, Section 10-0-0, pg. 12-13)

Why are these slats made of AL alloy when the others are not? What's special about those specific locations? Also, why is the nose made of aluminum?

I would think for both the leading edge and nose the reason for the use of AL is for bird strike certification. While composite could be used it would require titanium reinforcement to meet bird strike requirements, making it uncompetitive on cost.

Part of the design requirements for a wing is that systems need to be protected against damage of a bird strike.

OK, but what about the LE surfaces that are made of composite?

All of the slats have a hybrid construction, all have LE skins made from aluminium.

The difference with slats 3/4/5 is behind them there is a piccolo tube for bleed air to be used for wing anti ice and its predominantly metallic to enable heat transfer to the outer surface. They have a aluminium rear skin.

The outer slats (6/7) do have an aluminium outer skin, the slat tracks on them are made from steel, the attachment lugs and drive links from aluminium, the actual slat has a composite and aluminium box structure with a composite rear skin and aluminium front skin.

stratclub wrote:

That would be my guess. The leading edges of the horizontal and vertical stabilizers on Boeing aircraft are aluminum and they are not heated. I think that polished clad aluminum just might be a better material for critical aerodynamic areas than composite because it is less likely to degrade from airflow erosion than painted composite..

On the 787 Boeing STRONGLY discourages, and will not support, polishing Aluminum exterior surfaces.

FrmrKSEngr wrote:

stratclub wrote:

That would be my guess. The leading edges of the horizontal and vertical stabilizers on Boeing aircraft are aluminum and they are not heated. I think that polished clad aluminum just might be a better material for critical aerodynamic areas than composite because it is less likely to degrade from airflow erosion than painted composite..

On the 787 Boeing STRONGLY discourages, and will not support, polishing Aluminum exterior surfaces.

Boeing does not use this stuff https://en.wikipedia.org/wiki/Alclad on the 787 anymore for unpainted aluminum surfaces? What does Boeing recommend for maintenance/repair on unpainted Aluminum surfaces on the 787? Do you have AMM, SRM or general references for your statement?

In general, it has been found by Boeing that polished surfaces are more costly to maintain than painted surfaces.
https://www.boeing.com/commercial/aerom ... 01txt.html

stratclub wrote:

Boeing does not use this stuff https://en.wikipedia.org/wiki/Alclad on the 787 anymore for unpainted aluminum surfaces? What does Boeing recommend for maintenance/repair on unpainted Aluminum surfaces on the 787? Do you have AMM, SRM or general references for your statement?

AMM References, No. I have personally asked Boeing for technical guidance and been told flat out don't polish exterior aluminium on the 787. And it was not a quick conversation. There was quite a bit of back and forth. We wanted shiny metal.

As for the use of Alclad, yes they do use Alclad, they just don't want you polishing the finish off. Per Boeing, No shiny brite work on 787s.

Thanks for replying. It would be great to know the reasoning. I guess polishing the bright work throw a monkey wrench in Boeing's maintenance estimates. We had a couple of retired AAL B707-320's on lease and the bright work sure looked nice for old airplanes.

Same bright work as ours:



Talking about cost effective, I was doing some interior work on a contract we had with NMB miniature bearing's DC10-30F at TIJ and one day the hanger boss had must of been 30 or more of their local "mechanics" polishing the Leading edges by hand. This was IIRC 8 months into a "D"- check that they were doing.

Starlionblue wrote:

On the A350, slats 3, 4 and 5 can be heated, The rest cannot be heated. Slatsare counted from outboard.

I'm sorry, Starlionblue. I seem to have missed your answer. Thank you (and Zeke).

Why are these slats unheated? And if they are, it seems like an awful lot of trouble to redesign the components out of composite just because they aren't heated. What's the reason for this?

Simply not required to meet the icing requirements, not sure where you get this information that they were redesigned. As far as I am aware the configuration was very deliberate at design freeze.

zeke wrote:

Simply not required to meet the icing requirements, not sure where you get this information that they were redesigned. As far as I am aware the configuration was very deliberate at design freeze.

Forgive me. I don't mean that there was a change from design freeze. But it strikes me that it would be simpler to design all LE slats to be made of the same material, heated or not. Obviously, the people at Airbus are neither inexperienced nor stupid, so I'm sure there's a good reason for their decision to alternate materials.

None of the slats are the same size, why do you think it would be best to construct the same way ? They would all have different loads to carry and would all be attached to the aircraft at different widths.

Also I would assume they would come from multiple suppliers.

DocLightning wrote:

But it strikes me that it would be simpler to design all LE slats to be made of the same material, heated or not. Obviously, the people at Airbus are neither inexperienced nor stupid, so I'm sure there's a good reason for their decision to alternate materials.

Didn't Airbus start to use fiber reinforced thermoplastics for some aero surfaces on the A350XWB?
The thermoplastics would perfectly work in a non heated environment. heated :: less so

Just a guess.

stratclub wrote:

Talking about cost effective, I was doing some interior work on a contract we had with NMB miniature bearing's DC10-30F at TIJ and one day the hanger boss had must of been 30 or more of their local "mechanics" polishing the Leading edges by hand. This was IIRC 8 months into a "D"- check that they were doing.

That sounds a bit like the 89th at Andrews and their obsession with polishing the VC-25s.

I'll bet the MEL for the VC-25 is a blank sheet of paper....................

Walking around the plane yesterday I had a good look at the slats. As far as I could tell, the non-heated ones have what looks like a black "liner" behind the outside skin that sticks out a bit on the bottom side, while the heated ones do not. I don't know what the "liner" is made of or if it is on the entire rear of the slats.