Shenyang FC-31 / J-31 Fighter Demonstrator

taxiya said:

Click to expand...

The yellow wing section looks like it is before the one-piece green wing is installed. The wing does not have holes like the left wing here. So the yellow sections here are the panel below the carbon fiber skin, I assume it will have to be metal.

Maybe this pic can help to explain the green color wing is on top of a metal frame:



Here is the one piece carbon fiber wing for your reference

taxiya said:

I don't fully understand what you are saying. It will be easier for me to understand if you can tell me what the yellow pieces being attached to the wings are?

1. Are they composite? It should be, because F-35's skin are supposed to be all composite?
2. Is the yellow color from zinc chromate coating? Coated on the surface of composite (black/gray) sheet?
3. If they are composite, doesn't it mean that being yellow or green is not indicative of what the underlying material is (metal or composite)? This is what I was trying to say.

Click to expand...

That whole structure is the center fuselage/wing box, I don't have the engineering diagrams, or even a detailed construction manual... much of that is actually "classified", so I'm going to plead ignorance of all the details!

however, I'm going to walk you through this step by step, that forward fuselage section is uncoated, so its likely Titanium, in fact much of that center fuse/wing box structure is "welded up titanium, those fuselage "bulkheads" are indeed zinc chromated, and they support the fuselage skin.

Notice that the assembler is laying on a "pad", that bright yellow material he's laying on, is very likely the carbon fiber "skin", which is probably "bonded to the spar, ribs, leading edge etc. He's laying on a "pad" in order to prevent scratching or damage to the carbon fiber, which will induce a stressed area, which could affect the structural integrity of the carbon fiber.

Immediately behind the bright yellow is a bluish green skin section, the leading edge of which is serrated, that bluish green coated material appears to be "riveted" to the underlying surface, it could be aluminum or some alloy, or it could be titanium, notice the rear of the forward fuselage has a "gap" where the front of the engine will lay, so I'm going out on a limb and guessing that section is actually titanium as well???,,, it has to be very strong, that is a very, very, high stress area....

you will notice what is likely the titanium tub for the cockpit, and immediately aft of that the fuel bay, where the boomer flys the refueling probe in to refuel...

I'm going to stop here, but feel free to do a little research on basic structures, the fuselage has bulkheads, stringers, and upper fuselage longerons showing,, if you already understand those terms, then you will understand a little of what I'm trying to share with you...

the reason the aircraft in primer looks like a quilt, is because in preparartion for the outer coatings, each material has an underlying "primer" that protects and prepares that material to receive the outer coatings of RAM, indeed the F-22 in primer is indeed quite colorful, as is the F-35...

some of those "primers" may even be proprietary to Northrup Grumman who uses robotics to weld up that center fuse! or Lockheed Martin who receives that center fuse to be the "back-bone" of the whole build.

I hope this helps, it really is likely classified, but its also part of common practice in the US, China, and Russia, we all build airplanes in exactly the same manner.

Air Force Brat said:

...that bluish green coated material appears to be "riveted" to the underlying surface, it could be aluminum or some alloy, or it could be titanium...

Click to expand...

Isn't carbon fiber also capable of being riveted? I watched a Eurofighter documentary a long time ago, and it showed that carbon fiber skin (in a light clay-colored coating) was riveted onto the underlying structure.

And this is just a more general question not specifically addressed toward your post: do the colors of coatings necessarily correspond to specific underlying materials? I ask because I find it hard to believe that if a yellow coating is used, then the material underneath must be some kind of metal, or that if the coating is green, then the underlying material must be carbon fiber.

Air Force Brat said:

That whole structure is the center fuselage/wing box, I don't have the engineering diagrams, or even a detailed construction manual... much of that is actually "classified", so I'm going to plead ignorance of all the details!

however, I'm going to walk you through this step by step, that forward fuselage section is uncoated, so its likely Titanium, in fact much of that center fuse/wing box structure is "welded up titanium, those fuselage "bulkheads" are indeed zinc chromated, and they support the fuselage skin.

Notice that the assembler is laying on a "pad", that bright yellow material he's laying on, is very likely the carbon fiber "skin", which is probably "bonded to the spar, ribs, leading edge etc. He's laying on a "pad" in order to prevent scratching or damage to the carbon fiber, which will induce a stressed area, which could affect the structural integrity of the carbon fiber.

Immediately behind the bright yellow is a bluish green skin section, the leading edge of which is serrated, that bluish green coated material appears to be "riveted" to the underlying surface, it could be aluminum or some alloy, or it could be titanium, notice the rear of the forward fuselage has a "gap" where the front of the engine will lay, so I'm going out on a limb and guessing that section is actually titanium as well???,,, it has to be very strong, that is a very, very, high stress area....

you will notice what is likely the titanium tub for the cockpit, and immediately aft of that the fuel bay, where the boomer flys the refueling probe in to refuel...

I'm going to stop here, but feel free to do a little research on basic structures, the fuselage has bulkheads, stringers, and upper fuselage longerons showing,, if you already understand those terms, then you will understand a little of what I'm trying to share with you...

the reason the aircraft in primer looks like a quilt, is because in preparartion for the outer coatings, each material has an underlying "primer" that protects and prepares that material to receive the outer coatings of RAM, indeed the F-22 in primer is indeed quite colorful, as is the F-35...

some of those "primers" may even be proprietary to Northrup Grumman who uses robotics to weld up that center fuse! or Lockheed Martin who receives that center fuse to be the "back-bone" of the whole build.

I hope this helps, it really is likely classified, but its also part of common practice in the US, China, and Russia, we all build airplanes in exactly the same manner.

Click to expand...

Thanks for the details. However, I was always and only talking about the skin. The skin of F-35 being yellow does not necessarily mean it is metal.

I used Y-20's green to say it is not necessarily composite.

I said the two points to reject the conclusion that "because J-31 has large area being green it must be using lots of composite, or J-20 being always yellow it must be whole metal skinned."

That conclusion or notion was made by kurutoga when he posted the J-31 V2 photo.

kurutoga said:

The yellow wing section looks like it is before the one-piece green wing is installed. The wing does not have holes like the left wing here. So the yellow sections here are the panel below the carbon fiber skin, I assume it will have to be metal.

Maybe this pic can help to explain the green color wing is on top of a metal frame:

Please, Log in or Register to view URLs content!

Here is the one piece carbon fiber wing for your reference

Please, Log in or Register to view URLs content!

Click to expand...

"yellow sections......have to be metal".
That is what I was always talking about F-35 as example to object the connection of color and skin material. As far as I have gathered, F-35's skin, be it fuselage or wings, is fully composite. If that is right, it means that color yellow can not be used to conclude metal skin, nor can green be conclusively connected to compose (Y-20 example).

Regarding the two pictures that you provided, from watching the video that I posted, it seems that the green panels are applied on top of the yellow panels.

taxiya said:

"yellow sections......have to be metal".
That is what I was always talking about F-35 as example to object the connection of color and skin material. As far as I have gathered, F-35's skin, be it fuselage or wings, is fully composite. If that is right, it means that color yellow can not be used to conclude metal skin

Click to expand...

Yellow section is referring to the picture you presented. The yellow section is not the skin but the layer beneath the skin. I tried to explain in the last post but you did not seem to understand it. The skin of the wing is all green, one piece, and it will be added on top of the yellow metal section, see the details in the two images I presented in the last post.

F-35 as shown has a metal frame; and below the skin its inside is covered by metal panels.

by78 said:

Isn't carbon fiber also capable of being riveted? I watched a Eurofighter documentary a long time ago, and it showed that carbon fiber skin (in a light clay-colored coating) was riveted onto the underlying structure.

And this is just a more general question not specifically addressed toward your post: do the colors of coatings necessarily correspond to specific underlying materials? I ask because I find it hard to believe that if a yellow coating is used, then the material underneath must be some kind of metal, or that if the coating is green, then the underlying material must be carbon fiber.

Click to expand...

Carbon Fiber can indeed be welded, and the links posted by kurutoga do indeed show carbon fibre "skins" being riveted up to the center section. You will notice that the assembler is using "Cleco's", big Cleco's, to locate the skin section to the underlying wing structure, (spar, ribs, and that the directions on that skin specifically show highlights where they want Cleco's!

Cleco's locate the skin on the structure, and draw it down and hold it in place while its riveted, the Cleco's are then removed and rivets replace the cleco's...


They do indeed, as carbon fibre, aluminum, titanium each require an optimal primer prior to application of the RAM coating, it has to stick!

however, depending on the zinc content etc, etc, different zinc chromates are different shades of yellow/green!

Air Force Brat said:

Carbon Fiber can indeed be welded, and the links posted by kurutoga do indeed show carbon fibre "skins" being riveted up to the center section. You will notice that the assembler is using "Cleco's", big Cleco's, to locate the skin section to the underlying wing structure, (spar, ribs, and that the directions on that skin specifically show highlights where they want Cleco's!

Cleco's locate the skin on the structure, and draw it down and hold it in place while its riveted, the Cleco's are then removed and rivets replace the cleco's...


They do indeed, as carbon fibre, aluminum, titanium each require an optimal primer prior to application of the RAM coating, it has to stick!

however, depending on the zinc content etc, etc, different zinc chromates are different shades of yellow/green!

Click to expand...

Master Brat and why the new aircrafts during their first flight are multicolor with all different sort of materials no painted make sense as a new car an aircraft is painted curious

taxiya said:

"yellow sections......have to be metal".
That is what I was always talking about F-35 as example to object the connection of color and skin material. As far as I have gathered, F-35's skin, be it fuselage or wings, is fully composite. If that is right, it means that color yellow can not be used to conclude metal skin, nor can green be conclusively connected to compose (Y-20 example).

Regarding the two pictures that you provided, from watching the video that I posted, it seems that the green panels are applied on top of the yellow panels.

Click to expand...

Carbon Fibre can indeed be riveted or bonded to the structure beneath, sometimes a combination of both.

Skins on the other hand are "never" laid over one another,, skins may be overlapped and riveted, particularly in the case of monocoque construction,, in the case of the F-35, the skins are "butted" against one another...

If you need more strength you simply go with a "heavier" skin in that section.

FORBIN said:

Master Brat and why the new aircrafts during their first flight are multicolor with all different sort of materials no painted make sense as a new car an aircraft is painted curious

Click to expand...

"All" new aircraft have "squawks" that need to be corrected after the first flight, in fact every new aircraft "first flight" is "test flying 101", "every" new aircraft may require many, many hours of maintenance and subsequent "test flying" to iron all the "kinks" out.....

so you are putting it together and taking it apart, putting it together and taking it apart, over and over again, until you get it right,,, then, and only then, do you consider the application of the "top coat", and then you "test fly it some more".

In the case of L/O aircraft, that RAM in the F-22 was very, very, time consuming and tedious to apply and maintain,,, yet it was/is "mission critical"