China's transport, tanker & heavy lift aircraft

I found this from NASA. The goal objectine of their test is 120% Design Limit Load. Full article check the link below.

One thing we have to question is what is 100% Design limit load? Does this 100% DLL is for normal weather flight? or this 100% DLL is inclusive of severe bad weather flights and extreme conditions?

ChongqingHotPot92 said:

Could you explain a bit more what you mean by “deliberately set”? 111% seems a bit too even even for four engine military aircrafts. What if the Y-20 had to do extreme maneuvers ( like the C17 did through valleys and downtown Sidney). Can it still do that or fly through hurricanes with 111% though? Sorry i am terrible in details of aviation physics lol. I’m political science major lol

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I was only translating what the designer said in the TV program. If you watch it, you get the full answer.

The test engineer said that the test purpose is a figure between 100% and 120% load, they expect the wings to break at 120%, anything more than that means the wing is TOO strong than needed = overweight and overengineering. 111% is the final result from that test which sit in the middle of the desired figures. That is what I meant "deliberate". However, now I think again, I must emphasize that the test engineer's words must be treated as specific to that test (alone) in the video, not something about Y-20's production models.

As of 111% being too low, see my explaination to sunnymaxi below.

sunnymaxi said:

its actually 120% as per the video.. still low considering other Military airlifter.

C919 achieved 150% back in 2018. so i doubt there was a bottleneck or some material limit of AVIC from 2015 onward.
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this 'destructive test footage' is from early variant of Y-20.

i believe Y-20B is a lot different aircraft as compared to early variants.

waiting for @taxiya answer..

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I watched the video again.

The video (8:33) says that on September 28, 2014 AVIC structural strength institute conducted a "2.5G destructive test". 2.5G means 150% load (removing the static weight of 1G).


Then at 8:48 the test engineer said "we at the time set the max (test) load to 120%"


So I suspect that this specific test in the video is only one of many experiments that does not reflect the true load capacity of production Y-20 which should be 150%.

I now may have to withdraw my explaination in #6,324 where I assumed that the 111% or 120% being the final figure of Y-20's max structure load.

My new explaination (hope no need to withdraw again ) is that it is impossible to determine the minimum material and construction work that meet the desired strengh with pure theorotic work. So a circle of trail and break is done to find that sweet spot. The test in the video is one iteration of the circle to learn what load that specific construction can achieve. It is a process to accumulate data and experience to assist future design. XAC probably would have done some enforcement here and there in the next iteration to see when it breaks untill they find the minimum engineering effort that reaches just above 150% which then became the construction design for production Y-20. This is part of the work to move a maiden flight prototype to a serial production design.

What confused me and probably others is that the video showed the final certification test (150%) of C919, but only one of early tests of pre-production Y-20 (111%). Then I mistakenly equated the two as the same.

tankphobia said:

How many exactly does China need? The US has 279 C-17s and that's with global commitments in mind. Granted China has a large need for transport aircraft since SCS and far inland bases are more accessible via air transport, but is more than 150-200 really needed?

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I would hope significantly more. If they settle at 'only' 150 etc. they would find themselves severely lacking for large operations.
I would say double that number to have an effective airlift capability in times of large scale operations.

kwaigonegin said:

I would hope significantly more. If they settle at 'only' 150 etc. they would find themselves severely lacking for large operations.
I would say double that number to have an effective airlift capability in times of large scale operations.

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A lot of payload of the US army is transported with civilian cargo aircrafts like 747. If you take Tankers + C-17 + C-5 + Civilian charters working for the US military, it end with an astronomical digit.

You will need to dedicate a lot of Y-20 just for refueling in a large scale operation involving fighter aircrafts and ground operation. I cannot see them settle with 200. Depending of what China decide to use and the availability of other cargo aircrafts, the number will probably be way more than 200. Civilian variant of Y-20 could fill a gap too in state of urgency and be a great value in peace time for big cargo.

ChongqingHotPot92 said:

Could you explain a bit more what you mean by “deliberately set”? 111% seems a bit too even even for four engine military aircrafts. What if the Y-20 had to do extreme maneuvers ( like the C17 did through valleys and downtown Sidney). Can it still do that or fly through hurricanes with 111% though? Sorry i am terrible in details of aviation physics lol. I’m political science major lol

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There are two ways to consider what the meaning of 111% is which isn't made clear at least in the videos.

111% over capacity could mean 2.11 times design capacity NOT 0.11 or 11% over design capacity ie a factor of 1.11. If the semantics of the context of "100%" over capacity means 2x what the design limits are.

In building designs, operational design limits for service factors such as crack controls would be something like 1.0 to 1.2 factor depending on what factor is being focused on with strength being 1.2 to 1.5 factor. As stated, civilian airliner projects (C-919 being an example) aims for 2.5 capacity factor. Note that we're not talking about "factor of safety" but the force ratio at which designed failure point is exceeded by e.g. if my theoretical designed machinery/building component is calculated by material/component product constraints to be necessary to tolerate exactly 10KN of force, and my capacity limit factor is 2.5 as in the case with that Boeing 777 test and C-919 wing, then the critical component being tested needs to fail at no less than 25KN.

The other interpretation is that 100% capacity means at designed capacity. Using the 10KN example, this would be 10KN exactly where 111% capacity is 11.1KN.

I'm not an aeronautical engineer so I'm unfamiliar with the conventional lingo. In any case, the Y-20 video explained that engineers needed to design the wing failure to be at below 120% over capacity and above 100% over capacity. So 111% is basically smack in middle of the range set out by their theoretical design. That's saying more about the accuracy of the manufacturing there (impressive) to get it basically right on 110% which was middle of their calculated target range.

Why they set it at 110% is a question we can only speculate on. It is however, quite silly to claim a comparison between C-17 and Y-20. C-17 design parameters were decided to go with 150% over capacity (or "capacity" whichever the actual meaning is as explained above) whereas the Y-20 design parameters were decided on 110% over capacity.

Surely this does indeed mean the Y-20 isn't designed to take excess loads to the point C-17 is. Could simply be the differing specs laid out by the two militaries.

If the semantics is "over capacity" rather than "capacity" then I'd say 2.11 factor is already overengineering particularly for a military transport craft using four engines.

These factor numbers already have designs accounting for certain margins and extremes of loadings baked into the calcs which determine what "'capacity" is. e.g. if my bridge column is designed to sway under once in a century typhoon wind loads to be 50mm at max deflection zone, I can set this force combined with the worst case scenario loads adding to this load as my defined "capacity" when assessing my design for crack control and other utility concerns (not strength) and then set another factor of 2.11 or whatever, that's damn well overengineering and a total waste of material.

Skillful engineering is about how accurately you can achieve all this... obviously accurate manufacturing too as manufacturing defects are often again factored into mechanical engineered products.

I'm grounding my Y-20 until this issue is addressed.

Atomicfrog said:

A lot of payload of the US army is transported with civilian cargo aircrafts like 747. If you take Tankers + C-17 + C-5 + Civilian charters working for the US military, it end with an astronomical digit.

You will need to dedicate a lot of Y-20 just for refueling in a large scale operation involving fighter aircrafts and ground operation. I cannot see them settle with 200. Depending of what China decide to use and the availability of other cargo aircrafts, the number will probably be way more than 200. Civilian variant of Y-20 could fill a gap too in state of urgency and be a great value in peace time for big cargo.

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Exactly! Which was why I said double that at the very minimum. When SAC was around the airlift capabilities were humogous but even then USAF had to utilized some commercial cargo like you said.
If PLAAF wants to be serious I see no less than 400 Y20s.

A row of 8x Y-9s neatly lined. Posted by the official Weibo account of AVIC.

Typically for transport class aircraft, the design load is 2.5G, meaning you can safely pull 2.5G with no issues at all for the aircraft. The 2.5G load has an additional 150% safety factor, meaning the wings must not break below 3.75G. When you test the wing, you want it to break at 100%-120% of 3.75G.

The CCTV people maybe confused by all this? The so-called "2.5G destructive test" is a standard test. You load the wing at 2.5G * 150%, now 3.75G is your 100% test load, the wing broke at 111% of the that, which is 4.16G. More than strong enough.

Two nice screen captures of Y-20.