Hi everyone, my first post.
Question: why did china design the Y20 to be smaller than the C17? Are there limitations in technology or did her requirments only necessitate such a design?
The Y-20 is only a little bit smaller than the C-17 in terms of overall dimensions and only a little smaller than C-17 in maximum take off weight as well, when it gets its intended WS-20 engines.
The Y-20 would have been designed to fulfill Air Force requirements with whatever economic and industrial or technological constraints they had. But the fact that they chose a slightly smaller design than the C-17 could reflect a combination of those reasons. For instance, maybe they were quite capable of building a C-17 or bigger aircraft, but it would have cost an extra amount which the Air Force did not deem worthwhile for the investment versus the size of the present Y-20.
It is also best to avoid thinking that the C-17 would somehow represent the epitome of airlifter capability which the Y-20 needs to match. Other things such as development cost and time, procurement cost, production time, operating costs, operational requirements, availability rate, are all very important as well, and the Y-20 would have had to balance a variety of different prerequisites to get to its assigned specifications.
I have not introded. Didn't know. I've been lurking on here for a while and this question really perplexed me.
Is the C17 designed to land on unhardened runways? Could china have built a similar sized plane as the C17. The Y20 just looks very narrow. So am wondering if its going to do the sort of strategic lift that china needs?
Are china's runways that short?
First of all, the Y-20 is for all intents and purposes, a similar sized aircraft to the C-17. In fact a Y-20 with WS-20 engines will probably be the aircraft closest to C-17 dimensions, weight and configuration to the C-17 in the world.
Second, yes, Y-20 is intended to be capable of operating from unprepared runways to a degree. C-17 is also technically able to do so, but it generally. The Y-20 is also not very narrow, comparatively speaking -- its fuselage is much wider than say the Il-76, and similar to the A400M or the Kawasaki C-2. The Y-20's landing gear is also similar in configuration to that of the A400M, which of course is also intended to operate from unprepared runways.
Third, I want to re emphasize that Y-20 needs to be viewed within the context of Chinese Air Force requirements, and to not simply assume that developing a C-17 sized aircraft for the Chinese Air Force would have fulfilled their requirements.
So to answer your question about whether Y-20 can do the "sort of strategic lift that China needs" -- well the Y-20 will likely be able to meet its design requirements once it is mature and once it operates with its intended WS-20 engines. So if that can be achieved then Y-20 should well be able to fulfill the strategic lift that the Chinese Air Force "needs".
But the Y-20 won't be carrying loads that a C-5 or An-124 can carry, but it will be able to supplement and complement current Il-76s in service (it is important because Y-20 can be fully domestically produced without being reliant on a foreign manufacturer), and once Y-20s get their intended engines they will be able to exceed current Il-76s in indiviidual capability by a meaningful margin.