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LearningTranscript
00:00The first time I saw the WZ-7 Sword Dragon, I thought, here we go again, the Chinese delivered
00:08another world first.
00:11And the key question was, why?
00:14Why do they need this complexity?
00:18Isn't the reason apparent, sir?
00:20No Otis, this time is not obvious at all.
00:29The first news of these drones appears in 2006, when a mock-up was on display at Zhuhai
00:36Airshow.
00:37The story of the development, though, is not entirely clear.
00:40For example, we know that in 2011 it was seen undergoing electromagnetic compatibility
00:47tests, but we don't know when the first flight was.
00:52We know that serial production started in 2016 and the first units have been deployed
00:59in 2021.
01:00However, the aircraft has been seen operating even at an earlier date.
01:05The WZ-7 has been seen shadowing American ships in the Taiwan Strait, also controlling
01:13Korea flying from airfields in the Chinese Liaoning province.
01:18More recently it has been spot entering the Taiwanese air identification zone.
01:24All of this because, well, obviously, the Sword Dragon is an intelligence platform.
01:29Ok Otis, what numbers do we have about this drone?
01:34As usual, we do not have official figures for Chinese drones, but we rely on partial
01:39information collected mainly at airshows or estimates from Western analysts.
01:44The aircraft has a take-off weight of 7500 kg, a payload is 650 kg, and a maximum speed
01:52is 750 km per hour.
01:55The range is estimated to be 7000 km, the endurance is 10 hours.
02:01The engine is a Gizhou WP-13 turbojet with 43.1 kN thrust.
02:07Well done, thank you Otis.
02:09The aircraft's general configuration is typical of high altitude, long endurance, unmanned
02:16aerial decals.
02:17Long and thin wings, a dorsal air intake, a relatively clean and streamlined shape,
02:25V-tail, and some minimal stealth features.
02:29These are all typical features of an aircraft that is built for range and endurance rather
02:35than speed or maneuverability.
02:37Navigation sensors seem to be hosted in this canoe-shaped structure at the front of the
02:43aircraft.
02:44This ponson is the right size and shape for a side-looking airborne radar, probably an
02:51AESA one.
02:53From the position we may suppose that it is designed to look down, so this aircraft is
02:57likely a radar reconnaissance platform and an electronic intelligence system.
03:03This dome on the back could host an optical sensor, but it is most likely another antenna
03:09housing.
03:10I couldn't find a clear picture, so I'm not sure.
03:13So far so good, but I think that many among you will be on the edge of the seat about
03:20a unique feature of the Soar Dragon, and I can understand that because the obvious elephant
03:26in the room!
03:32Sorry, I keep forgetting every time I mention...
03:36So we have a big problem, sir.
03:38How big?
03:39As big as elephant-sized ejections, sir.
03:43Excuse me, excuse me.
03:49So...
03:54Bear with me, ok?
03:55Bear with me a minute, just a minute, bear with me.
03:58Ok, we are back and now we can finally address the mystery of the very peculiar wing of the
04:05WZ-7.
04:07In the sources it was sometimes called a Phi wing, like the Greek letter.
04:13I don't have any specific name for this configuration, so I believe we can adopt it.
04:18So it seems to be a tandem wing, with a big swept back wing in front and a smaller swept
04:26forward wing behind.
04:29The first question is...
04:31Is the aft surface lifting upwards, like a wing, or downwards, like a tail?
04:40So from the pictures it is impossible to say.
04:43None of the pictures that I could find is close enough to appreciate any detail of the
04:49aerofoil.
04:50It sort of seems to be symmetric, but laminar, but this seems unlikely because a symmetric
04:57aerofoil is probably not going to be very efficient.
05:00Also none of the pictures is close enough, or from the right angle, to assess the difference
05:06of the angles of incidence between the two surfaces.
05:11A negative angle of attack would be a giveaway of the aft surface acting like a tail, and
05:18vice versa.
05:19However, we need to consider that the aft surface is affected by the front wing downwash,
05:25so its effective angle of attack is reduced.
05:30So in the end, the tail could be lifting downward without being twisted too much.
05:35However, I believe that the aft surface is lifting.
05:40In fact, if we consider the position of the undercarriage, from that we can estimate the
05:47rearmost position of the center of gravity.
05:51And the center of gravity seems to be closer to the front wing, but between the two surfaces.
05:59This would mean that the aft surface would be lifting, but also that the aircraft is
06:06intrinsically unstable, and this would require fly-by-wire and a flight control system.
06:13Why would you do that on an aircraft that doesn't need to be really maneuverable or
06:18doesn't have a massive shift of the center of gravity?
06:23Well it beats me.
06:25It is more weight, more complexity, more development time.
06:30For what?
06:31Sorry, sorry, sorry for the interruption, this is the editing us a few days later.
06:37I did this analysis again, and now I have the impression that probably the center of
06:43gravity is slightly ahead of the aerodynamic center, and in this case the aircraft would
06:49be stable.
06:51This would mean that if the aft wing is lifting, then the only downward lift is from the V-tail,
07:01but it seems too small, so I would expect that the aft wing would be lifting down.
07:09So at this point I don't really know what to think.
07:13On with the show.
07:14So I can't really work out the rationale for such a configuration from an aerodynamic point
07:20of view.
07:21I'm sure that the designers at Chengdu will have compelling reasons, but I can't find
07:27them.
07:28It is also worth noting that in the most recent photos these nacelles at the junction of
07:34the two surfaces have been introduced in place of vertical surfaces.
07:40I believe that these have been introduced because those vertical surfaces were creating
07:47at the intersection with the wings a small system of vortices that was probably not giving
07:53any real lift benefit, but was just introducing extra drag.
07:58It is also worth noting that the aircraft has swept wings, not dissimilar from what
08:03you can find on a civilian airliner, so I do expect that the cruise speed is actually
08:09a bit above the declared 750 km per hour.
08:13With a wing like that we may expect it to be around Mach 0.8, that is about 850 km per
08:19hour.
08:20Which is pretty fast for a HALE aircraft.
08:33Ok, if we can't find a rationale for aerodynamic reasons, maybe there is one for structural
08:40reasons.
08:42So in flight the wing is bent upwards, and the bending moment increases from root to
08:48tip in this way.
08:50And obviously the wing must be designed to withstand the bending.
08:54Upper surface must resist compression, the lower surface must resist traction.
09:00The junction of the two wings is probably reducing bending moment on the main wing.
09:07And by the way, such an arrangement is pretty common, it happens every time you have a wing
09:12mounted engine.
09:13The aft wing will bear its own loads, but it also seems to be compressed by the main
09:20wing.
09:21Such a thin structure being compressed, well it's not ideal, it's probably prone to instabilities.
09:28And considering that on the horizontal plane the two wings obviously have an angle, I mean
09:33there's also a torsion, that yeah, it's complex and definitely not ideal load situation.
09:43I can see this configuration as a measure for reducing some structural weight, but I'm
09:50not entirely sure if this can really be achieved, and it is definitely quite a complicated arrangement.
09:58However, the bending of such long wings has never really been a problem.
10:02There have been several solutions and it's not particularly difficult to design.
10:09Every sport glider has a wing like that, so it's quite difficult to understand why they
10:14went to such a length just to make a slightly stiffer and maybe slightly lighter structure.
10:23The only real advantage that I can see is that a forward swept wing with the tip captive,
10:30like in this case, definitely won't have torsion problems.
10:35But even in this case, we have known for decades how to do that using composite materials.
10:43So again, it's not clear why the Chinese designers went into this complication even from a structural
10:50point of view.
10:52So I really can't find any compelling advantage in this configuration, maybe it's just me
10:58not seeing it.
10:59If anyone has a better idea, please let me know in the comments below.
11:04If any of the designers is watching this and wants to contact me to explain what happened
11:09here, they are welcome.
11:11We will go over again this aircraft and we'll see their ideas, obviously if it's not classified
11:16information.
11:17So I suppose that sometimes you should just accept that we are not understanding, well
11:22at least not entirely.
11:24However, this is not the first case that we are covering a very peculiar Chinese drone.
11:31And the relative video is going to appear beside me.
11:34So if you want to learn more about Chinese drones, Chinese aeronautics and so on, click
11:39on them.
11:40So if you are still here, thank you very much.
11:43And an even bigger thank you to all those who are supporting the channel on Patreon,
11:48or by being a member, or by one-off donations.
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12:03So thank you very very much for watching and see you there.