Chengdu next gen combat aircraft (?J-36) thread

[cdj20]

That’s why you don’t eyeball fluid dynamics. Flows often do stuff that don’t make sense at first glance or can be made to do stuff that don’t make sense at first glance.

I’d wager that if CAC designed it like this it meant that it worked well enough for its intended flight envelope (whatever that might be) in CFD and in wind tunnels at least.

having said that yeah the cockpit absolutely will mess with the flow to some degree depending on things like Reynolds number, Mach number, angle of attack, etc. it’s just that I think they think it’s controllable and/or acceptable

I totally agree with you. Given that the U.S. NGAD program has been canceled, the urgency of the J-36 may not be as high as the J20. Therefore, the fact that the J-36 has reached the prototype stage suggests that its fundamental stealth and flight performance meet the chief designer's expectations, which has been summarized in several papers. Thus, any visible flaws are either due to the unreliability of the "naked eye" or they are simply not important.

 

[Alfa_Particle]

Given that the U.S. NGAD program has been canceled

Well, it's not cancelled per se. Just put on hold.

 

[Schwerter_]

Actually it is the opposite. The curves will pull the air into the intake because the region right behind the cockpit will have low pressure thus very fast airflow.

You are maybe thinking about spraying the front of the airplane with a water hose? thus the cockpit blocks some of the sprayed water? No, you need to imagine the entire plane is submerged in water in a very fast current. The water body as a whole works in certain ways that can be counter intuitive.

Not quite. The streamlines (assuming flow is attached) will indeed follow the curvature and “pull” the air into the cockpit region but it still degrades the flow quality compared to, say, having no cockpit hump at all.

There’s going to be an adverse pressure gradient aft of the cockpit as the back of the aircraft drops down, and that can potentially cause issues like flow separation, a thick boundary layer, recirculation, etc, especially at high angles of attack. Essentially with increasing AoA the flow at the back of the cockpit experiences higher levels of adverse pressure gradient which slows down the flow in the boundary layer to the point that it stagnates, which causes the flow to separate locally which is basically a big F you to the dorsal intake

 

[jvodan]

Pitot tubes all serve the same function, so they're all kinda samey. Generally speaking though modern fighter jets don't have them on the tip of their nose anymore. Here you can see the J-20 through it's early development, notice how it started out with a pitot tube up front and later dropped it? The same will happen with the J-36.
You can also see a weird pitot tube setup on the B-21 prototypes, there it will also disappear in the future.

I reckon the reason why prototypes have pivot tubes on the nose is to allow them to gather calibration data against the location where the production sensors go

 

[EmoBirb]

Well, it's not cancelled per se. Just put on hold.

Not to mention that in a WESTPAC context the F/A-XX may be more of a consideration than the USAFs project. And the USNs project not only runs seperate and hasn't been put on hold, but also doesn't rely on the NGAP engine. Instead opting for a more powerful conventional engine, like two "super F135s" so to speak. Meaning the program should overall run into less issues because unlike the USAF the Navy seems to be more pragmatic about what they want to fit their needs.

And I think that, among with the reality that the NGAD situation can change rather quickly is more than enough incentive to pursue the CAC and SAC next generation aircraft with the needed resolve. Do I think that's to the detriment of the J-20? Not really.