Sounds fair, but how do you know the control surfaces that we see on the J-36 are insufficient for traditional fighter levels of agility?
Chengdu next gen combat aircraft (?J-36) thread
- Thread starter Blitzo
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Because you only look at thrust, you don't look at other parameters of the engine. Show me a plane that uses the J58 for subsonic travel. Possible, but inefficient. Show me plane that stacks CFM56 engines and travels at M4. Impossible. The point is mass airflow vs jet velocity. Stacking more WS-15s on any plane will not produce higher speeds than what the WS-15 was designed for, which is the J-20 max speed. It is possible to play with the CD nozzle a bit to increase the jet speed. It will definitely produce higher acceleration if the thrust to weight ratio of the aircraft is increased, but that is about it. If you want to produce a higher speed aircraft such as the ones I mentioned before, you will need to develop bespoke engines for them, period.
I love how you dug deep to find a plane that still holds the record for the longest flight time of over eight hours and around 13000km in the supersonic regime to this day, and compare it to the F-15. The F-15 is a tiny plane with tiny wings and it is designed for air superiority maneuvers, so it can easily withstand high stresses to reach M2.45, but how long can it sustain that speed and how far can it travel at that speed? I clearly did mention the fact that you can push higher speeds, but you would be operating outside of your efficient region, chugging fuel, damaging the plane, and defeating the purpose of the design. That is exactly why the F-15 has a lower cruise speed than the B-58. I also didn't just hinge my argument on aspect ratio and wing sweep alone. There were so many other factors that you conveniently ignored in order to formulate this cheap example, and many others that I have neither the time nor the energy to lay out.
The claim that the F-15 not being designed to minimize drag because its 4th gen is totally ignorant. Generations have nothing to do with, and these aerodynamic principles were all established long before the F-15 was designed. All planes are designed to minimize drag within the intended speed of the design. The reason modern VLO planes look more streamlined, is because LO design and low drag go hand in hand in the subsonic region, and the J-36 carries its load internally, unlike previous generation planes, so that automatically gives it a cleaner look and lower form drag. Does that mean it produces less drag than the X-15 at M5+? Absolutely not.
Of course they are designed to operate in highly contested airspace, but they will never ever do so unless the USF or the PLAAF are desperate and planning on humiliating themselves. The usual scenario we are used to is the country under attack gets bombed into the stone age. Then and only then do the B-2s and B-52s get deployed to bomb sheep herders unabated without a care in the world.
Nonsense. It absolutely is something you can eyeball within reason if you know enough about the subject. You can easily tell that a Tu-95 is subsonic while a F-104 is supersonic. The initial discussion was regarding the B-21 being unable to "runaway" because it is subsonic, and my counter argument that it had nothing to do with speed, but rather with the fact that the J-36 can execute more aggressive maneuvers due to the smaller wingspan and higher thrust.
We have no information about anything that comes out of the PLA, especially the PLAAF, because almost nothing in there is for sale.
The J-36’s wing sweep is narrower than the J-20’s or F-22’s, insofar as “eyeballing” goes. Drag is not just a function of volume either. The whole point of a flying wing is that for the same volume it’s got lower drag. Shaping matters. Whether shaping and sweep are sufficient to deal with higher volume though is a wind tunnel question. You are making assertions about which visual factors to dismiss or include in your conclusions well beyond what you can ascertain by “eyeballing”, so no, I would not say your “eyeballing” is “within reason”.
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Has anyone noticed this paper?
It was published in 2019, introducing a dorsal inlet design, just like what we saw on J-36.
Abstract. The air intake design system of the dorsal intake combined with the S-shaped inlet has been widely used in various combat aircraft due to its good stealth characteristics. In this paper, the numerical simulation of the flow characteristic and influence law of various parameters for a typical air intake design with dorsal S-shaped inlet was carried out using the in-house large-scale parallel computational fluid dynamics (CFD) solver. Firstly, the numerical method was introduced and the solver was preliminarily validated by the well-known RAE M2192 inlet model. Then, the numerical calculation of the target air intake design was conducted and the distribution of shockwave at the entrance area, the second flow in the inlet and the flow at the exit section plane were analyzed in proper order. In addition, the influence of the bump height and lip sweep angles on the inlet performance was also studied. The simulation results show that the unique S-shaped design in the inlet will result in flow separation and secondary flow, ultimately causing total pressure loss, and different external geometry parameters have a great influence on the inlet performance. Within a certain range, proper reduction of the bump height or lip sweep angle can improve the inlet performance.
It was published in 2019, introducing a dorsal inlet design, just like what we saw on J-36.
Numerical Investigation of Dorsal S-Shaped Inlet Flow Characteristic and Effects of Related Parameters
Abstract. The air intake design system of the dorsal intake combined with the S-shaped inlet has been widely used in various combat aircraft due to its good stealth characteristics. In this paper, the numerical simulation of the flow characteristic and influence law of various parameters for a typical air intake design with dorsal S-shaped inlet was carried out using the in-house large-scale parallel computational fluid dynamics (CFD) solver. Firstly, the numerical method was introduced and the solver was preliminarily validated by the well-known RAE M2192 inlet model. Then, the numerical calculation of the target air intake design was conducted and the distribution of shockwave at the entrance area, the second flow in the inlet and the flow at the exit section plane were analyzed in proper order. In addition, the influence of the bump height and lip sweep angles on the inlet performance was also studied. The simulation results show that the unique S-shaped design in the inlet will result in flow separation and secondary flow, ultimately causing total pressure loss, and different external geometry parameters have a great influence on the inlet performance. Within a certain range, proper reduction of the bump height or lip sweep angle can improve the inlet performance.
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According the the Christmas Salt Bae (folk I got the Christmas first flight rumor from) AI will be a strong focus of the CHAD series of aircraft. In fact this will offer a generation gap advantage compared with fifth gen aircraft. Remember how J-20/F-35 are easy to fly but difficult to fly well? Won’t be a problem on sixth gen since a lot of real time decision making is optimized through the use of AI.
Weird strawman. The CFM-56 is incomparable to the WS-15 and nobody says the J-36 is a Mach 4 aircraft. Your comment on thrust is flat out wrong and if you believe that you need to read more on jet engines. Top speed is where thrust equals drag. Regardless of the thrust curve more thrust means a higher top speed. The only exception is when the engine is temperature or pressure limited which I don't think is the case for the WS-15 at Mach 2.2.
You wandering into irrelevant things. The fact is the F-15 was faster despite being optimized for things that the B-58 weren't. It couldn't sustain that speed for long because it didn't have 45 tonnes of fuel and it was a draggier aircraft at all speeds.
If you are actually claiming this then you should really stop writing and do not discredit yourself further. One of the biggest revelations of the Vietnam war was that the speed wasn't that important. 4th gens were designed around sustained transonic turns, energy maneuverability, high-AoA and nose authority. They had much higher low-AoA drag coefficients compared to previous aircraft because of their oversized wings, control surfaces and ample vortex generation features. The F-16 has a glide ratio around 8:1 when clean for example. The F-18 is even worse. It is so bad that once McDonnell Douglas attempted to market how little performance the aircraft lost when bombs were attached (actually, the airframe is so draggy that the drag from the bombs wasn't that important)
What M5+ ? Stop your strawmans.
Hmm yes, PLAAF and USAF won't use their most survivable aircraft in contested air space. Air warfare is all about launching cruise missiles and less survivable aircraft are better for contested airspace. I was holding myself from being sarcastic but I don't think you realize what you are advocating for.
Yes, sustained turns are mainly influenced by those two. If an aircraft's altitude and speed are stable, it means the vertical component of the lift matches its weight and its thrust matches the drag. And the lateral component of lift is what turns the aircraft.
The formula for lift is 1/2 * coefficient of lift * air density * lifting area * velocity^2. An oversized wing means a smaller coefficient of lift is needed which means the aircraft would need a smaller angle of attack while turning. This is important because the coefficient of drag does not increase together with the coefficient of lift as the AoA increases. Airfoils tend to have an optimum point below 10 degrees. Anything above 15 degrees tends to be very inefficient. An example:
The goal with the 4th gens was having them efficient while pulling high G forces. They were very draggy while cruising but they had much less drag than the 3rd gens while pulling, let's say, 6 Gs. The third gens needed massive control surface deflections and an AoA near their stall points to generate such lifts. The 4th gens didn't.
A higher thrust helps the sustained turn performance from the other side. It allows the aircraft to be draggier while turning. Everything same, an aircraft with higher thrust would be able to use a higher AoA without losing energy. Thrust to weight ratio is actually not a great representation for this unless one is comparing aircraft of the similar size. Heavier aircraft need less of it because the surface area increases slower than the mass (scaling law). The J-36 having a TWR around 1 at its weight is quite huge.
FriedRiceNSpice
Captain
All this discussion about whether or not J-36 can reach M3 is bringing up memories of the dozens of pages of discussions 10 yrs ago about whether or not J-20 has a gun.
What’s even the point of Mach 3. I never understood the obsession with it.