Sorry a link to a forum post is hardly proof.
Again, if vectoring only bleeds 2 or 3% thrust then why not have it in more aircraft?
Better yet, why not keep vectoring on the F-35A/C when you already have it in the B?
Chinese Engine Development
- Thread starter jackbh
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Sorry a link to a forum post is hardly proof.
Again, if vectoring only bleeds 2 or 3% thrust then why not have it in more aircraft?
Better yet, why not keep vectoring on the F-35A/C when you already have it in the B?
The flat nozzle is also a convergent-divergent nozzle. There wouldn't be supersonic flow otherwise.
This whole 10% conspiracy thing is due to a 1998 interview with Victor Chepkin, the D-30 engine designer. During the interview, he was asked about the Su-27UB LL-UV(PS) and he stated that the losses were around 14-17% if I remember correctly. That plane flew in 1989 or 1990, yet many seem to consider this one example the benchmark. The problem mainly revolved around transitioning the flow from a round to a rectangular pipe with minimal losses and without extending the path to unreasonable lengths. Back then CFD was not mature enough and there were no supercomputers able to simulate such problems fast enough. Aerodynamicists have better tools at their disposal today, and a problem such as this can be definitely be solved with money.
It is very important to consider the scope of a design and the mission. Which is a priority? Is it LO, cost, mechanical efficiency? Sacrifices have to be made with any design. You can't have it all. Think of the F-117. That thing was literally a flying trash can (aerodynamically speaking) that prioritized LO over everything.
I made a post a while back regarding the LO and aerodynamic benefits of having a flat nozzle over an asymmetric one.
J-35 carrier fighter (PLAN) thread
though that's as much a fault of the bad original Chinese descriptions. Spend five minutes staring at the strake comment wondering what he meant. Sigh. Right. To clarify, what about the tailsting being extended relative to the fuselage gives the impression that it may have any relation to the...
www.sinodefenceforum.com
A flat nozzle will not necessarily reduce your IR signature. It depends on the cooling methods used. In the case of the F-117 and B-21, they definitely help by distributing the airflow over a wider area. In the case of the F-22, maybe the chevron shaped nozzles help mix the air more efficiently with the surrounding air. There are likely extra methods to help the F-22 cool its air down. The lower thermal efficiency of the flat nozzle results in more heat being produced, so it definitely needs help in that regard from the fan or even by bleeding air from the compressor and into the turbine.
It is not unlikely at all. Research and development can help achieve lower losses. If the USSR were able to produce a prototype with 14-17% losses in 1990, it seems plausible that 24 years of R&D later, these losses were cut down to somewhere around 5%. Compare the 1100lbf HeS-3 to the 9200lbf Al-222. Similar weights, yet worlds apart.
There are no laws in physics that say a 5% loss is unachievable, only that losses cannot be entirely eliminated. Also your analysis of 2-D vs 3-D does not take into account the RCS benefits, only the thrust vectoring benefit.
Because with the F119 specifically, the nozzle while having good performance with not much loss, is very heavy and the vectoring loads also require that the airframe is reinforced in the back to handle it. So it was dropped from the F-35A/C for weight reasons.
F-35B engine has lower thrust of 41,000 lbs compared to F-35A/C with 43,000 lbs, mainly because it had a shorter divergent nozzle section for STOVL so less expansion.
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Regarding the F119 flat nozzles, it’s a fully convergent-divergent design with variable throat area and the long exhaust petals for the divergent section also give it a higher expansion than most round nozzles. The F-22 nozzles are very good in performance, their main issue is that they’re very heavy, and the rear fuselage also needs to be built more heavily to handle the vectoring loads, part of why the F-35 didn’t go that route and went with a round nozzle.
The WS-15 looks like it’s going the F135 route of round nozzle with chevrons, which again will have noticeable benefit for IR signature.
The F119 nozzles cool the exhaust faster since it flattens the plume to increase cooling surface area. Also, the wedge shape of the flaps help it mix with cooling air better too, similar to the effect of a round nozzle with chevrons which has a noticeable benefit for IR signature. It’s not as much as the B-2 style exhaust trench, but it’s still a noticeable improvement. Again the issue with the F119 flat nozzle isn’t the performance, but the large weight and maintenance requirements.
The WS-15 looks like it’s going the F135 route of round nozzle with chevrons, which again will have noticeable benefit for IR signature.
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An academic paper on the geometric sensitivity analysis of low-observability DSI inlet. Posted by @Captain小潇 on Weibo.
Continued.
A few more.
And one last thing, air flow numbers need to be contextualized. Is it corrected airflow, actual airflow, etc? Because the former will depend on airspeed, rotor speed, and altitude, so without knowing the conditions these mass flow numbers aren't helpful for comparisons.
As far as why supercruising engines like F119 tend to be heavy and have lower OPR, at supercruise conditions a lot more of your air compression happens at the inlet, which drives up pressure and temperature and reduces how much heat addition you can add before you hit temperature limits either at the compressor exit or at the turbine. The engine needs to be heavily built and also have a large core because of the low bypass ratio.
So again given the T/W ratio goals of the WS-15 and izd.30/AL-51F-1, it's possible they're not as supercruise optimized as the F119 and maybe deliberately so. The WS-15 numbers are a bit murky, but we actually have some pretty good numbers for AL-51F-1, according the UMPO and Saturn the T/W ratio is 19% better than the AL-41F1 which already has a T/W ratio of 9, so it's even harder for me to believe that it's as optimized for supercruise like what the Sukhoi fanboys keep peddling.
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I do think it’s safe to assume that any airflow data that’s publicized is a theoretical maximum at sea level. That’s usually the standard way these figures are reported.
I think you’re making too many assumptions about supercruise optimization. Inlet and compressor flow conditions at different flight envelopes are not easily ascertained by general rules of thumb. Lots of flow optimization and compressor performance factors go into those determinations. For example, the F110 can actually supercruise despite having a very high OPR and a larger BPR than the AL-31 and F100. In simple terms pressure ratio between inlet and outlet at supersonic envelopes does tell you how well an engine can supercruise but you’re not going to get a clear answer about how well a particular engine does in those conditions just based on some shorthand numbers.
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