SDF Aerospace and Aerodynamics Corner

MiG-29 · Dec 16, 2011

Re: J-20... The New Generation Fighter III

Engineer said:
LOL! No need to wait and see. WS-10s are being used on J-11B now, that's a fact. Your denial isn't going to make this fact go away, nor does it make your claim any less wrong.

we will see , wait to see one year or two more, one J-10 prototype is not proof specially when 123 engines were bought and the 7 december J-10 delivered have Al-31

Engineer · Dec 16, 2011

Re: J-20... The New Generation Fighter III

MiG-29 said:
we will see , wait to see one year or two more, one J-10 prototype is not proof specially when 123 engines were bought and the 7 december J-10 delivered have Al-31

Except for the fact that rows and rows of J-11B are seen with WS-10s.

No need to wait and see. WS-10 is very much in service with PLAAF right now, debunking your theory that WS-10 is not ready.

As far as J-10 is concerned, the use of WS-10A on a prototype is an indication of faith and that J-10B will be equipped with Chinese engine; it's just a matter of time. However, J-10B is still undergoing flight testing, meaning we won't see J-10B in service with WS-10A for quite a while. Meanwhile, China will have to continue to produce J-10As and must use Al-31FN to do so. This just says China is putting up with Russian engine, not an indication that Al-31FN is better.

Engineer · Dec 16, 2011

latenlazy said:
It's a simple gearbox position change though, which I can't imagine being very difficult to address in the process of assembly.

If it is that simple they would have just installed the engines upside down. In any case, whether it is easy or difficult isn't the point. The point is that Al-31FN cannot be used on J-11, and Al-31F cannot be used on J-10. The same engine cannot be used interchangeably on two planes, so J-10A unable to take on a new engine is not impossible.

If J-10A could use WS-10A, we would have seen CAC testing one. This hasn't happened, so I'm inclined to believe this isn't a possibility.

latenlazy · Dec 17, 2011

Engineer said:
If it is that simple they would have just installed the engines upside down. In any case, whether it is easy or difficult isn't the point. The point is that Al-31FN cannot be used on J-11, and Al-31F cannot be used on J-10. The same engine cannot be used interchangeably on two planes, so J-10A unable to take on a new engine is not impossible.

If J-10A could use WS-10A, we would have seen CAC testing one. This hasn't happened, so I'm inclined to believe this isn't a possibility.

I addressed the "if it's that simple" in my response to paintgun. It was a bit of an oversimplification on my part. I'm willing to argue that the WS-10A could have been tested with the J-10A, but there would simply be no point when the J-10A is going to be phased out anyways.

MiG-29 · Dec 19, 2011

Re: J-20... The New Generation Fighter III

Engineer said:
Except for the fact that rows and rows of J-11B are seen with WS-10s. No need to wait and see. WS-10 is very much in service with PLAAF right now, debunking your theory that WS-10 is not ready.

As far as J-10 is concerned, the use of WS-10A on a prototype is an indication of faith and that J-10B will be equipped with Chinese engine; it's just a matter of time. However, J-10B is still undergoing flight testing, meaning we won't see J-10B in service with WS-10A for quite a while. Meanwhile, China will have to continue to produce J-10As and must use Al-31FN to do so. This just says China is putting up with Russian engine, not an indication that Al-31FN is better.

time will say, a few prptotypes are not reiments but it is possible J-11 might use it so only time will tell, but J-10 it will take longer

MiG-29 · Dec 19, 2011

]

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this is one of the most interesting pictures to have appeared recently, it claims J-20 has a Cruise speed of Mach 1.8, being lighter than F-22 and even PAKFA, faster than F-22 in fact as fast as a F-15 Mach 2.5 if true means the jet has surpassed american technology however the most likely it is not accurate at least now why:

The jet has fixed DSI intake as F-35, this limits the speed to mach 2, internal compression is the only posibility however this means variable geometry at least in B-70, this would meant a more modern system than F-35 but it is unlikely it has such system

Mixed-compression inlets, on the other hand, allow the flow to be supersonic within a portion of the inlet. The terminal shock is located inside the inlet and the shape of the inlet can be changed by moving either the inner centerbody or the outer surface (cowl) to re-position the terminal shock for optimum efficiency in flight. As a result of this configuration mixed-compression inlets are capable of high Mach number flight and they are exceptionally efficient when operating at their design Mach number. There are, however, numerous design issues that have plagued this design and these are responsible for the inlets being used only in missiles and a in limited number of (primarily) military aircraft. For example, inlet unstart and buzz are several of the features of mixed-compression inlets that the scientific community has been wrestling with since the mid-1960's to bring this approach to regular commercial use.

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It can be seen in figure 49-52 that the bumps are redirecting more of the airflow around theintake in the lower part than in the upper part. On the upper part, the airflow is also redirectedbut since the cowl is swept forward, the airflow is still entering the intake. Since the geometryof the intake was chosen not to be changed, the position of the bump should be changed insteadso that the airflow on the upper part also can be redirected outside of the intake. It is realizedthat if the bump is only repositioned further out from the intake, the airflow on the lower sidemight still be sucked into the intake. A possible solution would be to reshape the bump so that ithas amplitude before the cowls both on the upper and lower side of the intake, i.e. to make itmore square shape. This was the attempt for Intake & Mod [/B]

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[video=youtube;2HcFrlUcMHU]http://www.youtube.com/watch?v=2HcFrlUcMHU[/video]
From X-35 to F-35 the intake recieved a change to allow for better AoA handling thus the bump position was changed as the intake cowl was [video=youtube;XQyf2jeElyg]http://www.youtube.com/watch?v=XQyf2jeElyg[/video]
Diverterless Intake
The unassuming bump at the opening of the F-35 inlet works with the forward-swept inlet cowl to redirect unwanted boundary layer airflow away from the inlet. The diverterless inlet, as it is called, is a technology advancement introduced on the JSF. It meets aerodynamic and observables requirements in a less complex manner than previous designs.The geometry of the cowl itself changed from X-35 to F-35. The new geometry provides better airflow into the engine at higher angles of attack. The inlet itself was moved back several inches to reduce weight and cost. White paint on the internal surfaces is unique to the first aircraft. Internal surfaces of subsequent inlets will be painted gray.

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[/

Engineer · Dec 19, 2011

Re: J-20... The New Generation Fighter III

MiG-29 said:
time will say, a few prptotypes are not reiments but it is possible J-11 might use it so only time will tell, but J-10 it will take longer

There is no need to wait. These pictures indicate J-11B is already equipped with WS-10 and is in serial production. This is a fact, not a possibility.

Once again, I am still waiting for your statistics showing Al-31FN is more reliable than WS-10A. I am also waiting for your evidence to support your claim that WS-10A is not ready. Relying on Ad Nauseum denials isn't going to win an argument.

Engineer · Dec 19, 2011

MiG-29 said:
The jet has fixed DSI intake as F-35, this limits the speed to mach 2, internal compression is the only posibility however this means variable geometry at least in B-70, this would meant a more modern system than F-35 but it is unlikely it has such system.

While it is doubtful that J-10 will go that fast (Mach 2.5), there is no evidence to support DSI is limited to below Mach 2.0. Your claim of such limit is only your opinion. On the other hand, we have this from 2005:

For DSI, pressure recovery coefficient is higher than 0.91 at M0.8. At M2.0, the coefficient decreases to 0.87. This suggests that the DSI being tested can reach Mach 2.0. Note that by this description, the pressure recovery ratio is higher than that of F-4D in the following graph, implying pressure recovery coefficient of DSI is better than the variable-geometry-inlet on F-4D. This rebuts your claim that variable-geometry-inlet is absolutely superior to DSI.

The

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in 2011 is:

现在即将装备的 J-10B，对腹部进气布局的 Bump 进气道的鼓包和进气唇口进行了修改（唇口截面改得更方了），2.05Ma 时出口平均总压恢复系数接近 0.9，是高空高速大马赫数下的推力增加约 4% 的主要方面。

The important bit is that at Mach 2.05, the pressure recovery ratio approaches 0.9, which indicates two things. First, tests were conducted at Mach 2.05 which is already higher than Mach 2.0. Secondly, the pressure recovery ratio of 0.9 is higher than F-4D of 0.87. This improved ratio, combined with reduced weight of the intake, imply both improved engine performance and increase in thrust-to-weight ratio of the aircraft. In light of these evidences, your claim that DSI has an absolute limit of Mach 2.0 is extremely weak.

Also, fixed inlet is one type of inlet while DSI is another. Mixing the two terms to produce your own Frankenstien term isn't going to make your case any stronger. Even if we go by this Frankenstien term, F-22 with fixed inlets has a quoted top-speed of Mach 2.25, so your theory that fixed inlet is limited to below Mach 2.0 therefore DSI is limited below Mach 2.0 doesn't even work.

Finally, F-35 comparably low-speed has to do with the increased by-pass ratio of its engine. The increase of by-pass ratio increases thrust but reduces top-speed. There are many factors involved and not everything can be attributed to DSI. Your claim that F-35 cannot go at X speed therefore all aircraft with similar intakes cannot go at X speed is nothing but a grasp at straws to satisfy your own opinion.

MiG-29 · Dec 19, 2011

Engineer said:
While it is doubtful that J-10 will go that fast (Mach 2.5), there is no evidence to support DSI is limited to below Mach 2.0. Your claim of such limit is only your opinion. On the other hand, we have this from 2005:

For DSI, pressure recovery coefficient is higher than 0.91 at M0.8. At M2.0, the coefficient decreases to 0.87. This suggests that the DSI being tested can reach Mach 2.0. Note that by this description, the pressure recovery ratio is higher than that of F-4D in the following graph, implying pressure recovery coefficient of DSI is better than the variable-geometry-inlet on F-4D. This rebuts your claim that variable-geometry-inlet is absolutely superior to DSI.

The
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in 2011 is:

The important bit is that at Mach 2.05, the pressure recovery ratio approaches 0.9, which indicates two things. First, tests were conducted at Mach 2.05 which is already higher than Mach 2.0. Secondly, the pressure recovery ratio of 0.9 is higher than F-4D of 0.87. This improved ratio, combined with reduced weight of the intake, imply both improved engine performance and increase in thrust-to-weight ratio of the aircraft. In light of these evidences, your claim that DSI has an absolute limit of Mach 2.0 is extremely weak.

Also, fixed inlet is one type of inlet while DSI is another. Mixing the two terms to produce your own Frankenstien term isn't going to make your case any stronger. Even if we go by this Frankenstien term, F-22 with fixed inlets has a quoted top-speed of Mach 2.25, so your theory that fixed inlet is limited to below Mach 2.0 therefore DSI is limited below Mach 2.0 doesn't even work.

Finally, F-35 comparably low-speed has to do with the increased by-pass ratio of its engine. The increase of by-pass ratio increases thrust but reduces top-speed. There are many factors involved and not everything can be attributed to DSI. Your claim that F-35 cannot go at X speed therefore all aircraft with similar intakes cannot go at X speed is nothing but a grasp at straws to satisfy your own opinion.

a few details

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A rule of thumb often used is that 1% pressure loss reduces
thrust by 1%, but it became clear early on that the thrust loss
caused by pressure losses in supersonic flight increases
nonlinearly. For example, at a flight speed of Mach 2.2, a
typical engine losing 8% of the free stream total pressure
through the intake will suffer a reduction in thrust of 13% and a
5% increase in fuel consumption [1].

So your DSI at Mach 2 by losing 13% will lose around 20% of thrust and increase fuel consumption 9%; but that is not the only problem but creating supercritical states inside the engine duct, on mixed compression there is variable geometry not fixed.

and here is the question how J-20 achieves Mach 2.5?

Critical Conditions. Three general types of diffuser operation
exist (Fig. 3), which, though they can be considered independent
of the location of the oblique shock wave, are dependent upon the
normal shock-wave position relative to the cowl lip:
(a) If a normal shock occurs inside the diffuser, the inlet is said to be
operating super-critically. Pressure recovery during super-critical
operation is less than at critical because of the strong normal shock
wave inside the diffuser. In this case, maximum flow is captured.
(b) If no normal shock occurs inside the diffuser, sub-critical operation
exists, with the shock system completely expelled upstream of the
cowl lip. The diffuser pressure recovery is less than at critical due to
the changes in shock location. Here "buzz" may result and mass
spillage occur.
(c) Critical operation occurs when the normal shock wave is near the
cowl lip or leading edge of the ramp of the diffuser. This is the most
desirable condition because maximum pressure recovery exists, there
are no instabilities

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The
inlet cowl of this DSI is designed with a forward sweep that facilitates
the diversion of the boundary layer(14) as well.

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latenlazy · Dec 19, 2011

MiG-29 said:
a few details

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A rule of thumb often used is that 1% pressure loss reduces
thrust by 1%, but it became clear early on that the thrust loss
caused by pressure losses in supersonic flight increases
nonlinearly. For example, at a flight speed of Mach 2.2, a
typical engine losing 8% of the free stream total pressure
through the intake will suffer a reduction in thrust of 13% and a
5% increase in fuel consumption [1].

So your DSI at Mach 2 by losing 13% will lose around 20% of thrust and increase fuel consumption 9%; but that is not the only problem but creating supercritical states inside the engine duct, on mixed compression there is variable geometry not fixed.

and here is the question how J-20 achieves Mach 2.5?

Critical Conditions. Three general types of diffuser operation
exist (Fig. 3), which, though they can be considered independent
of the location of the oblique shock wave, are dependent upon the
normal shock-wave position relative to the cowl lip:
(a) If a normal shock occurs inside the diffuser, the inlet is said to be
operating super-critically. Pressure recovery during super-critical
operation is less than at critical because of the strong normal shock
wave inside the diffuser. In this case, maximum flow is captured.
(b) If no normal shock occurs inside the diffuser, sub-critical operation
exists, with the shock system completely expelled upstream of the
cowl lip. The diffuser pressure recovery is less than at critical due to
the changes in shock location. Here "buzz" may result and mass
spillage occur.
(c) Critical operation occurs when the normal shock wave is near the
cowl lip or leading edge of the ramp of the diffuser. This is the most
desirable condition because maximum pressure recovery exists, there
are no instabilities
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The
inlet cowl of this DSI is designed with a forward sweep that facilitates
the diversion of the boundary layer(14) as well.

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That lost in thrust applies to the loss of pressure recovery and is non unique to the DSI though. Even planes with variable compression don't have 100% pressure recovery at high mach, and so they are subject to the same phenomena.

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