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Chengdu J-20 5th Generation Aircraft News & Discussions

low drag will affect speed, but the effect is parabolic, which mean regardless of engine put, the speed will decrease due to drag and at a lower altitudes, the speed will drop slower as air is denser.

However , supercruise is the ability to stay above MACH without the use of afterburner. You can go above MACH regardless of w/d ratio as the speed provide (The forward momentum) would always greater than the Drag, thus, will always accelerate

However, the drag of a planes are always constant as the shape of the plane wont change, but if the engine efficiency is high enough to Pull the plane, that plane, regardless of drag would achieve supercruise, given the engine output or the efficiency stayed above the drag

Hence, you are wrong

You're roughly correct except last sentence.

Plus, drag is not constant, it related to shape, speed, windspeed, humility, temperature, etc.

It's not the efficiency of engine, it's the efficiency of aerodynamic of body to supercruise an aircraft.

We had jet engine before we achieved a supersonic flight only we found the efficiency body design.

I would like to say: Aircraft with enough low drag will achieve supercruise with any jet engine like British did it 60 years ago.
 
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You're roughly correct except last sentence.

Plus, drag is not constant, it related to shape, speed, windspeed, humility, temperature, etc.

It's not the efficiency of engine, it's the efficiency of aerodynamic of body to supercruise an aircraft.

We had jet engine before we achieved a supersonic flight only we found the efficiency body design.

I would like to say: Aircraft with enough low drag will achieve supercruise with any jet engine like British did it 60 years ago.
If that is the crux of your argument, then why not put ANY aircraft into thin enough air and say: 'Voila...Supercruise'.

Even wiki pegged you wrong...

Supercruise - Wikipedia, the free encyclopedia
The key challenge in attaining supercruise is not simply attaining a high thrust to weight ratio vis-à-vis the aircraft but a radical redesign of the engine because the air entering a jet engine must always travel at subsonic speeds, regardless of aircraft speed.
Look at your own argument back on post 4410...
British achieved supercruise 60 years ago with BAC Lightning, the engine it used is R-R Avon which is a turbojet only.
The engine is a TURBOJET type, not a turbofan.

The turbojet is much more efficient than a turbofan, which is used in the majority of jet engines, military and civilian, today. Beyond the turbojet would be the ramjet which is the most efficient of all and which is what the SR-71 uses.

The F119-PW-100 is technically a low bypass turbofan type but is efficient enough that it is considered to be 'near turbojet' type.

You dispute that engine efficiency is the key to supercruise but then brought on a source that shows EXACTLY what you challenged.
 
If that is the crux of your argument, then why not put ANY aircraft into thin enough air and say: 'Voila...Supercruise'.
Supercuise is not as important as you thought. It comes at cost of short range, less load.

It is not required by F-35 and future 6th gen aircraft.


The turbojet is much more efficient than a turbofan, which is used in the majority of jet engines, military and civilian, today. Beyond the turbojet would be the ramjet which is the most efficient of all and which is what the SR-71 uses.

The F119-PW-100 is technically a low bypass turbofan type but is efficient enough that it is considered to be 'near turbojet' type.

You dispute that engine efficiency is the key to supercruise but then brought on a source that shows EXACTLY what you challenged.

ARE YOU KIDDING ME????????

Do you really know what is turbojet and what is turbofan?

Or your many years aviation experiences before retirement was doing a vacuum job on commercial aeroplane?

No time to talk to all these keyboard-professionals, check it out yourselves and compare the efficiency of two engines:

Jet engine - Wikipedia, the free encyclopedia
 
If that is the crux of your argument, then why not put ANY aircraft into thin enough air and say: 'Voila...Supercruise'.

Even wiki pegged you wrong...

Supercruise - Wikipedia, the free encyclopedia

Look at your own argument back on post 4410...

The engine is a TURBOJET type, not a turbofan.

The turbojet is much more efficient than a turbofan, which is used in the majority of jet engines, military and civilian, today. Beyond the turbojet would be the ramjet which is the most efficient of all and which is what the SR-71 uses.

The F119-PW-100 is technically a low bypass turbofan type but is efficient enough that it is considered to be 'near turbojet' type.

You dispute that engine efficiency is the key to supercruise but then brought on a source that shows EXACTLY what you challenged.
WHAT? LOLOL

"Turbofans are generally more efficient than turbojets at subsonic speeds, but they have a larger frontal area which generates more drag." LOL

Jet engine - Wikipedia, the free encyclopedia
 
Supercuise is not as important as you thought. It comes at cost of short range, less load.

It is not required by F-35 and future 6th gen aircraft.
And yet you guys uses it to criticize the F-35 and insist the J-20 will have it.

ARE YOU KIDDING ME????????
No...I am educating you.

Do you really know what is turbojet and what is turbofan?

Or your many years aviation experiences before retirement was doing a vacuum job on commercial aeroplane?

No time to talk to all these keyboard-professionals, check it out yourselves and compare the efficiency of two engines:

Jet engine - Wikipedia, the free encyclopedia
I may not be a Propulsion specialist, but I understand the jet engine better THAN ALL OF YOU CHINESE ON THIS FORUM COMBINED.

jet_engine_civil_mil.jpg


For the above illustration, we see two different sub-types of the turbofan jet engine: high bypass (top) and low bypass (bottom).

The goal of the jet engine is to use ALL of intake air, but unfortunately, there are disadvantages to that...

Turbojets
Turbojets tend to be inefficient except at high speeds, so modern aircraft use turbofans instead. Since the basic operation of a turbojet is simpler, we will begin our discussion of jet engines with turbojets.

Propulsive efficiency of turbojets increases as the aircraft velocity increases, but the aircraft typically must be supersonic before turbojet propulsive efficiencies approach levels that can compete with propellers.
Because we want jet fighters to be as useful as possible at a widest possible range of altitude and airspeed, the turbojet is excluded which lead us to the turbofan design, which is what we see in the illustration above.

Bypass air is the airflow that DO NOT enter the combustion chamber...

Bypass ratio - Wikipedia, the free encyclopedia
The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of air drawn through the fan disk that bypasses the engine core (un-combusted air) to the mass flow rate passing through the engine core that is involved in combustion to produce mechanical energy.
A ramjet and turbojet have zero bypass air.
In a pure (zero-bypass) jet engine, all the air taken in is involved in combustion;...
The percentage of bypass air to combustion (burned) air is that bypass ratio, of which the civilian high bypass design is common and the military low bypass design is common.

If supercruise is no big deal, as you absurdly declared...

Supercuise is nothing new and thereof to be proud, there do have many aircraft are capable of it.
Then why is the J-20 not capable of it TODAY ?

Answer: Because the technical difficulties of supercruise in a TURBOFAN design is a big deal.

You want to supercruise ? Fine, then get a turbojet. But like I often said many times on this forum before: That I have a great deal of respect for the Chinese engineers who ACTUALLY WORKS ON JET FIGHTERS, a group does not includes the Chinese members here. These professionals know that in order to get a turbofan to supercruise a jet fighter, even as aerodynamically sleek as the F-22 or the J-20 or the smaller F-16, they need something very close to the efficiency of a turbojet -- without being a turbojet.

You are just like the other Chinese members here: Bring on a source but does not understand it.
 
thanks, nothing you contributed.
:cry:
I helped expand the comprehension skills of you and your comrade and provided a valuable example to readers with similar mental deficiency about the perils of posting sources without reading it themselves first.

Turbofans move more air and have better efficiency at low altitude and low speed giving short take-offs and much better range due to the fact that most jets don't need to go supersonic. However they get increasingly inefficient with increasing speed (not to mention draggier because of the big fan). Hence for super cruising aircraft like the Concorde or Tu-144, you'd take a turbojet.
 
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And yet you guys uses it to criticize the F-35 and insist the J-20 will have it.


No...I am educating you.


I may not be a Propulsion specialist, but I understand the jet engine better THAN ALL OF YOU CHINESE ON THIS FORUM COMBINED.

View attachment 195932

For the above illustration, we see two different sub-types of the turbofan jet engine: high bypass (top) and low bypass (bottom).

The goal of the jet engine is to use ALL of intake air, but unfortunately, there are disadvantages to that...

Turbojets

Because we want jet fighters to be as useful as possible at a widest possible range of altitude and airspeed, the turbojet is excluded which lead us to the turbofan design, which is what we see in the illustration above.

Bypass air is the airflow that DO NOT enter the combustion chamber...

Bypass ratio - Wikipedia, the free encyclopedia

A ramjet and turbojet have zero bypass air.

The percentage of bypass air to combustion (burned) air is that bypass ratio, of which the civilian high bypass design is common and the military low bypass design is common.

If supercruise is no big deal, as you absurdly declared...


Then why is the J-20 not capable of it TODAY ?

Answer: Because the technical difficulties of supercruise in a TURBOFAN design is a big deal.

You want to supercruise ? Fine, then get a turbojet. But like I often said many times on this forum before: That I have a great deal of respect for the Chinese engineers who ACTUALLY WORKS ON JET FIGHTERS, a group does not includes the Chinese members here. These professionals know that in order to get a turbofan to supercruise a jet fighter, even as aerodynamically sleek as the F-22 or the J-20 or the smaller F-16, they need something very close to the efficiency of a turbojet -- without being a turbojet.

You are just like the other Chinese members here: Bring on a source but does not understand it.

Hurry up!

In the previous post, you forgot to read properly the internet stuffs and pasted it too fast.

Now it's the time to google again! It's no use, whatever you do, it's just too late.

======

Check your post, wtf:

"The turbojet is much more efficient than a turbofan, which is used in the majority of jet engines, military and civilian, today. "

You really don't know what is turbofan and turbojet before my last post.

Haha, ciao.
 
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Hurry up!

In the previous post, you forgot to read properly the internet stuffs and pasted it too fast.

Now it's the time to google again!

Check your post, wtf:

"The turbojet is much more efficient than a turbofan, which is used in the majority of jet engines, military and civilian, today. "
Very good that you can read. Too bad what you posted debunked your own argument: That engine efficiency is less important than body drag.
 
You're roughly correct except last sentence.

Plus, drag is not constant, it related to shape, speed, windspeed, humility, temperature, etc.

It's not the efficiency of engine, it's the efficiency of aerodynamic of body to supercruise an aircraft.

We had jet engine before we achieved a supersonic flight only we found the efficiency body design.

I would like to say: Aircraft with enough low drag will achieve supercruise with any jet engine like British did it 60 years ago.

Lets look at it this way, why a perfectly aerodynamic clean low weight Formula One racer have less sustained too speed than a More Heavy, less aerodynamic stable of a bugetti Veyon?

For an object to supercruise, that object have to be able to have a larger forward momentum than the reaction force, and the second requirment is that this object have to be able to sustain the forward monentum, given if the reaction force unchange.

Now, in a 2 dimension plane, the forward momentum is the engine thrust pushing the object forward and the lift that generate from the air pass thru the wing. The reaction force is the weight of the craft as well as the dynamic turbulence that create a downward force and the reaction force that pull the object back to counter the thrust.

Now, for a given object flow thru air , there will be an optimal aerodynamic shape that either the object evolve to or natually come with the object. ThE optimal aerodynamic shape represent the lowest limit of the aerodynamic drag created by an object, and you cannot go any lower than that.

Say for an example, lets say for a J20 to get to optimal aerodynamic shape, it have to be clean , no external disruption, having 60% fuel and wing folded.

And any change in this configuration will disrupt the air flow to the object and unbalance the aircraft. If the aircraft have more fuel, the weight induce drag, if the aircraft have less fuel, the lift induced drag will be higher, if thecraft have external loading, it would creat drag and so on

Now if in this state you have an Engine it can supercruise at FL300, but it would not mean they can automatically achieve Supercruiser at an lower alt. Even at optimal aerodynamic form. As the air is denser in lower atmosphere, then the engine efficiency is the sole factor on can an object achieve supercruise as the optimal aerodynamic form is constant.

For an aircraft, there are only a few parameter it can be changed during flight, you can change the wing angle of attack and you can change the weight, but the optimal setting for each craft is set during the designing phase and that shape will be constant throughtout. In commercial aviation, the setting is ised to determine the optimal glide speed. Where the only other factor that can significant alter a flight profile is the engine output.

Come back to the question on why an aerodynamically clean F1 racer have a lower sustained too speed than a Veyron. The Engine, the engine on an F1 racer is limited to V6 capacity, at that stage, it cannot have enough efficiency to break a certain speed barrier while the veyron have a W16 engine, at 800bhp, every horsepower produced will only have 1/6 translated to pulling the car forward, the other goes to counter the.drag That is why aerodynamical shape is not as important than Engine in a sense of achieve a higher sustainable top speed
 
Gambit, please hear me out and through.

Supercruise the word is a juxtaposition of supersonic and cruise.
Supercruise is then the ability to maintain flight above Mach1, period.

Supercruise the capacity is doing so without using afterburners.
Any jet with enough dry thrust can do that. To be precise, many jets can maintain supercruise today and any of them can get there on dry thrust.

Supercruise hides the following facts however : power, drag, load and fuel fraction.

There are many ways to combine these :
A- a given engine dry thrust used on different aircrafts.
Any engine generating a supersonic exhaust flux can supercruise alone as in a rocket. If applied to a heavy enough or not sufficiently aerodynamic body however, it will not be powerful enough to attain M1 and thus the combination will not supercruise.

B- a drag factor can be changed up or down in many ways.
Have a more aerodynamic shape; reduce friction : either by flying in more rarefied air ( HA ) or by disrupting the air through any method thus cutting down its density, etc.

C- load variation : once the above two are combined, load comes into play and reducing overall weight favors achieving supercruise while heightening it can nullify the ability.

D- fuel availability : once the above three are combined the quantity of fuel available can be enough to supercruise for 1 Nautical Mile or for 1 000 NM.


Many fighters and at least one civilian aircraft ( Concorde ) can supercruise. This however varies in practical use.

Any plane that can fly over M1 on dry thrust can de facto reach that speed without afterburners. Which does not mean however that it can do so usefully. Thus, one must factor in all of the above to find what results can be gotten from this ability.

If you use say 80% of your fuel through dry thrust to reach M1, supercruise means getting airborne, breaking Mach, flying 1 NM, turning around and landing. In such a set-up, it would not matter what military load you carry, tactical application would be zero.

Using afterburners to reach M1 is the solution as it consumes more fuel for a shorter period but less overall and leaves more of the total available to cruise afterwards. Since drag is reduced considerably past the sound barrier and less fuel needs to be consumed, the result would be a greatly improved supercruise distance by that same aircraft. The same as above then provides say 40% instead of 20% remaining fuel and 10NM instead of 1.
Let us suppose for an instant that your M1 able engine-aircraft combination does not have afterburners. You would be left with one choice to augment supercruise distance : diminish load to reduce drag.
Strip the aircraft of all unnecessary weight : take off the weaponry for instance! The combo can now supercruise longer but tactical application is again zero. You can reach the enemy in time but not fight it once there.

Another precision : supercruise capacity varies in distance as we just saw but also in speed. Supercruising for an hour at M1 gets you less distance covered than supercruising at M1.4 for an hour and that in turn less than supercruising at M1.8.

Finally, the law of diminishing returns applies to all of the above so that all supercruise options outlined come at a cost that gets higher and higher as performances increase, again possibly resulting in zero tactical application under varying scenarii.

All of the above means that supercruise itself can be had without any military benefits ensuing and that each context of use is different, i.e. the word itself does not define the qualitative advantages of its implementation.


Is then the F-22 better at it than the rest?
You bet it is : head and shoulders above the rest in fact! The Raptor can supercruise at M1.5 / M1.7 with full air superiority armament ( 6 AIM-120 + 2 AIM-9 ) for over 200NM ( exact number being classified ).
Let us be clear : no other aircraft in use or under development as of today ( Feb_March 2015 ) can or will match this, period.

The best - Rafale / Typhoon / Gripen can supercruise at 1.4, 1.3 and 1.2 Mach in combat configurations respectively for instance, sure but ...
in all three cases, with less than maximum number of missiles and/or less than maximum number of external fuel stores.
Taking the Rafale as an example to avoid offending sensibilities, it goes something like 6 MICA ( out of a possible 10 ) and no fuel tanks or 4 MICA and a supersonic belly tank and so on, all at M1.4. That means the load and fuel fraction factors are well below the full configuration and tactical application below the ideal 100%. Range, for one, would be severely reduced.
To get to M1.5 on dry thrust, Rafale or Typhoon would need to be in clean configuration ( nothing hanging out ) which brings us back to zero tactical application.
Again, the Raptor can achieve its numbers with all fuel and weapons or full configuration if you prefer, thanks to its all internal stealth design.

Even then the cost however is immense : 25% reduction in max. range for 100NM travelled and again, the law of diminishing returns makes anything beyond more and more costly.
Oh! And for all, even the Raptor, this is only possible at high altitude.

What all of this means is that : the Raptor is the only plane that can boast of routine use of supercruise vs less than a handful that can make possible ( or occasional ) use of it and a long list of aircrafts that have the ability itself but just cannot extract any military use from it.

I hope you were able to last through this long diatribe of an explanation and that it will come in handy.

And, I am sorry to say this as it may sound disrespectful but it is not, merely preventive, without doubting your credentials, my sources for the above include the USAF itself. Here are a couple simple examples

F-22 demonstrates 'supercruise' for first time
" … In the context of the F-22 Raptor, supercruise is defined as the ability to cruise at speeds of one and a half times the speed of sound or greater without the use of afterburner for extended periods in combat configuration.Jul 21, 1999
"Sustaining the target Mach was not difficult for the Raptor," said Col. C.D. Moore, Combined Test Force commander, at Edwards Air Force Base, Calif. … "

F-22 Raptor > U.S. Air Force > Fact Sheet Display
" … The F-22 engines produce more thrust than any current fighter engine. The combination of sleek aerodynamic design and increased thrust allows the F-22 to cruise at supersonic airspeeds (greater than 1.5 Mach) without using afterburner -- a characteristic known as supercruise. Supercruise greatly expands the F-22 's operating envelope in both speed and range over current fighters, which must use fuel-consuming afterburner to operate at supersonic speeds. ...'

and a shorter version of my post for the most impatient of PDF members :
What Is Supercruise? (with pictures) from which :
" … A supercruise aircraft generally utilizes afterburners to accelerate from subsonic to supersonic velocity, although this is because of concerns about fuel efficiency rather than strict necessity, in most cases. …"

And a very good day to you all, Tay.
 
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The turbojet is much more efficient than a turbofan, which is used in the majority of jet engines, military and civilian, today. Beyond the turbojet would be the ramjet which is the most efficient of all and which is what the SR-71 uses.

The F119-PW-100 is technically a low bypass turbofan type but is efficient enough that it is considered to be 'near turbojet' type.

You dispute that engine efficiency is the key to supercruise but then brought on a source that shows EXACTLY what you challenged.


Your claim is totally wrong. Everyone knows a turbofan is more efficient than a turbojet.

----------
Turbofan Engine | NASA

"Most modern airliners use turbofan engines because of their high thrust and good fuel efficiency. ...Low bypass ratio turbofans are still more fuel efficient than basic turbojets."

----------
P3pHJVF.jpg

"TSFC - Thrust specific fuel consumption. Lower number indicates greater efficiency."
 
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China stealth fighter a 'masterpiece' of homegrown technology - Telegraph

"Jan 25, 2011 - A senior Chinese test pilot, Xu Yongling, told the paper that J-20 possessed advanced supersonic cruise ability and other 'breakthrough' ..."


Come on ! A report written in 2011 when that type was just unveiled and quoting a source like this way is simply a statement that the final version powered by WS-15 will have that capability, but not that the prototype already can supercruise.

Don't get me wrong and I even more do not want to underrate the J-20, its capabilities and even more its meaning for the PLAAF, but such reports cannot be taken word-by-word, esp. since we don't know the whole context of Xu's statement.
 
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