J-20 5th Gen Fighter Thread IV (Closed to posting)

[delft]

Quite right but the AB injects raw fuel into the AB section, allmost all US powerplants seem to have a red/yellow/blue flame, and in he case of F119 and F-135, not shortage of thrust...... So, a richer mixture runs MUCH COOLER! BRAT

I understood that the yellow is radiation from unburned carbon. If the mixing zone is long enough that carbon might still be burned and contribute to thrust.
I also learned but never understood that excessively leaning the mixture in piston engines leads to lower fuel consumption but higher cylinder head temperatures and in time engine failure.

 

[delft]

Roger that, but remember LockMart bought Yaks lift fan rights, and maybe the prototype aircraft, you lads make entirely to much of the indigenous deal, we used to refer to that as NIH or not invented here. Sometimes you have to pay for something you want, its not all about the deal, its about capability and if you have to buy it to get where you need to go, thats no big deal....get out the checkbook dudes?? Brat

I remember that Lockheed bought around 1970 a licence to combine bonding and spot welding as used in the Antonov An-2 biplane.

 

[Broccoli]

Could someone explain me this, if J-20 is a "bomber" why it has canards? I'm not aeronautical engineer at all, but wouldn't big delta wing suit better for bomber aircraft.

Something like seen in Boeing X-32.

Or perhaps something like this.

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[Air Force Brat]

I understood that the yellow is radiation from unburned carbon. If the mixing zone is long enough that carbon might still be burned and contribute to thrust.
I also learned but never understood that excessively leaning the mixture in piston engines leads to lower fuel consumption but higher cylinder head temperatures and in time engine failure.

The enemy of all engines is heat/lubrication breakdown whether recips or turbines, the lead in leaded fuel provided lubrication in recips for valves/pistons etc. Many older aircraft suffered catastrophic failures when low lead/unleaded fuels became the rule. As combustion temperatures go up--fuel efficiency is increased--because of more efficient burning of fuel, however, those same elevated combustion temperatures eliminate the very very slight excess of fuel that cools turbine blades, bearings, pistons, and valves by absorbing that same heat and conducting it away from the HOT SECTION, and out the exhaust. The afterburner cans are located behind the main engine, and inject raw fuel into the very hot gases, where it is "reheated" to provide additional thrust produced by the explosive combustion of that additional fuel, the main reason that AB is selected once the turbine has stabilised on the take-off roll, and one of the reasons that many early AB failures were not contained by the AB Cans is that very violent combustion, and the reason that the AB sounds like a BLOWTORCH when selected, it is! Hope this helps, AFB

Aircraft in AB are very in-efficient as the objective is massive thrust, the real reason that being able to Mach-out or super cruise without AB is such a BIG DEAL is this increased fuel efficiency, and why the F-22 is so far superior to other aircraft even though its max speed may be slower than others, is its very efficient cruiseing at Mach 1.8 without AB, very few aircraft have a "demonstrated" ability to do this, and of those that do, non are nearly as efficient as the lovely Raptor.

At some point we will hopefully know the true performance of the J-20 in super-cruise, I highly doubt that the J-20 will achieve this objective with the current power-plants, they are simply not powerfull enough to super-cruise the J-20 without AB???????? The main reason I continue to contend that the Chinese want the F-117s for the J-20, until the WS-15s are ready. BRAT

 

[MiG-29]

Could someone explain me this, if J-20 is a "bomber" why it has canards? I'm not aeronautical engineer at all, but wouldn't big delta wing suit better for bomber aircraft.

Something like seen in Boeing X-32.

Or perhaps something like this.

J-20 is very likely a multirole aircraft, doing from fighter to bomber roles, these is because all new jets are multirole, since modern air forces are being formed upon fewer types of aircraft, then aircraft become multirole.

A canard does not mean an aircraft is a fighter, there are many aircraft that use canards ranging from fighters (rafale), interceptors (Viggen), bombers (XB-70, Su-34), civil aircraft big (Tu-144) and small (Piaggio Avanti).

However because modern jets need to do many jobs from fighter to bomber to recce, and have a complex set of requierements ranging from stealth to supercruise, they have many compromises.

J-20 will very likely do many types of missions, since is unlikely China will build 6 or 7 types of different aircraft for each mission.

In the 1950s when the jet age started you could see, different aircraft in an air force, today you only see two or three models doing several duties.

Russia has the Su-27 flanker family doing from carrier aircraft Su-33, deep penetration tactical bomber Su-34, tactical fighter Su-30 and Su-35 air superiority.

F-35 is exactly the same, it is a naval, marines and USAF fighter.

J-20 will very likely follow that trend.

The current trend is make stealth fighters doing several roles at the same time, modifying an airframe to fulfill several roles like F-18, Su-27 or F-35 are or fitting advanced avionics like in Eurofighter or Rafale.


This is result of increases in costs that air forces are uncapable of finance more types of aircraft specialized in just one role like in the 1950s.

Originaly the F-111 was to be a naval fighter, in fact it was designed as a multirole aircraft, it ended as a bomber, but Panavia Tornado started as a bomber with secondary air superiority role, it ended as a interceptor with very advanced ASRAAMs.

Viggen started like a tactical bomber and ended as an interceptor.
MiG-23 and MiG-25 started as pure interceptors but developed recce, bomber and tactical support versions, MiG-25 in fact had even high altitude bomber versions.


Su-27 was a heavy scort fighter but it ended in so many modifications.

Since J-20 is still a prototype, we do not know how many variants it might spawn, it will depend in its avionics and the potential for modification of its airframe ands if China will adopt another fighter like J-31.

 

[duskylim]

I understood that the yellow is radiation from unburned carbon. If the mixing zone is long enough that carbon might still be burned and contribute to thrust.
I also learned but never understood that excessively leaning the mixture in piston engines leads to lower fuel consumption but higher cylinder head temperatures and in time engine failure.

Okay this is a little off-topic but all aircraft turbine engines, run lean, you only see red/yellow flames when they are in afterburner.

This is what makes them so challenging to design and build. They run the hot lean mixtures continually in the hot section of the engine, that really tests your metallurgy and cooling design.

In piston engines, they run stoichiometric on idle (or slightly rich), lean when cruising and rich during acceleration and full-power.

Lean mixtures can be tolerated in piston engines as long as the load is low - when cruising, giving the best fuel economy - but will destroy the engine at higher loads.

Rich mixtures also give more power than stoichiometric (chemically correct) mixtures, as the hydrogen in the fuel burns off 1st, before the carbon - some of which remains unburnt - hence the black deposits.

They are also used to ensure smooth acceleration.

 

[Engineer]

Could someone explain me this, if J-20 is a "bomber" why it has canards? I'm not aeronautical engineer at all, but wouldn't big delta wing suit better for bomber aircraft.

Something like seen in Boeing X-32.

Or perhaps something like this.

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The answer to that is simple: J-20 is not a bomber, but intended to be a highly maneuverable fighter with air-superiority as the primary role. It's just that some people insist on J-20 being a bomber or interceptor because they want to hang on to the belief that China can't build anything more maneuverable than a J-7.

As siegecrossbow has pointed out, MiG1.44 has nearly the same configuration as J-20 and was not a bomber. People are in fact contradicting themselves when they say J-20 is a copy while claiming the aircraft to be a bomber.

 

[delft]

The enemy of all engines is heat/lubrication breakdown whether recips or turbines, the lead in leaded fuel provided lubrication in recips for valves/pistons etc. Many older aircraft suffered catastrophic failures when low lead/unleaded fuels became the rule. As combustion temperatures go up--fuel efficiency is increased--because of more efficient burning of fuel, however, those same elevated combustion temperatures eliminate the very very slight excess of fuel that cools turbine blades, bearings, pistons, and valves by absorbing that same heat and conducting it away from the HOT SECTION, and out the exhaust. The afterburner cans are located behind the main engine, and inject raw fuel into the very hot gases, where it is "reheated" to provide additional thrust produced by the explosive combustion of that additional fuel, the main reason that AB is selected once the turbine has stabilised on the take-off roll, and one of the reasons that many early AB failures were not contained by the AB Cans is that very violent combustion, and the reason that the AB sounds like a BLOWTORCH when selected, it is! Hope this helps, AFB

Aircraft in AB are very in-efficient as the objective is massive thrust, the real reason that being able to Mach-out or super cruise without AB is such a BIG DEAL is this increased fuel efficiency, and why the F-22 is so far superior to other aircraft even though its max speed may be slower than others, is its very efficient cruiseing at Mach 1.8 without AB, very few aircraft have a "demonstrated" ability to do this, and of those that do, non are nearly as efficient as the lovely Raptor.

At some point we will hopefully know the true performance of the J-20 in super-cruise, I highly doubt that the J-20 will achieve this objective with the current power-plants, they are simply not powerfull enough to super-cruise the J-20 without AB???????? The main reason I continue to contend that the Chinese want the F-117s for the J-20, until the WS-15s are ready. BRAT

I studied turbine engines in University, not as an engine designer but as a potential user - aircraft designer. My ignorance concerns piston engines. I guess that the leaner mixture leads to a lower rpm and so to less effective cooling.
I haven't flown for a long time, the last time in 1967 in an Il-18 coming back from holiday. During that holiday several flights in Il-14 and before that in a Piper Cub, a Siebel 204D and a Beechcraft Queen Air. All but one with piston engines!

 

[Air Force Brat]

I studied turbine engines in University, not as an engine designer but as a potential user - aircraft designer. My ignorance concerns piston engines. I guess that the leaner mixture leads to a lower rpm and so to less effective cooling.
I haven't flown for a long time, the last time in 1967 in an Il-18 coming back from holiday. During that holiday several flights in Il-14 and before that in a Piper Cub, a Siebel 204D and a Beechcraft Queen Air. All but one with piston engines!

Right and likely all of those pistons had some means to lean the mixture, the Cub and Queen Air, both had a mixture control on each engine, starting and low altitude is always conducted with the mixture full rich, as you climb you pull the mixture back as the air thins to maintain an optimum mixture, you pull the mixture back to max rpm, and then enrich it slightly to prevent an overlean mixture, this is one of the reasons that recips become more efficient with altitude. As you approach to land, mixture full rich, and props forward to enable full power in the event of a go around. Brat

As I noted, many early AB cans exploded when the throttle was placed in AB, as in-efficient as AB might appear to the layman, that extra performance is a huge safety factor on military aircraft as gross weights go up, AB will shorten take off run and increase climb rate and even turn performance. Brat

 

[airsuperiority]

The answer to that is simple: J-20 is not a bomber, but intended to be a highly maneuverable fighter with air-superiority as the primary role. It's just that some people insist on J-20 being a bomber or interceptor because they want to hang on to the belief that China can't build anything more maneuverable than a J-7.

As siegecrossbow has pointed out, MiG1.44 has nearly the same configuration as J-20 and was not a bomber. People are in fact contradicting themselves when they say J-20 is a copy while claiming the aircraft to be a bomber.

Well while B-1 has the canards, I do agree with Engineer that it's just people's stupidity and refusal to believe the J-20 is a fighter. A bomber of the size of J-20 is really not too much of any real uses, and anyone who understands what the Chinese military needs will know that it's a waste of money to develop a "bomber" like that.