SinoDefence Forum

trkl

Supercruise is often thought of as a new technology for fighters like F/A-22 or mabey Typhoon, so it might seem odd to ask if an "old" and "low-tech" fighter like J-8 can supercruise. However, it is actually easier to make a supercruising turbojet aircraft than it is to make a supercruising turbofan aircraft as turbojets often have a better dry thrust/weight ratio and thrust decreases less with high speeds. Also, some old jets like F-104 and English Electric Lighting could go above mach 1 while in a "clean" configuration, though thier performance is really more transonic than supersonic.

J-8 has significantly better thrust/weight ratio than the f-104 or the EEL, especially the versions with newer engines. The newest f-8 engines (Kunlun II aka WP-14b) are said to be the most advanced turbojets in the world, though that is a somwhat dubious distinction now that almost all aircraft are powered by turbofans. So I was wondering, how fast can J-8 go without using afterburners? Can J-8 supercruise?

tphuang

nope, supercruise only counts if it can supercruise at supersonic speed. I doubt J-8 can do that.

If you are talking about subsonic supercruise, even JH-7A has it.

trkl

What makes you so certain of that? With the newer engines, J-8's dry thrust is greater than its (empty) weight, which is something that many newer fighters can't say. And, as I said before, the J-8's turbojets will be able to maintian that trust at higher speeds better than other plane's turbofans.

sumdud

The plane has a powerful engine and is light, but I doubt it can with its conventional wing, a large body, and bad aerodynamics. The design was simple.

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Give us a break. Don't try ranting at SDF.

trkl

The airodynamics are poor when it comes to manuverability, but the J-8 was designed as a high speed intercepter, so I don't think I should have a huge ammount of drag compared with most other aircraft. The more I think about it, the more it seems like the J-8 (with new engines) should be able supercruise. When the J-8 had older WP-13 engines it was able to go mach 2.2. It looks like the new Kunlun II engines have a dry thrust 79% as large as the full thrust of the older WP-13 engines, and it seems like a Mach 2.2 aircraft that looses 21% of its thrust should at least be able remain supersonic.

Gollevainen

Israel project Kurnas2000, aka Phantom whit Pratt&Whitney PW1120 turbofans was able to fly over Mach 1 whitout afterburner. PW1120 were scaled down F-100 and the possible engine choice for Lavi and even swedish Gripen, thus the swedens later choice went to F-404, as the PW1120 wasent in production yet and Swedens didnt want to be the first users of that new engine...

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MIGleader

j-8 wont supercruise. the chinese media would be bragging about it like there was no tommorow. the first to suoercrusie may be j10, since its pretty light.

walter

subsonic supercruise???? what is that? wouldn't it just be 'cruise' without the super, or did I miss the true meaning of supercruise?

MIGleader

i believe supercruise means to fly at mach1 plus without using afterburners. a subsonic cruse may mean that they canfly below mach 1 without afteburners, which all fighters can.

trkl

J-10? I doubt J-10 will ever be able to supercruise. While J-10 has excellent agility and low speed manuverability, it is not meant to be a high speed intercepter like the J-8, and it is difficult to make a fighter that can supercruise while only using a single turbofan. The J-8 and J-10 are very close to the same weight, but the J-8 actually has over 30% more dry thrust than the J-10. This is why the "old fashioned" J-8 has a much better chance of achieving supercruise than the more advanced J-10.

As for the Chinese media bragging about it, mabey they would and mabey they wouldn't. It's hard to tell sometimes what sorts of things the Chinese will play up for propaganda and what sorts of thing they will hide due to secrecy or because they avoid giving ammunition to the "China threat theorists". Or they could just assume that no one would care, since it is more of an academic curiosity than something with actual operational utility. The J-8's turbojets must use up a lot of fuel even while running dry, and the J-8 does not have internal stowage like the F-22 so putting weapons on it would significantly degrade it's performance.

trkl

There are two basic deffinitions. One is to simply be able to fly above mach 1 without using afterburners. This is not too difficult, and most modern fighters can probably acheive this, at least in a clean configuration. J-8 should deffinately be able to do this.

The other deffinition, which I think is better and more useful, is the ability to cruise in the fully supersonic regime rather than in the transonic regime. Baiscally there are three different speed regimes that fighters fly through: subsonic(<Mach .8), transonic (mach .8-mach 1.3), and supersonic (>mach 1.3).

From wikipedia:
The drag that the aircraft experiences goes up significantly in the in the transonic regime, but it actually goes down a bit when you enter the fully supersonic regime. An aircraft at mach 1.4 will likely experience less drag than one at mach 1.2, which is why an aircraft can experience a significant fuel savings if it can stay above the transonic speeds. This type of supercruise is harder to achieve than simply goning above mach 1, but it is much more useful. Concorde, F/A-22, Typhoon, and probably Rafale are capable of this, though I think the F/A-22 is the only fighter that can do it with a full weapons load. This the typ of supercruise that I was thinking of when I asked about the J-8.

adeptitus

Here's a great link to look at:
http://www.jet-engine.net/miltfspec.html

The first jet to supercruise is the BAC Lightning. Great performance - it could climb 50,000 ft per min and intercept U2's at 88,000 ft. Kinda of like a UK-made "Super MiG-21", but suffered poor range and weapons load (just like the MiG).

tphuang

J-10 actually achieved the fastest speed in plaaf history. For a single engine plane, it has a lot of thrust. Once we get the twin-engined version, I suspect it will have both tvc and supercruise capability.

As for "subsonic supercruise", yeah, pretty much every plane has it.

trkl

Fastest speed in PLAAF history? All the information that I have seen says that it has a max speed of only Mach 2. AL-31FN is a powerful engine, but it still can't match 2 WP-14b. And it is even further from being able to match 2 AL-31F...

tphuang

J-10's real top speed is classified. Let's just say that the fighter frame and engine allows for faster speed than mach 2. Its plane structure with canard and delta wing allows for greater speed. It seems that all the new fighters are just using mach 2 as the top speed, the real top speed is all classified. It's not just about total thrust, but also T/W ratio and stuff like that. Su-27/30 has even greater total thrust, but it hasn't travelled that fast with plaaf.

Here is the link
http://military.china.com/zh_cn/crit.../12264381.html