SinoDefence Forum

Vlad Plasmius

Well, J-8 has the thrust for supercruise, but lacks the aerodynamics. However, there are engines that can offer even more thrust.

trkl

If the estimates of its weight are anywhere near accurate, J-10 not only has less total thrust than J-8 and J-11, but it also has a lower T/W ratio.

Do you have a link in English? I can't really read Chinese and the article won't let me cut and paste it into a translating program. I think it says that J-10 flew at mach 2.4, but a souce I can read would be better.

tphuang

T/W ratio of the engine.

Of course it has less thrust than J-11, it has one engine. Once it gets WS-10A, it will no longer have less total thrust than J-8. I'd take 140 kN of turbofan thrust over 140kN of turbojet thrust anyday of the week.

If you just talk about speed, it's dependent on plane structure, material it's made from and engine. J-8 may have good thrust, but it's other areas are just sorely lacking. Let's put it this way, JH-7A has greater total thrust than both J-8 and J-10, but it's max speed is listed at mach1.69 I think?

What the article says is that in January of 2004, J-10 flied the fastest speed in plaaf history. It speculates whether plaaf has flied the claimed mach2.4 with su-27 or not. If that is true, then J-10's fastest flown speed is mach2.4, if not, then J-10's fastest speed is at least mach2.2


more on this:
http://news.china.com/zh_cn/domestic...2240249_1.html
another article claiming mach2.2 top speed for J-10

trkl

If you don't care about fuel consumption, the 140kn of turbojet thrust should actually be better, since it it should be better at maintaining thrust at high speeds than the turbofan. A new J-8 with 2 WP-18b turbojets should have 108 kn dry thrust and 153 kn total thrust.

I know there are a lot of facters that affect the top speed, including things like aerodynamics. And many fighters have their speed limited by what the materials that they are made of can withstand, rather than by thrust/drag relationships.

The idea that J-10 can go faster than mach 2 makes sense, since the J-10 is in a similar thrust and weight class as the Mach 2 F-16 and the J-10's variable inlet should give it a performance edge over the F-16's fixed inlet at high speeds. Still, it is surprising if J-10 can exceed the speed of aircraft like J-8 and J-11. Mabey J-8 and J-11 are limited by materials and J-10 can go faster due to better materials?

tphuang

let's put it this way, in an internal plaaf military exercise between the mkk and J-10. People who say this claimed that J-10 was faster and moved much better than mkk despite carrying much heavier payload.

If you read the article, it basically mentions that the engine and plane structure allows for really good manuverability at high speed. I don't know the exact physics behind this, but think about it this way:

f=ma, and F = thrust - drag. Normally, drag increases when speed increases, but decreases when you go higher up (less resistance).

Since J-10 has good aerodynamic configuration, therefore the drag doesn't increase that much at higher speed, so acceleration is still possible, so the speed can still go up.

On the other hand, J-8's configuraiton is nowhere near as good, so even with slightly larger thrust, the force becomes 0 when speed is really fast. Then, acceleration is no longer possible. Even if it's frame might be able to stand for greater speed, the drag will stop it.

As for J-11, it needs a greater difference between thrust and drag, because mass is greater, so acceleration is smaller if thrust and drag difference do not change. J-11 is also larger, so the drag will be much larger than that of J-8/J-10.

I can go on and on about this, but I need to sleep now.

trkl

If the aircraft is thrust-limited, it will reach it's maximum speed will be determined by how fast it can go before thrust=drag. As you said, drag increases with speed and decreases with altitude. However, drag is not the only variable. The thrust also decreases as speed increases, and it decreases more for turbofans than for turbojets. There are also some other facters that affect how well the engine will perform at high speeds, like the type of inlet used.

It is true that the J-10 has good aerodynamics, but I'm not convinced that the J-8's aerodynamics aren't good for a plane that wants to go fast. The J-8 was designed as an intercepter, so flying fast is what it is designed to do. It has a high ceiling of over 20,000m which also helps to reduce drag. If you compare it with similar aircraft, the fact that it can only go up to mach 2.2 is actually somewhat surprising. This is why I think that it is probably materials-limited rather than thrust-limited especially when you consider that even older versions with significatly weaker engines can also acheive mach 2.2.

If J-11 has the same net force acting on it, then yes it will accelerate slower. However, that really has no effect on top speed.

Being larger tends to work in the favor of the J-11. Drag tends to be roughly proportional to surface area, while thrust is more proportional to volume. That is why an old civillian passenger liner like Concorde can easily fly at mach 2 while some modern small fighters (such as FC-1 and LCA) can't. The Flanker's top speed is Mach 2.35, which is a pretty high target for a single engine fighter. If the J-10 really can fly at mach 2.4, then that is very impressive.

walter

most plane's max mach number is limited by buffeting effects, not available thrust. For the f-16, i know this to be the case. At speeds above Mach 2 flight becomes too instable due to buffeting. This is the case with most other modern fighters, as well, although I do not know for sure if it is true for the J-10.

MIGleader

i think most fighters can go much faster than given, but the gs fronm turninh would kill the pilot, and the heat would melt the cocpit.

tphuang

That's what I've been saying. One of the links I provided basically said that the way J-10 is build allows the engine to still maintain good thrust even at high speed. To even compare AL-31F to WP-13II is not good. They are two complete different level of engines.

From that article.
此外，可调节进气道所增加的高效整流压缩能力(在1.5马赫时为5%，在1.8马赫增加至15%，在2马赫 时为25～30%)极大地提高了飞机超音速飞行时的发动机推力，

It basically said that J-10's intake can be adjusted at high speed to improve the "air flow pressure?" and actually raise the thrust of the engine.

Once we get the DSI instake, J-10 would go even faster! wow!!!

J-10 has the same ceiling. That's why there are two speed listed, one for low altitude and one for high altitude. You simply cannot compare the two planes' aerodynamics. J-8 is based on Mig-21 design which is good for its generation, but J-10 is based on Lavi and MFI (at least CAC got a lot of help from Mikloyan on J-10's structure). It's more than just the plain material, J-8 actually has increased the composite material % from before.

J-11 is a lot big, so the surface area is much big. Remember, it's frontal RCS is huge. Normally when that is the case, the surface area going into air is much larger, so the drag is increased by quite a bit. Actually, Flankers a twin-engined. As I have said, J-10 is designed to be really manuverable. It's airframe is extremely advanced. I doubt anyone has flied J-10 at mach 2.4, because plaaf pilots are generally very conservative in flying.

trkl

Actually, if J-10 gets DSI it would probably make it slower. The J-10 has what is known as a "variable" inlet. That means that the shape of the inlet changes to adjust for different speeds and maintian a good amount of airflow at all speeds. This has the advantage of giving good performance, but it is also heavy, complicated, expensive, and maitenence-intensive. This type of inlet is pretty common, and I think J-8 and J-11 also have variable inlets.

Some other fighters like the have a "fixed" inlet. It does not change to adjust for speed, so the performance will usually be worse than for a variable inlet. Compared with a variable inlet, the fixed inlet is lighter, cheaper, and easier to maintain. The F-16 uses this type of inlet.

The new development in inlet design is the diverterless supersonic inlet, which is actually actually a type of fixed inlet. "Normal" fixed inlets need a device called a diverter to ensure that turbulent boundry layer air is diverted away from the engine. However, due to advances in computational fluid dynamics, engineers are now able to design inlets that can direct the turbulent air away from the engine without having to use a diverter. This makes the inlet even simpler and lighter than in a normal fixed inlet, but it still delivers about as much performance as the normal inlet.

Basically, if you compare the DSI inlet with the variable inlet, the DSI would be much cheaper, much lighter, and much easier to maintain than the variable inlet, but your perfomance at high supersonic speeds would not be as good.

Here is a good article on DSI:http://www.codeonemagazine.com/archi...ertless_1.html

You seem to assume that a "more advanced" aircraft should be able to fly faster than a less advanced aircraft, but that really isn't true. Back in the 50's and 60's, fighters were usually designed to fly as fast as possible. However, experience in Vietnam showed that faster wasn't always better and that low speed handling and manuverability was much more important than top speed. That's why some modern planes like the F-18 are much slower than older planes like the F-104 and F-4, and the reason why the Lavi(max speed=Mach 1.85) was much slower than the J-8.

As for the J-8's materials, it may use some composits now, but it is probably mostly made out of aluminum which will melt if it gets too hot.

tphuang

hmm, do you have any proof that J-8 has an variable inlet at the same level as J-10s? We've been arguing for a while, but you haven't seemed to find a single argument that J-8 would be able to fly faster than J-10 other than the thrust factor.

trkl

I Havent seen any articles on the J-8II that talk about it's inlets, but I have heard people say that the J-8II copied the inlets of the Mig-23 and the Mig-23 had variable inlets. I also found some people talking about the possibility of a Lavi-J-10 connection who said:http://www.china-defense.com/forum/i...ic=3020&st=195

high thrust is not the only reason why J-8 should be fast. It has large delta wings with a lot of wing area that help it fly much higher than most other aircraft. J-10 also has delta wings, but it's wings aren't quite as big so it might not be able to fly as high. All of the estimates for the service ceiling of the J-10 are much lower than the ceiling of the J-8, though the numbers for J-10's ceiling are probably as unreliable as the numbers for it's speed.

tphuang

CDF is a good source, but it's just by common-joes like you and me. If there is anyone that I do respect on that forum, it would be Tam. He seemed to have followed J-10 a long time and really knows what he is talking about. As for that comparison, I think what that guy was saying is that J-10 has a variable inlet and so does j-8 and j-11, but not that J-8's inlet is anywhere close to that of J-10. Personally, I'm guessing J-10's inlet is probably much more advanced.

As for the height factor, I guess we won't know for a while what J-10's ceiling is. Just as we won't know it's maximum speed or operation range or real payload.

And if J-8 has to fly higher than J-10 to achieve the same speed, then it really isn't faster than J-10, is it? You know, I read some of these Chinese articles about people seeing J-10 flying against su-27/mkk. They keep on echoing that J-10 vs su-27 in speed looks like su-27 vs J-8 10 years ago.

Anyway, as far as I'm concerned, I've already shown the article about J-10 being the fastest plane.

MIGleader

i thing in close combat, a smaller and more agile j-10 can outmanuver the su-27. but i dont believe a composite single engine j-10 can fly faster thaan the titanium twin engine su-27.

Sea Dog

The only thing I wonder, is if the J-10's could overcome some of the high AOA maneuvers of the Su-27's. I don't know much about J-10 maneuverability, but Su-27 has done impressive things in air demo's. I think it would be brutal to fight in short-range combat with one.