JH-7/JH-7A/JH-7B Thread

[latenlazy]

There are few if any drones well known to the public domain that would make good low altitude, high speed pentrators. Most offensive drones prioritize long loiter time over anything else. Hence they have long, straight, high aspect ratio wings that would snap off in high speed, low altitude penetration runs.

A good high speed, low altitude penetrator would have tiny low aspect ratio wings.

Not saying there's a drone to do the job right now, just that such a role might be better done with a drone.

 

[delft]

I am not sure about that.

J-16 obvious derives her airframe design from su-27. The su-27 prioritized combat maneuverability over high speed penetration of enemy airspace. As a result, su-27/j-16 has huge wings, low wing loading, and big engines for its size. This means j-16 can sustain high turn rates, fantastic climb rates, and high roll and,pitch rates. But achieving these same attributes means su-27/j-16 also has high induced drag and needs big engines to go fast, are highly sensitive to gust and offers a punishing ride at high speed low altitude flight. In other words they make poor airframes for deep high speed low altitude penetrations of enemy airspace.

If jh-7 on the other hand didn't seem to put much emphasis on combat maneuverability. So it has relatively small wings with high wing loading. This means Jh-7 can't turn or climb with the su-27/j-16, but it probably has low gust response, low induced drag, smooth ride at low altitude, high speed penetration role, and need less fuel comsumption to,achieve the same low altitude, high speed performance, and thus a longer range for the same fuel load.

Yes, both the US and Russia decided to base their current strike fighters off of air superiority fighter airframes. But that was not done because air superiority airframes makes ideal low altitude penetration strike airframes. That was done to save money by reusing big powerfully engined airframes that could carry a lot of weight by virtues of their big engines and big wings. A truly ideal penetration strike aircraft would have a whole different mix of wing size, engine power, and airframe design than f-15e and su-34.

Compare with the configuration of the late British TSR-2.

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[FORBIN]

 

[zaphd]

I am not sure about that.

J-16 obvious derives her airframe design from su-27. The su-27 prioritized combat maneuverability over high speed penetration of enemy airspace. As a result, su-27/j-16 has huge wings, low wing loading, and big engines for its size. This means j-16 can sustain high turn rates, fantastic climb rates, and high roll and,pitch rates. But achieving these same attributes means su-27/j-16 also has high induced drag and needs big engines to go fast, are highly sensitive to gust and offers a punishing ride at high speed low altitude flight. In other words they make poor airframes for deep high speed low altitude penetrations of enemy airspace.

If jh-7 on the other hand didn't seem to put much emphasis on combat maneuverability. So it has relatively small wings with high wing loading. This means Jh-7 can't turn or climb with the su-27/j-16, but it probably has low gust response, low induced drag, smooth ride at low altitude, high speed penetration role, and need less fuel comsumption to,achieve the same low altitude, high speed performance, and thus a longer range for the same fuel load.

Yes, both the US and Russia decided to base their current strike fighters off of air superiority fighter airframes. But that was not done because air superiority airframes makes ideal low altitude penetration strike airframes. That was done to save money by reusing big powerfully engined airframes that could carry a lot of weight by virtues of their big engines and big wings. A truly ideal penetration strike aircraft would have a whole different mix of wing size, engine power, and airframe design than f-15e and su-34.

You mean J-16 has higher parasitic drag than jh-7?

Lift-induced drag, aka induced drag, is inversely proportional to aspect ratio and wing area. The ideal formula for it is too long to write here, so I refer you to the last equation at

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This is why gliders have huge wings for low induced drag at low speeds, where it is the dominating drag component.

Parasitic drag scales linearly with wetted area, which increases with increasing wing area. It also scales linearly with dynamic pressure (0.5rho*speed^2), which makes it larger than induced drag at higher speeds. In an ideal case,
Parasitic drag = dynamic pressure * wetted area * drag coefficient
see

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Other than this mixup in terminology, I agree with your assessment and conclusions on the agility, low&fast flying properties and high speed range of the aircraft.

 

[Quickie]

I am not sure about that.

J-16 obvious derives her airframe design from su-27. The su-27 prioritized combat maneuverability over high speed penetration of enemy airspace. As a result, su-27/j-16 has huge wings, low wing loading, and big engines for its size. This means j-16 can sustain high turn rates, fantastic climb rates, and high roll and,pitch rates. But achieving these same attributes means su-27/j-16 also has high induced drag and needs big engines to go fast, are highly sensitive to gust and offers a punishing ride at high speed low altitude flight. In other words they make poor airframes for deep high speed low altitude penetrations of enemy airspace.

If jh-7 on the other hand didn't seem to put much emphasis on combat maneuverability. So it has relatively small wings with high wing loading. This means Jh-7 can't turn or climb with the su-27/j-16, but it probably has low gust response, low induced drag, smooth ride at low altitude, high speed penetration role, and need less fuel comsumption to,achieve the same low altitude, high speed performance, and thus a longer range for the same fuel load.

Yes, both the US and Russia decided to base their current strike fighters off of air superiority fighter airframes. But that was not done because air superiority airframes makes ideal low altitude penetration strike airframes. That was done to save money by reusing big powerfully engined airframes that could carry a lot of weight by virtues of their big engines and big wings. A truly ideal penetration strike aircraft would have a whole different mix of wing size, engine power, and airframe design than f-15e and su-34.

If jh-7 on the other hand didn't seem to put much emphasis on combat maneuverability. So it has relatively small wings with high wing loading. This means Jh-7 can't turn or climb with the su-27/j-16, but it probably has low gust response, low induced drag, smooth ride at low altitude, high speed penetration role, and need less fuel comsumption to,achieve the same low altitude, high speed performance, and thus a longer range for the same fuel load.

That is correct. This, plus its high wing position, basically makes the JH-7A a true-blue fighter bomber.

 

[Quickie]

You mean J-16 has higher parasitic drag than jh-7?

Lift-induced drag, aka induced drag, is inversely proportional to aspect ratio and wing area. The ideal formula for it is too long to write here, so I refer you to the last equation at

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This is why gliders have huge wings for low induced drag at low speeds, where it is the dominating drag component.

Parasitic drag scales linearly with wetted area, which increases with increasing wing area. It also scales linearly with dynamic pressure (0.5rho*speed^2), which makes it larger than induced drag at higher speeds. In an ideal case,
Parasitic drag = dynamic pressure * wetted area * drag coefficient
see

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Other than this mixup in terminology, I agree with your assessment and conclusions on the agility, low&fast flying properties and high speed range of the aircraft.

Actually, a larger wing area, i.e. a larger wing, will have a larger lift-induced drag. What happened is, in the equation, increasing the wing area also increases the lift force.

This makes sense since building a larger wing will give you a bigger lift but in return you should expect a bigger induced drag i.e. more engine thrust (more fuel) to take care of it, and NOT vice versa.

 

[zaphd]

Actually, a larger wing area, i.e. a larger wing, will have a larger lift-induced drag. What happened is, in the equation, increasing the wing area also increases the lift force.

This makes sense since building a larger wing will give you a bigger lift but in return you should expect a bigger induced drag i.e. more engine thrust (more fuel) to take care of it, and NOT vice versa.

The first equation at

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indeed has wing area in the numerator, but when you open up C_Di (induced drag coefficient), which has wing area squared in the denominator as shown in the 4th equation, you end up with the inversely proportional relationship shown as the last equation.

The reason why I think your logic doesnt hold is that while the lift generated by a wing does indeed increase with wing size if all else is equal, a bigger wing can create the same lift as a smaller one with a lower lift coefficient (eg. Lower angle of attack or thinner wing). And induced drag scales with the square of lift coefficient(substitute 2nd equation to first at that link), so the reduction in that leads to an overall decrease in induced drag if lift stays the same.

Here is also a picture from parasitic drag wiki. I'm not saying a bigger wing is less draggy. It is more draggy at high speeds because of parasitic drag. However, it has lower induced drag if lift (aka aircraft weight times load factor) stays the same.

 

[Quickie]

The first equation at

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indeed has wing area in the numerator, but when you open up C_Di (induced drag coefficient), which has wing area squared in the denominator as shown in the 4th equation, you end up with the inversely proportional relationship shown as the last equation.

The reason why I think your logic doesnt hold is that while the lift generated by a wing does indeed increase with wing size if all else is equal, a bigger wing can create the same lift as a smaller one with a lower lift coefficient (eg. Lower angle of attack or thinner wing). And induced drag scales with the square of lift coefficient(substitute 2nd equation to first at that link), so the reduction in that leads to an overall decrease in induced drag if lift stays the same.

Here is also a picture from parasitic drag wiki. I'm not saying a bigger wing is less draggy. It is more draggy at high speeds because of parasitic drag. However, it has lower induced drag if lift (aka aircraft weight times load factor) stays the same.

The first equation at

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indeed has wing area in the numerator, but when you open up C_Di (induced drag coefficient), which has wing area squared in the denominator as shown in the 4th equation, you end up with the inversely proportional relationship shown as the last equation.

I've already explained why it isn't necesarilly an inversely proportional relationship and the opposite is actually true. The first equation makes things easier to see by having all the variables in the numerator with the CDi being a constant.

The reason why I think your logic doesnt hold is that while the lift generated by a wing does indeed increase with wing size if all else is equal, a bigger wing can create the same lift as a smaller one with a lower lift coefficient (eg. Lower angle of attack or thinner wing). And induced drag scales with the square of lift coefficient(substitute 2nd equation to first at that link), so the reduction in that leads to an overall decrease in induced drag if lift stays the same.

Yes, I meant all else being equal. That means wings with the same aerofoil shape, camber etc.
What you're describing goes into the different aerofoil types, which was not the point of the discussion from the start.

A bigger thinner wing would give less induced drag (but more parasitic drag) for the same lift compared to a smaller wing with a higher lift coefficient but we know each of them have their own advantages and disadvantages.

Here is also a picture from parasitic drag wiki. I'm not saying a bigger wing is less draggy. It is more draggy at high speeds because of parasitic drag. However, it has lower induced drag if lift (aka aircraft weight times load factor) stays the same

The aircraft wouldn't be flying anymore at the lower values of induced drag at the right side of the chart because of the small or almost zero lift generated.

This is a more practical chart where the aircraft is actually flying. You can see a direct relationship where the lift coefficient increases with the induced drag coefficient.

 

[zaphd]

Here is

I've already explained why it isn't necesarilly an inversely proportional relationship and the opposite is actually true. The first equation makes things easier to see by having all the variables in the numerator with the CDi being a constant.



Yes, I meant all else being equal. That means wings with the same aerofoil shape, camber etc.
What you're describing goes into the different aerofoil types, which was not the point of the discussion from the start.

A bigger thinner wing would give less induced drag (but more parasitic drag) for the same lift compared to a smaller wing with a higher lift coefficient but we know each of them have their own advantages and disadvantages.



The aircraft wouldn't be flying anymore at the lower values of induced drag at the right side of the chart because of the small or almost zero lift generated.

This is a more practical chart where the aircraft is actually flying. You can see a direct relationship where the lift coefficient increases with the induced drag coefficient.

View attachment 38641

After doing some reading it appears I was somewhat mistaken. When substituting aspect ratio for wingspan squared divided by wing area, the wing areas cancel out for a case where we have two wings with identical lift and airspeed, but different wing areas. However, a larger wing span or aspect ratio will decrease induced drag, see gliders for example.

As for your chart, it shows higher lift coefficient means higher induced drag, and a larger span wing can have a lower lift coefficient for the same lift as a smaller wing, ergo lower induced drag coefficient. And for your claim that my chart was somehow irrelevant for a high subsonic to supersonic plane, lets just say I disagree based on what I've read.

I would like to clarify that I am not talking about the drags of a big, higher lift plane vs a small lower lift plane, but two planes with similar weight (and thus lift in level flight), which have different wing areas.

 

[siegecrossbow]

What really boggles my mind is the fact that they recently used the JH-7 for an interception mission recently. Can't they use something like a J-11 or even a J-8II instead?

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