J-20 5th Gen Fighter Thread VI


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Midgie

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However, the plane just completed a left turn, and right engine was supposed to give more thrust to create a torque. Without the use of afterburners, the left engine would generate more thrust than the right one that had a fully opened nozzle.
My guess is that before the turning, the pilot applied brakes. During the turning, he increased the thrust to catch up the speed and both engines' nozzles closed in. After the turning, the thrust needs to be reduced back to almost minimum. it seems that J-20 is programmed to open up the right nozzle first then the left (to avoid sudden change in the thrust, which is more important in the air for control stability). Of course, we need to watch the video to confirm the theory.
Watching the video won't confirm anything unless you positively know what the pilot is doing with their left hand. More likely whether or not it is coming in or out of power is that due to the split throttle nature of all twin engined fighters I can think of, that the pilot either decided to just use a little bit from the left to get up to speed of those he's following, or if they're coming out of power, they haven't come to idle perfectly synchronized. No crazy engine logic or programming, just manipulation of left and right engines with very fine movements from the left hand.
 

xyqq

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Watching the video won't confirm anything unless you positively know what the pilot is doing with their left hand. More likely whether or not it is coming in or out of power is that due to the split throttle nature of all twin engined fighters I can think of, that the pilot either decided to just use a little bit from the left to get up to speed of those he's following, or if they're coming out of power, they haven't come to idle perfectly synchronized. No crazy engine logic or programming, just manipulation of left and right engines with very fine movements from the left hand.
You suggested that the pilot controls two throttles separately, but they should be locked to move together in normal operation (unless one engine catches fire, for example), right?
 
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Midgie

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You suggested that the pilot controls two throttles separately, but they should be locked to move together in normal operation (unless one engine catches fire, for example), right?
Correct, but saying ‘separately’ will make many people think there are two spaces apart throttle controls. The entire HOTAS throttle is designed to fit nicely under one hand, so movements back and forward will move both left and right quadrants more or less equally. In case of an engine fire you’ll have to release the normal grip and just hold the side relevant to the engine in question and bring it back to ‘off’.

Plenty of images of Western twin engine fighter throttles show how the split works. There isn’t any lock to hold them together.
 

Inst

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Most of the sophisticated thrust control can be handled by the FBW system. No need for the pilot to manually coordinate the relative thrust unless he wants to.
 

xyqq

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Correct, but saying ‘separately’ will make many people think there are two spaces apart throttle controls. The entire HOTAS throttle is designed to fit nicely under one hand, so movements back and forward will move both left and right quadrants more or less equally. In case of an engine fire you’ll have to release the normal grip and just hold the side relevant to the engine in question and bring it back to ‘off’.

Plenty of images of Western twin engine fighter throttles show how the split works. There isn’t any lock to hold them together.
A multi-engine plane's throttles are typically locked together unless the pilot disengages them.
disengage.jpg
 

Midgie

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A multi-engine plane's throttles are typically locked together unless the pilot disengages them.
View attachment 55808
True for wide bodies. Not true for fighters. ‘Jetstream’ a Canadian F/A-18 documentary show some good examples of how the pilots make tiny movements on either engine to maintain AoA on approach to landing.

Anyway this is drifting off topic. Just trying to spread knowledge.
 

xyqq

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True for wide bodies. Not true for fighters. ‘Jetstream’ a Canadian F/A-18 documentary show some good examples of how the pilots make tiny movements on either engine to maintain AoA on approach to landing.

Anyway this is drifting off topic. Just trying to spread knowledge.
A good discussion, and I do not think it is too far off the topic as J-20 is a twin-engine fighter jet.
In the screenshot from the CF-18 documentary, the instruction is to "walk the throttles" and "don't flare". The video shows that the left hand twisted side by side to move forward a little bit a time (like walking). This actually suggests that the throttles are locked together, otherwise the movement will be a little bit too big for each engine (e.g., one forward and one backward). The FBW system probably calculates the average level of two throttles and send the signal to both engines. F18throttles.jpg
 
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xyqq

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Your statement here is perfectly correct. It doesn’t however imply locked throttles. Walking- left foot right foot. Left throttle right throttle.
On Su-27, those levers are used to disengage throttles for independent movement (need to open both).
Su-27-throttle-lock.jpg
 
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