Vi-va
Trusted Member
Lift to drag ratio is essential to top speed.
DSI has pros and cons, it indeed has some disadvantage in high speed, but we don't have any solid proof that J-20 can NOT fly at 2.5 mach.
Chinese 6th Generation Aircraft News & Discussions
- Thread starter SiliconBit (silicon0000)
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DSI has pros and cons, it indeed has some disadvantage in high speed, but we don't have any solid proof that J-20 can NOT fly at 2.5 mach.
NGAD IS THE BEST
Elite Member
And don't have any solid proofs either that J-20 CAN reach a top speed of 2.5 Mach with DSI
NGAD IS THE BEST
Elite Member
Because DSI geometry wont allow to go beyond Mach-2, pressure in front and back of the DSI intakes degraded significantly beyond Mach-2, under the Mach 2 it's work very well
Vi-va
Trusted Member
Bro, we all agree with the theory you presented, and most likely you are right to some extent.
The limitation of DSI is true, but we still don't have solid proof that J-20 can't fly at speed higher than Mach 2.0.
The J-20 has a Diverterless Supersonic Inlet, also known as DSI, it has the advantages of simpler manufacturing process, less need for larger amounts of Radar absorbing material than conventional inlets, no need for bleed systems, a diverter cavitiy and mechanical Variation, however all of this limits too the speed to Speeds below Mach 2.
The high pressure Gradient generated by the bump becomes a wall for the lower pressure boundary layer, but by the bump having no mechanical variation it limits the Mach number it is designed to operate.
The Bump can not change its size and position with respect the inlet cowl, thus limiting the speed range it can operate.
Pressure recovery tends to decrease at supersonic speed at all conditions. This is due to the fact that the shock waves at the inlet in supersonic condition causes additional pressure loss and hence it results in lower pressure recovery as compared (Goldsmith and Seddon 1993, Mattingly 2002). This phenomena is quite similar in fixed intakes (Ibrahim, Ng et al. 2011).
The results revealed that Boundary Layer Diverter Intake (BLD intake) configuration is more effective in subsonic regime as compared to DSI configuration, whereas at supersonic speeds DSI configurations gave superior performance.
Comparative Flow Field Analysis of Boundary Layer Diverter Intake and Diverterless Supersonic Intake Configuration I. Arif† , S. Salamat, M. Ahmed, F. Qureshi and S. Shah
The intake | chengdu-j-20
niubi
Registered Member
52km is not a reference to altitude. That would be ridiculous. Max altitude performance for most military turbofans is around 18km above sea-level. This is roughly where F-15, Mig-29, Su-27 etc fighters top out. No way J-20 flies t 52km above sea-level.
The quote from Chinese gov's own mouthpiece which is therefore classified as "official source" does claim that J-20 has covered a lateral distance of 52km in 1 minute. This does translate to just over mach 2.5.
Obviously if this is accurate and true, it would have been achieved with afterburner and this would be the top speed reached. The claim is military load which means with at least one missile. Even if we suppose it is on empty weight, that means the J-20 can easily surpass Mach 2.0 using just WS-10Cs.
DSI intakes do limit efficiency above mach 2. It isn't necessarily an absolute cap on intake speed. It allows for supersonic air.
Both sides of this are sort of wrong. DSI intakes can take an aircraft above mach 2. It just faces challenges doing so. There were talks way back in 2017 when J-20 was introduced to PLAAF service that the DSI intakes were not the traditional none moving ones in the JF-17 and J-10B/C.
The hints then were talking about internal shape modifications iirc from discussions online back then. It wasn't clear what they did but there were hints about the J-20's DSI intakes being "dynamic". Who knows, who cares. We'll never know until these things are fully disclosed.
Right now, one piece of official source did comment on the speed and puts a top speed of around 2.5 mach with afterburners using WS-10C.
While how well an intake allows the engines to breathe is absolutely a critical part of speed and engine performance, there are also other factors involved in top speed. We know DSI isn't an absolute restriction on mach number if somehow you combat that with some dynamic changes to the DSI intake. I mean people online were convinced that ion cloud blackout effect from re-entry means total comms block which is completely untrue.
The quote from Chinese gov's own mouthpiece which is therefore classified as "official source" does claim that J-20 has covered a lateral distance of 52km in 1 minute. This does translate to just over mach 2.5.
Obviously if this is accurate and true, it would have been achieved with afterburner and this would be the top speed reached. The claim is military load which means with at least one missile. Even if we suppose it is on empty weight, that means the J-20 can easily surpass Mach 2.0 using just WS-10Cs.
DSI intakes do limit efficiency above mach 2. It isn't necessarily an absolute cap on intake speed. It allows for supersonic air.
Both sides of this are sort of wrong. DSI intakes can take an aircraft above mach 2. It just faces challenges doing so. There were talks way back in 2017 when J-20 was introduced to PLAAF service that the DSI intakes were not the traditional none moving ones in the JF-17 and J-10B/C.
The hints then were talking about internal shape modifications iirc from discussions online back then. It wasn't clear what they did but there were hints about the J-20's DSI intakes being "dynamic". Who knows, who cares. We'll never know until these things are fully disclosed.
Right now, one piece of official source did comment on the speed and puts a top speed of around 2.5 mach with afterburners using WS-10C.
While how well an intake allows the engines to breathe is absolutely a critical part of speed and engine performance, there are also other factors involved in top speed. We know DSI isn't an absolute restriction on mach number if somehow you combat that with some dynamic changes to the DSI intake. I mean people online were convinced that ion cloud blackout effect from re-entry means total comms block which is completely untrue.
Michael
VIP Member
大汉奸柳传志
Registered Member
funny how they used to be just like China, churning out new airplane model every few years inthe cold war era
NGAD IS THE BEST
Elite Member
Explain me bro why F-35 can't achieve top speed of Mach 2, F-135 has enough thrust (43,000 lbs) that F-35 can easily achieve a top speed of beyond Mach 2.5?Bro, we all agree with the theory you presented, and most likely you are right to some extent.
The limitation of DSI is true, but we still don't have solid proof that J-20 can't fly at speed higher than Mach 2.0.
The J-20 has a Diverterless Supersonic Inlet, also known as DSI, it has the advantages of simpler manufacturing process, less need for larger amounts of Radar absorbing material than conventional inlets, no need for bleed systems, a diverter cavitiy and mechanical Variation, however all of this limits too the speed to Speeds below Mach 2.
The high pressure Gradient generated by the bump becomes a wall for the lower pressure boundary layer, but by the bump having no mechanical variation it limits the Mach number it is designed to operate.
The Bump can not change its size and position with respect the inlet cowl, thus limiting the speed range it can operate.
Pressure recovery tends to decrease at supersonic speed at all conditions. This is due to the fact that the shock waves at the inlet in supersonic condition causes additional pressure loss and hence it results in lower pressure recovery as compared (Goldsmith and Seddon 1993, Mattingly 2002). This phenomena is quite similar in fixed intakes (Ibrahim, Ng et al. 2011).
The results revealed that Boundary Layer Diverter Intake (BLD intake) configuration is more effective in subsonic regime as compared to DSI configuration, whereas at supersonic speeds DSI configurations gave superior performance.
Comparative Flow Field Analysis of Boundary Layer Diverter Intake and Diverterless Supersonic Intake Configuration I. Arif† , S. Salamat, M. Ahmed, F. Qureshi and S. Shah
The intake | chengdu-j-20
mikoyanmig29.wixsite.com
View attachment 109121
NGAD IS THE BEST
Elite Member
Can you provide a source of your claim? I highly doubt that WS-10 equipped J-20 can reach top speed of Mach 2.5, because thrust to weight ratio and lift-to-drag ratio is too low for WS-10 equipped J-20 to have top speed of Mach 2.5
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NGAD IS THE BEST
Elite Member
Top speed is not important dude it's useless in actual air combat, acceleration and maneuverability have most valuable in modern air combat
You can't defend yourself from BVR (beyond visual range air to air missiles) and SAMs (surface to air missiles)air combat relying only on top speed and agility/maneuverability, the only defense against BVR/SAMs is EW (electronic warfare) ECM (electronic countermeasure) and ECCM (electronic counter countermeasure)
大汉奸柳传志
Registered Member
could be lots of reasons like aerodynamic layout, overheating of subsystems/stealth coating, oxygen supply limitations, etc, etc....
or maybe the thrust to weight number is exaggerated like f119
Vi-va
Trusted Member
F-35 is stealth strike fighter, while J-35 and J-20 are stealth multirole combat aircraft.
Different design result in different top speed.
F-35 is wide, or fat. J-20 may fly faster than F-22, J-35 very likely fly faster than F-35.
NGAD IS THE BEST
Elite Member
Main reason of limiting the top speed of F-35 is not the reasons you gave but Main limiting factor of F-35 top speed is its intake design (DSI), as well as its engine, f-135 is high bypass ratio engine for fuel efficiency and quieter performance
Whereas J20 is using low bypass ratio engine which is fuel thrusty and louder engine similar to f119
NGAD IS THE BEST
Elite Member
Definitely brother J20 can fly faster than F-35 but Mach 2.5 is extremely unlikely may be it has a top speed of slightly above Mach 2 but not Mach 2.5
