Jura The idiot
General
#2857 Inst, Today at 5:50 PM
as I told you 31 minutes ago
OK I didn't say the nick, as I don't want to drag anybody into this conversation
Aerodynamics thread
- Thread starter siegecrossbow
- Start date
as I told you 31 minutes ago
come on Jura! didn't you watch "Crouching Tiger, Hidden Dragon", the laws of physics only apply to us poor old "Westerners"... LOL, you should know that by now....
anyway, back to the J-20,, I'm sure the J-20 is more than competent aerodynamically, and that it makes lots of lift in flight, even in supersonic flight it is extremely stable and maneuverable, much like the F-22...
but, all that lift and stability do create drag, and drag is drag, once you get past Mach 1?? (if you do that in dry thrust, not many really do?) but if you do,,,, drag still increases exponentially! and lift always creates drag, now you can pop a little forward stick into it, to decrease trim drag, in point of fact, the F-22 trims out pitch pressure with OVT, but the J-20 must of necessity trim with those canards and the aft mounted control surfaces..
The truth is, speed is expensive, it costs lots of money, fuel, and maintenance, even wear and tear on your airframe.
So in as much as we might suppose the altitude is around 10,000 meters, we have no reliable information about the J-20's super cruise or top-end.
There's another claim of 3062 k/m Max speed from here:
https://www.sinodefenceforum.com/j-20-5th-gen-fighter-thread-v.t7303/page-504
https://www.sinodefenceforum.com/j-20-5th-gen-fighter-thread-v.t7303/page-504
Jura The idiot
General
basically I just looked up an altitude to match M2.9 and 52 km per minute, didn't expect a problem LOL
Bub, the J-20 is an aerodynamic wonder, maneuverable and stealthy, beautiful in the old "form follows function" school of engineering, but it is NOT a Mach 2.9 airplane, when it gets the WS-15s, I'd say we might possibly see Mach 2.5,, you know I really don't know, nobody posting on anybody's defense forum has a top secret security clearance, if they did, they would NOT be posting on the Sino Defense Forum... they couldn't...
@Air Force Brat: This isn't impossible, we have an official Chinese media claim that the J-20 can reach Mach 2.9. There are reasons to distrust it; Mach 2.9 requires inlets that can allow the J-20 to function as high speeds, and so far, what we've seen are DSI inlets, not variable geometry inlets optimized for high speeds. Moreover, at very high speeds, you're going to be stressing the airframe at extreme levels, the stealth coating will likely burn off, your IR signature will resemble fireworks, and the engines will likely need replacement, as we saw with the Mig-25, but not necessarily the SR-71. Tactically, the only real use of a Mach 2.9 ability would be for escape; i.e, the J-20 fires off its missiles, begins a descent to 10,000 meters from higher altitudes, and tries to escape enemy AAMs.
On the other hand, there are reasons to believe this is possible. With a high fineness ratio of 1.62, as well as a design for supercruise with underpowered engines, the aircraft likely has a very low drag rate. According to the VTech documents, the J-20, with only the WS-10s / AL-31s, can achieve Mach 1.8 supercruise simply through having low drag. Put another way, the difference between the dry thrust of the AL-31 and WS-15 is only 20%. From drag force equations, this comes out to only 10% less max cruising speed between the engines. Even assuming 117 kN as with the F119, the difference is only 15%.
And once you scale it up to military thrust, instead of dry thrust, you can easily get to 27% additional maximum speed. With a Mach 1.8 supercruise, you'll easily get to Mach 2.3, and from 180 kN instead of 140 kN wet thrust, you'll get a figure of around Mach 2.6.
Quickie
Colonel
I was just commenting there're also other altitudes at the respective different machs at which the 52km can be covered in a minute. I was puzzled why it has to be at that altitude. Didn't expect it to be a problem.
You can't say affirmatively that it's not. The independent variable is the intakes; can the J-20 sustain reasonable levels of engine power at Mach 2.9? Put another way, one remaining possibility is that the news report is talking about a hypothetical WS-15 engine. The implication is that the current J-20 can achieve Mach 2.58 speeds at 140 kN, but the inlets can't really support further extended speeds, and it'll max out around Mach 2.6 or Mach 2.7.
Speed of sound is different at different altitudes.
Quickie
Colonel
Nah....it's the same, unless you believe those marvel comics heroes don't count.
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