J-20... The New Generation Fighter III

j-20 11
Thanks to =GT at CD

1) Is the spool time supposed to be that long?
2) Is that two elevators on the trailing edge I see?

It also just dawned on me that the J-20 doesn't need the WS-15s for peak flight test conditions so long as the plane's T:W (not the engine's, the plane's) matches specifications.

Also, the bobbing it does while on the runway seems to imply that the J-20 is very back heavy as it is right now.

Originally Posted by cataphract

1stly, as you can see, the F-22's intake duct isn't as you assumed. It is in fact closer to the F-35's intake duct of a continuous curve structure.
2ndly, you failed to account for duct geometry that would eliminate the reflected waves.
3rdly, you failed to account for the fact that DSI, being a round bulge structure outside of the aircraft scatters significantly more EMR more evenly. Thusly increasing overall rcs from sides.

And again you continue to assume RAM's effectiveness is 99.684%, a number that simply does not coincide with real world data or examples.

You can have a spherical metal ball with the rcs of 1000m^2, one of the WORST stealth shapes you could have (aside from corner reflectors)

This metal ball would have a radius of 17 Meters, and when coated with you magical RAM, it would have a radar cross section of 3m^2.

if RAM worked that well, you wouldn't need shaping to get an aircraft's rcs down to a golf ball from 1-2m^2.

Taking real numbers and torturing them until they give him whatever he wanted is Martian's specialty, I won't worry about him.

He's a sort of a less reasonable version of MiG-29, for China.

Originally Posted by Lacrimosa

Taking real numbers and torturing them until they give him whatever he wanted is Martian's specialty, I won't worry about him.

He's a sort of a less reasonable version of MiG-29, for China.

Martian throws more tantrums than Mig.

Anyways, there are ways to handle the signal returns from the bump, including making them out of materials transparent to the most difficult frequencies to take care of them with internal structures.

Originally Posted by latenlazy

j-20 11
Thanks to =GT at CD

1) Is the spool time supposed to be that long?
2) Is that two elevators on the trailing edge I see?

It also just dawned on me that the J-20 doesn't need the WS-15s for peak flight test conditions so long as the plane's T:W (not the engine's, the plane's) matches specifications.

Also, the bobbing it does while on the runway seems to imply that the J-20 is very back heavy as it is right now.

spool time seems normal for me - flaperon or elevon, i don't know

engine : which means this engine works just fine for airframe testing and validation
i think the prototype is not onto performance testing yet, also no point in testing peak performance if you have to change engine later, and work out the kinks all over again, no point gathering data with interim engine

back heavy = no radar installed

Originally Posted by paintgun

spool time seems normal for me - flaperon or elevon, i don't know

engine : which means this engine works just fine for airframe testing and validation
i think the prototype is not onto performance testing yet, also no point in testing peak performance if you have to change engine later, and work out the kinks all over again, no point gathering data with interim engine

back heavy = no radar installed

Made the comment about spooling before the plane got on the runway.

I think they'd probably opt to do some peak performance tests just to get data on the airframe's performance at different envelopes. Actual performance will of course also depend on the engine. This leads to another question of course, which is can the current engine supercruise?

If the plane is back heavy due to the lack of components, I wonder if they implement corrections for the center of gravity during flight testing.

Hey, I said he's a less reasonable MiG. Basically, MiG has two things going for him -
1) He concedes points, however rarely.
2) He posts real articles and analyses, however misplaced and irrelevant. Martian takes the sources and do random voodoo with them to give number he wants.

Anyway the DSI bump's return frequency is something that's well gone into already in the literature, it's not nearly as bad as it sounds or the F-35 won't have those.

New high definition flight video from 11-12-2011 (Chengdu time). I'll put up a video once it is on youtube.

j-20 11

Originally Posted by Lacrimosa

Hey, I said he's a less reasonable MiG. Basically, MiG has two things going for him -
1) He concedes points, however rarely.
2) He posts real articles and analyses, however misplaced and irrelevant. Martian takes the sources and do random voodoo with them to give number he wants.

Anyway the DSI bump's return frequency is something that's well gone into already in the literature, it's not nearly as bad as it sounds or the F-35 won't have those.

But Martian can read.

Anyways, the more I read about signals management the less convinced I am by all these short hand heuristics.

Martian does make some effort to explain his theory on why he make a particular claim - whether the theory is right or wrong is for people here to argue. Mig-29 will make inferences and conclusions from references and papers usually without explaining in detail how he has arrived at the conclusion. Whatever the case I think people here should discuss or argue against the theory or the subject matter at hand rather than making a general conclusion of what he thinks is right and at the same time making sniping comments on any of the posters.

latenlazy says in #1727:

Also, the bobbing it does while on the runway seems to imply that the J-20 is very back heavy as it is right now.

The peculiar bobbing seems to me the result of the very low picture rate of the video. You just do not do flight trials with an aircraft that happens to have its center of gravity rather aft because some equipment is missing. You just add ballast to compensate. The center of gravity of an aircraft with this type of undercarriage is such that in the static case about 15% of the weight is carried by the nose wheel(s). This enables you to estimate the place of the center of gravity very nicely.

Originally Posted by delft

latenlazy says in #1727:

The peculiar bobbing seems to me the result of the very low picture rate of the video. You just do not do flight trials with an aircraft that happens to have its center of gravity rather aft because some equipment is missing. You just add ballast to compensate. The center of gravity of an aircraft with this type of undercarriage is such that in the static case about 15% of the weight is carried by the nose wheel(s). This enables you to estimate the place of the center of gravity very nicely.

I noticed the bobbing because it's very periodic, which isn't something usually generated from handshaking (unless the person holding the camera has a partial complex seizure with periodicity ). Maybe it's just from a lack of fuel.

You bring up a good point about using the bobbing to figure something out about CG though.

Originally Posted by latenlazy

I noticed the bobbing because it's very periodic, which isn't something usually generated from handshaking (unless the person holding the camera has a partial complex seizure with periodicity ). Maybe it's just from a lack of fuel.

You bring up a good point about using the bobbing to figure something out about CG though.

Actually I see only slight bobbing during the take off which could be due to a slight flipping of the elevon during that time. I remember seeing a video of the elevons and stabilizers flipping wildly during take off. The oscillation could also be due to the undulating surface of the runway somehow matching close to the oscillaton frequency of the undercarriage.

I think the J-20 has two landing parachutes instead of one like single engined J-10, so that each chute catches part of the thrust from each of the two engines.

If you only have one chute, it might deviate and catches jet exhaust from one of the two engines predominantly, making it dangerous for the plane during landing.

Originally Posted by paintgun

back heavy = no radar installed

Not true. A block of lead would sit in place of the radar and other avionics in cases like this. Otherwise, the aircraft's configuration does not match the final configuration and flight tests wouldn't give the correct results.