J-20... The New Generation Fighter III

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latenlazy

Brigadier
paintgun said:
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
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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.
 
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Lacrimosa

New Member
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.
 
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latenlazy

Brigadier
Lacrimosa said:
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.
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But Martian can read.

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

Quickie

Colonel
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.
 
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delft

Brigadier
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.
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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.
 
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latenlazy

Brigadier
delft said:
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.
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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 :D). 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.
 
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Quickie

Quickie

Colonel
latenlazy said:
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 :D). 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.
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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.
 
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no_name

Colonel
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.
 
Engineer

Engineer

Major
paintgun said:
back heavy = no radar installed
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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.
 
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