J-20 5th Gen Fighter Thread V

[Air Force Brat]

This is the best visual explanation on wing planform w/o getting too technical..
basically high AR = long span therefor reduce drag and higher lift and vice versa. Cargo/passenger aircrafts for ex generally have high AR because lifting ability is more important than speed or reduction in induced drag and maneuverability (lower roll rate).

Sorry Deino, feel free to move these posts to the aerodynamics thread.

First off Pmichael, it is very "UNKOOL" to call a brother, Honey, so please if you can't be respectful, at least be KOOL? The Air Force Brat is 24 Volt, straight Negative Ground, DC.

The picture shows the tips lopped off diagonally on the "aft edge", so there is NO reduction in wing span, and minimal reduction in "wing area", all on the aft edge of the ailerons. While that does indeed reduce "mass" at the tips, it also more importantly reduces forces at the tips that "increase" on the side of the aileron deflected down, and "decrease" on the side with the aileron deflected up, reducing the overall "rolling moment" produced by full deflection of the ailerons either right or left.

and that will decrease the "rate" at which the aircraft is capable of being rolled! as I noted the change is very minimal, the F-22 has similar clipping of the aft edge, of the tip on both sides, for signature reduction.

Jeff Head or the Eng could explain it to you further, but apologies to Master Deino, this will be my last post on the J-20 thread, and yes please Mods, do move this off topic discussion to the aerodynamic thread, apologies again, but I loath in-accuracies.

but not as much as I loath being called "honey" by some????

 

[Pmichael]

You don't even know if you want to talk about clipped wings or cropped delta, which are two different things.

I guess you mean the cropped delta of the J-20. Your argument that the cropped delta affects the roll-rate negatively because of the reduced area of the aileron, which isn't the case here.
It would be a problem for the F-35 for example but in a canard-delta design the aircraft use the canards AND aileron to control the movement around the aircraft's longitudinal axis. That design choice makes it possible that the J-20 only needs small ailerons (similiar to her European canard counterparts), so the aircraft can use go with a cropped delta wing design which help the aircraft to improve tip drag at high angles of attack.
We also know that the Eurocanards have all excellent roll rates.

 

[FORBIN]

yup! more quills than a porcupine?? she got stuff sticking out all over, but she do have "directional stability" out the wazoo! and that my friend is a great thing for a fighter aircraft, Dr. Song said she had to be able to recover from "post stall flight" without OVT, and she will, like an arrow, she has very good primary directional stability, very, very, good!

I really like this airplane, I would fly it in a heartbeat with a couple of hours in the simulator, and I am not a fan of canard's, but on this bird, they are "right on"!

Not a Porcupine your funny

It has been demonstrated numerous times that canards, when aligned perfectly parallel with the planform, are not a significant contributor to its frontal RCS.

J-20 only stealth fighter which don' t have all her horizontal planes/surface not aligned even J-31 have, J-20 have 3 different points not aligned don' t think it is good for stealh...

Rafale and Typhoon get canards also but don't have the point 3 in more a stealth fighter need have the more clean shape and you can see there J-20 don' t have.
J-20 is stealth ofc but curious things...

 

[Blitzo]

J-20 only stealth fighter which don' t have all her horizontal planes/surface not aligned even J-31 have, J-20 have 3 different points not aligned don' t think it is good for stealh...

Rafale and Typhoon get canards also but don't have the point 3 in more a stealth fighter need have the more clean shape and you can see there J-20 don' t have.
J-20 is stealth ofc but curious things...

View attachment 27678

From what I understand, the point of edge alignment by angle is that it allows radar waves to be controlled and deliberately scattered in a direction away from the original emitting source, so having "more" exposed edges to oncoming radar may not be a significant issue so long as all the edges are sufficiently aligned (and treated with RAM etc).
The point of edge alignment is not necessarily to have all the aerofoils on the same "level".

The physics is far beyond me, but I suspect that in J-20's case, having "more" exposed edges compared to F-22, F-35 or T-50 technically means the more edges will make it "less stealthy" (at least in terms of RCS from aerofoils), however we can see all those aerofoils are properly edge aligned and likely one of the important spots treated with RAM so I also suspect the actual contribution to RCS is relatively low.

So I think the best way to view J-20's additional aerofoils in terms of their contribution to RCS is that the presence of additional aerofoils themselves would add slightly to RCS, but probably only in a very minor way due to edge alignment and RAM treatment... and minor relative to things like having round/curved surfaces which causes uncontrolled scattering of radar

I expect the designers were very conscious of the decisions they made for J-20, and probably determined any additional RCS of the ventral fins and the slightly angled canards could be controlled, and would be worth the aerodynamic benefits.

 

[Air Force Brat]

Not a Porcupine your funny



J-20 only stealth fighter which don' t have all her horizontal planes/surface not aligned even J-31 have, J-20 have 3 different points not aligned don' t think it is good for stealh...

Rafale and Typhoon get canards also but don't have the point 3 in more a stealth fighter need have the more clean shape and you can see there J-20 don' t have.
J-20 is stealth ofc but curious things...

View attachment 27678

you are of course right, and if you read Blitzo's post you will note that it seems he concurs with several of your point's. Very nice illustrations of each of these aircraft, you will note that the J-20 and F-22 have a very pro-nounced anhedral that "falls away" in a continuous curve, with very significant "wash-out of the wingtips", one of the reasons I state that the Raptor is "organic". The J-20 also has that very complex, compound curve.

 

[Hyperwarp]

There is only one other major 5th gen designs that utilized canards, at least I can think of would be the NATF-23 proposal by Northrop. It seems Northrop was confident using canards, and this was after the YF-23 failure.

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There are a few similarities with the J-20 including the design of the all-moving tail.

 

[FORBIN]

I add with J-31 right now only a demonstrator and position of the nozzles for IR stealth, US much more well masked more back, i have read for IR signature better 2 less powerful engines as F-22 that F-35 with one more powerful the hot air flow is more diluted remains significant ofc.

T-50 have also its reactors only half masked, blades nozzles which is a point very important for stealth matter.

 

[Blitzo]

I add with J-31 right now only a demonstrator and position of the nozzles for IR stealth, US much more well masked more back, i have read for IR signature better 2 less powerful engines as F-22 that F-35 with one more powerful the hot air flow is more diluted remains significant ofc.

T-50 have also its reactors only half masked, blades nozzles which is a point very important for stealth matter.

View attachment 27723 View attachment 27724

Your phrasing is very strange and difficult to understand, however I think I get the gist of what you're trying to say.

There are a lot of factors which come into play in regards to IR shielding, and it depends which aspect one is looking from. I think in the case of all the fighters you listed, the degree of recess does not have a major effect from the tail aspect -- that is to say, for an IR guided missile or IR sensor coming from the aft aspect, it doesn't really matter if the engine source is a meter and a half "further away" from the IR sensor itself. So the degree of recess of an aircraft's engines is probably not that important from the aft.

However, the degree of recess probably does have a factor in terms of IR shielding from the side aspect. From the side aspect, it is more beneficial to have a more recessed engine to allow its vertical and horizontal tails to partially cover up both the hot nozzles, as well as the immediate exhaust air coming from the nozzle itself. That helps to reduce side on vulnerability to IR sensors, especially that of missiles, to a slight degree.

In that way, none of the fighters listed do a particularly impressive job at concealing their IR signature, because their engine nozzles are all quite visible from the side and their vertical tails and horizontal tails are not designed deliberately to conceal the nozzles or the exhaust from the side on view. If one looks at F-22, F-35, T-50, J-20, FC-31, they all have relatively exposed nozzles from the side, and their vertical and horizontal tails are not place in a way which helps to significantly shield the overall nozzle geometry nor the exhaust geometry. Out of these aircraft, T-50 probably has the most exposed engine nozzles form the side aspect, followed by F-35 and FC-31, while J-20 and F-22 do a better job of it, F-22 because it is slightly more recessed forward into the fuselage, while J-20 uses its ventral fins to help shield the engine nozzles from the side aspect.

The stealth fighter with the best IR suppression would have to be the YF-23, which had not only highly recessed engines with a deliberate "cooling tray" extending behind the engine (like the B-2), but it also had vertical tails placed in a way which helped to cover the entire cooling tray/nozzle part of the engine from the side aspect as well.

 

[Totoro]

Planes always fly with several degrees of nose-up angle. Which means if rear horizontal tails were at same level as wings when plane was sitting on tarmac, they're not at same level anymore but are a bit under the wings and view is not covered if the plane is looked at from the same altitude as sensor is. airborne sensors can be higher or lower, of course. if plane is at 12 km altitude, usual awacs will be positioned slightly lower and will also get a view of the rear horizontal tails.

Ground based radars will get an even more pronounced tail view, and the difference will increase as the plane approaches those radars.

As for alignment of surfaces, more different surfaces are definitely worse off stealth wise. 3 differently aligned surfaces, instead of altering a radar once, will alter radars three times as the plane passes it by. 3 aligned surface will alert the same radar once. The fact that one time will have a larger RCS spike is irrelevant as once a certain treshold is passed it doesn't matter if RCS spike shown on enemy's sensor is 20 dbsm or 40 dbsm.

Depending on the angle differences, the plane doesn't need to really pass by the radar for all 3 of the above nonaligned surfaces appear on the said radar. In case of j-20, it will have a similar nose curve return as f-22 (or any other plane) has. Intake is a large creator or radar signature, surely treated against high frequency bands but against lower frequencies it may struggle. (same comment applicable to f-22. J-20 has angled start of outer intake wall, different from the wing angle. it follow the same angle as the lerx. it is definitely an additional surface, something f22 doesn't have. But at the same time, due to the nose curve that's a constant radar return, those surfaces will "only" add another spike as enemy radar approaches 65 degrees off nose (just as with most of nose curve). Wings/canards are more dangerous, as their surface is at roughly 45 degrees off nose and will get noticed sooner). F-22 has a similar issue.

Basically, if treated right with RAM, neither f22 nor j20 should have tactically significant RCS against X, C and possibly S band radars until they reach 45 or so degrees against radar. (IF radar is at same level!! which most of the time it won't be). J20 will have an additional spike which f22 won't have in the 65 deg range and both will have another spike at 90 deg. IF radars are lower than the plane, rcs of both planes will significantly start to spike up due to side walls once radar is at 70-90 degrees azimuth wise, but that will happen only a few tens of kilometers away from the plane - IF the plane is cruising and not banking. Vertical tail movements should suffice for change of course and not require excessive banking while plane is still quite far from the enemy.

All this falls apart for both j20 and f22 once they find themselves crossing the country's border or sensor perimter or even worse, entering deep into enemy's airspace, where mutiple/dozens radars may look at them from multiple/dozens of directions. In such situation it's next to impossible to remain hidden. Though getting a clear targeting info for the interceptor missile might still be hard.

 

[Jeff Head]

If it's too good to be true, then it probably is. But still a nice image, nevertheless.

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It may well be CGI...but it is beautiful all the same and certainly represents what the real thing will look like when/if we ever get such a shot.

Very nice.