J-20... The New Generation Fighter III
- Thread starter siegecrossbow
- Start date
- Status
Plawolf,
you're right that the slats on a fighter's wing are used to improve agility, i.e. turning performance.
Now, since turning is basicly "climbing around a circle", you need additional lift to perform that maneuver. The increased "Gs" you pull in a turn, are "produced" by the increased lift the aircraft is obtaining during these turns (by increasing AoA)
Now slats are deployed (moving forward & down) so a gap forms between them and the main wing. Air being forced through that gap is accelerated (energized) wich makes the air stick better to the wing during higher AoAs, that in turn allows you to produce more lift, wich in turn increases your turn performance / agility.
So it's all just two sides of the same coin (Does that phrase exist / make sense in english?)
In slow flight, this is used to support the higher AoA required to produce enough lift. The flaps in turn decreasing necessary AoA for a certain amount of lift production by changing the profile of a wing (it's camber). But you can't really deploy those rather big aerodynamic surfaces in combat, too much twisting forces (and drag).
Those vortices forming around an aircraft are also no sign of flightpath direction, but lift production. They always appear (given enough moisture in the air) when you pull on the stick, i.e. have a high AoA to produce lift so you can turn / pitch, even if your nose is pointing straight down.
In these modern, unstable designs with FBW computers and what not, several functions may be performed by any one controll surfe at once, depending on the situation. So it's indeed possible they do some flow control, attitude controll, trim ...
Thinking about it, I'm wondering if the degree of instability such a design exhibits may change with airspeed. In low speeds I could imagine there's not much excess pressure, or however one wants to call it, that foces the plane out of equilibrimum at any one point, so canard movement is rather pronounced to force a change in attitude in the first place. At higher speeds a small movement may well be enough to do that and then the counteracting, preventing it getting out of hand, becomes more of an issue.
AirForceBrat,
looking at the vids now more closely, I'd guess the quick controll surface movement is indeed the FBW. The quick reaction is probably due to electric signals steering the respective hydraulic pumps.
The flickering is the computers reaction to environmental influences. If it's powered up, it wants to keep the controlls in the perfect position at all times to comply with the pilots commands. So if it's gusty and the wind change somewhat, the computer immediatly adjusts the controll surfaces to compensate, even on the ground.
I think I've seen something similar on F-16s on the taxi way on a windy day. Can't find a vid of such a thing right now.
If you go from stabilators to canards up becomes down & vice verca, add in aerodynamic instability for increased agility, and it becomes a mess ...
As to the russians, really I don't know if they couldn't figure out a working flight controll software, or if they couldn't master certain production techniques that were required for such a design, or if it was too daunting to do something new, or if they genuinely figured the T-50 was the better design somehow.
A big delta seemed wise. Good transsonic / high speed performance. Good turning even at higher altitudes / big wing area. A big jet for good endurance / range / speed to cover Russias vast airspace. Should also have good payload capability. Maybe they thought the MiG 1.44 wasn't stealth enough and then followed what has proven it's worth in that direction for the US.
you're right that the slats on a fighter's wing are used to improve agility, i.e. turning performance.
Now, since turning is basicly "climbing around a circle", you need additional lift to perform that maneuver. The increased "Gs" you pull in a turn, are "produced" by the increased lift the aircraft is obtaining during these turns (by increasing AoA)
Now slats are deployed (moving forward & down) so a gap forms between them and the main wing. Air being forced through that gap is accelerated (energized) wich makes the air stick better to the wing during higher AoAs, that in turn allows you to produce more lift, wich in turn increases your turn performance / agility.
So it's all just two sides of the same coin (Does that phrase exist / make sense in english?)
In slow flight, this is used to support the higher AoA required to produce enough lift. The flaps in turn decreasing necessary AoA for a certain amount of lift production by changing the profile of a wing (it's camber). But you can't really deploy those rather big aerodynamic surfaces in combat, too much twisting forces (and drag).
Those vortices forming around an aircraft are also no sign of flightpath direction, but lift production. They always appear (given enough moisture in the air) when you pull on the stick, i.e. have a high AoA to produce lift so you can turn / pitch, even if your nose is pointing straight down.
In these modern, unstable designs with FBW computers and what not, several functions may be performed by any one controll surfe at once, depending on the situation. So it's indeed possible they do some flow control, attitude controll, trim ...
Thinking about it, I'm wondering if the degree of instability such a design exhibits may change with airspeed. In low speeds I could imagine there's not much excess pressure, or however one wants to call it, that foces the plane out of equilibrimum at any one point, so canard movement is rather pronounced to force a change in attitude in the first place. At higher speeds a small movement may well be enough to do that and then the counteracting, preventing it getting out of hand, becomes more of an issue.
AirForceBrat,
looking at the vids now more closely, I'd guess the quick controll surface movement is indeed the FBW. The quick reaction is probably due to electric signals steering the respective hydraulic pumps.
The flickering is the computers reaction to environmental influences. If it's powered up, it wants to keep the controlls in the perfect position at all times to comply with the pilots commands. So if it's gusty and the wind change somewhat, the computer immediatly adjusts the controll surfaces to compensate, even on the ground.
I think I've seen something similar on F-16s on the taxi way on a windy day. Can't find a vid of such a thing right now.
If you go from stabilators to canards up becomes down & vice verca, add in aerodynamic instability for increased agility, and it becomes a mess ...
As to the russians, really I don't know if they couldn't figure out a working flight controll software, or if they couldn't master certain production techniques that were required for such a design, or if it was too daunting to do something new, or if they genuinely figured the T-50 was the better design somehow.
A big delta seemed wise. Good transsonic / high speed performance. Good turning even at higher altitudes / big wing area. A big jet for good endurance / range / speed to cover Russias vast airspace. Should also have good payload capability. Maybe they thought the MiG 1.44 wasn't stealth enough and then followed what has proven it's worth in that direction for the US.
Last edited:
The most amazing thing is to watch the Raptor do a tailslide and see the stabilator trying to maintain that orientation as it slides backwards, as each side functions independantly of the other it looks like seal flippers, it would be interesting to know which aircraft are capable of tailslides, cool but scary looking, I'm fairly certain the Flanker Family qualifies, prolly F-18s. The flicking of the J-20 control surfaces during the preflight checks makes it look alive. As I said the laws of aerodynamics never change, but they have learned to cheat, in a good way. Engineer!
Well Scratch watch the SU-35 vid with the pink smoke, it has canards and stabilators, no doubt they have a firm handle on flight control systems. My personal take is that the conventional layout of the Pak Fa is much more practical from an aerodynamic standpoint given its Flanker lineage. Now somewhat toungue in cheek, it was intimated that some of the mig folks had to much invested in their baby to let it pass quietly, and may have encouraged someone, the J-20 is very good for all the reasons you mentioned...but when push comes to shove the Raptor is and will be the gold standard when it comes to stealthy low observables technology, and one on one with any other platform if tactical performance were the issue, a lot of smart people would put their money on old faithfull. The bottom line is this, Honda, Suzuki, Yamaha, and Kawasaki, all make 1000 cc sport bikes to compete against one another, in test after test they are so close its comical, they each have strengths they each have weaknesses, thats not a bad place for the players in our little game to be, there is a great deal to be said for parity. Now back to the J-20, how does that canard work, keep it coming gentlemen, I am waiting for enlightenment. All of these airplanes are wonderfull in so many ways, it will ultimately come down to desire and ability to come up with the answers or buy the answers, and execute the play.
Last edited:
airsuperiority
Captain
I seriously wonder when we can see the TVC version. Knowing that there should most likely be another one, 2003, coming out makes me totally curious what the real product will be like.
Let's consider the whole thing. The undercarriage is an ordinary nose wheel u/c, so with the aircraft just standing on the ground about 15 % of the weight is carried by the nose wheel. This allows you to find the position of the center of gravity along the length of the fuselage. It is about 3/17th of the distance between nose and main wheels in front of the main wheels. Lift is produced by the wing, the fuselage and the canards. The wing is mostly behind the center of gravity, the fuselage in front. At a large angle of attack the vortices coming from the front of the fuselage will greatly contribute to the lift and might make it unnecessary to have a large contribution from the canards. At the same time the angle of attack of the canards will still be positive. Indeed it might well be that with the canards at zero angle of incidence, i.e. parallel to the fuselage axis, they might stall while the wing is protected from the same by deflection of the leading edge flaps. I think indeed that they are leading edge flaps, not slats.
All together the design looks very well balanced.
All together the design looks very well balanced.
While I agree with your reasoning for the most part, I don't think that the canards will actually stall. They are controll surfaces, so letting them stall will greatly decrease the planes maneuvering ability in such a situation.
But combining that with the rest of you reasoning, it's indeed a good point that when the plane is at a high AoA, having the canards deflected "down" is just in relation to the fuselage while they still have a positive AoA (relative to the oncoming air). So I'd say that's then precisely to not let the canards stall at high AoA.
On a different note. Having gone through the "slats" principles I described in an earlier post, I might have screwed it up a little.
While slats increase the AoA at wich a wing can produce lift, it's not really because air flowing through them is accelerated and energized. Airflow is, however, influenced in a way that will change the pressure gradient of the airflow and do other suff to it, that in the end will have the air stick to the wing at a higher AoA.
But combining that with the rest of you reasoning, it's indeed a good point that when the plane is at a high AoA, having the canards deflected "down" is just in relation to the fuselage while they still have a positive AoA (relative to the oncoming air). So I'd say that's then precisely to not let the canards stall at high AoA.
On a different note. Having gone through the "slats" principles I described in an earlier post, I might have screwed it up a little.
While slats increase the AoA at wich a wing can produce lift, it's not really because air flowing through them is accelerated and energized. Airflow is, however, influenced in a way that will change the pressure gradient of the airflow and do other suff to it, that in the end will have the air stick to the wing at a higher AoA.
The canards are always generating lift, and in fact contribute to the load carrying ability of the aircraft, unlike conventional aft mounted stabilators or horizontal stabs and elevators. Scratch is correct in stating that the canards won't completely stall, what their supposed advantage was in general aviation was that when they reached the limit of producing nose up pitch, as they let go, they reduced the angle of attack of the main wing preventing a stall. What you would get as you approached that limit was a bobbing as it was impossible to stall the main wing. Since the main wing would regain lift as the nose bobbed down as the angle of attack was reduced, you never stalled the wing, avoiding the break and the loss of directional control preceding a spin. Therefore restoring control is a simple matter of reducing pitch and all is well, you may still be in a high rate of sink because you are behind the power curve and the solution for that is power up and reduce pitch. Having said that, it is still a gross oversimplification.
Last edited:
With a conventional wing as you approach the stall, the application of aileron to pick up a wing, may in fact cause that wing to stall, as you have effectly increased the angle of attack of that wing by the downward deflection of that aileron. This picks up the wing with the upward deflected aileron and will result in a spin as the aircraft pivots around the center of the yaw axis. Depending on the size of the aircraft and its flying qualities, this may result in something so innocous as a slight rotation around the yaw axis as the nose drops and flying speed is restored in a light docile aircraft, or in a heavily wing loaded high performance aircraft in a high g turn, it may roll completely inverted and tear itself completely apart. Now back to the J-20, again a very heavy, very high performance aircraft, the canards in conjunction with the very, very, cool flight control computer make this a much much more docile aircraft as its being jerked around by a fighter pilot trying the get position on his adversary. Again this is a "gross" oversimplification as you add forward strakes, a fuselage that also provides lift, thrust vectoring, and in the case of the Su-35 an aft stabilator or elavons. delft adds even more interesting and acurate information as he discuss the center of gravity and the center of lift. Again a "gross" oversimplification.
- Status