Aerodynamics thread

[Engineer]

They provide pitch control, the best fighter is not because it has canards or LEVCONS but the one that has the best combination and the best tactics, any way in the PAKFA video the Sukhoi engineers say LEVCONS have their advantages over canards

The question is, does LEVCON provide more pitch control over canard? You spoke of experimental data but you clearly lack such data to give an affirmative answer. Better means doing more, and when LEVCON cannot provide the same pitch authority as long-coupled canard, than LEVCON is doing less than canard thus is not better.

 

[F-15]

LEVCON being much closer to the aircraft's center-of-gravity than long-coupled canard cannot generated as much pitch moment. .

Uhmmmm is it?

could you tell me where is the CG in each aircraft?

By the way LEVCONS do not work that way, they create lift in a way they reduce stall, the main wing will lose less lift thus that is the way they will control pitch

 

[thunderchief]

Now back to LEVCON. Of course there are reasons why Sukhoi chose it, but that doesn't mean LEVCON is equivalent to or better than canard. Moreover, it is risky to design an aircraft with canard due to the requirement of very sophisticated FCS, which in turn requires a lot of devotion in money and time. Just because Sukhoi had developed canard designs in Soviet time, that doesn't mean they can repeat the same today. Given Russia needs an answer to F-22 quickly but with less money, LEVCON could just be a poor man's canard for Sukhoi, and does no prove LEVCON can do what canard can. I rest my case.

Not really. Sukhoi developed many fighters with canards recently and could do that at request of the customer ( Su-30MKI vs Su-30MKK ) . Main reason that they deleted canards on Su-35 and PAKFA is reducing RCS . They felt that those planes are already maneuverable enough, and it is notoriously difficult to create both stealthy and effective canards . To be effective, canards need to be offset somewhat from the wing and that could create some unwanted reflections at certain angles . Therefore FCS would need to make sure not only to move canards in order to insure stable flight , it would also have to make sure they do not create unnecessary reflection. And that would be one of the main problems that designers of J-20 would have to solve .

 

[Engineer]

Uhmmmm is it?

Yep, the canard on the J-20 is placed further forward.

By the way LEVCONS do not work that way, they create lift in a way they reduce stall, the main wing will lose less lift thus that is the way they will control pitch

Delaying stall is not the same as providing pitch authority.

 

[Engineer]

Not really. Sukhoi developed many fighters with canards recently and could do that at request of the customer ( Su-30MKI vs Su-30MKK ) .

Those are more of traditional fighters with added pair of canards, rather than whole new designs that base entirely on the canard configuration. Aircraft such as Grippen, Rafale, Eurofighter, J-10 and J-20 would be what I meant by canard configurations.

Main reason that they deleted canards on Su-35 and PAKFA is reducing RCS . They felt that those planes are already maneuverable enough, and it is notoriously difficult to create both stealthy and effective canards. To be effective, canards need to be offset somewhat from the wing and that could create some unwanted reflections at certain angles . Therefore FCS would need to make sure not only to move canards in order to insure stable flight , it would also have to make sure they do not create unnecessary reflection. And that would be one of the main problems that designers of J-20 would have to solve.

I have a strong feeling that Sukhoi's choice of not using the canard is based more on avoiding those difficulties you have mentioned. I do not buy the argument about stealth though, since radar reflection concentrates on edges and employing LEVCON does not reduce the total number of edges.

 

[F-15]

Yep, the canard on the J-20 is placed further forward.


Delaying stall is not the same as providing pitch authority.

wait wait then this has to be the best fighter ever

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[Engineer]

wait wait then this has to be the best fighter ever

Clearly, canard is placed that far forward as anything attached to the wing (such as LEVCON) would not have provided enough pitch authority. As you see, my statements are applicable for fighters and non-fighters.

 

[Air Force Brat]

Yep, the canard on the J-20 is placed further forward.
Delaying stall is not the same as providing pitch authority.

Yes, it is rather clear that F-15 does not understand the difference between pitch authority/control, and lift enhancement, although any device that moves forward or backward on the main wing to enhance lift, will of necessity change pitch TRIM, and necessitate re-trimming to maintain airspeed or attitude???

To answer another question, most pilots/engineers may look at an aircraft and ascertain with reasonable accuracy where the center of gravity or the center of lift are located. That LEVCONs may be included in an aircrafts FBW for aircraft control, while somewhat novel, is not necessarily revolutionary or earth shaking, as lift enhancing devices are used every day by pilots for such purposes without a consideration, but they are never an aircrafts PRIMARY pitch or roll control. To maintain otherwise is to illustrate a rather profound lack of understanding of aircraft operation or aerodynamics...... but that is obvious as well.

 

[Equation]

Now back to LEVCON. Of course there are reasons why Sukhoi chose it, but that doesn't mean LEVCON is equivalent to or better than canard. Moreover, it is risky to design an aircraft with canard due to the requirement of very sophisticated FCS, which in turn requires a lot of devotion in money and time.

Just out of curiosity Eng, why is that? With today's more sophisticated super computer, more rigorous wind tunnel testings, and more sophisticated CAD software design one would assume that it would make it less costly to design.

 

[thunderchief]

Those are more of traditional fighters with added pair of canards, rather than whole new designs that base entirely on the canard configuration. Aircraft such as Grippen, Rafale, Eurofighter, J-10 and J-20 would be what I meant by canard configurations.

Sukhoi produced Su-33, Su-34 and Su-30MKI . These are all unstable fighters with canards . They also had Su-35 prototypes with canards and finally Su-47 . Therefore, like it or not, considering canards technology they are at the top

I have a strong feeling that Sukhoi's choice of not using the canard is based more on avoiding those difficulties you have mentioned. I do not buy the argument about stealth though, since radar reflection concentrates on edges and employing LEVCON does not reduce the total number of edges.

It is not number of edges, problem with canards is that they do not lay in same plane with the wing . 4.5th gen fighters like Rafale or Typhoon are not even optimized to have canards parallel with the wing (YF-23 was) . Therefore, EM wave could at certain angles (mostly from the side) bounce back from canards down to the wings and back like in waveguide. I will try to find picture to explain better .