J-20 5th Gen Fighter Thread IV (Closed to posting)

[Jeff Head]

Actually, the original statement was regarding moving surfaces. The ventral fins are fixed.

I understand, but I am just stating that there are eight surfaces on the J20 that impact stabilzation and control.

I know on the J20 they are fixed, and are fixed on most aircraft...but not on all.

My point is that there are a different number of those types of surfaces on the two aircraft that can contribute to RCS.

As to moving surfaces...well then you have to get into the ailerons, elevators, rudders, flaps, slats, spoilers, entire wings/canards/stabilizors that move, etc. which may be the same number, but are probably not the same sizes.

 

[chuck731]

I don't think the correlation between stealth characteristics and number of control surfaces is that simple. It may be true that if an aircraft's flight control system takes no account of location of enemy radars when manipulating flight control surfaces during maneuvers, then more control surfaces means more opportunities for accidentally presenting the enemy radar with a reflection hot spot.

But if the aircraft with more control surfaces also feature tight integration between flight control software and electronic defence management software, and the flight control software is sophisticated enough to chose from multiple alternative combinations of control surface deflection to achieve the same desired maneuver, and can factor in where the enemy radars are, and how different control surface deflections effect the reflection hot spots of the aircraft in its choice, then it would seem to me the aircraft with more control surfaces would have more combination of control surface deflections to choose from to achieve the same maneuver, and would therefore actually be more stealthy in a dynamic situation because its flight control software has more options to choose from to minimize sending any reflections back to the enemy radars.

 

[Blitzo]

I understand, but I am just stating that there are eight surfaces on the J20 that impact stabilzation and control.

I know on the J20 they are fixed, and are fixed on most aircraft...but not on all.

My point is that there are a different number of those types of surfaces on the two aircraft that can contribute to RCS.

As to moving surfaces...well then you have to get into the ailerons, elevators, rudders, flaps, slats, spoilers, entire wings/canards/stabilizors that move, etc. which may be the same number, but are probably not the same sizes.

I think if we were to properly speculate at their impact on RCS, we should also consider that the F-22s V tails are far larger than J-20s. it has been speculated whether J-20s V tails may be small because of the additional control provided by the ventral fins.

Whether J-20s smaller V tails + ventral fins have a greater RCS return than F-22s larger V tails is a question worth asking. (That is to say, the "number" of control surfaces may not wholly be indicative of RCS return, but we also need to look the size of the control surface. Where the tipping point for this relationship is is anyone's guess)

But regarding the original statement, the crux of tphuang's position relied on there being more moving control surfaces on J-20 than F-22 which we've all repeatedly pointed out isn't the case. If he was saying J-20s ventral fins added to that, then that is a different position.



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Edit: to use a humorous and extreme example, we can say that the B-52 technically only has five control surfaces. The main wings, the horizontal stabilizers, and a single vertical stabilizer. But clearly it doesn't mean it is more beneficial to RCS.
In fact, the single vertical stabilizer versus the dual V tail stabilizer in RCS return is a good example of why looking at control surfaces isn't a good rule of thumb way to judge RCS, because clearly a V tail is more stealthy than a single vertical stabilizer, yet it provides two surfaces instead of one.

 

[latenlazy]

I don't think the correlation between stealth characteristics and number of control surfaces is that simple. It may be true that if an aircraft's flight control system takes no account of location of enemy radars when manipulating flight control surfaces during maneuvers, then more control surfaces means more opportunities for accidentally presenting the enemy radar with a reflection hot spot.

But if the aircraft with more control surfaces also feature tight integration between flight control software and electronic defence management software, and the flight control software is sophisticated enough to chose from multiple alternative combinations of control surface deflection to achieve the same desired maneuver, and can factor in where the enemy radars are, and how different control surface deflections effect the reflection hot spots of the aircraft in its choice, then it would seem to me the aircraft with more control surfaces would have more combination of control surface deflections to choose from to achieve the same maneuver, and would therefore actually be more stealthy in a dynamic situation because its flight control software has more options to choose from to minimize sending any reflections back to the enemy radars.

To that point, it's probably better to say the number of control surfaces is a good design heuristic, but as with all heuristics it's best not to lean on them too much when drawing analytical conclusions. If it were that simple a great many more people could become aerospace engineers, and with considerablyles education.

 

[chuck731]

As to the number of control/stabilizor surfaces between the J20 and the F-22 that can impact to one degreee or another the RCS, here's what I count:

Most people foget the ventral fins on the J20.

Both F22 and J20 have separate inboard flapperon in addition to outboard aileron on the trailing edge, as well as leading edge flaps on each wing (shown deflected on the F-22 picture but undeflected in the J-20 picture), so there are three movable control surfaces per wing, giving each aircraft 10 movable control surfaces.

 

[Jeff Head]

In fact, the single vertical stabilizer versus the dual V tail stabilizer in RCS return is a good example of why looking at control surfaces isn't a good rule of thumb way to judge RCS, because clearly a V tail is more stealthy than a single vertical stabilizer, yet it provides two surfaces instead of one.

I have never posited that more or less is better.

I do posit that the various types of, orientation of, make-up of (as in what they are made of), anlge of, size of the various moving (and no-moving) surfaces, deflection, etc. all contribute to RCS.

We would have to go much further and do a much more thorough and mathematical analysis into the angles, the material, the orientation, the amount of movement and angle, etc., etc. to really make come up with a real imperical determination of which had the most or least impact on RCS.

As to basic shape of the two, and the various more general stealth characteristics...clearly some general observations and detemrnations can be made.

 

[Jeff Head]

Both F22 and J20 have separate inboard flapperon in addition to outboard aileron on the trailing edge, as well as leading edge flaps on each wing (shown deflected on the F-22 picture but undeflected in the J-20 picture), so there are three movable control surfaces per wing, giving each aircraft 10 movable control surfaces.

Exactly...and I agree. My post and pictures specifically said surfaces, not moving surfaces.

That is why I stated to Bltizo:

As to moving surfaces...well then you have to get into the ailerons, elevators, rudders, flaps, slats, spoilers, entire wings/canards/stabilizors that move, etc. which may be the same number, but are probably not the same sizes.

Which then moves into the discussion and points you raise.

The fact is, how those things move, what defelction they have, what material they are made of, what active and other measures are taken to mitigate any RCS impact, and numerous other factors have to be considered for each of those moving parts to really come to terms with the relative impact on RCS between the two.

 

[kwaigonegin]

I think if we were to properly speculate at their impact on RCS, we should also consider that the F-22s V tails are far larger than J-20s. it has been speculated whether J-20s V tails may be small because of the additional control provided by the ventral fins.

Whether J-20s smaller V tails + ventral fins have a greater RCS return than F-22s larger V tails is a question worth asking. (That is to say, the "number" of control surfaces may not wholly be indicative of RCS return, but we also need to look the size of the control surface. Where the tipping point for this relationship is is anyone's guess)

But regarding the original statement, the crux of tphuang's position relied on there being more moving control surfaces on J-20 than F-22 which we've all repeatedly pointed out isn't the case. If he was saying J-20s ventral fins added to that, then that is a different position.



--


Edit: to use a humorous and extreme example, we can say that the B-52 technically only has five control surfaces. The main wings, the horizontal stabilizers, and a single vertical stabilizer. But clearly it doesn't mean it is more beneficial to RCS.
In fact, the single vertical stabilizer versus the dual V tail stabilizer in RCS return is a good example of why looking at control surfaces isn't a good rule of thumb way to judge RCS, because clearly a V tail is more stealthy than a single vertical stabilizer, yet it provides two surfaces instead of one.

Not entirely correct. Everything else being equal the more surfaces or the larger surface area of an object overall the more RCS period! that is the fundemental law of physics that cannot be altered. As we all know things like canted or angle planes and RAM materials do minimize RCS but ultimately the surface area is still the fundemental problem.

Your example of V tail vs single is misleading. Yes a V shape tail do mimimize stealth due to it's angle of reflectivity however it doesn't necessary have less RCS than a single vertical tail. The reason it may have more RCS is because the vertical tail is well straight and vertical. If you angle a single vertical tail it will also minimize RCS as well although I don't know from an aerodynmics standpoint how well a plane with a single canted tail can fly but you get my point.

 

[Jeff Head]

Deino...please please, use whatever influence you have for the 2011.

Let this thing fly!

So we can raise ourselves and our discussion up out of the weeds, and once again sore into the heavens with this latest J-20.

Surely it must be soon!

 

[Blitzo]

I have never posited that more or less is better.

I do posit that the various types of, orientation of, make-up of (as in what they are made of), anlge of, size of the various moving (and no-moving) surfaces, deflection, etc. all contribute to RCS.

We would have to go much further and do a much more thorough and mathematical analysis into the angles, the material, the orientation, the amount of movement and angle, etc., etc. to really make come up with a real imperical determination of which had the most or least impact on RCS.

As to basic shape of the two, and the various more general stealth characteristics...clearly some general observations and detemrnations can be made.

Yep, yep. I agree with most things you said (although highlighting the "greater" number of control surfaces on J-20 made me infer you held a position about the number of surfaces and their influence on RCS).

Mostly I just disagree with tphuang's notion that J-20 has more moving surfaces than F-22.