J-20 5th Generation Fighter VII

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Volpler11

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ougoah said:
I reckon J-20's is probably around the end of the weapons bays or between them and the front section of engines. But he is right that the structure absolutely would require beefing up in order to carry those forces to desired locations and this would be designed with a particular desired CoG of design. So he's not wrong in saying that the engineers would have needed to find ways to appropriately support this particular design and that usually would involve some weight penalties although honestly this probably isn't significant at all to the point of not worth mentioning except to say that it is certainly required.
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Why, could you explain the reasoning. For example, on F-20 all the weight forwards of the wing need to be transferred back to the wing where lift is generated. Whereas on the J-20 the canard can generate some lift, reducing the amount of load that needs to be transferred back.

The only scenario that I can think that canard is detrimental to the structural load is when you have the front roll in CW and rear roll CCW or vice versa. But this seems like a stupid configuration to be in. You are more likely wanting the front and rear to roll in the same direction, in that case the canard would reduce the amount of torsion the chassis need to handle.

Think of it this way, if you hold a piece of paper on one end, you will see large deflection, whereas if you hold both ends, it will not bend as much.
 
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Volpler11

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latenlazy said:
It’s not compelling at all because there’s more than one way to design load bearing structures. These airframes are not solid objects but a combination of different struts and hollow shapes. You don’t need to add extra mass to reinforce these structures. You just need to position different structures in different ways to transfer or absorb the expected loads.
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That is not the argument though. I am well aware that there are alternative designs. But the argument is that the use of canard results in an additional load that means the structure must be reinforced.

I think the claim can be separated into 2 parts and becomes much clearer:
1. Weapon bay results in a structural weakness that must be compensated. This is an issue for all 5th gen aircraft so I don't see it as a problem for J-20.
2. Canard places additional load on the chassis, requiring the structure to be reinforced, leading to higher weight. My reasoning is the forces generated by the canard is actually beneficial and reduce the amount of load that needs to be handled, therefore is weight saving.

The 2nd point is a bit counterintuitive and is the opposite of what the video claims.
 
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enroger

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Volpler11 said:
since you are more likely to be trying to turn the plane by matching the force applied at the front and back, it actually reduces the amount of force needed to be applied at the middle where the opening is located..
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This exactly. Yeah some people like to pretend expert on the internet and it is usually not worth the time to discuss those videos, but in this case it brings out an interesting point about the benefit of canards on structural loading.

Not only is canards beneficial in torsion load due to matching torque (from canard and aileron) as you mentioned, it is also beneficial in longitudinal load distribution as canards contribute a bit of lift force so less lift is needed to be distributed from the main wing to fore section.
 
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latenlazy

Brigadier
Volpler11 said:
That is not the argument though. I am well aware that there are alternative designs. But the argument is that the use of canard results in an additional load that means the structure must be reinforced.

I think the claim can be separated into 2 parts and becomes much clearer:
1. Weapon bay results in a structural weakness that must be compensated. This is an issue for all 5th gen aircraft so I don't see it as a problem for J-20.
2. Canard places additional load on the chassis, requiring the structure to be reinforced, leading to higher weight. My reasoning is the forces generated by the canard is actually beneficial and reduce the amount of load that needs to be handled, therefore is weight saving.

The 2nd point is a bit counterintuitive and is the opposite of what the video claims.
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My point is that not every instance of potential structural weakness requires reinforcement. Without knowing what the actual frame design is and what load distribution is across that frame you simply don’t know if you can design around a potential weak point with a particular geometry or whether you need to add extra reinforcement material, or whether you even need to. This sort of eyeball engineering is little more than make believe smart talk.
 
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taxiya

Brigadier
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ougoah said:
Depends on where the centre of gravity is. I really doubt canards position would be allowed to place any major strain at the centre of the weapons bays are located as a result of how the forces applied by the aerodynamic conditions created by canard deflection.

A conventional layout 5th gen fighter like F-22 does not "pivot" the aircraft along the axis that is at where the horizontal stabilisers are. On the F-22, it would probably be a bit further along the fuselage between weapons bays and mid section of engines. Just like with J-20's canards, the F-22's horizontal stabilisers themselves would be carrying and transferring the loads appropriately and that includes the internal forces in the section itself.

I reckon J-20's is probably around the end of the weapons bays or between them and the front section of engines. But he is right that the structure absolutely would require beefing up in order to carry those forces to desired locations and this would be designed with a particular desired CoG of design. So he's not wrong in saying that the engineers would have needed to find ways to appropriately support this particular design and that usually would involve some weight penalties although honestly this probably isn't significant at all to the point of not worth mentioning except to say that it is certainly required.
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"But he is right that the structure absolutely would require beefing up in order to carry those forces to desired locations"

requiring beefed up structure to carry those forces (twisting forces generated by control surfaces aft) to the desired locations (the front fuselage of J-20) is only needed if you don't have the canard control surface at the desired locations.

Imagine, if you hold a not very rigid rubber stick on one end, and swing it, it will be very floppy because the force from your hand has to be transferred by the elastic stick to change the momentum of the tip. But if you have another hand holding the tip and swing both ends in sync, the stick would act more stiff. Your other hand is doing the canard's work, you don't need to reinforce the stick to acquire the same rigidness.
 
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ougoah

Brigadier
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taxiya said:
"But he is right that the structure absolutely would require beefing up in order to carry those forces to desired locations"

requiring beefed up structure to carry those forces (twisting forces generated by control surfaces aft) to the desired locations (the front fuselage of J-20) is only needed if you don't have the canard control surface at the desired locations.

Imagine, if you hold a not very rigid rubber stick on one end, and swing it, it will be very floppy because the force from your hand has to be transferred by the elastic stick to change the momentum of the tip. But if you have another hand holding the tip and swing both ends in sync, the stick would act more stiff. Your other hand is doing the canard's work, you don't need to reinforce the stick to acquire the same rigidness.
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I deal mostly with statics and I'm no aerospace engineer but using your analogy, my understanding with aircraft control surfaces is your first analogy, relating it to canards and how deflections and aerodynamic forces on the surfaces do work on the CoG. Anyway this topic is more fitting for the aerodynamics thread.
 
by78

by78

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A newly released old image.

51722308539_df23bb01ac_k.jpg
 
Deino

Deino

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escobar said:
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Well ... if true it would be indeed a surprise since even if a former 2nd Air Division regiment was not unlikely, it was usually more the 4th or 6th AR, which were elite units. Also its J-10Cs are quite young but the 4th Air Brigade's J-11As would need a replacement more urgently and the 6th Air Brigade just converted to Su-35 in 2016-2018.
 
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