Simple test. Built two rectangular wireframes. Pull one hard horizontally at one corner and pull the other one vertically at one corner until both are out of shape. Please show us the results
J-15 carrier-borne fighter thread
- Thread starter Jeff Head
- Start date
Simple test. Built two rectangular wireframes. Pull one hard horizontally at one corner and pull the other one vertically at one corner until both are out of shape. Please show us the results
Quickie
Colonel
Boy, you're pesky. Who said anything about the nose landing gear NOT having to be re-enforced further for CATOBAR operation? Should not this be a given as all the stress forces originate from here in a catapult launch?
I was talking about reinforcement of the overall air-frame of the aircraft needed for STOBAR as well as CATOBAR operation, which unfortunately cannot be seen from the outside. Can you see the structural re-enforcement between the front nose gear and the main landing gear within the aircraft fuselage? I don't think so.
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Quickie
Colonel
If the wire frame is light enough, the shape won't change much if any.
No, that's not how physics works. Only acceleration is transmitted to the whole aircraft, force varies along the length of the aircraft.
Here's an analogy:
Imagine a chain of five monkeys dangling off a branch. The monkey at the very top of the chain needs to support the weight of five monkeys. The monkey below him needs to support four monkeys, and so on and so forth until the last monkey which only needs to support its own weight.
Same logic with arrested recovery. The parts of the aircraft towards the rear needs to hold on to the force of the rest of the aircraft while the middle portion only needs to hold onto the front half of the aircraft, and the very tip of the aircraft only needs to hold onto the radome. This means an aircraft reinforced only for STOBAR has a decreasing amount of structural reinforcement as it progresses from the rear to the front.
I doubt it.
An F-18 is catapulted to 165 knots while its landing speed for arrested recovery is 139 knots. The landing and takeoff distances are about the same but because takeoff requires a larger Δv, the forces involved are greater. Here's the class and here's so you can see that an F-18's landing distance is about the same as the takeoff distance.
Additionally, continuing on with the dangling monkeys analogy, the parts of the aircraft immediately around the front landing gear needs to hold onto the rest of the aircraft while the rear of the aircraft only needs to hold onto itself. Thus, the reinforcement scheme for catapult launch is the inverse of the scheme necessary for arrested recovery. In other words, the amount of reinforcements for catapult launch decreases as it progresses along from the front of the aircraft towards the rear.
As I said above, the reinforcement scheme for arrested recovery and catapult launch are inverses of each other. Thus, an aircraft designed for both will require reinforcements that satisfies both of those situations. A simplified model of what I'm talking about is below;
It's unlikely that the J-15, based off the T-10K prototype, would have implemented the reinforcements necessary for catapult launch as the PLAN likes to minimise risk and take things slow. The PLAN would have first pursued simply achieving STOBAR and using what they'd have learnt as a solid foundation upon which to develop further. Now that STOBAR has been achieved, they have developed a prototype -- J-15A? -- that implements the additional reinforcements (the red line) necessary for catapult launch.
HOWEVER, we have digressed from my original objection, which is specific to the front landing gear. Simply put, a landing gear designed for ski-ramps primarily needs to deal with compression forces while a catapult-compatible landing gear requires a huge reinforcement against counter-clockwise bending moment.
You raised the point that simply reinforcing the landing gear would've solved the problem because the rest of the aircraft should be sufficiently reinforced for catapult-launch stresses but in this reply, I've told you why that is not quite so (hint: dangling monkeys).
To sum up, no. Your assertion that "CATOBAR is said to be already "deployed", albeit minus the CATOBAR equipment on the aircraft carrier" is incorrect for all the reasons I've just listed.
LOL I'M pesky? The entire forum has clearly united together to repeatedly stomp on your ridiculous and humorously persistent pseudo-theory, and you have the gall to call someone else "pesky"?
Reinforcement of the "overall air-frame" is certainly not the same as reinforcement of the nose gear attachments, but this is not what I'm talking about. I'm talking about the reinforcement of the fuselage itself right in the area where the nose gear attaches to the fuselage. As others have already pointed out, the additional and severe stress from a catapult applying enough force to accelerate a fully-loaded fighter from 0 to 150 knots is NOT the same stress that's designed into the airframe to withstand multiple traps, which means that STOBAR J-15 airframes will not be designed to withstand multiple launches. You are simplistically thinking of the airframe as some kind of ridiculously homogenous single metal bar so that you can equalize tensile stress acting on the rear of the fighter to tensile stress acting on the front of the fighter. Well the J-15 isn't a single metal bar, tough guy. It's a collection of cast, welded, and screwed-together parts that will stretch, squeeze, and torque all sorts of funny ways while taking off from a carrier, that are significantly different from the stretching, squeezing and torqueing that occurs while landing on a carrier. That you don't get this simple fact is a testament to your.... peskiness.
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Quickie
Colonel
LOL I'M pesky? The entire forum has clearly united together to repeatedly stomp on your ridiculous and humorously persistent pseudo-theory, and you have the gall to call someone else "pesky"?
Reinforcement of the "overall air-frame" is certainly not the same as reinforcement of the nose gear attachments, but this is not what I'm talking about. I'm talking about the reinforcement of the fuselage itself right in the area where the nose gear attaches to the fuselage. As others have already pointed out, the additional and severe stress from a catapult applying enough force to accelerate a fully-loaded fighter from 0 to 150 knots is NOT the same stress that's designed into the airframe to withstand multiple traps, which means that STOBAR J-15 airframes will not be designed to withstand multiple launches. You are simplistically thinking of the airframe as some kind of ridiculously homogenous single metal bar so that you can equalize tensile stress acting on the rear of the fighter to tensile stress acting on the front of the fighter. Well the J-15 isn't a single metal bar, tough guy. It's a collection of cast, welded, and screwed-together parts that will stretch, squeeze, and torque all sorts of funny ways while taking off from a carrier, that are significantly different from the stretching, squeezing and torqueing that occurs while landing on a carrier. That you don't get this simple fact is a testament to your.... peskiness.
LOL I'M pesky? The entire forum has clearly united together to repeatedly stomp on your ridiculous and humorously persistent pseudo-theory, and you have the gall to call someone else "pesky"?
Lol, you remind me of a-long-ago colleague with a very similar character.
Did I ever make such a statement or imply such things?
How do you suggest to build the re enforcement then?
You seem to suggest the idea of building additional re enforcement around the front of the aircraft to handle the pulling forces but this would entail adding additional weight which i think is not a good idea and unnecessary. My idea of it is in my earlier post which I will not repeat.
Why would the stress along the length the aircraft would be any much less during a trap than during a catapult launch, which in addition, is assisted by the engine thrusts?
Also, both are essentially longitudinal along the length of the aircraft. In any case the trapping of an aircraft would involve more complicated forces at play in more directions as the aircraft gets trapped while landing at an angle to the deck.
Look, I never said the aircraft air-frame is a single metal bar or anything in the rest of the above .
And I will not repeat again the points which I have already made a few times in my previous posts.
Quickie
Colonel
No, that's not how physics works. Only acceleration is transmitted to the whole aircraft, force varies along the length of the aircraft.
Here's an analogy:
Imagine a chain of five monkeys dangling off a branch. The monkey at the very top of the chain needs to support the weight of five monkeys. The monkey below him needs to support four monkeys, and so on and so forth until the last monkey which only needs to support its own weight.
Same logic with arrested recovery. The parts of the aircraft towards the rear needs to hold on to the force of the rest of the aircraft while the middle portion only needs to hold onto the front half of the aircraft, and the very tip of the aircraft only needs to hold onto the radome. This means an aircraft reinforced only for STOBAR has a decreasing amount of structural reinforcement as it progresses from the rear to the front.
I doubt it.
An F-18 is catapulted to 165 knots while its landing speed for arrested recovery is 139 knots. The landing and takeoff distances are about the same but because takeoff requires a larger Δv, the forces involved are greater. Here's the class and here's so you can see that an F-18's landing distance is about the same as the takeoff distance.
Additionally, continuing on with the dangling monkeys analogy, the parts of the aircraft immediately around the front landing gear needs to hold onto the rest of the aircraft while the rear of the aircraft only needs to hold onto itself. Thus, the reinforcement scheme for catapult launch is the inverse of the scheme necessary for arrested recovery. In other words, the amount of reinforcements for catapult launch decreases as it progresses along from the front of the aircraft towards the rear.
As I said above, the reinforcement scheme for arrested recovery and catapult launch are inverses of each other. Thus, an aircraft designed for both will require reinforcements that satisfies both of those situations. A simplified model of what I'm talking about is below;
It's unlikely that the J-15, based off the T-10K prototype, would have implemented the reinforcements necessary for catapult launch as the PLAN likes to minimise risk and take things slow. The PLAN would have first pursued simply achieving STOBAR and using what they'd have learnt as a solid foundation upon which to develop further. Now that STOBAR has been achieved, they have developed a prototype -- J-15A? -- that implements the additional reinforcements (the red line) necessary for catapult launch.
HOWEVER, we have digressed from my original objection, which is specific to the front landing gear. Simply put, a landing gear designed for ski-ramps primarily needs to deal with compression forces while a catapult-compatible landing gear requires a huge reinforcement against counter-clockwise bending moment.
You raised the point that simply reinforcing the landing gear would've solved the problem because the rest of the aircraft should be sufficiently reinforced for catapult-launch stresses but in this reply, I've told you why that is not quite so (hint: dangling monkeys).
To sum up, no. Your assertion that "CATOBAR is said to be already "deployed", albeit minus the CATOBAR equipment on the aircraft carrier" is incorrect for all the reasons I've just listed.
Wow, a lot of stuffs which I think I don't have the time to read.
But just to comment on this line.
Actually, the force remains a constant along the whole length of the aircraft (assuming the force is applied across both ends). The stress changes though depending on the cross sectional area of the particular point along the length.
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....
No, it doesn't.
Force = mass x acceleration. Mass changes, ∴ force changes.
The mass that requires anchoring decreases as the distance from the force transmission point (tail-hook/front landing gear) increases. Mass is not constant when you're analysing axial loading along length of aircraft. It's only constant when you're analysing the aircraft as a point mass within a larger system like the entire carrier. Read my reply to you and especially the dangling monkeys analogy.
It that's too simplistic and non-rigorous for you, here's actual lecture material from a few semesters ago that shows variability in axial force as a function of length. Notice that P(y), which is internal axial loading (force), is a function of 'y', which is length along the object. The length matters because at different lengths, different masses require supporting by their respective internal axial force. The rest of the equations are not relevant as we were finding strain and axial loading was just the first component of the question.
So, no. What you've said here -- "the force remains a constant along the whole length of the aircraft" -- is incorrect.
Quickie
Colonel
....
No, it doesn't.
Force = mass x acceleration. Mass changes, ∴ force changes.
The mass that requires anchoring decreases as the distance from the force transmission point (tail-hook/front landing gear) increases. Mass is not constant when you're analysing axial loading along length of aircraft. It's only constant when you're analysing the aircraft as a point mass within a larger system like the entire carrier. Read my reply to you and especially the dangling monkeys analogy.
It that's too simplistic and non-rigorous for you, here's actual lecture material from a few semesters ago that shows variability in axial force as a function of length. Notice that P(y), which is internal axial loading (force), is a function of 'y', which is length along the object. The length matters because at different lengths, different masses require supporting by their respective internal axial force. The rest of the equations are not relevant as we were finding strain and axial loading was just the first component of the question.
So, no. What you've said here -- "the force remains a constant along the whole length of the aircraft" -- is incorrect.
Did you edit the line that I wrote?
It was actually this
I specifically added the boded line to prevent any confusion.
If the force is a pushing or a pulling force at one end only, then of course the force along the length would be decreasing to zero at the free end, or increasing to the max force at the pulling or pushing end.
Let's move on before the mod....
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