J-15 carrier-borne fighter thread

Quickie

Colonel
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
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class and here's
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so you can see that an F-18's landing distance is about the same as the takeoff distance.

I recall during a trapping, the aircraft would only suddenly decelerate after the halfway point. Using the above figures and assuming the bulk of the deceleration happens only after the halfway point, then the trapping restraining force could still be 1.4 times larger than the launch pushing force, which is composed of the catapult force and thrust of the engines.

The catapult force = launch pushing force - engine thrust, meaning that the stress on the front nose gear is further reduced, thanks to the thrust of the engines.

I went ahead with this post since I figure this is maths only and there's no chance of the torment of a subjective argument. :)
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Iron Man

Major
Registered Member
Lol, you remind me of a-long-ago colleague with a very similar character.
Does your "colleague" look like you? :)

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.
That is exactly how reinforcement works. More metal, more welds, more bolts, or a combination thereof. And yes, more weight. Are you telling me that giant retraction actuator on the CATOBAR J-15 is somehow the same weight as the retraction actuator on the STOBAR J-15? In the same way the section of the airframe that this giant actuator is attached to also needs to be further reinforced to accept the new stresses of sudden takeoff that the original STOBAR J-15 was not designed to tolerate.

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.
Multiple people have been telling you that the stresses at the nose gear do not get fully transmitted to the tail, and the stresses at the tail hook do not get fully transmitted to the front of the plane. You humorously ask why I accuse you of trying to simplify a fighter into a single metal bar. Well you've proven here (once again) why my accusation is spot on. Your statements here clearly indicate that you are simplistically thinking of a fighter as being exactly one long metal bar. Your entire fantastically flawed thesis hinges on this erroneous assumption. And even if it WERE one long metal bar, if the bar were sufficiently long enough the tensile stresses acting at one end would not necessarily get transmitted all the way to the other end, depending the degree of force, the type of metal, and the length of bar. And even if it were transmitted all the way to the other end of the bar, the force would still be greatest at the one end and least at the other end. This is due to a combination of the metal's elasticity (yes, metals have it) and the inertia of the bar. The end of the bar receiving the tensile force will experience the greatest stress and will deform first and will experience the greatest deformation. But this is all moot, since a fighter fuselage isn't even a metal bar, it's a collection of metal parts attached to each other by various means. Which makes your pesky theory flat out wrong to begin with.

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.
See above.
 

Quickie

Colonel
Does your "colleague" look like you? :)


That is exactly how reinforcement works. More metal, more welds, more bolts, or a combination thereof. And yes, more weight. Are you telling me that giant retraction actuator on the CATOBAR J-15 is somehow the same weight as the retraction actuator on the STOBAR J-15? In the same way the section of the airframe that this giant actuator is attached to also needs to be further reinforced to accept the new stresses of sudden takeoff that the original STOBAR J-15 was not designed to tolerate.


Multiple people have been telling you that the stresses at the nose gear do not get fully transmitted to the tail, and the stresses at the tail hook do not get fully transmitted to the front of the plane. You humorously ask why I accuse you of trying to simplify a fighter into a single metal bar. Well you've proven here (once again) why my accusation is spot on. Your statements here clearly indicate that you are simplistically thinking of a fighter as being exactly one long metal bar. Your entire fantastically flawed thesis hinges on this erroneous assumption. And even if it WERE one long metal bar, if the bar were sufficiently long enough the tensile stresses acting at one end would not necessarily get transmitted all the way to the other end, depending the degree of force, the type of metal, and the length of bar. And even if it were transmitted all the way to the other end of the bar, the force would still be greatest at the one end and least at the other end. This is due to a combination of the metal's elasticity (yes, metals have it) and the inertia of the bar. The end of the bar receiving the tensile force will experience the greatest stress and will deform first and will experience the greatest deformation. But this is all moot, since a fighter fuselage isn't even a metal bar, it's a collection of metal parts attached to each other by various means. Which makes your pesky theory flat out wrong to begin with.


See above.


Show me the post I ever said this:

the stresses at the nose gear ... get fully transmitted to the tail, and the stresses at the tail hook ... get fully transmitted to the front of the plane.

Again, you're making up stories that I said this and that.

Look I've no interest with arguing with you any further.
This forum is for a friendly discussion, to do otherwise will bring down the standard of this site.
 

Quickie

Colonel
I'm not exacerbated by your editing, only your assertion that the original STOBAR J-15 was likely suited to CATOBAR ops from the very beginning. Don't go off on a tangent about edits and post timing when I hadn't asked you to clarify them.

I asked you to clarify your original assertion from page 218 of this thread. You somehow seem to think tail-hook reinforcements implies the existence of catapults reinforcements when there's absolutely no evidence whatsoever for it. This argument would come to a quick conclusion if you just admitted you misunderstood physics and blurted out a ridiculous proposition that has since elicited doubt and derision from multiple members of this forum, questioning both your understanding of physics and the obvious lack of evidence for your original proposition.

I've already said what I wanted to say in my previous post which seemed to went past a few of you. Look, people here post their opinion here in their free time and they don't have the obligation to explain everything they say, and certainly would not when they get pissed off which is how I'm feeling now.
 

jobjed

Captain
I've already said what I wanted to say in my previous post which seemed to went past a few of you. Look, people here post their opinion here in their free time and they don't have the obligation to explain everything they say, and certainly would not when they get pissed off which is how I'm feeling now.

Don't go off on a meta rant when your arguments have its holes pointed out to you.

You made an assertion on page 218 that the original J-15 was likely fit for CATOBAR duty in addition to STOBAR. I have provided counter-arguments to you which you have not properly addressed, either making excuses for yourself like "have no time" or agreeing with one of my premises and then completely ignoring how that premise links back to your original argument.

Either address the counter-arguments properly if you still think you're right or admit you misunderstood something and proposed an unlikely scenario.
 

Quickie

Colonel
Don't go off on a meta rant when your arguments have its holes pointed out to you.

You made an assertion on page 218 that the original J-15 was likely fit for CATOBAR duty in addition to STOBAR. I have provided counter-arguments to you which you have not properly addressed, either making excuses for yourself like "have no time" or agreeing with one of my premises and then completely ignoring how that premise links back to your original argument.

Either address the counter-arguments properly if you still think you're right or admit you misunderstood something and proposed an unlikely scenario.


Why should you think anyone is obligated to explain everything to you especially with the manner of tone you've come across?

And I stand by my argument.

Why is it a problem designing a STOBAR aircraft in such a way as to it being easily up-gradable to a CATOBAR type?

As an example, they would share the same basic design of re enforcing structures and frames (other than the front landing gear and perhaps some structural re enforcement specific to the type) with the flexibility of changing just the size of those re enforcing structures, but its overall shape and its position in the air frame would remain the same, just so the standardization of air-frame parts and their fitting would not be jeopardize between the 2 aircraft type.

That's all I will add to this discussion
 
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