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G limit


Mking

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How dare you bring rational thought and logic into this!

 

Did you have something to add to the discussion?

 

When someone says 'we've set a fairly reasonable number' in the realm of a simulator built on hard charts and known numbers, it is quite logical to comment that that 'sounds arbitrary'.

 

The process was still not explained, but the answer of 20G's took the concern away and that's fine. Heatblur have a fantastic reputation and I trust them, no need to try to derail a logical discussion with comments like that.

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Let's put it like this: In the F-14 you should be able to pull what'ever G's the F-15 is capable of without concern as the two airframes share the same ultimate load factor (13.5 G's). The F-14 was bench tested beyond this as well with no catastrophic failures observed at 14 G's. So the thing was tough, like REALLY effin tough!

 

Also IIRC no US fighter design has before or since seen as many airframes submitted for stress testing as was the case with the F-14.

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While all of that is true, there's one big factor that is consistently forgotten about the F-14 and ridiculous G numbers: as Mach increases, the Tomcat's max CL decreases as a function of the wing sweep. This has been mentioned before, as the original program didn't start the transition until after 0.8 to maintain CL, but was swapped for the Ps schedule it had for all but the first block. That bit of CADC code changes the level of danger immensely.

 

In the regime you're really going to test the load capability (around M 0.7 to 0.95), the sweep schedule is going to make it more challenging than most any other aircraft to get a number higher than 10 or so on the gauge, because the rate of bleed and required control authority versus available Ps is so high. And as the Mach number gets higher for a given equivalent air speed (the ultimate determinant of how much G you can put on the plane) as altitude increases, the availability of big loads goes down even more as the sweep occurs earlier.

 

If she can survive multiple bumps of her ultimate load, that's fine. But unless you've really goofed up to begin with, it's a number you're going to be hard pressed to see.

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I was thinking (for a moment there) we'll be getting somewhat battered F-14's with quite few notches on their belts and thus have somewhat lower g-expectations from them.

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While all of that is true, there's one big factor that is consistently forgotten about the F-14 and ridiculous G numbers: as Mach increases, the Tomcat's max CL decreases as a function of the wing sweep. This has been mentioned before, as the original program didn't start the transition until after 0.8 to maintain CL, but was swapped for the Ps schedule it had for all but the first block. That bit of CADC code changes the level of danger immensely.

 

In the regime you're really going to test the load capability (around M 0.7 to 0.95), the sweep schedule is going to make it more challenging than most any other aircraft to get a number higher than 10 or so on the gauge, because the rate of bleed and required control authority versus available Ps is so high. And as the Mach number gets higher for a given equivalent air speed (the ultimate determinant of how much G you can put on the plane) as altitude increases, the availability of big loads goes down even more as the sweep occurs earlier.

 

If she can survive multiple bumps of her ultimate load, that's fine. But unless you've really goofed up to begin with, it's a number you're going to be hard pressed to see.

 

Perhaps we can get one of the first (20?) airframes with the early scheduled MSP that calculated max lift vice max Ps...........

 

I know....not gonna happen.

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Perhaps we can get one of the first (20?) airframes with the early scheduled MSP that calculated max lift vice max Ps...........

 

I know....not gonna happen.

 

I'm not sure you'd want these. The TF30's didn't provide much thrust as it is, having the wings popped out (which you can probably do anyway in the emergency override handle) up to or above mach 0.8 isn't really going to help you acceleration and/or energy recovery ability. Especially in military power.

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Perhaps we can get one of the first (20?) airframes with the early scheduled MSP that calculated max lift vice max Ps...........

 

I know....not gonna happen.

 

 

I'm not sure you'd want these. The TF30's didn't provide much thrust as it is, having the wings popped out (which you can probably do anyway in the emergency override handle) up to or above mach 0.8 isn't really going to help you acceleration and/or energy recovery ability. Especially in military power.

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I'm not sure you'd want these. The TF30's didn't provide much thrust as it is, having the wings popped out (which you can probably do anyway in the emergency override handle) up to or above mach 0.8 isn't really going to help you acceleration and/or energy recovery ability. Especially in military power.

 

TF-30s installed in the F-14A provide 60k total thrust at Mach .9 at sea level....but they're horrible when slow- less than the 40k(20k per) you see quoted in books. The F-14 doesn't bleed as much as a super bug and is an energy maker if kept low and maneuvers are crisp. IF its the general virtual pilot dogfight where both goons pull on the stick and chase each others tail until energy falls off, yeah you're not gonna like the F-14A. If you know the best maneuver to counter what you see you should enjoy it. F-14A beat up on plenty of F-14Bs and F-14Ds- remember its a bit lighter and has the best wing loading- just not the thrust that forgives and keeps you in the fight until the tanks are empty.

 

F-14A ACM mantra was to set the motors in AB and fight, only the true vets moved the throttles during ACM.

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You gonna struggle getting to mach 0.9 with the wings popped out. You gonna struggle even more sustaining turns under such conditions. Not to mention the fragile nature of the early block's engines. Lack of ARI. Dubious IRS instead of the TCS. And on the developer's side, a modified 3D model to boot.

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An aside and not sure if its even relavant but in the RAF they refused to activate auto wing sweep as it was to slow to react, so my question is can we

Manually bring the wings forward when we enter a fight?

 

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An aside and not sure if its even relavant but in the RAF they refused to activate auto wing sweep as it was to slow to react, so my question is can we

Manually bring the wings forward when we enter a fight?

 

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You shouldn't be able too. The F-14's wing sweep scheduler allows the pilot to manually select any sweep angle greater than the current optimal sweep angle. You cannot command it to sweep the wings farther forward than the computer thinks is optimal unless you use the emergency wing sweep slider, which again, you shouldn't.

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That may be bad as you have the equivalent of VNE and VNO for wingsweep, normally the computer works to VNO but a human will start the wings forward at VNE for the wingsweep, as the aircraft is gonna slow as you pull max g anyway.

 

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That's not what the CADC does on the airplane in question. It doesn't care about VNO, and forward sweep's limitation is applied load, not speed. You would stop accelerating before the wing assembly was under threat of failure. But what will do it is excessive high loading- at least long term, hence the reprogramming. Meanwhile, the sweep mechanism transitions in excess of 7 degrees per second even under maximum load, while normally completing it in just over three seconds, thus responsiveness is just fine.

 

I'm not certain it's particularly useful comparing an airplane designed with automatic sweep functionality added on against one designed with it from the start with full automation and a higher designed load factor. Besides- it slows down just fine in aft sweep, and transitioning to automatic after a big opening angles grab with the pitch rate in the swept configuration picked a lot of grapes off the vine- whether the F-14 actually entered fast or not.

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Hmm on the Tornado it wasnt added it was there from the start just not implemented in the RAF, the Saudis used the Auto wing sweep. It was really a question so it sounds like the 14 has a much better system. I am surprised that that the sweep is not a function of speed tho.

 

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Hmm on the Tornado it wasnt added it was there from the start just not implemented in the RAF, the Saudis used the Auto wing sweep. It was really a question so it sounds like the 14 has a much better system. I am surprised that that the sweep is not a function of speed tho.

You are correct to be surprised and you are right... The sweep is a function of speed & altitude.

wingsweep.thumb.jpg.45302bd0a2611c364227abebe3667da2.jpg

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Thanks good info, I was thinking it would suck if the dam thing put the wings back when you were pulling g in combat.

 

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You are correct to be surprised and you are right... The sweep is a function of speed & altitude.

 

Thanks good info, I was thinking it would suck if the dam thing put the wings back when you were pulling g in combat.

 

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I there was a miscommunication between Windy and Lunaticfringe here. There was never any doubt about the wing sweep not being air speed/mach dependent, but load dependent. The air data computer always calculated the current wing sweep angle based on either mach or air speed (dependent on altitude). What Fringe was referring to was the limitations of the wing sweep override and the wing sweep mechanism itself. I.E. the load the system would be under if the wings popped up during a higher then recommended air speed, or under loaded turns.

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Quote

 

"There was never any doubt about the wing sweep not being air speed/mach dependent, but load dependent. "

 

Sorry being a bit of a pedant and I have had a couple of glasses of wine, but I think you have an extra "not" in the sentence. Wing sweep is a function of speed / Mach like the Tornado and the F111, ( the two aircraft I am familiar with , flying formation with a B1 doesn't count).

 

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The wing sweep is ofcourse dependant on speed, what Fringe & Dalan no doubt were trying to get across is that the F-14's auto sweep system isn't inhibited by G loads, and that under max loads it would still be sweeping the wings in excess of 7 deg/sec.

 

The Tornado was different in this regard as the wing sweep function (auto and manual) was halted altogether at a certain G load, and it was designed like this from the start. I believe a big reason for this was the fact the Tornado's sweepable wings also had to carry external stores.

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F-14 wing sweep is affected by G-load, but is better than and should not be compared to -other wing sweep designs. The Tornado is a completely different system and while it can be used in dogfighting-it is a compromised design that needs to shoot and disengage as it will not sustain in WVR at all. The F-14 wing sweeps forward faster than it does sweeping back, the time it takes is reduced under heavy G but operates up to 7G IIRC- it may operate after that but might not be designed to do it -in the late 80s or early 90s F-14s had shavings in their wing pivots that introduce a horrible G restriction for a while until they fixed the issue-5.5g I think. Anyone with more info please speak up.

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