Why is 5G fighters so much heavier than 4Gs?

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megasun

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Unread post09 Mar 2012, 23:41

Not sure if this has been talked before…

It's well known that fighter aircrafts are sensitive to weight gain, and F-35 still faces overweight problem.
I can't help wonder why 5th generation fighters weigh so much more than their precedents.

Empty weight:
Twin engine: F-22: 19,700kg vs F15C: 12,700kg
Single engine: F-35A: 13,300kg vs F16C Blk30: 8,570kg

5Gs weigh significant more, but are approximately same size in term of overall length or width.
What contributes to the weight? They'd better worth it. As tons of money were put to build these new aircrafts, yet F-35 is barely as agile as a F-16 from what I heard.

New engines are heavier, but they only provide better thrust/weight ratio, not worse.

Larger wings, almost 50% larger in area, this is only the result of weight gain, to compensate it.

New electronics are powerful, but electronics always grow smaller and lighter as time goes.
And AESA radar is also equipped on F-15.

Bigger internal tank to carry more fuel, that's true. But there are 4G fighter like Su-27 who carries no less.

Internal weapon bays, plus bigger tank make 5G fighters larger in volume though may not in length or width. They are fat. And maybe the change of internal structure to provide spaces yet maintain max g-load of 9 is difficult and contribute to weight gain. Is it so much? I see the Silent Eagle can carry 4 AIM-120s internally without much restructuring, another example is F-111's internal weapon bay.

Is it because of the stealthy capability? Composite materials are supposed to be lighter and better.

I don't get.
Advanced material and designs and powerful engines and large wings only keep 5G fighters at similar thrust/weight number or wing loading number, as they are 50% more heavier than 4Gs. Why do they have to be heavy? What if their competitors, like T-50 or J-20, are not so heavy, will they out-speed/out-manuver F-22?
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SpudmanWP

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Unread post10 Mar 2012, 00:39

All the pods, fuel, and basic weapons are now internal. this means that the internal volume (and structures to support it) has to grow.

There is also the issue of added weight due to RAM.
"The early bird gets the worm but the second mouse gets the cheese."
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deadseal

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Unread post10 Mar 2012, 01:40

yup
viper fuel weight-7k
f 35 fuel weight-19K ish?
TGP-700lbs
ecm about 700 as well
etc....
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popcorn

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Unread post10 Mar 2012, 03:10

I don't even know if the figures are available but I'm curious as to how much volume the F-22 and F-35 occupy.. Not just the internal weapons bays but the whole aircraft. Hmm.. Should be easy enough to find out given a big enough bathtub..
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exorcet

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Unread post10 Mar 2012, 07:43

It's probably the stealth. Both RAM and whatever they're using to reduce IR signature. The internal weapons bays also contribute to the weight as well because you need more structure to encase them and the machinery to operate the doors. In the case of the F-22, I'd also guess that the airframe is more durable than most other aircraft because its intended to operate at higher speeds. Also, for the record while the Flanker carries a similar amount of fuel, but it's actually not much lighter than the F-22.

Also, while weight is a big factor, so is drag, and the performance gains from internal weapons (along with new engines and better aerodynamic design) helps the F-22 and F-35 outperform the F-15 and F-16 despite being heavier.
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cola

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Unread post10 Mar 2012, 09:32

exorcet wrote:Also, while weight is a big factor, so is drag, and the performance gains from internal weapons (along with new engines and better aerodynamic design) helps the F-22 and F-35 outperform the F-15 and F-16 despite being heavier.


Yea well...
Been seeing this argument beat till death, so let me just pop a few pointers.

Although the resulting drag coefficient may be lower than for separate external installations, the overall cross section (equally important piece of equation) is usually considerably larger than for the planes with external stores, so the actual value of total drag and supposed advantage of internal installations, is a very moot point.

F22 flies good cause it has two big engines, not because of internal installations.
Cheers, Cola
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delvo

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Unread post10 Mar 2012, 10:56

The cross-section argument is a myth. You can test it for yourself by getting frontal pictures of the planes and scaling them to a single common scale and seeing how big their silhouettes really are. There's not really much difference. There's a reason why internal weapon bays don't add much cross section: they're located behind and in front of other parts that need to be there anyway, like the air intakes. And even to the extent that there is more of a bulge there at all, it's conformal, which is a shape that's much better for aerodynamics than an equivalent cross section of non-conformal shapes.

* * *

Anyway, the increase in weight from generation 4 to 5 is consistent with the general trend since the World Wars, and it's caused by governments wanting their fighters to be able to do more and more than their predecessors could do, whether in terms of range, or sensors, or communications, or engine power, or weapon range & size & variety of types, or pilot safety, and so on. Keeping weight down would mean leaving out something somewhere that does some job, and the governments buying planes seldom want to hold back on planes' abilities like that.

Like they say in the house construction business, it's easier to upsell than to downsell; once the customer has told you what they want you to build and how much they want to spend, they'll often end up going over budget and deeper in debt for "upgrades" to fancier features or bigger sizes, but very seldom reduce their material specifications in order to go under budget.
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em745

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Unread post10 Mar 2012, 11:32

cola wrote:Although the resulting drag coefficient may be lower than for separate external installations, the overall cross section (equally important piece of equation) is usually considerably larger than for the planes with external stores, so the actual value of total drag and supposed advantage of internal installations, is a very moot point.

That must mean the Concorde was VERY draggy then. :roll:

delvo wrote:The cross-section argument is a myth. You can test it for yourself by getting frontal pictures of the planes and scaling them to a single common scale and seeing how big their silhouettes really are.

You rang? :wink:

Image

Yeah, cola drink... Big, HUGE difference in cross-section. :roll:

Myth BUSTED! (Or is that myth CONFIRMED? :shrug: )
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cola

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Unread post10 Mar 2012, 11:58

delvo wrote:The cross-section argument is a myth.


It's a myth, for laymen perhaps.

There's not really much difference.


It seems you and this em745 guy really need CT, if you can't tell the difference.
Cheers, Cola
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sferrin

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Unread post10 Mar 2012, 13:06

em745 wrote:
cola wrote:Although the resulting drag coefficient may be lower than for separate external installations, the overall cross section (equally important piece of equation) is usually considerably larger than for the planes with external stores, so the actual value of total drag and supposed advantage of internal installations, is a very moot point.

That must mean the Concorde was VERY draggy then. :roll:

delvo wrote:The cross-section argument is a myth. You can test it for yourself by getting frontal pictures of the planes and scaling them to a single common scale and seeing how big their silhouettes really are.

You rang? :wink:

Image

Yeah, cola drink... Big, HUGE difference in cross-section. :roll:

Myth BUSTED! (Or is that myth CONFIRMED? :shrug: )


You seem to have left off the external tanks 4th gen always fly with. :lol:
"There I was. . ."
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em745

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Unread post10 Mar 2012, 13:29

cola wrote:It seems you and this em745 guy really need CT, if you can't tell the difference.

(Oh boy... :roll: )

In the pic I posted, all the 4th gen-ers are CLEAN--no missiles or tanks. That aside, methinks it is YOU who needs "CT" ( :?: ) if you seriously think the F-22's cross section is larger than the other full-sizers (F-14/15/Flanker).

Also, if a larger cross-section is the aerodynamic bugaboo you say it is, then what does that say about the EF's aerodynamics vs. the F-16 and Gripen?

If you're going to troll, you should really put more effort into it. (Just a suggestion.)

sferrin wrote:You seem to have left off the external tanks 4th gen always fly with. :lol:

Deliberate on my part.

Stores configs can vary greatly. With all of them clean they can be compared more fairly (the 4th gen's at least).
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cola

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Unread post10 Mar 2012, 15:11

em745 wasn't it you who claimed tails are better than canards, because they add to the lift? :D

em745 wrote: That aside, methinks it is YOU who needs "CT" ( :?: ) if you seriously think the F-22's cross section is larger than the other full-sizers (F-14/15/Flanker).

You don't get it, do you?
F15 (and other legacy fighters) was designed around technology of their time.
Today PW or GE can build an F100 class engine in the F404 size class, so if you wanna build a plane of F15's performance today, you'll get a fighter of significantly smaller front cross section and consequently drag.
Even as it is now, the F15 is still smaller than F22, while featuring M2.5+ intakes (which are major portion of its silhouette).
How much more clues do you need?

Also, if a larger cross-section is the aerodynamic bugaboo you say it is, then what does that say about the EF's aerodynamics vs. the F-16 and Gripen?

Yea well, even in your baby picture it's plain obvious the F35 has twice the cross section of F16.
If you can't see it, then CT perhaps isn't enough, but MRI might help. :D

As for comparison pictures, there was guy here (think his nick was "dwightlooi") which did all comparisons in scale...you may want to check those.
Cheers, Cola
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bumtish

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Unread post10 Mar 2012, 15:31

Dwightlooi scale comparisons can be found here:

http://www.f-16.net/f-16_forum_viewtopic-t-8192.html

If I remember correctly, dwigtloois (et al.) argument was that having one engine to do do the work of two frees up a lot of space for internal carriage.
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shingen

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Unread post10 Mar 2012, 16:36

Is the purpose of the plane to have paper numbers, or is the purpose to fight?

Troll boy thinks it's the former and he's said as much on the forum.

CREF the Japan selects F-35 thread and various others.

Don't feed the "sig management < aero" animals, send 'em back to the moron board where they belong.

Edited a typo
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em745

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Unread post10 Mar 2012, 16:44

cola wrote:em745 wasn't it you who claimed tails are better than canards, because they add to the lift? :D

Yep... With *UNSTABLE* platforms, wing-tails are indeed superior to canard-deltas in terms of lift/drag.

Explaining this to you would be pointless.

cola wrote:Even as it is now, the F15 is still smaller than F22, while featuring M2.5+ intakes (which are major portion of its silhouette).
How much more clues do you need?

:bang:

Here, does THIS help?

Image

An F-22 will be SC-ing at over Mach 1.7 with a full AtA loadout, which is a lot faster than a loaded Eagle.

Yea well, even in your baby picture it's plain obvious the F35 has twice the cross section of F16.

I wasn't talking about the F-35.

It's obvious the EF's cross-section is significantly larger than the F-16 or Gripen. So the EF must be one draggy sum'bitch compared to those other two, eh?

(That's it. I'm done feeding the animals.)
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