How have your opinions of the JSF changed over the years?

[andreas77]

...
So I suppose having a large internal volume of fuel is a design flaw in the Flanker too? I've only seen one source claim an 8% increase in range, with EFTs, so I'll take that claim with a grain of salt. I have on the other hand seen other charts showing a combat radius for the F-35C, with EFTs, at 900+nm.

I never said it was a design flaw, not for any of the planes. But putting so much fuel inte the fuselage always comes with a cost. The Flanker will have great trouble showing its agility with full internal fuel load, and several sources states that the normal fuel load of a Flanker is about 60% of the full capacity.

You are right regarding the sources, but I actually would expect LM to come forward and correct the numbers if they were completely wrong.

[sewerrat]

Ok, so how many turning engagements happen right after wheels up? That's the only way that an F-35 will go into a "knife fight" with full internal fuel. Or...... No, also right after mid air refueling. Otherwise, I dare say that an F-35 will be several thousand pounds short of full internal fuel.

You keep going back to "penalties" for having a lot of internal fuel, but you never look at penalties for hanging weapons and extra fuel tanks under your wings.

For the flanker point you're making: I don't know if thats right or wrong, but how many missions do the Flankers fly where they need full internal fuel?

Look, its like this: when the F-35 needs it, there's a large amount fuel able to be stored inside, and when it doesn't need all that fuel, it doesn't have to carry it.

The specifications for the JSF being a LO strike fighter necessitated the requirement for 2 internal weapon storage bays. That fact then in turn necessitated a larger volumetric size greater than that of a non-LO airplane. So, that being the case, with the large volumetric size being required in order to be a LO fighter, there is a by-product of having extra internal volume.

I’m not even going into the Marines requirements for having enough internal volume to house a giant lift fan that’s basically the size of the A-10s turbofans!

“So, what to do with that extra space? Leave it empty? Why do that? Ok, let’s fill it with fuel and make that extra real estate useful.”

[wrightwing]

...
So I suppose having a large internal volume of fuel is a design flaw in the Flanker too? I've only seen one source claim an 8% increase in range, with EFTs, so I'll take that claim with a grain of salt. I have on the other hand seen other charts showing a combat radius for the F-35C, with EFTs, at 900+nm.

I never said it was a design flaw, not for any of the planes. But putting so much fuel inte the fuselage always comes with a cost. The Flanker will have great trouble showing its agility with full internal fuel load, and several sources states that the normal fuel load of a Flanker is about 60% of the full capacity.

You are right regarding the sources, but I actually would expect LM to come forward and correct the numbers if they were completely wrong.

Everything is a trade off, when designing an aircraft. Carrying everything externally is one too. Nobody is going to be fighting with a full load of fuel, but.....even with a full load, the F-35 is agile. At 50% fuel, it should compare well to pretty much any competitor, AND have the avionics and signature reduction advantages.

[mor10]

spazsinbad: Do you have the link to the tread about the advantages on the flight line I alluded to?

Andreas: You are kicking a dead horse. Your argumentd have been put to death a long time ago in many threads on this site. The F-35 is supposed to be as agile and reach as far as a clean fighter with its huge internal tanks, so from the start it does not fear any worse than the others. On the day a commander can actually order that a fighter is not topped up, but I seem to remember a quote that said something like "The only time lots of fuel is a bad thing is during a fire". There is also a suitable quote from the artillery that is valid here; "If you can hit the enemy, then they can hit you", so having longer legs than the enemy is not a bad thing.

[andreas77]

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Andreas: You are kicking a dead horse. Your argumentd have been put to death a long time ago in many threads on this site.
...

Ahhh, there's nothing like the F-16.net group thinking...

[sewerrat]

spazsinbad: Do you have the link to the tread about the advantages on the flight line I alluded to?

Andreas: You are kicking a dead horse. Your argumentd have been put to death a long time ago in many threads on this site. The F-35 is supposed to be as agile and reach as far as a clean fighter with its huge internal tanks, so from the start it does not fear any worse than the others. On the day a commander can actually order that a fighter is not topped up, but I seem to remember a quote that said something like "The only time lots of fuel is a bad thing is during a fire". There is also a suitable quote from the artillery that is valid here; "If you can hit the enemy, then they can hit you", so having longer legs than the enemy is not a bad thing.

Ever heard the quote, "One fighter, one tanker, one hour."? The F-35 does away with having such a short leash as the legacy fighters have.

Also with that "extra" fuel tucked away inside the airframe, the F-35 will actually be able to engage afterburners way, way longer than a legacy fighter. Not only that, but because its clean, and when in afterburner, the F-35 will actually be able to hit its designed speed limit whereas the legacy planes never go to their max speed because of drag from having all that crap under the wings. The -35 will be able to spend more time supersonic than a -16, -15, 18.

So there you have it... that magical word, "drag". the F-35 has less drag than a legacy -16, -15, -18 when actually loaded for combat and not for just flying over NASCAR events.

[Maks]

Hi sewerrat,

As you are obviously in the know: could you please provide drag (i.e. thrust) data for the F-35 for typical conditions as you have described? I was always interested in that kind of numbers. Example: M 0.8 & 1.2, typical A-A & A-G loadout. Fuel burn (range) numbers would be nice as well.
This as a first step to be able to compare it to other platforms.

My opinion has not changed much the last couple of years: the platform will be very capable. Today I just think that the numbers will get more reduced than I did 2-3 years ago. On affordability I would like to include the following statement:

Old news (Feb. 2004), but still interesting to read:
"...
"Affordability is the cornerstone on which the JSF program is built, and we're beginning to see how a continuous moving assembly line could help us meet our commitment to keep costs low," said Tom Burbage, Lockheed Martin executive vice president and F-35 JSF program general manager. "We are in the process of weighing the up-front investments against the long-term returns. So far, we like what we see."
..."

Maks

[caux]

The 414 offers equal or more (EPE) thrust with lower weight.

Equal or more than what? The F-135 has as much or more thrust dry, as the F-414EPE does in full afterburner.

Of course I mean 2 x GE414

1 F-135 is very similar in thrust to 2 F-414s, in afterburning thrust, and with the advantage of less weight, lower fuel usage, lower maintenance/logistical requirements. The only advantage 2 F-414s have, is if you lose an engine.

The engine seems to be heavier than previously indicated in different tabs.

If P&W reaches its goal, the 250th F135 engine will cost the same as the F119 that powers the Lockheed F-22A Raptor, although the former weighs 680kg (1,500lb) more and produces 20% more thrust, Boley says.

http://www.flightglobal.com/articles/20 ... pment.html

If an F-119 weight is 1767Kg we have:

1767+680=2447Kg!!

If so trust/weight ratio does not seem exceptional.
Is there someone who can confirm that? It's strange for a modern engine.

[wrightwing]

http://www.flightglobal.com/articles/20 ... pment.html

If an F-119 weight is 1767Kg we have:

1767+680=2447Kg!!

If so trust/weight ratio does not seem exceptional.
Is there someone who can confirm that? It's strange for a modern engine.

Actually, the F-135 has a similar T/W ratio to the F-119, given that 43,000lbs isn't the true thrust limit of the F-135.

[delvo]

Actually, the F-135 has a similar T/W ratio to the F-119, given that 43,000lbs isn't the true thrust limit of the F-135.

What is the limit then, and why is a wrong number usually given?

[wrightwing]

Actually, the F-135 has a similar T/W ratio to the F-119, given that 43,000lbs isn't the true thrust limit of the F-135.

What is the limit then, and why is a wrong number usually given?

http://www.aviationweek.com/aw/generic/ ... line=Pratt

and the dry weight of the F-135 is considerably less than 2447kg(more like 1701kg).

[caux]

That article is 1 year old and it doesn’t say anything about F-135 weight.
Perahaps 2447kg is too much but 1710 is too low…
If trust/weight ratio is the same of F-119, F-135 weight must be higher and not lower, because F-135 has 20%/-30% more power than F-119.
In any case Flightglobal article I have just posted is more recent about weight question and it is written “680Kg” more than F-119.
My question is: is there someone with news about that?
680Kg is “invented” or not?
If not... and if trust/weight ratio is 9-10...the F-135 real trust or the "potential" of this engine is "a little" bit more than 43000lb...
Am I wrong?

[gtg947h]

Actually, the F-135 has a similar T/W ratio to the F-119, given that 43,000lbs isn't the true thrust limit of the F-135.

What is the limit then, and why is a wrong number usually given?

I don't know the "true" thrust limit (what it can actually do), but the engine could be restricted for several reasons. There may be a mass-flow limit through the intakes, or the engine could just be dialed back because 43k is all that's required for the mission and they want to improve engine life.

[wrightwing]

That article is 1 year old and it doesn’t say anything about F-135 weight.
Perahaps 2447kg is too much but 1710 is too low…
If trust/weight ratio is the same of F-119, F-135 weight must be higher and not lower, because F-135 has 20%/-30% more power than F-119.
In any case Flightglobal article I have just posted is more recent about weight question and it is written “680Kg” more than F-119.
My question is: is there someone with news about that?
680Kg is “invented” or not?
If not... and if trust/weight ratio is 9-10...the F-135 real trust or the "potential" of this engine is "a little" bit more than 43000lb...
Am I wrong?

Which means that they achieved that milestone, over a year ago, in other words. As for the engine weights, the discrepancy may be that one weight is the dry weight vs. the weight with all of the oil/lubricants.

[wrightwing]

Actually, the F-135 has a similar T/W ratio to the F-119, given that 43,000lbs isn't the true thrust limit of the F-135.

What is the limit then, and why is a wrong number usually given?

I don't know the "true" thrust limit (what it can actually do), but the engine could be restricted for several reasons. There may be a mass-flow limit through the intakes, or the engine could just be dialed back because 43k is all that's required for the mission and they want to improve engine life.

The B model would be limited by the lift fan. The A/C models would only be limited by air flow.