Forum: General F-35 Forum

I knew a 111 driver that said 2.7 in a shallow dive was easy.

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Gee? you mean a thick, wide bodied aircraft like the F-111 and it's internal bomb load doing MACH 2.5+ with only a bit over 41K of thrust? Busting through the front lines NOE @ MACH 1.3?

Not an thick, wide body internal load F-35 powered by a single 43K motor...

Oops forgot my [sarcasm/] TEG

F-111 can do Mach 2.5. It's just that it can only do it with an internal bomb load and even then it takes years to get to speed thanks to the poor performance of the TF-30s and the fact that the F-111 is such a large airframe that the engines aren't adequate to accelerate it to speed at the rate of, say, a clean F-15 or F-22.

That_Engine_Guy wrote:

This statement from PW doesn't say if the 28% is MIL 'specification', or MAX 'specification', or any other specific 'specification'. It also didn't say if the 'specification' was the original 40K or the newer 43K that was provided by PW in the final engine design. The final F135 product makes more power and weighs less than 'specification' already

I know I know, was just having poke. Twisted Evil

I've read your explanation on the matter previously.

That_Engine_Guy wrote:

hcobb wrote:

The F-35 has a much heavier max weight than the F-16, so compare it to the F-105 instead.

tacf-x wrote:

WHAT?! We just concluded on another thread that the F-105 is no F-35! Both are optimized for completely different flight regimes!

Second that TAC!

F-35 'Jack-of-all-Trades' and LO
F-105 'Bust-trough-at-MACH-1-drop-Neuk-run-like-hell' and polished aluminum!

Not to mention the J75-P-19W at MIL created just 17,500lbs of thrust or 26,500lbs at MAX (and weighed almost 6000lbs!)

tacf-x wrote:

It's almost like saying that an F-22 is the equivalent of an F-111 because both are two engined fighters that weigh over 60,000 lbs. loaded.

[sarcasm=heavy]No comparison there, the Raptor is such a slouch, only 'MACH 2 Class'... we all know the F-111 could hit MACH 2.5; the Aardvark would simply tap it's TF30s 41,600lbs of combined power and pull away from the Raptor unscathed....[\sarcasm]

Doh

TEG

Thank you, APA Laughing

I will agree, however. Compare the performance of an F-16C with 2*AIM-120 and 2*GBU-31/32 to that of an identically-loaded F-35 and then we can have an apples-to-apples comparison. I won't misconstrue myself as an F-35 fan, but it deserves a fair shake Wink

Just some thoughts:
1.) One shouldn't confuse the acceleration at subsonic, transsonic and supersonic speed
2.) The outaccelerated F-16s were fitted with external stores and Burbage points this fact out (clean vs dirty)
3.) That the performance isn't affected fully loaded is nonsense, as the weight of the aircraft has a direct impact on performance. You need lift force to counter the weight force, the heavier the aircraft the more lift is needed. More lift requires greater speeds or a higher AoA, both affect drag and thus acceleration.

the acceleration of a 47,000 lb airplane is only going to drop by 10% when you add the weight of the ~5,000 lb payload, however top speed will be largely unaffected. And for what others are mentioning (the F-16) then you are taking a 26,000 lb airplane and dropping its acceleration by ~35-40% (added weight is 20% of basic weight, added stores increase drag by ~15-20%). So if in a "clean drag race" from take off the M1.2 the F-16 wins by 10% (arbitrary number), once loaded for war not only would the F-35 now win by 15-20%, but the F-16 would never even get to M1.2.

Subsonic the acceleration of the CLEAN F-16 is roughly the same as the F35 and F-22 based on pilot anecdotes, transonic the F-35 falls behind, supersonic the F-22 pulls ahead (all relative to the F-16)

Lockheed is saying a partial truth, to compare with the acceleration of other aircraft you have to configure both aircrafts for a similar mission. So, if both an F-18e and an F-35c are configured for a bombing mission at 600 miles distance without refuelling and carrying say 6,000 pounds of weapons, then you can check their acceleration and see if it is that slow. The F-35 will probably go only with internal fuel and the F-18 will require two or three drop tanks, the drag and weight of those tanks is going to affect the F-18 performance a lot. They will be much closer.
But a simpler comparison is just looking at the empty weight and maximum thrust of both aircraft, and there you can see that the current Super Hornet weighs empty 32,000 Pounds and has 44,000 pounds of thrust (and GE is offering the EPE option so they could take this to 53,000 pounds) that gives ratios from [Link pending approval] to [Link pending approval] The F-35 weighs empty 35,000 pounds and has 43,000 pounds of thrust, which is only [Link pending approval] If it is true that both P&W and GE were able to reach 50,000 pounds of thrust, that ratio becomes something like [Link pending approval] Still below the Super Hornet (similar story with the A version and the F-16). This is physics, it is hard to see that the F-35 is going to be better than its predecessors in that performance area (Assuming similar specific fuel consumption at least, it is hard to see it, it is probably going to be worse). The bottom line is that the F-35 is a heavy aircraft and with the 43,000 pound engine it is underpowered. The fact that the F135 is the biggest engine of the type is irrelevant, because the aircraft is proportionally heavier, (unless it is true that the engine reaches 50,000+ pounds of thrust)

That_Engine_Guy wrote:

munny wrote:

But it reached 51K on the bench tests.

P&W wrote:

The test also demonstrated the F135 propulsion system’s ability to produce margin relative to thrust with this engine producing 28 percent more thrust than the specification requirement.

This statement from PW doesn't say if the 28% is MIL 'specification', or MAX 'specification', or any other specific 'specification'. It also didn't say if the 'specification' was the original 40K or the newer 43K that was provided by PW in the final engine design. The final F135 product makes more power and weighs less than 'specification' already.

It simply indicates the F135 has 'thrust margin' and could be capable of more thrust if required, needed, wanted, and most importantly funded. It was a demonstration to counter GE's F136 claims that their engine had 'thrust margin' there-by suggesting the PW F135 had no 'growth potential'. PW smartly countered these statements with their own 'test' of an engine in a controlled manner/test-environment that showed their engine was just as flexible for future requirements.

An F100 once saw a 'test' that had it at 37,000lbs of thrust over the PW-229's 29,000lbs. A PW-232 was offered for a while at 32K, but at 37k the same motor would have not lasted long and would have burnt too much fuel to be useful for more than a few seconds at power. Technology and time has given us the PW-229EEP; notice from it's specs that PW did NOT opt for a 20% increase of thrust, but a 50% improved TBO; IE - cheaper to own for 20-30 years or more.

So while a 50K F135 would be 'cool' to the kiddies on F-16.net; at what cost to the program?

Decreased TBO? Increased weight? Increased fuel consumption? Reduced range? Additional stresses the airframe was NOT designed to handle?

Aviation is a HUGE compromise; can't have something for nothing, and you'll never get everything.

Now if/when/why LM wants the F135-PW-150\450\650; sure why not. I'm sure PW will be ready, willing and able to provide just as soon as the ink dries on the contract.

Keep 'em flyin' Thumb

TEG

It's 50,000lbs+ (the extra % is in afterburner). This has been discussed many times here and the relevant quote (from an AvWeek article) posted many times as well.

None of these planes use afterburner more than momentarily in real flights. Take a look at their thrust numbers without afterburner.

What's the transsonic acceleration of the Raptor when armed with two nuclear bombs?

Oh, you say the F-35 will be the world's first nuclear armed supersonic stealth aircraft?

What was that again about an F35 outaccelerating clean F16? Very Happy

On this issue I fail to see any real point in comparing JSF to other jets. The bottom line here is that one version is at risk of failing that specific KPP. Probably not a major issue for the operators but still it's always good to exceed KPP's in early versions seeing how jets typically just grow heavier with age.

I don't think that 50,000 pounds is just "cool for the Kiddies in [Link pending approval];. If you don't have the acceleration, your TBO becomes irrelevant after you are shot down. I understand extending Engine TBO for reliability and accepting the trade off with maximum thrust, it is a good practice, obviously. But it is also important to have the option of having a more powerful engine.
BTW I don't see why we should worry that much about the downside of the extra thrust. "Additional stresses that the airframe was not designed to handle?" Look, the thrust is a force on the longitudinal axis, and it is in the 1 - [Link pending approval] range. Combat aircraft are designed for the 7 -9 G stresses (with actual peaks of 13 G or similar), I know it is in a different axis, but I doubt the engineers will design for 10G vertical and 1 horizontal. If you look at jet fighters since well, forever, they have been able to handle thrust increases pretty well (F-16 went from 24K to 32K, F-14 went from 42K to 56K, 1954's Grumman F-11F-1 went from 10K to 18K, pretty much all of them have managed substantial thrust increases).
On the fuel consumption, your main concern will be the specific fuel consumption, but if the latter is fairly constant, the higher thrust is a plus, yes, you will burn more fuel, but only when you are at performance levels that are impossible for the prior versions. If you don't push the engine to the maximum you get the same fuel flow (or slightly worse, probably the engine is a little heavier which translates into somewhat higher induced drag)
The only issue I see in increasing F-35 thrust is that only the A and C versions will get the full benefit of it. But the B version probably won't

cola wrote:

What was that again about an F35 outaccelerating clean F16? Very Happy

Read the entire DOT&E report on the F-35 and you will see it has only to do with the F-35C and only in certain parts of the transonic range. Nothing about the F-16 statement has changed and you Sodaboy are still a troll.

http://www.dote.osd.mil/pub/reports/FY2011/

Forum: General F-35 Forum

F-35 Does Not Match Predecessor's Acceleration Specs