Acceleration

Discuss the F-35 Lightning II
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element1loop

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Unread post28 Jul 2019, 04:29

Higher speed does not reduce burn rate, it just improves specific-consumption in terms of allowing a slightly better range achieved (if drag is low enough at speed) for a full fuel load than a lower speed does (obviously there's a cross-over speed where that's no longer true ... i.e. high-speed cruise). Unlikely to hold true for the F-35 due to its ample frontal cross-section as speed rises.

I'd be OK with slower dash and more stealth, loiter and maneuver time when I get there (especially as DAS-type sensor nets proliferate).

charlielima223 wrote:Its ability to supercruise will allow the F-22 larger patrol areas, and permit the Raptor to enter and exit hostile areas in quick fashion ...


The F-35A is more likely to enter a minute or two later and stay for 20 to 30 minutes - good mix, IMO.
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charlielima223

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Unread post28 Jul 2019, 07:17

Over Syria, F-22s have already been shown to be valuable forward ISR assets. F-22s flying forward or with strike packages and then staying around to provide information to follow on aircraft and assist in C&C. The F-35s more comprehensive and advanced sensor suite makes it better in this regard. Im sure the Raptors ability to quicky accelerate or supercruise will give it some advantages if it needs to respond to a pop up threat. Much like how in Afghanistan Vipers, Mudhens, Rhinos, and Bones had larger AORs than the A-10 because they could respond and quickly go from point A to point B (granted in a premissive environment).
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doge

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Unread post28 Jul 2019, 23:25

I came up with a sudden. 8) (!) My mediocre F-35 tactics opinion or idea...

First of all. (Organize.)
    ・F-22's subsonic Radius is about 590 nmi. (...It should be.) I think that the radius at the time of Super Cruise is about 460 nmi. (maybe.)
    ・F-35's Radius is known to be 669~max 760 nmi.
The difference in its Radius is up to about 300 nmi. (760-460=)

So, I came up with... 8)
At the expense of "Fuel" of its Radius 300 nmi, Is it possible for F-35 to approach F-22's mission/tactics, or to close the gap between?

In other words, I want to use fuel with a radius of 300 nmi for the afterburner and make F-35 a "pseudo" Raptor.

If it's possible use the idea of gaining speed at the expense of this radius and making it the same as the F-22 Super Cruise radius, The F-35 should be able to become a "pseudo" F-22 raptor.

Anxiety factor here...
    ・In the afterburner, is Fuel consumption too intense too much?
    ・Is a Fuel with a Radius of 300 nmi not enough for an afterburner? Not enough fuel?
    ・With a fuel of Radius 300 nmi, How long time can the F-35 sustain supersonic speed?
    ・Isn't it realistic...?
I have no idea at all... :shrug:
This is my mediocre idea who is a mediocre person. :notworthy:
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spazsinbad

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Unread post29 Jul 2019, 01:46

MEDIOCRE you ain't - you have the best avatar known to the web for starters. 8) Without answering your questions I would generalise that this sort of fuel equation can only be known from flight manual fuel usage figures. We could all work out details with imagined figures but that is all they would be <garbage in> <garbage out> Why an 'ersatz F-22'? It's an F-35.
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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steve2267

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Unread post29 Jul 2019, 03:05

I'm about to grab a beer, so I'll grab a napkin too.

In round numbers -- and I better use crayon while I'm at it -- out and back 300nm is 600nm. This is about an hour, maybe a little more, of flying time at cruise for an F-35. From some numbers that Spurts was throwing around... an hour of cruise from an F-135 is on the order of 4500lbs. (Prolly somewhere between 3500 and 5500lbs.) So... you've got "4500lbs" of gas to play with for your pseudo-Raptor mission. I know the F-35 afterburner is "staged" and articles have mentioned a "min burner" usage... but even in "min burner," I'm guessing an F135 will still drink the gas quickly, but how quickly? Don't have the Dash One that Spaz refers to... so we're kinda stuck.

TEG (ThatEngineGuy) had some decent rule-of-thumb SFC numbers for modern gas turbine engines in terms of lbs gas / lb thrust / per minute (or per hour). Multiplying by thrust numbers for the F135 seemed to give hourly burn rates comparable to Spurts numbers. FWIW.
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viper12

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Unread post29 Jul 2019, 04:26

I'll use the numbers posted there : https://www.hs.fi/kotimaa/art-200000613 ... 1bd4a3b646

There's 11,089kg/h for mil thrust, 10.2kg/s for afterburner. The new KPP has been given as 63 seconds for accelerating from Mach 0.8 to Mach 1.2. Assuming it's at 30,000ft, Mach 1.2 equals 707 knots TAS.

Let's suppose that after that acceleration, you can maintain Mach 1.2 with mil thrust or barely more than that, so the 11,089kg/h =~ 24,450lb/h fuel consumption would be a good approximation. The number that floats around for normal cruise is some 5,000lb/h, and it's probably around Mach 0.9.

With a very napkinesque assumption, let's say the acceleration between 0.9 and 1.2 Mach is constant (and is the same as between Mach 0.8 and Mach 1.2), so it's 3.74 knots TAS per second ; integrate that between Mach 0.9 and Mach 1.2, and you've covered 29,230 knots-second, or 8.12nm, in those 47.25 seconds. The fuel needed for that acceleration, assuming it's full afterburner, would be around 1,063lb.

In comparison, staying at Mach 0.9 would have covered 6.96nm in that time, and burned 65.6lb of fuel. So you flew an extra 1.16nm, pretty much negligible for the rest of the calculations. And roughly an extra 1,000lb of fuel for the acceleration over staying at Mach 0.9.

At Mach 1.2, you got k1 = 707/24,450 = 0.0289nm/lb of specific range, while you got k2 = (3/4)*707/5,000 = 0.106nm/lb at Mach 0.9. So the question is when do we have x/k1 + 1,000 = (x+600)/k2, as that's the condition for equal total fuel burn for accelerating and then sustaining Mach 1.2, while covering an extra 600nm at Mach 0.9.

So you got x*k2 = (x+600)*k1 - 1,000*k2*k1 => x*(k2-k1) = 600*k1 - 1,000*k2*k1 => x = [600*k1 - 1,000*k2*k1]/(k2-k1) = [17.34 - 3.063]/0.0771 =~ 185nm.

So it means you that if you accelerate from Mach 0.9 to Mach 1.2 (about 8nm), then fly at that speed for 185nm, you've burned the same quantity of fuel as flying some 792nm at Mach 0.9.

Now one important thing to note ; the thing used around 7,464lb of fuel, so you probably don't want to fly at that speed for too long considering the reserves.
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doge

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Unread post29 Jul 2019, 23:06

spazsinbad wrote:

Thank you very much! :notworthy: I'm extremely happy you said that so about me. :thanks:
"F-35 is not F-22".I think so, too. I tend to have excessive expectations for the F-35 due to my strong desires or aspirations. My bad point. :doh:

steve2267 wrote:

Thank you very much for touching my idea! :notworthy:
Even it's a mini-afterburner will consume lot of fuel, I think so too. The words "Afterburner is Wasteful fuel" or "Afterburner is dripping of fuel" I see a lot on the web.

viper12 wrote:

Thank you very much for doing complicated calculations! :notworthy:
Calculation is a difficult area for me. :doh: However, I understand that I consume a lot of fuel by that. After all, afterburner seems better not to use for a long time.
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Unread post30 Jul 2019, 00:02

It's not just afterburner that gulps fuel ; with the assumptions made above, the specific range at Mach 0.9 is about 3.7 times better than at Mach 1.2, which means you burn 3.7 times less fuel to cover a given distance. Fuel consumption between idle (or nearly) and military power has a pretty big gap apparently on the F-35.

It's basically like switching from a light hybrid car to a sports car in terms of worsening the fuel consumption, and as the old saying goes, there's never too much fuel on a plane...unless it's on fire. :mrgreen:
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wrightwing

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Unread post30 Jul 2019, 00:52

viper12 wrote:It's not just afterburner that gulps fuel ; with the assumptions made above, the specific range at Mach 0.9 is about 3.7 times better than at Mach 1.2, which means you burn 3.7 times less fuel to cover a given distance. Fuel consumption between idle (or nearly) and military power has a pretty big gap apparently on the F-35.

It's basically like switching from a light hybrid car to a sports car in terms of worsening the fuel consumption, and as the old saying goes, there's never too much fuel on a plane...unless it's on fire. :mrgreen:

The standard cruise speed for the F-35 is between M.95 and .97. It doesn't require AB to maintain M1.2, though. We'd need to calculate fuel burn at MIL power.
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Unread post30 Jul 2019, 01:20

“The standard cruise speed for the F-35 is between M.95 and .97.”

What does “standard cruise speed” mean? Where does that term come from? When is that speed used (in a mission profile) and for what purpose?

“It doesn't require AB to maintain M1.2...”

Not according to the people who fly it. There’s a previous thread on this.
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Unread post30 Jul 2019, 09:09

quicksilver wrote:“The standard cruise speed for the F-35 is between M.95 and .97.”

What does “standard cruise speed” mean? Where does that term come from? When is that speed used (in a mission profile) and for what purpose?


Where does cruise speed come from, and what is it's purpose?
“It doesn't require AB to maintain M1.2...”

Not according to the people who fly it. There’s a previous thread on this.

Actually, it is according to the people who fly it.
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Unread post30 Jul 2019, 11:37

Still waiting...

Tell us where ‘standard cruise speed’ comes from, and who (not Steve O’Bryan some years ago who was wrong or misquoted) said the jet does 1.2 in mil.

We can pull out the old thread if you’d like...or I can give you the answer...

At altitude, F-35 requires afterburner (or a dive in mil) to achieve supersonic flight. If one ‘unloads’ the jet (a routine practice in fighter aircraft) it will do so much more quickly; the downside is one does not always have some altitude to give away to do so). Once you take the jet out of AB, it will start to decelerate to a subsonic number. The good news is that the decel rate is fairly slow comparatively speaking. In some jets, in some configurations, a similar action (pulling the throttle to mil from ab) is like using the speed brake.

Back to ‘standard cruise speed’; where did you get that? Only ‘standard cruise speed(s)’ I ever learned were ‘max range’ and ‘max endurance’ — everything else was a circumstantial expedient. Where did your claim wrt F-35 ‘standard cruise speed’ come from?
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Unread post30 Jul 2019, 13:39

“Where did your claim wrt F-35 ‘standard cruise speed’ come from?”

I’m guessing you read it on the internet someplace (not named f-16.net).

Apart from the fact that my F-35-flying neighbors and former colleagues have told me the reality (...years ago), for most fighter aircraft, the general problem with ‘cruising’ in that (claimed) Mach number range (.95-.97) would be that it puts the jet in the middle of drag divergence — where small increases in Mach number above ‘max range’ require significantly disproportionate increases in fuel flow. Therefore ‘cruising’ (sustained flight) in that Mach range — while possible — is circumstantial, not ‘standard’. In common terms, you’re using a s___load of fuel to go just a tiny bit faster.
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steve2267

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Unread post30 Jul 2019, 15:49

Hey QS, while this will vary with altitude and conditions, have your former colleagues driving Lightnings stated how fast the jet will true out at, at max Mil power setting?

More of a curiosity question than anything. And, of course, may be privileged info...
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Unread post30 Jul 2019, 16:45

steve2267 wrote:Hey QS, while this will vary with altitude and conditions, have your former colleagues driving Lightnings stated how fast the jet will true out at, at max Mil power setting?

More of a curiosity question than anything. And, of course, may be privileged info...

"In full war equipment operates F-35 effortlessly 10,000 to 15,000 feet higher than our F-16 can, without using afterburner. The speed in 'cruises' is without further 50 to 80 knots higher. " I think it was Dobly that said that. I only have it credited as "Norwegian test pilot"
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