F-35 Lightning II vs Dassault Rafale

The F-35 compared with other modern jets.
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Raptor_One

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Unread post11 Aug 2006, 23:32

dwightlooi wrote:The only aircraft in the world (known to the public at least) that maintained high supersonic speeds throughout its flight profile through continuous use of afterburner was the A-12/SR-71. Again though, max AB was used to get up to cruising speed and then throttled back to some lower AB stage.

Actually, it is the opposite. the SR-71 is practically in continuous AB use during cruising. The J58 engine is not a typical turbojet or turbofan. The "turbo" part of the engine is basically to enable the aircraft to take off, fly to altitude and.. ahem... refuel with a tanker. The SR-71 then lights is AB and get past Mach 2.5. At around this speed, the airflow to the engine core is basically shut off while ram air is compressed by the intake, bypasses the core and introduced straight to the afterburner can where it is mixed and burned with fuel. In otherwords, once the SR-71 gets up to speed, the engine effectively becomes a RAM JET and the afterburner can is continuously in use.


Something tells me you didn't read my whole post. I'm quite sure I said exactly what you just typed. I'll go check and get back to you though. :)
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Raptor_One

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Unread post11 Aug 2006, 23:42

Raptor_One wrote:The only aircraft in the world (known to the public at least) that maintained high supersonic speeds throughout its flight profile through continuous use of afterburner was the A-12/SR-71. Again though, max AB was used to get up to cruising speed and then throttled back to some lower AB stage. The only time max AB would be engaged during the flight profile was (I think?) to gain a bit more altitude and airspeed to avoid being intercepted by a SAM or enemy fighter interceptor. The SR certainly didn't cruise at max AB. But it could curise relatively efficiently in AB due to its unique engine/inlet design which bypassed all the moving parts in the turbojet's core past a certain Mach number. So it was basically a ram jet... not really fair. :)


Ahhh... yes. Here we go Dwight. I'm not sure why you selectively quoted only a portion of the above paragraph. I clearly said that the SR-71 was the only plane to use AB continuously throughout its mission profile and that above a certain Mach number the thing essentially becomes a ramjet-powered aircraft, bypassing the engine core entirely. Perhaps you misread the part where I said that I don't think maximum AB was used throughout the entire flight. I remember reading (in Ben Rich's Skunkworks I think) that maximum AB was used to get up to crusing speed and to possibly climb higher and go a little bit faster in case of SAM or fighter-interceptor threat. You don't have it out for me, do you?

One more thing... throttling back to a lower AB stage should not be interpretted as turning off the afterburner. I assume the SR-71 had a number of AB "stages"... maybe more than 5 like an F-15 or F-16 has.
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dwightlooi

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Unread post11 Aug 2006, 23:49

I revised the post... go back and look at the updated one
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Raptor_One

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Unread post12 Aug 2006, 00:17

dwightlooi wrote:I revised the post... go back and look at the updated one


Yeah, but that's what I said, basically. I said it becomes a ram jet and thus it's not really a fair comparison. Hence the "not fair" comment. Ben Rich himself wrote in Skunkworks that the A-12/SR-71 was the only aircraft to continuously use its AB in flight (regardless of whether the core flow was bypassed or not) to effectively perform its mission. He referred to it as afterburner and I'm not sure what else you would call it. The combustion still happens where it happens when the core flow isn't bypassed, so the afterburner is still being used. You wouldn't call it the burner (in a semi-technical sense) because that would too easily be confused with the combustor. Anyway, I don't believe the SR-71 is a typical ram jet. Doesn't the combustion process generally take place much earlier (in terms of distance from the inlet) in a ramjet? You don't necessarily see flame shooting out the back of a ramjet, or am I wrong? It's been a while since I studied ramjet propulsion.
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LordOfBunnies

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Unread post12 Aug 2006, 01:00

You are correct, usually the combustion for a ramject occurs far enough upstream that the flames won't shoot out the back. Another thing to think about, most of the pictures of the SR-71 are below design condition. Thus the backpressure changes and you'll get Mach disks from... um Underexpanded? (I'm not exactly sure at this time which it is, I'm out of school for the moment and don't care) flow. Now when you get up to altitude, I bet design condition prevails and you get perfectly expanded flow. Also, the combustion chamber of the SR-71 may not have been as long as it needed to be to act like a normal ramjet because of weight considerations. The engine was already big and heavy and needing to make a duel cycle or combined cycle engine means even more weight. Now your payload is two peole and a couple hundred pounds of camera equipment. So not much there. Too bad G didn't change much.
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Raptor_One

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Unread post12 Aug 2006, 01:56

I think it's underexpanded. Isn't overexpanded flow what you see from, say, the solid rocket boosters on the space shuttle just before they burn out and are jetisonned? I'm not exactly sure what under/over-expansion has to do with the visibility of the afterburner plume though. The shock disks, diamonds, or whatever you call them in the AB plume certainly make the plume more visable, but you can still see it if the lighting conditions are correct when it's perfectly expanded to atmospheric pressure. Anyway... good discussion LOB. Unless you're talking about a propulsion specialist, you probably know more now about propulsion than most practicing aerospace engineers. I would say that propulsion concepts are one of the first things to leave one's mind. You'd have to be a genius to remember how to perform a full engine cycle calculation years after taking a propulsion course. Hehehe. You did get open book/open notes for your propulsion course exams, right? That was standard practice at U of Michigan. :)
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Unread post12 Aug 2006, 02:33

So uh yeah, I'm actually going to become a propulsion specialist :D.

Anyway, I thought of some more stuff. What causes normal jet exhaust to be less visible? Well you're sending it through turbines which cools and drops the pressure. That will change the spectrum that the exhaust puts out changing it possibly out of the visible spectrum. Now on a ramjet you've got nothing to change the temperature, thus more energy and a different spectrum. Wow, this is good for pulling out of my @$$. Anyway, you've got just your flame temp and the same pressure you combusted at. Speaking of which, how do you get higher pressure in a ramjet? Then you send it through a CD nozzle (which requires some higher pressures is the reason I say anything) which gives you lots of thrusties. The SFCs of ramjets are horrendous if I remember my homework but they work up to about Mach 7 or something. Scramjets are good above about Mach 5. Morphing engine technology, I may look at it as my master's thesis if I get the chance.

Open book exams? Hell yeah, when you have 8 different tau values in an equation and you start dealing with efficiencies it's just mean to make you remember that.
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toan

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Unread post12 Aug 2006, 02:57

http://new.isoshop.com/dae/dae/gauche/s ... fox3_8.pdf

"The Rafale is ideal for the job," stresses one of the two duty pilots. "It can climb to 40,000 feet in under two minutes and accelerate very rapidly to supersonic speed. More significantly, it can supercruise in dry power, even with four missiles and a belly drop tank (1,250L) ............"
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Unread post12 Aug 2006, 03:14

You can actually measure thrust output by looking at the color of the exhaust plume given you know enough about the properties of the exhaust plume (which you generally should). You probably saw the same program on the History Channel, but that's how they indirectly measured the thrust output of that crazy nuclear-powered cruise missile engine in the late 1950s (Project Pluto and the Tory-IIA and Tory-IIC engines). There was no sensor rake that could withstand the conditions in the exhaust plume. :) I'm not saying that thrust has a color, but exhaust gas temperature was obviously the missing variable in their equations and they determined it from the color of the exhaust gasses. If you read more about that project, you begin to realize how practically insane some of our governments proposed weapons of mass destruction really were. That cruise missile was truly a doomsday device making ICBMs look like bunker busters. Just flying that thing over a populated area with the reactor turned on would fry the hell out of everyone. Sick stuff. Plus the thing had practically unlimited range and could loiter around for months on end waiting to strike. Very, very bad idea.
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toan

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Unread post12 Aug 2006, 03:20

Unlike Eurofighter Tranch 3, the possibility of production of Rafale F4 after 2012 is near 100% ~ Up to now, French air-force and navy only buy 120 Rafale (F1 to F3) in total (This number may be reduced to 112 finally in order to provide the fund for the development of new equipments for Rafale F4, such as RBE-2 AESA radar, FSO upgrading, NG MAWs and so on.....) , and it should be obvious that the air-force requirement of a country like France can't be supported by just 112~120 fighters.

(As for UK, even the project of Eurofighter Tranch 3 is cancelled finally, it has procured 144 EF-2000, Tranch I&II + 138 F-35B...........)
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skrip00

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Unread post12 Aug 2006, 05:11

Yes, the French did sacrifice airframes to secure more funding for the Rafale's future growth.

At this moment though... the aircraft isnt all that great in terms of overall capability.

The Typhoon and Rafale are like the PlayStation 3. You're buying future capability... jk. :wink:
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Unread post12 Aug 2006, 06:42

Skrip, that's actually not bad. If you can get the damn thing to work the way you want it too... it'll be bad @ss. But if you can't, you've got junk sitting around collecting dust. Actually the Tiffy looks to be pretty good. The French, I believe, still need a better fighter platform for fleet defense. The Rafale seems to be a great striker with massive weapons loads possible. It's also always been designed to be a striker so it should have better striking capability through its life (as it constantly develops) than the Tiffy (which is having to play catch up). The Tiffy will probably eat the Rafale for lunch in A2A. What do the recent competitions say about the strike capabilities of the different platforms (that's a real question not asking rhetorically or anything)?
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skrip00

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Unread post12 Aug 2006, 07:09

The Tiffy/Rafale IMO is basically everything too late. While I understand a work in progress... The Typhoon and Rafale both have alot of issues that have they need to work out. Alot.

Unlike teenagers, modern nations really cant wait for overly expensive future "potential". Hence why in alot of cases, a heavily upgraded new-build F-15E tends to be a way better deal.

The French, I believe, still need a better fighter platform for fleet defense

What Fleet? They barely have a carrier. Barely.
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Corsair1963

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Unread post14 Aug 2006, 00:22

skrip00 wrote:The Tiffy/Rafale IMO is basically everything too late. While I understand a work in progress... The Typhoon and Rafale both have alot of issues that have they need to work out. Alot.

Unlike teenagers, modern nations really cant wait for overly expensive future "potential". Hence why in alot of cases, a heavily upgraded new-build F-15E tends to be a way better deal.

The French, I believe, still need a better fighter platform for fleet defense

What Fleet? They barely have a carrier. Barely.



I think they real question is will the later models of the Rafale and/or Typhoon be superior to the forthcoming F-35B & C? Personally, I doubt that and both would be better off to secure as many sales as it can now. Because they may not be there in the future............. :roll:
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skrip00

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Unread post14 Aug 2006, 03:54

The F-35 will have stealth and alot of room for future technology. No matter how you cut it... thats an advantage.
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