747400sp
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Why A F-18 E/F Can Not Supercruise?

Sat Aug 07, 2010 9:48 am

The SAAB Gripen 39 N/G which is powered by one GE F-414, was able to supercruise at mach 1.2. The F-18 E/F ( Rhino) has two of these engines, and it can barely brake the sound barrier. Now what the problem with the Rhino, it has good engines, so the bird just be poorly built?
 
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par13del
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RE: Why A F-18 E/F Can Not Supercruise?

Sat Aug 07, 2010 1:00 pm

Bird was built to be an all in one a/c not a fighter a/c, it is the reverse of the F-16 or F-22 which are designed fighters being pressed into the attack role. So no, the a/c was not poorly built, it was designed primarily for the attack role, so the frame does not help the engines in any way to achieve high mach numbers.
 
spudh
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RE: Why A F-18 E/F Can Not Supercruise?

Mon Aug 09, 2010 10:25 pm

The outward cant of the weapon pylons cant be doing much for drag characteristics!!
I can't remember if this was a fix for weapon seperation or wing flutter but I do remember that supersonic performance was not high on the priority list and degradation of this performance aspect was readily accepted when the fix was put forward.
IIRC this reasoning was backed up emphatically by combat statistics from Vietnam where fighters/attack aircraft went supersonic far less often than was anticipated or than that they had been designed for.

My own gut feeling is that speed is one thing you can't have too much of in a combat aircraft but the trend is the other way
 
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par13del
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RE: Why A F-18 E/F Can Not Supercruise?

Mon Aug 09, 2010 10:40 pm

Quoting spudh (Reply 2):
I can't remember if this was a fix for weapon seperation or wing flutter

Im my memory is correct it was first wing flutter fixes, the weapon seperation was affected resulting in additional fixes. I think in general the Navy was in a state where one a/c was already cancelled and the cost of a major redisgn of the wing to correct the wing flutter would have delayed tha a/c entry into serrvice as well as increase the cost, so the compromise was accepted.
Once done I'm sure they could find figures to justify the fact that speed was not the end all to everything. 
 
BMI727
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RE: Why A F-18 E/F Can Not Supercruise?

Mon Aug 09, 2010 11:23 pm

Quoting par13del (Reply 3):
I think in general the Navy was in a state where one a/c was already cancelled

That's their problem. They were too impatient with one plane and then forced compromises on the next one. Not a particularly good way of doing business.
Why do Aerospace Engineering students have to turn things in on time?
 
SP90
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RE: Why A F-18 E/F Can Not Supercruise?

Tue Aug 10, 2010 12:44 am

If Wikipedia is to be believed the GE F-414 on the Saab produces 20% more thrust than the version used on the F-18E/F.

The extra structural weight of the F-18 due to carrier operations also can't help. I wonder if they flew the F-18E with just internal fuel and a clean wing if it can achieve supercruise.

http://en.wikipedia.org/wiki/JAS_39_Gripen
 
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cpd
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RE: Why A F-18 E/F Can Not Supercruise?

Tue Aug 10, 2010 2:27 am

Quoting spudh (Reply 2):
My own gut feeling is that speed is one thing you can't have too much of in a combat aircraft but the trend is the other way

Remember a quote from Maj. Brian Shul, USAF - in his book Sled Driver:

"In thrust, we trust".

Referring to the powerful and seemingly tough engines on the SR-71, and that effortless speed the thing had. Having a really fast plane seems to be a big benefit.

[Edited 2010-08-09 19:50:47]
 
spudh
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RE: Why A F-18 E/F Can Not Supercruise?

Tue Aug 10, 2010 11:20 am

Quoting SP90 (Reply 5):
The extra structural weight of the F-18 due to carrier operations also can't help. I wonder if they flew the F-18E with just internal fuel and a clean wing if it can achieve supercruise.

BTW, not alone can the F18E not supercruise, it can't even go supersonic clean at low level so its got aerodynamic 'issues'.

F14B/D could supercruise but I'm not sure what configuration. At the very minimum that would have been with 4 sparrow missiles but it could have been with much more.

I'm not sure what the tipping point for ability to supercruise is. The F14A with PW TF414 at 10,800 each (max continuous thrust) could not supercruise but the B with GE F110 at 14,700 each (max continuous thrust) could. The F14 is a significantly lower drag airframe than the F18 but also heavier. There is also the issue of inlet duct configuration. The F14 gains a significant boost from the ram effect of its inlet configuration which I doubt the F18 benefits from.
I don't have the fgures for the Gripen but it would be interesting to do some Thrust/weight/wing loading (as an indicator for drag) ratios for a few of the later supercruisers.

Anyone know if any variants of the F15 or F16 can supercruise?
 
UH60FtRucker
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RE: Why A F-18 E/F Can Not Supercruise?

Tue Aug 10, 2010 3:37 pm

Quoting 747400sp (Thread starter):
and it can barely brake the sound barrier.

Well... maybe that's the problem??? Every time it approaches the sound barrier, it hits the brakes! hahaha

Quoting 747400sp (Thread starter):
so the bird just be poorly built?

It be a mystery. Arh!
Your men have to follow your orders. They don't have to go to your funeral.
 
dragon6172
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RE: Why A F-18 E/F Can Not Supercruise?

Tue Aug 10, 2010 7:45 pm

Quoting UH60FtRucker (Reply 8):
It be a mystery. Arh!

Geez.... I thought "Talk Like a Pirate Day" wasn't for a few more months?
Phrogs Phorever
 
wvsuperhornet
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 09, 2010 8:41 am

Quoting spudh (Reply 7):
F14B/D could supercruise but I'm not sure what configuration. At the very minimum that would have been with 4 sparrow missiles but it could have been with much more.

None the F-14 could not supercruise in any varient. The F-22 was the first US and to my knowledge the first aircraft to be design to supercruise. The Euro-fighter in the later varients I believe can supercruise. If A gripen did supercruise it had to do it without any weapons attached, which in a battle situation does you absoloutly no good. The Superhornet was never designed to be a supercruise aircraft. Just a fill the void aircraft until the F-35 came in production. The F-14's were getting old and beaten to death with the carrie landings.

Quoting spudh (Reply 7):
Anyone know if any variants of the F15 or F16 can supercruise?

None although with the f119 engines if put in the newest varients of the F-15 they could probably achieve supercruise the F-16 wont.
 
fridgmus
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 09, 2010 11:11 am

Quoting cpd (Reply 6):
Remember a quote from Maj. Brian Shul, USAF - in his book Sled Driver:

"In thrust, we trust".

If I recall correctly, "In Thrust We Trust" was stitched on a patch that was from the J-58 engine shop.

If I'm wrong, someone please correct me.

Thanks,

F
The Lockheed Super Constellation, the REAL Queen of the Skies!
 
nomadd22
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 09, 2010 11:32 am

Quoting wvsuperhornet (Reply 10):
The F-22 was the first US and to my knowledge the first aircraft to be design to supercruise.

You might get some B-1B argument there.
Anon
 
Shmertspionem
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 09, 2010 11:36 am

Actually you cant just gauge a fighters effectiveness by super-cruise or lack thereof.

an aircraft's ability to supercruise depends on TW ratio theoretically 1 or >1 means it can super cruise -
The gripen with the 18k lbf engines already had a TW ratio of .97 very close to 1 - the addition of 22klbf engines has obviously put that in the >1 category
The Gripen was built around the 18k thrust and no supercruise - the F-18E was designed from the start around the 22k version.

The f-18E with the 22k thrust version had a TW ratio of .93 so no supercruise. But There's no reason that more powerful engines cant be fixed in later.

here's the latest evaluation from ausairpower and Carlo Kopp

for man who is a dead set anti F-18E/F activist - his epiphany is a tribute to the F-18 - especially where he says that the F-18 will be a formidable opponent even against the Su-27/30 family.

He still opposes the "decision" to buy a stop gap filler - but then the analysis is excellent and apparently any attempt to use this article as an "endorsement" of the F-18E/F is a

Quote:
intentional and mischievous misrepresentation.
http://www.ausairpower.net/SuperBug.html
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moriarty
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 09, 2010 2:02 pm

Sidenote: I believe super cruise is part of the design goals of the later version of Gripen, called Gripen NG. It has done Mach 1.2 without afterburners during trials (as mentioned in first post). But I am not sure in what configuration though (but a quote from Saab themselves indicates they have or intend to perform super cruise with loadout: "Today’s supercruise flight is part of the ongoing high speed supersonic testing that will include supersonic flights, with different load alternatives. " - source )
As for older versioins of Gripen I don't know. Heard rumors about super cruise there too, under certain circumstances. Not sure they are true though.

[Edited 2010-09-09 07:05:20]
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spudh
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 09, 2010 9:39 pm

Quoting wvsuperhornet (Reply 10):
None the F-14 could not supercruise in any varient.

To the best of my knowledge the GE engined F14's could supercruise, albeit at Mach 1.05. What I don't know is if that was true supercruising on military power alone or if it had to use A/B to break the sound barrier but was then able to maintain supersonic flight without burner. Also I don't know if they were still able to do it after they fixed the inlet ramps in a single position. But they did indeed supercruise.

Quoting wvsuperhornet (Reply 10):
The F-22 was the first US and to my knowledge the first aircraft to be design to supercruise.

I believe it was the first fighter designed with that as a requirement in the RFP. The F-22 is a true supercuiser, going at over mach 1.4 without burner as against the Eurofighter, Rafale and F14 which just break the sound barrier as a happy consequence of suitable aerodynamic qualities.

Quoting nomadd22 (Reply 12):
You might get some B-1B argument there.

I think this is where the F14's ability came from. The B1 was definitely designed for at least sustained high subsonic speed maybe even supersonic. The GE F110 engines would have been specificallly designed for that regime so when they were shoved into the relatively lithe Tomcat ( think this is about the only context in which an F14 can considerd light ) with its low drag airframe they were ripe for some serious speed.

Quoting Shmertspionem (Reply 13):
an aircraft's ability to supercruise depends on TW ratio theoretically 1 or >1 means it can super cruise -

I think there is a whole lot more to it than that. If that was true the F15 would have been supercruising since 1973 and an F100 would have been firmly subsonic even in afterburner. I would say that drag has a whole lot more to do with it than T/W ratio, particularly transonic drag. Thats going to be the defining factor, the ability of the available power to overcome the extra drag as the aircraft approaches the speed of sound. You will notice that the gen 4/4.5 aircraft that claim to have some supercuise ability all have highly swept wings = low transonic drag.
And then you have to consider the design of the engine. The F120/F119 engines were again specifically designed for sustained supercruise at high mach no.s. IIRC its got a lot to do with the design of the convergent/divergent nozzle and the management of airflow through the engine as much as shear power.

And that's the simple truth about the Superhornet, its jack of all trades design requirements and their subsequent 'fixes' have reulted in a high drag airframe in fighter terms. So to borrow an illustrious phrase from another era that heralded its predecessor, 'all the thrust in christendom won't make a supercruising fighter out of that airplane'
 
HaveBlue
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 09, 2010 10:14 pm

Quoting wvsuperhornet (Reply 10):
The F-22 was the first US and to my knowledge the first aircraft to be design to supercruise.

I believe the SR-71 and Concorde maintained supersonic flight without afterburners, as well as the XB-70. And even if they used burners to 'punch thru' then relied on military power its still impressive as they were doing between Mach 2.2 (Concorde) and Mach 3+ (SR, XB) for a LONG time.

Add to that that I've talked to an ex Phantom driver who did military maintenance test flights when F-4's where returned to service after depot/maint. and he laid out the entire profile of those flights... which included going supersonice without burner. And he was positive about that.

And I agree with Spudh completely, its not about 1:1 ratio or better for supercruise as several fighters have had that thrust to weight ratio starting with the F-15 and on, including obviously the very subsonic Harrier. It is about the disproportionate amount of drag as you go transonic to supersonic and also with the inlet design. Just having a better than 1 to 1 is not giving you supercruise.
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Shmertspionem
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RE: Why A F-18 E/F Can Not Supercruise?

Fri Sep 10, 2010 5:12 am

Quoting spudh (Reply 15):
I think there is a whole lot more to it than that.

Hence my use of "theoretically" and not "practically" to qualify >1 thrust

The actual physics of it is quite complex - especially given that one of the critical components is the shaping of the air intake duct which needs to ensure that air inflow remain SUBsonic at all times.

design speed limitation is another factor - you could shove a pair of GE-90-115 engines on a 737 and i doubt it would ever manage to take off - let alone go supersonic

But the fact of the matter is that as far as the F-18 is concerned the crux of the matter is thrust. As a design it can and does go supersonic when "wet" thrust is used. So theoretically being supersonic capable.......... a thrust increase should be able to super-cruise it.....

As for intake geometry - THEORETICALLY - the F-18 is also suited for this given its more pronounced engine shielding (hence natural S ducting) and the same radar blocker insert as the Sukhoi T-50. So if the T-50 can super-cruise with virtually non existent shielding and air intake speed reduction - so can the F-18.

Quoting spudh (Reply 15):
If that was true the F15 would have been supercruising since 1973
Quoting spudh (Reply 15):
You will notice that the gen 4/4.5 aircraft that claim to have some super-cruise ability all have highly swept wings = low transonic drag.
Quoting HaveBlue (Reply 16):
It is about the disproportionate amount of drag as you go transonic to supersonic

WRT the wing - i dunno if highly swept wings are essential to supercruise - Do they make things easier ? yes undoubtedly since highly swept wing enable higher speeds with lower drag - but outside of that basic physic - i don't think they actually enable or the lack thereof - disable super-cruise.

by your own example - since the F-15 has highly swept wing for low trans-sonic drag - why isnt it able to supercruise?



Quoting Moriarty (Reply 14):
Heard rumours about super cruise there too, under certain circumstances. Not sure they are true though.

yes I think this is correct - I read about it in AFM - basically gripens were super-cruising without realising it- and the SweAF realised this only after local residents complained of sonic boom.

Quoting HaveBlue (Reply 16):
I believe the SR-71 and Concorde maintained supersonic flight without afterburners, as well as the XB-70. And even if they used burners to 'punch thru' then relied on military power its still impressive as they were doing between Mach 2.2 (Concorde) and Mach 3+ (SR, XB) for a LONG time.

The first super-cruise was the English Electric lightning - way back in 1954.


But i think we're all wrong and the F-15 is the proof

I said TW has to greater than 1 - the F-15 does and still can't super-cruise
Spudh noted highly swept wings - the F-15 has those and still can't super-cruise
Haveblue noted low transonic drag - The F-15's is visibly lower than the Su-35BM (which can super-cruise)
everybody here noted air intake shaping/slowing - the F-15 has that and still cant super-cruise.


This is turning out the be like the six wise men of Hindustan who went to see the elephant.


There were six men of Hindustan,
to learning much inclined,
Who went to see an elephant,
though all of them were blind,
That each by observation
might satisfy his mind.

The first approached the elephant,
and happening to fall
Against his broad and sturdy side,
at once began to bawl,
"This mystery of an elephant
is very like a wall."

The second, feeling of the tusk,
cried, "Ho, what have we here,
So very round and smooth and sharp?
To me 'tis mighty clear,
This wonder of an elephant
is very like a spear."

The third approached the elephant,
and happening to take
The squirming trunk within his hands,
thus boldly up and spake,
"I see," quoth he,
"the elephant is very like a snake."

The fourth reached out an eager hand,
and felt above the knee,
"What this most wondrous beast
is like is very plain" said he,
"'Tis clear enough the elephant
is very like a tree."

The fifth who chanced to touch the ear
said, "E'en the blindest man
Can tell what this resembles most;
deny the fact who can;
This marvel of an elephant
is very like a fan."

The sixth no sooner had begun
about the beast to grope,
Than seizing on the swinging tail
that fell within his scope;
"I see," said he, "the elephant
is very like a rope."

So six blind men of Hindustan
disputed loud and long,
Each in his own opinion
exceeding stiff and strong;
Though each was partly in the right,
they all were in the wrong!
Vi veri universum vivus vici
 
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747classic
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RE: Why A F-18 E/F Can Not Supercruise?

Fri Sep 10, 2010 9:25 am

In following article you can find a comparison of the F-14 D Super Tomcat and the F/A -18 E/F Super Hornet.

Interesting for this thread is the detailed description of the aerodynamic shortfall of the Super Hornet :

http://findarticles.com/p/articles/m...0202/ai_n9030925/?tag=content;col1
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
nomadd22
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RE: Why A F-18 E/F Can Not Supercruise?

Fri Sep 10, 2010 11:30 am

Quoting spudh (Reply 15):
I believe it was the first fighter designed with that as a requirement in the RFP. The F-22 is a true supercuiser, going at over mach 1.4 without burner as against the Eurofighter, Rafale and F14 which just break the sound barrier as a happy consequence of suitable aerodynamic qualities.

Most speculation about the F-22 was mach 1.6 supercruise, but when testing was done, they claimed it would hold mach 1.78. There was some discussion as to whether they were that far off in their estimates or iintentionally pushed low numbers. I never did see fuel burn at that speed, or is it was done with external tanks.
Anon
 
Max Q
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RE: Why A F-18 E/F Can Not Supercruise?

Wed Sep 15, 2010 6:29 am

Quoting HaveBlue (Reply 16):


I believe the SR-71 and Concorde maintained supersonic flight without afterburners, as well as the XB-70. And even if they used burners to 'punch thru' then relied on military power its still impressive as they were doing between Mach 2.2 (Concorde) and Mach 3+ (SR, XB) for a LONG time.

Concorde would use Afterburners to get through Mach one and accelerate up to Mach one point seven, they were then turned off for the rest of the flight during which she supercruised at M2 plus and up to 60,000 feet.
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HaveBlue
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RE: Why A F-18 E/F Can Not Supercruise?

Wed Sep 15, 2010 5:10 pm

Quoting Max Q (Reply 20):
Concorde would use Afterburners to get through Mach one and accelerate up to Mach one point seven, they were then turned off for the rest of the flight during which she supercruised at M2 plus and up to 60,000 feet.

Thank you for clarifying, I thought it was something like that but wasn't sure.  
Here Here for Severe Clear!
 
BMI727
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 16, 2010 1:12 am

Quoting Max Q (Reply 20):
Concorde would use Afterburners to get through Mach one and accelerate up to Mach one point seven,

I believe that the Concorde could break the sound barrier and accelerate without afterburners. The reason they used them was that the extra fuel used by the reheat outweighed the additional fuel burn from spending more time suffering from wave drag in the transonic region.
Why do Aerospace Engineering students have to turn things in on time?
 
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cpd
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 16, 2010 5:45 am

Quoting BMI727 (Reply 22):
I believe that the Concorde could break the sound barrier and accelerate without afterburners.

That's indeed right - from memory, if it serves me right.

It was faster and more efficient to blast through the M1.0 to M1.3 high drag region with reheat. At M1.7 checklist point, they were switched off and from there on it climbed (using the mode MAX CLIMB) steadily on full 'dry' power up to the **corner point at M2.0 / 49,000ft. The plane then steadied at M2.01 and once steadied - MAX CRUISE would engage automatically. As speed started to increase - the plane would climb steadily to maintain M2.0. If it gained speed that the climb couldn't control, then the auto throttle MACH HOLD would engage automatically until the speed was stabilised. If the speed dropped below M2.0 - then the plane would pitch down to regain the speed, with the general trend of gradually drifting higher as the fuel load decreased during flight.

As you can see, Concorde was very good at maintaining very high speeds across long distances.

**Corner point: Meaning the transition between the climb portion of the flight and the cruise-climb section of the flight. Probably also talking about the transition from MAX CLIMB to MAX CRUISE mode, and also the change of engine rating setting from climb to cruise from memory. (an electronic setting that only has effect to slightly reduce power in extremely cold atmospheres).

[Edited 2010-09-15 22:49:47]
 
474218
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 16, 2010 4:30 pm

All you have to do is go back to "how airplanes fly".

Thrust overcomes drag.

So the FA-18E/F engines do not produce enough thrust to over come the amount of drag produced by the airframe.
 
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Zkpilot
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RE: Why A F-18 E/F Can Not Supercruise?

Thu Sep 23, 2010 7:32 pm

Quoting 747classic (Reply 18):
In following article you can find a comparison of the F-14 D Super Tomcat and the F/A -18 E/F Super Hornet.

Interesting for this thread is the detailed description of the aerodynamic shortfall of the Super Hornet :

http://findarticles.com/p/articles/m...;col1

Excellent article! thanks for posting!
I had never heard of any proposals or mentioning of canards for the F-14... That would have been interesting. I know that Grumman themselves offered to refit/new build F-14s with thrust vectoring and increased power with less consumption engines.
I was saddened by the retirement of the F-14... It was a GREAT aircraft. With a modernization program (to improve servicability and reduce mx requirements plus a few other tricks the 'cat could have lived for another 15years as the frontline aircraft of the USN...by which time the likes of the F-35 would have been established.
56 types. 38 countries. 24 airlines.
 
sovietjet
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RE: Why A F-18 E/F Can Not Supercruise?

Mon Sep 27, 2010 4:31 am

The most obvious difference is that the leading edge sweep angle on the hornet and gripen are quite different. This has a big effect on the drag.
 
wvsuperhornet
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RE: Why A F-18 E/F Can Not Supercruise?

Fri Oct 01, 2010 6:37 am

Quoting HaveBlue (Reply 16):
I believe the SR-71 and Concorde maintained supersonic flight without afterburners, as well as the XB-70. And even if they used burners to 'punch thru' then relied on military power its still impressive as they were doing between Mach 2.2 (Concorde) and Mach 3+ (SR, XB) for a LONG time.

Very true I forgot about the SR71 and the B-1B but in all I was just sticking with fighters since that was what we are talking about

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