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Elite 1K Joined: Aug 02, 2006 Posts: 1003 Status: Offline

Supercruise is not advertised of F-16 or F-15, even though both aircrafts will do it without bulky external stores and at high altitudes to the tune of Mach 1.1~1.25 depending on the engines installed and specifics of the variant. This is also not required for the F-35 and in fact officially denied. Nonetheless, an engine with a dry thrust rating of 28,000lbs is a lot of motor for an aerodynamically very sleek aircraft and relatively light aircraft like the F-35A carrying its fuel and weapons internally.

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Senior member Joined: Jul 01, 2007 Posts: 368

Read the latest Code One Magazine by Lockheed. They were able to cruise in the high subsonic region at about 40 percent of available mil power. You can interpolate from there. I still don't like the 28k pound empty weight, but I love the fact that it'll carry 20k pounds of dinosaurs internally.

Active Member Joined: Nov 22, 2004 Posts: 134

dwightlooi wrote:

Supercruise is not advertised of F-16 or F-15, even though both aircrafts will do it without bulky external stores and at high altitudes to the tune of Mach 1.1~1.25 depending on the engines installed and specifics of the variant.

As always, it depends on what one means by "supercruise." For the F-22, it's an operational requirement, obviously, so the development team had to certify that the engines and airframe can withstand the physical demands of this capability when used in a tactically meaningful way; basically, the F-22 and the F119 have to hold up well when running hard at high speed and high altitude for extended periods on what could be a routine basis. Indeed, there were problems with things like heat buildup and structural weakening over time that had to be addressed, which cost the program time and money, and made the F-22 even heavier still. Of course, this is in addition to the fact that the speed must be fast enough. While going supersonic does have a major effect on how really fast cruising is accomplished, obviously, it is not significant in and of itself--in retrospect, "supercruise" was an ill-chosen marketing term, although this does not take away from the F-22's capability.

The fact that some other fighters can "supercruise" (albeit barely in most such cases) is a testament to their generally high level of performance, but on top of the external stores issue, they were simply not designed for this capability. Even if a fighter happens to be "fast enough" and just happens to be able to handle everything else I've mentioned above (how likely is that?), the fighter must also be able to maneuver to a useful degree, which should rule out nearly all of them (although it could be argued that since stealth is not an issue for any other fighter besides the F-35, you could light the burners during maneuvers).

dwightlooi wrote:

This is also not required for the F-35 and in fact officially denied.

Right, so despite everything the F-35 has going for it--which I don't need to tell you is quite considerable--the engineers are not going to concern themselves with it. Getting it done was a pain with the F-22, despite the fact that it was specifically designed for this flight regime, and I doubt that it's just going to come for free with the F-35. Who knows, maybe it will because of how every aspect of this issue works out at a significantly lower "supercruise" speed, but we don't know that, the engineers don't care, and we should set our expectations accordingly.

dwightlooi wrote:

Nonetheless, an engine with a dry thrust rating of 28,000lbs is a lot of motor for an aerodynamically very sleek aircraft and relatively light aircraft like the F-35A carrying its fuel and weapons internally.

It depends on how much motor the installed F135 is going to be under "supercruise" conditions, not how hard it can push while sitting on a test stand near the ground. Like the F-35 as a whole, it was not designed to "supercruise" (even though it uses essentially the same core as the F119), and the engineers don't care whether it can (they may test it, but they won't make it work). That said, you make some good points about how clean the F-35's aerodynamics are, as well as its internal stores capability, so we'll just have to wait and see.

SnakeHandler wrote:

Read the latest Code One Magazine by Lockheed. They were able to cruise in the high subsonic region at about 40 percent of available mil power. You can interpolate from there.

By direct extrapolation, its supercruise speed at 100% mil power should be approximately Mach 2.0-2.3. Well, that settles it, then...NOT! Razz

SnakeHandler wrote:

I still don't like the 28k pound empty weight, but I love the fact that it'll carry 20k pounds of dinosaurs internally.

It's actually more like 29k and 18.5k, respectively, for the CTOL variant, but all things considered, that's very good. I guess our expectations are pretty high these days....

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

SnakeHandler wrote:

Read the latest Code One Magazine by Lockheed. They were able to cruise in the high subsonic region at about 40 percent of available mil power. You can interpolate from there. I still don't like the 28k pound empty weight, but I love the fact that it'll carry 20k pounds of dinosaurs internally.

No, I haven't been able to find any article with such content. Link?

if we assume that wave drag is already fully in effect at these "high subsonic speeds" than increasing to full mil power would only increase speed by ~16%. more likely 10% due to increases in wave drag. This could be as insignificant as .9M to .99M. However... 0.9M at 40% power at altitude means some low fuel burn at high speed... long range.

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

sprstdlyscottsmn wrote:

if we assume that wave drag is already fully in effect at these "high subsonic speeds" than increasing to full mil power would only increase speed by ~16%. more likely 10% due to increases in wave drag. This could be as insignificant as .9M to .99M. However... 0.9M at 40% power at altitude means some low fuel burn at high speed... long range.

Wave drag spikes at Mach 0.95~1.05 probably a little narrower in many cases. After that it drops to a level that is still higher than at Mach 0.9 but significantly less than at Mach 1. Usually, by M1.1, the drag is only around 20~30% higher than at Mach 0.9 although at M1.0 it can be almost twice as high.

At what altitude ? How much internal fuel ? I voted for the first variant because it`s a bomber engine not a fighter engine. It has high trust and good range but: rate of climb and acceleration are classified so a accurate estimation cannot be done without aerodynamic tests of the airframe.

The link to Lockheed Martin Aeronautic Company magazine "Code One" is http://www.codeonemagazine.com/

The link to Lockheed Martin Aeronautic Company magazine "Code One" is http://www.codeonemagazine.com/

Active Member Joined: Nov 22, 2004 Posts: 134

sprstdlyscottsmn wrote:

if we assume that wave drag is already fully in effect at these "high subsonic speeds" than increasing to full mil power would only increase speed by ~16%. more likely 10% due to increases in wave drag. This could be as insignificant as .9M to .99M.

Duly noted, although that would be assuming a lot, considering the only number we have is 40% thrust (a complex issue in itself). If we assume the worst, the F-35 would have to use afterburner to "punch through the Mach." Once past this region, however, it has some qualities above and beyond those of most other fighters that could potentially make it a "true supercruiser," such as internal stores and an exceptionally high fuel fraction, although the questions I had raised earlier still apply.

sprstdlyscottsmn wrote:

However... 0.9M at 40% power at altitude means some low fuel burn at high speed... long range.

You can never have too much range. Thumb

Cad wrote:

At what altitude ?

Just about any reasonable altitude (e.g. 30000-50000 feet) would be impressive and probably useful to some degree.

Cad wrote:

How much internal fuel ?

Good question. The aircraft itself is fairly light, considering its capabilities, anyway, but that's a lot of fuel weight to push on a single engine. That said, with any luck, enough fuel would be burned off getting to the combat zone to make this a non-issue for the vast majority of missions (hypothetically speaking, of course).

Cad wrote:

I voted for the first variant because it`s a bomber engine not a fighter engine.

Oh, it's a fighter engine, sure enough, even if it's optimized for a flight envelope more like that of the F-16 as opposed to the F-22. If the F-16 and other fighters of that generation can fly slightly faster than the speed of sound under some conditions, I'm reasonably sure that the F-35 could, too. The burning question is whether it can "supercruise" in the manner of the F-22, albeit at an undoubtedly slower speed.

For our reference regarding the latter, it seems that the F-22 is currently intended to be flown in combat at up to Mach 1.73 without afterburners. It can carry and successfully release the GBU-32 at this speed (certified in flight test). Some statements from those in the know seem to suggest that it could get to Mach 2 (conditions unknown), although the fastest known supercruise speed mentioned explicitly by an F-22 pilot thus far is Mach 1.9 (conditions also unknown).

Cad wrote:

It has high trust and good range but: rate of climb and acceleration are classified so a accurate estimation cannot be done without aerodynamic tests of the airframe.

Right, they're really just getting started, and there's still quite a ways to go.

Davy wrote:

The link to Lockheed Martin Aeronautic Company magazine "Code One" is http://www.codeonemagazine.com/

I couldn't find the reference--perhaps the latest issue has not been posted online yet.

Mach 1.9 supercruise ? Whatever that pilot is smoking , i want some...

Active Member Joined: Nov 22, 2004 Posts: 134

Cad wrote:

Mach 1.9 supercruise ? Whatever that pilot is smoking , i want some...

I don't know what Lt. Col. David Krumm might have been smoking, but here is what he said in an interview, apparently regarding supercruise:

Quote:

That saves us a lot of gas and opens up a whole host of things when you start talking about dropping bombs. You can imagine if you are 60,000 feet doing mach 1.9 (about 1,400 mph) and these bombs are flying out of your airplane, the swath of hell you can produce going through a country saying "I'll take that target, and that target."

Well, he's not short on bluster, in any case. Smile

Here is a link to the full article:
http://aimpoints.hq.af.mil/display.cfm?id=8529

Note that the parenthetical 1400 mph speed given, whether it was from Krumm himself or the writer or editor, actually works out to be Mach 2.12 at that altitude (standard conditions), which I find more doubtful. I usually just stick with the Mach 1.73 figure that I calculated from the speed at which the F-22 successfully released a GBU-32, which was published as 1142 mph. A quick Google search reveals that the most common figure on the Internet is Mach 1.72, which is close enough.

Let my translate this in english. At 60.000 feet the Mach ( speed of sound) is 295 m/s or less. ground level it`s 340 m/sec.
Mach 1.9 at 60.000 feat means 2017 km/h. I`m from Europe so please excuse me for posting the speed of sound in m/sec ,it helps.
The lt. col. Krumm did not sad that they are dropping bombs on super-cruise. He sad that they are dropping bombs on mach 1.9. And yes super-cruise saves a lot of gas. But a mach 1.9 super-cruise is not realistic figure.

Active Member Joined: Nov 22, 2004 Posts: 134

Cad wrote:

Let my translate this in english. At 60.000 feet the Mach ( speed of sound) is 295 m/s or less. ground level it`s 340 m/sec.

That's correct, and the ratio is exactly 0.44704 m/s for each mile/h.

Cad wrote:

Mach 1.9 at 60.000 feat means 2017 km/h. I`m from Europe so please excuse me for posting the speed of sound in m/sec ,it helps.

No problem, I'm equally comfortable with both systems.

Cad wrote:

The lt. col. Krumm did not sad that they are dropping bombs on super-cruise. He sad that they are dropping bombs on mach 1.9.

You are right that there is some room for doubt as to whether his statements are related. I have this same doubt, among others, which is why I generally stick with Mach 1.73. I brought up this article primarily for the sake of completeness. That said, since both of his sentences involved bombing and at least appear to have been spoken consecutively, the unproven implication is that the F-22 can supercruise and drop bombs at Mach 1.9 at the same time. Also keep in mind that an F-22 pilot would very rarely even consider using afterburner just for a bombing run because of the major compromise to stealth involved, which favors this interpretation.

Cad wrote:

And yes super-cruise saves a lot of gas.

It saves fuel over using afterburners at a given speed, but one of the main points is to keep the aircraft's IR signature minimized while limiting the time of exposure to enemy defenses.

Cad wrote:

But a mach 1.9 super-cruise is not realistic figure.

Probably not (although we don't know for sure), but this doesn't mean that the F-22 cannot reach Mach 1.9 in level flight in mil power. Perhaps it can't be used all the time for some reason (e.g. poor fuel economy and range), but I doubt that the F-22 is fully maxed out in mil power at Mach 1.73, especially as fuel is burned off. This is merely the highest known operational speed for now, and maybe it's the highest that will be allowed or the highest practical speed, and if so, then it's probably not quite at 100% mil power.

Let's get back to the F-35, to which the same rules apply. Exceeding Mach 1.0 in mil power should be easy enough, but the questions are: how fast can it go for long periods without damaging itself in some way, what supersonic speed would be the most practical, and what's the absolute maximum speed that could be achieved in mil power? We could guess, but we don't have much to go on yet. Maybe if we compared it to the F-22 point by point in detail, we could speculate on a slightly more solid basis, although it would still just be speculation.

Elite 1K Joined: Aug 19, 2004 Posts: 1092

dwightlooi wrote:

sprstdlyscottsmn wrote:

if we assume that wave drag is already fully in effect at these "high subsonic speeds" than increasing to full mil power would only increase speed by ~16%. more likely 10% due to increases in wave drag. This could be as insignificant as .9M to .99M. However... 0.9M at 40% power at altitude means some low fuel burn at high speed... long range.

Wave drag spikes at Mach 0.95~1.05 probably a little narrower in many cases. After that it drops to a level that is still higher than at Mach 0.9 but significantly less than at Mach 1. Usually, by M1.1, the drag is only around 20~30% higher than at Mach 0.9 although at M1.0 it can be almost twice as high.

Nobody really talks about wave drag when speaking about real aircraft. It's more of a theoretical concept than something one actually attempts to determine accurately for a real 3D object. What you should be talking about is CDmin, or minimum drag coefficient. While CDmin might decrease once an aircraft fully supersonic, this isn't always the case. It generally doesn't increase much however. As far as a decrease... it's nothing so drastic as to make CDmin at Mach 1.1 only 20-30% higher than at Mach 0.9. Again, you wouldn't bother to estimate the wave drag component of an actual aircraft, so I have no idea how the wave drag component of a real aircraft would vary from 0.9-1.1 Mach. I don't even know how you'd accurately determine it to begin with. Mind you, I am not talking about analytical or empirical aerodynamic methods. I'm talking about wind tunnel testing, flight testing, or CFD simulation. In any of these, wave drag isn't something that just jumps out at you and says, "Here I am, calculate me!"

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