[CLOSED, NO BUG] F-15C able to Supercruise.

[Capn kamikaze]

The term has been around a lot longer than that.

[SinusoidDelta]

The term has been around a lot longer than that.

 

If this is true please provide a source. To my knowledge there is no source, MIL spec or otherwise, that explicitly states criteria for supercruise.

[Capn kamikaze]

I have no source other than hearing it used since at least the late 80's.

[Ogami Musashi]

If this is true please provide a source. To my knowledge there is no source, MIL spec or otherwise, that explicitly states criteria for supercruise.

 

The term supercruise was invented in the 70's in the infancy of the ATF program, when it was a ground attack plane.

 

You have multiple research papers from manufacturers, nasa, and other gov office of supercruisers.

 

Here is one example:

 

http://www.dtic.mil/docs/citations/ADB022011

 

It was then thought the plane would travel long distances (more than 250 miles) at supersonic speeds not using afterburner.

 

Due to several changes in the propulsion dynamics, the fuel consumption in supersonic is far greater than in subsonic even in a supercruising engine (yes, supercrusing is not only an aerodynamics requirements but you need to build a special engine for it, that some mass flow characteristics) and thus you always lose some range when supercruising.

 

When the ATF program was switched to an air superiority fighter, requirements for the supercruising leg diminished towards a 100 nm dash+ a subsonic leg. Far later in the F-22 program fuel capacity was decreased from 12 to 8,2 tons so the subsonic leg was cut.

 

The F-22 currently loses 100nm of combat radius for 100nm of supercruising at mach 1.5 and 40k feet.

[RoflSeal]

I'm pretty sure supercruising is just cruising (so the regime which is most fuel efficient) that happens to be greater then Mach 1. Blackbird cruises with its afterburners on. F-15 cannot supercruise because it is most fuel efficient at ~ M0.8-0.9.

[Ogami Musashi]

I'm pretty sure supercruising is just cruising (so the regime which is most fuel efficient) that happens to be greater then Mach 1. Blackbird cruises with its afterburners on. F-15 cannot supercruise because it is most fuel efficient at ~ M0.8-0.9.

 

Nope :) see my post above.

[SinusoidDelta]

The term supercruise was invented in the 70's in the infancy of the ATF program, when it was a ground attack plane.

 

You have multiple research papers from manufacturers, nasa, and other gov office of supercruisers.

 

Here is one example:

 

http://www.dtic.mil/docs/citations/ADB022011

 

It was then thought the plane would travel long distances (more than 250 miles) at supersonic speeds not using afterburner.

 

Due to several changes in the propulsion dynamics, the fuel consumption in supersonic is far greater than in subsonic even in a supercruising engine (yes, supercrusing is not only an aerodynamics requirements but you need to build a special engine for it, that some mass flow characteristics) and thus you always lose some range when supercruising.

 

When the ATF program was switched to an air superiority fighter, requirements for the supercruising leg diminished towards a 100 nm dash+ a subsonic leg. Far later in the F-22 program fuel capacity was decreased from 12 to 8,2 tons so the subsonic leg was cut.

 

The F-22 currently loses 100nm of combat radius for 100nm of supercruising at mach 1.5 and 40k feet.

 

Thank you for this. I stand corrected, there are numerous other documents available regarding a conceptual supercruiser. It's unfortunate only the abstract is available for the document provided. As of today, the term supercruise is more of a "buzz word" as it lacks a true definition.

[Scytale]

Just for the record, all normal gasdynamic shocks have a subsonic downstream in the shock frame, which, if the shock isn't moving relative to the aircraft, is also the aircraft reference frame. The re-entry capsules for the Apollo missions suffered bow shocks on re-entry. So, despite travelling at around Mach 25, I suppose they were transonic?

 

There is no "weak" variant of a normal shock for a given freestream Mach number - normal shocks are normal shocks, and all bow shocks are normal at the apex. Only oblique shocks - that is, shocks with some velocity component in the shock-tangential frame - feature 'strong' and 'weak' variants.

 

edit: I do recognize the meaning and usefulness of the term 'transonic', and that it applies especially around the range 0.8-1.2 Mach. But I think strict application of the "subsonic region" rule is dangerous because it's quite probable that all truly supersonic aircraft feature a subsonic region somewhere on their body, however small. e.g. stagnation points.

Edited September 23, 2015 by Scytale

[pr1malr8ge]

So, if im flying a cessan 172 and the prop tips are supersonic I must be super cruising?

[=4c=Nikola]

So, if im flying a cessan 172 and the prop tips are supersonic I must be super cruising?

 

Absolutely.

[fltsimbuff]

So, if im flying a cessan 172 and the prop tips are supersonic I must be super cruising?

 

You have a supersonic Cessna too?

 

[Scytale]

lol obviously not, but that's still an hilarious picture

[VincentLaw]

I do recognize the meaning and usefulness of the term 'transonic', and that it applies especially around the range 0.8-1.2 Mach. But I think strict application of the "subsonic region" rule is dangerous because it's quite probable that all truly supersonic aircraft feature a subsonic region somewhere on their body, however small. e.g. stagnation points.

Right, even if your vehicle is traveling Mach 3 there will be regions of the flow that are subsonic, including stagnation points, behind strong shocks, within boundary layers, inside open weapons bays or open cargo bays, inside the engines, and maybe in the wake. Of course any flow that includes both a supersonic and subsonic region is considered transonic flow. The way you get around that is by drawing a control volume around the vehicle that excludes the subsonic regions, and then you are only looking at a supersonic flow.

 

Generally speaking, you can say any aircraft with a free stream Mach greater than 1 is in supersonic flight. In that case, all freestream flow sufficiently far away from the vehicle in any direction will be supersonic. However, I found some literature that defines supersonic flight differently, so I dropped the argument. There is more than one definition for supersonic flight depending upon what sources you use.

 

As a historical note, the first "manned supersonic flight" only reached Mach 1.06, so it was still in the transonic regime.

Edited September 24, 2015 by VincentLaw

[=Mac=]

According to the latest newsletter from Boeing Boing, the F-15 Maserati Eagle is currently under flight testing at Area 51's Skunk Works. It has a single Lycoming O-360 nitro-methane burning engine instead of the two Pratt & Whitney F-100's and is rated not only above supersonic but superluminal. Fuel consumption is rumored to be in the area of 30 mpg on the highway.

 

Argentina has ordered two of them while Iran claims to have shot one down over the SOH.

[strikeeagle]

Ok dudes. When I was on active duty crewing Strikes at SJ, a pilot and I were discussing this very thing in comparing the Craptor ability to super crusie vs the 15. My pilot said that the 15 can super cruise. It has to climb pretty high (upper 30's - 40's) and must go into burner first to get there. He also said it could stay there using mil power depending on its weight.

 

Take that FWIW.

[Scytale]

Right, even if your vehicle is traveling Mach 3 there will be regions of the flow that are subsonic, including stagnation points, behind strong shocks, within boundary layers, inside open weapons bays or open cargo bays, inside the engines, and maybe in the wake. Of course any flow that includes both a supersonic and subsonic region is considered transonic flow. The way you get around that is by drawing a control volume around the vehicle that excludes the subsonic regions, and then you are only looking at a supersonic flow.

 

Generally speaking, you can say any aircraft with a free stream Mach greater than 1 is in supersonic flight. In that case, all freestream flow sufficiently far away from the vehicle in any direction will be supersonic. However, I found some literature that defines supersonic flight differently, so I dropped the argument. There is more than one definition for supersonic flight depending upon what sources you use.

 

As a historical note, the first "manned supersonic flight" only reached Mach 1.06, so it was still in the transonic regime.

 

It is compelling to distinguish between 'idioms' of flow and flight in this manner, makes a lot of sense to me.

 

I'm curious as to how one may draw a control volume excluding subsonic regions around a craft with a bow shock, though I suppose you could ensure that the flow through all the control surfaces are supersonic. This would maybe be equivalent to considering freestream conditions to be the defining ones?

 

Then again, most such discussions don't usually pertain to craft with bow shocks (I imagine) so it's probably a moot point anyway

[Capn kamikaze]

There is no "weak" variant of a normal shock for a given freestream Mach number - normal shocks are normal shocks, and all bow shocks are normal at the apex. Only oblique shocks - that is, shocks with some velocity component in the shock-tangential frame - feature 'strong' and 'weak' variants.

 

I love how you put that across as if you're scoring some kind of point, we're talking about the whole aircraft (an F-15, not a re-entry vehicle, nice strawman) and you said earlier on, that the speed behind a shock is subsonic, you made no distinctions, but a rather general statement that was just wrong..... well it isn't subsonic in all cases as I said, and in the case of a supersonic flow, as you've agreed, behind an oblique shock (like what you get around a vehicle) the flow either side can be supersonic, which constitutes a weak shock....

[kingfish]

It is compelling to distinguish between 'idioms' of flow and flight in this manner, makes a lot of sense to me.

 

I'm curious as to how one may draw a control volume excluding subsonic regions around a craft with a bow shock, though I suppose you could ensure that the flow through all the control surfaces are supersonic. This would maybe be equivalent to considering freestream conditions to be the defining ones?

 

Then again, most such discussions don't usually pertain to craft with bow shocks (I imagine) so it's probably a moot point anyway

 

Bow shocks are oblique shocks, and flow behind an oblique shock can still be supersonic (though it does necessarily have a lower Mach number). If the aircraft is travelling fast enough (i.e. thoroughly out of the transonic regime), all of the flow, including that behind the bow shock and any other oblique shocks coming off the body, will be supersonic. That said, inside of closed areas like intakes, flow may be subsonic, though this is generally not considered as far as the "is it supersonic" question.

 

Formally, "supersonic" occurs when the free stream velocity is greater than 1. "Transonic" is a bit of a fuzzy term without a precise definition. Its generally about M0.8 to 1.2, but thats only because thats where the transonic effects are most dominant. At M0.75, you'll still have supersonic regions (probably, it depends on exact geometry), and likewise at M1.3 you'll probably still have some small subsonic regions.

[Capn kamikaze]

Correct, a normal shock is what you get for example along the wing's upper and lower surfaces (trailing edge to leading edge) and as the name implies it is normal (90 degrees to the airflow) and is found on wings where the airspeed is the same as the critical mach number for that point on the wing, generally first appearing at the thickest part of the wing, and as the aircraft accellerates the shock moves forward until it reaches the leading edge, at which point that part of the aircraft transitions from being described as transonic, to supersonic, and a weak oblique shock is formed at the leading edge root.

[Scytale]

My apologies if my comment appeared aggressive - I did not mean to score points in any manner, and should work on my phrasing if that's the case.

 

Regarding the re-entry vehicle: I also do not mean to make it somehow equivalent to an F-15, or to any modern jet, civil or military, because it's clearly very different. My point in mentioning it is that there are subsonic regions of flow in any airborne craft - it's certainly the case with re-entry vehicles for one thing, and obviously the case for transonic craft.

 

My point - or rather my question to you, because I'm not properly versed in the military terminology here - is this: Is it fair to refer to a craft as being in transonic flight if there is *any* subsonic flow, anywhere in the craft? I argue no, with the extreme counterexample being a re-entry vehicle. Another possible example is that flow in most aircraft engines, certainly in the burner sections, is most often subsonic (consider e.g. ramjets in the SR-71 for an explicit example). But I suppose it's a moot point if we consider engine internals to count for this discussion, and am willing to concede these examples.

 

Cap'n Kamikaze, in post 44 I agree; however kingfish in post 43 I do not completely agree. While it's true bow shocks are oblique in large parts of their geometry, but at their apex they are normal. See the image in the linked wikipedia article for an example.

https://en.wikipedia.org/wiki/Bow_shock_(aerodynamics)

 

Again, not trying to pick a fight here, and I'm not trying to say that since there is subsonic flow around a re-entry vehicle, therefore there is no such thing as transonic flight - that would be ridiculous - but I'm wanting to point out that one could argue there are subsonic regions of flow - however small - in many truly supersonic applications (e.g. stagnation points, once again).

 

Do we at least agree that normal shocks do feature supersonic upstream and subsonic downstream in the reference frame of the shock?

[Capn kamikaze]

No worries, the internet isn't the best form of communication.

 

My point - or rather my question to you, because I'm not properly versed in the military terminology here...

 

It's not military terminology as such, it's the latent aero engineer in me that takes issue with the idea of calling what are transonic speeds supersonic purely because the fuel consumption differences between the two makes the idea of any sort of cruise at transonic speeds laughable, no plane cruises in the transonic regime, burner or not it will be guzzling fuel in that speed regime...

 

Subsonic yes, supersonic yes, in between, only by pure fluke.

 

Cap'n Kamikaze, in post 44 I agree; however kingfish in post 43 I do not completely agree. While it's true bow shocks are oblique in large parts of their geometry, but at their apex they are normal. See the image in the linked wikipedia article for an example.

https://en.wikipedia.org/wiki/Bow_shock_(aerodynamics)

They're not really what should be called a normal shock (yes it is normal to the direction of travel) but that term is used to describe a shock that is attached to a surface but which is at 90 degrees to the flow, if you say that to an aeronautical engineer that is what they will assume you're talking about, a detatched shock (like a bow) is a different case, and as that page says, it is only in certain special cases where it obeys the strong shock (supersonic to subsonic) conditions.

 

Do we at least agree that normal shocks do feature supersonic upstream and subsonic downstream in the reference frame of the shock?

Yes, but again we have to be very careful of terminonlogy, since we're talking about an engineering and therefore science based subject.

[Scytale]

They're not really what should be called a normal shock (yes it is normal to the direction of travel) but that term is used to describe a shock that is attached to a surface but which is at 90 degrees to the flow, if you say that to an aeronautical engineer that is what they will assume you're talking about, a detatched shock (like a bow) is a different case, and as that page says, it is only in certain special cases where it obeys the strong shock (supersonic to subsonic) conditions.

 

Then it is indeed a terminology issue - my background is fluid mechanics in a research-based setting, where a normal shock is defined according to whether or not there is a tangential velocity component in the shock frame. Not having the strictly aeronautical application must be how I've been miscommunicating.

 

Otherwise it seems we're in agreement.

[FlyGuyF119]

Super Cruise means, Capable of taking off with full weapons and fuel and be able to super cruise. Now the F-15 can super cruise once you lose the drag and a lot of fuel.. This is realistic.

[Dappman]

Su25 can supercruise too.

 

Not really. The definition for supercruise is going something like Mach 1.5 without afterburner.

[Exorcet]

Not really. The definition for supercruise is going something like Mach 1.5 without afterburner.

 

It's been said before, but there isn't really a strict definition.

 

The most common is Mach 1.0 or faster without AB, again nothing to do with fuel consumption or shockwaves.