Listed Performance vs Real Performance

[KJ_Lesnick]

I was thinking about a lot of stuff, but among them are the performance figures listed for a lot of military airplanes and their true capabilities. In some cases there's some evidence to suggest that the actual capabilities of some of these airplanes is way above what they list. Engine capabilities also in many cases seem to be capable of going to higher mach numbers than listed, and in some cases producing more thrust.

Starting with engines, the J-93, which powered the XB-70 Valkyrie, was capable of performing well above Mach 3.0 -- in fact according to multiple sources, but one I can readily recall was Steve Pace's "Valkyrie: North American XB-70": The J-93 were rated for Mach 4 performance. Many people state, and many people seem to believe that even modern day you can't push a turbojet much above Mach 3.5, and back in 1957 the US already had an engine that could do Mach 4 on a routine continuous basis, it didn't have a bad pressure-ratio either (8.8 : 1) either. Consider that back then the air-cooling technology was only 20% of what it is today (and the J-93 used liberal amounts of air-cooling) if not less, and we have drastically superior metallurgy and materials in which to make engines out of. With that said, the J-58 was capable of Mach 4 also, even before any bleed-bypass system was added to the design. This is evident in the fact that the J-58 was used as a competitor to the J-93 after the J-91 (Pratt & Whitney's original contender from which the J-58 was an 80% scaled down derivative of) was no longer in the competition and was said to have had rivalable performance to the J-93. The J-91 was also capable of the same speeds as the J-93. It wasn't proportionally, in terms of power to weight ratio, as powerful as the J-58 in terms of sea-level thrust which is explainable by the fact that the J-58 had a higher pressure ratio (8:1 - 8.8:1 vs 7:1 for the J-91): This seems to be the result of improvements in air-cooling and metallurgy, and perhaps the variable IGV which the J-58 possesses (I'm not sure of the J-91 had the variable IGV -- if it did the greater pressure-ratio and power-to-weight ratio would be solely due to improvements in air-cooling and improved metallurgy) which essentially lowers the airflow's AoA relative to the compressor-blades and thus the pressure ratio once the compressor-inlet temperature exceeds a given amount which in turn lowers the turbine temps. With that said, the claim of the A-12/SR-71 being able to achieve "only" Mach 3.5 or Mach 3.7 is obviously bogus. The bleed-bypass system was added to increase the maximum speed of the airplane (efficiency was obviously part of the equation but the J-58 and J-93 could already cruise continuously at Mach 4 on low-afterburner reasonably enough) significantly. While the shockwave could theoretically disrupt the airflow into the inlet, it would obviously be at a somewhat higher mach number than the plane actually was designed to fly at -- and it's at that speed (cruise), that the J-58 was modified to operate at, up to the maximum speed of the airplane. Something on the order of 65% of the airflow actually was discharged off the compressor at maximum speed, which is then routed around the engine into the afterburner (which increases the air pressure entering the afterburner and increases thrust, allowing less fuel to be burned) -- that's a lot of air which is discharged off the compressor largely to maintain a reasonable turbine inlet temp! This doesn't even count other such modifications built into the J-58 which include; an engine-trim system which can adjust the fuel/air ratio while maintaining the same RPM to keep the engine-temp within tolerable limits; a derich system which reduces the fuel/air ratio of the afterburner to avoid overheating the burner; an active cooling system which cycles fuel around the afterburner to keep it cooled; the JP-7 which also doubles as a hydraulic fluid for the engine and operates the engine controls also probably absorbs some heat off the compressor; an expandable turbine casing and turbine (Sounds crazy, and I'm not sure about this particular detail, but allegedly one of the reasons the plane followed a fairly precise climb schedule was because under some circumstances turbine case and turbine blades didn't expand at exactly the same rate... the engines diameter was stated to have increased at higher-speeds) which to my knowledge is very unusual and suggests substantial effort to be able to tolerate unusually severe heating; the design probably featured a great degree more air-cooling too over the original J-58 design. That's some extensive list of modifications just for the purpose for dealing with excessive engine-heating. And that's what has been written in books (all NON-classified). It's obviously fairly easy to conclude that the A-12/SR-71 would be capable of drastically exceeding Mach 3.2 in terms of both cruise (cruise and max would be fairly close in such a high-speed design) and dash-speeds.

While these may be "extreme-engines" in terms of their speed-capabilities, there are many other more less extreme jet-engines that are capable of performing well above what most people give them credit for. The J-75, for one can exceed Mach-3. There was even a documentary (probably Discovery Wings, it was definetly a TV documentary, but I saw the video on YouTube) about the Vought F8U-III Super-Crusader, which outright said that it was powered by a J-75 engine to propel it to speeds of Mach 3+. When the XF-103 Thunderwarrior was developed the upper turbine temp limit for high-performance engines of the day was Mach 3.0, so they developed an under-and-over turbo-ramjet system that allowed it to achieve hypersonic speeds. What would constitute a high-performance engine of that era? The J-57 probably (not sure actually, definetly high Mach 2's), the J-67 definetly (The XF-103 was to be powered by it - granted, production delays prevented the XF-103 from using it...). Later models of the Rolls Royce Avon seemed to be able to do at least Mach 2.5, as the English Electric Lighting could achieve at least that speed (Allegedly the upper end of the performance envelope was even higher, I talked to a British guy who worked in the aerospace industry, with the past few years some of his experience included making some Concordes into museum pieces-- he had interesting pictures crawling around inside the fuel-tanks, pictures of the plane with the upholstery removed btw, etc). While developed slightly later, the J-79 could probably do Mach 3 as well as it had a higher turbine temp capability than the J-57.


You know I planned to type more but I'm tired as hell... I'll add more tomorrow

KJ_Lesnick
Let's hope I didn't say anything I shouldn't have. Let's hope I don't get a heart-attack

 

[KJ_Lesnick]

Okay, part two...

There are a lot of things that are written online, and even in aerodynamic textbooks that just aren't entirely accurate, are exaggerations, or just ain't so. One of the most common one is that air temperature drastically rises from Mach 3.0 to 3.2, going from 600 to something like 800 to 900 degrees. First of all, aerodynamic heating isn't exact for every single airplane -- sure, there's a minimum and maximum, but it varies from plane to plane. A highly streamlined aircraft at Mach 3 will probably not heat up as much as less streamlined-design. Second, the truth is that as you start going above Mach 2, you generally start getting temperatures that are hot enough to start requiring higher temperature metals. Mach 3 designs often contain significant amounts of titanium, honeycomb-metals, or in modern days: high-temperature composites, but the temperature around Mach 3 to 3.2 is not gigantically different. Significant jumps in temperature actually occur often in the hypersonic speed-range, which is above Mach 5. For this reason, vehicles that fly at such high-speed in addition to being made out of high-temp materials-- titanium and high temp stainless steels and refractory metals, also have blunted noses. The blunt nose can take more heat, and reflect more heat than a sharp one can which actually can under some conditions reduce drag (although it would be higher at lower speeds) even though it produces a rather powerful, normal-shock, the flow has so much energy that it quickly re-accelerates to supersonic/hypersonic speeds without significant trouble (Recently though, there have been types of sharp-nosed vehicles for hypersonic flight that usually involve a heat-reflective substance which produces similar temperature reduction effects to the blunted nose but with less-drag). Another thing that's not entirely accurate is that it's impossible to fly above Mach 2.2 without an almost all titanium structure -- an airliner maybe, but not a fighter. They can go a bit higher on an aluminum structure for a couple of reasons: 1.) Heat weakens aluminum long before it melts, and fighters have much sturdier structures and thicker skin: all designed to resist high-G-loads and such... they don't weaken enough until higher speeds are achieved. 2.) Fighters don't typically fly at high-speed all that long, it takes upwards of 20 minutes to heat-soak an airplane. 3.) Reynolds numbers: They're a function of scale - A small scale-model of a wing at a given speed generates a fairly smooth airflow compared to a scaled up version of the exact same airfoil shape at the same speed, which features more turbulent flow. The more turbulent flow on a wing, or airplane for that matter, the more kinetic heating happens - as an interesting note, a proposal during the 1980's or 1990's for a supersonic airliner which involved the use of Laminar flow-control offered low enough skin temps at Mach 3.0 or 3.2 that a nearly all aluminum structure could be used. I'm not sure how much this factors into kinetic heating differences between fighters, and large aircraft however.


Listed Performance vs Real Performance

Keep in mind, these are guesstimates... I'd like to hear your opinions and of course additional data if you have any, reasonably speaking.

F-100 Super-Sabre: Listed performance planes the speed of this airplane around Mach 1.3 to 1.4. However two people, an ex-USN pilot speculated, and an ex-USAF said quite authoritatively that it could do Mach 2. While the design did not appear to be particularly area ruled the area rule doesn't apply under all cases, certain fineness ratios, and the wing-area and thickness (The fact that the nose is an intake and has razor sharp edges compared to a regular nose and most of the air flows in to the engine which ends up producing more thrust than the drag the inlet produces might play a role too). The F-102 for example had a much larger wing-area (Delta) compared to the F-100 (which featured a swept wing). While it's wingsweep was 45-degrees, it's not just wingsweep that determines how fast you can go. Wing thickness and leading-edge shape also plays a role (The F-104, for example, had a tapered, but more or less straight wing: But it was thin as hell and sharp as a knife and it worked excellent at supersonic speed. I see no reason why either source would overrate the performance of the F-100, and no reason to suspect they would underrate it's performance either (They didn't fly the plane -- no reason to overrate for bragging, and no reason to underrate for security reasons, Mach 2 is way faster than listed, and the plane is old and obsolete). The plane definetly had a maximum indicated airspeed of at least 600 kts even while supersonic additionally, which at altitude (35,000 to 45,000 feet) would intersect Mach 2.

F-101 Voodoo: It's speed used to be listed in the Mach 1.85 area, but now figures are coming out listing it as Mach 2.25. Mach 2.25 may well be it's maximum speed, but I'd be willing to guesstimate as high as Mach 2.4. In either case, I remember reading something to the effect of the F-101B being faster (on the order of about 0.15 Mach). So, if the regular F-101 could do 2.25, it would be able to do 2.4. If the F-101 could do Mach 2.4, it could probably do Mach 2.55. (As an interesting note, the F-101B was actually designed not just to fill in the gaps before the F-102A's came online, but also as a stopgap for the LRIX/F-108 as a twin-seat high performance interceptor that could operate both inside and outside of the SAGE system).

F-102A: If I had to speculate, I would guess at least Mach 2.5. The F-102 (non area-ruled) was capable of 812 miles an hour, and the F-102A was "more than twice as fast", which would be 1,624+ mph or 2.46+ (meaning around 2.5). It might be even faster than that. Keep in mind where the design traced it's roots from, the Lippisch P.13A, which was a crazy idea the Germans cooked up towards the end of the war. It was rocket-boosted and ramjet powered flying wing with a ramjet inlet in the front, and the pilot sat at the base of the tiny aircraft's vertical stabilizer (which was actually as big as one of the wings) -- it was capable of Mach 2.6. The XP-92A which the design evolved into featured a larger ramjet with a conical spike up-front in which the pilot actually sat in. It was boosted to altitude by 4 large, and 50 small rockets (which doubled initially as flame holders for the ramjet), that then evolved into the XF-92 which was kind of a proof-of-concept for the F-102. The conical spike was changed into a wedge, which was placed inside the intake duct/fuselage, a more normal cockpit was placed in between the wedge, and a turbojet was placed in the back in lieu of a ramjet. Larger wings were fitted, and the design flew as the XF-92A. The F-102 was ultimately the result of lessons learned in all those designs. It may very well have been capable of Mach 2.6 like the original Lippisch P.13A. It was considered to be faster than the F-101 Voodoo, even the -B model...

F-104 Starfighter: A common misconception about the F-104 is that it's max speed is Mach 2, not so. It is capable of cruising on a 15-minute radius at Mach 2, using afterburners for acceleration only. I'm not sure if this radius accounts for the wingtip tanks or not to be honest with you, but it is said to have an excellent supersonic radius in excess of some modern fighters. Some later models which used a J-79 GE-19 which increased the service ceiling into the 73,000 foot range. Allegedly, it could sustain Mach 2.3 or 2.4 at 73,000 feet continuously with an expected KEAS of 315 or 325 kts using no afterburner. It was a real rocket. As for it's maximum speed... I have no idea, although it's aluminum skin placed limitations officially at 2.2 Mach, although with fighter designs it could be anywhere from 2.2 to 2.5. This is strictly rumor, but I heard some rumblings that the plane could physically do Mach 3 for very short bursts although factually the aerodynamic shape of the plane could if no temperature limitations were in effect (a big if) could allow speeds even higher. The J-79 can achieve Mach 3 speeds. The other misconception about the F-104 was that it was not very maneuverable. This is partially true, at low indicated-speeds it would be considered by some to be un-maneuverable. However when supersonic and at high airspeed, it was actually very agile and difficult to catch so long as they kept their airspeed nice and high. Later modifications were even made to allow for flap extensions at speeds of up to 550 kts, even while supersonic to tighten up turns further.

F-106 Delta-Dart: I was told more or less to the effect that the plane could redline at Mach 2.80. Two mechanics, of which one was even told by an F-106A pilot that it could redline at Mach 2.8. There's another individual who served in the USAF, who got a ride in an F-106B once, which turns out to be a tenth of a mach number faster due to it's superior area ruling (Mach 2.9), said that during a shallow dive the airplane achieved a speed which would amount to around 1,800 (yes, one thousand eight hundred) knots. That's about Mach 3.15, considering the level maximum speed, this is within the capabilities of the plane. This individual stated that the plane could probably do 3 in level flight, but I'm not sure as to the accuracy of that statement although the engine can obviously work at Mach 3.

F-4 Phantom II: I've been told that it was almost as fast as an F-106A when both were flying at optimum altitude for high-speed. That would probably amount to around Mach 2.7, maybe 2.8 depending on who's account was accurate (The guy who said it could do Mach 3 in level flight, or the two mechanics, and the pilot who listed Mach 2.8). The F-4 to my knowledge was stressed for higher indicated airspeeds (meaning it could fly at very high speeds at lower altitudes than the F-106 could and could easily hold supersonic speed over the deck without a really rough ride).

XB-70 Valkyrie: The chief engineer on the project, Walt Spivak stated that the inlets were designed to operate at Mach 4. The J-93s were rated for that speed, and were largely designed for the XB-70. Honeycomb-metals due to their high internal surface-area (able to reflect lots of heat) compared to normal metals, combined with the fact that they were stainless-steel seem to support this. Aircraft 62-0001 only seems to have done Mach 3, as it was the requirement for the test program and the plane lost pieces of it's skin at high-speed due to defects in the brazed-honeycomb panels. These defects were eventually fixed in 62-0001. The second aircraft, 62-0207 did not have such problems as the quality-control improved during that timeframe and definetly exceeded Mach 3, probably by a much higher figure than listed (3.08). Unfortunately it was lost in a mid-air collision in June, 1966.

 

[rousseau]

The J-75, for one can exceed Mach-3. There was even a documentary (probably Discovery Wings, it was definetly a TV documentary, but I saw the video on YouTube) about the Vought F8U-III Super-Crusader, which outright said that it was powered by a J-75 engine to propel it to speeds of Mach 3+.

Would you please to share the video link?

 

[Sferrin]

The J-75, for one can exceed Mach-3. There was even a documentary (probably Discovery Wings, it was definetly a TV documentary, but I saw the video on YouTube) about the Vought F8U-III Super-Crusader, which outright said that it was powered by a J-75 engine to propel it to speeds of Mach 3+.

Would you please to share the video link?

Discovery Wings has made it's share of mistakes. The test pilots said they thought have reached Mach 2.9 - 3.0 but all this speculation probably belongs in the Bar section IMO since it definitely qualifies as "bar talk" ;D "Lemme tell ya' bout the time I had my F-16 going Mach 2.8 in a 90 degree dive on my run to drop four two-thousand pounders."

 

[overscan (PaulMM)]

I agree, Scott. KJ, I think some of your conclusions here are off, especially on the F-102A.

In the case of the Lightning this aircraft was derived from the experimental P1, designed originally for Mach 1.5, but without needing afterburners, as Britain had minimal experience in such devices at the time. The production Lightning therefore had two big engines and bucketloads of extra thrust when burners were lit, and - according to pilots - was still accelerating as it hit Mach 2.0. Perhaps, it would have thrust enough to hit Mach 2.3 or higher - but the simple engine inlet design was optimised for Mach 1.5 -1.8. At just under Mach 2.0 it started vibrating quite nastily, in way that firmly discouraged any higher speed attempts. Therefore, in reality, Lightnings rarely exceeded Mach 2.0. With a new inlet design, it might have gone faster, but there was no desire or requirement to do so.

Its certainly true that aircraft service speed limits aren't necessarily set at the actual maximum speed of the design. There's a big difference between an experienced test pilot, fully familiar with the risks, taking a plane up to test just how fast it can go, and what you want your average Joe service pilots to do. Structural integrity concerns, canopy heating, engine life and safety issues, just as much as engine thrust or aerodynamics, will dictate the safe limits.

Obviously some service pilots will test those limits and often find they can exceed them once or twice without ill effect. That doesn't mean the USAF was misleading the world as to to the actual capabilities of their aircraft. I think you'll find, with the exception of the A-12/SR-71, it was realised that this part of the flight envelope was of little practical military significance and little Mach 2+ flight has ever been done in USAF service. If you read a good account of the A-12 program - see the Aerofax by Goodall and Miller, for example - you will soon appreciate how tricky it was getting it to reliable Mach 3 operation.

In terms of engines and high speed performance, as speed increases the compression ratio of the inlet and engine together create very high pressures and temperatures in the hot section of the engine. With any given engine technology level, fuel economy comes from a high compression ratio. However, the higher the ratio, the hotter the hot parts of the engine get, and so the limiting factor is the materials of the turbine and combustors. When you are flying fast, the air is already compressed a lot by the intake system. Therefore, if you use a high compression ratio engine, the overall compression ratio of the whole intake/engine system becomes so high that the temperatures in the turbine would be unacceptable.

Very high speeds therefore require either a low compression ratio engine, or extremely expensive materials and advanced cooling techniques. The first gives very poor fuel economy at lower speeds, the second increases cost and complexity of the design.

 

[KJ_Lesnick]

overscan,

In terms of engines and high speed performance, as speed increases the compression ratio of the inlet and engine together create very high pressures and temperatures in the hot section of the engine. With any given engine technology level, fuel economy comes from a high compression ratio. However, the higher the ratio, the hotter the hot parts of the engine get, and so the limiting factor is the materials of the turbine and combustors. When you are flying fast, the air is already compressed a lot by the intake system. Therefore, if you use a high compression ratio engine, the overall compression ratio of the whole intake/engine system becomes so high that the temperatures in the turbine would be unacceptable.

I never said there wasn't a limit. However, books that are considered reliable sources have stated the J-93's capabilities as Mach 4 capable, the aircraft designers admitted it. The J-91 and J-58 were both at one time or another competitors to the J-93 and had the same Mach 4 capability.

Keep in mind, compression/kinetic heating temperatures do not ridiculously spike above Mach 3 like as often stated. They are higher than Mach 2.5 or 2.8 yes, but they are not on the order of 900 degrees. Since turbulence plays a role in the heating effects, the inlet-efficiency would play a role in how hot it would be at the compressor face.

Very high speeds therefore require either a low compression ratio engine, or extremely expensive materials and advanced cooling techniques. The first gives very poor fuel economy at lower speeds, the second increases cost and complexity of the design.

Depends on what you define as very high-speeds. Mach 3 could be achieved by certain high performance engines of the same era as the XF-103A's conceptual/mockup stage (never flew, but still), that's why they resorted to the under-and-over turbo-ramjet set-up, to exceed those limitations. The J-67 seemed to be able to reach Mach 3 since it was the engine to power it, the J-75 had a higher turbine-inlet temp than the J-57 (which probably either was close to or equal to the J-67 as it was used in lieu of the J-67 on the F-102A) to the best of my knowledge as the J-79.

Regarding the J-93, it was constructed out of high temperature metals, featured an elaborate air-cooling system.

I think some of your conclusions here are off, especially on the F-102A.

In what area?

In the case of the Lightning this aircraft was derived from the experimental P1, designed originally for Mach 1.5, but without needing afterburners, as Britain had minimal experience in such devices at the time. The production Lightning therefore had two big engines and bucketloads of extra thrust when burners were lit, and - according to pilots - was still accelerating as it hit Mach 2.0. Perhaps, it would have thrust enough to hit Mach 2.3 or higher - but the simple engine inlet design was optimised for Mach 1.5 -1.8. At just under Mach 2.0 it started vibrating quite nastily, in way that firmly discouraged any higher speed attempts. Therefore, in reality, Lightnings rarely exceeded Mach 2.0. With a new inlet design, it might have gone faster, but there was no desire or requirement to do so.

I am not an expert on the English-Electric Lightning. All I know comes from some online reading (not much), and a conversation with a guy with an aviation background who was refurbishing Concordes into museum pieces. I have no knowledge how efficient the inlets were, but it does seem as if it's common practice to list an airplanes performance as being a little bit lower than it really is capable of.

If you read a good account of the A-12 program - see the Aerofax by Goodall and Miller, for example - you will soon appreciate how tricky it was getting it to reliable Mach 3 operation.

The A-12 was designed for speeds substantially above Mach 3. As I said, it's engine was capable of Mach 4 before it was extensively modified to make it able to go faster, more efficiently (notably faster). There is no point in modifying an engine for such capability if the plane was never meant to reach those speeds. It would have had to have been faster than Mach 4 obviously.


Kendra

 

[overscan (PaulMM)]

The A-12 was designed for speeds substantially above Mach 3. As I said, it's engine was capable of Mach 4 before it was extensively modified to make it able to go faster, more efficiently (notably faster). There is no point in modifying an engine for such capability if the plane was never meant to reach those speeds. It would have had to have been faster than Mach 4 obviously.

Kendra

Sorry, don't buy it. Lots of evidence for A-12/SR-71 being limited to not much above Mach 3 (say, Mach 3.3 at most). Never seen any evidence for anything approaching Mach 4.0, let alone exceeding it. Temperatures of 1,600°F can be generated by inlet air compression alone at Mach 4 - thats going to cause issues with any 1950s technology engine. Don't forget, in 1958, engine designers had no real experience of Mach 3+ flight to go on.

As for J-67 being a Mach 3.0 engine, thats simply untrue. I have detailed specs on early Olympus, which J-67 is based on, and its good for Mach 1.8-2.0 at best. The XF-103 used a combination of J-67 and a ramjet; at the higher speeds the J-67 core is sitting pretty.

 

[overscan (PaulMM)]

Oh, and don't forget Sidney Camm's saying:

"There's no such thing as a good aircraft engine."

;D

 

[Simon666]

Another thing that's not entirely accurate is that it's impossible to fly above Mach 2.2 without an almost all titanium structure

The Space Shuttle orbiter structure is made primarily from aluminum alloy and its flying at Mach 25. With a proper thermal protection system, you can use aluminium structure up to almost any speed.

 

[KJ_Lesnick]

Overscan...

Never seen any evidence for anything approaching Mach 4.0, let alone exceeding it.

As I said, there's information about the J-93 which states it was capable of continuous Mach 4 performance. One source includes Valkyrie: North American XB-70 by Steve Pace, page 6, right half of the page, about 2/3rds down.

Temperatures of 1,600°F can be generated by inlet air compression alone at Mach 4

Huh? Last I checked, low hypersonic speeds produce temperatures of 1200 degrees...

As for J-67 being a Mach 3.0 engine, thats simply untrue. I have detailed specs on early Olympus, which J-67 is based on, and its good for Mach 1.8-2.0 at best. The XF-103 used a combination of J-67 and a ramjet; at the higher speeds the J-67 core is sitting pretty.

According to stuff written about the XF-103 was that the upper limit for the jet engines of the era was Mach 3.0, which is why they used the turboramjet system to get around it. May I see what the specs you possess about the Bristol Olympus are? Does it actually list the maximum temperatures, or does it simply list the max mach number?


KJ_Lesnick

 

[overscan (PaulMM)]

It would be helpful if you actually post what it says about J-93.

In terms of Olympus I have thrust curve diagrams showing it limited to just over Mach 2, engine temperature specs, and comments from Sir Stanley Hooker. The first limiting factor was the use of aluminium in the compressor.

 

[overscan (PaulMM)]

According to Landis and Jenkins the allowable flight envelope of the YJ93-GE03 extended to Mach 3.2.

 

[KJ_Lesnick]

Can I see the diagrams you have?

Also, how many jet engines of that era used aluminum in the compressor?

 

[LowObservable]

Best thing I have seen on this subject:

http://www.codeonemagazine.com/archives/1993/articles/apr_93/stretch/index.html

To extend Dryden's argument, there are several factors that can physically limit the speed of any aircraft. If those limits reflect issues that can compromise the safety of the aircraft immediately, or the safety of the aircraft over time (like the F-16 canopy mentioned in the article), or even cause pieces to wear out prematurely, then the flight manual limits will be lower than the physical limits. Or, alternatively, the user simply has not tested to a value higher than what's needed operationally; for example, why bother to test a fighter at a speed that it can't reach carrying weapons?

Ultimately, an airplane's maximum speed is determined by one of three factors:

* The engine and inlet are swallowing as much air as they physically can, and the engine is burning as much fuel as the oxygen will support, and the thrust equals the drag.

* Some component is at its physical limit. For a supersonic jet that limit is likely to be thermal and the normal place for that limit is at the compressor exit. A basic difference between an F119 and an F100, for instance, is that the F119 is built to run hotter and does not have to be throttled back at supersonic speeds.

* The aircraft is outside a safe range for its flight controls. (For example, subsonic airliners don't like going transonic.)

I have a 1956 Observer's Book of Aircraft somewhere, for instance, that says that the XF-104 "is stated to have exceeded Mach 2.8" so the rumours of the F-104's amazing speed have always been around. I have also heard from credible sources of early F-4s going to Mach 2.6 and the Crusader III going that fast or faster. And if you look at Dryden's article, you can see all these things are credible.

Same way, many people have said that the Blackbird series had the thrust capability to go beyond the "official" speeds, and it was tested to speeds that were not approved in operations. However, you're clearly up against thermal limits, too. So a BB probably can't get to its thrust/drag limit safely.

But I'd be really dubious about Mach 2.4 F-101s, let alone Mach 2 F-100s.

 

[avatar]

however as far as the combat capabilities of many aircraft are concerned they are way below specs in the tropics .... one of the reasons that has compelled India and Pakistan to got to war mostly during winter in the past

 

[KJ_Lesnick]

overscan,

The J-67 simply would have to be able to achieve speeds in excess of Mach 2.0. Publicly-available data about the XF-103 often lists the speed at which transition to ramjet occurs around 2.25 Mach to 2.5 Mach (I've heard both, although the former is more common). This is excess of 1.80 to 2.0 or slightly over to the best of my knowledge

Regarding the comments about the J-93, in the B-70 book it simply said that the X-279E, which became the YJ-93 was rated at Mach 4. That's all I can readily quote. However, I remember reading from other sources (wish I had them) that confirmed the same mach-capabilities of the J-93.

I was told by a reliable individual who has all sorts of data on the XB-70 that Walt Spivak, the Chief Engineer of the XB-70 stated that the XB-70's inlets were designed to be capable of operating at Mach 4. Normally I would not give anecdotal evidence as much weight, but...
1.) The individual who told me this is an aerospace engineer, has loads of data on the XB-70, and has never been the type to embellish
2.) The data does seem to mesh with the other statements about the J-93 possessing a Mach 4 capability


Kendra Lesnick

 

[Lee]

"Ultimately, an airplane's maximum speed is determined by one of three factors:
* The engine and inlet are swallowing as much air as they physically can,...
* Some component is at its physical limit....
* The aircraft is outside a safe range for its flight controls...."

All three criteria are valid.
However, in a old past issue of Aviation Week that I came across, there was printed a picture of an SR-71 that had had an engine failure on one side and was making headway back to its base at low altitude on the other engine while that good engine was running full throttle on the afterburner. The tailplanes was canted as far as possible the other way from the bad engine to compensate for the unbalanced thrust.

The exhaust stream had the typical Mach diamonds one sees when fighters and bombers take off. In all other pictures I had seen before, even advanced American and European engines were showing 9-10 diamonds, thus indicating for every diamond, the exhaust was being slowed by the atmosphere one Mach number per diamond.

The J58 had 13 diamonds (I counted twice) and also another 5-8 feet of flame past the last diamond, based on the known dimensions of the plane and compared to the length of the whole flame. The exhaust velocity of the J58 is about 30-40% greater than any engine flying today. No wonder it's still classified.
The Blackbird was rumored in the Air Force (and should be capable) of going Mach 5 at 100,000 ft. and do that for 5,000 miles, starting with a full fuel load in the tanks.

There could be a reason: I had an acquaintance on the internet, who told me when I mentioned the J58, that every part of the engine, and possibly the fuselage as well, was forged from beta titanium parts that had to pass the most rigorous test standards of any plane until then. Forging parts increases the strength of metals 2-3 times over typically available methods.

The CIA made a mistake declassifying that picture. The SR-71 should be capable of Mach 4-5, by my estimation.

There might be something else: if you look at a picture of an SR-71 from the side, you'll see the centerline of the engines are pointed toward the ground by about 10-15 degrees from parallel to the fuselage centerline. That's because aerospace engineers know when a plane flies faster than about Mach 3, the average thrust vector becomes more toward vertical toward the nose the faster the plane goes. That's why Space Shuttle SSME's are always pointed about 30-40 degrees up to allow for the powerful thrust vector to then be forward, rather than nose-high.

Also, the latest version of the F-104 had the aft end of the fuselage bent up deliberately after installing the latest, biggest engine (about 17,900 lbs. thrust with a new compressor and new nozzle). I strongly suspect the newest versions of the F-104 could go Mach 3+.

 

[KJ_Lesnick]

The J58 had 13 diamonds (I counted twice) and also another 5-8 feet of flame past the last diamond, based on the known dimensions of the plane and compared to the length of the whole flame. The exhaust velocity of the J58 is about 30-30% greater than any engine flying today. No wonder it's still classified.

What would the exhaust velocity ammount to?

There could be a reason: I had an acquaintance on the internet, who told me when I mentioned the J58, that every part of the engine, and possibly the fuselage as well, was forged from beta titanium parts that had to pass the most rigorous test standards of any plane until then. Forging parts increases the strength of metals 2-3 times over typically available methods.

What are the temperature limits of beta-titanium or forged beta-titanium? (for airplane uses)

Also, the latest version of the F-104 had the aft end of the fuselage bent up deliberately after installing the latest, biggest engine (about 17,900 lbs. thrust with a new compressor and new nozzle). I strongly suspect the newest versions of the F-104 could go Mach 3+.

I thought they all had the tail bent up slightly... I figured it was to help deal with trim-drag (center of pressure tends to shift aft a lot on unswept wings)

Regarding the Mach-3 capability, I have heard rumblings about the plane having such a capability at least for a quick dash. I also heard something mentioned here that a prototype did Mach 2.8. Now I'm not sure if it already had the half-cone inlets or not, but if that's true...

It was capable of a supersonic cruise of Mach 2 for about 300-350 miles -- allegedly, a modified version to carry a Genie (well it wasn't exactly modified, it was fitted with a Genie Rocket carried on a modified trapeze set-up as part of some USAF requirement) had a 650 mile supersonic radius. I'm not sure if that 650-mile radius was with just the wing-tip tanks, or if it had tanks under the wings too. '


K.J.

 

[Lee]

K.J., quoted:
"What would the exhaust velocity amount to?"

A great many college and research texts I read indicated the average turbofan would have an exit velocity of ~3600-4000 ft/sec in the inner core of the exhaust and ~3200-3600 ft/sec in the outer fan area of clean air, depending on pressure ratio. Many engines have mixers to reduce noise and thermal signature, though. Overall thrust increase would be about 1.6-1.7X at sea level for an engine like the TF30, I think. That's what I read.

(Modified later. I had the exhaust velocities backwards, but they're right now.)



K.J.:
"What are the temperature limits of beta-titanium or forged beta-titanium? (for airplane uses)"

I read 850 deg. C. max. Safe operating temperature was considered 650 deg. C.
The SR-71 was rumored to have the best leading edge wing insulation available because it go so fast. It had nothing to do with "radar absorption". Also, I read the newest Metal/Metallic Carbide (MMC) composite laminates were said to be good to 1700 deg. C.
(Modified later.)




K.J.:
"I thought they all had the tail bent up slightly..."

Please visit: http://www.flightsimkid.be/pages/f104_starfighter_foto_gallerypag.html ,
and look at both the upper and lower picture. The 'G' model (bottom picture) has more bend in the aft fuselage. I remember the original patent and prototype had no bend at all.



K.J.:
"I figured it was to help deal with trim-drag (center of pressure tends to shift aft a lot on unswept wings)"

Well, the all-moving tail of the Bell X-? rocket aircraft had to be canted down at Mach 1+ because the center-of-pressure moved forward to make the plane nose heavy. Several pilots were killed before Chuck Yeager got it right and lived through the experience.
the same thing happens to the American KC-135 (I worked on them in the Air Force) and the Concorde (read that in a nonfiction historical expose' of the plane.
The F-106 and B-58 were different: The delta wing(s) forced designers to link the controls opposite in direction above Mach 1, thus making the trailing edge parts deflect up to dive, and down to climb. (I learned that in job specialty training in the Air Force.) That's just the physics of delta wings, I guess.




K.J.:
"...heard something mentioned here that a prototype did Mach 2.8."

A test pilot was said to have dived at Mach 3 or more and was considered foolish for the stunt. "Living dangerously" was the phrase his buddies used.




K.J.:
"...It was capable of a supersonic cruise of Mach 2 for about 300-350 miles --
...had a 650 mile supersonic radius. I'm not sure if that 650-mile radius was with just the wing-tip tanks, or if it had tanks under the wings too."

Mach 2 with afterburner and at, say, 50,000 ft. The F-22 & F-35 can supercruise without A/B because of their big, high pressure engines.
650 miles, if possible, would probably require tip tanks and no afterburner, or else range would be cut short in a hurry. I don't think the F-104 engine(s) were powerful enough for supercruise without A/B.




K.J.:
"Regarding the Mach-3 capability, I have heard rumblings about the plane having such a capability at least for a quick dash."

I'd say so, too. There was a rumor in the Air Force that the B-58 could go Mach 3 for a few minutes until the airframe was stressed by heat and forced to decelerate. The F-104 should have been no different. This performance guzzled fuel at a fantastic rate, as well as being risky. Even the MiG Foxhound is time limited to Mach 2.8-2.85 indefinitely. Mach 2.9-3.0 has about a 20-minute time limit with the engines possibly requiring overhaul at the base. Not a good idea unless absolutely necessary. (Read that in a British aerospace magazine a while ago.)
The Foxbat was clocked at Mach 3.2 over Egypt by the Israelis one time. A defecting pilot later said the engines were trashed by the heat stress and high RPM's and could quit running.

 

[KJ_Lesnick]

A great many college and research texts I read indicated the average turbofan would have an exit velocity of ~3000-3200 ft/sec in the inner core of the exhaust and ~3600-4000 ft/sec in the outer fan area of clean air, depending on pressure ratio. Many engines have mixers to reduce noise and thermal signature, though. Overall thrust increase would be about 1.6-1.7X at sea level for an engine like the TF30, I think. That's what I read.

The fan area would have a higher exhaust velocity? (I know the fan area is just pure air, but I thought it's pressure ratio would be lower than the core which has a 65% air content roughly)

I read 1000-1200 deg. C. The SR-71 was rumored to have the best leading edge wing insulation available because it go so fast. It had nothing to do with "radar absorption". Also, I read the newest Metal/Metallic Carbide (MMC) composite laminates were said to be good to 1700 deg. C.

What mach numbers would have to be achieved on a fairly streamlined aircraft (keep in mind the more streamlined the plane, the less kinetic heating, and chines also work well even at hypersonic speeds IIRC) to reach skin temperatures of 1000-1200 C?

Did the Blackbird have MMC composites on it? If so, what mach numbers would you have to achieve to reach those temperatures with a streamlined design?

Please visit: http://www.flightsimkid.be/pages/f104_starfighter_foto_gallerypag.html ,
and look at both the upper and lower picture. The 'G' model (bottom picture) has more bend in the aft fuselage. I remember the original patent and prototype had no bend at all.

Something might be wrong with my computer, the background loaded but no images. I can probably find some pictures online via a google image-search.

Well, the all-moving tail of the Bell X-? rocket aircraft had to be canted down at Mach 1+ because the center-of-pressure moved forward to make the plane nose heavy. Several pilots were killed before Chuck Yeager got it right and lived through the experience.

the same thing happens to the American KC-135 (I worked on them in the Air Force) and the Concorde (read that in a nonfiction historical expose' of the plane.

It was more than just the shift in the center of pressure that nailed a lot of pilots, which occurs just before you break the sound barrier as the upwash ahead of the wing goes away, but also, as the shockwave would go over the crest you'd lose the downwash which would deprive the tail of much of it's downward load. Supersonic flow over the tail, shockwaves and resulting turbulence would deaden the flow behind it making the elevators ineffective, eventually the shockwaves would move over the elevator surface potentially jamming the surface (not sure about that one, but I remember hearing about that once) or causing vibration, and possibly flutter.

In regards to the KC-135, it doesn't have a stabilator. Primary pitch-control is accomplished with elevators, with the pilot trimming the plane with the stabilizer -- Most jet-airliners actually, are set-up this way. Of course, the KC-135A was faster than most jetliners (Wing optimized for Mach 0.88, stabilizer fitted with large vortex-generators to maintain energetic flow over it to enable safe flying up to Mach 0.95).

Interestingly the F-86 prototype didn't have a stabilator (it had elevators and stab-trim) either, but it could break the sound-barrier in shallow-dives. The pilot would probably use stab-trim to get him out of the dive, but the F-86 probably had very minor Mach-tuck problems compared to the X-1 with it's 35-degree sweepback. Later models were fitted with a stabilator -- I'm guessing it was predominantly to help improve the amount of G's the pilot could pull, more actually than to assist dive recovery though it probably helped.

The Concorde doesn't have a horizontal-stabilizer at all -- it's a delta-wing and has elevons for trim control -- that, along with shifting fuel aft as ballast for supersonic flight.

The F-106 and B-58 were different: The delta wing(s) forced designers to link the controls opposite in direction above Mach 1, thus making the trailing edge parts deflect up to dive, and down to climb. (I learned that in job specialty training in the Air Force.) That's just the physics of delta wings, I guess.

Huh? To the best of my knowledge, a delta-wing's elevons deflect trailing-edge up for nose-up, and trailing-edge down for nose-down...

I think you might be mistaking that for this
-Increase angle of attack, vortices form
-Increase it further, plane "stalls", starts to sink but remains controllable
-Lower it below that point and lift goes back up and the sink rate actually drops (when you lower the nose below critical alpha)

A test pilot was said to have dived at Mach 3 or more and was considered foolish for the stunt. "Living dangerously" was the phrase his buddies used.

Was this before or after the half-cone inlets were added?

Mach 2 with afterburner and at, say, 50,000 ft. The F-22 & F-35 can supercruise without A/B because of their big, high pressure engines.
650 miles, if possible, would probably require tip tanks and no afterburner, or else range would be cut short in a hurry. I don't think the F-104 engine(s) were powerful enough for supercruise without A/B.

What speed would the F-104 be capable of supersonic with no afterburner? (Because to my knowledge, it didn't need burner for Mach 2)

I'd say so, too. There was a rumor in the Air Force that the B-58 could go Mach 3 for a few minutes until the airframe was stressed by heat and forced to decelerate. The F-104 should have been no different. This performance guzzled fuel at a fantastic rate, as well as being risky. Even the MiG Foxhound is time limited to Mach 2.8-2.85 indefinitely. Mach 2.9-3.0 has about a 20-minute time limit with the engines possibly requiring overhaul at the base. Not a good idea unless absolutely necessary. (Read that in a British aerospace magazine a while ago.)

I've heard similar things about the B-58 as well, and claims made about the honeycomb-sandwhich panels able to take higher temperatures than traditional aluminum. I'm not sure the exact details, but it might partially be due to the particulars of the panel design.

 

[starviking]

There might be something else: if you look at a picture of an SR-71 from the side, you'll see the centerline of the engines are pointed toward the ground by about 10-15 degrees from parallel to the fuselage centerline. That's because aerospace engineers know when a plane flies faster than about Mach 3, the average thrust vector becomes more toward vertical toward the nose the faster the plane goes. That's why Space Shuttle SSME's are always pointed about 30-40 degrees up to allow for the powerful thrust vector to then be forward, rather than nose-high.

In the hypersonics section of British Secret Projects 4 a reason given for thrust deflection is that it cuts down on the amount of lift that needs to be derived from the wings, thus allowing the plane's orientation to be closer to the horizontal which decreases drag.

As for the SSME's on the Shuttle - the reason for their deflection is because they have to deal with the centre of mass being outside the Shuttle itself - due to the large external fuel tank.

Starviking

 

[Lee]

KJ, quoted: "The fan area would have a higher exhaust velocity?"

I think the theoretical reasoning is that the fan air can rise higher in temperature because it's cooler to start with and has no unburned fuel, carbons dioxide or water vapor to inhibit further combustion. Higher velocity, yes.




KJ: "What mach numbers would have to be achieved on a fairly streamlined aircraft (keep in mind the more streamlined the plane, the less kinetic heating, and chines also work well even at hypersonic speeds IIRC) to reach skin temperatures of 1000-1200 C?"

I read Mach 4-5 at 90,000 ft., but a higher altitude has the effect of lower skin temperatures more.




KJ: "Did the Blackbird have MMC composites on it? If so, what mach numbers would you have to achieve to reach those temperatures with a streamlined design?"

The Blackbird was made of titanium; it was all they had in the 60's. The MMC laminates are a recent development. For 1,000-1,200 deg C. nose temperatures, maybe Mach 6-7 at 100,000-110,000 ft.





KJ: "It was more than just the shift in the center of pressure that nailed a lot of pilots, which occurs just before you break the sound barrier as the upwash ahead of the wing goes away, but also, as the shockwave would go over the crest you'd lose the downwash which would deprive the tail of much of it's downward load...."

I hadn't heard of that. It's new to me.





KJ: "...Supersonic flow over the tail, shockwaves and resulting turbulence would deaden the flow behind it making the elevators ineffective, eventually the shockwaves would move over the elevator surface potentially jamming the surface (not sure about that one, but I remember hearing about that once) or causing vibration, and possibly flutter."

Subsonic T-tail airliners are also prone to downstream wash effects in a stall when turbulence aft of the wing impacts operation of the T-tail and adds to the controll-ability problem.





KJ: "Interestingly the F-86 prototype didn't have a stabilator (it had elevators and stab-trim) either, but it could break the sound-barrier in shallow-dives. The pilot would probably use stab-trim to get him out of the dive, but the F-86 probably had very minor Mach-tuck problems compared to the X-1 with it's 35-degree sweepback. Later models were fitted with a stabilator -- I'm guessing it was predominantly to help improve the amount of G's the pilot could pull, more actually than to assist dive recovery though it probably helped."

Quite possibly. There was a TV special on American PBS concerning the Korean War and the F-86 was considered much safer in a supersonic dive than a Mig because of the improved tail controls.


KJ: "The Concorde doesn't have a horizontal-stabilizer at all -- it's a delta-wing and has elevons for trim control -- that, along with shifting fuel aft as ballast for supersonic flight."

Right. Standard procedure for that type of aircraft.




KJ: "Huh? To the best of my knowledge, a delta-wing's elevons deflect trailing-edge up for nose-up, and trailing down for nose-down...
I think you might be mistaking that for this
-Increase angle of attack, vortices form
-Increase it further, plane "stalls", starts to sink but remains controllable
-Lower it below that point and lift goes back up and the sink rate actually drops (when you lower the nose below critical alpha)"

No, really! That's what I was told in the Air Force. But, to qualify myself: it was 35 years ago and I wasn't told by a qualified aerospace engineer with a degree. I could have been told something out of ignorance, but my correspondent was sincere at the time. I hadn't heard of your assertions.



Lee: "A test pilot was said to have dived at Mach 3 or more (in an F-104) and was considered foolish for the stunt. "Living dangerously" was the phrase his buddies used.[/quote]"
KJ: "Was this before or after the half-cone inlets were added?"

I'm not sure. The implication was that the prototype was redlined at about Mach 2.9- 3.0.





KJ: "What speed would the F-104 be capable of supersonic with no afterburner? (Because to my knowledge, it didn't need burner for Mach 2)"

Well, I didn't say in the original posting that I had seen an Internet reference to an experience an F-104 pilot had with the latest model of that fighter. They had the biggest engine and a new nozzle to be able to 'practice/training intercept a U-2 at 75,000 ft for a few minutes and at Mach 1.
I did a math experiment (with performance assumptions) that indicated it was possible as long as the F-104 had only about 1,000 or maybe 1,500 lbs of fuel left to get back to its base. A couple of minutes was all it could stay at the altitude and no afterburner.
But, I honestly say it couldn't go faster without A/B. Otherwise, there would be no logical need for supercruise today with the F-22 & F-35 if they had it on the F-104, then.






KJ: "I've heard similar things about the B-58 as well, and claims made about the honeycomb-sandwhich panels able to take higher temperatures than traditional aluminum. I'm not sure the exact details, but it might partially be due to the particulars of the panel design."

Right, good point. Titanium has more strength at higher temperatures than aluminum and also U.S. Patents exist that maintain overlapping 'spliced' fuselage panels are stronger than those merely joined at the edges. Whether that extends to honeycomb panels is open to discussion. I have no precise experience with the last point on honeycomb panels.

 

[KJ_Lesnick]

I think the theoretical reasoning is that the fan air can rise higher in temperature because it's cooler to start with and has no unburned fuel, carbons dioxide or water vapor to inhibit further combustion. Higher, velocity, yes.

Especially if you have a multi-staged fan...

I read Mach 4-5 at 90,000 ft., but a higher altitude has the effect of lower skin temperatures more.

You know, I thought the X-15 reached approximately 1,200 Farenheit at Mach 6...

While this might not be the most intelligent question, out of curiousity, was the forged beta-titanium wing leading-edge insulation honeycombed or just regular sheets?

The Blackbird was made of titanium; it was all they had in the 60's. The MMC laminates are a recent development. For 1,000-1,200 deg C. nose temperatures, maybe Mach 6-7 at 100,000-110,000 ft.

How would an MMC laminate yield a higher mach number for the same temperature as a forged titanium-beta piece? And what would 1,700 C ammount to?

I hadn't heard of that. It's new to me.

Yeah, it's true though to the best of my knowledge.

Subsonic T-tail airliners are also prone to downstream wash effects in a stall when turbulence aft of the wing impacts operation of the T-tail and adds to the controll-ability problem.

Yeah, a deep-stall. There are ways around the problem though. The Ilyushin Il-62 for example used a dog-tooth somehow to prevent a deep-stall. There are some Learjets that use highly-swept ventral-fins to shed a vortex over the tail enabling it to avoid the problem.

No, really! That's what I was told in the Air Force. But, to qualify myself: it was 35 years ago and I wasn't told by a qualified aerospace engineer with a degree. I could have been told something out of ignorance, but my correspondent was sincere at the time. I hadn't heard of your assertions.

While he may have been sincere, he was wrong. The elevons work on the same principle as elevators when used for pitch control
-Pilot pulls back on stick, elevons deflect up: Upward deflection of air forces the trailing edge of the wing and tail down, and consequently forces the nose up
-Pilot pushes forward on the stick, elevons deflect down: Downward deflection of air forces the trailing edge of the wing and tail down, and consequently forces the nose down

Regarding my assertions about delta-wings (or any wing to my knowledge) with leading-edge sweep-angles approaching, equalling or exceeding 60-degrees at low alphas produce lift like any ordinary wing. As the alpha increases, a vortex is formed on the leading-edge energizing the flow augmenting overall-lift beyond that of a straight-wing of the same exact cross-section and t/c-ratio, and substantially delaying stall. As the delta wing reaches it's "critical-alpha" it "stalls" which isn't exactly a traditional-stall, the amount of lift falls off, yes, and a sink-rate developes, but the vortex maintains a reasonably energetic flow over the wing allowing control-surface effectiveness. Lowering the alpha below critical causes the high levels of lift to be restored -- the sink rate drops as the alpha and nose-pitch are reduced.


KJ

 

[Lee]

KJ_Lesnick, quoted: "Especially if you have a multi-staged fan..."

Right, but there's a tradeoff in greater weight vs higher thrust/more fuel burned.





KJ: "You know, I thought the X-15 reached approximately 1,200 Fahrenheit at Mach 6...

It did. But not for any great length of time, though. I had a book I don't have now (serious financial difficulty) that went into the complete design specifications and performance parameters of the plane.





KJ: "While this might not be the most intelligent question, out of curiously, was the forged beta-titanium wing leading-edge insulation honeycombed or just regular sheets?

For any of the the X-15, SR-71, B-70, etc? Sheets should have been the way to go. Honeycomb was made of very lightweight sheet and would have deformed under the stress first, and excessive heat second, yes?
This opinion is from personal experience in the design of slower aircraft at lower altitudes having more dynamic pressure on the fuselage.





KJ: "How would an MMC laminate yield a higher mach number for the same temperature as a forged titanium-beta piece? And what would 1,700 C amount to?

MC whiskers, especially long-aspect-ratio nano-scale ones, would impart considerable extra strength to a titanium sheet laminate. If it's stronger, it can be made lighter, allowing for a higher altitude to operate at, thus effectively lowering heat flux impacting the fuselage.
But whether or not something like cold rolled metal sheet for maximum yield strength is the same as forging the sheet, I'm not sure. Metalurgy isn't a subject I've kept up with, since the field changed continually and some of it's classified now and in the past.

1700 deg. C. as speed?
Well, I saw on another SP thread, the SR-71 near the nose was experiencing about 550 deg. C. If the Concorde was at 275 or so, then I could try and extrapolate:
Concorde Mach 2.2 @ 55,000 ft = 275 deg. C.
SR-71 " 3 @ 80,000 " = 550 "
X-15 " 6 @ 100,000 " = 650 " (1200 deg. F.)
Sanger TSTO " 10 @ 120,000 " = 800-900 " (?)
Orient Express " 15 @ 150,000 " = 1200-1500 " (?) (skipping stone climb-and-glide maneuver)
Shuttle reentry " 17-18(?) @ 175,000-200,000(?) " = ~1700 "(?) " (~3,000 deg. F.)
" " = ~ 2000 (?) " (Shuttle max ~= 3600 deg. F.)

As a sidebar explanation, I'd say I've seen Patents and Internet accounts that maintain hafnium diboride(HfB2) or possibly tantalum carbide(TaC) powder or whiskers embedded in a properly prepared sintered weave carbon fiber matrix sheet on the leading edge of a wing can handle up to 2,000 Deg. C. in a typical breathable atmosphere. The technology was so promising, it appears the military disallowed further public disclosure(s) in press releases and may have classified some of the information.

MMC laminates are very expensive and therefore not seen on unclassified projects that I've heard of.

 

[KJ_Lesnick]

Right, but there's a tradeoff in greater weight vs higher thrust/more fuel burned.

Wait... I figured it would add weight, but increase thrust and REDUCE fuel consumption?

It did. But not for any great length of time, though. I had a book I don't have now (serious financial difficulty) that went into the complete design specifications and performance parameters of the plane.

But if it reached 1,200 Farenheit at Mach 6... and the Blackbird reached 1,200 Celsius... Think about it...

Well, I saw on another SP thread, the SR-71 near the nose was experiencing about 550 deg. C.

Then why would it be designed with titanium alloys to resist up to 1,700 C?

If the Concorde was at 275 or so, then I could try and extrapolate:
Concorde Mach 2.2 @ 55,000 ft = 275 deg. C.
SR-71 " 3 @ 80,000 " = 550 "
X-15 " 6 @ 100,000 " = 650 " (1200 deg. F.)
Sanger TSTO " 10 @ 120,000 " = 800-900 " (?)
Orient Express " 15 @ 150,000 " = 1200-1500 " (?) (skipping stone climb-and-glide maneuver)
Shuttle reentry " 17-18(?) @ 175,000-200,000(?) " = ~1700 "(?) " (~3,000 deg. F.)
" " = ~ 2000 (?) " (Shuttle max ~= 3600 deg. F.)

The shuttle isn't moving at Mach 25 when entering the atmosphere? I thought it would hit it while moving at a full 17,500 or very close.

The Orient-Express, the 305-pax hypersonic-jetliner idea (~1985) to my knowledge was only designed for Mach 5 and flew a climb-path similar to the Concorde... Takeoff, Climb to supersonic penetration speed, Accelerate to speed, reach the start of the cruise-climb, then drift up to max, slow down and descend, go subsonic, approach airport, and land. Different altitudes and speed than the Concorde sure...

Were there multiple Orient-Express design proposals designed for different speeds, or was the Mach 5 speed just inaccurate?

The Concorde at Mach 2.2 might reach 275-F, however during cruise (Mach 2), nose temperature is approximately 260 Farenheit.


Kendra

 

[Lee]

I'll finally get around to answering these questions:

KJ, quoted: "Wait... I figured it would add weight, but increase thrust and REDUCE fuel consumption?"

Okay, a misunderstanding. I meant specific fuel consumption, since the overall pressure ratio in that part of the engine will be higher. More fuel, with air, is being burned and thrust is greater as a result.



Lee: "Well, I saw on another SP thread, the SR-71 near the nose was experiencing about 550 deg. C." (Actually it might have been deg. F.)
KJ: "Then why would it be designed with titanium alloys to resist up to 1,700 C?"

It might have gone Mach 5-6 and gotten that hot. But, then, the leading edges and nose might also been made of something other than titanium (like molydemum or a tantalum/halfnium compound to stand up to the heat. (I would have used that stuff if I was working on the design team and I knew it could and would do the job.)

If the Concorde was at 275 or so, then I could try and extrapolate:
Concorde Mach 2.2 @ 55,000 ft = 275 deg. C.
SR-71 " 3 @ 80,000 " = 550 "
X-15 " 6 @ 100,000 " = 650 " (1200 deg. F.)
Sanger TSTO " 10 @ 120,000 " = 800-900 " (?)
Orient Express " 15 @ 150,000 " = 1200-1500 " (?) (skipping stone climb-and-glide maneuver)
Shuttle reentry " 17-18(?) @ 175,000-200,000(?) " = ~1700 "(?) " (~3,000 deg. F.)
" " = ~ 2000 (?) " (Shuttle max ~= 3600 deg. F.)

KJ: "The shuttle isn't moving at Mach 25 when entering the atmosphere?

It is. About 5 1/2 miles/second. About 29,000-30,000 ft/sec. About 8-9 klicks/second.





KJ: "I thought it would hit it while moving at a full 17,500 or very close.

I think the Shuttle (or anything else) will slow down some before experiencing maximum heating, but the temperature would be about 3,600 deg. F at max. (Enough to cause a radio blackout from ionization.)





KJ: "Were there multiple Orient-Express design proposals designed for different speeds, or was the Mach 5 speed just inaccurate?

There were probably competing company proposals on the drawing boards at the time being paid for by company funds. I strongly suspect many of them were finally considered expensive, unworkable or unsalable, so they were thrown out.




KJ: "The Concorde at Mach 2.2 might reach 275-F, however during cruise (Mach 2), nose temperature is approximately 260 Farenheit.

Sorry, you're right. I get confused sometimes between metric and American units. I do remember reading as a teenager that weight was saved in the Concorde nose when they used a heat-resistant aluminum alloy instead of steel or titanium. 260 deg. F. is about the max for aluminum.

 

[KJ_Lesnick]

But, then, the leading edges and nose might also been made of something other than titanium (like molydemum or a tantalum/halfnium compound to stand up to the heat. (I would have used that stuff if I was working on the design team and I knew it could and would do the job.)

What's the capabilities of molybdenum, tantalum/halfnium compounds?


KJ_Lesnick

 

[Lee]

KJ_Lesnick, quoted: "What's the capabilities of molybdenum, tantalum/hafnium compounds?

Molybdenum can stand up to, say, 2000. deg. C. uncooled and maybe 3600 well-cooled. That's why designers use it in exhaust turbines.

Tantalum carbide can stand 2500-3000 deg. C and hafnium diboride can stand up to 2000, but neither is strong enough to use in compressors or turbines. Leading edges of wings and noses are highly favored---as long as they're reinforced with a substrate of something like carbon-carbon matrix of woven plastic material and then have it heated treated to integrate-bond the whole structure.

The U.S. military probably classified the information, because I hear nothing today about it, but patents still exist to be seen publicly at least they used to be around. They may also have been classified. GOOGLE Advanced Patent Search is the way to go for that.

 

[KJ_Lesnick]

Are you sure the Blackbird had them in it's design?

 

[Lee]

KJ_Lesnick, quoted: "Are you sure the Blackbird had them in it's design?

No, the Blackbird was built of titanium bought from Russia, since they have a lot more of the metal available than the U.S. What saved the SR-71's airframe was that fuel (high temperature) was circulated around the chines and used to cool the rest of the plane.
Another member corrected stated that even if the Shuttle was made mostly of aluminum, the TPS was efficient enough, most of the time, to keep the fuselage from melting. Unfortunately, the TPS isn't tough enough to stand being hit by falling ice or foam from the liquid fuel tank, which caused the loss of a Shuttle over Texas.
The Blackbird is made of stronger metal than aluminum, but nevertheless isn't strong enough to, say, handle an attempt to break the Foxbat's climb-to-height record of about 115,000 ft., I think. Hence the fuel-cooled fuselage.
The SR-72 could certainly do it, but the reentry would be fatal to plane and pilot. I don't believe the plane was ever designed to put up with 5-6 Gs deceleration and serious random vibration on top of that.

 

[KJ_Lesnick]

Lee,

It used active-cooling throughout the chines? Are you sure? If the skin reached 1,200C with active-cooling, how hot would the skin have been without it?

From what I remember, I just thought the fuel was used to cool the electronics, the pilot, parts of the engines (it operated the engine controls but probably would have provided an active cooling function) and the afterburner.


Regarding high-speed aircraft thermal-protection systems. Paul Czysz mentioned something about McDonnell's hypersonic designs, and the aerospace plane they had from 1964 to at least 1979, that they all used light weight thermal-protection systems in lieu of a hot-design. How did they manage to manage to keep the TPS tough enough? From what Czysz said, the planes they developed were about as easy to operate as a B-52.


Kendra Lesnick

 

[Lee]

KJ_Lesnick, quoted: "Lee, It used active-cooling throughout the chines? Are you sure?

That's what I heard, although I didn't learn that until recently.
Try this: http://en.wikipedia.org/wiki/SR-71_Blackbird
Wikipedia has sometimes been criticized for being a 'soapbox' for someone's personal agenda, but then the references should always be considered carefully before judgement in any case.





KJ: "If the skin reached 1,200C with active-cooling, how hot would the skin have been without it?

To last 25 working years at Mach 3-5, heat stress on the airframe should be kept to a minimum. JP-10 was described to me as being barely pourable on the ground, so supersonic environments would be able to take off a lot of heat without it coking in the fuel lines and clogging them. Hot hot? I'm not sure, but my practical experience would lead me to believe 450-500 deg F.--down from the skin temperature of about 1200 would be reasonable. Even the Mach 5 civil transports would have similar problems with heat.





KJ: "From what I remember, I just thought the fuel was used to cool the electronics, the pilot, parts of the engines (it operated the engine controls but probably would have provided an active cooling function) and the afterburner."

Sounds right to me. Don't forget the tires. Dry N2 and I think(?) special rubber was used.





KJ: "How did they manage to manage to keep the TPS tough enough? From what Czysz said, the planes they developed were about as easy to operate as a B-52."

They probably were that easy to operate. As for the TPS, I myself would put a sheet of heat-resistant material welded over the spars and/or honeycomb sheet. Then a lightweight TPS over that and bonded to the sheet. Lastly, a load-bearing skin of something both strong and heat-resistant. Titanium doesn't have a big weight penalty at Mach 4-5 and Inconel does have any such weight penalty, but also has strength advantages at that speed and temperature. Tradeoffs may need to be made, here.

 

[KJ_Lesnick]

Lee,

You read about the active cooling of the chines from a wikipedia article, or did you also read this in other sources? Because some things written in that article don't sound quite right, like the statement of the plane doing a quick sprint to warm up the airframe prior to refuelling. I've seen pictures of the plane refuelling and it seemed to be wet... in some areas. Still, active-cooling of the chines doesn't sound too far out there and may very well be possible.

JP-10? I thought the Blackbird used JP-7 as it's fuel.
Out of curiosity, should they have decided to fly faster and using the active cooling to keep the skin at that temperature (1,200 C)... how many degrees would the fuel have trimmed off at those higher temperatures (still 450 F to 500 F or less)?

Regarding the tires of the Blackbird. The main gears featured aluminum bits in the rubber which provided a heat-reflecting effect and made them silver in color. I know it used nitrogen to inert them, but I don't recall dry N2 being used in the gears. However liquid N2 was used for inerting the tanks.

 

[Lee]

KJ, quoted: "Lee, You read about the active cooling of the chines from a wikipedia article, or did you also read this in other sources?

There was another source as well long ago, but I don't have it now. It said the same thing as Wikipedia. (Wikipedia entries should be carefully researched, since all entries are Internet public generated and therefore only someone's opinion.)





KJ: "...I've seen pictures of the plane refuelling and it seemed to be wet... in some areas...."

That's what I was told in the Air Force as well. Fuels tanks leaked fuel slowly, but continuously. Also, the plane flew for 1/2 hr at sea level before landing so maintenance workers could touch it without burning themselves, it was that hot all over(!)




KJ: "Because some things written in that article don't sound quite right, like the statement of the plane doing a quick sprint to warm up the airframe prior to refuelling."

You're right in your hunch. I saw a Blackbird take off at U-Tapoa Air Base in Thailand and the Blackbird headed straight for the refueling tanker that took off after it so that the Blackbird was immediately behind it rather than fly unnecessary distance in catching the tanker that could have theoretically taken off before it and would have been 5-10 miles away by the time the Blackbird reached the end of the runway.
Blackbirds refuelled at sea level.





KJ: "JP-10? I thought the Blackbird used JP-7 as it's fuel."

Okay, you're right; I'm not extremely familiar with the plane. Additionally, however, I was told the fuel of the Blackbird was like molasses at sea level. Really. Is JP-7 that thick? My correspondant may have been kidding me at the time. Rumors are rampant in the military. Especially amongst first-term *grunt* troops.





KJ: "Out of curiosity, should they have decided to fly faster and using the active cooling to keep the skin at that temperature (1,200 C)... how many degrees would the fuel have trimmed off at those higher temperatures (still 450 F to 500 F or less)?"

There's a limit, of course. NOTE: While researching this posting, I skimmed an NTRS report the went into the SiC/beta-titanium heat/strength issues and test results at the back showed at 815 deg. C, most test specimens were 1/2 as strong or less than at room temperature. The conclusion was to limit temperature(s) to a max of 650 deg. C.
(is actually about equal to 1200 deg. F)
Unfortunately, I didn't keep the title or URL address of the paper because I didn't have money to print it off.
To answer your question: 1,200 deg. F would probably have to be as high as one can go with metallic Ti or MMC composites. How heat resistant is JP-7? Is that information classified? The Blackbird information in general is probably classified and subject to official disinformation, which is also rampant in the Gov't, in my opinion.
And, also, the "JP-7" may have been a special blend that was different than typical JP-7? Those KC-135s were assigned specifically to the SR-71s and that's all they serviced, I was told. JP-7 may not be easy to run in ordinary jet engines.
BTW, I read two books in the past on the Blackbird and one of them(for sure) said the fuel had to be pre-ignited in the J58 combustion chamber by a spontaneously flammable borane compound sprayed into the burner to get the engine to start. The fuel had a real low vapor pressure---which lends credence to it being hard to pour at S/L.




KJ: "Regarding the tires of the Blackbird. The main gears featured aluminum bits in the rubber which provided a heat-reflecting effect and made them silver in color."

True. They were like that.





KJ: "I know it used nitrogen to inert them, but I don't recall dry N2 being used in the gears. However liquid N2 was used for inerting the tanks.

Water would have boiled at Mach 3-5, yes? Steam has a volume ~800-1000 times water and could have burst the tires at supersonic speeds. The fuel tanks were inerted with N2, right.

 

[Loon]

The KC 135Q carried JP 7, just for the blackbirds. The crews said they could burn the JP 7 if they had to but it would send they engines to the shop after. The fuel has to be heated to burn, by using it as a coolant and hydralic fluid, it heats up. The fuel has low vapor presure because at 70 to 80,000 ft there isn't much presure. The fuel tanks leaked on the ground, when the metal was heated up by high mach it expanded sealing the gaps.
One thing I heard back in the 80's was that if the russians broke the speed record, we'd take it back the next day. The Air Force wouldn't let them set any more records until they were broken. The glass on the canopy got to 400 to 500 F, hot enough to warm food on long missions. Each flight was like a space mission, presure suits, alot of specialized maintence, fueling at the last minute, precise nav, tankers and the mission target.
One thing I've always thought of, the SR was origionally RS, as in Recon Strike. The D21 drone would have made an excellant mach 3+ cruise missle.

 

[KJ_Lesnick]

There was another source as well long ago, but I don't have it now. It said the same thing as Wikipedia. (Wikipedia entries should be carefully researched, since all entries are Internet public generated and therefore only someone's opinion.)

Seems to make more sense since it's there's more than one source that confirms it. Especially since it's not just wikipedia.

That's what I was told in the Air Force as well. Fuels tanks leaked fuel slowly, but continuously. Also, the plane flew for 1/2 hr at sea level before landing so maintenance workers could touch it without burning themselves, it was that hot all over(!)

Sea-level? Do you actually mean at zero feet? Was this even done on the record setting flights too?

You're right in your hunch. I saw a Blackbird take off at U-Tapoa Air Base in Thailand and the Blackbird headed straight for the refueling tanker that took off after it so that the Blackbird was immediately behind it rather than fly unnecessary distance in catching the tanker that could have theoretically taken off before it and would have been 5-10 miles away by the time the Blackbird reached the end of the runway.
Blackbirds refuelled at sea level.

Was this a routine practice to refuel the plane just after the KC-135 took off? From what I read most refuellings were done at 25,000 feet with the tanker at Mach 0.95 (KC-135 Mmo = 0.95, Vmo = 350 kts)

Okay, you're right; I'm not extremely familiar with the plane. Additionally, however, I was told the fuel of the Blackbird was like molasses at sea level. Really. Is JP-7 that thick? My correspondant may have been kidding me at the time. Rumors are rampant in the military. Especially amongst first-term *grunt* troops.

I don't know if it was as thick as molasses, but it was probably thicker than typical jet-fuel.

There's a limit, of course. NOTE: While researching this posting, I skimmed an NTRS report the went into the SiC/beta-titanium heat/strength issues and test results at the back showed at 815 deg. C, most test specimens were 1/2 as strong or less than at room temperature. The conclusion was to limit temperature(s) to a max of 650 deg. C.
(is actually about equal to 1200 deg. F)

What's the NTRS?
Regarding the 1,200 C figure, it *does* seem to mesh with some data on the Blackbird.

Unfortunately, I didn't keep the title or URL address of the paper because I didn't have money to print it off.
To answer your question: 1,200 deg. F would probably have to be as high as one can go with metallic Ti or MMC composites. How heat resistant is JP-7? Is that information classified? The Blackbird information in general is probably classified and subject to official disinformation, which is also rampant in the Gov't, in my opinion.
And, also, the "JP-7" may have been a special blend that was different than typical JP-7? Those KC-135s were assigned specifically to the SR-71s and that's all they serviced, I was told. JP-7 may not be easy to run in ordinary jet engines.

I am aware of at least one type of Titanium-Aluminide that could take temperatures of 3,500 degrees... I'm not sure I understand what you meant about the JP-7. To the best of my knowledge JP-7 is JP-7. It was a high temperature fuel designed almost exclusively for the Blackbird. Although I've been told the X-43 now uses it.

BTW, I read two books in the past on the Blackbird and one of them(for sure) said the fuel had to be pre-ignited in the J58 combustion chamber by a spontaneously flammable borane compound sprayed into the burner to get the engine to start. The fuel had a real low vapor pressure---which lends credence to it being hard to pour at S/L.

Yes, that's true that in order to get it's engines started they needed to spray TEB into the combustor while spraying in fuel. TEB autogenously ignites in air and it burns real hot -- enough to set off the fuel. The plane has a special tank with a capacity for I think 16 metered-shots of TEB. It typically takes 2-4 shots to start each engine, and one shot to start the burner. Since it's possible to run out on long flights, the burner at least uses a catalyltic device that enables the burner to be ignited without TEB if necessary.



KJ

 

[Lee]

Lee, quoted: "...Also, the plane flew for 1/2 hr at sea level before landing so maintenance workers could touch it without burning themselves, it was that hot all over(!)"
KJ, quoted: "Sea-level? Do you actually mean at zero feet?

Yep, and here's the reason: sea level atmosphere has a typical temperature of 50-90 deg. F. at European and American latitudes most of the year, right? Air will carry away heat by convection across the fuselage, but a majority of metals retain heat well, depending of atomic properties peculiar to each one. Eventually, the skin temperature will return to safe levels before landing. With most fuel burned on returning to the base, throttle settings on the engines can be conservative compared to takeoff.

KJ: "Was this even done on the record setting flights too?"

All flights above Mach 3.





KJ: "Was this a routine practice to refuel the plane just after the KC-135 took off?"

I only saw the plane take off once, but that's what it did. Logically, it occurs to me that gross takeoff weight(GTOW) depends on mission requirements, but the J-58 was known to be fuel hungry at sea level.
Moreover, I happened to come across a picture of a Blackbird taking off with both engines running normally, not with one engine out as I had said happened once to another blackbird in an emergency landing on site.
I counted 10 Mach diamonds in the second(normal takeoff) picture and and about 13 1/2 in the first(emergency landing) picture. My point is: SR-71's take off with less than full afterburner to save fuel normally. The maximum exhaust velocity of the J-58 is 30-40 % higher than the J-75 or J-79.





KJ: "From what I read most refuellings were done at 25,000 feet with the tanker at Mach 0.95 (KC-135 Mmo = 0.95, Vmo = 350 kts)"

Well, the tanker and Blackbird would have been over the horizon by that time, so you probably have a point. What I meant was, the Blackbird refueled subsonically and merely sprinting a ways to heat the airframe to seal the tanks would be a waste of time if it cooled(and leaked) while refueling.



KJ: "I don't know if it was as thick as molasses, but it was probably thicker than typical jet-fuel. ...I'm not sure I understand what you meant about the JP-7. To the best of my knowledge JP-7 is JP-7. It was a high temperature fuel designed almost exclusively for the Blackbird. Although I've been told the X-43 now uses it."

The B-70, for example, was considered for experimentation to burn triethyl borate 50% and kerosene jet fuel 50% to increase range. Nothing can of it, though. Engine wear cost too much to bother with for the return in better range. That's what I was thinking by more that one type of JP-7.





KJ: "What's the NTRS?"

National Technical Report Server. It and STINET(Science and Technical Information Network) are the federal 'Web servers to allow public researchers (like our members and others around the world) to download reports and academic papers that NASA and other Agencies have archived indefinitely. Not all are available for free off the 'Web, but those that aren't downloadable, can be purchased from the Gov't. Both can be GOOGLed.





KJ: "I am aware of at least one type of Titanium-Aluminide that could take temperatures of 3,500 degrees...

I think that would be the maximum temp. Rene' could stand a few hundred more, but it was pretty weak at that temperature. There should be even newer stuff, but it/they might also be classified. You're right, though: TiAl and Ti3Al can take more heat than the usual titanium alloy.


I'll remember what you said overall about starting the J-58. It seems reasonable to me.

 

[KJ_Lesnick]

Yep, and here's the reason: sea level atmosphere has a typical temperature of 50-90 deg. F. at European and American latitudes most of the year, right? Air will carry away heat by convection across the fuselage, but a majority of metals retain heat well, depending of atomic properties peculiar to each one. Eventually, the skin temperature will return to safe levels before landing. With most fuel burned on returning to the base, throttle settings on the engines can be conservative compared to takeoff.

You know... I have seen pictures of the Blackbird flying a few thousand feet up which might be what you're talking about. However I thought most of those were for photo-ops. Wouldn't flying at subsonic speed at 35,000 feet be way better?

It's -55 F, to -70 F up there... wouldn't that cool you down way faster?

All flights above Mach 3.

Would explain why it took "only" 1:55 from the US to England.

My point is: SR-71's take off with less than full afterburner to save fuel normally. The maximum exhaust velocity of the J-58 is 30-40 % higher than the J-75 or J-79.

The Blackbird typically takes off with 55,000 lbs of gas. I'm guessing the more fuel in the tanks the more it leaks. Plus when they did tests of the Blackbird taking off at full weight, a number of tire-blowouts happened which sometimes started massive fires that set the plane ablaze.

It would seem though for the most part the plane went up to 25,000 feet to refuel with a tanker.

Well, the tanker and Blackbird would have been over the horizon by that time, so you probably have a point. What I meant was, the Blackbird refueled subsonically and merely sprinting a ways to heat the airframe to seal the tanks would be a waste of time if it cooled(and leaked) while refueling.

That makes sense.

The B-70, for example, was considered for experimentation to burn triethyl borate 50% and kerosene jet fuel 50% to increase range. Nothing can of it, though. Engine wear cost too much to bother with for the return in better range. That's what I was thinking by more that one type of JP-7.

Yeah, the B-70 was to use HEF-3. Instead they went with JP-6. With all the aerodynamic changes made on the design and the new-fuel and clean-burning characteristics of the fuel, it was almost as good.

You thought the SR-71 was using some kind of high-energy fuel in addition to regular JP-7?

National Technical Report Server. It and STINET(Science and Technical Information Network) are the federal 'Web servers to allow public researchers (like our members and others around the world) to download reports and academic papers that NASA and other Agencies have archived indefinitely. Not all are available for free off the 'Web, but those that aren't downloadable, can be purchased from the Gov't. Both can be GOOGLed.

Oh, I know what you're talking about. Still keep in mind, most of the data on that site probably states the Blackbird is capable of at most Mach 3.5 and skin temperature jumping to 800 degrees at Mach 3.2.

I think that would be the maximum temp. Rene' could stand a few hundred more, but it was pretty weak at that temperature. There should be even newer stuff, but it/they might also be classified. You're right, though: TiAl and Ti3Al can take more heat than the usual titanium alloy.

I'm not entirely sure if the 3,500 F figure was it's maximum or routine operating temperature.

Regarding the 1,000 C to 1,200 C limits you were talking about. If that was the limit what would you speculate would be reached during cruise. How much of a difference, would it be a little bit or significant (Since high-speed long range planes often cruise near their max speed)

 

[Lee]

KJ, quoted: "You know... I have seen pictures of the Blackbird flying a few thousand feet up which might be what you're talking about. However I thought most of those were for photo-ops."

Maybe so, but the RARE one I saw with the Blackbird underway with one engine told me the true power of the J-58. That should have remained classified.





KJ: "Wouldn't flying at subsonic speed at 35,000 feet be way better?
It's -55 F, to -70 F up there... wouldn't that cool you down way faster?
It would seem though for the most part the plane went up to 25,000 feet to refuel with a tanker."

The ambient pressure at 35,000 ft, as well as the Blackbird fuel tanks being artificially pressurized would increase leakage. Sea level has higher pressure, but the engines burn more fuel, too. Looks like a tradeoff unless I learn more about the exact nature of the Blackbird tankage.





KJ: "The Blackbird typically takes off with 55,000 lbs of gas. Plus when they did tests of the Blackbird taking off at full weight, a number of tire-blowouts happened which sometimes started massive fires that set the plane ablaze."

I didn't know about the plane fires. Most volume inside the Blackbird is taken up by fuel. The tire blowouts at maximum takeoff weight make sense, though.








KJ: "You thought the SR-71 was using some kind of high-energy fuel in addition to regular JP-7?"

No. I knew they only experimented with boron on smaller engines and rejected it. To expensive, costly maintenance, and poisonous to boot.





KJ: "Still keep in mind, most of the data on that site probably states the Blackbird is capable of at most Mach 3.5 and skin temperature jumping to 800 degrees at Mach 3.2.


That could also be official disinformation propaganda. Kelly Johnson(if he's still alive, he should be about 80 like my Dad) would be one of the few who really knows what the Blackbird's top speed is.





KJ: "I'm not entirely sure if the 3,500 F figure was it's maximum or routine operating temperature."

Rene' and molybdenum are about the strongest very high temperature material available. The figure I stated was from a graph in a research paper and the strength was falling pretty fast. ONLY 'carbon/carbon' was stronger above that temperature and it's difficult to make in quantity and quality, I've read.





KJ: "Regarding the 1,000 C to 1,200 C limits you were talking about. ...what would you speculate would be reached during cruise. How much of a difference, would it be a little bit or significant (Since high-speed long range planes often cruise near their max speed)"

For presently available Ti3Al, that temperature would seem to be the maximum allowable during a typical cruise. After that, poor strength was becoming an issue without insulation of cooling.
Bear in mind, jet turbine blades have air bleedoff cooling from the compressor and this alters the situation significantly. Active cooling on a wing or chine should be just as important.

 

[KJ_Lesnick]

Maybe so, but the RARE one I saw with the Blackbird underway with one engine told me the true power of the J-58. That should have remained classified.

Probably so. However there is another shot of a J-58 undergoing a routine run on a stand and it shows 13 diamond-shocks as well. It's obviously not classified, or a slip. It would appear as if the USAF for one reason or another did not classify it.

The ambient pressure at 35,000 ft, as well as the Blackbird fuel tanks being artificially pressurized would increase leakage. Sea level has higher pressure, but the engines burn more fuel, too. Looks like a tradeoff unless I learn more about the exact nature of the Blackbird tankage.

The footage I've seen of the blackbird at low altitude seems to suggest it flying at a few thousand feet.

No. I knew they only experimented with boron on smaller engines and rejected it. To expensive, costly maintenance, and poisonous to boot.

Like during the early Archangel and Angel series? The A-2 had in addition to a pair of J-58's, a pair of ramjets with pentaborane. That you mean?

That could also be official disinformation propaganda. Kelly Johnson(if he's still alive, he should be about 80 like my Dad) would be one of the few who really knows what the Blackbird's top speed is.

Clarence L. "Kelly" Johnson died in 1990 at the age of 80 (b. 1910).

For presently available Ti3Al, that temperature would seem to be the maximum allowable during a typical cruise. After that, poor strength was becoming an issue without insulation of cooling.
Bear in mind, jet turbine blades have air bleedoff cooling from the compressor and this alters the situation significantly. Active cooling on a wing or chine should be just as important.

So the airplane would reach 1,000 C to 1,200 C without active cooling during cruise? Would active cooling (JP-7 circulated through the chines) shave off 450-500 F (like you said pertaining to an aircraft with a 650 C skin temp I think), or would the cooling benefit be less at such extreme temperatures?


Kendra