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Starglider
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B-70: Was There Ever A Serious Mach 4 Requirement?

Mon Feb 12, 2007 8:51 am

Some publications claim that the B-70 design could have extended its limits to a Mach number of 4 with relatively minor changes to the known design (environmental control systems and hydraulic systems). No mention was made of changes in structural materials or wing design, which in my opinion, obviously also would need to be modified.

However, i cannot find any information in many of the manufacturers or NASA publications to support this claim.

What i do know is the following from publications so-far which had to do with engine selection and touched the Mach 4 issue:

"In the beginning of the program several engines, such as the Pratt & Whitney J91, were under active consideration. These evaluations prompted the B-70 Program Office to comment that further dilution of its engineering effort in such studies would hinder development work on the basic GE J93 design. Nonetheless, a distracting, intermittent consideration of other engines continued. But an analysis in the summer of 1957 concluded that the J93 was superior for the needs of the B-70. On November 6, 1957 Air Force Headquarters selected the J93 engine for the B-70 (then still a bomber program to succeed the B-52). Since the budget permitted only one Mach 3 turbojet project in Fiscal Year 1958, all support of the P&W J91 was to cease. In the meantime, the Navy had contracted with Pratt & Whitney to develop a scaled down version of the J91 called the J58. Instead of a second development effort, the Air Force would monitor the Navy program to a modified J58 designed to be almost interchangeable with the J93 powerplant. The annoyance of informal competition continued, however. At the end of 1957, the J93 was challenged again, this time by the Allison PD24 and Wright DC36, plus 2 new versions of the J58.

The nuisance value of these distractions was far greater than the possibility that the Air Force would drop the J93. None of the proposed alternative engines were serious competitors. The only real claim of the advanced Wright DC36 was the suggestion that it could power a future, improved version of the B-70 at speeds approaching Mach 4.

On February 17, 1958, Air Force Headquarters envisaged just such an advanced model and directed the Air Research and Development Command (ARDC) to start a competition for an advanced propulsion system. The Pentagon limited this undertaking by specifying that the improvement should be accomplished without major changes in the aircraft configuration and without affecting the J93 development program. In response, the B-70 Program Office listed arguments against further dilution of its engineering effort. The engine then in development could propel the B-70 to the temperature and Mach 3 limits of the airframe, and major changes would be necessary to push performance any further. Moreover, the proposed Wright DC36 engine was competitive with the J93 only when speed considerations reached Mach 4. Since that point was somewhere in the future and required a highly-modified airframe, an immediate decision on advanced propulsion was unnecessary."

And so the aircraft remained a Mach 3 design, equipped with J93 engines.

From there on, the Mach 4 trail turns cold and as far as i know it never passed the proposal stage and was never seriously pursued. Consequently, the Mach 3 design was completed, the bomber program was terminated, resulting in the XB-70 as it exists today.

So here is my question, is there any information available as to what the B-70 design would have looked like, if research was actually done on a Mach 4 variant?



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Starglider
 
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Stitch
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 1:46 am

The XB-70 has been a favorite of mine for decades, so I have read a great deal about her and the commercial SST program. In all those books and articles and papers, I do not recall having ever seen a serious Mach 4 desire/requirement for the XB-70, though it may have been part of the initial "pie in the sky" stage of the Weapons System 110 program.

And since the Long-Range Interceptor, Experimental (LRI-X) / Weapon System 202A program called for a Mach 3 interceptor that could also conceivably escort the XB-70 to her targets, it seems unlikely that Mach 4 was ever seriously considered.
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 4:52 am

Probably wasn't pursued for the same reasons that the B-70 itself was canceled - because cruise missiles launched from other platforms, as well as ICBM's/SLBM's were more cost effective. The B-70 also would have been less usefull in conventional conflicts. It was a good bluff - the B-70 tricked the Soviets into building the MIG-25. The Soviets spent a lot of resources on the Mig-25. Yet all it was good for was going after the B-70.
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 5:32 am

Quoting Cloudy (Reply 2):
Yet all it was good for was going after the B-70.

Yup. It really didn't have a shot at reaching the Blackbird. Maybe, it might have gotten close on a very good day, but most likely not. A stripped down F-15 could do a "zoom-climb" if we needed to shoot down a Recon Mig-25...
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 5:49 am

Quoting Cloudy (Reply 2):
all it was good for was going after the B-70

I would say that the various missions performed by or postulated for Soviet Foxbat units based in East Germany and Poland during the 1980s would argue against that.

Quoting GQfluffy (Reply 3):
It really didn't have a shot at reaching the Blackbird

Remember that the MiG-25 didn't have to reach an SR-71. Its job was to get its load of AA-6s to 50,000 feet and Mach 2 and let them do the chasing from there.
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 7:00 am

Quoting Vzlet (Reply 4):
Remember that the MiG-25 didn't have to reach an SR-71. Its job was to get its load of AA-6s to 50,000 feet and Mach 2 and let them do the chasing from there.

I read somewhere that the Russian had worked on a strategy of position several MiG-25's in a certain arrangement to create a sort of kill box that theoretically could bring down the -71.
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 9:23 am

Of course, the nice thing about the altitude the Blackbird flew at and with SAR and side-view cameras, she never had to get anywhere near a nation's territory to spy on them, so all the MiG's could have done is wave up at her from their lower ceiling as she cruised along snapping pics and processing radar returns.  Smile
 
Starglider
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 9:27 am

Quoting Stitch (Reply 1):
The XB-70 has been a favorite of mine for decades, so I have read a great deal about her and the commercial SST program. In all those books and articles and papers, I do not recall having ever seen a serious Mach 4 desire/requirement for the XB-70, though it may have been part of the initial "pie in the sky" stage of the Weapons System 110 program.

And since the Long-Range Interceptor, Experimental (LRI-X) / Weapon System 202A program called for a Mach 3 interceptor that could also conceivably escort the XB-70 to her targets, it seems unlikely that Mach 4 was ever seriously considered.

Same with me, the XB-70 has been my favorite plane since i was 11 years old when i found out about its existence, which was when she was rolled out on May 11, 1964, and have gathered information about her ever since. I lived in the States for a couple of years back in the mid sixties and remember whenever it broke new records, it was headline news, as i recall, it was also frequently seen on TV in a B.F. Goodrich tire commercial back then. In all the years of gathering information, I never found any information about an effort to increase performance to Mach 4 either.

In the WS110 period the concept was actually targeted at a slower supersonic dash speed of Mach 2.75, and cruising at subsonic speed. That was before the North American M3 cruise design was selected.

That said, i would not rule out there might have been some studies for future growth versions when it was still considered a successor to the B-52, before politics terminated the program. For instance, i have read reports describing wind tunnel tests with models up to speeds of Mach 3.5 but in the final analysis it was concluded that M3 was the best speed for the design. In the same report they experimented with fairings on the lower fuselage sides, and canting the tips of the vertical tails several degrees inboard relative to their roots, intended to decrease the sidewise radar reflectivity. So-far the closest i have found are wind tunnel tests conducted (in 1961) on a 74 deg, swept back delta wing for Mach numbers of 2.8 to 4.1, and 5.3 but there was no direct relation to the B-70.


Starglider
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 4:21 pm

I recall reading a few years back that NASA/Langley's SCAT-15F design was tested at mach 4.6 in a wind tunnel. The design was optimized for mach 2.7 and had an l/d ratio of 9.3 at that speed, making it to this day one of the most aerodynamically efficient SST's ever designed. It was tweaked in the tunnels and by the first computer code modelling ever done. Designed between 1959 and 1967, it was used for various SST proposals all the way into the '80s. Despite having a delta wing with a sweep of 74 degrees, engineers were able to solve all potential low speed handling problems. I think it's the most beautiful supersonic design of all time.

For more info, check out the Nasa Langley website at: history.nasa.gov/monograph39/mon39_a.pdf


cheers,

Jon
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 13, 2007 11:31 pm

SCAT-15F,

How did they deal with the rearwards shift in the center of pressure? Did they use ballast tanks, or could the design inherantly cope with it like the L-2000?

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 14, 2007 1:41 am

Quoting Blackbird (Reply 9):
How did they deal with the rearwards shift in the center of pressure? Did they use ballast tanks, or could the design inherantly cope with it like the L-2000?

The longitudinal instability or "pitch-up" and "deep stall" problems caused by the radically swept arrow wing were solved by a 60 degree deflection of the wing leading edge flaps forward of the center of gravity, a "notched" wing apex, fowler flaps, and a very small aft horizontal tail. (the 2 short vertical stabilizers were 2/3 of the way to the wingtips - outboard)

cheers

-Jon
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 14, 2007 5:00 am

No, I'm not talking about deep-stall's and pitch-ups,I'm talking about the tendency for the center of pressure to shift aft as a result of the airplane going transonic/supersonic. How did the SCAT-15F designs plan to cope with this without excessive trim-drag? To they plan to use ballast-fuel, or did they plan to use a solely aerodynamic means to do this?

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 14, 2007 5:14 am

Quoting Blackbird (Reply 11):
No, I'm not talking about deep-stall's and pitch-ups,I'm talking about the tendency for the center of pressure to shift aft as a result of the airplane going transonic/supersonic. How did the SCAT-15F designs plan to cope with this without excessive trim-drag? To they plan to use ballast-fuel, or did they plan to use a solely aerodynamic means to do this?

That, I have not been able to find any information on as yet.


-Jon
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 14, 2007 7:19 am

Quoting Blackbird (Reply 11):
No, I'm not talking about deep-stall's and pitch-ups,I'm talking about the tendency for the center of pressure to shift aft as a result of the airplane going transonic/supersonic. How did the SCAT-15F designs plan to cope with this without excessive trim-drag? To they plan to use ballast-fuel, or did they plan to use a solely aerodynamic means to do this?

At supersonic speed a substantial part of the wingtips were drooped 65 degrees downward. I think that it was the XB-70 way to deal with the forward center of lift shift at supersonic speed.

I really don't know, it's just a semi-qualified guess.
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 14, 2007 8:48 am

I got a question to Starglider,

According to what you said: some variants of the Boeing 804 were capable of Mach 4, some using J-93's, or a type of bleed J-58, however the Boeing 804-4 was a Mach 3.0 airplane, right?

According to Steve Pace's VALKYRIE: North American XB-70 (Page 6)
"Boeing's new WS-110A CBP (Chemically Powered Bomber) appeared as it's Model B-804, a 200-foot-long delta-wing design with variable geometry canard foreplanes (FIG. 1-4). It resembled Boeing's own Bomarc pilotless surface-to-air interceptor missile. Boeing's rejuvinated studies of aircraft configurations, exotic fuels, BLC systems, aerodynamics, metallurgy, and powerplants prescribed the use of six podded, underwing General Electric X-279E
turbojet engines. Maximum takeoff weight had dropped to an acceptable 500,000 pounds. The deficiencies of their prior design now boasted a missile-like airframe and matchless performance. In fact, its engines were rated at a Mach number of 4! The proposal was well received."

Figure 1-4 shows the final-canard arrangement which folded up at low speed and down to provide trim-control for supersonic speed, indicating that this is the final model. And the wording "MATCHLESS" performance makes me wonder if they had Mach 4.0 seriously in mind...

Andrea K
 
Starglider
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 14, 2007 10:16 am

Andrea,

Here Mr. Pace, again, is incomplete because although he refers correctly to a model B804, he does not specify which dash number. Model B804-1 through -6 were Mach 3 designs of which only model B804-4 was submitted to the Source Selection Board evaluation team during a meeting of 4 to 6 November 1957. Model 804-4 was formally rejected by the Air Force on 23 December 1957. This design had a gross weight of 542,000 pounds and indeed, had the upward folding canards. Model B804-4 was just over 206 feet long with a wingspan of 94.5 feet. It had 6 X279J (a later version of the X279E) turbojets in six individual pods. The X279 series engines eventually evolved into the J93 when it was officially designated XJ93-GE-1 on 25 September 1957.

Quoting Blackbird (Reply 14):
Figure 1-4 shows the final-canard arrangement which folded up at low speed and down to provide trim-control for supersonic speed, indicating that this is the final model.

This is model 804-4, the model submitted to the Air Force but not the final model. Model 804-7 through 804-10 were Mach 4 designs with different engines but NONE were submitted to the Air Force.

As to the statement "the proposal was well received" . . .well . .uhh . . . not well enough because North American got the contract to build the B-70, not Boeing.

"Matchless" performance, in my humble opinion, should be read in comparison to Boeing's previous WS110A proposal shown in Fig. 1-1 on page 5 of mentioned book. A sort of three plane formation, too heavy and too large.


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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 15, 2007 5:19 am

But he did say the proposal was well received... which indicates it was likely submitted, or at least that someone other than Boeing officials saw it.

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 15, 2007 6:52 am

Quoting Blackbird (Reply 16):
But he did say the proposal was well received... which indicates it was likely submitted, or at least that someone other than Boeing officials saw it.

Andrea K

Ask yourself the question which model he was referring to that was submitted. Since the author did not mention the different dash number variants and their different specifications, his writing appears to have "hashed" them all together, making the reader incorrectly believe there was only one B804 design with all the goodies to make it a Mach 4 design, which it was not. He did not really go into any detail at all, describing the 804 in less than a half a column of text on a 2 column page. In all fairness to the author, he wrote the book back in 1984 (2nd edition 1990) Perhaps at the time not all information known today, was available to him at the time.

By the way, the X279J engine selected for the 804-4 was basically an "infant" J93 engine married to a Mach 3 inlet.


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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 15, 2007 7:09 am

When you say an "infant J-93" do you mean like stripped down?
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 15, 2007 7:40 am

No, just that the X279 engines were not yet fully developed. When they were developed into a mature engine, the designation was officially changed into J93.
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 15, 2007 11:52 am

But even the X-279E could do Mach 4 (whether the plane could do it or not) right?

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Fri Feb 16, 2007 7:10 am

Quoting Blackbird (Reply 20):
But even the X-279E could do Mach 4 (whether the plane could do it or not) right?

The X279 target was Mach 3, however, at some point in time (1957) there were apparently plans to develop it into a dual cycle powerplant for the Boeing model 804-9, intended for mach 4 cruise. When the X275 (a scaled up J79) morphed into the X279, it basically had that potential in it since it was in the process of evolving into the J93 (a designation change actually because the X279J version was the XJ93-GE-1). So-far i guesstimate that Mach 4 could theoretically have been within reach if the development J93 had continued beyond the YJ93-GE-3.

However, there is a recent lead that reveals the J93 never went past the Mach 3.2 design limit. Limit of Mach 3.2 is for the YJ93-GE-3 (XB-70A with JP-6 fuel), J93-GE-3R (Production B-70 with JP-6 fuel and Thrust Reverser), and J93-GE-5 (Production B-70 with HEF-3).

Since 2002, GEAE together with NASA, started development of what is called a "Revolutionary Turbine Accelerator (RTA) technology demonstrator." And here comes the catch: In a paper dealing with RTA technology it is stated that:

"The overall objective of the RTA program is to develop a turbine-based-combined-cycle (TBCC) propulsion system. Present turbine propulsion systems can propel aircraft to Mach 3. These current systems are costly, have high maintenance, and have low durability. In the RTA project, near term development goals concentrate on turbine accelerators that will reach at least Mach 4 and provide dramatic increases in maintainability and operability."

The RTA features an augmentor/ramburner, a key technology to be developed for the Turbine Based Combined Cycle (TBCC) engine. During take-off and transition to supersonic flight, this device will serve as a conventional augmentor boosting the turbine engine thrust approximately 50%. Between Mach 2 and 3, the augmentor transitions to a ramburner, accelerating the vehicle to speeds above Mach 4.

Mid scale testing (according to an AIAA paper from 2002) is to start in 2007, this year . . . .50 years further on in time than your question reverts to. I would not be surprised if GE has dusted off the J93/GE4 concept (or parts of it) and apart from RTA, is adding advanced technologies to these designs. Although, the GE website mentions:

"The RTA is planned for use on the first stage of a 2-stage vehicle capable of hypersonic flight. At Mach 4, the second stage takes over and propels the vehicle into orbit. The two combined propulsion systems are a candidate to help NASA meet the agency's goal of developing safe, cost-effective access to space.

Advanced technologies from NASA's Ultra Efficient Engine Technology (UEET) Program and the DOD's Integrated High Performance Turbine Engine Technology (IHPTET) programs will be leveraged in the RTA project."

But i would not rule out the use of J93/GE4 technology. If they could be modified to incorporate RTA.


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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Fri Feb 16, 2007 1:27 pm

Wasn't the Sukhoi T-4 the Russian answer to the XB-70?

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Starglider
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Fri Feb 16, 2007 6:54 pm

Quoting Scbriml (Reply 22):
Wasn't the Sukhoi T-4 the Russian answer to the XB-70?

Yes, it was (also called Project 100). Although designed for Mach 3, it never reached that speed.
It had an articulating nose but in the up position all forward vision was lost. The nose section and fuselage had some resemblance to the Boeing model B804, having a spine/dorsal fairing and similar tail configuration.



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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Fri Feb 16, 2007 10:47 pm

Quoting Blackbird (Reply 9):
How did they deal with the rearwards shift in the center of pressure? Did they use ballast tanks, or could the design inherently cope with it like the L-2000?

As Concorde used its fuel for this purpose, you might pick from articles on Concorde where they got this concept - they were very proud of it, so it could have been new.
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Sat Feb 17, 2007 6:07 am

To Baroque,

I'm well aware that fuel-ballast was used on the concorde. However it was not new. The B-58 used it and it first flew in 1956, to my knowledge the SR-71 used such a ballast-configuration as well. Lockheed even during the development stages of the L-2000 wwere considering (should they not be able to control the shift in the C/L aerodynamically)


To Starglider. The RTA's Mach 4 capability is probably substantially under-rated. Many people do not know that in the late fifties and sixties that some engines had been conceived with Mach numbers and capabilities in the Mach 4-class. Most people are only aware of Mach 3.0 capability being the max. So they simply listed Mach 4 because it sounded higher than Mach 3 without having to reveal the real speed of the engine.

In 1960 there was a concept for a hypersonic passenger plane by Bell (they made the X-1) which used some kind of variable cycle engine which worked as a turbojet, a turbojet/ramjet mix, and a ramjet for speeds up to Mach 5.2. After that the second stage would be launched from the carrier-plane and would use rockets to boost up to Mach 15, and would fly half way around the world, using extendable turbojets for low-speed maneuvering and landing. Supposedly it influenced a couple of space-shuttle design studies early on. To my knowledge, no airline expressed major interest.

Second, I see little reason to suggest the X279 or J-93 couldn't reach Mach 4.0 The J-75 could indeed do Mach 3 [i](It's been officially acknowledged), and the J-93 had a lower pressure ratio, higher thrust and a far higher turbine inlet temperature with extensive air-cooling. It would appear as if it was set up from day one, or at least early on for that speed.

Third. You made a statement about the XB-70 being limited by the same factor that limited the Lockeed Super Constellation (tail-height). However, this does not appear to be so. The early XB-70 designs had much larger tails (Tail's were taller too) and less folding-wing area. Later on, the design was modified with an increased folding-wingtip area since it provided the same directional control with less drag than the larger tails (The new design featured half the tail-area)

Fourth... do you have any data on that production design with thrust-reversrs? What kind of reversrs were used?

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Sat Feb 17, 2007 10:29 am

Quoting Blackbird (Reply 25):
The RTA's Mach 4 capability is probably substantially under-rated.

For RTA phase 1 and 2 related to turbo-machinery see figure below:

Big version: Width: 577 Height: 339 File size: 43kb
RTA Phase 1 and Phase 2


Quoting Blackbird (Reply 25):
Many people do not know that in the late fifties and sixties that some engines had been conceived with Mach numbers and capabilities in the Mach 4-class. Most people are only aware of Mach 3.0 capability being the max. So they simply listed Mach 4 because it sounded higher than Mach 3 without having to reveal the real speed of the engine.

In the time-frame you refer to, for starters, there were no engines that could handle 1600 degree F temperatures at the compressor inlet!! To quote from a NASA RTA-Hyperburner report:

"The first engineering challenge is to construct a compressor, combustor, and turbine that withstand temperatures of 1,600°F generated by inlet air at Mach 4. Such materials are traditionally costly or heavy, penalties the RTA program can ill afford. New materials must also be developed and tested for the rotating components. Until now, rotating turbomachinery never had to operate above Mach 3."

Until you can provide specific data on any current turbojet or turbofan engine that can comply with these criteria, i will consider your claim as speculation.

Quoting Blackbird (Reply 25):
In 1960 there was a concept for a hypersonic passenger plane by Bell (they made the X-1) which used some kind of variable cycle engine which worked as a turbojet, a turbojet/ramjet mix, and a ramjet for speeds up to Mach 5.2.

As you correctly stated, a concept, often when i wake up in the morning my head is filled with concepts. It does not mean i'll have a working system before nightfall though, neither did Bell in a fifty year time-span.

Quoting Blackbird (Reply 25):
Second, I see little reason to suggest the X279 or J-93 couldn't reach Mach 4.0 The J-75 could indeed do Mach 3 [i](It's been officially acknowledged), and the J-93 had a lower pressure ratio, higher thrust and a far higher turbine inlet temperature with extensive air-cooling. It would appear as if it was set up from day one, or at least early on for that speed.

The J93 could not take a Mach 4, 1600F compressor inlet air temperature (will discuss this issue later in my reply). Indeed, the turbines were air cooled but Turbine Inlet Temperature was limited to:
Below Mach 2: 2,100F
Above Mach 2: 1,990F

After the HEF fuel program was canceled and the J93-GE-5 was terminated, the J93-GE-3 (JP-6 fuel) had another feature designed into it to obtain the same performance in range, in-flight refueling altitude, takeoff distance, and rate-of-climb-at-takeoff. The most critical item for the B-70, the rate of climb on a hot day with one engine inoperative at takeoff, was resolved by incorporating an overspeed facility to develop a higher turbine inlet temperature (2,300F) on takeoff and thereby provide the necessary higher rate of climb. Obviously, this overspeed condition was limited to takeoff, after cleanup at sufficient airspeed and climb gradient established, the overspeed setting was returned to normal.

For the record, regarding compressor inlet temperatures:
At mach 2: 230F
At Mach 3: 630F, the effects of the compressor stage raise temperature to 1,200F.
Now, consider what happens to the compressor stage temperature, if the compressor inlet temperature at mach 4 is already 1,600F . . . .


The J75, according to my data, was capable of limited Mach 2 operation, but it was too heavy for satisfactory performance in sustained supersonic flight due to a poor thrust-to-weight ratio. The J75 found application in the F-105 Thunderchief and F-106 Delta Dagger, Mach 2 dash aircraft at the most.

Quoting Blackbird (Reply 25):
Third. You made a statement about the XB-70 being limited by the same factor that limited the Lockeed Super Constellation (tail-height). However, this does not appear to be so. The early XB-70 designs had much larger tails (Tail's were taller too) and less folding-wing area. Later on, the design was modified with an increased folding-wingtip area since it provided the same directional control with less drag than the larger tails (The new design featured half the tail-area)

This is what i wrote in the thread you refer to:

"Calculations made me realize that there was another reason the Mach 4 concept never really catched on from day one. The very basic reason was that the Air Force put a similar requirement to the B-70 as Howard Hughes did to the Lockheed Constellation as owner of TWA. The "Connie" had to fit in the TWA hangars so the typical triple vertical tails were born to fit under the hangar door openings. The B-70 had to fit in the same hangar as the B-52. That requirement limited it's size and basically, it's speed. If Mach 4 was in the game, the B-70 would have had to be considerably larger to allow for more fuel (higher fuel fraction) to deliver the same payload."

What i meant to say was the overall dimensions of the B-70 were restricted to certain criteria to enable it to fit in the same hangars as the B-52. The reference to Hughes and the "Connie" tails were only to explain similar circumstances that eventually were a factor in defining the shape and size of an aircraft, it was not meant to specifically address the B-70 tail size.

Quoting Blackbird (Reply 25):
Fourth... do you have any data on that production design with thrust-reversrs? What kind of reversrs were used?

No exact details, but originally the reverser was a design requirement for the F-108 Rapier, using the same engines as the B-70. The reverser was an option for later B-70 production aircraft but not a requirement. Therefore, the reverser was designed to be readily removable depending on which aircraft the engine was installed. The F-108 was canceled and many commonalities between it and the B-70 were no longer an issue (neither was the B-70 production aircraft later on in the program).

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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Sat Feb 17, 2007 3:36 pm

Quoting Starglider (Reply 26):
The J75, according to my data, was capable of limited Mach 2 operation, but it was too heavy for satisfactory performance in sustained supersonic flight due to a poor thrust-to-weight ratio. The J75 found application in the F-105 Thunderchief and F-106 Delta Dagger, Mach 2 dash aircraft at the most.

One of the series books by Lou Drendell on the F-8 crusader talks about the Crusader 3 competitor to the F-4. It was powered by a J-75 and achieved mach 2.6 in testing w/o water injection or any other means to cool the compressor. The only reason they stopped at mach 2.6 was because of the concern of windscreen failure. With the addition of an auxiliary rocket motor (which was never test flown), the Crusader 3 was to achieve mach 3.0 dash for short periods.
I would assume that this would mean that the J-75 was rated at mach 3.

We also know for a fact that the J-58 has flown to at least mach 3.56, and if you said that the J-93 was at least capable of mach 3.2, I can't see why both engines would not be rated at mach 4, and I would assume (maybe incorrectly) that an engine has to be rated higher than the cruise speed of these particular aircraft - at least for safety concerns. I would think that the J-93 and J-58 would be rated at least at mach 3.75 or 3.8.


-Jon
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Sat Feb 17, 2007 10:21 pm

Quoting SCAT15F (Reply 27):
One of the series books by Lou Drendell on the F-8 crusader talks about the Crusader 3 competitor to the F-4. It was powered by a J-75 and achieved mach 2.6 in testing w/o water injection or any other means to cool the compressor. The only reason they stopped at mach 2.6 was because of the concern of windscreen failure. With the addition of an auxiliary rocket motor (which was never test flown), the Crusader 3 was to achieve mach 3.0 dash for short periods.
I would assume that this would mean that the J-75 was rated at mach 3.

Indeed, several books mention that Crusader 3 reached Mach 2.6 briefly on a test flight powered by a J75-P-4. I checked the "F8 Crusader in Action" series No. 7 (Lou Drendel, 1973), and No.70 (Jim Sullivan, 1985) from Squadron Signal Publ. In the copy i have from Drendel, the Crusader 3 is not mentioned once. In series No.70 the Mach 2.6 speed is mentioned. I find it strange, however, that this speed apparently was attained at only 35,000 feet?? I would expect such speeds at altitudes closer to 60,000 feet.

Other publications,

http://www.faqs.org/docs/air/avcrus2.html#m7


above link updated March 1, 2002, mentions that "Test flights were terminated after the aircraft had demonstrated a speed of Mach 2.3. Vought believed the aircraft was capable of Mach 2.9, but the windscreen material wasn't up to that kind of punishment, and the program was killed before Vought could make the necessary changes. Two XF8U-3s were passed on to NASA for high-altitude and sonic boom flight tests, while the third was sent to Edwards Air Force Base for flight testing. They were all scrapped after a year or two." In this publication the aircraft was powered by a Pratt & Whitney J75-P-5A turbojet with 7,480 kilograms (16,500 pounds) dry thrust and 13,380 kilograms (29,500 pounds) afterburning thrust.

To underline the demonstrated Mach 2.3 speed, referring to Don Mallick's (test pilot) book, published in 2003, "The Smell of Kerosene", Chapter 5 "Super Crusader":

Don Mallick flew the Crusader 3 for NASA and here are a few of his experiences with the aircraft since June 1959:

"We established a baseline speed of Mach 2.0 for all altitudes from 35,000 feet to 60,000 feet. The F8U-3 was easily capable of reaching Mach 2.2, and had even reached Mach 2.38 on a speed run at Edwards Air Force Base in California some months earlier."

He goes on describing he was extremely impressed by the aircraft and it's J75 engine. He had to actually control the aircraft's speed using speed brakes to stabilize at Mach 2. Then he goes on describing (text slightly condensed by me):

"The pilot's windscreen was unusual. Almost all fighter aircraft, at the time, had a piece of thick bullet proof glass installed directly in front of the cockpit. The F8U-3 did not have this. It had only standard Plexiglass like the rest of the canopy. This limited our cruise time at Mach 2. After 10 minutes, its reduced strength left it vulnerable to catastrophic failure. We therefore set a five-minute limit on cruise at Mach 2.0. The test conductor kept an eye on time spent on cruise conditions. Once the pilot reported reaching Mach 2.0, a clock started on the ground and the pilot was given a call when he had been at that speed for five minutes."

I disagree that if an engine, in this case the J75, would be able to reach a speed of Mach 3 or in the case of the J93, Mach 4 briefly, it is considered to have the rating for that speed. An engine would be rated for such speeds if they actually demonstrated attaining that speed for a defined period of time (including durability testing). For supersonic cruisers in heat soaked, cruise conditions. Especially for the J93, installed in a supersonic cruiser such as the B-70, it would be part of the certification process defining its capabilities as mentioned on a Certification Data Sheet. That document probably states Mach 3.2.



Starglider
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Sun Feb 18, 2007 1:29 am

Starglider, there was a video in which they specifically stated the J-75 was to push the airplane to Mach 3+ (F8U-3 Super Crusader). So it turned out, the windows would become opaque past a certain temperature and mach number. There may have been additional limitations...

The J-75 can take maximum turbine inlet temperature for 30 minutes.

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Sun Feb 18, 2007 1:32 am

Quoting Starglider (Reply 28):
Especially for the J93, installed in a supersonic cruiser such as the B-70, it would be part of the certification process defining its capabilities as mentioned on a Certification Data Sheet. That document probably states Mach 3.2.

Of course not mentioned as speed limit but translated in static sea level thrust ratings (Take-off, max. continuous), rotor RPM, maximum permissible temperatures for engine components, oils, and fuels.

The engines mentioned only accept subsonic airflow, no matter what the speed of the airframe is.
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Mon Feb 19, 2007 4:48 am

Quoting Blackbird (Reply 29):
Starglider, there was a video in which they specifically stated the J-75 was to push the airplane to Mach 3+ (F8U-3 Super Crusader). So it turned out, the windows would become opaque past a certain temperature and mach number. There may have been additional limitations...

The J-75 can take maximum turbine inlet temperature for 30 minutes.

Well, Crusader 3, the J75 with a thrust of 29,500 pounds, max. turbine inlet temp. limit for 30 minutes as you explain, and operational weights roughly between 32,000 and 38,000 pounds, i would not be surprised it could have reached speeds near mach 3. The windscreen limitation goes to show that a Mach 3 speed in 1958 was still undiscovered country. Only Capt. Milburn (Mel) Apt had reached Mach 3 with the Bell X-2 in September 156 but sadly did not live to tell.



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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Mon Feb 19, 2007 5:54 pm

Quoting Starglider (Reply 31):
the J75 with a thrust of 29,500 pounds

This is interesting data- I have only heard of two thrust ratings given for the J-75: 24,500 lbf and 26,500 lbf thrust (with water injection). However, I did read that the non-afterburning version of the J-75 used for the TR version of the U-2 had 17,000 lbf thrust vs 15,000 lbf dry thrust for the afterburning version, which would equate to about 29,500 lbf for the "U-2" version w/ afterburner.

Is there a source for this data? This 29.5k version would certainly have given the F-106 and F-107 a nice performance boost!
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 20, 2007 2:14 am

It was a fabulous aircraft for sure.
However, Mig-25 would not have been the main problem, more likely the SA-5 SAM.

(I understand one reason for Israel's very rapid buy of F-15's in the 70's, including some re-furbed pre series aircraft, was due to recon overflights near or over their territory by Soviet Mig-25's, based in the ME for this.
Also, it may have influenced Iran to buy the AWG-9/AIM-54 radar/missile system on the F-14, after Mig-25's overflew them).
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 20, 2007 8:29 am

Quoting GDB (Reply 33):
However, Mig-25 would not have been the main problem

Probably not because the engines of the MiG-25 tended to burn out above Mach 2.8. Pilots were forbidden to exceed mach 2.5 without permission and the mach gauges for the MiG-25P (Foxbat A) were red-lined at Mach 2.8. These engines initially had a short life of about 150 hours, later improved to 1000 hours, but still poor when compared to western standards. The MiG-25 could reach Mach 3 in a clean reconnaissance configuration, but that would have been of no use trying to stop an operational B-70. Furthermore, if the B-70 would have been developed into a mature weapon system and had met its projected range of between 7,500 to 10,000 miles as specified, with one air refueling it would have had sufficient flexibility to avoid interception, using tactics, deviating from its anticipated flight path when necessary, keeping its adversaries guessing at what the designated target would be.

I keep thinking about the fact that not one SR-71 was ever shot down by an interceptor or SAM. It was essentially operating in the same flight regime as the B-70 would have operated. The B-70 (the production version would have been aerodynamically improved and the folding wingtips would have contained fuel), because of its longer range capability, using above mentioned flexibility, to my opinion would have had at least the same chance of survival as the SR-71 had during its life span.


Starglider
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Tue Feb 20, 2007 10:46 pm

Quoting SCAT15F (Reply 32):
This is interesting data- I have only heard of two thrust ratings given for the J-75: 24,500 lbf and 26,500 lbf thrust (with water injection). However, I did read that the non-afterburning version of the J-75 used for the TR version of the U-2 had 17,000 lbf thrust vs 15,000 lbf dry thrust for the afterburning version, which would equate to about 29,500 lbf for the "U-2" version w/ afterburner.

Is there a source for this data? This 29.5k version would certainly have given the F-106 and F-107 a nice performance boost!

Here is a link to the 29.5k version:

http://www.vectorsite.net/avcrus_2.html#m7


Starglider
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 12:26 am

Starglider,

You're not getting me... the plane could sustain afterburner for 30 minutes... hence it could hold Mach 3 for thirty minutes.

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 1:11 am

Quoting Blackbird (Reply 36):
Starglider,

You're not getting me... the plane could sustain afterburner for 30 minutes... hence it could hold Mach 3 for thirty minutes.

Andrea K

Ohh . . .i get you allright . . . theoretically the F8U-3 could perhaps reach Mach 3, but apart from the "soft" windscreen, the aircraft had a fixed inlet and had many inlet unstarts to prove the inlet would need fixing to make it a mature design. Maybe at the time (1958) the idea was that it could reach Mach 2.9 or Mach 3 but with hindsight and knowing what it took to actually design an aircraft to cruise at those speeds . . . . . . . . . . . . . ?

Well with brute force you can let a plane, fitted with barn doors instead of wings, fly that fast. Honestly i don't think the plane was designed for such speeds and it was sort of a test pilot "rodeo ride" to see how fast it would go. Maybe the soft windscreen saved pilots lives to prevent them from going any faster in case of the F8U-3. . . .many things happen for a reason . . . . ohh . .and uhh Mach 3 for 30 minutes brings us back to another discussion we have sometimes . . . have you thought about heat soaking, i wonder what materials the Crusader 3 was made from if they did not even take consideration about the wind screen?   

[Edited 2007-02-20 17:15:17]
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 3:28 am

Quoting Starglider (Reply 37):
i wonder what materials the Crusader 3 was made from

According to the Lou Drendell book I have on the F-8, the F8U-3 was built primarily out of titanium w/ some stainless steel (the color photos give evidence to this also) So, the airframe was most likely capable of mach 3 flight and maybe even mach 3 cruise - although I agree that the J-75 would not be up to that task, (at least the mach 3 cruise part). It would seem to be in the class of the Mig 25/31: "capable" of mach 3, but really more of a mach 2.8 aircraft (w/proper windscreen, of course).  beady 
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 7:07 am

Starglider, you sure the inlet wasn't variable geometry? I remember reading the biography of a test-pilot, and he was talking about flying the F-8U3 Super Crusader and talked about being it having variable geometry inlets... maybe he was talking about variable geometry bypass doors, I'm not sure... (don't variable geometry bypass-doors and variable geometry inlets go hand in hand?) I see a pair of vents below the wing leading-edge. I would assume these are the bypass doors.

Regarding the window problem, they were working on a type of laminated-glass during the flight-test program, I would assume it was never actually implemented though as the plane was cancelled.

I'm actually uncertain as to the metallurgical content of the F-8U-3, even if it could get to Mach 3, I don't know how long it could stay there! The J-75 however had no problem achieving Mach 3.

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 9:48 am

Andrea,

The F8U-3 certainly was a very impressive aircraft with regard to performance. Basically the F8U-3 nose radome extends to inside the inlet and functions as a shock cone with bypass doors (at both sides of the fuselage just below the wing leading edge) to adjust the inlet terminal shock. The bypass doors started to open at mach 1.4. The F8U-3 had a problem with compressor stalls. Engine stalls occurred without warning during supersonic runs. There was no method to restart the inlet or clear the stall until the aircraft had slowed to subsonic speed. The F8U-3 had to slow to Mach 0.9 before engine stalls could be cleared. The reason the inlet under certain conditions had problems matching engine demand was the fact that the afterburner had only one segment. It was either off (mill power) or when selected, in full afterburner. Production engines would have had more A/B segments. The highest speed attained was Mach 2.38 but remarkably even at this speed the aircraft continued to accelerate, going Mach 0.1 faster every 17 seconds! Experience gained from the flight test program predicted a (rather pessimistic) maximum speed of Mach 2.6 but near Mach 2.9 was probably more likely. Still, the aircraft was designed as a Mach 2+ aircraft. With some modifications a Mach 3 dash would have been within reach. At an altitude of 35,000 ft (10,700 m) at Mach 0.98 the first prototype needed only 3 minutes and 54 seconds to accelerate to Mach 2.2. Only a few fighters of today can match that!

The second prototype with its slightly lower powered engine however needed no less than 9 minutes to accelerate to that speed, and it was predicted that the production aircraft's figure would lie somewhat in the middle. Maximum altitude was also not bad, the F8U-3 could sustain 60,000 to 65,000 ft. With a ballistic "zoom climb" trajectory the aircraft could reach 90,000 ft.

Sustained Mach 3 was out of the question for the simple reason that i have discovered that the temperature limitation on it's structure was 425F. For mach 3 the limitation would have been approx. 600F.


Starglider
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 11:07 am

Starglider,

Can you put the footage of the XB-70 doing mach 3 on youtube or something so I can hear it with my own two ears?

Andrea K
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 12:04 pm

Oh... can you also check this image... I'm not sure if the indicators that read AICS Mach Sched... which each indicator listing pressure ratio goes up to 3.2 about. Is that pressure by mach number? Or is that like 32 : 1 PR?

http://www.nationalmuseum.af.mil/sha...todb/photos/060621-F-1234P-002.JPG
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 12:56 pm

Quoting Starglider (Reply 34):
I keep thinking about the fact that not one SR-71 was ever shot down by an interceptor or SAM. It was essentially operating in the same flight regime as the B-70 would have operated.



Except that it never actually overflew the nastiest SAM protected sites or faced significant numbers of interceptors in a situation where they might actually shoot. Mind you I’m only counting SAMs and interceptors adequate to the task – while Hanoi circa 1970 might well have been the nastiest SAM site in the world, it was largely useless against the ’71.

It's said that there was an incident in the mid eighties over the Sea of Japan where four MiG-31s managed to make a good geometry box around an SR-71 (in international airspace), which would have allowed at least a reasonable missile shot (IOW the geometry and energy requirements were such that a missile with a good lock would have a reasonable chance of guiding to the '71).


(edit: first paragraph lost on iniital post)

[Edited 2007-02-21 05:01:06]
 
Starglider
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 7:30 pm

Quoting Blackbird (Reply 41):
Can you put the footage of the XB-70 doing mach 3 on youtube or something so I can hear it with my own two ears?

I will see what i can do, will let you know.

Quoting Blackbird (Reply 42):
Oh... can you also check this image... I'm not sure if the indicators that read AICS Mach Sched... which each indicator listing pressure ratio goes up to 3.2 about. Is that pressure by mach number? Or is that like 32 : 1 PR?

These are the Inlet Pressure Ratio gauges. One for each inlet, and indicate the ratio of inlet static pressure to pitot pressure. The gauges indicate inlet efficiency. An increase in pressure ratio reading indicates forward movement of the shock wave (high performance). A decrease in reading indicates aft movement of the shock wave (low performance).

These Inlet Pressure Ratio gauges are used together with the 2 indicators above them, the Inlet Shock Wave Position indicators, which indicate the location of the shock wave in the respective inlet. Each indicator reacts to signals received from tape sensors in the respective inlet walls which sense the shock wave location. The pointer moves on a scale which has the two extremes marked FWD and AFT. Inboard of these indicators on top are the left and right inlet throat mach schedule indicators and below them the inlet bypass area indicators.

The center switches between the Inlet Pressure Ratio gauges:
- the top two are left and right inlet throat Mach schedule standby switches (INCR - DCR, spring-loaded to OFF, "off" not printed on the panel ).
- the bottom two are left and right inlet bypass door standby switches (INCR - DCR, spring-loaded to OFF, "off" not printed on the panel).

There were several differences in AICS operation between A/V-1 and A/V-2 but the read-out on the above indicators and operation of the 4 mentioned switches was the same. Judging the AICS control panel in the picture you provided, this represents A/V-1.

The switches outboard of the bypass door stby switches (Primary-OFF- Alternate) were specific to A/V-1 only. These are inlet bypass door standby SYSTEM selector switches. Normally set to OFF, set to Primary in case of a malfunction requiring the standby system. However, in case of a malfunction of the primary stby system, moving the switch to Alternate restores control to the bypass doors.

A/V-2 had inlet AICS mode switches (Auto/Emergency) at those locations, supplemented with a duct performance switch (High/Low) and an AICS reset switch/light.

There were more controls to operate AICS but these are not visible in the picture. These controls were located on the Co-pilot's control pedestal (A/V-1 only) and on the Co-pilot's (RH) console with different functions, depending on A/V-1 or A/V-2 operation.

To assist you with the various functions mentioned above, i have included a simplified AICS schematic diagram below:

AICS schematic diagram



Regards,
Starglider

[Edited 2007-02-21 11:37:34]
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 8:09 pm

Quoting Rwessel (Reply 43):
Except that it never actually overflew the nastiest SAM protected sites or faced significant numbers of interceptors in a situation where they might actually shoot. Mind you I'm only counting SAMs and interceptors adequate to the task -- while Hanoi circa 1970 might well have been the nastiest SAM site in the world, it was largely useless against the '71.
The same would have been applicable to the B-70, regardless if it was visible on radar or not. Perhaps, the B-70 would have had at least as much chance of survival if only because it could "jinx" (not as dramatic as a fighter of course, but still . . .), tactically altering it's course on it's way to a target more liberally, having more range capability when compared to the SR-71. Before the program was reduced to a research program there were also designs tested to reduce IR footprint and radar cross sections of the B-70. There are test reports that, if the B-70 would have gone operational, investigated the effect of fairings on the sides of the inlet/lower fuselage and inward canted vertical stabilizers during wind tunnel tests at mach 3 to 3.5, reducing radar reflections.

North American developed a "finish system", a paint, that provided a low emittance at wavelengths used buy the Soviet infrared detecting devices, while radiating most of the excess heat from the surface of the airframe in wavelengths not normally under surveillance. The finish used a low emittance basecoat with an organic topcoat. The top coating was opaque. This finish was relatively invisible to infrared detecting equipment while still allowing the skin to radiate excess heat overboard to maintain it's structural integrity. The finish would not be white as the finish applied to the prototypes but would have been opaque silver.

Like the SR-71, it is unlikely the B-70 would ever have to pass directly over it's designated target. It's mach 3 speed alone would have made any weapon released, a stand-off weapon.

Edited for text correction.

Regards,
Starglider

[Edited 2007-02-21 12:11:09]

[Edited 2007-02-21 12:29:59]
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Wed Feb 21, 2007 11:22 pm

Quoting Blackbird (Reply 42):
which each indicator listing pressure ratio goes up to 3.2 about. Is that pressure by mach number? Or is that like 32 : 1 PR?

In addition to my previous reply, the inlet pressure ratio gauges go up to 3.2 but should be read as 32 (indicated value X 10). Notice each gauge has a smaller indicator in it (each revolution of the small dial equals 10) for fine tuning purposes.

The diagram below is self-explanatory regarding inlet pressure ratios versus gauge read-out on the flight-deck:

Big version: Width: 801 Height: 603 File size: 64kb
XB(RS)-70 Inlet Pressure Ratio




Starglider
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 22, 2007 4:25 am

Is 32 a common compression rate for Mach 3 or 3.2?

Just out of curiousity... what was the Concorde's compression ratio?

Andrea K?
 
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 22, 2007 10:26 am

Quoting Blackbird (Reply 47):
Is 32 a common compression rate for Mach 3 or 3.2?


Mach number/airspeed, Inlet/engine, bleed/bypass, altitude and temperature are all factors affecting inlet pressure ratio. So inlet pressure ratio may vary per aircraft design.

Quoting Blackbird (Reply 47):
Just out of curiousity... what was the Concorde's compression ratio?


I assume you mean at cruise speed. Inlet pressure ratio for Concorde is approx. 12:1 at 60,000ft (standard atmosphere: static pressure at 60,000 ft is 1.048 psi / Compressor N1 inlet press. is between 10 to 12 psi).

Inlet design of the Concorde has a splitter-plate between engine pairs. So basically each engine has it's own inlet and they are very efficient. During Supersonic cruise only 8% of the power is derived by the engines with 29% being from the nozzles and an impressive 63% from the intakes.



Starglider

[Edited 2007-02-22 02:28:26]

[Edited 2007-02-22 02:30:39]
 
Blackbird
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RE: B-70: Was There Ever A Serious Mach 4 Requirement?

Thu Feb 22, 2007 11:36 am

Does 32:1 Compression Ratio look high, about right, or low for Mach 3?

Andrea K

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