Forum: Modern Military Aircraft

I know the original was designed to fly fast and low to make it hard to track and shoot at in a pre-stealth world, but then got modified to reduce radar signature at the cost of nearly half its speed (both because of the advent of reliable stealth technology and because the fast-&-low approach was found not to be as effective as expected). But exactly what were those changes and why did they have to compromise speed? I've seen some pictures of B-1A and don't notice anything different about its shape from B-1B. Is it entirely because of what they did to the airflow into the engines to hide the fans in front, or are there also changes to the body and control surfaces that I haven't spotted yet? And are radar-absorbing materials used at all?

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The B-1A was actually designed for both HIGH and LOW speed (M2 and M1.2 respectively) The low altitude speed limit was dropped to M.85 for manufacturing reasons, vastly decreasing the effectiveness of its penetration at low altitude. With the defection of Viktor Belenko and his description of the "Super-Foxbat", likely MiG-31 with look down-shoot down, there came a threat for both the M.85 low altitude incursion AND the M2 high altitude incursion. With the developement of the ALCM for the B-52 it was determined that the B-52 could more effectively strike targets beyond the defensive line and do it for less money. Thus the B-1A was cancelled. The Soviet trifecta of the SA-10, MiG-31, and AWACS meant that the B-52 was becoming increasingly vulnerable. This prompted development of the B-1B with an increased low alt speed of M.92 and lower RCS. The B-1B also had improved ECM over the B-1A. The B-52 was capable of similar speed and could be outfitted with similar ECM, but the B-1B had a higher payload, better take-off performance (increasing basing options), and better gust response from the nose vanes and higher sweep angle. As for the reduction in top speed, that comes from the transition from a variable inlet to a fixed inlet which limited the ability of the intake to handle super sonic shockwave formation but allowed for the reduced RCS. Did I miss anything?

I wouldn't characterize the B-1B as having lost half it's speed. Perhaps 400kts, but in exchange for a 100x RCS reduction, and greater low altitude speed. Now add in improved ECM, and the ability to drop PGMs.

Bone-A #2 hit MACH 2.22 during testing.

Bone-B is said to make MACH 1.25; not half but a large drop.

I'm sure the total Kts would depend on altitude, but the important thing was the Bone-B has the better low-altitude penetration speed.

Amazing how inlets can change the dynamics of an aircraft's high-speed performance.

Keep 'em flyin' Thumb

TEG

Cost was another big reason for the switch to the -B. The material costs to produce a M2+ capable machine of that size were going to put a squeeze on DOD. The new design allowed them to axe a lot of titanium from the leading edge surfaces. Much has been learned about working with titanium since the late 70s but even now it is still a very expensive solution.

To clarify what others have said, one of the big costs of the A-model was the variable geometry inlets that allowed the Bone-A to go M2+. When the program was revived by Pres Reagan, the inlets were changed to fixed geometry, optimized for low altitude dash and basic cruise. This reduced the maximum speed as noted above but reduced costs and RCS significantly.

Of course after the USAF spent a fortune optimizing the fleet for low altitude penetration (LANTIRN, Bone, F-111, etc...) because of the reduced SAM threat at lower altitudes, Desert Storm came along and we learned that (1) Stealth ops at altitude worked and (2) low altitude was not as safe as thought we bailed on that idea.

walls of flak suck at low altitude.

It sucks worse the bigger you are.

Perhaps some veterans can fill in my history gaps here, but as I recall the value of the low altitude target ingress was 'proven' during the interim B-1A - B-1B period, when the 4 prototypes (or was it only 3 after the bird strike?) were used in trials. Do you think that the constant availability of mountain west canyons to block search radars may have over-contributed to the acceptance of low altitude as a cure for AA threats?

The Desert Storm reference points to a wide open terrain where there are guns everywhere firing blindly into the sky. Not where you want to be if flying low is your plan, hense the F-117 flying at medium altitude.

Last edited by aaam on Feb 03, 2012 - 10:30 PM; edited 1 time in total

Some thoughts, for what they're worth.

First, the B-1A was canceled because as part of his philosophy and low opinion of Defense, Jimmy Carter repeatedly made a campaign promise that if elected, he would cancel the B-1 right away. In fact, he made it one of the Democratic Party's platforms. After he got in, and reviewing the results of B-1 testing so far, he reportedly started to have 2nd thought (reportedly his own DoD recommended keeping it), so the action was postponed. However, during the late Spring his supporters pushed for him to keep his promise and so on June 30, 1977 he killed the program.

Although USAF started the ALCM program in 1974 (rather than just go with the less expensive option of just using an air launched version of the Navy's Tomahawk missile already in development), this wasn't done just to allow the B-52 to do the penetration mission. The B-1A was also intended to carry it as well. Part of the reason, of course, was that it made sense, but also because for certain targets the launch aircraft was going to have to penetrate significant defenses in order to reach the launch point and to get there and that the B-52 wouldn't be able to do. There was big talk about accelerating cruise missile development in lieu of the B-1, and there were Administration PR events showing how many more cruise missiles would be carried using modified 747-type carriers, but in reality neither of those initiatives were ever actually launched. Cruise missiles were just used as a rationale to deflect criticism for the cancellation.

Production B-1As would have had their penetration speeds lowered to M.85-.9, similar to B-52 speeds. The difference is that the B-52 was designed as a high-altitude bomber and when it went to the low level profile it dramatically increased the wear on the airframe and reduced operational life, even with the modifications. The B-1 was designed for low level operations from the start and its structure was built with this in mind. It's worthy of note that significant redesign and increases in cost resulted when in the development stage AF added low altitude penetration to the B-2 mission. The main reason for the reduction in speed was cost/benefit. Analysis with the F-111 and the B-1A showed that once you get M.8 or thereabouts at low altitude, you don't gain that much more in survivability from another .4 Mach, but it costs a lot more. Of course, the B-1 was much more agile than the B-52.

Regarding the top speed, the plan as I remember it was that production B-1As would retain the variable intakes, but they would be deactivated in normal operations. This would save a significant amount on maintenance, and if it was later determined that on certain missions the capability would be needed, they would be activated. I don't know if activation involved just pushing in certain circuit breakers and telling the FCS the intakes were back or whether external actions had to be taken on the flight line. The Navy followed the exact same stratagem on the F-14D. The variable ramps were there, but deactivated.

On the B-1B, it's not just the intakes that limit its top speed to M1.25. The B can actually go faster than that. But in order to reduce the empty weight of the a/c (the gross of the B is 25% greater than that of the A) as well as cost, structure was removed from the wings since they no longer needed to withstand higher Mach flight. As a result, you start getting too much faster than its current top speed and vibration sets in that can affect flight characteristics and cause damage. In effect, it advises the crew, "Hey! That's it, foot off the gas pedal"!

Another thing that isn't remembered much today is that the B-1A also had a major conventional and tactical mission that figured in its design. One of the reasons they were going to build 244 of them is that it would take over the F-111 mission (it was the cancellation of the B-1A that required the development of the F-15E). As a result, it would be equipped to deliver just about every kind of conventional a/g in the AF inventory. In addition, there were equipment bays in the fixed portion of the forward wing roots containing retractable sensor packages. One held streamlined LLTV and optics to aid in navigation and flight, especially at very low levels. The other contained a sensor and designator turret similar in concept to the Navy's TRAM turret on the A-6E. Couple these with the B-1A's 6,100 mile range and payload and you had one formidable strike package. Consider the impact on the Warsaw Pact in a conventional conflict of planes based in the UK that could basically run their fighters out of fuel through course changes, had defensive countermeasures designed to penetrate the Soviet Union itself, and were each carrying, say, 60+ Mavericks...

In short, the B-1B was definitely more stealthy and had greater range/payload, but the B-1A was faster, somewhat more agile and more versatile.

sprstdlyscottsmn wrote:

The Desert Storm reference points to a wide open terrain where there are guns everywhere firing blindly into the sky. Not where you want to be if flying low is your plan, hense the F-117 flying at medium altitude.

What we found in Desert Storm was that low altitude ingress works very well for individual flights that achieve surprise. However, if there is also a medium altitude package approaching, that's going to be detected, and the wall of lead that arises will prove very hazardous to things approaching at low level.

The F-117 flew at medium altitude because if you're already very hard or impossible to detect on radar, then there's little or no advantage to flying low.

Wasn't the USAF considering the A-12 as an f-111 replacement? I seem to recall that being an option seeing as Low Observability allows for higher and safer altitudes against AAA batteries as demonstrated by the survivability of the F-117 in Desert Storm.

tacf-x wrote:

Wasn't the USAF considering the A-12 as an f-111 replacement?.

You speaking of the McDonnell Douglas/General Dynamics A-12 Avenger II aka "Dorito Chip" or the Lockheed A-12 Blackbird?

I don't think it's the latter, but you should have read the description of an A-12 Blackbird dropping a 1000lb solid tool steel bomb from 85K' and Mach 3. The results would have been eye watering!

TEG

Talk about a kinetic kill. Now what would the glide range of a SDB be, assuming it survives the launch.

Forum: Modern Military Aircraft

Differences betwen B-1A and B-1B?