Hacker News Reader

Comment by jasonwatkinspdx | Hacker News Reader

Just to elaborate, the B-2 has the shape it does because it was designed for two missions, one flying at high altitude, the other at low. This requirement significantly complicated the aerodynamics, however the low level penetration mission is now regarded as suicidal, hence, the B-21 is designed for high altitude alone.

View on HN

What's the benefit of low-altitude capabilities for these bombers? Increased accuracy/precision? I would think that modern bombers would be incredibly accurate in any situation.

At one time low altitude was the best way to evade air defense as fighters didn't have look down/shoot down radar capability. They do now, so the low altitude mission might help with ground based radar (by using the earth and geographic features to hide), but an enemy with modern fighters and AWACS capability makes this profile difficult.

When computers sucked and there were a lot fewer smart bombs/missles, flying low gave you extra accuracy, but now that modern bombs include gps, IR, and probably 6 other tracking technologies it's a lot less useful.

> What's the benefit of low-altitude capabilities for these bombers?

You can hide from radar under the horizon and within terrain. (Mostly the former. Flying wings aren’t optimised for manoeuvrability.)

Terrain following significantly decreases detection range.

Not being shot down by longer-range surface to air missiles.

Why is the low level mission considered suicidal?

Russian and Chinese Surface to Air Missile (SAM) systems are really good. Modern versions can detect and target most stealth aircraft at a range of 15-35 miles, depending on radar cross section and electronic countermeasures in use.

Not correct because of physics. Ground based radar is still blocked by terrain and the horizon, meaning that low altitude attacks are still quite effective against only ground defense. That is why Ukraine's air force still exists and is still causing issues for Russia. It is also why shaheed drones are causing problems for Ukraine.

The bigger problem for low altitude attack is AWACS + fighters and interceptors with look down/shoot down capability. The MIG-31 has been a major problem for Ukraine because it has long range radar + long range missiles that can hit low targets. NATO and other US allies have integrated air defense where data from AWACS and other aircraft can be used to target low altitude targets.

As far as stealth goes, the notion that stealth aircraft can be targeted at medium ranges has not been tested on the battlefield.

> Russian and Chinese Surface to Air Missile (SAM) systems are really good

Their radars seem good. Russian “hypersonic” missiles [1] and S-400 batteries [2] are being taken out by decades-old Patriots and ATACMS. They’re demonstrably garbage.

[1] https://www.businessinsider.com/ukraine-stopped-russian-crui...

[2] https://www.newsweek.com/russian-s-400-destroyed-attack-ukra...

The Russian and Chinese air defense systems might detect but not target at a long enough range to matter. Those are two different tasks and fundamentally how stealth works in practice. Knowing an aircraft is out there does no good if you can't resolve a firing solution. Detecting at a range of 15-30 miles is a small comfort when an F-35 can carry anti-SAM missiles with a range of 100 miles.

There is also quite a bit of empirical evidence in recent months that the Russian systems do not work that well generally, since they seem to be incapable of defending themselves against non-stealth Cold War era US tech.

When you're flying low, stealth doesn't work because people can look up and see you (and then your 2 billion dollar bomber gets brought down by a 20k dollar shoulder mounted weapon).

Will the radar on a shoulder mounted missile overcome the stealthiness of a B-21? Presuming it has infrared countermeasures as well.

Stealth reduces detection range, it does not eliminate it. If an adversary has information on the path the target is likely to take it makes things much easier. This is how a F-117 got shot down over the Balkans. They kept using the same route and someone figured it out. At the ranges MANPADs operate, a couple km at most, thermal stealth is effectively impossible.

MANPADS do not use radar, they are all infrared or beam riders. You would not expect a B-21 to ever be within range of those weapons, which are really only designed to be used against helicopters and close air support aircraft.

Reply on news.ycombinator.com