As many readers know, I'm a veteran of military service. I've traveled in military helicopters, including high-speed insertions into "hot" landing zones. I therefore have a "grunt's eye view" of the use of helicopters when things get hairy.
Consider the size of many helicopter landing zones. Some of them are open spaces, which offer room for aircraft to maneuver, such as this one:
Others, however, can be cramped, and dangerous to the helicopters because of encroaching tree branches, rocks, and other obstacles - and, in urban LZ's, buildings, electrical wires and other man-made hazards. Here's an example of a confined area landing in a forested environment.
Nicely done by that pilot . . . but a bit hair-raising, nonetheless. It can get even worse than that, as combat experience has shown all too clearly.
I can recall with unpleasant clarity sitting in a South African Air Force Puma helicopter, flying low-level in the operational area, watching tree tops go past above my head, almost within touching distance, as the pilot flew down a narrow road cut through the bush. His fuselage was between the trees and bushes, with his rotor above them, as he tried to stay as low as possible to avoid possible shoulder-fired ground-to-air missiles. One miscalculation and we'd have crashed. Not a happy experience, that. I would call it a "brown-trouser moment", except that our uniform trousers were brown anyway!
Now, look at this video of Bell's V-280 Valor technology demonstrator for the US Army's Future Vertical Lift (FVL) program. It's a tilt-rotor design, as you can see from the video clip.
The aircraft's performance is claimed to be "next-generation". Bell boasts that it has "Twice the speed, twice the range of current helicopters". That's great . . . but what about its tactical utility? Consider its effective span, from the outer tip of one rotor to the outer tip of the other. Bell doesn't give specific figures in its publicity material, but it does supply this graphic:
Note two things. The first is that the V-280 wing is superimposed on the Blackhawk fuselage. They aren't facing in the same direction. That's a critical issue if we're talking about a tight LZ. How will the pilot fly into a narrow LZ - sideways? I doubt it! Also, how will he or the crew see the ends of the rotors, and their separation distance from potential hazards, if they're that much further away from them? The second point is that the V-280's rotors aren't shown at full extension, with the outer blade in line with the wing. That's a bit of a cheat, and tends to make the comparison look more favorable to the V-280. I'd want to see the exact dimensions, but already I'm willing to bet they won't look good for the V-280.
When you consider safe separation distances in a landing zone, combined with the probability of having to perform insertions and extractions in confined terrain (natural or man-made - i.e. urban), I'm not at all sure how well the V-280 design will perform, simply because it's so big. It may be forced to land and take off in more open spaces, further away from the action. That will force troops to march further to where they're needed, or fight their way back to their helicopters for extraction. That'll add time and, probably, casualties to the operation - and that can't be a good thing.
(If it comes to that, the pilot couldn't fly a V-280 down a narrow bush road, as that SAAF pilot did his Puma. The wing would hit the trees on either side, even if the rotors didn't. That's another potentially vital consideration.)
Sikorsky-Boeing's SB-1 Defiant proposal for the FVL program, on the other hand, has a similar footprint to conventional helicopters, despite being much faster. It's not flying yet, but here's a promotional video from Sikorsky-Boeing, showing what it will look like. Note that they're showing it operating in a confined urban environment - perhaps deliberately, to emphasize that it'll be compact enough to be able to work there.
A smaller scout and attack helicopter design, the S-97 Raider, is already flying in prototype form to prove the technology involved.
From a purely tactical perspective, looking at the likely size of available landing zones, and the ability to set down and lift off as close as possible to the fight, I'd say the Sikorsky-Boeing SB-1 concept is going to be a lot more flexible than the Bell V-280. I'm not knocking the latter's capabilities, of course; I'm sure it'll be a very good aircraft . . . but that's not necessarily the only consideration. From a combat utility standpoint, I think its sheer size will impose limitations.
What say the combat veterans among my readers?