...But the 'planform' of this contraption is considerably larger (and therefore in my view more vulnerable) than the Raider concept. Plus, with the tilt-rotor you have two unique heat signatures effectively giving your assailant unnecessary opportunity...
Savoia- For sure, reducing IR is much easier with a conventional helo. The Comanche was a great example of how effectively it can be done. With a tiltrotor having tilting engines the long length (3 or 4 feet) of an engine exhaust IR suppression device can create ground clearance issues.
FVL won't enter service for at least another decade, and the model specs for each of the (4?) variants are still very much a work in progress. However,
the BAA issued for the JMR phase I TD aircraft has requirements for DGW of 30,000lb or less, and a speed of 230+kts. Sikorsky had to push hard to reach 250kts with their X2 demonstrator design, which was optimized for only going fast. Once compound helo designs like X2 or EC's X3 make the compromises needed to meet FVL program requirements for payload, range, cabin volume, etc., they will be hard-pressed to attain 250kt speeds. On the other hand, tiltrotors can easily achieve 250kt speeds.