Originally Posted by
noneofyourbusiness
Fuel burn - Let's say a fully loaded V-280 cruises at 280 knots. A fully loaded Defiant maybe 220? knots. Because the Defiant is slower, that makes its fuel burn look better than it really is. A fixed wing provides 15? lbs of lift per lb of thrust - a clear advantage for the V-280 Valor. Does Defiant have to carry more fuel to meet the Army range requirements? That would be a significant penalty, both in terms of weight, and in fuel cost.
Defiant-X definitely has a lower cruise efficiency (L/De) than V-280 but actual fuel consumed also depends on cruise speed and engine SFC, etc. They appear to have been successful in talking down the speed requirement which would also reduce the power required to cruise. Is it enough lower to overcome the poor L/De (relative to a tilt rotor) and require less fuel to cover the same distance as V-280 but at lower speed? Unknown. Could well be slower AND take more fuel to meet the mission radius. They haven’t said what engine Defiant-X will use and that’s an important variable in the question.
Of course, Defiant (nor Raider) can hit 230 knots in level flight, despite that speed being inside design requirements for both demonstrators. So we’re discussing the fuel efficiency of a solution that hasn’t been shown to meet the speed requirement, regardless of power/fuel consumed.