I think the 21 minute deficiency refers to the maximum total mission time . I think they have defined a mission , transit time to target , number of minutes at hover and then return to the ship. With the current engines and fuel it misses the mission profile by 21 minutes
from original requirement:
3.5.2.3.1.2 Payload/Endurance
3.5.2.3.1.2.1 [M] The MH shall launch from a HFX with 10 Kts of relative wind, at MMCW at
ISA, remain airborne for a minimum of two hours and 50 minutes and return to ship at the DELTA
HOVER ASTERN position with a 30 minute FUEL RESERVE while meeting the following
conditions:
Maritime Helicopter Project MHRS Draft Rev. 0 December 18, 2002
16
a. 60 minutes is spent in an out of ground effect (OGE) hover in zero wind condition;
b. the 60 minute hover OGE time is IAW SOI Scenario 8 with the remainder of flight completed at
Maximum Range Cruise Speed;
c. generate a minimum vertical hover ascent of 250 feet per minute or greater Vertical Rate of
Climb (VROC) from the initial OGE hover (T+20 min.); and
d. the VROC time must allow for the recovery of the full sonar cable length out of the water.
http://www.aero.polimi.it/~rolando/b...rements-mh.pdf