Yeah, and it sounds like they can't fly that long without parts failure. It's hard to find thorough information on how long heavy lift helicopters can run for, but a new CH-54K only has an 88.6% reliability rate for missions lasting only 2.25 hours. Shit's looking bad for the helicopter idea.

  However, the current estimate for mission reliability is still below the required threshold (i.e., minimally acceptable) requirement. The program office reported in November 2020 that the helicopter demonstrated an 84.5 percent reliability rate, which is short of the program’s threshold requirement and below where the program office expected the reliability to be at this point in development.15 The program office projects that the helicopter should reach mission reliability of 88.6 percent after operational testing.16 According to program officials, the main causes of the reliability shortfalls have been technical issues identified during developmental testing. For example, the reliability of the main gearbox has been one of the main factors affecting the helicopter’s overall mission reliability metric.17 As mentioned, the program office has mitigation plans in place to address many of those technical issues, but has not yet demonstrated the required level of overall helicopter mission reliability.

Source: https://www.gao.gov/assets/gao-21-208.pdf (p13/14)