---
kind: "section"
citation: "14 C.F.R. § 27.547"
title: "14"
number: "27.547"
heading: "Main rotor structure."
url: "https://uscodex.org/cfr/14/27.547"
---

# §27.547. Main rotor structure.

- (a) Each main rotor assembly (including rotor hubs and blades) must be designed as prescribed in this section.
- (b) [Reserved]
- (c) The main rotor structure must be designed to withstand the following loads prescribed in [§§ 27.337 through 27.341](/cfr/14/27.337..27.341.md):
  - (1) **Critical flight loads.**
  - (2) **Limit loads occurring under normal conditions of autorotation.** For this condition, the rotor r.p.m. must be selected to include the effects of altitude.
- (d) The main rotor structure must be designed to withstand loads simulating—
  - (1) For the rotor blades, hubs, and flapping hinges, the impact force of each blade against its stop during ground operation; and
  - (2) **Any other critical condition expected in normal operation.**
- (e) The main rotor structure must be designed to withstand the limit torque at any rotational speed, including zero. In addition:
  - (1) The limit torque need not be greater than the torque defined by a torque limiting device (where provided), and may not be less than the greater of—
    - (i) The maximum torque likely to be transmitted to the rotor structure in either direction; and
    - (ii) The limit engine torque specified in [§ 27.361](/cfr/14/27.361.md).
  - (2) The limit torque must be distributed to the rotor blades in a rational manner.

## Notes

### Amendments

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27-3, 33 FR 14105, Sept. 18, 1968]

### Authority

Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701-44702, 44704.

### Source

Source: Docket No. 5074, 29 FR 15695, Nov. 24, 1964, unless otherwise noted.

### Amendments

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27-3, 33 FR 14105, Sept. 18, 1968]