If maximum longitudinal/lateral cyclic blade pitch input is given, by how many degrees does the thrust vector (or rotor disc) change? Is the magnitude in the order of $\pm5^\circ$ or more in the order of $\pm15^\circ$?

Can this be assumed to be the same as the maximum blade flapping angle?


1 Answer 1


Assuming you mean, in-flight, it depends on the main rotor design. A fully articulated head can allow for angles great enough for an H53 to chop-off it's own refueling boom (See Here: https://www.bing.com/videos/search?q=h53+chop+fueling+boom&qpvt=h53+chop+fueling+boom&view=detail&mid=1AD065C255D15A52813F1AD065C255D15A52813F&&FORM=VRDGAR ).

Helicopter designs employing non-articulated rotor systems often have a cockpit indicator for "Mast Moment" in order to alert the pilot that excessive cyclic input is being commanded, risking Rotor/Head/Mast failure. These types require the blades themselves to absorb most or all of the rotor's dynamic articulation forces, hence much less angular deflection of the disc.

Additionally, the duration of the deflection needs to be factored-in. During maintenance test flights of the old UH-1 Huey, a "Pylon Rock Check" is performed. From an IGE hover an instantaneous full deflection and return to neutral (less than 1 sec for the full maneuver) is conducted either left or right. Somewhat violent and not something you would want to do every day for the sake of the transmission mounts. Sorry I can't provide exact disc angles though.

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    $\begingroup$ That's all interesting information, but it sounds like you don't know the answer to the question being asked. $\endgroup$
    – Sneftel
    Jul 30, 2018 at 9:58
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    $\begingroup$ I don't know the answer.This question is somewhat like asking how much control deflection does it take to snap-roll a 747. $\endgroup$
    – Walker
    Jul 30, 2018 at 17:17
  • $\begingroup$ Every rotor head has its stops, and the flapping articulation has its own stops too. The maximum deflection of the rotor disk is different according to the construction, but it's always the deflection allowed by the rotor head stops, plus 1/2 the flapping amplitude allowed by the flapping stops... $\endgroup$
    – xxavier
    Aug 29, 2018 at 11:00
  • $\begingroup$ Plus the extra deflection due to the flexibility of the blades themselves, that –under extreme conditions– may be enough for the tail to be chopped off... $\endgroup$
    – xxavier
    Oct 28, 2018 at 10:04

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