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Hey folks I'm middle of doing my cfi, and I cannot find any material that states how do manufacturers go about determining the reference datum point on a helicopter, particularly those that are outside of the aircraft, any help would be greatly appreciated thanks

 

The helicopter’s datum is established by the manufacturer as required under §27.1589 or §29.1589; however, its location is purely the choice of the manufacturer to describe and illustrate. Once the datum has been selected, all moment arms and the location of CG range are measured from that point. As a general rule, most manufactures place the datum forward of the nose. As a result, all values are positive when calculating the longitudinal CG. The datum is referenced from some point on the helicopter, as an example, the main rotor centerline. You can refer to the references below for more information:

 

§ 27.1589 LOADING INFORMATION

 

Explanation. Control of the rotorcraft weight and balance is an operational

function and is the responsibility of the operator. However, instructions necessary to

enable loading of the rotorcraft within the established limits of weight and center of

gravity and to maintain the loading within such limits are required by the operating

regulations, and inclusion of such loading instructions in the Rotorcraft Flight Manual is

required by this rule. Approved loading instructions, therefore, must be presented in the

Rotorcraft Flight Manual and, at the option of the applicant, may be included in the

approved portion or in the unapproved portion.

 

(iii) Dimensions and Datum Line Locations. The dimensions and relative

location of rotorcraft features associated with weighing and loading of the rotorcraft and

with weight and balance computations should be described and/or illustrated….

 

Pg. G-48.2 – G-49

AC 27-1B - Certification of Normal Category Rotorcraft

Edited by iChris
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