The Sultan
29th Jan 2021, 02:55
A recent article in Defense News covering development of the CH-47F Block II
https://www.defensenews.com/land/2021/01/27/latest-chinook-helo-variant-has-excessive-rotor-blade-vibrations-heading-into-major-test/
There was a lot of surprise when the Army passed on mass production of the latest variant of the Chinook, this article starts to flesh out the reasons for this decision. The main take away is:
The new Advanced Chinook Rotor Blade, or ACRB, on the CH-47F Block II aircraft “produces excessive vibrations in ground, hover, and forward flight that may cause a safety of flight risk,” the report stated. “Aircrews reported prolonged fatigue and other physiological conditions due to excessive vibrations following a developmental test flight using the redesigned ACRB’s.”
As the main reason for the 47F-II was the increased performance from the new blades, crippling (both figuratively and literally) vibration explains the Army’s production decision. A manufacturing problem controlling weight distribution or blade shape (generally associate with 1/rev) might be fixable with higher diligence in the fabrication process. A blade stiffness or tuning issue which can affect 1/rev, 3/rev and higher harmonics can only be fixed with a blade redesign. Relief from some form of vibration suppression system is generally only localized, results in even higher vibration elsewhere, and does nothing to reduce damaging loads.
This program can be added to Boeing’s ever growing list of recent design failures (737 Max, KC-46, Starliner, SB-1: etc).
https://www.defensenews.com/land/2021/01/27/latest-chinook-helo-variant-has-excessive-rotor-blade-vibrations-heading-into-major-test/
There was a lot of surprise when the Army passed on mass production of the latest variant of the Chinook, this article starts to flesh out the reasons for this decision. The main take away is:
The new Advanced Chinook Rotor Blade, or ACRB, on the CH-47F Block II aircraft “produces excessive vibrations in ground, hover, and forward flight that may cause a safety of flight risk,” the report stated. “Aircrews reported prolonged fatigue and other physiological conditions due to excessive vibrations following a developmental test flight using the redesigned ACRB’s.”
As the main reason for the 47F-II was the increased performance from the new blades, crippling (both figuratively and literally) vibration explains the Army’s production decision. A manufacturing problem controlling weight distribution or blade shape (generally associate with 1/rev) might be fixable with higher diligence in the fabrication process. A blade stiffness or tuning issue which can affect 1/rev, 3/rev and higher harmonics can only be fixed with a blade redesign. Relief from some form of vibration suppression system is generally only localized, results in even higher vibration elsewhere, and does nothing to reduce damaging loads.
This program can be added to Boeing’s ever growing list of recent design failures (737 Max, KC-46, Starliner, SB-1: etc).