New Chinook variant suffering from excessive vibration

[NutLoose]

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.

https://www.defensenews.com/land/2021/01/27/latest-chinook-helo-variant-has-excessive-rotor-blade-vibrations-heading-into-major-test/

[kintyred]

https://www.defensenews.com/land/2021/01/27/latest-chinook-helo-variant-has-excessive-rotor-blade-vibrations-heading-into-major-test/

Interesting article. Having flown the RAF Mk2 straight from the docks on delivery more years ago than I care to remember and another nation’s aircraft from the factory, I know that Boeing expect their product to vibrate significantly less at the crew stations than the RAF tolerates.

[KG86]

Interesting article. Having flown the RAF Mk2 straight from the docks on delivery more years ago than I care to remember and another nation’s aircraft from the factory, I know that Boeing expect their product to vibrate significantly less at the crew stations than the RAF tolerates.

On a couple of occasions, I had US Army pilots in the other seat of my RAF Chinook. Invariably, when I lifted to the hover, they would say that the vibration was so severe, to them, that in the US they would land back on and give it to the maintainers to fix. As I recall, the US Army changed whole (balanced) rotor blade sets, rather than one blade at a time in the UK. So the US comments about excessive vibration could probably be taken with a small pinch of salt. It could be SOP for us!

Vne for a US Chinook was 170 kts. RAF limited it to 160 kts. Flight at that speed tested the security of one's teeth fillings.

[MG]

Excellent, another Chinook thread.

Could I ask that Tucumseh and Chualug2 immediately inform us that excessive vibration is, of course, the fault of the regulatory system and RAF VSOs?

[brett s]

US Army didn't change entire blade sets in my day, with either metal or composite blades.

The old metal blades were easier to get smooth than the composite blades that replaced them in the 80's. If my memory is correct the goal was less than 0.2 IPS.

[Shackman]

The RAF tried to persevere with the Chadwick-Helmuth tracking kit, which was the standard kit for Wessex, Pumas etc.On the Chinook, it seemingly could only track (and not really balance) one head at a time, and as soon as the other head was done the first one wolud go outside limits. I think the record was something like 50 hrs to get one aircraft (just) into limits. The introduction of Rotortune was like a game changer - once the engineers got their act together, The first track and balance I did with rotortune (and their own people) took about 1 hour and was then the smoothest Chinook on the fleet. (plastic bladed Mk1). Once our own engineers were up to speed most of the rest followed. I never flew a US one, but a Canadian one seemed worse, albeit subjectively.

Sorry, my bad - I should have said Helitune, not rotortune (it was a very long time ago it seems now). My thanks to Bonkey below

[kintyred]

On a couple of occasions, I had US Army pilots in the other seat of my RAF Chinook. Invariably, when I lifted to the hover, they would say that the vibration was so severe, to them, that in the US they would land back on and give it to the maintainers to fix. As I recall, the US Army changed whole (balanced) rotor blade sets, rather than one blade at a time in the UK. So the US comments about excessive vibration could probably be taken with a small pinch of salt. It could be SOP for us!

Vne for a US Chinook was 170 kts. RAF limited it to 160 kts. Flight at that speed tested the security of one's teeth fillings.

Spot on! The RAF also changed the lubricants used by Boeing which was reputed to change the vibration characteristics. I'm sure the experts will say that the RAF rotirtuning regime works in terms of reducing vibration induced stresses on the aircraft, but the frames do seem to crack very frequently.

[PPRuNeUser0211]

Spot on! The RAF also changed the lubricants used by Boeing which was reputed to change the vibration characteristics. I'm sure the experts will say that the RAF rotirtuning regime works in terms of reducing vibration induced stresses on the aircraft, but the frames do seem to crack very frequently.
But the UK do also, iirc, use an increased Max AUM when compared to the US Army?

[Bonkey]

The best one I know of for Track and Balance is the Helitune product. Great support and those fellas really know what they are talking about. Great BRITISH company and product :D

[kintyred]

But the UK do also, iirc, use an increased Max AUM when compared to the US Army?

RAF limit is 24500kg or 54000lbs (give or take)