Omega 3
 

Hi Chaps,

I am aware that this has probably been posted quite a few times by now:

Could anyone shed some light on the topic of Omega 3 vibrations?

We do operate an EC 120 where they are quite pronounced.

I am just tired of having to explain the thing to type-rating aspirants/students and not being able to do it properly. :{

Already tried to google it - no luck...

Could anyone please explain or point me to an existing thread?

Cheers :ok:

I haven't heard the terminology "Omega 3" before, so I could be way off topic. Omega is sometimes used to indicate rotor speed and a 3 bladed rotor will have a vibration at 3 times the rotor speed, so I'm guessing Omega 3 is this. Terminology I've used is "3 per" which is short for "3 per revolution" or in general, N-per (N is the number of blades).

These N-per vibrations occur due to blade interference with something like the fuselage or the tail rotor. Because each blade is supposed to be doing the same thing at the same azimuthal position, the vibration occurs for each blade giving a "beat" every time a blade passes through the area where the interference occurs. Hence you get N beats per revolution at a frequency of Omega x 3. That might be what you're talking about.

1-per vibrations are related to the track and balance of the main rotor and can normally be reduced whereas N-per vibrations aren't directly affected by t&b.

Am I close?

Matthew.

Hi Mathew,

it seems we are talking about the same thing.

I usually tell the students/aspirants that Omega frequencies occur every time one of the blades passes over the tailboom. Then I explain that the weights mounted under the belly cowling are there to counter these very frequencies.

So that corresponds with what you have said. However I was actually looking for a somewhat 'deeper' explanation of the whole affair.

You have probably met your share of students as well and know how intricate they can be at times when it comes to 'dig deeper into the subject'.

Or am I too zealous in finding out all the mysteries behind Omega x3;)

WSPS

This may be of some help;

HELICOPTER FUSELAGE VIBRATIONS INDUCED BY THE ROTOR

@Dave

Looks good.

I will try to read through it over the weekend.

Cheers

Think Nick maybe able to help you with this topic..
Darren