Helicopter vibration analysis

[ghostrider203]

Hi all,

I'm doing some R&D regarding an external mounted pod for some common machines out there.
It would be installed on various machines like the B206/L, B407, AS350/5.

The question is, how do I obtain values for the frequency and amplitude each helicopter vibrates at? (eg, at the pilots seat)

I know you can deduce the basic frequency by inverting the main and the tail rotor RPM quantity but I still need amplitudes and confirmation that the machine keeps the basic vibration frequency intact throughout the airframe.

These numbers would help in the design of an effective damping system for our sensors mounted internally to the pod.

[cdnpilot77]

私はｉが助けになることができたならいいのにと思います

What you wrote is the same as how this looks to me. However the above apparently means, "I wish I could help" but for all I know it could also mean "I walked a desk into the porkchop". So who really knows?

[ghostrider203]

Sorry about the confusion.

For eg. the B206III main rotor vibration is around 6Hz, (with secondary, ie tail vibes at 13 Hz), just looking for more precise values for the other ships.

I hope thats less Kanji-like !!

[Heliian]

Well, you are looking for a giant pile of data there. Basically, a helicopter flies by vibrating so much that the ground rejects it.

Seriously though, helicopter vibrations can be present across a large spectrum, especially in multiples of of the rotor RPM and vary from type to type. A helicopter designed with 2 blades will be different from a 3, 4, or 5 bladed machine. As for amplitude, the target balance for a helicopter is usually 0.2 inches per second(ips) in all phases of flight. When the helicopter is hovering the ips reading may be higher or lower than when in cruise flight as all blades do not produce exactly the same flight qualities. Some helicopters use dampening systems on the m/r and in the cabin to mask offensive vibrations at certain positions on the airframe. To get the data you're looking for, you are going to need a helicopter, your pod and vibration analysis equipment. Then you'll truly know the vibe levels on that type of helicopter, with your pod in whatever location you decide to mount it. This is just some basic information, I hope it helps.

Cheers,

I

[sky's the limit]

Wish I could help, but I just fly them and complain to the Wrenches when they shake too much...

Good luck,

stl

[fel]

Any monitoring and diagnostics we carry out on our machines, the "Box" has all the oem expected vibe levels of all the pick-ups at the positions embedded in the software for the specific model. We can look at specific vibe levels at any position a pick-up has been installed (under pilots seat/at MGB/at TGB.... etc), along with limits above or below acceptable. The vibe data would originate from OEM, but companies producing Track/balance/hums/vibration diagnostics such as the link below would have specific model info. Maybe check or query them....not sure this will help.........


http://www.dsi-hums.com/Honeywell-Chadw ... 0-Plus-V2K+

[Herleston]

I am a little beginner in this and I want know why this analysis is so important to a helicopter pilot. What is the impact of vibration on controlling the helicopter on its course?

[ghostrider203]

I am a little beginner in this and I want know why this analysis is so important to a helicopter pilot. What is the impact of vibration on controlling the helicopter on its course?

A little vibes dont have a big effect on everyday operations but the pilot and passengers will report being more tired at the end of a long day in a ship that is less than ideally balanced.