Well 1 G is about 387 Inch per second per second. First derivative is velocity (v = 1/2 a ?).
These ranges doesn't match what I saw with clipped (exceeded) signal on my +-5G accelerometer.
I must be missing something .

Finn

rijakits wrote:

You will need a vibration range of about 0.03 to 2.0 IPS (InchPerSecond) acceleration, whatever g-load that is.....

Anything above 0.7 IPS on a prop/engine combination is considered "rough". If you get over 1.0 it is getting dangerous.

With new bearings and tolerances in spec you should be able to balance down to 0.02 IPS. Most aircraft spec 0.2 IPS as max.

Thomas J.

----- Original Message -----

From: Finn Lassen

To: Rotary motors in aircraft

Sent: Sunday, May 15, 2005 12:10 PM

Subject: [FlyRotary] Re: Prop balancing?

Cheap man's way:
I'm sure you have access to an oscilloscope.

Mount a position pickup (for prop) and connect to trigger input.

Get an accelerometer (http://www.analog.com/en/prod/0,2877,ADXL105,00.html, or similar - I bought mine from Newark many yers ago) and hook up to Y-input. Mount on tip of PSRU (or remove PSRU and mount on engine to check its balance).

You'll need some filtering circuit like a tunable notch filter. Actually doen't have to be tunable - adjust RPM to hit the notch.

I tried it with only the accelerometer and no filtering circuit and couldn't read through it. Actually not sure if the G range doesn't have to be bigger, like 20 Gs - seem to remember signal being clipped with the 5-G sensor. Some of our physists on the list can undoubtledly answer that.

Finn

Russell Duffy wrote:

I'm not familiar with the Chadwick unit, but it probably operates on the same principle using a vibration sensor on the engine and an optical sensor to pick up reflective tape on one prop blade. No reason it shouldn't work.

 

Thanks for the info Perry.  The Chadwick was just as you describe,  a vibration/optical sensor that mounted to the redrive plate, and a piece of tape on the prop.  The guy who was running it admitted that it was probably something he just didn't know how to set.  The unit actually belongs to his son, but he's working two jobs, and I never see him anymore.  

 

At least it's good to know that it should probably work.  

 

BTW, does anyone have any idea how much these things cost?  I assume "a lot". 

 

Cheers,

Rusty