SK720 vibrations help please

[A VIKING]

Yes to a lateral vibration being in a left/right direction.

[A VIKING]

...let me also add.
Don't fixate on the vibration being a fore and aft vibration or a lateral vibration...they are the same in that they are an out of balance condition.
When a wheel is out of balance, that imbalance can be felt through the entire 360 degree rotation as it spins.
Because of its mounting system or strength of the mounting system the heavy spot on the wheel will be allowed to "jut" out from its normal spinning path.
That sudden "jutting out" of the heavy side of the wheel will be seen by the Skookum and also its amplitude in the severity of movement at that moment will be shown to us on the vibe spectrum chart.
It will show us the direction of the imbalance as a lateral, fore and aft or vertical and how much movement it saw at that time such as 1,2,3,4,5 and so on.
The accelerometers on board the Skookum are used for this purpose.

So now you know what direction (lateral, fore and aft or vertical) and amount of vibration you have.
Because of the limitations of the system we don't really know where on the wheel, or in this case or motor can, the heavy side exists only that its out of balance somewhere.
This is where the experimenting with the position of the tie-wrap or packing tape on the can comes into play.
We need to identify the light side of the can to counter balance the heavy side with the addition of weight to the light side.

In the full scale world knowing the direction of the vibration will help us determine if the airframe supporting structure or rotating components are worn or lose. So we always inspect first before going through the balancing process. That way your not covering up a more severe airworthiness issue by balancing.

For us in the small scale world this logic can be helpful as well.
If you balance your new ship down to the lowest level you can and with the passage of time you see the lateral vibration you originally had slowly turn into a fore and aft vibration, this is telling you something is changing in the structure of the ship. Something is wearing out or you may have a crack somewhere. This is worthwhile to pay attention to.

How sensitive is the position of the vibration to changes in airframe structure? In some full scale ships I can change the vibrations position just by changing the fuel load on board. As an example, a full tank of fuel makes the fuselage more ridged and it will move the vibration in a different direction than with a fuel tank half full.

Interesting stuff and it seems as though voodoo is used to eliminate it but what it comes down to is you have a light side and a heavy side, find the light side and add some weight to counter the heavy side.

I am going out on a limb here and will guess that after finding the light side of your motor can and with a vibe score of 6 you will end up needing 3-4 epoxy spots added to the can for balance.
This is if you cut a round tooth pick in half and use the cut flat side to apply the epoxy as I have done to make the addition of epoxy consistent between applications. Important also to lay the motor horizontally to prevent the epoxy from running while it dries. This will make a nice aerodynamic dot of epoxy on the can. Clean the can with alcohol before applying the epoxy weight.

There are many methods out their to balance the can, this is just my method and shouldn't be thought of as the only method.

[Colin Broughton]

I appreciate your time you've taken to explain this A VIKING, really helps understanding what I'm looking at. I'm glad I picked up this sk720 as its an all new learning experience, this hobby amazes me

Now I just need to process all this and continue to dab in the log reading process etc and study the Skookum vibration Wikipedia

[Luvmyhelis]

Originally Posted by A VIKING

...
There are many methods out their to balance the can, this is just my method and shouldn't be thought of as the only method.

Ahh, after all the brilliant posts, I finally got ya.

[A VIKING]

Originally Posted by Luvmyhelis

Ahh, after all the brilliant posts, I finally got ya.

Dam...fingers to fast for my mind...or my mind to fast for my fingers.
At least I spelled it right even though it was the wrong choice of the word.
I usually spell it thier.