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CG-Meter
Tool for measuring the center of gravity on F2D models
First published: 24/6 2015 - Last update: 1/4 2018 - By Henning Forbech

     
1/4 2018: Update with video

How do you find the position of the center of gravity (CG) on your models?

The CG-Meter is an instrument designed to point out the position of the center of gravity on a F2D model.

Model trim is often a subjective exercise where the pilot tries to make the model "feel" good.
It would be easier to trim models if you were able to measure precisely what changes you are doing to the model.
The sensitivity of the CG-Meter is better than what most pilots will be able to observe by test flying a model.

   
What dose "CG-Meter" mean?

CG is short for
Center of Gravity
This is also known as the
balancing point of the model
 
 

 
The CG-Meter is an instrument to find the center of gravity on F2D models

When you find a trim that suits your flying skills and style it will be easy to set up more models with the exact same trim

If you adjust the trim of your model by adding a coin to the rear of the model you will typical move the center of gravity by 2 mm. With the CG-Meter you can measure the location of the center of gravity with a precision of 1 mm. This is better than what most pilots will be able to observe by test flying a model.

When a model is hanging in the balance in the CG-Meter it is easy to add extra weight to get just the right balance of your model. If you have a series of models you can adjust them to exact the same setup without test flying each of the models.

After a series of test flights you can also measure the trim of the model you like the most and transfer this trim to other models.

Even throw all models in a series seem equal a test measurement shows that each model needs an individual adjustment to get the center of gravity in the same position. In a series of high quality models I found a variation within the models of 2 mm. It would take a lot of test flying to find and eliminate these small differences, but with the CG-Meter it can be done home in your hobby room without even starting an engine.

Repairing a broken model may add extra weight to the model and change the trim of then model. With the CG-Meter it will be easy to rebalance the repaired model and get it center of gravity back to the right position
 
 


A model hanging in the CG-Meter. The pointer will show the locations of the center of gravity.







 
The CG-Meter consists of four main parts: The cardan head, the piano wire holder for the engine, the piano wire holder for the tail and a CG pointer. To build the CG-Meter you will need the 3D printed plastic parts from Shapeways, four old FORA front ball bearings, some M3 screws, thin piano wire, brass tube, nylon string, etc.

The piano holder for the tail is made from a 1 meter long piano wire (ø0.8 mm). Two eyelets are bended for screwing it on to the cardan.

The front piano is also made from ø0.8 mm piano wire. One end has a eyelet to screw it on to the cardan and the other end have an eyelet that fit the propeller nut on the engine. The drawing show the size that fit the carbon models from Yuvenko. You may have to adjust this to fit other model designs. The front piano is balanced with some soldering wire to get the CG-Meter in a neutral balance. Use a balsa stick with the same length as your model and balance with soldering wire until you have the CG in the same positon as on your model.

The pointer is made from a piece of nylon string with a melted nut at one end.
The string is put through the center hole in the cardan and the melted nut prevents the string from falling out of the cardan. It can be a little tricky to get this string through the cardan (will be fixed in the next update). A brass tube (ø4 mm) is hanging from the string and inside this tube a ø3 mm piano wire are hold in place by a piece of silicon tube. This arrangement allows you to adjust the length of the pointer.
   
Drawings for the CG-Meter:
2D drawings, pdf, A4

CG-Meter
CG-Front
CG-Back
CG-Pointer

Get the plastic parts from Shapeways

Here is some
balancers for RC-models:
Balancing RC airplanes

EZ Balancer
HobbyKing

To adjust the elevator you need the
Klap-o-Meter
 
 

The spanish F2D team with the CM-Meter in Riga 2016


The CG-Meter must hang from a proper support to give a stable reading


Transferring the trim from one model to another
 
 

 
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