Cheryl's Blog http://www.e-techgarage.com/Cheryl My Engineering Blog Fri, 13 Jan 2012 23:32:51 +0000 en hourly 1 http://wordpress.org/?v=3.2.1 My Homemade CG Tool! http://www.e-techgarage.com/Cheryl/2011/10/21/my-homemade-cg-tool/ http://www.e-techgarage.com/Cheryl/2011/10/21/my-homemade-cg-tool/#comments Fri, 21 Oct 2011 18:11:18 +0000 admin http://www.e-techgarage.com/Cheryl/?p=14 Our team has started a new project!  We acquired an RC airplane and we are going to replace the transmitter and receiver with two Programmable XBees.  We have already received the plane and put it together.  We also did a preliminary flight test.  We found out that the plane was really tail heavy and difficult to fly. 

One thing Larry discovered was that we had left some ballast out when putting the plane together.  Larry velcroed it in as far forward as he could place it. 

My next job was to research center of gravity on the internet and make sure the plane was balanced. 

I looked up a lot of information about center of gravity on RC planes and about CG tools.  There are elaborate CG calculators out there and then there is the rule of thumb school.  I decided to go with the easier method. 

I marked CG a third of the chord length back from the front of the wing:

  

The above picture is from the Wikipedia article on aircraft chords at http://en.wikipedia.org/wiki/Chord_(aircraft).   This is a commonly used rule of thumb for CG on this type of wing. 

The next step was to construct a CG tool to balance the plane on at the center of gravity.  There are CG tools made out of wire, PVC pipe, and wood.  I went with wood because I had some scrap lumber and could build my CG tool with a purchase of $.83 for a 36″ dowel, 1/4″ diameter and a $.99 package of pencil erasers.  Here’s the tool:

 

 With the ballast added in, the wing on, and the battery inserted the picture below shows that the plane is pretty balanced!

 

 

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