jt01
Squadron leader
Posts: 166
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Post by jt01 on Feb 1, 2007 15:48:21 GMT 1
A lot of guys have been asking where the cog is on there cub.I've made a simple tool from stuff I had around the house. I used a piece of 3/4 plywood cut 12" x 12" for the base,5/16" steel rods (wooden dowels flex too much) set at 60* and topped with pencil erasers. Works pretty good and found my cog at 2" behind the leading edge. Jim  |
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Post by SCC on Feb 2, 2007 23:08:01 GMT 1
Nice tool Jim. I have got the hardware to make one, but how do i drill holes at 60*  |
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jt01
Squadron leader
Posts: 166
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Post by jt01 on Feb 3, 2007 1:47:54 GMT 1
I clamped 2 three quarter inch boards to my drill press to raise the back of the base board. I don't know that the 60* needs to be that accurate but both holes must be at equal angle.I just used 60* to clear the wing struts.If you don't have a drill press you may be able to drill an angled hole in a piece of 2x4 and use it as a jig to drill both holes with a hand drill
Jim
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jt01
Squadron leader
Posts: 166
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Post by jt01 on Feb 17, 2007 16:08:18 GMT 1
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wjcjr
Squadron leader
Posts: 103
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Post by wjcjr on Mar 7, 2007 1:56:30 GMT 1
Jim the link you provided helped me understand and troubleshoot my plane. Thank-You very much.
For anyone who has not looked at the link above take a gander, break out a pencil and run the equations. You may be surprised at the numbers you find and or may be able to learn how to get more from your plane.
Wayne
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Post by flydiver on Mar 14, 2007 1:33:53 GMT 1
Is that 2" COG with battery in. If so, how many cells?
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jt01
Squadron leader
Posts: 166
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Post by jt01 on May 13, 2007 16:18:30 GMT 1
Is that 2" COG with battery in. If so, how many cells? Sorry I took so long to reply.The 2 in. was with a 7 cell battery and complete stock plane before I made the adjustments to get it at 1.75" from leading edge. |
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Post by cjg on May 14, 2007 2:32:30 GMT 1
I liked Jt1's COG balancer so much I built one myself out of stuff laying around. In this case dowel rods. They are short enough they don't flex, and since I cut them off at a slight angle they have a bit of a "knife" edge to balance on. I used his idea of a 2x4 as a "jig" to drill equal angles. I guessed at the angle, I should have used a bit more, but it works. Pictures attached. I used plastic tack in the nose to balance it. I like mine with the COG 1/8 inch in front of the COL.    |
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Post by geekmedic on Aug 1, 2007 19:25:42 GMT 1
I have learned so much from this site and a few others on the www.. I went ahead made one of these COG tools based on jt01's design.
Now my question: When I tried to find my COG how do I know that I have it? I've put the SC on and anywhere between 1.5 - 2.25 inches (guessing here) it seems to balance. What do I need to look for on the SC as it sits on this? Bottom surface of the wing level with the ground, Batt box level with ground, tail feathers, what clues me to the true COG?
Also how close to the fuselage are the uprights?
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Post by trollsplitter on Aug 2, 2007 2:02:14 GMT 1
just ceriouse but that is the point of the angle on the poles of the base. could they not be stright up and down?
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Post by cjg on Aug 2, 2007 2:13:38 GMT 1
just ceriouse but that is the point of the angle on the poles of the base. could they not be stright up and down? that would probably work, but this way gets more of an edge in contact with wing, for a smaller pivot area. It also clears landing gear, etc better. |
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Post by geekmedic on Aug 3, 2007 16:05:14 GMT 1
Please, what am I to be looking for with my SC on this? As I said earlier, Should have clarified it sits/hangs differently throughout those measurements, nose down, nose up. But heck it's on there and no part of the aircraft is touching the ground   How do I Pinpoint the CG? I've also read through this as well, it makes more sense every time I re-read it. This is all relatively new to me and I'm trying to learn. I'm guessing that the bottom of the SC wing should be level to ground as it balances. Does it matter where the uprights are, related to the fuselage? |
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Post by cjg on Aug 3, 2007 23:36:19 GMT 1
Please, what am I to be looking for with my SC on this? As I said earlier, Should have clarified it sits/hangs differently throughout those measurements, nose down, nose up. But heck it's on there and no part of the aircraft is touching the ground How do I Pinpoint the CG? I've also read through this as well, it makes more sense every time I re-read it. This is all relatively new to me and I'm trying to learn. I'm guessing that the bottom of the SC wing should be level to ground as it balances. Does it matter where the uprights are, related to the fuselage? Essentially the bottom of the wing should be level with ground. What you are interested in is where the COG is in relation to the COL. The COL is fixed at 25% behind the leading edge on a wing which is uniformly wide through its length. Optimum balance is when the COG and COL are the same spot. With the COG a bit forward it will handle better but be a bit more sluggish in turning and climbing. With the COG behind the COL it will tend to porpoise in flight, but will glide nicely without power. |
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Post by geekmedic on Aug 4, 2007 5:08:06 GMT 1
CJG thanks that is what I was looking for
What would be the best way to determine level? TLAR method, or actually puting a level on?
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Post by cjg on Aug 4, 2007 5:56:19 GMT 1
I use a Mark 1 Eyeball to tell if it is balanced level ;D
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