CG question (Superstar Select EP)
03-19-2004, 01:43 AM
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CG question (Superstar Select EP)
Hi All,
Okay...I have fixed the forward bulkhead (turned out very nice) and made a couple changes to help secure the battery but nothing major.(added small balsa pieces and very small pieces of foam so along with the velcro the battery has no lateral movement whatsoever) I still haven't secured it to not allow forward movement but of course can't do that until I CG is determined...this brings up several questions.
I don't have the Great Planes CG device the instructions specify to use...but look at my pictures and see if you think my improvised method will accomplish the same thing-am I going about this the right way? there are four pics...two side views to show my "device" and two underwing views, one of which is shot from an angle so you can see both forward and aft CG marks in the range. The other pic shows the CG falling about 1/16 inch behind the forward mark. The battery is where I want it...but I had to put one penny on the fuse just in front of the rudder.
This brings up my other question. Is it better to make adjustments by shifting the battery or by adding small weights to nose or tail. (within reason...not talking about more than one or two pennies, etc.) Adding weight seems like a better method to me because to shifting the battery seems like a very time-consuming trial and error type of thing. And then after I get that down and mark the battery and then add foam or whatever method I choose to keep the battery secure and unable to shift forward....then the CG will have changed again from THAT added weight. I also would prefer not to move the battery because its aft end is butted up against some balsa runners and I'd have to cut these to shift the battery aft, and those mods would change the CG again.
Am I thinking and stressing about this too much? Any pointers welcome.
auto5man
Okay...I have fixed the forward bulkhead (turned out very nice) and made a couple changes to help secure the battery but nothing major.(added small balsa pieces and very small pieces of foam so along with the velcro the battery has no lateral movement whatsoever) I still haven't secured it to not allow forward movement but of course can't do that until I CG is determined...this brings up several questions.
I don't have the Great Planes CG device the instructions specify to use...but look at my pictures and see if you think my improvised method will accomplish the same thing-am I going about this the right way? there are four pics...two side views to show my "device" and two underwing views, one of which is shot from an angle so you can see both forward and aft CG marks in the range. The other pic shows the CG falling about 1/16 inch behind the forward mark. The battery is where I want it...but I had to put one penny on the fuse just in front of the rudder.
This brings up my other question. Is it better to make adjustments by shifting the battery or by adding small weights to nose or tail. (within reason...not talking about more than one or two pennies, etc.) Adding weight seems like a better method to me because to shifting the battery seems like a very time-consuming trial and error type of thing. And then after I get that down and mark the battery and then add foam or whatever method I choose to keep the battery secure and unable to shift forward....then the CG will have changed again from THAT added weight. I also would prefer not to move the battery because its aft end is butted up against some balsa runners and I'd have to cut these to shift the battery aft, and those mods would change the CG again.
Am I thinking and stressing about this too much? Any pointers welcome.
auto5man
03-19-2004, 09:37 AM
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RE: CG question (Superstar Select EP)
When you balance the plane, you want to balance it on the wing. The plane is literally hanging from the wing.
While what you're doing will achieve the same result, it's going to be a lot more difficult to get an accurate measure of the CG location. The main mass of the plane is above the point on which you're balancing it, and it will be a lot less stable. It'll want to tip very easily.
Balancing the plane does not have to be so sophisitcated. Your fingertips will work fine. Mark the balance point on the underside of the wing on each side of the fuselage. Place a fingertip on each mark, and lift the plane.
While what you're doing will achieve the same result, it's going to be a lot more difficult to get an accurate measure of the CG location. The main mass of the plane is above the point on which you're balancing it, and it will be a lot less stable. It'll want to tip very easily.
Balancing the plane does not have to be so sophisitcated. Your fingertips will work fine. Mark the balance point on the underside of the wing on each side of the fuselage. Place a fingertip on each mark, and lift the plane.
03-19-2004, 04:37 PM
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RE: CG question (Superstar Select EP)
That sounds a lot easier than my method. I was having to lay on my back under the dining room table making minute adjustments for about 15 minutes until I got it to balance. You're right it was very tippy using the underside of the fuselage...don't know what I was thinking!
auto5man
auto5man
