Time to get the rudder cable strung up. Mounting of all the misc stuff, RX, switch, battery, fuel tank, plumbing and so on needs to be done. The model is not just about ready to fly. I always leave mounting of the switch and battery pack to the end after I check the CG. The RX doesn’t tend to weigh much and the length of servo leads will limit the location a bit. So I mounted up the RX just behind the fuel tank. I made a small tray that span the fuse and used thick CA to attach the tray to the lower ¼ x ¼ stringer on the floor of the fuse.

Leave the Battery loose and just stick it in the model. We are going to check the CG location and perhaps have to move the battery. I selected a JR 1650nimh 4 cell pack to power the system. I will be using the JR X9303 2.4ghz system. I flew this system last year in my 2 meter models on the 1650 4 cell and also the 2300mah 4 cell packs. These are fairly light. I think the battery pack weighs in at about 4.5-5oz. You could save some weight here doing a smaller pack also. Saving weight on this model may be an issue we will know in a little bit. Rich now my guess is about 8.5 to 8.75lbs. This is just a guess. I'm using heavy stuff like the battery pack and wanted to get an idea of where it could come in with just normal stuff.

For now I want to check the CG. Since the battery pack could move in the end, I don’t want to mount up the switch just yet either. The location of the switch could limit how far I put the battery away without adding an extension. Again I want to get it close and save the weight of an extra lead. So just leave the switch in a “middle location in the Fuse….after checking the Cg we can choose were to put in and the battery pack.

The photo shows a 5 cell 2300mah pack. I first tried the Cg location with this pack as the 1650 was charging. Yes this pack weighs more but from the photo you can see the battery is right about on the center of the fuel tank. So it is very close to the CG. This pack weighs about 1 oz more than the pack I will use in the model. I sometimes will take a larger pack to have better leverage in moving it around. I was concerned about the model being tail heavy as a previous poster had shown. So I grabbed a larger battery to give me a little more mass to move to help get the CG…..

Now for the magic part. The CG was right on with the battery in this location. Sorry could not keep that secret long.

I want to explain how I calculate the Cg location. The designer asked for a CG of 6.5in behind the LE of the wing. I want an accurate CG location being an engineer I came up with a method about 8years ago to get my CG and also the models weight very accurately. Here is the radio compartment install and the battery pack location photos. Next post I’ll explain the method I use to get the CG…it has huge advantages over a couple fingers under the wing, and is even better than picking up the fuse without the wing and trying to guess if it hanging tail low. This method gives you accurate number.