Increasing Battery Capacity

A goal I had with this Extra is that I wanted it to be a reasonably capable racing machine. Compared to many of the flying wings out there today, this simply isn't a very efficient airframe. In order to be competitive, that means having to run bigger, more aggressive props which are spun by bigger motors. Or more simply, I needed the power system to push more amps.

Unfortunately, the factory battery capacity is only a 2200mAh 3S. Nothing larger will fit without cutting foam, and the power system I wanted to run could drain this in about 1m30s to 1m40s at full throttle. Without wanting to ditch my stock of 3S packs, the only option left was to cut away enough foam to allow me to run a second pack in a 6S configuration. 

My original intent was to stack the two batteries on top of each other with the ESC then on top of that stack, as shown below:

After taking a closer look at things, I decided there wasn't quite enough space for the ESC there. As a result, the configuration I went with has the two batteries stacked as shown, but with the ESC attached to the exterior of the front cowling with velcro. While not cosmetically pleasing, that does allow for plenty of ESC cooling, and with the intended high power draw, more ESC cooling is always a good thing.

With the interior layout figured out, it is time to cut foam. Start by removing the front bulkhead to allow access to the foam:

You can see the space for the single battery the plane was design to carry. The two protrusions from the sides of that channel are what need to be removed:

Starting to look pretty good. Let's give it a test fit with the 3D printed battery blanks:

I would say that looks just about perfect. Note the gap above the second pack - that is clearance to allow for pack installation/removal. Without that gap, the wing spar blocks the slot.

With the foam done, let's glue the front bulkhead back on and then get that new motor installed.


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