Adding a rear battery bay

After determining I would need approximately 750g of battery weight to get the range out of the Sky Eye that I needed for 30 miles of flight, I loaded the plane up with roughly that amount of weight of spare 4-cell batteries I had on hand to see what kind of performance I could expect.

Well the first thing is that it is nose heavy at that weight. Not unflyable, but it needed substantial elevator trim to maintain level flight, even with all of the weight shifted as far aft in the compartment as possible. Since a nose heavy condition is far more draggy, I started cutting away at the rear fuselage to add a battery compartment on the aft-side of the wings.

When I began cutting away, I was met with a pretty nice surprise regarding the Sky Eye’s build quality:
IMG_20140307_201526616
There is actually a large carbon spar that runs the length of fuselage. I had noticed that the stiffness of the tail was quite a bit better than other long-tailed planes I have flown (cough cough Radian cough) but given that they couldnt even put bearings on the wheel, I didn’t expect a second, very large spar!

There are also foam struts between hollow cavities running all the way back to the tail. These double as nice guides for the elevator/rudder pushrods. Given that the Bixler doesnt have any such fuselage struts or spars, I know that they are not required for flight but it is nice that HobbyKing has beefed this thing up so much.

Anyhow, I carved out two of the struts to make room for a battery bay accessible by a taped on side hatch. I ran a charging harness along with a power lead up into the front so I won’t have to remove this battery very often.
IMG_20140307_203051409

The battery fills the gap that was left by the strut I removed quite well and supports the pushrod tubes. It fits in quite snugly and doesnt need any extra attachment.

After patching everything back up, adding my big batteries and re-checking CG, I was elated to see that I’m back near the tail-heavy side of things! I will shortly begin flight tests for the cruise/climb/longetivity of this configuration.

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