|Dec 30, 2012, 10:22 AM|
NE Sailplane EZ 400G Rebuild
I bought this plane from Northeast Sailplanes at their Toledo booth upwards of 10 years ago. It's a wonderful little floaty plane, depending on the power system it's between 15-20 oz and with a thick airfoil and a 60" wingspan it flies a lot like a Carl Goldberg Gentle Lady. However, until now I've had a string of hard knocks and outright failures of the motors, batteries and speed controls on this plane. Or should I say I knew nothing about brushed or brushless motors and so I kept blowing them up, putting on the wrong props, and generally releasing the magic smoke from the speed controls.
So fast forward to this year and I now own a watt meter, a big selection of Li Po batteries, and the beginnings of a creeping knowledge of how to put all this junk together and not smoke them. Gosh I'm hard headed but I like to think I eventually "get it." Originally this plane came with a geared speed 400 brushed motor spinning about a 10" prop. It was powered by a 7 or 8 cell NiMh or Nicad battery pack. Back when it was new I'd fly with the 8 cell AA pack out of an electric Zagi and it would fly but gosh was it heavy. That gearbox started to go bad and I never did have luck finding a replacement that wouldn't grind hard too. Perhaps the motor mount system was to blame, I'm sure I "optimized" it to the point where it didn't work any more. That's kind of my specialty, messing with things till they break and I put them back on the shelf. Been doin' it since I was a little kid.
Anyhow 2012 almost 2013 and the weather is gnarly outside, nothing to do but build so I realized I had an extra motor from Dave Thacker's Radical RC. Dave sold me this little GWS 2205/15T-2160 to put on a biplane kit I also bought from him. Well turned out Dave's idea of nice motor and my flying ability weren't a great match since my thumbs were nowhere near fast enough to keep up with that darty little plane. So I put a smaller motor into the bipe and now I have this great little motor lying around. The bipe was about 8 oz, and this slow flyer is about 15 oz....hmm...seems like a reasonable transplant candidate.
So I got out the rule of thumb calculator and turns out maybe it wasn't such a crazy idea. If they say 50 watts/lb is a mellow flying plane then this setup would meet that criteria just about perfectly. The prop that Dave sold me with the motor was a 6 x 4. Looking up the motor on RCGroups and see a good thread on it where that is on the low side of what people are propping it for, but really considering I want to be able to run this motor, climb up to thermal height and turn off the motor, a smaller prop would be less drag anyway.
Now came engineering a new front fuse for this plane. The carbon tube had broken off about an inch or two in front of the landing gear. I thought long and hard about a new box section plywood front end just so I could keep the motor mounted with the spinning body towards the rear, the way it was setup in the bipe. However, I found some carbon tubes in my shop (Toledo 2011? from CST Composites) that are exactly the same as the original "fuse" of the EZ400G. I poke around and realize I can slide in a new tube on top of the existing tube and it will lock into place nicely. I slide that in and glue it up with the thread as a reinforcement. Looks bomb-proof. But then as I'm mounting the motor on the front with just a few layers of plywood I realize that darn motor firewall is going to break off with the first dork landing. However there's a nice gap and a perfect jutting out on the upper pylon/wing mount that would be a perfect backstop for a new upper fuse. About 5 minutes of crafting the tube to get the ends angled and beveled and it's glued into place and now the motor mount itself should survive minor indiscretions much better.
The other thing I've learned in the last couple years is that serious sailplane folk like an elevator setup with very little incidence to the main wing. Since I'm trying to make a plane capable of indicating lift properly I "fixed" this by cutting off a perfectly well mounted tail and installed a new wedge shaped spacer of balsa to try to attain that neutral incidence. The wedge pushed up the leading edge of the horizontal stabilizer.
Finally after test flying it yesterday I can see that it's going to be a pretty strong setup. It climbs out pretty well and isn't anemic in the way I feared it might be. Definitely 3 cells would be crazy strong unless you dropped the prop way down in size, perhaps a 5 or even 4 inch prop! But running with the 6 x 5.5 APC prop on 2 cells the motor stays cool, we're only at 11 Amps or so and battery and speed control should be happily under their limits as well. Now I just need to get this thing out there and catch some thermals in the breaks between rounds at the contests in 2013.
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