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Old Feb 06, 2012, 02:44 PM
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Build Log
Retro-RC Babe'Moth Build

My kids gave me this kit for my birthday yesterday:
Retro-RC Babe'Moth

While I've been building models for years, this will be my first real RC build. I decided to do a build thread, because I've received some good help and ideas from others' threads and input on RCG.

The model has:
Wingspan: 24"
Wing Area: 188 sq. in.
Weight: 10 oz

I'm going to cover the body in Parklite and the wings in Coverlite (I have fresh rolls on hand and the kids are picking the colors, thus the mix). This will be my second covering job and the first with large sheeted areas.

Their recommended power setup is an 1806 2100kv outrunner, 2s 900mah lipo, and 6x3 or 6x3.5 prop. They actually sell the outrunner they use in their setup, it's a basic Chinese made AX1806N/2100 KV that's available from HK and other low-price sources. I'm considering it but I'm definitely willing to invest in higher quality. I would welcome suggestions on a power system. Not sure what the maximum prop diameter it would handle based on clearance, but will look at that this evening. I'm also looking towards sport aerobatic performance, not interested in hovering.

For battery, I was considering using the 2s 800mah batteries that came with my PZ Brushless Decathlon. Two reasons: they are about the right size so I could use batteries between both, and I have a charger for them.

So far I've opened the package and bent the wood for the top deck. The deck has to be formed on a 1" radius, so I obtained a large 1x36" dowel, soaked the wood, and wrapped the wood onto the dowel using an ace bandage, which provides pretty even pressure (the instructions recommended cloth strips, but I think the bandage is simpler). Tonight I'll be starting some actual construction.
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Old Feb 12, 2012, 09:46 AM
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I've gotten most of the fuse made up. I left the deck pieces wrapped for several days. Construction is fairly straightforward so far, like a jigsaw puzzle as others have described similar builds from Mountain Models, Stevens Aero, or similar makers.

On something like a Guillows build I would normally cut every single piece out for a major part (fuse, wing, stab, etc.) With this I'm avoiding that because they are not labeled. I'm trying to cut them out as needed, but find I frequently don't cut enough - In one or two spots I ended up a step farther than where I originally planned and had to go cut out mid step.

The laser cutting is good, but I will say the brown edges are annoying. I'm sanding them all, but they still tend to make my hands brown and get brown dust over my work board. I'm constantly having to wipe it down.

My only complaint so far is that while the instructions are complete, and include full-color pictures, the pictures are so small that in many cases they are not very helpful.
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Old Feb 12, 2012, 09:52 AM
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My next question is on the power for this. Based on what I see, it looks like the e-Flite Park 250 would be an appropriate equivalent to their recommended powerplant:

http://www.e-fliterc.com/Products/De...rodID=EFLM1130

Based on what I put into Web-O-Calc, it seems like this on my 2s 800mah batteries with a 10 amp esc and 6x4 or so prop will be pretty good. Am I missing anything? This is really the first time I've had to make this kind of choice.
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Old Feb 12, 2012, 08:53 PM
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United States, KY, Hopkinsville
Joined Feb 2008
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It looks like you are there with Web-O-Calc. That E-Flight motor looks like a really good match. Good luck with the build. That is a nice looking plane.

Freddy
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Old Feb 13, 2012, 09:48 AM
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Thank you, Freddy. I hadn't used it before, and I got several odd results before figuring it out, so I wanted to make sure I really had figured it out.

I've pretty much completed the main portion of the fuse. I just have to add the hatch.

Family things will keep me from doing a lot of work on this over the next few weeks. Once I'm done with the hatch I'll probably work on the tail feathers.

Dennis
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Old Feb 20, 2012, 03:06 AM
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Good progress made. I've completed the fuse and hatch, filled, and sanded them. Some notes and issues:

I didn't notice that the curved deck was too tall for the formers when I glued the rear deck. Clearly the deck was designed to be too tall so you can trim it to exact size, but I didn't notice, and by the time I did, it was too late. Because of that, when I made the hatch, I had to build it so that the rear deck was also a little high, leaving a gap above the former.

Aside from that, When I worked on the hatch, I had a hard time getting it to fit well. The formers made the hatch too short - there was a pretty wide gap between the front of the hatch and the front deck. I solved this by adding in a 1/16th former.

Also, I cracked the bottom wood just behind the landing gear cross member. I tried re-gluing it but it came out rippled. I'm going to cut out the section that's rippled and replace it.

There are definitely some oddities besides the deck size in the directions that I'm reporting back to Retro-RC. Just little niggling things, like the same directions in two steps, and some other areas that are not super clear. One thing I do need to check on with them is regarding the wing joiner tube that goes through the fuselage. It is a hair wider than the fuse and protrudes about 1/16th on each side. I don't know whether that's right or not. If not, I'm going to have some careful grinding to do, as that tube is epoxied in place.

The filler spots are all due to my errors, and I'm picky in terms of having a flat surface before covering. Most are for minor scratches or divots, except near the front deck, where I just didn't build cleanly in one spot.

All in all an easy build, way easier than most old-style building. I've done the stabilizers and am working on wings, those will be in a later post.
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Old Feb 21, 2012, 01:59 PM
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Some more pictures. I've fixed the bottom, and the wings and ailerons are built. I did determine the tube was too long, as were the tubes in the wings. If left as is, the root ribs would have been about 3/8" off the fuselage. I cut the ones on the fuse off.

Electronics and motor arrive today. I am expecting that if I don't finish this week, I will come close.I will post additional pictures later.
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Old Feb 22, 2012, 11:26 AM
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One more picture - all of the items complete (the other wheel was still being clamped but is done).
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Old Feb 27, 2012, 11:40 AM
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The good, the bad, and the ugly...

The good:

I'm mostly done. Covering is complete, I just have some details to add like the undercarriage wheels, windscreen, and pilot. Covering went pretty fast overall.

The wheels are just on temporarily in the picture. I'll be putting them on for real tonight. I still have to organize the radio compartment and come up with a battery mount. What seemed like a huge compartment to me got small really quickly.

I used Dubro EZ mini connectors for the connections. The manual recommended just getting close with a fixed length rod, z- bent at servo, and 90-degrees at the horns, taking out the difference with trim. I wasn't thrilled by that method, and found the EZ connectors to be a good solution.

The bad:
I punctured the covering in two small spots by rubbing it unintentionally on a straight edge. I also broke the rudder at the control arm while working on the rods. The rudder was an easy repair, I haven't tried to repair the two small holes yet.

The ugly:
Installing the motor was a real PIA. If I were to do it again I would install the mount before the deck was installed. I ended up making some gaping holes (repaired under the covering) during the installation. Heaven forbid I have to take it out and replace it.

The aileron linkage was really fiddly and I couldn't achieve the recommended differential (3/8" up, 1/4" down). I ended up with 3/8" up and 1/8" down. I had to build it in mechanically, since it's a single servo setup. I did this by rotating the arms 45 degrees, not sure that's the best solution. The same required elevator differential was easy with just one servo, as I could move the arm about 30 degrees, which is what is needed. If I could find a double arm with 30 degrees off the straight axis, it would be great.

I'm debating leaving it like it is or moving to a straight no differential setup. I imagine I'd end up with some adverse yaw on that though.

I still need to do some slight bending to improve hatch clearance for the aileron rods.

Balance looks to be tail heavy, even with the battery fully forward. I'm working on the compartment organization still, but would hate to have to add nose weight. As the manual says, it's fairly short coupled and I'd hate to try to fly it tail heavy.
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Old Feb 27, 2012, 01:09 PM
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very cool plane and nice covering job.

well done sir!
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Old Feb 29, 2012, 12:10 AM
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Thank you! I'm complete now except for three items: the pilot, which I haven't painted, some form of battery hold down, and I also want to balance the props, but don't have a balancer yet. I have both a pair of APC 6x4 sport and Master Airscrew 6x4 electric props. Besides that, it's time to wait for the rain to stop in the lovely northwest.

On Retro's site, the expected AUW is 10 ounces. With prop and battery I hit 8.22 ounces. Much better than I'm expected; I may be a bit on the high power side. I was concerned it wouldn't balance before adding the wheels, prop, and battery, but they seem to have brought it pretty close to right on, using my high-precision fingertip balancers.

I forgot to take a picture of the whole plane - I'll do that when the pilot's ready. I have two young camera operators ready to film the maiden when it happens.

The one change I'd make on electronics would have been to get an end pin receiver. The 6115 was tight going in the compartment, and I'd have to pull it completely to change out any wiring. What seemed like a cavernous compartment wasn't quite as big when I actually put things in it.

I'm going to have to build itemized list of things I'd do differently and things that could be improved on the kit/equipment, I did email Mark at Retro with some stuff but haven't heard back. I'm sure I'll let him know more. It's been a fun build and is a nice plane (to be verified in flight, of course).

Dennis
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Old Feb 29, 2012, 03:04 PM
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Nice JOB! So this is the smaller version? It looks like the same size as mine.
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Old Feb 29, 2012, 05:05 PM
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It is the smaller one. When I look at your pictures, you can really see the difference between the fuselage sizes where the servos mount. The bigger one also has individual aileron servos in the wings. I keep thinking that would be the better way, and that they would have fit even on the small model. I see a few other minor differences - the hatch shape, the wheels, etc. Still, it's amazing how without reference they're hard to tell apart.
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Old Jun 10, 2012, 07:11 PM
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I finally(!) was able to have a decent maiden. It's been a challenge because I've been waiting for an opportunity where both the weather was nice and both kids and the wife could come along, since they bought me the kit.

I had tried once before but bit it on takeoff, cracking the elevator (small repair). I determined after that flight that the elevator was a little twisted, with the right half higher than the left, and that there was too much play in the ailerons due to my tape hinges not being done well. I replaced those hinges with ca hinges and used my iron to correct the elevator after the repair.

It flew well on about half throttle for about a minute. I was circling my flying site. On my last left turn, I lost sight of orientation and put it into a spin. it was a very soft, slow spin. No damage at all, I cut throttle and it landed softly in some nice soft tall grass.

On a previous turn, I had stalled it also, but had orientation and easily recovered. Both times were turning into the downwind leg, so it's clear I wasn't maintaining enough airspeed turning downwind.

Unfortunately that was it. I was flying on some private property that I use as my regular flying site, and while I was retrieving the plane, a security guard came up and told my wife we'd have to leave. Bummer - now I have to go somewhere else, but I guess it is time I joined a club.

My daughter tried to film, but she couldn't track it for most of the flight, and what she did track was blurry. Also her camera did something odd where the video is almost slow motion at the end and out of sync with the sound.

Can't wait to fly it again - as soon as I choose a club. Luckily weather is better and I won't have to wait for the family in future.

Dennis
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Old Sep 27, 2012, 02:18 PM
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Lessons Learned?

Dennis,
In an earlier post you mentioned a list of changes you would make next time and other advice for Mark at Retro RC. Did you ever complete that list? I am thinking about getting the Babe' Moth and have found your build log very interesting. You ended up wit a nice looking model. Was the E-Flite 250 a good motor choice?
How were the future flights?
Thanks,
Keith
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