Nitroplanes Pitts Model 12 20cc Build

Surfing Facebook the other day, I ran across an offer I could not refuse, and picked up a 15cc sized Nitroplanes Pitts Model 12, in the color scheme option I preferred (don't like that blue one). I decided to binge a bit, and have made a few parts purchases, making me pace myself as they come in. What I love about this plane is that its a bit bigger at 15cc sized aerobat, its a bipe, it has an ultimate wing, and a round cowl. Love this look! This model came with no manual, which from what I found online is fine as the manual was ripe with mistakes and misguidance. Its kinda fun doing this build using just my own experience and knowledge, dare I say, skills.

One version of the real plane.

This is the model's Python scheme. I am not planning on ordering the Python graphics since I don't really care if its scale, I just want to fly it. I will personalize it though! I am hoping Joe Nelson sends me some RSCF-USA Skull Logo stickers.

I started by fuel-proofing the anterior fuse. I did most of the interior, all sides, not just for the fuel proofing, but also to add some tensile strength. I use 15 min epoxy diluted out with alcohol and brush it on thinly.

After several careful dry fits and increasing the gap of the hinge slots, I epoxied in nylon Du-Bro hinges. I prefer the strength on gassers, although the provided CA hinges would work. I have never had a nylon hinge loosen, but several CA hinges, so I tend to avoid them.

Since the horizontal stabilizer could be installed either side up, I opted with the star side up. Not sure what the real Python has displayed. Here the horizontal stab and rudder are installed, all with the nylon Du-Bro hinges. I used the larger ones on the rudder since it also takes some of the forces from the tail wheel.

Installed the tail wheel. It is the standard design with the gear "tiller" end attached into a hole I drilled into the rudder providing yaw force to the tail wheel, and added epoxy support along the attachment to the rudder. There is CA in that hole securing the "tiller", and epoxy around the exposed part contacting the front of the rudder. I open the cote under that metal support, CA, then double screw: screw in the retaining screw, unscrew it and apply CA then re-insert it. That thing is secure.

Here are some of the coming parts.

ZYHobby 500ml gas tank.

Master Airscrew 15x7x3 prop. I happen to have one on hand. Painting the tips yellow with a black middle stripe. Love these props. Durable with great performance. I have a 14x7 Master Airscrew Scimitar coming that I will use to break in the engine. I also have a 2.75in aluminum 3 blade spinner coming from ZYHobby on eBay coming.

RCGF-USA 20cc RE engine.  I am a total RCGF-USA Fanboy. This plane is described as "70 class", inferring a 0.7 cu in or roughly between 10 and 15cc sized plane (0.6 cu in is 10cc). I like a little power, and another builder put a 20cc engine in the plane with excellent results. I am trying to get away from engines less than 15cc since their carbs are a pain to manage, so, bought a new engine from Joe Nelson at RCGF-USA. Always the best personal support on the best and most affordable engines that run reliably and awesomely. Really excited about this engine!

I have on hand:

Tech Aero Designs UBEC.  (Manual here). This takes power through the receiver and acts as a remote ignition cut-out switch. It also protects the receiver from any hardwire ignition noise. I don't use a mechanical ignition switch (see below).

Step down voltage regulator.  I will be using the 2S (7.4V) 5300 mA battery from the Ultra Stick in this plane. The servos are not high voltage, so it will need a step down to 6.6V. 

DS3218 Digital RC Servo Motor 20KG High Torque Full Metal Gear. This plane has 4 aileron surfaces, each driven by its own servo, which is a bit overkill, but good for a high powered aerobat. Using a 20kg high torque servo just adds more power to these surfaces. Each side will require a Y-harness to the receiver. This was a 4 pack, convenient. I have had very good results with generic servos.

Since I had to order 2 more servos (I have a throttle servo), I bought this 2 pack of high torque servos, one for the rudder (a pull-pull setup), and one for the elevator.

Spektrum AR637T Receiver.  I had bought this with other plans for it, and have had it on hand for over a year, NIB. I decided its a good fit for this plane. I will be programming the AS3X, but won't be using SAFE. The ailerons will be Y-harnessed to AIL and AUX1, each of the other servos will of course have their own channel. GEAR will be used for the Tech Aero Ignition UBEC/Cut out.

The remaining decision it the receiver power switch. I have had mechanical switches fail, never in flight, just not working one day, on a couple of occasions. I don't feel the need for redundant systems, though I appreciate their application in larger planes. What I wanted was a simple flag-and-pin style fail-on switch. I found one that was $60 (see below, from Australia), that was a simple stand alone switch, not one like DUALSKY or Smart-Fly redundancy bus systems. Why no one else makes a simple affordable switch capable of handling the battery pack voltage and amps is beyond me, I think there is a good market for one.  

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My idea had been to take one of these (Left is DUALSKY, right is Smart-Fly) as an inline on-off switch, placing it on the negative side of the battery lead. They are not designed for that, instead are designed for microamp signals to a power control system. A couple of experienced folks (Thanks Cody Wojcik and Jerry Leach) felt they probably would NOT handle the amps. The gauge of the wire isn't the issue, its the internals of the switch itself that are of concern. Bummer. Someone needs to make one that is just simple but can carry the volts and amps of the battery pack. 

This one from Australia (the ONLY place I can find one) is expensive, and shipping almost doubles the cost. Its pretty much exactly what I need, though a simple switch and LED without the expensive switch plate is more my desire. I would build one myself, but I can't find the damn switch. I want one that I remove the pin, not place one, to power the circuit. I could easily make one that plugged in to power on, I want one to power on when I remove the pin. I welcome ideas!

The wing servos are arriving today from Amazon, so I will start on the wings. The top wing is one piece, 54" in wingspan. This creates a transport problem as it isn't going to fit in my car nor my wife's SUV attached to the fuse. The bottom wing is two piece joined in the middle. I will need to remove the wings to transport it. Since the top wing is one piece, and the bottom wings two parts are joined in the middle, I plan to permanently join the two bottom halves, epoxying the wing spar in place, and putting a thin fiberglass layer on the top and bottom of the wing at the wing joint. Since I have to use a large wing bag for the top wing, I might as well make the bottom wing one piece as well. Adds strength, and makes transport a tad easier. What this leaves is a LOT of tiny screw and nylock nuts that need to be put on and taken off with every transport. I will need to carry a bag of replacements, as those damn things will disappear like chocolates at a sorority house.

I haven't heard from Horizon Hobby about my iX12 transmitter, which is there for service.  Its there, and hopefully I will hear something this week. They have such great service and turn around is really quick.

More to follow!

UPDATE: I did find this flag-and-pin switch from RadicalRC for $11 plus reasonable shipping:

I don't understand RadicalRC "generally not recommending its use in high vibration environments" since its a "single contact" switch due to lack of redundancy. All switches are single contact. These ARE used with powersafe systems as the sole switch in high vibration aircraft (ie gassers), so I don't understand why they wouldn't. I'm going to give it a shot.