RC BLog: Pretorian 435: Nitroplanes Pitts Model 12 20cc Nearly Done!

Sunday, August 1, 2021

Nitroplanes Pitts Model 12 20cc Nearly Done!

I haven't posted for a few days, but I have been busy. An unexpected delay in the arrival of the fuel tank had to be worked around, it should arrive tomorrow. Here are some updates. Things went really well.

Combo shot of the aileron and its control horn, the servo hardpoint. The wing side had to be expanded to allow the servo to fit, hence the carve outs. There were a few weaknesses in the design that required this sort of fix. The standard servo barely fit on the cover/hardpoint.

The top wing.

The elevator halves are joined by a balsa "rod" between the halves. I wanted some more stiffness across the halves since the servo is attached to the port side (see below) and drives both elevator sides. I put a steel rod I bent into shape across the cross over, and this worked as designed.

This is the starboard side. Not shown is that I went on to double the control horn putting another one over the existing horn. When I drilled a larger hole for the larger control rod, the margins around the hole were much less than desired. This strengthened the control horn and the connection.

This is the port side with the servo. The elevator and rudder are the 25 kg torque version of the 20kg ones on the ailerons. I really like the quality of these servos. The control rod provided were way too long, so I used this Traxxas one I had laying around as it was perfect. It uses an M3 bolt, hence needing to drill out the control horn. Sturdy undies to be sure. Also here is the rudder pull-pull connection.

Installed the RCGF-USA 20cc Engine. I love this engine! Its like it was made for this airplane, fits perfect with no modification.

The throttle servo set up I had to rig. Works well. My notations on the rail mark the WOT, middle and stop throttle positions I used to set mid throttle on the servo. I had to make the opening smaller for the servo so it would secure correctly.

One of those design issues. The cowl bolt heads are inside the cowl, I don’t have a hex screw driver long enough. Also, the way the cowl is set on it has to come up from underneath a bit and gets pushed up into place, so this really is the only way. I need to figure something out.

Perfect center. You can see the cowl mount bolts inside the upper right and left sides. Putting s 2.5 inch aluminum 3 blade spinner over the Master Airscrew 15x7x3 prop, after breaking it in with a MA Scimitar 2 blade.

The rudder pull-pull system.

The underside of the lower wing, the center of which is where I laid down the fiberglass under the AMA sticker. Came out nicely. Painted the control rods flat black, the stock white was just wrong.

The big M4F sparky doesn't hold onto the RCExcel ignition spark plug wire (neither does the CM6 I tried). I set up the cowl cut-outs to allow part of the cowl to hold it in place.

The cowl cut-outs for the muffler pipes and the tip of the spark plug wire.

Painted the aft part flat black.

Internal electronics layout, the battery not in place. Spektrum AR637T receiver, Tech Aero UBEC that filters noise from the ignition nd is the ignition on-off switch, the flag-pun powerswitch, the rudder servo. Underneath is the voltage regulator taking the 7.4V battery packmdown to 6.6V.

The underside, above the wing. Wiring and the voltage regulator.

The Ignition LED and the flag-pin fail-on reciever power switch. Works perfectly! Wonder how long before I snap the pin off...

The backside of the flag-pin switch. I added some support to the fuselage balsa to support use of the switch. Battery pack. Imhad to search for some time before I found this flag-and-pin fail-on switch at RadicalRC, one designed to not to need a power regulator system, but to act as primary switch.

Very clean electronics bay. Missing the fuel tank still. It will be mounted to the port side forward of the receiver. One antenna horizontal, one vertical.