Engine and Fuel
The enormous cowl meant that I could fit virtually any power source and most of it would be hidden. Having already built a P51D in electric I really wanted some noise so opted for a glow motor. The one I chose is a Jen 91 but the engine dimensions are no more than a 61. Because of the scale exhaust stacks that are pre-fitted in the cowl a side on fit wasn't practical allowing the glow motor exhaust to be lowermost. It was decided that inverted would be the best option but in this caused a headache. An exhaust for a two stroke. Plus any exhaust exiting from the back of the motor would be very close to the firewall and the pipes facing downwards too. Here it must be said that thanks to Jen Engines they created me a custom Pitts style exhaust that sits real tight to the back of the glow motor with twin outlets pointing downwards from the dimensions and photos that I supplied them. Perfect! (See Photos)
The fitting of the engine and mounting was a little trying due to the template was supplied was for four stroke I would imagine and even then it was inaccurate. So, back to common sense, alignment with centre line of fuselage and the cowl drilled holes and located engine mount (the slotted hole type) using my own 4mm socket head screws and spike nuts to secure. THe slotted mounting enabled me to slide the engine into the best location and clearance for the spinner to cowl. (See Photos)
Cutting the grp cowl was relatively easy to accommodate the exhaust outlets and the cylinder head. To get the cowl to slide over the engine required removing the cylinder head and then marking roughly where it was from the outside using measurements and eyesight. Removing the cowl then using the cylinder head as a guide marked with a pencil the outlines. First using a small pilot drill and refitting the cowl I could see where the cylinder barrel centre was. Relaligning the pencil marks as necessary. Using a small drill along the pencil outlines and wiggling the holes into each other. Pushing out the scrap and filing the hole until the barrel was central. Refitting the head now allowed for final clean up. The exhaust I did mainly by measurement first and using the same method of drilling and filing created two slots that allowed the cowl to slide over the outlets and drop down into position. See Photos)
The tank supplied is 14oz and is a good fit through the bulkhead in the fuselage. All the fittings were supplied so I used these and they were pretty standard from any model shop. The battery is fitted under the tank. I wrapped a 2000maH Sanyo Eneloop 4.8v flat pack in foam and located under the tank. With lines connected and marked where they fit the tank was positioned and the fuel lines connected. I prefer a three line system, one for exhaust back-pressure, one to the carb and one to the fuel dot filler. The carb line has fuel filter in circuit.
With the Fuselage virtually complete I decided now was the time to fire up the glow motor. Dropping the fuselage into my frame support I fuelled up. Binded the receiver to the JR DSX9 and first set the retract servo to no travel for now. Checked and set dual rates, direction of travel. With this all as near as damn it for now, I then set the throttle travel. Here I found I had to use a nearer to centre of servo arm hole position for the control snake.
I had opted to start with a 14x6 prop though I could have gone a few down and possibly one up to 15x7. . With prop fitted I flicked the crank over a few times, finger over carb to draw fuel up. In the airframe cradle the fuselage sits upside down so the engine was now upright! The throttle was set a very small opening after priming up. Fuel needle at 2.5 turns out. Snapping on the glow plug I cautiously flicked the prop about three times and she fired up lovely. Not as noisy as I thought it might be with custom exhaust. I let it warm up a bit before opening the throttle to about one third throttle. Repeated this a few times and then shut down.
The one thing that did cross my mind, is priming up or starting from cold with an inverted engine at the field. Maybe two fingers stuck in the exhaust outlets!
At this time too I decided I must cutout the cowl to access the mixture control and low jet. With this done I made up a wire extension to fit into the mixture control so it appears through the cowl, albiet very close to the prop!