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<u>Engine Install</u></span></div>
At Nitroplanes support forum (
http://www.rcdiscuss.com/index.php?board=84.0 ) I asked about larger engines (Saito .72’s). I was told it would fly okay but it would be way over scale. Well, that’s what I want! I even went one step farther and installed Magnum .91 XL’s so it should have plenty of power. I bought a fish scale to measure thrust and am playing with different prop setups to get the most out of these engines. For now I’m using APC 14 x 6 props front and back. In reserve I have a Master Airscrew 3 blade pusher 13 x 8 that I might try on the rear engine. I like the look of the 2” conical spinners but try to find a 3 blade pusher prop spinner! More on that later.
I am breaking in these engines with Omega 10% nitro and am getting readings of a combined thrust of 15.5 lbs. on my fish scale. My goal is to get it up to around 18lbs.or more with 15% nitro so I can do vertical with ease! Plane dry weight is 14lbs. 11oz. Loaded with full tanks its around 16lbs. 12oz.
Nothing special about the front engine installation. Make room for plenty of air movement in the cowlings. I think I might have taken a little too much away from the front cowl.
The rear engine looked weird with a forward facing muffler so I made some modifications to the exhaust pipe and muffler. I mounted the muffler on the firewall. But before I did this I prepared the firewall with high heat insulation. I found it at an auto parts store where they call it Tan Exhaust Pipe Wrap. It is made by Design Engineering Inc. Web site:
http://www.deicycle.com. It’s like a tight mesh burlap fabric that can withstand temps up to 1500 degrees. I also wrapped the muffler and secured the fabric with wire provided in the package. A copper pipe clamp loosely holds the muffler to the firewall. The insulation should help absorb vibration.
I used 3/8” copper tubing to reroute the exhaust pipe. I bent it with one of those long spring pipe benders. The best way to bend pipe is to pack it with wet sand and use the spring bender. This will help prevent the pipe from collapsing at the tightest bends. 3/8” copper tubing just fits over the exhaust pipe from the engine (Magnum .91 FX) and an additional exhaust pipe going into the muffler. You might have to ream the ends of the copper pipe to make them fit your particular engine. I tried to cut the pipe with a rolling pipe cutter but this caused the pipe ends to collapse too much. A Dremmel or hack saw does a better job. Just make sure you file and clean everything before you bring it near the engine. The 2 junctions were wrapped with rubber exhaust pipe tubing that I purchased at a local hobby shop and are held down with 4 hose clamps - One on each side of the joints. This rubber tubing is also called Thermal Exhaust Sleeve. You can find it a high performance auto stores.
The only visible exhaust component at the rear cowl is the Du-Bro exhaust deflector. Nice clean look!