I have never run a piped engine. I've had one pipe for years that was never used. It was a .29-.40 pipe for I don't remember what engine. Maybe my old OS .28. Irrelevant.
I now have two OS .15 CV-A engines. These are the most fantastic engines I've ever had. Went to Tower a couple months ago to buy four more just because and found out they're out of production.
Anyway, I have a header and a tuned (not muffled) pipe for one of them. I don't plan to pipe the other but know I can get pipes and headers even if the engine is discontinued.
Yesterday I received three (3) NovoRossi Rex RFX-15TC engines from Planet Hobby (
http://www.planethobby.com/collectio...ducts/rfx-15tc).
I want to put all three engines on one plane so am willing to give up extreme performance in exchange for more reliability. If I build this plane I am strongly considering mixing the two wing mounted engines to the throttle from a separate channel. When it comes time to land I can cut the wing engines and come in on the fuselage mounted engine thus taking out the risk of an engine dying on approach. Don't know if it's a good idea or not but something I'm thinking about.
I plan on using 15% fuel even though I have some 30%. Again, I want reliability over speed. Allen at Planet Hobby assures me that the plugs that came with the engine will like the 15%.
All three of these engines are rear-exhaust. I have identical headers and muffled pipes for all three engines.
Now I may make a twin with two of them and use the third on something else. But I really want the three-engine plane so I might buy one more.
OK, on to questions.
The OS has a header that is a little over 5-1/2" from the center of the plug to the end. Seems WAY too long as a starting point.
Question 1) Is there a safe header starting length so I can pre-cut off a chunk or do I start tuning with it as is?
Question 2) Are head shims always a necessity with pipes or is it a "maybe I need them and maybe I don't" situation?
Question 3) How do I even know if I need to add shims? What are the symptoms I will see?
Question 4) I didn't get any silicone coupler tubing. I looked around Tower and they gave some I.D. dimensions but what is the rule for choosing the tube size? I assume if it's too small it will seal but have a short life.
Question 5) If I build the triple engine beast then I will get the engines as close to the wing root as possible. I'm assuming I will never use a prop larger than 7" so will put the centerline of the engine 4" from the fuselage side giving me 1/2" clearance. Sound reasonable? The question is more about appropriate props than engine location. What size props should I be experimenting with? I can buy several sizes to try but at least want to be in range. I guess I could actually read the instructions that came with engine. They probably tell me.
Question 6) I've read about pipes since forever and recall that when tuning the engine you keep cutting a small amount off the header as long as the RPM increases with each cut. When the RPM goes down put the last cut in the tubing with the header. Is that still the way it's done or has that been updated?
Question 7) Do the pipe and header touch inside the silicone or is a small gap left?
Question 8) Is silicone coupler something I'll go through a lot of or does it last for a few seasons?
Question 9) How long should I break in the engine before trying to tune the pipe?
If I didn't ask something it means I probably didn't know to ask so don't hesitate to share your wisdom.
Thanks!