I have just found that I will have to have a new exhaust system made for the HKS engine that is going in my Kolb, because of a physical interference problem between the exhaust I got with the engine, and the airframe.
The stock exhaust system has steel or stainless steel exhaust pipes from the exhaust port on the cylinder to a steel muffler can. There are "swivel joints" just downstream form the exhaust ports, held together with springs. The space taken up by these swivel joint and spring components (as opposed to a simple solid bent pipe) is the reason that the exhaust interferes with the airframe.
The stock muffler location relative to the engine also is not ideal for this airframe. Muffler's near the pilot's head, and the steel muffler is very heavy.
So, faced with a clean sheet of paper (because I have to make the new exhaust miss the trailing edge of the wing), I would like to move the muffler to another location on the airframe, and have a lighter aluminum muffler instead of a heavy steel one.
Engine: HKS 700E, 58-60HP nominal, approx 700 CC, non-turbocharged, 10-1 compression, rated at 5800 RPM max. Will run on premium auto fuel and/or 100LL avgas (both approved by HKS).
Airframe: Kolb Firestar 2 lightweight "low and slow" LSA. Engine NOT fully cowled or "inside"... typical ultralight top of wing trailing edge location. See similar installation photo below.
I have virtually no experience with this stuff, so I have to ask all of you way-big smart folk for a few answers:
1) I have heard there are light weight aluminum mufflers for all sorts of engines. Do they work well, and how much weight do they save? Is there one alloy that works better than others... lasts longer, etc.?
2) How large or heavy of an aluminum muffler would I need for a "pretty darn quiet" result with this type of engine? I want it quiet, I'll be flying over hostile neighbors here in Los Angeles (all 10 million of them).
3) I would like to move the muffler further away from the engine for more than one reason. The stock exhaust system does not appear to be "tuned", there is no "2 into 1" joint anywhere other than where the pipes enter the muffler can, but this is on opposite sides of the can, not joined pipes. With these assumptions, can anyone estimate how much power/torque will I lose by making the pipes between the engine and muffler two or three feet longer than they are now? I'm hoping to move the muffler under the tailboom... if I can keep the pipes from screwing up the inflow to the propeller.
4) I have another potential concept, putting the muffler vertically just behind the fuselage cage (in front of the lower prop blade in the photo below). This could allow me to make the muffler into a triangular cross section, and use it as a fairing for the back of the cage. This would allow the muffler to have a larger internal volume. Is there a huge benefit to this extra effort from a nose or power loss standpoint?
OK engine guys, let me have it with both barrels and all the brain cells you got
The stock exhaust system has steel or stainless steel exhaust pipes from the exhaust port on the cylinder to a steel muffler can. There are "swivel joints" just downstream form the exhaust ports, held together with springs. The space taken up by these swivel joint and spring components (as opposed to a simple solid bent pipe) is the reason that the exhaust interferes with the airframe.
The stock muffler location relative to the engine also is not ideal for this airframe. Muffler's near the pilot's head, and the steel muffler is very heavy.
So, faced with a clean sheet of paper (because I have to make the new exhaust miss the trailing edge of the wing), I would like to move the muffler to another location on the airframe, and have a lighter aluminum muffler instead of a heavy steel one.
Engine: HKS 700E, 58-60HP nominal, approx 700 CC, non-turbocharged, 10-1 compression, rated at 5800 RPM max. Will run on premium auto fuel and/or 100LL avgas (both approved by HKS).
Airframe: Kolb Firestar 2 lightweight "low and slow" LSA. Engine NOT fully cowled or "inside"... typical ultralight top of wing trailing edge location. See similar installation photo below.
I have virtually no experience with this stuff, so I have to ask all of you way-big smart folk for a few answers:
1) I have heard there are light weight aluminum mufflers for all sorts of engines. Do they work well, and how much weight do they save? Is there one alloy that works better than others... lasts longer, etc.?
2) How large or heavy of an aluminum muffler would I need for a "pretty darn quiet" result with this type of engine? I want it quiet, I'll be flying over hostile neighbors here in Los Angeles (all 10 million of them).
3) I would like to move the muffler further away from the engine for more than one reason. The stock exhaust system does not appear to be "tuned", there is no "2 into 1" joint anywhere other than where the pipes enter the muffler can, but this is on opposite sides of the can, not joined pipes. With these assumptions, can anyone estimate how much power/torque will I lose by making the pipes between the engine and muffler two or three feet longer than they are now? I'm hoping to move the muffler under the tailboom... if I can keep the pipes from screwing up the inflow to the propeller.
4) I have another potential concept, putting the muffler vertically just behind the fuselage cage (in front of the lower prop blade in the photo below). This could allow me to make the muffler into a triangular cross section, and use it as a fairing for the back of the cage. This would allow the muffler to have a larger internal volume. Is there a huge benefit to this extra effort from a nose or power loss standpoint?
OK engine guys, let me have it with both barrels and all the brain cells you got
