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HomeAircraftHelicopterBeginners Corner › Exhaust pressure nipple placement.
10-22-2013 07:24 PM  4 years agoPost 1
nrad2000

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USA

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The original exhaust nipple was located on the top of the Century tri flow muffler. The nipple stripped loose. I noticed another tapped threads on the bottom side that is plugged by a screw. So, I switched the screw and nipple locations. Now the nipple is on the bottom. The last few flights I noticed after 1 min of flight the engine rpm slowly ramps up and the pitch of the engine increases. Showing severe signs of leaning out. Could this be the cause of the nipple being on the underside of the muffler? After landing I notice oil filling up inside the fuel tubing that is under the muffler. Could this oil be blocking the pressure return? I'm running an OS 50 hyper w/ century tri flow muffler in a century hawk pro helicopter. 15% cool power heli fuel. No inverted flying. Just plain hovering.

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10-22-2013 07:26 PM  4 years agoPost 2
JKos

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Redondo Beach, CA

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After landing I notice oil filling up inside the fuel tubing that is under the muffler. Could this oil be blocking the pressure return?
Yes.

- John

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10-22-2013 07:30 PM  4 years agoPost 3
fastrc1

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Planet Brooklyn, NY-USA

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Nope you're seeing oil in the line because its pooling above the nipple and draining. The reason for two holes in the muffler are right hand exhaust n left hand exhaust. The pressure doesn't change unless the stripped hole is not properly plugged and or there is a leak somewhere else. Try a fresh plug. The oil in that line will blow back into the tank and you may see it traving through the line as well

RIP Roman Pirozek Jr.
Team Futaba USA
Team Kontronik USA
http://flysrw.com

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10-22-2013 07:43 PM  4 years agoPost 4
Ladymagic

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South Korea

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Yes,the two nipple locations are pre drilled options for you to use at your discretion base on your pipe's orientation relative to your heli. You should only be using the top position.

If you are using the lower nipple in that position, you are basically gravity feeding spent fuel and oil back into your clean fuel. This spent fuel would normally be forced out of the pipe, but instead, some of it is being pushed back through your pressure line as it collects at the bottom of your pipe. Since it's so thick, it's clogging at the lowest point in your line, making your engine work harder to draw fuel from low or no back pressure, whilst also messing with your mixture settings.

Recommend that you retap the top nipple port or size up the nipple and relocate your pressure line back up top before you burn up your piston from prolonged lean runs. No too difficult Good luck and fly safe.

Mellisa

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10-22-2013 07:45 PM  4 years agoPost 5
JKos

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Redondo Beach, CA

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The pressure doesn't change
I thought about this before answering. I believe the viscous nature of the oil inside the narrow passage (the tube) will reduce the effective pressure reaching the tank. Try blowing the oil through the tube. Look up flow resistance and head loss.

- John

RR rules!

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10-22-2013 07:54 PM  4 years agoPost 6
fastrc1

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Planet Brooklyn, NY-USA

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I thought about it too but realize that unless you have an extremely long return line; by the time u get to hovering speed the line is blown through. That oil is the end product of the burn ie lube I run an occasional engine with the lower nipple line and I personally don't see the effect you guys are speaking of but obviously this chap is having an issue. IDK.

RIP Roman Pirozek Jr.
Team Futaba USA
Team Kontronik USA
http://flysrw.com

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10-22-2013 07:56 PM  4 years agoPost 7
fastrc1

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Planet Brooklyn, NY-USA

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Btw the YS system, although pressurized blows oil through the check valve as well and it's located on the backplate. Hmmmm

RIP Roman Pirozek Jr.
Team Futaba USA
Team Kontronik USA
http://flysrw.com

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10-22-2013 10:15 PM  4 years agoPost 8
Ladymagic

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South Korea

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YS systems pressurize the tank through the crank case which is why you need a check valve to bleed off excess pressure and prevent junk from entering the fuel system. Spent oil and fuel is bled through the crank case and exhaust port.

Mellisa

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10-23-2013 12:07 AM  4 years agoPost 9
doorman

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Sherwood, Arkansas

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Problem Before????
If you did not have the problem before you moved it to the bottom, then guess what!!! Put it back on top??
I would pull the muffler and the bolt/screw you put in the top.. clean everything with alcohol... then mix up some jb weld and let it cure completly...then drill and tap and put your pressure tap back in and put some gasket seal on the plug and put that back in the bottom..go fly and have fun!!!
Good Luck,
Stan

AMA 2918-Team Spin Blades,,Castle Creations, Unique Aircraft

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10-24-2013 07:05 AM  4 years agoPost 10
nrad2000

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USA

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I j-b welded the top, tapped, and re-inserted the nipple back on top. Now the engine runs fine. Crazy.

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10-24-2013 01:49 PM  4 years agoPost 11
Ace Dude

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USA

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Using crank pressure the YS system generates about 6PSI. Muffler pressure only generates about 1PSI.

  

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