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twin cyl. air make up

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twin cyl. air make up

Old 02-10-2016, 07:32 PM
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Stick 40
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Default twin cyl. air make up

I am putting a OS 1.60 flat twin in a plane, there is no muffler so no muffler pressure.

I am not sure what to do with the air make up for the fuel tank. if I run a fuel line down and have it exit at the bottom of the plane.

I wondered if fuel would run out when the plane goes inverted, or does the fuel draw keep fuel from that?

I could put a check valve on the end of the line.
Old 02-11-2016, 02:59 AM
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TomCrump
 
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I don't worry about it, but I don't fly inverted for extended periods.

How will the exhaust exit your cowl ? It may be possible to add an extension to the exhaust pipe. You could add a pressure fitting to that extension. I did that, once, and it worked wel.
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Old 02-11-2016, 06:41 AM
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RBACONS
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Like Tom, I use K&S brass tubing (11/32" I believe) to make exhaust extensions. Its a good tight slip-fit on the OS exhaust stubs. I also make a pressure tap using 3/32" K&S brass tubing. The OS 1.60 twin runs better with the pressure tap. Cut a 45 deg angle on one end of the 3/32" tubing, drill a tight hole in the exhaust extension, and insert the 1/16" tubing half way in with the long end facing down. Secure with regular JB Weld. Holds just fine. I also solder a slice of the next size larger tubing to the tap to serve as a fuel barb.

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Old 02-11-2016, 08:55 AM
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Seems to me your engine will not run correctly without the back pressure of the muffler. Glow carbs are not pumped. Not sure you are going to get a good run without head pressure on the tank. If you were to install a perry pump you might be ok.
As far as your vent line run the line like we do with gassers, vent line up and loop on top of tank then back and out the bottom of the plane.
but with head pressure you can't have a vent

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Old 02-11-2016, 11:29 AM
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Originally Posted by jetmech05 View Post
Seems to me your engine will not run correctly without the back pressure of the muffler. Glow carbs are not pumped. Not sure you are going to get a good run without head pressure on the tank. If you were to install a perry pump you might be ok.
As far as your vent line run the line like we do with gassers, vent line up and loop on top of tank then back and out the bottom of the plane.
but with head pressure you can't have a vent

The 1.60 is an older design. The carb draws well without pressure, if desired.
Old 02-11-2016, 06:45 PM
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yes this is a "older" OS. I have had it for 25 years and got it "new in the box" but it was bought at a swap shop.

I have broke it in on the bench, run about 25 min. as the book says and it ran great.

I will have to put exhaust extensions on the pipe's . I had thought about putting taps on the extensions but not sure about doing it.

glad Tom came in about being a older engine, but still not sure.

I am putting a glow driver in and having it come on about 1/4 thr.
sticks
Old 02-13-2016, 06:42 AM
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No glow engine requires muffler pressure if the tank setup is correct. If the center of the tank is in line with the center of the carb the engine will draw fuel from any attitude. This holds true for all glow engines.
Old 02-13-2016, 04:53 PM
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DGrant
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Four stroke engines in general run fine with no tank pressure(provided the tank is set up correctly).... as well run fine with no muffler, just a straight pipe works.

If there's any issues with fuel leaking from the overflow/vent, just put a loop(no kinks of course).. in the line. Its pretty easy to just secure a loop onto somewhere/firewall/etc... That's what we've done many times with gas engines(that don't use or need tank pressure)... and it works. I've got a few aerobats that get the fuel sloshed and tossed in every flight, but with the vent line rigged with a loop, it nary spills a drop(that means it doesn't leak).
Old 02-14-2016, 04:17 PM
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Stick 40
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great, just a loop in the vent line. if it leaked a little , I would not mind.

I don't plan a lot of aerobat's, just a toll, loop, etc.

thanks for all the help.

sticks
Old 02-15-2016, 06:03 AM
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Stick 40
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I have been thinking about that loop.
There are gaps between the metal fire wall mount and the engine, I am planning to have the fuel and air makeup coming out thru those slots,

I can loop the air make up around one corner and then run it down to the bottom.

when the plane is inverted the air make up tube will be pointed up and help reduce fuel from coming out, great.

sticks
Old 02-15-2016, 04:49 PM
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Bring the loop above the top of the tank, then out at the bottom below the fuse. When you turn it upside down it won't leak.
Old 02-15-2016, 08:35 PM
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Originally Posted by Stick 40 View Post
yes this is a "older" OS. I have had it for 25 years and got it "new in the box" but it was bought at a swap shop.

I have broke it in on the bench, run about 25 min. as the book says and it ran great.

I will have to put exhaust extensions on the pipe's . I had thought about putting taps on the extensions but not sure about doing it.

glad Tom came in about being a older engine, but still not sure.

I am putting a glow driver in and having it come on about 1/4 thr.
sticks
If you have a plumbing store in your town check with them, the store in my town had some 5-16" tubing that was flared already and is chrome plated, they come 1 foot long, The copper is very soft and bends very easy. After you get bent you can drill a hole in the tubing and solder in a pressure fitting

Bob
Old 02-18-2016, 09:16 AM
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Hi!
The OS 1.60 doesn't need pressure!
But it's very important that the tank is mounted right( according to the tank mounting rule) and that the tank vent line is pointed forward ,into the air, and not hanging down as it then draws fuel out from the tank.
Old 02-23-2016, 01:41 PM
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Originally Posted by jaka View Post
Hi!
The OS 1.60 doesn't need pressure!
But it's very important that the tank is mounted right( according to the tank mounting rule) and that the tank vent line is pointed forward ,into the air, and not hanging down as it then draws fuel out from the tank.
yes, it would draw fuel out, if it pointed straight down. we used that in the shop as a vacuum to draw metal chips away from drills while they drilled.
thanks for all the help.
my computer went down a couple of weeks ago. just got it back up.

sticks

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