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Looking for 912 fuel return line alternatives

 
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lgold(at)quantum-associat
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PostPosted: Fri Mar 09, 2007 9:42 pm    Post subject: Looking for 912 fuel return line alternatives Reply with quote

I forgot to add a fuel return lines from the 912 ULS carbs back to the fuel
tanks and am looking for alternatives. The fuel tanks have already been
enclosed in the wings of my high-wing Zenith 701 airplane project. It would
be very difficult, even ugly to add a fuel return back to a tank at this
point.

How important is it to install this return? Are there other good
alternatives, like returning fuel to a "T" going into a gascolator or just
letting fuel drip?

Thanks for your answer,
Rgds,
Les


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NYTerminat(at)aol.com
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PostPosted: Sat Mar 10, 2007 6:59 am    Post subject: Looking for 912 fuel return line alternatives Reply with quote

Les,

I think that you will find that most installations do not use a fuel return line. I don't have one in my 701 with a 912ULS.

Bob Spudis


In a message dated 3/10/2007 12:42:51 A.M. Eastern Standard Time, lgold(at)quantum-associates.com writes:
Quote:
I forgot to add a fuel return lines from the 912 ULS carbs back to the fuel
tanks and am looking for alternatives. The fuel tanks have already been
enclosed in the wings of my high-wing Zenith 701 airplane project. It would
be very difficult, even ugly to add a fuel return back to a tank at this
point.


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Roger Lee



Joined: 10 Jan 2006
Posts: 1461
Location: Tucson, Az.

PostPosted: Sat Mar 10, 2007 7:16 am    Post subject: Re: Looking for 912 fuel return line alternatives Reply with quote

Hi Les,

Bob is right. Most 912uls installations don't have return lines. If you have certain types of avionics that specify one then you would need it. My last plane did not have one.


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lgold(at)quantum-associat
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PostPosted: Sat Mar 10, 2007 9:28 pm    Post subject: Looking for 912 fuel return line alternatives Reply with quote

Roger and Bob,
Your consensus is that no return is needed. So do we just let the return
line leak down through the cowling?
Rgds,
Les

[quote] --


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Roger Lee



Joined: 10 Jan 2006
Posts: 1461
Location: Tucson, Az.

PostPosted: Sun Mar 11, 2007 7:44 am    Post subject: Re: Looking for 912 fuel return line alternatives Reply with quote

Hi Les,

Just run the return/overflow line down and out away from the engine to the outside of the cowling. Don't put it down in the airstream, but up just inside the cowling so it can drip if need be to the outside and not on a hot engine or exhaust.


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PostPosted: Sun Mar 11, 2007 11:38 am    Post subject: Looking for 912 fuel return line alternatives Reply with quote

I think you are talking two different things here! The short tube off the side of the carb is what the carb senses the different altitudes to automatically change the fuel mixture. This should not be changed. If you are using the Rotax carb/heat box then they attach to the carb/heat box otherwise leave them alone. Along with the Rotax carb/heat box came the carb trays that mount below the carb to catch any overflow out of the tube and the trays have a 1/4" line that you can divert to just below your bottom cowl. Getting bak to the fuel return line, There was a setup that Rotax had to return excess fuel back to the tanks if you wanted to. I just had my fuel line out of the Rotax fuel pump split tint a T and go to the two carb inlets, That's It!
Did I make it more confusing? I hope not!!
Bob Spudis

In a message dated 3/11/2007 11:45:38 A.M. Eastern Daylight Time, ssadiver1(at)yahoo.com writes:
Quote:
--> RotaxEngines-List message posted by: "Roger Lee" <ssadiver1(at)yahoo.com>

Hi Les,

Just run the return/overflow line down and out away from the engine to the outside of the cowling. Don't put it down in the airstream, but up just inside the cowling so it can drip if need be to the outside and not on a hot engine or exhaust.

--------
Roger Lee
Tucson, Az.




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JetPilot



Joined: 10 Jan 2006
Posts: 1246

PostPosted: Tue Mar 27, 2007 1:33 pm    Post subject: Re: Looking for 912 fuel return line alternatives Reply with quote

Be careful not to change those carb pressure sensing lines, or outlets. There was a case where someone routed tubing from those down to the bottom of the plane to dump any overflow overboard... As luck would have it, it changed the pressure enough that the engine would quit ONLY IN FLIGHT when the airspeed created a very low pressure on those carb overflow tubes Shocked Talking to the pilot, it was a very very close call for the pilot and plane.

Mike


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PostPosted: Tue Mar 27, 2007 2:43 pm    Post subject: Looking for 912 fuel return line alternatives Reply with quote

I have 110 hours on my Rotax 912 UL and I have those carb pressure
sensing/overflow lines connected together with blue primer line and
routed to one side of the firewall and inserted in a vented bottle so I
can see if there is any overflow. I have no problem with rough running,
and I have never seen any overflow. All the same, if there ever is any
overflow, I don't want it to run down on the hot exhaust.

Unrelated to this, I also DO have a fuel return to the fuel tank. It is
very simple: I simply TEE'd into the fuel line half way between the two
carburettors and ran a line with a home made restrictor back to the fuel
tank. So it is not a true return line for each carb, but it bleeds out
any air or vapors very effectively, because the TEE is at the highest
point in the fuel system.

Jack

Skyranger N233GH

JetPilot wrote:
Quote:


Be careful not to change those carb pressure sensing lines, or outlets. There was a case where someone routed tubing from those down to the bottom of the plane to dump any overflow overboard... As luck would have it, it changed the pressure enough that the engine would quit ONLY IN FLIGHT when the airspeed created a very low pressure on those carb overflow tubes [Shocked] Talking to the pilot, it was a very very close call for the pilot and plane.

Mike

--------
&quot;NO FEAR&quot; - If you have no fear you did not go as fast as you could have !!!


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=103266#103266


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JetPilot



Joined: 10 Jan 2006
Posts: 1246

PostPosted: Wed Mar 28, 2007 5:30 pm    Post subject: Re: Looking for 912 fuel return line alternatives Reply with quote

Very intresting way to get rid of the air bubbles... I see them in my line, not a lot, dont know if I really need to get rid of them or not. The down side is, the more lines and connections, the more risk of a leak. Im not sure if it would be worth it or not.

With your carb overflow lines, you dont have enough pressure differental to cause yourself a problem, thats good ! That warning is more for those that might be wanting to do the same thing, its bitten people before. Mine wont go onto the exhaust, but it will go onto the hot engine Sad But my engine is not enclosed, so its not quite so bad. You can see a picture of it here


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