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Laser tank breather

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Glenn Stevenson04/04/2019 19:39:49
38 forum posts
3 photos

Hi, I have installed a Laser 80 in my seagull i-sport and am trying to work out the tank breather, I gather it should just be a tube straight out the front somewhere but wouldnt that let the fuel run out when inverted?

Thanks

Glenn

Jon - Laser Engines04/04/2019 20:29:37
4899 forum posts
188 photos

The two easiest options are:

Glue a small wooden block into the front of the cowling then drill through it with a 3mm drill. Stuff a small section of brass tube up the middle, more glue, job done. It should poke out a few mm and point directly forward.

The alternative is to take one of those bent brass tubes from a dead fuel tank and clamp it to the firewall with an undercarriage saddle clamp. This can then drop down just below the cowling and again be pointed into the airflow.

This photo (sorry its sideways) shows option one employed on my acrowot xl

breather 1.jpg

and this shows option two on my hurricane. where the silver cowl joins the white you can just see it.

breather.jpg

Hope this helps

Edited By Jon - Laser Engines on 04/04/2019 20:30:08

Don Fry04/04/2019 20:51:26
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4150 forum posts
48 photos
Posted by Glenn Stevenson on 04/04/2019 19:39:49:

Hi, I have installed a Laser 80 in my seagull i-sport and am trying to work out the tank breather, I gather it should just be a tube straight out the front somewhere but wouldnt that let the fuel run out when inverted?

Thanks

Glenn

To , pedantically, answer, Jon has explained what is good in reality. If you were to fly inverted you will loose some fuel, not much, as there is some pressure on the tank to reduce loss. See his explanation. But you would have to love inverted flight for you to notice in terms of fuel consumption per flight.

Martin McIntosh04/04/2019 20:51:49
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2976 forum posts
1090 photos

Mine is like that too. With fuel being drawn from the tank by the motor it cannot spill out, also the carb. needle aperture is so small that even with the motor stopped it is unlikely to happen, and if it did then the motor would be starved of fuel and stop.

spitfire 72 041.jpg

The bung is only there for transport.

bert baker04/04/2019 21:19:52
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1491 forum posts
305 photos

4f6b7c60-eb6b-4cad-9c96-59e7ecaeaa98.jpeg

bert baker04/04/2019 21:21:30
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1491 forum posts
305 photos

The pipes on my old pup form a u bend, so if inverted it can’t escape

Frank Skilbeck04/04/2019 21:33:50
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4519 forum posts
101 photos

As the engine is always drawing fuel, then that empty space in the tank has to be replaced, which is the point of the breather, so unless you have a really long breather which is full or fuel it's not going to have enough force (Height of fuel and s.g.) to pull against a partial vacuum and reverse flow (also the engine would stop first). If the engine stopped when the plane is inverted then air would come back through the needle and yes it would drain then, but I don't think that would be too big a concern wink

Also pointing the vent at the propeller (tractor installation) means that the vent is acting like a pitot tube and is partially pressurised

Glenn Stevenson04/04/2019 22:27:19
38 forum posts
3 photos

Thanks everybody for clarification.

Looking forward to trying this engine.

Glenn

Jon - Laser Engines05/04/2019 08:17:03
4899 forum posts
188 photos

no problem Glenn

Its a question i often get asked, i suspect due to people being used to pressurised systems. I have also noticed that sometimes there is tendency to over think it and make it too complex. When it doubt, just keep it simple

Also, Berts example will work fine but as the breather is also the tank overflow when filling you do risk spraying fuel all over the inside of the cowl when the tank is full. Thats why i recommend having the pipe outside the cowl. Just make sure you know where its pointing or you may end up with fuel soaked trousers....ask me how i know

Ron Gray05/04/2019 09:00:01
1553 forum posts
367 photos

Connect a bit of fuel tube to the vent pipe and have that in a small fuel bottle to catch any overflow, keeps the site clean!

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