Best refueling method/connections
02-12-2015, 07:55 PM
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Best refueling method/connections
Gday guys,
This will be my first large engine, K180. Because of the high suction/pressure onr the refuel line with a large engine I'm thinking I'll use a different method from my usual on this one.
What is everyone using on theyre large engines for best results? ie no chance of bubble getting sucked thru the refuel line what so ever.
All suggestions welcome and appreciated.
Cheers FlyDoc 405
This will be my first large engine, K180. Because of the high suction/pressure onr the refuel line with a large engine I'm thinking I'll use a different method from my usual on this one.
What is everyone using on theyre large engines for best results? ie no chance of bubble getting sucked thru the refuel line what so ever.
All suggestions welcome and appreciated.
Cheers FlyDoc 405
02-13-2015, 05:00 AM
#3
Suction or pressure on the fill line is not the issue here, I can't see any reason for this to depend on engine size/pump throughput.
The two relevant issues to me are 1) how fast can you fill fuel, and this is dependent on engine size since larger engines have larger tank capacity and it takes more time to fill them .. and you don't want to wait "all day" and 2) an air leak in the fill line is a fatal flaw since it drains the UAT or other bubble trap before the fuel tanks and flames out the engine, probably just afer takeoff .. or if you are VERY lucky, on taxi out.
To address #1, I like to use the larger (3/16") Tygon and the large fuel tank fittings from Gary Mueller. The critical point in the fuel system are the vent lines between tanks in a multi-tank series-plumbed setup. When you are filling the tank, you fill the "first" tank, then its vent has fuel in it flowing to the next tank, and so on if more than two tanks. I have seen the pressure increase rapidly in the tanks closest to the fuel can because of flow resistance as liquid flows through the vent lines. In extreme cases it can fracture tanks. So defense #1 is to have large diameter lines, defense #2 is to have a short section of small (I use 4mm festo) line in the fueling hose to make sure that no matter how fast the pump is, the flow rate is limited. This approach gives reasonable fueling rates and minimizes the chance of stressing the fuel tanks. Of course this is mostly an issue for rigid fiberglass or kevlar tanks. I honestly don't think the large bore lines are a big deal for normal fuel flow to a running engine .. it's more about the fill (and perhaps the empty) from the fuel can.
To address #2, I like to use a jetcat valve AND a plug on the fill line .. think of it as belt and suspenders .. to make sure no leak in the fill line. Personally I like to use the Luer Lock fittings (from McMaster Carr) on the fill line, too many people report tygon "bits" in their fuel system from repeated insertion and removal of barbed fittings. This might be a paranoid approach, but this seems to me a rather critical element of the fuel system, as you note in your original post.
Dave
The two relevant issues to me are 1) how fast can you fill fuel, and this is dependent on engine size since larger engines have larger tank capacity and it takes more time to fill them .. and you don't want to wait "all day" and 2) an air leak in the fill line is a fatal flaw since it drains the UAT or other bubble trap before the fuel tanks and flames out the engine, probably just afer takeoff .. or if you are VERY lucky, on taxi out.
To address #1, I like to use the larger (3/16") Tygon and the large fuel tank fittings from Gary Mueller. The critical point in the fuel system are the vent lines between tanks in a multi-tank series-plumbed setup. When you are filling the tank, you fill the "first" tank, then its vent has fuel in it flowing to the next tank, and so on if more than two tanks. I have seen the pressure increase rapidly in the tanks closest to the fuel can because of flow resistance as liquid flows through the vent lines. In extreme cases it can fracture tanks. So defense #1 is to have large diameter lines, defense #2 is to have a short section of small (I use 4mm festo) line in the fueling hose to make sure that no matter how fast the pump is, the flow rate is limited. This approach gives reasonable fueling rates and minimizes the chance of stressing the fuel tanks. Of course this is mostly an issue for rigid fiberglass or kevlar tanks. I honestly don't think the large bore lines are a big deal for normal fuel flow to a running engine .. it's more about the fill (and perhaps the empty) from the fuel can.
To address #2, I like to use a jetcat valve AND a plug on the fill line .. think of it as belt and suspenders .. to make sure no leak in the fill line. Personally I like to use the Luer Lock fittings (from McMaster Carr) on the fill line, too many people report tygon "bits" in their fuel system from repeated insertion and removal of barbed fittings. This might be a paranoid approach, but this seems to me a rather critical element of the fuel system, as you note in your original post.
Dave
02-13-2015, 05:16 AM
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Thanks for the reply fellas.
Im thinking Ill use 4mm line off UAT to a festo ball valve, with a plug into a line coming outta that. Just mate said belt and braces approach. I'm all for that.
Btw the rest of the system is going to use 6mm line for max flow, less restriction.
Matt
Im thinking Ill use 4mm line off UAT to a festo ball valve, with a plug into a line coming outta that. Just mate said belt and braces approach. I'm all for that.
Btw the rest of the system is going to use 6mm line for max flow, less restriction.
Matt
02-13-2015, 06:40 AM
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If you use a UAT/CAT etc once you have fuelled you can see any air that has entered the fuel system as it should be in the UAT/CAT and visible if the air trap is transparent or translucent - to remove just pop the jets nose up so the fill connector on the UAT/CAT is in the air and reverse the fuelling pump for a second or two and the air is gone. On the CAT which I manufacture the fill barb was designed to be smaller than the main tank feed and the output to the pump to stop over filling pressure etc, it's also positioned at the top of the tank so air trapped in the CAT can be purged very simply and quickly.
The same technique will apply to most other bubble traps albeit slightly different procedures to draw the air out.
Do keep it simple, one way valves are great but have many tiny components inside along with seals which can and do over time fail and break, a piece of pipe and a stopper are really all thats needed IMO, nothing more frustrating that getting to a flying site and not being able to fuel up!
All the best with your project and the first 'big block' turbine.
marcs
The same technique will apply to most other bubble traps albeit slightly different procedures to draw the air out.
Do keep it simple, one way valves are great but have many tiny components inside along with seals which can and do over time fail and break, a piece of pipe and a stopper are really all thats needed IMO, nothing more frustrating that getting to a flying site and not being able to fuel up!
All the best with your project and the first 'big block' turbine.
marcs
02-13-2015, 09:37 AM
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My friend makes a nice plug of aluminium with knurled edges. About 1/2" diameter so my clumsy hands can grab it easily. Is a nice fit. Kiss is always best. Good advice above about fueling pressure with multiple tanks.
02-13-2015, 03:27 PM
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Thanks fellas, I like kiss principle.
Marc, I'm using Intairco Uat, it has the smaller fitting on the fill line. I don't run to much pressure any how on fueling. I've done a few multi tank set ups.
Was just concerned about sucking air from the fill line, and possibly empting the uat or introducing air to the pump then engine.
Ive always used a simple set up b4 with good results, upto the K140, which was in my F15 5 tank set up.
I think I will run a tap from uat then a simple bung into the fuel tubing. Simple and redundant. Is that an oxymoron?????
Cheers
Matt
Marc, I'm using Intairco Uat, it has the smaller fitting on the fill line. I don't run to much pressure any how on fueling. I've done a few multi tank set ups.
Was just concerned about sucking air from the fill line, and possibly empting the uat or introducing air to the pump then engine.
Ive always used a simple set up b4 with good results, upto the K140, which was in my F15 5 tank set up.
I think I will run a tap from uat then a simple bung into the fuel tubing. Simple and redundant. Is that an oxymoron?????
Cheers
Matt
