Card V Fuel Tank Location
10-04-2009, 05:57 AM
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Card V Fuel Tank Location
Hi all,
Relatively new to RC flying and would appreciate a reasonably practical explanation as to WHY it is recommended that the carb on a glo engine (OS46AX) has to be lower by about 1/4" - 3/8" (5 - 10mm) then the TOP of the tank. Seems to the uninitiated that the TOP of the tank is irrelevant as the level of the fuel continually drops during flight and goes well below the level of the carb (in level flight). I have been told that the engine will cut out due to running too lean. I can't see the physics in this. Can someone please explain.
Frank
Relatively new to RC flying and would appreciate a reasonably practical explanation as to WHY it is recommended that the carb on a glo engine (OS46AX) has to be lower by about 1/4" - 3/8" (5 - 10mm) then the TOP of the tank. Seems to the uninitiated that the TOP of the tank is irrelevant as the level of the fuel continually drops during flight and goes well below the level of the carb (in level flight). I have been told that the engine will cut out due to running too lean. I can't see the physics in this. Can someone please explain.
Frank
10-04-2009, 06:12 AM
#2
RE: Card V Fuel Tank Location
G'day Mate,
I believe you have been misinformed, the centreline of the tank should be level with or no more than 10mm lower than the fuel inlet at the carby, (not the needle valve).
As you will notice, this is to allow for fuel usage, during the flight.
The engine should be tuned, so that, when the nose of the aircraft is raised to vertical, at full throttle, the engine will be rich enough to pick up speed slightly, this will allow for the take off angle of the aircraft & also allow for unloading in the air.
I believe you have been misinformed, the centreline of the tank should be level with or no more than 10mm lower than the fuel inlet at the carby, (not the needle valve).
As you will notice, this is to allow for fuel usage, during the flight.
The engine should be tuned, so that, when the nose of the aircraft is raised to vertical, at full throttle, the engine will be rich enough to pick up speed slightly, this will allow for the take off angle of the aircraft & also allow for unloading in the air.
10-04-2009, 06:38 AM
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RE: Card V Fuel Tank Location
Thanks Alan.
The measurements I quoted are straight from the OS Manual with a diagram.
A couple of (VERY experienced) guys suggested I should lower my engine mount as the carb is just about level with the TOP of the tank. Last weekend, the engine cut out twice after about 5 mins and they suggested it was running too lean. Today, I had 3 successful flights with it set just a tad on the rich side and no problems. They still maintain that to run the engine at an optimum mixture setting, it will cut out after just a few minutes.
As I said, I'm looking for the explanation (read physics) for the correct location / height of the fuel tank.
Confusion reigns supreme,
Frank
The measurements I quoted are straight from the OS Manual with a diagram.
A couple of (VERY experienced) guys suggested I should lower my engine mount as the carb is just about level with the TOP of the tank. Last weekend, the engine cut out twice after about 5 mins and they suggested it was running too lean. Today, I had 3 successful flights with it set just a tad on the rich side and no problems. They still maintain that to run the engine at an optimum mixture setting, it will cut out after just a few minutes.
As I said, I'm looking for the explanation (read physics) for the correct location / height of the fuel tank.
Confusion reigns supreme,
Frank
10-04-2009, 01:02 PM
#4
RE: Card V Fuel Tank Location
Its easy to understand why the Fuel tank/spray bar height relationships are so important with any Suction/muffler pressure system when you factor in flight loads and flight dynamics and all can and will tend to hinder the fuel systems ability to consistantly deliver fuel. Suction/Muffler pressure systems are relatively just up to the job and reasonable tank installations are important.
Alan has given you the best information concerning this relationship.
On your needle setting I have no doubt it was set to lean for the flights you talked of If the problem goes away by enrichment. Setting excessively lean needles is a very common tendency for new folks and some old timers as well.
John
Alan has given you the best information concerning this relationship.
On your needle setting I have no doubt it was set to lean for the flights you talked of If the problem goes away by enrichment. Setting excessively lean needles is a very common tendency for new folks and some old timers as well.
John
10-04-2009, 05:08 PM
#5
RE: Card V Fuel Tank Location
G'day Frank,
I have just had a look at the OS manual, for the 46AX & the 120AX, they vary slightly, the 120AX shows the tank centreline level with the fuel inlet, which is the same as I stated in my last post. The 46AX states that the TOP of the tank should be 5-10mm above the level of the needle valve, & allowing for the size of tank they are referring to, it is about right.
So either way I stand by what I stated earlier, I won't repeat it.
But I will give you a very useful tip on tuning, this only works for 2 stroke engines.
We are trying to find the tuning range of a particular engine, doesn't matter what size, it works for all.
Open needle valve an extra 1/2 turn, no matter what it was set to.
Start engine, run up to full throttle, it should be running quite rich, if not richen some more, slowly lean the needle valve & I mean slowly, as the remote needle on the 46AX takes time to react. Slowly lean & listen carefully to the engine, as you lean it, it will pick up revs, when it begins to slow down, THAT is your leanest point, note where that is, I use needle extensions, which give me a visual indication, slowly richen the needle, the speed will pick up again, continue to richen the mixture, slowly, until it begins to slow down again, THAT is your richest point, now comes the critical adjustment, slowly lean the needle, about 4 clicks, or until the engine is running smoothly again, leave it there, don't be tempted to lean it any further, & fly your plane, if done correctly you should have one sweet running engine, that will continue to run happily throughout the tank of fuel.
That range from lean to rich & visa versa, is your tuning range.
2 stroke engines should be run at the rich end of the tuning range, the width of the tuning range will vary depending on nitro content of the fuel, prop size, & glow plug etc.
If your plane will not fly at this rich mixture setting, you need a bigger engine.
Enjoy.
I have just had a look at the OS manual, for the 46AX & the 120AX, they vary slightly, the 120AX shows the tank centreline level with the fuel inlet, which is the same as I stated in my last post. The 46AX states that the TOP of the tank should be 5-10mm above the level of the needle valve, & allowing for the size of tank they are referring to, it is about right.
So either way I stand by what I stated earlier, I won't repeat it.
But I will give you a very useful tip on tuning, this only works for 2 stroke engines.
We are trying to find the tuning range of a particular engine, doesn't matter what size, it works for all.
Open needle valve an extra 1/2 turn, no matter what it was set to.
Start engine, run up to full throttle, it should be running quite rich, if not richen some more, slowly lean the needle valve & I mean slowly, as the remote needle on the 46AX takes time to react. Slowly lean & listen carefully to the engine, as you lean it, it will pick up revs, when it begins to slow down, THAT is your leanest point, note where that is, I use needle extensions, which give me a visual indication, slowly richen the needle, the speed will pick up again, continue to richen the mixture, slowly, until it begins to slow down again, THAT is your richest point, now comes the critical adjustment, slowly lean the needle, about 4 clicks, or until the engine is running smoothly again, leave it there, don't be tempted to lean it any further, & fly your plane, if done correctly you should have one sweet running engine, that will continue to run happily throughout the tank of fuel.
That range from lean to rich & visa versa, is your tuning range.
2 stroke engines should be run at the rich end of the tuning range, the width of the tuning range will vary depending on nitro content of the fuel, prop size, & glow plug etc.
If your plane will not fly at this rich mixture setting, you need a bigger engine.
Enjoy.
10-04-2009, 05:39 PM
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RE: Card V Fuel Tank Location
Thanks again Allan.
I actually have the engine out of the plane at the moment but I'll give your tuning advice a run later in the week when it's reinstalled.
The plane I have is a scratch built Hustler from plans I have kept for 25+ years. I don't have the option of raising the tank at all without destroying the look of the plane. Also, I have very limited space to lower the engine - maybe 3-4 mm but that means filling the existing holes with epoxy and redrilling for the engine mount - not something I really want to do if I can avoid it.
Do you think the 46AX will run OK based on your tuning with the current setup where the top of the tank is about level with the carby fuel inlet. As I said, it ran fine yesterday - just a tad rich.
Cheers,
Frank
I actually have the engine out of the plane at the moment but I'll give your tuning advice a run later in the week when it's reinstalled.
The plane I have is a scratch built Hustler from plans I have kept for 25+ years. I don't have the option of raising the tank at all without destroying the look of the plane. Also, I have very limited space to lower the engine - maybe 3-4 mm but that means filling the existing holes with epoxy and redrilling for the engine mount - not something I really want to do if I can avoid it.
Do you think the 46AX will run OK based on your tuning with the current setup where the top of the tank is about level with the carby fuel inlet. As I said, it ran fine yesterday - just a tad rich.
Cheers,
Frank
10-05-2009, 03:56 AM
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RE: Card V Fuel Tank Location
Ta Mate.
I have been using the APC 11x6 prop and it works fine. Looking forward to going through the tuning procedure you provided but that may be a week or two away. I'll let you know how I go.
It's really nice to get some 'common sense' advice instead of just unqualified opinions as has been the case with a number of people I've spoken to.
Cheers,
Frank
I have been using the APC 11x6 prop and it works fine. Looking forward to going through the tuning procedure you provided but that may be a week or two away. I'll let you know how I go.
It's really nice to get some 'common sense' advice instead of just unqualified opinions as has been the case with a number of people I've spoken to.
Cheers,
Frank
