Help! Fuel Tank & Engine Position

[elty19]

Setting up a cosair with a Saito 82, and to make it more 'scale', I'm inverting the engine and setting it up 'upside down', which I think is commonly done.

Problem is, with this setup, the Fuel tank (midpoint) would be quite a bit higher than the carb. It should be slightly below it so it doesnt flood right?

Is it absolutely Necessary that the tank be slightly below the engine?

Any other solutions?

[bigfilsing]

Good question and 1 i've thought about quite a lot too. If the theory that it shold be just below the carb to not flood is correct ( it sounds logical to me) It must only be relevant during starting. Otherwise how do the guys do sustained upside down flight ???

I hope the more experienced guys can shed some light on this !

[elty19]

anyone?

yeah.... more exp folks... please comment?

[SniperWj]

It should be slightly below it so it doesnt flood right?

yes~ saito dun like force feed

[BabyBoy]

The tank should be slightly lower than the carb. This will prevent the engine from dying when you throttle down.(when plane is idle on the ground or you walk your plane to the runway or landing, and 4 stroke have better torelence than 2 stroke) You will experience a lot of dead stick while coming in for landing when you throttle down or when you throttle down to idle in mid air to slow down your plane. Unless you are a speed demon than no issue and you come in landing HOT!

[bigfilsing]

Think i may have an idea!
doesn;t really matter where the carb is as long as the fuel line passes a high point that is slightly higher than the mid point of the tank. This way the set up will be the same as if the motor was upright.

It will still need tank pressure to push the fuel "up over" the high point irrespective of where the carb is after the high point. Thats the theory anyway. I hope you get what i mean

[bigfilsing]

Here's a picture taken from an old Super tigre manual. I've highlighted in red the high point.
Of course any fuel level higher than the high point could in theory flood the carb but thats the same issue if the engine the normal way up or upside down ...At least i think it is

[BabyBoy]

Think i may have an idea!
doesn;t really matter where the carb is as long as the fuel line passes a high point that is slightly higher than the mid point of the tank. This way the set up will be the same as if the motor was upright.

It will still need tank pressure to push the fuel "up over" the high point irrespective of where the carb is after the high point. Thats the theory anyway. I hope you get what i mean

The reason for the fuel tank to be lower than the carb is not to flood the engine while in idle. No matter how you position the fuel line doesnt matter.

[BabyBoy]

Setting up a cosair with a Saito 82, and to make it more 'scale', I'm inverting the engine and setting it up 'upside down', which I think is commonly done.

Problem is, with this setup, the Fuel tank (midpoint) would be quite a bit higher than the carb. It should be slightly below it so it doesnt flood right?

Is it absolutely Necessary that the tank be slightly below the engine?

Any other solutions?

Run your engine on the ground. Put it to idle for about 10mins. It the engine dun quits you are safe.

[bigfilsing]

The reason for the fuel tank to be lower than the carb is not to flood the engine while in idle. No matter how you position the fuel line doesnt matter.

Sorry mate i have to disagree with your statement.

The TS's issues is a concern that the carb is lower than the tank middle line. Nothing to do with flooding during idle, specifically.

Basic physics and fluid dynamics will tell you that if the fuel line is higher than the tank more energy ...in this case exhaust pressure ...will be needed to "push" the fuel up the pipe.
I agree with you in as much as the actual effect will be minimal, especially if we take into account that ...for example a 50mm high tank (when full) only excerts ( at it's mid point) 25 / 10000 =0.04bar ( based on water as i dont know the specific gravity of nitro fuel)
For me the unknown is the pressure provided by the exhaust and this being the energy source needed to push the fuel "up" the fuel line if the fuel line is any higher than the tank (fuel) level.

To come back to the earlier picture from the old Super tigre engine manual. They recommend the fuel tank middle line to be on centre with the carb barrel centre or lower, but no further than 3/8" ( +/- 9mm)
This suggests their concern at the fuel delivery if the carb is any higher than 9mm above the centre line.

It just so happens that i'm having problems with the old Super tigre engine after a rebuild ( yes we crashed the plane ) and this is one of the the things i'm looking into for a poor performing engine in the high rev range.

Cheers

[BabyBoy]

Sorry mate i have to disagree with your statement.

The TS's issues is a concern that the carb is lower than the tank middle line. Nothing to do with flooding during idle, specifically.

Basic physics and fluid dynamics will tell you that if the fuel line is higher than the tank more energy ...in this case exhaust pressure ...will be needed to "push" the fuel up the pipe.
I agree with you in as much as the actual effect will be minimal, especially if we take into account that ...for example a 50mm high tank (when full) only excerts ( at it's mid point) 25 / 10000 =0.04bar ( based on water as i dont know the specific gravity of nitro fuel)
For me the unknown is the pressure provided by the exhaust and this being the energy source needed to push the fuel "up" the fuel line if the fuel line is any higher than the tank (fuel) level.

To come back to the earlier picture from the old Super tigre engine manual. They recommend the fuel tank middle line to be on centre with the carb barrel centre or lower, but no further than 3/8" ( +/- 9mm)
This suggests their concern at the fuel delivery if the carb is any higher than 9mm above the centre line.

It just so happens that i'm having problems with the old Super tigre engine after a rebuild ( yes we crashed the plane ) and this is one of the the things i'm looking into for a poor performing engine in the high rev range.

Cheers

I'm refering to the engine when mounted upside down. (If your teory is correct than we wont have so much of a problem). I have an engine mounted upside down. The needle setting is totally different from recommended factory setting. eg. factory setting 2.5 turn but when the engine is upsidedown start with 1.5 turn and work from there.

Some engine have the fine low rpm needle setting. You need to ensure that the setting is correct before you adjust the high rpm needle to get the best out of your engine.

Cheers

[baby_zyklon]

Don't wish and have no time to start any debate, but IMHO,

Position of the fuel line doesn't matter. Its the height of the tank that matters.

A fuel tank that is too much higher than the carb level might flood the engine before you start it or attempting to start it, unless it has a regulator(which I suppose not in this case since this is a saito). Normally its ok for the center line of the tank to be slightly higher up as long as you can get it to idle to the flight line and take off because your fuel level would have drop below the center line of the tank by the time you go to idle down and attempt to land. Anyway your prop will probably be big enough to help the idle-down when bringing it in for landing. By idle down, I mean the idle down function in your TX.

As for why the height of the fuel line doesn't matter while the height of the tank matters, pls consult any decent physics or fluid text book. Potential energy, work done etc for fluid in this case, does not depend on the process, but the initial and final state, which happens to be the tank and carb height. Whatever height it gains along the way, will be lost by the time the fuel reach the carb. Just my humble opinion.

[bigfilsing]

Baby zy >>debates are what forums are for mate!

So you just want to have your say and be done with it. Hardly fair.
Just because we disagree doesn;t make me right and you wrong or vice versa

I dont know where you took physics but you may want to reconsider your "doesn't matter how high the fuel line is" statement.

Unless of course you've found fuel that can defy gravity

Right! back to the original topic. While trying to research my own problems i found this that the TS may find useful.

http://saito-engines.info/engine_mount.html

got some info on mounting angle and fuel delivery

Cheers

[baby_zyklon]

school sem has started. Not much time for posting. My physics/fluid is not exactly as good as I am required to be and I can be wrong, but heres my 2 cents.

Think of bernoulli's equation, taking point 1 as tank center line, point 2 as highest point of fuel line and point 3 as carb entry. Only point 1 and 3 matters for TS's case. Point 2 is just process, unless you want to take into account losses, which in any case, shouldn't be affected by height, but rather by the length of pipe.

Think of a water tank, with a hose that goes over the top of the tank and then out of the tank, with the outlet of the hose below the tank. Water will flow through once it starts flowing through.

Alternatively, draw the energy/hydraulic grade line for the two different type of system(low and high fuel line).

Where I learnt my things from.
Fundamentals of fluid mechanics By Munson, Young and Okiishi.
Physics for Scientists and Engineers By Jewett and Serway.
Engineering Mechanics-Dynamics By Bedford.

While these are fundamental and basic text and do not take into account of everything, they serve their purpose well in basic everyday life and can be easily understood by pretty much anyone who understand english.

[bigfilsing]

I see where you're coming from. siphon (syphon)action (see pic)

but in order to work (siphon) it needs two fundamental things to be present.
the opening at the end has to be at least as big as the intake This isn't the case in RC as the carb/needle/fliter restrict it.
and
the volume of fluid on the down side pipe ( after the high point) has to be greater than the volume on the uptake side pipe. Thats why any high point (even a minimal one) in a fuel line should be as closer to the carb than to the tank.

I think that by normal set up there wont be much of a problem until below half full tank. When, if my theory is correct, most of the pressure energy from the exhaust feed will be used in "pushing" the fuel up the tube to the high point and this in turn results in less fuel flow at WOT and a leaning effect.

Cheers