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Old Jan 26, 2013, 07:29 AM
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Twin tanks

Monocoupe....short nose.....no room for fuel.....

I need the pros and cons on "saddle" tanks, one on each side, 8 oz.,6" apart...Tank 1, feeding tank 2, through the vent.( #1 has the vent, it's pickup line goes to tank 2's vent).

Mostly 'circle' flying, no aerobatics.

I DO have room for a 12 oz. tank, cross ways, but would prefer the extra 4 ozs.
Let me have it !
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Old Jan 26, 2013, 07:32 AM
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Works fine Earl, us jet guys have been running multiple tanks for decades. You can do them serial or parallel with no problem.
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Old Jan 26, 2013, 08:12 AM
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Originally Posted by S3NFO View Post
Works fine Earl, us jet guys have been running multiple tanks for decades. You can do them serial or parallel with no problem.
Great ! thanks- I knew you guys were limited for space, but didn't know for sure how you did it...
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Old Jan 26, 2013, 08:30 AM
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Originally Posted by S3NFO View Post
...You can do them serial or parallel with no problem.

No way, S3NFO!

With parallel tanks, if one empties before the other, your engine will ingest air, even if the other tank is still half-full! Suction always takes the path of least resistance.

Air is much more easily drawn than air. So, once either clunk is in air, that's all that will come.
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Old Jan 26, 2013, 08:42 AM
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With saddle tanks,(all things being equal,height, line size and length,a "Tee" feeding the engine) why would one tank empty faster than another?

We're assuming a scale model flying about in circles,-no aerobatics.
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Old Jan 26, 2013, 08:57 AM
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You should be fine. I did this years ago with RC planes. I used dual fuel tanks many years ago with cross country RC flying. It worked out quite well. At the time it was a Fox .60 engine with dual 16 ounce fuel tanks connected in series. The plane was a Ugly stick with the fuselage made a little more wide for the fuel tanks. We were holding cross country racing at the time. Where we flew in various events with distances of 50 miles and 100 miles at the time.

Connect the fuel tanks in series not parallel. Series will empty both tanks. Parallel will wind up letting the engine to suck air if one tank empties before the other does. Plus the Tee connector winds up increasing the inner diameter of the fuel line tubing and can cause a more weak fuel draw too. But it depends on the engine and how well it draws fuel though. It may not be a problem if the engine has a strong fuel draw and good muffler pressure.
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Old Jan 26, 2013, 10:49 AM
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Back to back

Tanks in series is the way to go- I just wondered about why one parallel tank would empty faster.

Obviously they will, which is one of the reasons full scale has tank selectors, for wing mounted tanks, gravity feed.Like the Monocoupe,
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Old Jan 26, 2013, 11:39 AM
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Originally Posted by epoxyearl View Post
Tanks in series is the way to go - I just wondered about why one parallel tank would empty faster.
Earl,


Tanks never flow exactly the same. A small burr at the end of one tank's outlet, a slight length difference, or a slight kink in the fuel-line.

Since in an R/C model you cannot select which tank to use; serial connection is the only way.
The further one should empty first and be filled last (in series).
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Old Jan 26, 2013, 11:54 AM
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becuase you don't actually flat fly! the higher tank will empty first! like as in if your mostly going in a left hand pattern, the right tank would empty first!

I have a boat with 2 1000 gal. tanks, and it only takes a 1 or 2 deg. list too get the fuel moving from one tank to the other, so I go out on one, and come back on the other!

series seems like the proper way ta go!

personaly I can't stand at the flight line that long! I would hafta take turns with someone ta fly that long!
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Old Jan 26, 2013, 12:02 PM
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Originally Posted by whiskykid View Post
becuase you don't actually flat fly! the higher tank will empty first! like as in if your mostly going in a left hand pattern, the right tank would empty first!

I have a boat with 2 1000 gal. tanks, and it only takes a 1 or 2 deg. list too get the fuel moving from one tank to the other, so I go out on one, and come back on the other!

series seems like the proper way ta go!

personaly I can't stand at the flight line that long! I would hafta take turns with someone ta fly that long!
Well you cleared that up for me! I don't think I could fly out 2,000 gallons either ! ha ha ....I heard what you said-it makes sense.
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Old Jan 26, 2013, 01:01 PM
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Originally Posted by DarZeelon View Post
Earl,


Tanks never flow exactly the same. A small burr at the end of one tank's outlet, a slight length difference, or a slight kink in the fuel-line.

Since in an R/C model you cannot select which tank to use; serial connection is the only way.
The further one should empty first and be filled last (in series).
Dar,

Before you start spreading your theoretical info, put your dots on the I and crosses on the T, why don't you go and TRY first..... Or ask somebody who has actual experience with it......

I am running a helicopter (Bell 47G), 15 cc 4stroke, with twin tanks, no pump, no exhaust pressure, tanks in parallel, Y-connection above the tanks.

This one: http://www.helischool-oldeberkoop.nl...-47g&Itemid=69

As we all know, helicopters do not glide very well, and are very particular on their fuel supply system.

My tanks are hand made, and therefore VERY not equal....
There are not even clunks in the tanks, just fixed pick-up tubes.

And still..... this helicopter is allready 12 years old, and has NEVER had any problems with its fuel supply.

It works, and NONE of the issues you mention, manifest themselves during real life flight....

The tanks tend to level out, because they are communicating vessels: if for whatever reason one of the tanks is lowered more, the pressure in that fuel pick-up line is lower (even if it is just 1 cm level difference) and the highest tank will start to flow slightly faster.

I have tested this with one tank full and the other tank 1/4 filled. After 15 minutes both tanks were equalized in level. It matters slightly if length of fuel tubing is not equal, but not even that much (it amazed me too, slightly)

I have done extensive tests before the maiden flight, because I do not have the habit of gambling with a helicopter of U$ 2000 (approx)

Provided they are mounted at the same level and you are avoidig knife-edge flight: Twin tanks in paralel, WORK! Period!

@ Whiskykid: if your plane is banking in a left hand circuit, the resulting forces are still perpendicular to the wings, perpendicular to the fuselage floor, and perpendicular to the tanks. In a plane, there is no "high side" like in a boat. Flying a left hand circuit, the tanks will still be drawn empty at an equal pace. Tested that too.

Brgds, Bert
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Old Jan 26, 2013, 03:19 PM
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Bert-for the same reason, (plus) $1k and 250 hours, I don't want my engine to stop..
I do know that as a child I swung water buckets in a circle and lost nary a drop,with my arms straight out,at full tilt.

It's how gravity feed airplanes do loops and (barrel) rolls.

I want to LEARN ! Are your tanks connected, other than the pickup line at the "tee'?
I see the wisdom of the tanks connected in series, just curious of your connections.
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Old Jan 27, 2013, 01:04 AM
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Originally Posted by Brutus1967 View Post
Dar,

Before you start spreading your theoretical info, put your dots on the I and crosses on the T, why don't you go and TRY first..... Or ask somebody who has actual experience with it......

I am running a helicopter (Bell 47G), 15 cc 4stroke, with twin tanks, no pump, no exhaust pressure, tanks in parallel, Y-connection above the tanks.

This one: http://www.helischool-oldeberkoop.nl...-47g&Itemid=69

As we all know, helicopters do not glide very well, and are very particular on their fuel supply system.

My tanks are hand made, and therefore VERY not equal....
There are not even clunks in the tanks, just fixed pick-up tubes.

And still..... this helicopter is allready 12 years old, and has NEVER had any problems with its fuel supply.

It works, and NONE of the issues you mention, manifest themselves during real life flight....

The tanks tend to level out, because they are communicating vessels: if for whatever reason one of the tanks is lowered more, the pressure in that fuel pick-up line is lower (even if it is just 1 cm level difference) and the highest tank will start to flow slightly faster.

I have tested this with one tank full and the other tank 1/4 filled. After 15 minutes both tanks were equalized in level. It matters slightly if length of fuel tubing is not equal, but not even that much (it amazed me too, slightly)

I have done extensive tests before the maiden flight, because I do not have the habit of gambling with a helicopter of U$ 2000 (approx)

Provided they are mounted at the same level and you are avoidig knife-edge flight: Twin tanks in paralel, WORK! Period!

@ Whiskykid: if your plane is banking in a left hand circuit, the resulting forces are still perpendicular to the wings, perpendicular to the fuselage floor, and perpendicular to the tanks. In a plane, there is no "high side" like in a boat. Flying a left hand circuit, the tanks will still be drawn empty at an equal pace. Tested that too.

Brgds, Bert
Bert,


When answering a question regarding something I have yet to actually try, I never 'try it first' on my own, but rather prefer to analyze its theory.
I prefer in such cases not to learn from the good experience of others; although learning from their mistakes can bring new variables into the theoretical analysis.

As an experienced R/C helicopter pilot, I am quite sure you never fly your models til 'the lights go out'. So, as long as there's some fuel in both parallel tanks, it is quite clear fuel supply is never impeded.

But since there are theoretical reasons for the fuel to be depleted in one tank, earlier than in the other; which in addition to those already mentioned, are also a slight difference in mounding level, as well as flight with the rudder trim off (the 'ball' is off to one side); which is very common; there is little to convince me to trust such a setup!

The only theoretical 'disadvantage' (not counting added complexity and more points of potential failure) of using a serial tank connection, is that once the rear tank empties, suction of fuel becomes much easier...
With a normal glow carburettor; with or without muffler pressure, the mixture strength will increase and the engine will run significantly richer than it did; and this could alter the engine's behaviour and power.

This issue, though, can be ignored for gas engines with diaphragm-pump equipped carburettors.

So the best solution is obviously just to use a larger single regular tank.
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Old Jan 27, 2013, 07:41 AM
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Originally Posted by DarZeelon View Post
Bert,


When answering a question regarding something I have yet to actually try, I never 'try it first' on my own, but rather prefer to analyze its theory.
I prefer in such cases not to learn from the good experience of others; although learning from their mistakes can bring new variables into the theoretical analysis.

As an experienced R/C helicopter pilot, I am quite sure you never fly your models til 'the lights go out'. So, as long as there's some fuel in both parallel tanks, it is quite clear fuel supply is never impeded.

But since there are theoretical reasons for the fuel to be depleted in one tank, earlier than in the other; which in addition to those already mentioned, are also a slight difference in mounding level, as well as flight with the rudder trim off (the 'ball' is off to one side); which is very common; there is little to convince me to trust such a setup!

The only theoretical 'disadvantage' (not counting added complexity and more points of potential failure) of using a serial tank connection, is that once the rear tank empties, suction of fuel becomes much easier...
With a normal glow carburettor; with or without muffler pressure, the mixture strength will increase and the engine will run significantly richer than it did; and this could alter the engine's behaviour and power.

This issue, though, can be ignored for gas engines with diaphragm-pump equipped carburettors.

So the best solution is obviously just to use a larger single regular tank.
Your theory is great Dar, but my practical application from dozens of glow DF jets beats your theory every time. As long as the fuel line from the tanks to the T's is the same length, I've never, ever had a problem with one tank running dry while the other still had fuel.
I'd bet there are several thousand old school DF guys out there who've run 2 saddle tanks in parallel with no problems.
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Old Jan 27, 2013, 09:44 AM
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A better idea ?

The solution,in my case is NOT a single tank....I want the extra fuel that only two tanks can provide..
I watched a video recently of a pattern plane with a clear tank mounted outside the airplane.....at times the fuel was suspended at the top of the tank in level upright flight. There was fuel movement the entire flight. At time the pickup was uncovered and the engine continued to run,from the fuel in the lines. It was immediately replaced by muffler pressure when the clunk became resubmerged.

You did understand that I'm using muffler pressure to the single vent, and it's a 4 stroke, with excellent fuel draw, correct?
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