Why two seperate fule tanks?

[rogerbacon]

Why does the Long-ez have to have two seperate fuel tanks and not have a setting for "both"? I can't think of any advantage to having only "left" and "right" selections and not a "both" so I surmise that it must be required by the design. What I can't understand is why.

[mak790]

Why does the Long-ez have to have two seperate fuel tanks and not have a setting for "both"? I can't think of any advantage to having only "left" and "right" selections and not a "both" so I surmise that it must be required by the design. What I can't understand is why.

I believe for safety reasons. If your left fuel tank start leaking in flight you will loose fuel only from left left tank. That's why these tanks are seperated. (thats the only logical explanations ) but maybe I'm wrong.

 

Mak

[Terry]

A gravity feed fuel system works with a "both" postion (Cessna 172). A fuel system requiring a fuel pump will suck air if you try to feed from two tanks when one is empty(Piper Cherokee).

[TMann]

I'm running both tanks to a central sump built as a passenger thigh support. Check valves prevent backflow and crossover.

 

Because I am building with retracts, I will have a reserve tanks in the hell hole.

[magnum]

"I'm running both tanks to a central sump built as a passenger thigh support. Check valves prevent backflow and crossover."

 

This is my design as well. I'm not to the plumbing on this yet but would like a source for the back flow valves if you would be so kind.

Press on

Tom

[TMann]

I'm not to the plumbing on this yet but would like a source for the back flow valves if you would be so kind.

Andair makes a good checkvalve. Spruce carries them.

[emteeoh]

Why does the Long-ez have to have two seperate fuel tanks and not have a setting for "both"? I can't think of any advantage to having only "left" and "right" selections and not a "both" so I surmise that it must be required by the design. What I can't understand is why.

I'm having a hard time finding the *GOOD* conversations on it, but there are several conversation on this forum about the fuel selector. The arguments in favour of a both setting seem to boil down to reduced pilot load. The arguments in opposition are basically that bad fuel from one tank cannot contaminate the other, and if one tank is draining in flight, you won't drain both tanks. (there is a posting on this forum somewhere in which this happened to an Aerocanard, IIRC. The pilot had forgotten to put back on the fuel cap of one tank, and both tanks bled dry as a result) Further, any attempts to address these issues just lead to increased complexity, etc.

 

 

ok, I've spent two hours looking, and I can't find anything other than:

http://www.canardzone.com/forum/showthread.php?t=3496

 

But I'm sure there are better threads on the subject.

[TMann]

..... and if one tank is draining in flight, you won't drain both tanks. (there is a posting on this forum somewhere in which this happened to an Aerocanard, IIRC.

Hence the use of check valves.

My point of fueling is in the turtleback that features a cap and a door.

 

The plane referred to did not have check valves.

[longezdave]

I believe for safety reasons. If your left fuel tank start leaking in flight you will loose fuel only from left left tank. That's why these tanks are seperated. (thats the only logical explanations ) but maybe I'm wrong.

 

Mak

This is true and the separate tanks provide redundancy on the tank vents too.

[TMann]

This is true and the separate tanks provide redundancy on the tank vents too.

The Berkut design has 3 vent outlets for each strake.

[longezdave]

I'm NOT saying that it is likely and I'm not totally convinced that one design is better than the other, but..... What if a fuel cap is left off AND a check valve fails at the same time? I would think that the kind of check valves used in the above mentioned systems would have a very low pressure differential to initiate flow (typical break out pressure of less than 1 PSI). If this is true, I would also think that it would not take much of a contaminant to keep the valve from seating and therefore leaking when it needs to prevent backflow.

[TMann]

Can't say how that would play out is such an unlikely situation. I'm working from a set of Berkut drawings for this.

I know it's a proven fact as to how it works without the check valve. Both sides are sucked dry.

[Lynn Erickson]

Hence the use of check valves.

My point of fueling is in the turtleback that features a cap and a door.

 

The plane referred to did not have check valves.

thats like the worst place to have the fuel cap. the vari ezs have a cap for the aux tank in that location and it is a pain to use. standing in the back seat to fill the tank, sucks. and on the berkut you would have to reach around the canopy or over the cowling and that would be very difficult. over the cowling is next to impossible if parked nose down. the turtleback can't be reached without standing or climbing on something.

[mak790]

What about valve (fuel selector) similar to this one with 4 options:

 

1 left

2 right

3 both

4 off

 

http://www.aircraftspruce.com/catalog/eppages/fs20tYPE4.php

 

Why not use something similar to this or maybe 3 separate valves one for right side, one for left and one main valve. (only idea) of course we can use checkvalve up to you the final result will be similar.

 

Mak

[TMann]

For fuel injection where you are running at higher fuel pressures, you need a return as well. It's not the same as a gravity feed system.

[mak790]

For fuel injection where you are running at higher fuel pressures, you need a return as well. It's not the same as a gravity feed system.

 

Of course you are right for example in my car which I did I have Motronic-Bosch fuel injection system. I have electric fuel pump (which works all the time at the same speed-presure) the presure in the main line is 3 bars and in the returning line is about 0,3-1,5 bar depend from engine RPM (sometimes engine need more fuel sometimes less). My intention was to show that we can use selector with 4 options-positions instead these check valves. Selector mentioned by me is designed for high wing planes like cessna or piper cub etc thats why I wrote similar to this.

Here you can find technical data for the selector mentioned by you. But I believe you know that page very well.

http://andair.co.uk/pdfs/FS20-20-D2.pdf

 

Mak

[TMann]

Mak,

I wasn't discounting the information you posted.

I was more or less addressing the subject of the pressure required to override the check valve. The Duplex Fuel Selector basically limits your selection to two sources and off.

By combining both wing tanks in the single sump, I can use that as one selection option and save the second selection option for my reserve tank in the hell hole. That should provide enough run time to give me at least 100 nm to find a place to put down.

 

At least that is my thinking at this point.

[mak790]

Mak,

I wasn't discounting the information you posted.

TMann

We just have different opinion and we are discussing I dont feel like someone is going to discounting someone else information and you are in better position because you are familiar with berkut fuel system and we don't. And you are building so that mean you made much more research then I.

 

That should provide enough run time to give me at least 100 nm to find a place to put down

Yes but what if you will be in a half way to I dont know let's say to Jamaica, Hawaii or Kuba I know that you have lot of sharks out there.

 

Mak

[TMann]

Yes but what if you will be in a half way to I dont know let's say to Jamaica, Hawaii or Kuba I know that you have lot of sharks out there.

.......... I'm in Nebraska which is about as close as you can get to the center of the US (which is why they built the Strategic Air Command here.)

There is no water that you can't see over.

Most of the state is so flat, you can watch your dog run away for three days before he would be out of view.

[mak790]

.......... I'm in Nebraska which is about as close as you can get to the center of the US

Yes but I was talking about some kind of holidays (I know you have Cali and Florida so you dont need to go abroad) Long Ez is a great plane one guy from Switzerland did 2 trips around the world I heard about one man from Brazil who flew to Oskosh but first he flew to Africa next to Europe and from Europe through Atlantic to USA so you never know.

 

Most of the state is so flat, you can watch your dog run away for three days before he would be out of view.

Lol:ROTFLMAO: great description.

 

Mak

[Wayne Hicks]

Was said--> For fuel injection where you are running at higher fuel pressures, you need a return as well. It's not the same as a gravity feed system.

 

I reply --> It depends on the type of fuel injection system you're using. For Bendix servos, one type needs to return fuel to the tank. The other type doesn't. My Lyc IO-360 (fuel injected) does NOT need a fuel return line. One is labeled "RSA", the other is just "RS," but I can't ever remember which is which.

[Lynn Erickson]

Was said--> For fuel injection where you are running at higher fuel pressures, you need a return as well. It's not the same as a gravity feed system.

 

I reply --> It depends on the type of fuel injection system you're using. For Bendix servos, one type needs to return fuel to the tank. The other type doesn't. My Lyc IO-360 (fuel injected) does NOT need a fuel return line. One is labeled "RSA", the other is just "RS," but I can't ever remember which is which.

The RS is the older system and has the return. The RSA is the improved model and does not need a return

[Drew Swenson]

I also run with L, R, Both. My guess is that the L, R was just a simpler valve. But to prove to yourself of the potential danger of running in both on a low wing aircraft (no check valves---or no visual monitoring of fuel level), try the following. Take two glasses of water and fill them to the top with water. Stick a straw in each glass and drink from both glasses at the same time----no problem. Now, dump one of the glasses out and try it again (one straw in the glass of water and the other straw in the glass of air). You will find that as long as you are in both, that you won't be able to grab any fuel from the other tank----if one is empty.

[Wayne Hicks]

Better yet, start with two bottles of beer....

[mak790]

Better yet, start with two bottles of beer....

 

Great idea. I think I should try it:D .

 

Mak