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Old 10-23-2011, 07:58 PM   #1
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Hi all -


I am building an Acroduster with both upper wing and fuselage tanks. The wing tank will only be used for cross country flights and I'm trying to decide how I should design the fuel system. Should I keep it as simple as possible and gravity feed the wing tank into the fuse tank with an on/off valve on those rare occasions when I fill both tanks? Or should I add some complexity and allow the wing tank to feed the engine and/or the fuselage tank? The design is already somewhat complex, in that it has an acro tank built into the lower section of the fuse tank with venting for inverted and upright flight. Flop tube, etc.


Your opinions and experience with either design would be greatly appreciated.


Thanks,
Robert Marshall



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Old 10-23-2011, 08:09 PM   #2
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I'm doing a tank that drains into my fuse tank. If it was a certified airplane, they would not let you over fill your main tank and spill and possibly catch fire. Also if the fuel doesn't flow out as fast as you may need it could cause a sputter or lean condition.



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Old 10-23-2011, 08:21 PM   #3
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"If it was a certified airplane, they would not let
you over fill your main tank and spill and possibly catch fire."
The Flint Aero tanks in a C150 that I owned pumped fuel from the aux to the main tanks. It was possible to over fill the mains and pump fuel overboard.

"Also if
the fuel doesn't flow out as fast as you may need it could cause a
sputter or lean condition."
Are you are talking flow out of the wing tank to the main tank or straight to the engine? If you plumb to the engine you should use the same size of plumbing from both tanks and flow should be checked. If you plumb from the aux. to the main the normal technique is to burn the main down by the number of gallons in the aux and then transfer the aux fuel to the main.




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Old 10-23-2011, 08:36 PM   #4
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Quote:
Originally Posted by darylat8750
The Flint Aero tanks in a C150 that I owned pumped fuel from the aux to the main tanks. It was possible to over fill the mains and pump fuel overboard.



Ditto Maule MX-7-235. You can see the tank vents from the cockpit to remind you you're being an idiot and pumping fuel overboard. Not that I've ever done that.......
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Old 10-23-2011, 09:18 PM   #5
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A million years ago an old airplane crashed, because they pumped a full tank over and as a result the vent somehow caused the fuel to enter the fuselage and a relay to short and blow the plane to pieces.

I flew a beech 1900 that would let you transfer fuel from aux to mains, but it had a shutoff if it were to get full. Normally the engines could out burn the transfer.

The maule I don't know about, but the 150 would be an STC so that wouldn't surprise me.

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Old 10-23-2011, 10:02 PM   #6
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My two bits...I am building a Firebolt. The upper wing tank will be for cross country use only and I will be plumbing it directly into the main tank. Perhaps a slightly larger fuel line for a quicker transfer. It seems straightforward enough to me. Run the main tank to the 1/2 level and transfer all fuel from the upper tank to the main. Done.

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Old 10-23-2011, 10:20 PM   #7
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I did it that way too. I tested a -4 line with a cooler box at the right height, I got something like 2 mins a gallon...plenty of fudge room.

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Old 10-24-2011, 11:09 AM   #8
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Quote:
Originally Posted by wminear
The maule I don't know about, but the 150 would be an STC so that wouldn't surprise me.
It came from the factory as I described. I believe the aux tanks are an option but when they're so equipped they use transfer pumps with no other components to prevent over-filling.

In the Maule I generally feed from the left main first to help with roll trim, then keep switching back and forth between mains. If you use BOTH, the tanks don't drain evenly anyway so you never really know what has been used. I like to get the fuel transferred early so I'll know if one or both of the pumps isn't pumping and that can lead to over filling if you don't pay attention. With a gravity feed system that has good flow, this would not be necessary.
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Old 10-24-2011, 05:33 PM   #9
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A number of certified airplanes have fuel systems that are not fool proof. The BE18 with high pressure carbs returns fuel to the main tanks. If you don't burn some fuel out of the mains before going to aux fuel you will pump some out the vents... If you have the low pressure carbs it is not an issue.

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Old 10-24-2011, 08:11 PM   #10
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And so does a PA31-350... Daryl you've got a little one upper in ya... I know your a mod but..

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Old 10-25-2011, 03:07 AM   #11
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Marshall With Starduster aircraft there are three different ways that are common in plumbing the main and the wing tank. If the airplane is to be used as an aerobatic mount for local flying and only used for cross country flying on occasion a main tank with an aerobatic sump that has a flop tube installed and the correct venting system to insure upright and inverted flight should be the first consideration.

The wing tank should be next and used for cross country flying when needed.

Generally speaking they can be plumbed three ways.

The first and simplest with Acrodusters is the main tank feeds the engine from the flop tube in the sump with an on and off shut off valve and the wing tank through a second shutoff valve dumps the wing tank into the main via gravity. The wing tank is used to extend the range of the airplane by providing more fuel.

The second way is similar to the first with one exception it has it has a three way valve. One is from the sump with the flop tube, two is an additional outlet port in the bottom of the top portion of main tank with a finger strainer that allows the selection of the sump (Flop Tube) for aerobatic flight. Or the upper main tank for normal flying, and the third position is off! It also has the previously mentioned additional valve from the wing tank that allows you to dump the fuel into the main tank via gravity.

The third has a four way valve that is plumbed to, One the sump, two to the upper portion of the main tank, Three the wing tank and four off! With this system the pilot can select the sump the main the wing or turn the system off! This system is the way my airplane is plumbed and has served me well for over 20 yrs and 2400 hrs! But I am not much of an aerobatic pilot and am a sport flier.

The reason for the dump valve on Aerobatic airplanes like the Acroduster Too is that the structural integrity of the wing tank is compromised if it has fuel in it or partial fuel as it was not designed to withstand hi "G" load cycles and therefore must be empty when hard aerobatics or hi "G"s are imposed. Usually what happens is that the riveted baffles that have the heads welded can pull loose and can incur leaks this is why the tank needs to be empty or drained into the main tank, before aerobatics are attempted. Does this make sense? If you send me an E-Mail address I can send you a Schematic for the recommended system for the Acroduster Too.

There are advantages and disadvantages to all three systems the more things that are added to the system and the more complex it is the chance of mismanagement or fuel starvation is increased at least in my opinion, so the simpler and basic it can be installed the better it is. My opinion.

We have not talked about fuel line size, fuel tank external or internal venting and fuel cooling nor have we talked about fuel line routing, selector valve boost pump (Type or pressure requirements) or gasqlator (Strainer) placement. All have a number of ways that they can be installed that will work satisfactory. Fuel system considerations are and can be quite dangerous if installed incorrectly. Dave


Edited by: Dave Baxter
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Old 10-25-2011, 12:07 PM   #12
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Thanks everyone, for the responses.


Although much of the work has been done already (another builder started the project) my inclination at this point is to make some changes to simplify the design. Primarily the Duster will be used for local and acro flights, with the occasional cross country in which the capacity of both tanks will be required.


Having the wing tank feed directly into the fuse tank only, seems to fit with my goal of keeping it as simple and light as possible.


Dave -


I have the "Building the Duster" book and know of two of the design options they suggest, but would like to see that schematic you mentioned. Also, talk about fuel and vent line sizing and gascolator location. I'll PM you.


Thanks again, guys.

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Old 03-14-2012, 05:07 PM   #13
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I'm planning on plumbing my wing tank the simple way, straight to the main tank.
Instead of a manual switch, I'm using a Solenoid shut-off valve (http://www.aircraftspruce.com/catalo...lsolprimer.php)

The solenoid will be operated by a red guarded switch.

Drain the main down enough to accept the 9 gals from the wing tank, open the red guard, flip the switch and wait for it to drain into the main.

This also keeps from running more fuel lines to the aft cockpit.

Simple, easy plumbing. Anyone see any problems with this?

Thanks


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Old 03-14-2012, 05:27 PM   #14
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I really like your idea!!!! I'm going to get a solenoid!!!

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Old 03-14-2012, 06:05 PM   #15
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Quote:
Originally Posted by StinsonPilot
Instead of a manual switch, I'm using a Solenoid shut-off valve (http://www.aircraftspruce.com/catalo...lsolprimer.php)
Although I like the idea of an electric solenoid valve for filling the bottom tank, the one you have linked only has a 1/8" orifice. How fast is that going to flow?

Also, ACS does not specify the duty rating of that solenoid. How long can it stay energized?
Edited by: cashflyer
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Old 03-14-2012, 06:25 PM   #16
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I like that. On the aux tanks we build we restrict them through a no.30 hole in a special restrictive fitting we make. It takes about 45 mins to pump out 15 gal.

Although now that I think about it, that's being pumped. Flowing only by gravity there should be a good vent and maybe a bigger orifice in the solonoid.Edited by: smizo

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Old 03-14-2012, 07:31 PM   #17
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Ok... I gave this some more consideration. I looked over some physics references and got out the calculator.

With no other restrictions, a 1/8" orifice will flow about 2.45 gpm. So transferring a 9 gallon tank should take ~ 3.7 minutes, and a 15 gallon tank should take ~ 6.2 minutes. Line friction will increase the time required.

Putting a pump on this system does not change the flow (Boyle's Law) but does ensure positive flow. Either way, the tank must be properly vented to allow air in as fuel flows out.

If your fuel burn is around 15 GPH (or .25 GPM) the flow through the 1/8" orifice is faster than your burn, and should be safe.

The other question I cannot find an answer to... is the solenoid rated to be energized that long. I guess worst case scenario would be that it overheats and quits. Or sets something on fire.


[edited to correct numbers]

Edited by: cashflyer
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Old 03-14-2012, 07:43 PM   #18
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Two comments;
1) Given no fuelgaugein the aux tank -- I'd want enough flow to see the fuel level rise in the main tank. It's the only indication you'll have that things are happening as they should.
2) An 1/8"orifice is more likely to become clogged than a larger one. If it is partially clogged the fuel burn mayexceed the flow rate through the orifice. If it is completely clogged, the slow normal delivery ratewill mask the problem.
I'd want a bunch of flow, 1/4" sounds about right to me. No need to get too clever here.

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Old 03-14-2012, 08:16 PM   #19
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Not real smart here but at 2.5 gpm... 9 gallons that's like 3.6minutes?

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Old 03-14-2012, 09:25 PM   #20
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Quote:
Originally Posted by wminear
Not real smart here but at 2.5 gpm... 9 gallons that's like 3.6minutes?
Yeah.... my / button is right next to my * button. [img]smileys/smiley11.gif[/img]
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Old 03-14-2012, 10:02 PM   #21
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I came up with .3521 gpm. That would be about 25 minutes.
That's 21.165 gph. My engine burns around 10 gph.

Using this: http://www.pumpcalcs.com/calculators/view/103/

Diameter of .125
Pressure: .65 head pressure (figured 1 1/2' vertical drop)
Specific Gravity: .77 for 100LL
Orifice constant: .82

I'm not this smart, I'm at work and had some help from a very sharp Aeronautical Engineer [img]smileys/smiley2.gif[/img]

I think I'm with you Bill, a little larger orifice for more flow would be nice.

If anyone comes up with a larger solenoid, let us know.



Edited by: StinsonPilot
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Old 03-14-2012, 10:36 PM   #22
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See what you think about this one: http://www.dan-marcrvparts.com/12vomufushof.html

.6502 gpm for 9 gals would be about 13 minutes.
39 gph.

And this one has 1/4" orifice: http://store.dan-marcrvparts.com/12vo1ormupus2.html

1.4027 fpm aor 9 gals would be about 6 1/2 minutes.
84 gph.




Edited by: StinsonPilot
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Old 03-15-2012, 01:38 AM   #23
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Now that I've thought about it, my inlet to the tank is the pressure carb return line that's not being used. It's a 1/8" NPT, so looks like I'm stuck with that.
With the numbers above, should work for me.


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Old 03-15-2012, 02:39 AM   #24
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After taking in all the good advice, from here and elsewhere, I decided to make the fuel system as simple as possible. I removed one of two selector valves and a few unnecessary lines and this is what I have now:


I changed to a four position selector valve which points up to feed the engine from the wing tank, inboard to feed from the fuse tank, down to feed from the acro sump and outboard for Off.


I suspect no more than 5% of my flying will require filling the wing tank and simplicity won out over all other concerns so this seems like the best compromise for me.

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Old 03-15-2012, 02:52 AM   #25
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This is the way bo[img]file:///C:/Data/Pictures/Scans/DSC06759small.JPG[/img]th of ours are plumbed. Dave



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