Fuel System Ideas

[stretchedpacer]

Since I am building an experimental stretched pacer I have the opportunity to deviate from the traditional pacer/tri-pacer fuel system. Not sure I want to deviate from the known quantity but thought I would see what others have done in this department.
My concern is the that there is no header tank in this plane which seems to present a problem in some situations. I have yet to see anyone add a header tank of any sort but many other pipers of similar vintage seem to have them. Basically, this is an area I simply do not know but, if I can improve the safety of the plane I would sure like to incorporate any changes time has shown to be a good idea. Thanks for any input.

Brad

[pistoncan]

Brad,
Like you, I have been looking into the fuel tank system and have talked to a few guys building wagabonds. From what I can asertain, the header tank was eliminated in the compromise to install yokes instead of sticks in the later PA20's Most of the wagabond guys are doing a header tank of some kind, but a trimmer type rerouteing is also an option. From what I can see, a header tank is the simplest way to go if you are using sticks and want to eliminate the need to use a certain tank for certain manovers Gary, topsaddle at first-comm.net

[Gilbert Pierce]

I removed the header tank from my Clipper. Left the fuel tank selector valve in the middle of the firewall where it was originally in the Clipper.
I then plumbed the new right wing tank rear outlet down the rear of the front door post like the Pacer to a gascolator under the right seat then up the right side of the boot cowl to the firewall. Across the firewall to the fuel selector valve. The right tank front outlet comes down the right front windshield post ala Pacer and tees into the rear outlet just in front of the front door post.

After completeing this I put 1 gallon of gas in the right wing and 10 gallons in the left wing, took off on the left wing. I switched to the right wing tank, did steep turns, stalls, steep climbs etc. until the engine quit. Switched back to the left tank and landed. I drained about a pint of fuel out of the right tank.
As far as I am concerned the problem with the right is solved in my airplane.

[stretchedpacer]

Thanks for the info guys.

Gilbert,

It appears that you used 1/2 inch fuel lines in your plane. Am I seeing that correctly?

As for the right wing tank problem, I thought pacers and tripacers had that problem even though they have the setup you described. I have to admit that this is an area I know very little about. The real problem I am trying to avoid is the problems I am told about with the right tank and steep turns. Thanks again for the input.

Brad

[Gilbert Pierce]

Brad,
All of the fuel lines are 3/8".
The Pacers and T-P that came from factory with right wing tanks had a convoluted fuel plumbing system that ran to the tank selector valve that is on the left side under the window, just about the pilots left knee. In my opinion that is the problem. The fuel line from right tank runs up and behind the instrument panel over to the left hand fuel selector valve and then down to the gascolator. See drawing #12708 on the Short Wing Piper drawing CD.

With my fuel selector valve on the tubing behind the firewall the distance is shorter, it does not rise as high as it does not go above the bottom of the instrument panel and there are less restrictions caused by fittings.

Steep turns with the right tank below 1/3 and selected are no problem as long as the turns are coordinated.

[Glen Geller]

Aw geez you mean we gotta make coordinated turns? What fun is that?
Actually, I wonder if a strong slip (to left or right) on final with your setup under <1/3 right tank would still be safe and satisfactory?

[Gilbert Pierce]

Glen
Since I don't have any of those high tech speed reducing lift enhancing flaps I frequently slip on landing. I fly off a 2700' grass strip with 50' trees on one end. I delight in showing the UL guys how to land and make a 750' from the end of the runway turn-off which most of them can't do. I usually don't pay attention to which tank I land on or how much fuel is in it but you bring up an interesting point. Never had an engine sputter while slipping but you are only in the slip for maybe 10 seconds max.

After I return from Sun'N Fun I will do some tests with uncoordinated turns and see what happens with the right tank.

[Bultaco Jim]

Those pictures really are great Gilbert. A lot of people are enjoying/using them, I'll bet! Piper should have done it that way, even with yokes.

[Hillbilly]

I'm going to solve the right wing limitations with a fuel pump from a Saturn V rocket engine, those things burn 11,000 pounds per second ...Think that will be enough? :shock:

[Gilbert Pierce]

I don't suppose you have given any thought as to how your are going to power that pump?

[Hillbilly]

I don't suppose you have given any thought as to how your are going to power that pump?

C'mon Gilbert tsk Why nuclear reactor of course....

[Bultaco Jim]

Sounds like that reactor might run my Shuttle Flight Computer, which arrived today, by the way. Send installation instructions please.

[Hillbilly]

Sounds like that reactor might run my Shuttle Flight Computer, which arrived today, by the way. Send installation instructions please.

Just go to housewares at your local Wal-Mart and look for the Black and Decker "Mr Fusion" ...instructions included,
Plutonium 237 available by special order and 3 box tops...

[Bultaco Jim]

Sounds like too much work. I'll just add another fusible link to the old Gill. Hope this works-- as it is, the GPS dims when I fire up the Hot tub!

[Hillbilly]

Sounds like too much work. I'll just add another fusible link to the old Gill. Hope this works-- as it is, the GPS dims when I fire up the Hot tub!


...........BWAHAHAHAHAHAHA!

[Glen Geller]

Sounds like too much work. I'll just add another fusible link to the old Gill. Hope this works-- as it is, the GPS dims when I fire up the Hot tub!
I was just reading about saving weight by changing a few brass weatherhead fittings to aluminum aircraft fittings, sounds like you might want to consider it.
It made all the difference when we plumbed in the beer taps!

[Bultaco Jim]

Let's see, Hot tub---beer taps. Hot tub----beertaps. Hot tub----beer taps. ....OK, you win!

[Glen Geller]

Y'know, with a 180hp upgrade, you can carry both! Nothin's too good for us Shortwingerers!

[Bultaco Jim]

No, I've been thinking the hot tub takes up too much space. Plus, I can only stand it for aprox. 30 minutes, but Beer Taps! Usable for the entire flight!

[Glen Geller]

Ain't it stimulating when giant intellects get together?

[Bultaco Jim]

I'm sure that these conversations go on every day in the White House.

[Glen Geller]

Not for much longer they won't....

[RonJones]

Hey guy;s we have converted several short wing planes with longer fuselage/wing combinations and feel comfortable solving the fuel feed by using a 4-port selector valve allowing a "both on" position for take off or landing. Same solution as Cessna and others eliminating the need for a header tank for slips or any unusual attitudes, (except for pilot).

[stretchedpacer]

Ron,

Thanks for the information. I was thinking the four port valve would make the best option. Do you have any pics of the fuel line routing or did you just follow the stock routing? Thanks again.

Brad

[Stephen]

Hey guy;s we have converted several short wing planes with longer fuselage/wing combinations and feel comfortable solving the fuel feed by using a 4-port selector valve allowing a "both on" position for take off or landing. Same solution as Cessna and others eliminating the need for a header tank for slips or any unusual attitudes, (except for pilot).

In your conversion, can you join the front and rear fuel line ports from the tank in the wing root and only have one line coming down the front of the door?

[stretchedpacer]

I thought I would go ahead and dredge this thread back up as I got the bulk of the fuel system temporarily installed tonight. My goal here is to post some info that someone in the future (doing an experimental like me) might find useful.
So here is the deal. I used a slightly modified Maule system (which is similar to eddie trimmer's system). I had to add a few brackets which I have attached a picture of. I am not crazy about the fact the fuel system sends the fuel down and then back up to the selector valve but in researching the matter I have been surprised by the number of systems that do almost the exact same thing. All of the fuel lines in the pictures are 3/8 aluminum fuel line for what its worth. Regular aluminum AN fittings. The low points below the seat both have safeair drains. None of the clamps are installed and the line from the selector valve to the gascolator on the firewall has not been installed. Trimmer uses 1/2 inch line. Not sure what I will do. I cant fathom that the fuel flow actually increases with the 1/2 inch line since the valve restricts the flow but I will do some more research before putting that line in (and before purchasing the gascolator which need to fit that line).Certainly I would love to hear from anyone with hard data on that subject. At the end of the day, fuel flow testing will give the answer regarding whether I can supply enough fuel to the engine with this system. Please feel free to post any questions.

Brad

[taildraggerpilot]

According to Trimmer's drawing, the line from the valve to the gascolator uses a 3/8 in. dia. line. His prototype pictured on his website is a 1/2 in. dia. line.

[Steve Pierce]

I know Steve Pankonin with Steve's Aircraft used 1/2" lines on his first 180 hp Pacer to eliminate the need for mechanical and electric fuel pumps to meet the fuel feed requirements. The 180 hp Super Cubs use a pressure vented fuel cap and meet the requirements with 3/8" fuel lines. Maybe Steve or Brian will comment on what they did.

[taildraggerpilot]

I should also note Trimmer's mod also uses pressure vented caps with his system to attain the required flow. This system was developed to allow installation of 180 hp engines on shortwings without the need for fuel pumps as well.

[Steve@StevesAircraft]

Fuel systems are designed based on horsepower and "minimum" fuel flows. The basic routing is critical in the sense of everything arriving at the selection point with the least amount of head pressure loss. The testing position of the system is with a nose high attitude of 15 degrees. The testing outlet for gravity feed is 19 inches above the carburetor. That represents 1/2 standard atmosphere pressure, and is about equal in height to the fuel tank outlet on the Pacer. Pressure systems are tested at the fuel pump outlet. The amount of fuel flow required depends on the engine horsepower using a formula of 1/2 lb per hrsp per hour + 150%. That means for a 180 hrsp. 1/2 lb per hrsp = 90 lbs / 6 = 15 + 150% = 37.5 gal per hr. minimum fuel flow for gravity systems. (125% for pump systems) I hope my engine does not burn that much fuel in an hour. Now to get there, factors such as fuel line sizing, and routing come into play. The original Pacer system of 3/8 lines will run up to 160 hrsp, but falls short for the 180 hrsp. Now one must keep in mind that we are not talking about enough fuel to run the engine with the head pressure of full tanks, but the minimum head pressure of minimum fuel where the FAA test such things. Eddie's system of coupling both tanks head pressure with 3/8 lines with a "both" out with 1/2 inch line will allow the minimum flow rate to feed 180 hrsp. I do not currently know if his STC has an "unusable" associated with it, but my suspicions are there is one. On our 180 / constant speed STC with 3/8 lines, the unusable is 2 gals with fuel pumps. On my 180 Pacer with 1/2 lines and gravity feed, the unusable is 3 gals. Now, the "unusable" is the amount of fuel required to fill a completely empty system to get to minimum fuel flow. That is supposed to be enough fuel to get you around the patch if you blow your landing. The "unusable" is quite "usable" in level flight. As far as the fuel cap tubes are concerned, there is no regulation requiring a positive input pressure that I am aware of. The standard vent caps are still used on our Pacer's 180/constant speed STC. However, there is a stickler that whenever you use a "both" position, the fuel tanks have to be vented together. Now, even though I could not get away with it on my 180 Pacer with gravity feed, Eddie may have been able to circumvent that requirement with the pressure tubes on the caps.
I hope this sheds some light on basic requirements.

Steve

[stretchedpacer]

Wow. Thanks for the info steve. Once I get the wings built I will certainly have to do a fuel flow test to see where this system ends up. Tried to stay with the maule/trimmer setup with a minor variation in which side of the valve the fuel goes into (which alters the plumbing down by the sumps a bit). Once I test it I will post whether it meets the requirements (or whether I get to take another crack at it) and what the actual flow is. If I can figure the unusable fuel I will post that as well. I am hoping to get away with not using the forward vented caps but that may be unavoidable. Thanks again for the great information.

Brad

As a post script -

In my previous post I said there were three brackets added to enable me to add the extra plumbing. That was incorrect. I added a fourth bracket (visible on the far left of the bracket's picture). Its just a simple blade of .063 chromoly so that I can adel clamp both fuel lines and a ferrul for the cable to help keep the cables from rubbing the lines if they get slack.

[Curly]

One thing I am constantly amazed by on this site is the generosity of those who post.

The wealth of information from years of experience and experimentation, that is readily shared (i.e. Steve's previous post on fuel systems) by those contributors is truly amazing.

In a lot of cases these people earn their bread and butter from the information they freely share, and it could be conceivable that they are doing themselves out of part of their income - this makes the generosity even more remarkable.

I have learnt so much about Shortwings, engines and aeroplanes generally, in the short time I have been reading this and the SWPC site and hope one day to get the opportunity to personally say "thank you'.

I was going to list them here, but I am afraid I might miss someone out, so to all of you, for so generously sharing your knowledge - my heartfelt thanks!

Curly

[longpacer]

I have a “both” fuel position in my experimental Pacer and I like it a lot. I used a standard valve that was drilled it out, and I have a vent line connecting the two tanks. But here is one feature that I didn’t anticipate. On a flight of several hours, the engine will draw more fuel from the left tank than the right tank. It would not be unusual for me to see 1/4 on the left fuel gage and 3/4 on the right gage after a couple hours of flying. This is a bigger differential than I have seen when flying Cessnas or other planes with a “both” fuel system, and it is consistently the left tank that is lower. I have the 30 gal Dodge tanks, but I don’t think that is a factor. I also don’t seem to be flying with a wing down or uncoordinated.

Instead, I think problem is due to the unequal lengths of the lines running to the fuel valve. The path of the right fuel line goes up and across the back of the panel, making it perhaps four feet longer than the fuel line on the left side. This extra length is added resistance to the flow of fuel, and I suspect it causes differential consumption.

Eddie Trimmer’s STC that routes the right side fuel line directly to the valve would reduce this effect, although there would still be some differential. Another approach would be to use 1/2 inch lines from the right side to reduce the flow resistance and allow more equal fuel draws from the tanks.

In practice, of course, it’s not a big deal because you can just switch to the right tank for a while to even out the fuel consumption. But it is an interesting quirk of the “both” system in a Pacer.

Bob

[paulgagnon59]

Fuel systems are designed based on horsepower and "minimum" fuel flows. The basic routing is critical in the sense of everything arriving at the selection point with the least amount of head pressure loss. The testing position of the system is with a nose high attitude of 15 degrees. The testing outlet for gravity feed is 19 inches above the carburetor. That represents 1/2 standard atmosphere pressure, and is about equal in height to the fuel tank outlet on the Pacer. Pressure systems are tested at the fuel pump outlet. The amount of fuel flow required depends on the engine horsepower using a formula of 1/2 lb per hrsp per hour + 150%. That means for a 180 hrsp. 1/2 lb per hrsp = 90 lbs / 6 = 15 + 150% = 37.5 gal per hr. minimum fuel flow for gravity systems. (125% for pump systems) I hope my engine does not burn that much fuel in an hour. Now to get there, factors such as fuel line sizing, and routing come into play. The original Pacer system of 3/8 lines will run up to 160 hrsp, but falls short for the 180 hrsp. Now one must keep in mind that we are not talking about enough fuel to run the engine with the head pressure of full tanks, but the minimum head pressure of minimum fuel where the FAA test such things. Eddie's system of coupling both tanks head pressure with 3/8 lines with a "both" out with 1/2 inch line will allow the minimum flow rate to feed 180 hrsp. I do not currently know if his STC has an "unusable" associated with it, but my suspicions are there is one. On our 180 / constant speed STC with 3/8 lines, the unusable is 2 gals with fuel pumps. On my 180 Pacer with 1/2 lines and gravity feed, the unusable is 3 gals. Now, the "unusable" is the amount of fuel required to fill a completely empty system to get to minimum fuel flow. That is supposed to be enough fuel to get you around the patch if you blow your landing. The "unusable" is quite "usable" in level flight. As far as the fuel cap tubes are concerned, there is no regulation requiring a positive input pressure that I am aware of. The standard vent caps are still used on our Pacer's 180/constant speed STC. However, there is a stickler that whenever you use a "both" position, the fuel tanks have to be vented together. Now, even though I could not get away with it on my 180 Pacer with gravity feed, Eddie may have been able to circumvent that requirement with the pressure tubes on the caps.
I hope this sheds some light on basic requirements.

Steve


Steve

can you confirm the math on fuel flow?
do you add 150% or multiply by 150%?.

eg..
160 hp
O320 14 us gal/hr max fuel flow at sea level....required ..
FAA wants 150% of that required to be available to carb?
14x150%=21us gal/hr

so on your formula ....160 hp engine
160x.5=80
80/6=13us gal/hr x 150%= 20 Gal/hr. required fuel flow....makes sense.

If we add 150% we get.... 32.5Gal/hr?.??
My pacer produces 33.82gal/hr at the carb gravity feed from left tank.....less on right tank...with standard 3/8 inch lines and standard fuel selector

20 us gal/hr at carb seems more reasonable ?

thanks again for you informative posts .......we all benefit

[Steve Pierce]

I got this in a "Report Post" email but I think it was meant to be posted here. Steve Pankonin, can you comment?


Steve

Good day

I was reading your post on fuel flows of 2008.
Can you confirm for me the math?

1/2 hp divided by 6 times 150%= required fuel flow for engine

In your post you have plus 150% not times?

Please correct my math

O320 sea level max fuel flow 14 us gal/hr
Need flow of at least 150% of that number for the FAA..

14x150%=21
21us gal/hr rate required?.....

In your example it would be 35gal/hr

I am just trying to confirm the numbers and make sure I am doing it correctly

Thank you for your posts
Very informative

Cheers

Paul Gagnon

[stevesaircraft(Bri)]

I got this in a "Report Post" email but I think it was meant to be posted here. Steve Pankonin, can you comment?

Guys, We cant figure out dads password so I logged in for him to comment.....
Steve is following after this line.....


The math can be screwed up real quick with the wrong sign. It is supposed to be X (times) 150%, not + (plus) 150%. My apologies. The actual regulations are basically the same between CAR3 and 23.955. As written in 23.955 (b) Gravity Systems. The flow rate for gravity systems (main and reserve supply)must be 150 percent of the takeoff fuel consumption of the engine. (c) Pump Systems. The fuel flow rate for each pump system ( main and reserve supply ) for each reciprocating engine must be 125 percent of the fuel flow required by the engine at the maximum takeoff power approved under this part. In reality, 50% more on gravity feed systems and 25% more on pump systems. While in a coversation, I usually say, 1/2 lb. per horespower per hour plus 50%. So a 180 divided by 2 = 90 divided by 6 ( gal weight ) =15 gal takeoff fuel flow. Regs require 150% so that needs to be times not plus which equals 22.5. Not the plus of 37.5 gals. I stand corrected.

Steve