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Inverter fuel system - header tank required?

agent4573

Well Known Member
I've read a lot about the mods most people do to the wing tanks for flop tubes/barn door baffle/etc. Has anyone had issues with this type of pickup that warrants building a header tank into the system as well? Thanks.
 
Forget the header tank. They are used in certain aerobatic planes to ensure fuel delivery at low fuel quantities as are often preferable when flying acro displays/airshows/competition sequences. Rather than having a flop tube flopping around in a large tank, you have a flop tube flopping around in a small tank which allows (negative G) acro ops with much lower fuel quantities without sucking air. Fuel injection alone will deliver fuel for quite a few seconds, flop tube or not, so for lazy loop and roll RV acro, it makes no sense to consider a header "acro" tank.
 
Header tank

I am going to put a header thank in RV4 original battery location rather than tear into a perfectly fine tanks to put in a flop tube . When inverted I will be highest part ( almost ) of the plane . Fuel line runs thru that area already and will be plenty large enough and custom welded so mounting is easliy handled . Maybe 3 lbs ...
 
I vote NO on the header.

The standard flop tube in the wing tank with a barn door in the baffle works just fine. I have no problem with inverted flight even down to three gallons in the tank.
 
The standard flop tube in the wing tank with a barn door in the baffle works just fine. I have no problem with inverted flight even down to three gallons in the tank.

Good to hear. Sounds like it's one or the other, both flop tube and header tank is overkill.
 
The standard flop tube in the wing tank with a barn door in the baffle works just fine. I have no problem with inverted flight even down to three gallons in the tank.

I am planning to convert my O-360 to FI with an airflow performance system. In the installation manual, there are severe warnings about air in the fuel.

So with a floppy tube in the wing tank, there will sometimes be some air in the fuel. Just consider flying 0G for some seconds, with only 5 liters in the tank.

So, what HAPPENS when some air is sucked into the fuel line? Some rough running or does the engine shut down completely?

Same when running empty in one wing - if you switch over to the other tank when you notice you are running dry, will the engine recover like it does with a carburetor, or will something worse happen?

Not being able to run a tank dry would substantially increase the minimum volume you can fly on.

I am changing to FI for acro flying, so please advice if it will work fine, else I will save my money.

Ron - you are writing "barn door in baffle". Sry I donot understand that, what does it mean?

//HR
 
I am planning to convert my O-360 to FI with an airflow performance system. In the installation manual, there are severe warnings about air in the fuel.

So with a floppy tube in the wing tank, there will sometimes be some air in the fuel. Just consider flying 0G for some seconds, with only 5 liters in the tank.

So, what HAPPENS when some air is sucked into the fuel line? Some rough running or does the engine shut down completely?

Same when running empty in one wing - if you switch over to the other tank when you notice you are running dry, will the engine recover like it does with a carburetor, or will something worse happen?

Not being able to run a tank dry would substantially increase the minimum volume you can fly on.

I am changing to FI for acro flying, so please advice if it will work fine, else I will save my money.

Ron - you are writing "barn door in baffle". Sry I donot understand that, what does it mean?

//HR

Anyone that can help me with my questions?
 
Anyone that can help me with my questions?

Hi Hans,

I flew my RV-8 with the same airflow performance FI. Yes, you will occasionally get air in the fuel line but the FI is seldom stumbles with a small amount of ingested air. I have run a tank dry on many occasions, usually on purpose. If you watch your fuel pressure while approaching empty you can see a decrease in pressure and quickly turn on the electric fuel pump and switch tanks before the engine stumbles. If you don't catch it, don't worry, the engine will start right back up when the FI purges all the air and starts feeding from the full tank.

I never noticed any engine stumbling while doing acro. I used a flop tube and always kept the electric pump on while doing aerobatics.

The "barn door" is just a small hinged door in the inboard tank rib that opens to allow fuel to flow towards the fuel pickup and closes when fuel tries to flow towards the wing tip.
 
Hi Hans,

The "barn door" is just a small hinged door in the inboard tank rib that opens to allow fuel to flow towards the fuel pickup and closes when fuel tries to flow towards the wing tip.

Thanks Ron.
Sound like it is possible to do w/o an acro tank.
The barn door sounds smart, making sure fuel stays close to the pickup
I haven't yet removed the tank (and I have not built the plane) so I do not know how it looks like, but I guess the barn door would require to cut the tank open, mount the barn door and then weld it together again.

Can you do four point or slow rolls both ways w/o problem?
 
Thanks Ron.
Sound like it is possible to do w/o an acro tank.
The barn door sounds smart, making sure fuel stays close to the pickup
I haven't yet removed the tank (and I have not built the plane) so I do not know how it looks like, but I guess the barn door would require to cut the tank open, mount the barn door and then weld it together again.

Can you do four point or slow rolls both ways w/o problem?

No need for an acro tank.

If you happen to be into your tank for some other reason it would be a good idea to put a door in the rib. I wouldn't open up the tank just to do that. With a tank at least 1/3 full I doubt you would ever uncover the fuel pickup long enough to notice unless you were doing extended knife edge flight or slip with the tank on the down wing selected.

Yes you can do 4-points and slow rolls in both directions. No problems.
 
Hmmm I fly acro with just a couple of gallons to keep weight down.

I typically start a practice session with 6 or 7 gallons in each tank but have started with more than that with little noticeable difference. I'm sure I have run a tank down to 3 gallons or so many times with no issues.
 
I typically start a practice session with 6 or 7 gallons in each tank but have started with more than that with little noticeable difference. I'm sure I have run a tank down to 3 gallons or so many times with no issues.

Thx Ron.
But that's with the "barn door".

I guess I will just have to try.
 
Extra fuel

How big of a header tank are we talking about? There's tons of options for extra fuel capacity. Wing tip tanks, outboard leading edge tanks, race car tanks in the passenger seat, etc. A 4 gal header tank is ~30 minutes of fuel (depending on engine and power setting).
 
A typical Sportsman sequence doesn't have any sustained knife edge flight. I don't think you will have any issues even without the door.

Let's say a four point roll, wrong direction, then it will suck air during the 90 degree stop. Would that not be a problem?
I think a barn door will be needed, would do you reckon?
 
Thanks Ron.
Sound like it is possible to do w/o an acro tank.
The barn door sounds smart, making sure fuel stays close to the pickup
I haven't yet removed the tank (and I have not built the plane) so I do not know how it looks like, but I guess the barn door would require to cut the tank open, mount the barn door and then weld it together again.

Can you do four point or slow rolls both ways w/o problem?

These tanks aren’t welded.. they are riveted and sealed with a sealant. You shouldn’t weld on 2024 aluminum..
 
These tanks aren’t welded.. they are riveted and sealed with a sealant. You shouldn’t weld on 2024 aluminum..

Thx for advise. As you understand, I have not built my RV-8.
I guess then the tank roof and floor is the skin of the wing? Might make it more difficult. Can I access the tank to even mount the floppy w/o removing the wing?

Found this website showing a design of a trapdoor to keep fuel close to the floppy. http://jtsrv8project.blogspot.com/2007/09/inverted-flight-fuel-tank-mod-pt2.html
 
Thx for advise. As you understand, I have not built my RV-8.
I guess then the tank roof and floor is the skin of the wing? Might make it more difficult. Can I access the tank to even mount the floppy w/o removing the wing?

Found this website showing a design of a trapdoor to keep fuel close to the floppy. http://jtsrv8project.blogspot.com/2007/09/inverted-flight-fuel-tank-mod-pt2.html

Removing a tank is not too difficult and can be done in a few hours. Remove the wing fairing and all the #8 screws around the tank perimeter. Remove the bolt attaching the nose of the tank to the fuselage fitting as well as the fuel pickup and vent lines and the wire to the fuel level sender.
Remove the wing access panels from the bottom of the wing and then remove 21 AN-3 bolts that secure the Z-brackets on the back of the tank from the spar. (There are seven Z-brackets with three screws in each. You will do some of these by feel alone so count the bolts and make sure you get all of them!) Many people paint over all the #8 screws on the tank skin so that may make it difficult to remove these. There is a tool that scores the paint around these screws which makes the job a bit easier and does less damage to the paint. I painted my tanks separately from the wing and never painted the screws. Best decision I ever made!

I would leave this project alone until after Christmas as you don't want to spoil the holiday with profanity and busted knuckles. Merry Christmas.
 
ronschreck;1488507 I would leave this project alone until after Christmas as you don't want to spoil the holiday with profanity and busted knuckles. Merry Christmas.[/QUOTE said:
Thx Ron for a very detailed description!

I will wait with the tank until I have the FI installed.

However, here in Sweden we have ****ty flying weather october - jan, so I dont even have it insured, so it is a very good period for some work.

The pic of the trap door, is it about your barn door design?
 
Yes. You should put a tab on the door to make sure it can't open more than 90-degrees so it closes easily when fuel tries to flow back through the opening.

I wiil be attending an EAA sheet metal course. This might be a use case for the course!
 
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