Jason builds a plane

Fuel tanks part 1

15/1/2022

0 Comments

 
Fuel lines and fittings have arrived.  Stainless braided Auto-Flex line and Swivel Seal fittings.  Expensive but the peace of mind this provides is worth it.  This is one area of the plane I refuse to compromise on.  Very impressed with the quality of Earl's Performance products.  With these in hand I can start laying out the fuel tank plumbing. 
Picture

I've been wanting to figure out a way to measure the fuel level in the tank that requires no internal sensor - less holes in the tank means less chance for leaks.  There are several stories on the builders forums about tank sensors mounted through the sides of the tank leaking or being terribly inaccurate, hard to service and generally failing.

I wondered if there was a better way, and I originally came up with the following.  A very sensitive presssure transducer (the chrome unit with yellow label below) that will measure the "head" pressure of fuel in the tank via a "T" in the fuel line next to the tank.  In theory this should work using an Arduino microcontroller to read the sensor and output a value to a gauge.  Here is the assembly mocked up on the bench.  From right to left - finger strainer (inside the fuel tank), tank fitting (through wall of tank), threaded adapter, threaded "T", coupler and pressure sensor), fuel line fitting elbow.
Picture

Testing of the system has proven difficult.  I've been unable to get consistent readings from the sensor in a static set-up.  The programming of the Arduino works fine, I'm just not happy with the accuracy of the output due to the very low spread between empty tank head pressure and full tank head pressure, which given the depth of the tank is about 1.5 PSI.  I'd hoped a programming algorithm within the Arduino to amplify the input values and stabilize the readings would work, but it's become too much of a tail chase to get it right.  From there I'd still need to figure out how to smooth the values to account for changes in atmospheric pressure (fuel changes "weight" with changes in altitude) and aircraft attitude - banking towards the sensor increases head pressure, banking away reduces head pressure.

In an effort to focus on the build getting moved forward, I've decided to abandon this concept in favour of a top mounted float sensor.  Yes, this means another hole in the tank, but if mounted from the top, the risks of leaks is minimized and the ability to service the sensor if needed is much easier.  More on this later.

So removing the pressure transducer from the fuel line leaves just the tank strainer, the tank fitting and the elbow.  I'll need to order the fitting that goes between them, but they are inexpensive and easy to obtain.
Picture

The tank fitting is a one direction NPT thread.  This picture shows the fitting as it looks from the outside of the tank.
Picture

These fittings were gifted to me by another builder.  They are actually the larger style, so I need to modify them slightly to fit the tank side rib so the strainer sits nearest to the bottom of the tank as possible.  Trimmed them using the bandsaw, then cleaned them on up the disc sander.
Picture

The smaller diameter of the fitting needs to fit through the tank rib from the inside.  I don't have a drill bit this size to make the hole, so I had to improvise.
Picture

I confirmed the fitting was trimmed enough by laying in on the outer face of the tank rib:
Picture

I drilled a pilot hole equivalent to where the centre of the fuel strainer will be on the tank:
Picture

Used a large step bit to create the general shape of the hole almost up to full size in the tank rib:
Picture

Laid the fitting centred over the hole on the tank side of the rib and traced the final size/shape:
Picture
Picture

Clamped the rib to the bench elevated on some blocks, then used the Dremel tool with spiral cutting bit to carefully bring the hole close to size using the trace lines as my guide:
Picture

Filed the hole to final size to ensure a tight fit:
Picture

Here is the fitting in it's final position looking from the inside of the tank rib.
Picture
Picture

​On the outside of the rib, the fit is really good:
Picture

​With the finger strainer in place
Picture
Picture

Bending the tank skins can be tricky.  It is paramount to ensure the bends are as tight as possible to the corners of the tank ribs to reduce any gaps that will need to be filled when the tanks are welded.

I wrapped and finger clamped one of the ribs with the seamstress measuring tape (very handy long ruler for any project) to get a general measurement of where the corners of the tank skin will be.  This picture is of the second tank taken later in the day (left tank had already been through this process and I forgot to get a picture for the blog):
Picture
Picture

The throat depth of the wide bender isn't deep enough to get to the middle tank skin bends, so I needed to use the heavy bender. To allow full access we moved it out into the open floor area, rather than roll up the paint booth curtain (Ron is painting currently).
Picture

First I laid out the 025 skin and marked the approximate location of the first bend.  Like the slat skins, order of bending is important here, working from middle out to ends. I've left the skin a bit long at each end to make sure it doesn't come up short once it is bent to shape:
Picture

The heavy bender allows for material to pass through, giving full access to the middle of the sheet:
Picture
Picture

First bend complete, next was measuring the second bend closely to make the corners tight
Picture

Finger clamped the ribs in position to get a good measurement where the next bend would be:
Picture

Second bend line laid out (note the little circled "2" I used to remind me of the bend order):
Picture

Back on the bench, I discovered the second bend was slightly overbent and the process on the bender had opened up the first bend as well....  I corrected both before moving forward, but swapped the bend order on the second tank which prevented this from happening again.
Picture

Left tank skin rear corners corrected and test fit shows good:
Picture
Picture

Marked out the location of the fuel filler neck:
Picture

Front side of the tank skin bent up to meet the top skin and close off the tank:
Picture

The front side of the tank skin needs to have a 5mm flange bent forwards to create the seam for welding.  I puposely waited to bend this flange as I didn't know where the bend would be until I mocked up the tank:
Picture

I tipped the tank forward on its nose and clamped the forward tank skin onto a piece of aluminum angle at the bench edge:
Picture
Picture

Using a deadblow hammer I caefully bent the 5mm flange forwards to match the top corners of the tank ribs:
Picture
Picture
Picture
Picture

Reassemble the tank and use Cleco vise clamps to hold it together.  Some final tweaking of the rib flanges squares it all up - very happy with the final shape!  The extra material overhang on the top side of the skin will be trimmed back to match the flange.
Picture
Picture

Marked out the fuel tank drain location which is directly below the fuel line fitting.  This is the lowest spot in the tank once it is mounted in the wing.  It is from here that fuel is drawn during pre-flight to check for contaminants such as debris or water:
Picture

The right wing tank went faster now that I have the benefit of a process from the first.  Fuel outlets are on the opposite side of the left tank (the face inwards towards the fuselage:
Picture

I drilled and sized the fuel line fitting for the right tank after creating the tank so we could move the bender back out of the way.  The process for the fitting was the exact same as the left wing, just the opposite side of the tank:
Picture

Picture of the top front of the left wing tank.  I've laid out the location of the top mount fuel tank sensor and the fuel filler neck.
Picture

Both tanks clamped together, resting on top of the wing and awaiting parts for the fuel filler neck and fuel level sensor.  These will be fitted before final weld-up.
Picture
Picture

Very pleased at how the tank assemblies turned out, hopefully welding and subsequent leak testing goes as well.  Getting ready to order the fuel filler necks, fuel caps and the parts needed for the fuel level float sensors.

This doesn't fit under either the engine or avionics category, I guess it is part of the wings?  Maybe under other......

Thanks for following along, stay tuned for more.
0 Comments



Leave a Reply.

    New here? Try starting at:

    blog #1

    Author

    Husband, father and 911 dispatcher.  Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be.  First time aircraft builder. Looking to fly my own airplane.

    Categories

    All
    Airframe
    Airport
    Avionics
    Decisions
    Engine
    Interior
    Keep Looking
    Mentor
    Milestone
    Mission
    Motivation
    Paperwork
    Philosophy
    Priorities
    Scrounging
    Tools
    Ultralights
    Welcome Aboard
    Workshop

    Archives

    January 2023
    December 2022
    November 2022
    October 2022
    September 2022
    August 2022
    June 2022
    May 2022
    April 2022
    March 2022
    February 2022
    January 2022
    December 2021
    November 2021
    October 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    January 2021
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    September 2019
    August 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    June 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    February 2017
    January 2017
    December 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015

    RSS Feed

    build log

    Item Hours
    Engine 39
    Tail 151
    Wings 726.5
    Fuselage 239
    Interior 5
    Controls 11.5
    Avionics 27
    Other 66
Powered by Create your own unique website with customizable templates.