Help Wanted (with metal fuel line plumbing)

[skippydiesel]

On 07/05/2023 at 10:29 AM, onetrack said:

Only brake lines are double flared, because they have to resist substantial pressure levels. I have a Rothenberger RoFlare double-flaring tool, it's the dux nuts for perfect double flares on Bundy tubing. I've only ever done double flaring on steel (Bundy) or copper lines, I've never used or tried double flaring aluminium tubing.

 

Copper is unsatisfactory for brake lines as it "work hardens" with vibration and the pulsing of brake pressure, so it must not be used in that application.

 

https://www.amazon.com.au/Rothenberger-26033-RoFlare-Compact-Flaring/dp/B002JASATC

 

No mention of the flare angle (that I could see)

[skippydiesel]

In summary: 

 

Some helpful tips - along side quite a bit of "noise"

No offer of an aviation grade flaring tool for loan, hire or purchase - disappointing

[Area-51]

Unless you want to spend the time learning and enjoy making a lot of frustrating mistakes along the way its quicker and cheaper to just pay an experienced operator to do these sort of tasks... in the end its about knowing your tools and their limitations.

 

Things that mostly go wrong:

- forgetting to put the nut on before the flare

(make the pipe again)

- bending the last bend the opposite direction to required

(make the pipe again)

- bending the last bend while the flare nut is on the wrong side of the bend

(make the pipe again)

- running the corner bend too early or too late

(make the pipe again)

- running a bend too close to the last or to the end and the flare tool will not fit

(make the pipe again)

- wrong thread on flare nut pulled out of storage bin

(make the pipe again)

 

All you need is lengths of coat hanger wire soldered together as a template for the fabricator.

 

if all the bends are 90deg you measure out through the centreline of the pipe; add 8.0mm to each end for the flare. Take your sketch and measurement to the fabricator and come back to collect and fit... often it takes two goes to get it right...

 

So if you still want to do the job yourself and experience any of the above don't think you are special, the stuff ups are totally normal. 😃

[facthunter]

The "normal" flare nuts don't give any support to the pipe near the flare, so  if there's any load or vibration it's likely to fail without warning.  Nev

[skippydiesel]

13 minutes ago, Area-51 said:

Unless you want to spend the time learning and enjoy making a lot of frustrating mistakes along the way its quicker and cheaper to just pay an experienced operator to do these sort of tasks... in the end its about knowing your tools and their limitations.

 

Things that mostly go wrong:

- forgetting to put the nut on before the flare

(make the pipe again)

- bending the last bend the opposite direction to required

(make the pipe again)

- bending the last bend while the flare nut is on the wrong side of the bend

(make the pipe again)

- running the corner bend too early or too late

(make the pipe again)

- running a bend too close to the last or to the end and the flare tool will not fit

(make the pipe again)

- wrong thread on flare nut pulled out of storage bin

(make the pipe again)

 

All you need is lengths of coat hanger wire soldered together as a template for the fabricator.

 

if all the bends are 90deg you measure out through the centreline of the pipe; add 8.0mm to each end for the flare. Take your sketch and measurement to the fabricator and come back to collect and fit... often it takes two goes to get it right...

 

So if you still want to do the job yourself and experience any of the above don't think you are special, the stuff ups are totally normal. 😃

Mate! your a gem.

 

I take it the above is a list of your  hard won experience.

 

Thanks for the shape transfer(coat hanger) tip & the 90deg bend measurements.

 

I will be doing my own pipe cutting/flaring & fitting , (even if I have to purchase a new flaring tool just to do this one small job).

 

I am sure I will have plenty of "stuff-ups" (will be purchasing way much more pipe than the job requires). I have been my own "tradie" all of my  life.  I enjoy the challenge & satisfaction of lerning new skills. I just take my time, apply a bucket load of common sense,  work through the stuff-ups/frustration and usually end up with a job I am proud of. 

[Geoff_H]

Skip I take it that your fittings are the 37 deg flare.  I think that the blue aluminium fittings are.  

[Geoff_H]

Other size is 45 deg.  A square can be used to find the angle on the fitting

[skippydiesel]

1 hour ago, Geoff_H said:

Skip I take it that your fittings are the 37 deg flare.  I think that the blue aluminium fittings are.  

I will be using the aviation standard 37 deg flair & fittings to suit (seem to be blue but have seen some green)

[Geoff_H]

My homebuilt tool adaption seems to work for me.  If you buy a standard Bunnings 45 deg I can make a 37 degree brass adaptor if you wish.

[skippydiesel]

9 minutes ago, Geoff_H said:

My homebuilt tool adaption seems to work for me.  If you buy a standard Bunnings 45 deg I can make a 37 degree brass adaptor if you wish.

I may take you up on that Geoff  - I guess that both male press & female die would have to be so modified ?

[Geoff_H]

Actually no.  The male forms the flare, even if it is fractionally out the nut forces the aluminium to shape.  Done with this tool I have 100psi air from my aircompressor sealed.  It uses anealed aluminium and blue alloy fittings.

[Area-51]

Skippy its easiest to use something like 2.5mm braising rod; its a bit more robust... make the template up, make sure you can feed it through everything in the airframe afterwards, it may not be possible as a single piece line...

 

You lay the template out next to your straight pipe and just follow along one bend to the other, checking backwards that the fresh pipe is correctly orientated before you lay the next bend... give yourself about 8" -10" more length than you calculate from the template, it will get eaten up as you form.

 

Practice some bends first on scrap and mark where the bend starts and ends by placing a marker line every 10mm on the fresh straight piece... do the bend (90,45,75...) and measure the linear length along the centerline.. get to know where the bending tool actually commences the bend on the pipe... then you know how much length a bend requires... its a bit of a mathematical nightmare but it prevents stuff ups... its all done by knowing the bend radius and linear length, and adding/subtracting from the distances between bends... I generally just run a piece of string along the template and add 8-10", then start in a very methodical way; and still manage to stuff up!

 

Double, Triple, and Quadruple nested pipes; all hand fabricated and laid out to mm tolerance according to prior design... took weeks to complete.

 

[skippydiesel]

A work of art Area-51 -Fortunately my fuel line modifications are very much simpler. 

 

The objective is to simplify the existing fuel delivery system and at the same time make it more flexible/have redundancy.

 

Currently all TO/Landings must be on one/both  30L Wing tanks, because the Boost pump only feeds from them.

The Header is a gravity feed only and must be isolated when using the Boost pump.

The new concept will be that the  40L Header will also be able to feed through the Boost pump

 

To acheive this:

The Main fuel line currently has a T fitting where the header tank comes in - this will be swapped for an elbow.

The Header's  short delivery line, will be replaced by a longer line paralleling the main line. The  new Header line will be plumbed in to the Boost pumps  fuel IN line.

This will facilitate TO/Landings on the Header tank and if the pilot so wishes using the Wing tanks to refill the Header

 

I am also considering a bypass line (with one way valve) around the Boost pump  as per Rotax recommended best practise.

 

[Area-51]

One thing recently noted after fitting a header tank to an AC, and everybody should be aware of if running a Rotax.

 

The fuel return line has been plumbed back to the header tank rather than one of the wing tanks.

 

As a result, under extended full power the low level lamp for the header is activating; after purging the header tank the low level lamp went out.

 

What was found was the header tank was being pressurised by the return line preventing fresh fuel from entering the header tank under gravity; basically an air lock; however the system is functioning exactly as designed by purging, and warning points are performing correctly... so take this into consideration if you are running 912 and return is to the header.

 

Happy fabricating...

[Thruster88]

6 hours ago, skippydiesel said:

 

 

 

Currently all TO/Landings must be on one/both  30L Wing tanks, because the Boost pump only feeds from them.

 

 

I am also considering a bypass line (with one way valve) around the Boost pump  as per Rotax recommended best practise.

 

If I understand correctly your current fuel selector allows the option of selecting both wing tanks. This is not acceptable in a low wing aircraft. It only works correctly in high wing (cessna) aircraft. 

 

In a low wing aircraft air will enter the system from an empty tank regardless of the other tanks contents if both was selected. Piper, Beech, Van's RV aircraft never have the both option, only left or right or off.

Edited May 15, 2023 by Thruster88

[skippydiesel]

9 hours ago, Area-51 said:

One thing recently noted after fitting a header tank to an AC, and everybody should be aware of if running a Rotax.

 

The fuel return line has been plumbed back to the header tank rather than one of the wing tanks.

 

As a result, under extended full power the low level lamp for the header is activating; after purging the header tank the low level lamp went out.

 

What was found was the header tank was being pressurised by the return line preventing fresh fuel from entering the header tank under gravity; basically an air lock; however the system is functioning exactly as designed by purging, and warning points are performing correctly... so take this into consideration if you are running 912 and return is to the header.

 

Happy fabricating...

Interesting!

 

My fuel return goes back to the header, which has a breather to atmosphere so should never have a pressurisation issue.

I have written, elsewhere", about my low fuel suppress warning on TO. In part this has been addressed by using a smaller apertures return line jet. The origional (Rotax supplied) jet was returning a little over 7 L/hr. This 7 L plus engine consumption, at Max power, was "line ball with the documented best pump delivery. 

 

The next part of the (temporary) solution is answered in my response to Thruster88 below.

[skippydiesel]

4 hours ago, Thruster88 said:

If I understand correctly your current fuel selector allows the option of selecting both wing tanks. This is not acceptable in a low wing aircraft. It only works correctly in high wing (cessna) aircraft. 

 

In a low wing aircraft air will enter the system from an empty tank regardless of the other tanks contents if both was selected. Piper, Beech, Van's RV aircraft never have the both option, only left or right or off.

 

Hi Thruster,

 

I agree its not entirely desirable decision to select Both wing tanks, however it has helped a current (hopefully soon to be remedied) fuel delivery situation.

 

Your statement "not acceptable in a low wing aircraft. It only works correctly in high wing (cessna) aircraft." is overly alarmist and incorrect, where the Pilot knows the Wing tank fuel quantities are sufficient, to prevent such an occurrence.

 

As written elsewhere and in part, my response to Area -51 (above). My aircraft has had a fuel delivery problem at Max engine power settings. . 

 

In my investigation/theorising on how/why I have this problem, it occurred to me (prompted by others) that the fuel volume supply/availabity may somehow be restricted.

 

Possible restrictions could be:

• The Boost pump  itself
• The lack of  a fuel bypass line around the Boost pump. Rotax recommenced a bypass fitted with a non return/one way valve.
• The length/ID of the fuel line from each wing tank.
• A kink or partial blockage in the fuel delivery system
• Two or more of the above

Back to the Wing tanks Selector valve - I have Left, Both, Right,  Off,  on my Selector. 

 

Experimenting with selecting Both has revealed:

• A marked fuel deliver preference for the Right Wing tank.  Conclusion - the the left Wing tank has a restricted flow rate (it works just fine if it is selected in flight) compared with the Right.
• The fuel pressure drop on Max power/TO is markedly less, than if one tank is selected ie with Both wing tanks selected, sufficient fuel is available to the Boost/Mechanical pump, so fuel pressure drop does not drop below Rotax Min of 2 psi. Conclusion - the problem of reduced fuel delivery is likely to be the length & configuration of both Wing tanks fuel lines.

Changes to the fuel reticulation system are soon to happen (see earlier posts). Until then I will be selecting Both Wing tanks for all Max engine power situations.

[IBob]

Skippy, re your 'marked fuel deliver preference for the Right Wing tank.'
A couple of things from my own experience of chasing uneven fuel feed (albeit in a high winged aircraft).

 

1. Different tank pressures will cause different rates of feed, and this can be caused by having separate tank vents that are not receiving identical airflow. Cessna get round this by having just one main tank vent (situated behind the strut to avoid damage but also perhaps to reduce pressurisation) then cross porting the upper tanks.
In my own aircraft I was able to reduce uneven feed by altering the angle on the end of the vents.

 

2. Any undulations in lines may capture air in the undulations, with fuel having to make it's way past the air. In a worst case of multiple undulations, the effects of this are cumulative. And unevenness will vary, depending on whether a line is flooded or contains some or a lot of air.
My L tanks fuel lines run across the back upper cockpit to my selectors on the RH wall (where i can see them). They are hoses, had slight undulations, and I saw a marked change once i got rid of those.

Having said that, I have never achieved equal flow, and I am told by experienced pilots that most aircraft have some unevenness of delivery when both are selected.

 

I should also add that I once tried forward facing tank vents, but abandoned that after one short flight where I had massive cross-feeding. I was also not happy with the degree of pressurisation from this, and what it may be doing to the wing tanks and wing structure.

[IBob]

If I could neatly and easily do it, I would cross-vent my tanks like the Cessna setup.
But it needs to be done from a high point in the tanks.
 

[IBob]

Consider this:
If your tank is, say, 250mm deep (and full) then the pressure at the tank outlet due to the weight of the fuel is approx 2kPa (0.3PSI)
So an increase of just 2kPa (0.3PSI) due to a forward facing vent doubles the pressure of the fuel coming out.
So even a very small difference in how separate tank vents are positioned and facing can result in large differences in fuel pressure at the outfeed.
And as the tanks empty, that small pressure difference will result in increasing difference in flow.

We have seen a 4-tank setup, all with separate forward facing vents, where it was not possible to isolate the inboard tanks. And after about an hour of flight, the fuel levels in those tanks were all over the place.

[fallowdeer]

IBob’s referring to a delivery flight in a Savannah I did that he was also involved in.  
 

First time flying that particular plane.  Stopped at an isolated airstrip (Cape Campbell) to check everything out prior to a 50nm over cold water and hungry sharks.  As IBob said, shallowish four tanks all open but on dipping them up to 150mm difference in the levels.  
 

Didn’t really enjoy the next 45 minutes….. Yep that convinced me of the effect minuscule differences in vent pressure can have.

[Marty_d]

12 hours ago, Area-51 said:

One thing recently noted after fitting a header tank to an AC, and everybody should be aware of if running a Rotax.

 

The fuel return line has been plumbed back to the header tank rather than one of the wing tanks.

 

As a result, under extended full power the low level lamp for the header is activating; after purging the header tank the low level lamp went out.

 

What was found was the header tank was being pressurised by the return line preventing fresh fuel from entering the header tank under gravity; basically an air lock; however the system is functioning exactly as designed by purging, and warning points are performing correctly... so take this into consideration if you are running 912 and return is to the header.

 

Happy fabricating...

I'm building my 701 with a header tank, but will be plumbing the return line to one of the wing tanks.   This should avoid that issue and I believe Savannah specify return to the wing tank rather than to header, is that correct Bob?

[IBob]

32 minutes ago, Marty_d said:

I'm building my 701 with a header tank, but will be plumbing the return line to one of the wing tanks.   This should avoid that issue and I believe Savannah specify return to the wing tank rather than to header, is that correct Bob?

Marty, yes, ICP run the return line back to high on an inboard tank.

Note also that the later Savannahs have also a vent line from the top of the receiver to high on the other inboard tank. This is because the unvented receiver has no reliable way of getting rid of air, and a bubble there could give false low fuel indications.
With that overall arrangement, I would think you can return fuel either to a wing tank or to the receiver, without any problems. The only remaining consideration (if returning to the receiver) is how to entirely isolate the fuel supply if necessary. One option is to put an isolating valve on the return line, but I choose not to do that, as the return plays such an important part in avoiding vapour lock EFATO. On balance, I chose to follow the recipe, and return to a wing tank.

[Blueadventures]

1 hour ago, Marty_d said:

I'm building my 701 with a header tank, but will be plumbing the return line to one of the wing tanks.   This should avoid that issue and I believe Savannah specify return to the wing tank rather than to header, is that correct Bob?

That's is the very best way to do it.  Don't listen to any advice to return to a gascolator or surge / collector tank.  if your collector tank has 2 inlets just use one as vent to tank. (Access to tank can be via the upper contents tube connection; using a 'T' if a dedicated access is not available; this is what I did.)

[IBob]

And just to round out that conversation on fuel vents (as applied to the simple systems many of us fly.)
The received wisdom seems to be that a small positive pressure in the tanks is desirable.
But
Consider (also) this:
Your fuel tank is, say 500 wide x 500 long.
You fit a forward facing vent, and it raises the pressure in flight by 7kPa (1PSI).
The size of the vent doesn't matter, a smaller one will just take longer to get there.
The result is that the top and bottom of your tank are now bugging out due to an increased pressure over each of the top and bottom surfaces of 177Kg (390lb).

 

My tanks sit flush to the upper wing skin: after my short and far too interesting flight with fully forward facing vents, I looked up there, half expecting to see the skins bugged out and a few rivets missing......(