Use of wing fuel tanks

[Mark B]

I mentioned previously that when I left the glider parked with fuel in the wing tanks and the tanks connected I lost fuel via the overflow from the clear plastic bottle at the back of the baggage area. Therefore if I am leaving the glider with fuel in the wing tanks I normally disconnect the wing tanks (both fuel pipe and breather) until just before flying.

Does everyone else do the same? If not, what do you do? Could there be a problem with fuel expanding with heat while the breathers are disconnected?

[Heini Schaffner, SN 71]

After three leaking HFK-wing tanks in only 45 flights (would be worth a special chapter!) and in order to avoid unwanted fuel drainage from filled wing tanks into the main tank with subsequent overflow outwards, I decided to modify the unsatisfactory fuel system. The initial idea was a simple, rapid and smell-free way to lock/unlock either wing tank, be it after landing or prior to TO. I therefore installed inline (in addition to the quick release connector) a mechanical ball valve on either side, as well as a further checkpoint into the checklist. Engaging wing fuel only if really needed inflight would avoid the prior total evacuation of the unlocked wing tanks before refilling them with a known volume. Unfortunately the ball valve can impossibly be operated inflight by the copilot/passenger so far. I then was thinking about electro-magnetic valves (€ 25 each) operated from the front seat instead of the ball valves, but this would need quite some current to keep the valve open during the long lasting emptying/refilling procedure.

[Jorgen Thomsen]

In November/December 2013 I experienced fuel leak in 3 wing tanks. All 3 tanks started leaking by the Banjo bolt at the fuel line.
The tanks of 2013 year manufacture had Festo washers. I contacted the manufacturer Heimann, and we agreed that replacing the Festo washers with copper or aluminium would be a good solution.
I learned from Heimann that a few of the tanks of 2013 year manufacture had a fault in the welding seam with too little overlap. This resulted in an opening of 6-10 mm in the welding, and a lot of fuel in the wing tank compartment of the wing. luckily none of this fuel entered the fuselage.
After the initial leaks, I decided to only use Avgas in the wing tanks.

In spring 2014 I installed a ball valve on each quick connector, and can keep the valve closed until needed. The lever is longer on mine as those Heini have installed, and I can operate the valves from the back seat. I have a pending modification to be able to open the valves from the front seat also.
This solution also prevents fuel from moving from one side to the other when parked on the ground.
I always refuel the wing tanks via an outside pump acquired from Schempp Hirth.

I have had no further leaks with the wing tanks, since modifying the tanks with Aluminium washers, and I have learned that Heimann now uses Copper washers.

I now find that with the ball valves, I have a system with better controllability and less hazzle. I often use Mogas in the fuselage tank.
 

[Heini Schaffner, SN 71]

To my advice the HFK-fuel bladders suffer from a design flaw. Although I was filling these strictly according to the manual (emptying them totally before refilling with only 10 l from a jerrycan holding just this volume. The first fuel leak/depletion occured overnight, detectable by vertically descending oil stripes at the fuselage).

 

The right sided wing tank had been exchanged free of charge at the factory, but SHK was not willing to unveil to me the site or mechanism of the leak. The following season a second fuel leak occured inflight at the left WT (detectable by oblique passing oil stripes at left side of fuselage) and soon again also to the already replaced right WT, this time after only 8 fillings. This amounts to 3 leaky HFK fuel tanks in 45 flights or an average of 15 fillings per fuel bladder...!

 

I then decided to replace both WT by myself during wintertime and found that both fuel bladders were in fact well welded around and itself seal; but both surrounding imitation-leather-envelopes showed rolled up borders without any found trace of the formerly used contact-glue. The fuel leak at one bladder stemmed clearly from loose Banjo bolts/screws at the in-/outlet, as well as at the vent. On the other fuel bag it concerned only the in-/outlet Banjo screw, detectable by the split and separated blue color dots. There was no thread-sealing glue (i.e. Loktite) detectable at the Banjo fittings and I also missed some safety wire withholding the Banjo screws from unscrewing.

 

These HFK-fuel bladders have not been airworthy. Of course the different leaks occured during alpine summer camps in SE-France and Austria. How could the present design (with whatever washers it may be fitted) be seal with ground temperatures up to 35 °C and freezing temperatures while flying the wave up to FL 195. In addition the sometimes bumpy alpine gliding may well have aided to unscrew the Banjo-in-/outlets.

 

Understanding finally the way it leaks and realizing meanwhile that SHK still hesitated to look for a better supplier, I decided to install two well proven australian fuel bags from www.turtlepac.com. They arrived for  AUD 1'760.-both (about € 1'200 .--, shipment by FedEx included). Compare this amount to the 2 x € 1'450.-- that SHK billed for the HFK-bladders, if installed prior to delivery! The turtlepac bladders have a volume of indicated 15 l, a much stronger protecting envelope that is solidly sewed (not only glued), clever fuel in-/outlets both situated on the dorsal side, with Loktite sealed threads for the Banjo screws, as well as a much wider sealing area between bladder and compressing alu plates.

 

In meanwhile 56 days and nights (including 16 alpine flights) with the same permanently filled and blocked turtlepac wing tank, there was no leak at all and no more fuel smell (I generally use lead free Mogas 95) after opening the canopy in the morning. After having to tie down for the very first time the Arcus M in a left wing down position (the IMI wing-stands had already been transported to arrival destination...), I noticed next day during the preflight check some vertically downpassing oil stripes on the right side of the fuselage. It turned out that this must have been a burden of the past, because there was no fuel smell within the right wing (lid at its underside removed). What are the communitiy's experiences in this behalf?

On Friday, August 12, 2016 at 1:04:24 AM UTC+2, Mark B wrote:

[johanda...@gmail.com]

Our HFK bladder had loose banjo bolts and a pinhole opposite to the connection of the fuel line. According to Heimann this tank could not be repaired. I contacted Aerotech Services and Penney (co-owner of the company) advised me to come over and bring the tank with me. So today I visited them near Los Angeles. The company owner, Denny, looked at the tank and said that repair was possible. He made a 10 inch cut in the top side of the tank, turned it inside out, and removed all the hardware. The large hex-nuts on the inside of the tank had very sharp edges, these had caused the pinhole at the fuel line connection. He glued reinforcement patches into the tank opposite to the banjobolts and mounted the bolts with copper washers. The sharp edges of the hex-nuts were sanded before they were used again. Then he turned the tank normal again and closed the large cut he made before. The tank is not leaking anymore now.

According to Denny the quality of the HFK bladder material is good, but the hardware used to connect the lines isn't. He informed me that Aerotech can make bladders like this as a replacement for the HFK bladders. I am impressed by what I have seen in their shop today! They make high quality bladders for all kind of purposes, from warbirds to racecars. They can be a good alternative for the original HFK tank, and Penney and Denny are very helpfull. We certainly consider Aerotech when we have to replace our HFK in 5 years from now.

[Mark]

Johan,

What year is your Arcus?

Mark

[johanda...@gmail.com]

Our Arcus is from Februari 2012, production number 26. HFK tank number is 02122310. A clubmember recently ordered HFK tanks for his ASH-25M via Alexander Schleicher. These tanks have different fittings (see pics)

Johan