fin/wing tanks freezing

On Thursday, June 6, 2013 3:41:20 AM UTC+12, Matt Herron Jr. wrote:
Can anyone share some wisdom on using water at high elevations for long durations? How do you know your fin or wing tanks will not freeze? If I am at 18K for 6 hrs in the Sierras, I really don't want my vertical stab splitting open in flight. Has this ever happened? Any guidance would be appreciated.



Matt

I fly at Omarama and we spend a lot of time high and cold. -10 to -20 C is common, sometimes less. As I mostly fly a Duo Discus I almost always have tail water and occasionally wing water.

I've never heard of any-one having a problem with wing water causing structural problems by freezing in flight. What does cause problems is the dump valves freezing and being unable to dump. You also see people having problems with leaking valves. They land with enormous ice sculptures under the wing.

Tail water does freeze, but I've never seen it break anything structural. The dump valves do fail when they freeze. Water going out the overflow holes freezes and can jam the rudder. I have seen a thin rod of ice forced out of the top overflow hole.

Some people do use anti-freeze in the tail, others prefer not to due to fears that the anti-freeze will damage the seals and such.

The real danger is if you load up with water and the tail valve freezes. The wings dump and you are left with the tail water and an aft C of G. In a Duo that isn't a problem because with two people you have the tail mostly full anyway for trim. In a single seater you might get into real trouble.

Different systems have different problems, but actual ballast turning solid and bursting the structure isn't a problem. Dump valves getting damaged and leaking does happen. That's just a nuisance.

Water getting into controls and freezing does happen. Being unable to dump the ballast does happen. That is much more serious.

--
Philip Plane

Had a Nimbus 3 in the shop some years ago with massive structural wing
damage due to freezing tanks. Took the upper wing shells clean off the
spars and/or cracked the shell right through just in front of the spar (the
width of the tanks), and the resulting 'new' aerofoil made flying it very
interesting according to the pilot. Interesting repair as well.

Damage can be massive, control problems and weight/balance problems would
be an issue too with freezing water. Most flight manuals specifically
state: water to be dumped before reaching freezing level. Even when not
using common sense these factors should be enough to make up your mind, I
would say.

I mix half a liter of methanol in the tail tank of a Ventus C. I don’t put any in the wing tanks which have a higher mass to surface area ratio and thus a longer thermal time constant. I’ve been doing this for 20 years and have not had a problem yet. Your mileage may vary.
This system was put to the test recently on a particularly cold (for the southwest U.S.) early-season flight at altitudes up to 17,500’. The OAT got down to -10 C and was probably below freezing for 2 hours straight.
I have often had water leak from the wing valves, run back into the gap between the flap and wing fairing, freeze, and jam the flaps (which are interconnected to the ailerons). As a previous poster noted, this is quite unpleasant. I was encouraged by the fact that this did not occur on my recent flight for which I had been particularly diligent with the application of Chap Stick to the mating surfaces of the valves prior to filling.
Other than the leakage, I have never dumped untreated water when the OAT is below freezing. Considering the flap jamming issue and the potential for freezing on tail surfaces, this would seem to be a bad idea.
Methanol (methyl alcohol) is readily available at hot rod shops, reasonably priced, and relatively benign environmentally (it will evaporate before reaching the ground).
Mike Koerner

What I was wondering is whether there are any gliders out there with
thermometers in the tanks. My hunch is that, together with non-leaking
valves, that would allow a great deal of added flexibility. It would also
reduce the amount of speculation in that thread

Best
--Gerhard

Can anyone share some wisdom on using water at high elevations for long durations? How do you know your fin or wing tanks will not freeze? If I am at 18K for 6 hrs in the Sierras, I really don't want my vertical stab splitting open in flight. Has this ever happened? Any guidance would be appreciated.

I have had 3 different malfunctions as a result of prolonged flights above the freezing level when carrying water ballast.

1. In an ASW 20 with a aftermarket brass valve actuated tail ballast system.. The valve froze and I was unable to dump the tail ballast. I wasn't aware of the malfunction until after landing and the valve thawed and water came running out. It was fashionable at the time to fly the ASW 20 right at or slightly behind the aft limit so dumping the wings and not the tail resulted in a dangerously tail heavy condition. I was blissfully unaware of any change in the behavior of the aircraft and landed uneventfully. The fix was to put a pint of RV antifreeze in the tail tank. RV antifreeze is propylene glycol and is safe even if you drink a little.

2. In a Nimbus 3 when flying with full wing ballast water would bubble out of the vent in the filler plugs on the wing top surface and run back over the flap aileron junction on the trailing edge and freeze, resulting in frozen controls. It was quite alarming but not too hard to dislodge with a vigorous thrashing of the controls. I learned to cycle that gap frequently to break it off before it became thick enough to be a problem.

3. I have always used the wax from wax toilet mounting rings to seal the dump valves on Schempp Hirth gliders. After a long wave flight in NZ in my Nimbus 3 I landed at Omarama and promptly did a wild ground loop. Omarama is a wide grass field and the glider escaped unscathed. On most airport runways I probably would have done heavy damage. The wax had become so stiff that one valve stayed stuck shut, and there was enough slack in the dump linkage to allow the cockpit dump handle to stow in the dump position, so I had no way of knowing that one wing was not dumping. Interestingly, although I had been flying for some time with one wing empty and the other full, I was not aware of the asymmetry until the heavy wing went down on the landing. The solution was to switch to chap stick which stays fairly soft when cold. It doesn't seal as well but is a wiser choice.
I guess one could conclude that when flying for extended times, in below freezing temperatures, with water ballast it is advantageous to have been born lucky.

DLB

The fix was to put a pint of RV antifreeze in the tail tank. RV antifreeze is propylene glycol and is safe even if you drink a little.

DLB


Dale, My significant other suggested I use White Zin. I countered with Gewurztraminer. Since it is not fit for human consumption, there is no conflict in pulling the dump actuator ;-)

Craig R.

"Craig R." wrote:
The fix was to put a pint of RV antifreeze in the tail tank. RV
antifreeze is propylene glycol and is safe even if you drink a little.

DLB


Dale, My significant other suggested I use White Zin. I countered with
Gewurztraminer. Since it is not fit for human consumption, there is no
conflict in pulling the dump actuator ;-)

Craig R.

Just watch which vintage of wine you're using. In the late 80s there was a
major scandal with various producers of Spättlese spiking the wine with
ethylene glycol. ;-)

Pete

Not having studied thermal dynamics, etc, I have two rookie questions. How does the container material (thin plastic "milk jug" in freezer vs layered fiberglass for tail tank) and the shape of the container (minimal surface area of a milk jug vs long thin tail) effect these calculations? ... also, head space in jug is zip and in tail tank is large....

On Jun 6, 3:37*pm, wrote:
What I was wondering is whether there are any gliders out there with
thermometers in the tanks.

I think some, if not all, LS gliders, have tail tank thermometers and
that it was a requirement of the type certificate. Never understood
why it should be required for one make/model but not for gliders from
other manufacturers.

When I had my ASW-19b I was concerned out wing ballast temperature.
Since the 19 uses bags it was easy to fit a thermistor probe under one
of the ballast bags and connect to a cockpit thermometer. (Radio Shack
indoor/outdoor thermometer with a connector break in the outdoor probe
lead). I was surprised at how warm the ballast stayed despite long
cold soaks at altitude.

The risk of tail ballast failing to dump is taken seriously by some
manufacturers but not by others. For the ASW-28 the aft cg limit
moves forward as mass is increased. If I operate within limits I
will not exceed the aft CG limit if my tail tank fails to dump.

On the other hand, the Duo Discus handbook recommends an increase in
minimum front seat mass if a tail tank is fitted. It then goes on to
say it's only a recommendation and you can ignore that safety
protection if you want to.

Failure to dump the tail ballast is not just a freeze risk. The valve
can jam or the cable can break when it's nice and warm outside. I've
even seen a well meaning crew tape over ballast vent holes.

Andy

I think some, if not all, LS gliders, have tail tank thermometers and
that it was a requirement of the type certificate. Never understood

Not the brandnew LS10 I was flying in Chile 2 1/2 yrs ago (manufactured
by DG)...

lead). I was surprised at how warm the ballast stayed despite long
cold soaks at altitude.

Water does has a high heat capacity... And if bags are used, they could
potentially made from some insulating material (are they?).

Best
--Gerhard