fin/wing tanks freezing

[Matt Herron Jr.]

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

[jfitch]

On Wednesday, June 5, 2013 8:41:20 AM UTC-7, 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 know in the Duo Discus I used to own (part of) the OAT gage was a required instrument just for this reason. It will take a long time for a wing tank, or even a fin tank to freeze. But we did have an incident where a dribbling leak from the fin tank collected in the rudder counterbalance and froze, freezing the rudder solid. This was on a day when the return from Mt. Whitney to Truckee was a no-turn romp at 17,999 ft. It did finally unfreeze as the Duo descended on final. I don't know of anyone who has had a fin tank freeze.

[Peter Scholz[_3_]]

Am 05.06.2013 17:41, 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
>

They will freeze. Depending on the layout of the tanks, it may do damage
to the tank or wing structure.

If you fly in air mass below freezing point, either
- do not use water ballast
- or add the appropriate amount of antifreeze to the water.

If possible, you can land with the ballast water and then recollect the
antifreeze mixture. I know of several pilots that have done it that way.

--
Peter Scholz
ASW24 JE

[Matt Herron Jr.]

I fly a Ventus C with integral tanks (no Bags) any issues with antifreeze and carbon/fiberglass tanks? What would be the recommended amount? Sounds like an environmental hazard to dump, and I certainly dont want to land wet unless I have to.

I have had issues with the Ventus fully loaded with water where the flaps seem to stick a bit. Not sure if it was a freezing leak or what, but was a little scary. Frozen rudder must not have been too fun.

Matt

[Croft Brown]

It is folly to fly at high altitudes with water ballast on board. It is a
requirement to have an outside air temp gauge if your sailplane has water
tanks fitted (even if they are never used). I am amazed that this question
has even been posted.
cb



At 16:23 05 June 2013, Matt Herron Jr. wrote:
>I fly a Ventus C with integral tanks (no Bags) any issues with antifreeze
>and carbon/fiberglass tanks? What would be the recommended amount?
Sounds
>like an environmental hazard to dump, and I certainly dont want to land
wet
>unless I have to.
>
>I have had issues with the Ventus fully loaded with water where the flaps
>seem to stick a bit. Not sure if it was a freezing leak or what, but was
a
>little scary. Frozen rudder must not have been too fun.
>
>Matt
>

[Bob Kuykendall]

On Jun 5, 9:23*am, "Matt Herron Jr." > wrote:
> I fly a Ventus C with integral tanks (no Bags) any issues with antifreeze and carbon/fiberglass tanks? *What would be the recommended amount? *Sounds like an environmental hazard to dump, and I certainly dont want to land wet unless I have to.
>
> I have had issues with the Ventus fully loaded with water where the flaps seem to stick a bit. *Not sure if it was a freezing leak or what, but was a little scary. *Frozen rudder must not have been too fun.
>
> Matt

The factory probably has a recommended antifreeze agent; if so, use
that. In the absence of such a recommendation, I would probably use
propylene glycol-based antifreeze intended for winterizing RVs and
cabins; it is pretty safe stuff. I would be very wary about using
ethylene glycol antifreeze unless I knew for certain that the ballast
system bags, tanks, linings, plumbing, seals, and valves were all
compatible with it. And even then I probably wouldn't use it for
environmental reasons.

Thanks, Bob K.

[Peter Thomas[_2_]]

even if it doesnt freeze in the tanks, it may well when dumped. I
know of a case of this in the uk, the ice buildup at the base of the
fin apparently made things interesting.

Anyone understand the the issues of high altitude limiting speeds
and a ballasted glider?

At 15:41 05 June 2013, Matt Herron Jr. wrote:
>Can anyone share some wisdom on using water at high elevations
for long
>dur=
>ations? How do you know your fin or wing tanks will not freeze?
If I am
>a=
>t 18K for 6 hrs in the Sierras, I really don't want my vertical stab
>splitt=
>ing open in flight. Has this ever happened? Any guidance would
be
>apprecia=
>ted.
>
>Matt
>

[jfitch]

In the Sierra, we fly every day at high altitudes with water ballast on board. Literally 10s of thousands of flights. 18,000 feet is common, 24,000 not unusual, OAT of around 20 F is normal. I have never heard of anyone that filled his tanks with antifreeze. Routinely landing with full tanks would be a far greater hazard. I suppose if you were contemplating a dawn-to-dusk record winter wave flight, it might be worth considering.

But perhaps we are all guilty of folly.

[[email protected]]

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

[[email protected]]

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

[Eric Munk]

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.

[TravisBrown73[_2_]]

On Wednesday, June 5, 2013 9:51:04 AM UTC-7, Croft Brown wrote:
....... I am amazed that this question has even been posted......
>
> cb
>
>
>
You could focus on coaching instead of deriding a fella for asking a genuine question.

>
>
>
>
> At 16:23 05 June 2013, Matt Herron Jr. wrote:
>
> >I fly a Ventus C with integral tanks (no Bags) any issues with antifreeze
>
> >and carbon/fiberglass tanks? What would be the recommended amount?
>
> Sounds
>
> >like an environmental hazard to dump, and I certainly dont want to land
>
> wet
>
> >unless I have to.
>
> >
>
> >I have had issues with the Ventus fully loaded with water where the flaps
>
> >seem to stick a bit. Not sure if it was a freezing leak or what, but was
>
> a
>
> >little scary. Frozen rudder must not have been too fun.
>
> >
>
> >Matt
>
> >

[Croft Brown]

Of course your right. We must focus on coaching. Read the flight manual
section on water ballast.
cb




At 13:32 06 June 2013, TravisBrown73 wrote:
>On Wednesday, June 5, 2013 9:51:04 AM UTC-7, Croft Brown wrote:
>....... I am amazed that this question has even been posted......
>>
>> cb
>>
>>
>>
>You could focus on coaching instead of deriding a fella for asking a
>genuine question.
>
>>
>>
>>
>>
>> At 16:23 05 June 2013, Matt Herron Jr. wrote:
>>
>> >I fly a Ventus C with integral tanks (no Bags) any issues with
>antifreeze
>>
>> >and carbon/fiberglass tanks? What would be the recommended amount?
>>
>> Sounds
>>
>> >like an environmental hazard to dump, and I certainly dont want to
land
>>
>> wet
>>
>> >unless I have to.
>>
>> >
>>
>> >I have had issues with the Ventus fully loaded with water where the
>flaps
>>
>> >seem to stick a bit. Not sure if it was a freezing leak or what, but
>was
>>
>> a
>>
>> >little scary. Frozen rudder must not have been too fun.
>>
>> >
>>
>> >Matt
>>
>> >
>
>

[[email protected]]

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.

[[email protected]]

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

[Andy[_1_]]

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

[[email protected]]

> 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

[[email protected]]

On Wednesday, June 5, 2013 8:41:20 AM UTC-7, 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


What you're basically looking for is a solution to a reasonably straight-forward heat transfer problem. We can make a set of assumptions to make this a solvable problem.

1) The temperature of the water is basically spatially uniform.
2) The temperature of the surrounding atmosphere doesn't change.
3) The fluid properties (density and specific heat) are constant.
4) The heat transfer is convective only (from cold air flowing around the water container). No conduction or radiation.
5) There's no forced convection (i.e. no fans or forced flow into the ballast tank)
6) The free convection heat transfer is fairly efficient or the cold air motion outside of the water container is substantial (i.e. Gr and Pr are large)

If you do this, you end up with an equation that looks like this:

-h * A * (T - To) = rho * V * (Cp * dT + hfs) / dt

h = the convective heat transfer coefficient, which basically measures how efficiently heat is being transferred. With our assumptions, we can roughly approximate h = 1.52 * (T - To)^(1/3).
A = the surface area of the water container
T = the temperature of the water at time t, We'll use 32 °F here since most of the heat transfer will be occuring while the water is undergoing the phase change
To = the outside temperature (this needs to be below 32 °F)
rho = the density of the water
V = the volume of the water
Cp = the specific heat of the water (assume around 4.2 kJ/ kg K)
dT = the difference between the initial and final water temperatures
dt = the time it takes to freeze
hfs = the enthalpy of fusion (about 334 kJ/kg)

Rearrange the equation and we set the energy required to freeze the water (hA(T-To)) is equal to the energy required to cool it (rhoVCpDT/dt) plus the energy required to turn it into a solid (rhoVhfs/dt).
Suppose you have a typical water bottle as a simple example.

Starting with h, if you begin at room temperature, h = 1.52 * (25-0)^(1/3) = 4.4 (W/m^2 K)

Assume a cylindrical container meauring about 6" x 2.5". So PI * D * L = 0.03 (m^2)

The outside air is at 0 °F (-18 °C) and the water starts at about room temperature (20 °C). So T - To = -40 (°C)

The volume is about 500 mL, the density is about 1000 kg/m3, so the mass is about 0.5 kg.

The specific heat we said above was 4.2 (kJ/kg K) or 4200 (J/kg)

The temperature change will be from room temperature to freezing, so 20 °C.

The enthalpy of fusion from above is 334,000 J/kg.

Plugging all this in and solving for dt gives a time of 31,667 s or about 8 hr. 48 mins. For any volume of room temperature water going into a freezing environment, the only thing that will change will be the surface area (A), and the volume (V). The rest you can keep the same as a basic approximation so you have:

t = 1,900,000 V/A

where V and A are in m^3 and m^2, respectively.

The V/A for tail tanks and wing tanks vary only slightly. We should probably adjust the heat transfer coefficient downward a bit from the above example since the tanks in most gliders are insulated with the composite/foam sandwich of the structure. This will make the time longer. If it's warmer than 0 °F it will take longer still, so for normal thermal soaring you would expect never to get to frozen solid. Maybe on a really long wave flight you should worry.

Lastly, as has been pointed out, depending on your venting, valving and CG considerations, you may have localized water management issues from small-scale freezing, but I wouldn't worry about a giant block of ice exploding from my wing or tail.

9B

[Tom K (ES)]

After reading this post I am just glad my elementary school math teacher was wrong when she said I needed to learn math because I wouldn't always be walking around with a calculator.

[Dan Marotta]

I don't recall a thermometer in the tail tank as a requirement in either of
my LS-6s. Maybe because they were early models...

My LAK-17a Pilot's Manual requires an OAT gauge if water ballast is carried
and states further:

Warning:
Flight with water ballast must be conducted at an OAT greater than 1° C
(34°F). If there is a risk of freezing temperatures, all water must be
dumped before freezing temperatures are reached.

Being somewhat of a "test pilot", I often fly with water at below freezing
temperatures (it's cold at 18,000' MSL regardless of seasons), but I
generally don't spend more than a couple of hours at those altitudes and
temperatures. I also spend plenty of time on the descent to allow things to
warm up at a reasonable rate.

Having said that, I've had a stuck wing dump valve more than once. It's not
noticeable until the glider comes to rest.

"Andy" > wrote in message
...
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

[Craig R.]

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.

[Jim[_31_]]

On Friday, June 7, 2013 8:53:49 AM UTC-4, wrote:
> On Wednesday, June 5, 2013 8:41:20 AM UTC-7, 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
>
>
>
>
>
> What you're basically looking for is a solution to a reasonably straight-forward heat transfer problem. We can make a set of assumptions to make this a solvable problem.
>
>
>
> 1) The temperature of the water is basically spatially uniform.
>
> 2) The temperature of the surrounding atmosphere doesn't change.
>
> 3) The fluid properties (density and specific heat) are constant.
>
> 4) The heat transfer is convective only (from cold air flowing around the water container). No conduction or radiation.
>
> 5) There's no forced convection (i.e. no fans or forced flow into the ballast tank)
>
> 6) The free convection heat transfer is fairly efficient or the cold air motion outside of the water container is substantial (i.e. Gr and Pr are large)
>
>
>
> If you do this, you end up with an equation that looks like this:
>
>
>
> -h * A * (T - To) = rho * V * (Cp * dT + hfs) / dt
>
>
>
> h = the convective heat transfer coefficient, which basically measures how efficiently heat is being transferred. With our assumptions, we can roughly approximate h = 1.52 * (T - To)^(1/3).
>
> A = the surface area of the water container
>
> T = the temperature of the water at time t, We'll use 32 °F here since most of the heat transfer will be occuring while the water is undergoing the phase change
>
> To = the outside temperature (this needs to be below 32 °F)
>
> rho = the density of the water
>
> V = the volume of the water
>
> Cp = the specific heat of the water (assume around 4.2 kJ/ kg K)
>
> dT = the difference between the initial and final water temperatures
>
> dt = the time it takes to freeze
>
> hfs = the enthalpy of fusion (about 334 kJ/kg)
>
>
>
> Rearrange the equation and we set the energy required to freeze the water (hA(T-To)) is equal to the energy required to cool it (rhoVCpDT/dt) plus the energy required to turn it into a solid (rhoVhfs/dt).
>
> Suppose you have a typical water bottle as a simple example.
>
>
>
> Starting with h, if you begin at room temperature, h = 1.52 * (25-0)^(1/3) = 4.4 (W/m^2 K)
>
>
>
> Assume a cylindrical container meauring about 6" x 2.5". So PI * D * L = 0.03 (m^2)
>
>
>
> The outside air is at 0 °F (-18 °C) and the water starts at about room temperature (20 °C). So T - To = -40 (°C)
>
>
>
> The volume is about 500 mL, the density is about 1000 kg/m3, so the mass is about 0.5 kg.
>
>
>
> The specific heat we said above was 4.2 (kJ/kg K) or 4200 (J/kg)
>
>
>
> The temperature change will be from room temperature to freezing, so 20 °C.
>
>
>
> The enthalpy of fusion from above is 334,000 J/kg.
>
>
>
> Plugging all this in and solving for dt gives a time of 31,667 s or about 8 hr. 48 mins. For any volume of room temperature water going into a freezing environment, the only thing that will change will be the surface area (A), and the volume (V). The rest you can keep the same as a basic approximation so you have:
>
>
>
> t = 1,900,000 V/A
>
>
>
> where V and A are in m^3 and m^2, respectively.
>
>
>
> The V/A for tail tanks and wing tanks vary only slightly. We should probably adjust the heat transfer coefficient downward a bit from the above example since the tanks in most gliders are insulated with the composite/foam sandwich of the structure. This will make the time longer. If it's warmer than 0 °F it will take longer still, so for normal thermal soaring you would expect never to get to frozen solid. Maybe on a really long wave flight you should worry.
>
>
>
> Lastly, as has been pointed out, depending on your venting, valving and CG considerations, you may have localized water management issues from small-scale freezing, but I wouldn't worry about a giant block of ice exploding from my wing or tail.
>
>
>
> 9B

Interesting calculation. I wonder why use such assumptions as "temperature of the surrounding atmosphere doesn't change", which it does as altitude changes and weather changes through a long flight. Also, "room temperature" is hardly close when filling tanks in winter or from well water..How does the result look if these assumptions are at their worst maximum?

-Jim

[Andy Blackburn[_2_]]

Jim > wrote:
> On Friday, June 7, 2013 8:53:49 AM UTC-4, wrote:
>> On Wednesday, June 5, 2013 8:41:20 AM UTC-7, 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
>>
>>
>>
>>
>>
>> What you're basically looking for is a solution to a reasonably
>> straight-forward heat transfer problem. We can make a set of assumptions
>> to make this a solvable problem.
>>
>>
>>
>> 1) The temperature of the water is basically spatially uniform.
>>
>> 2) The temperature of the surrounding atmosphere doesn't change.
>>
>> 3) The fluid properties (density and specific heat) are constant.
>>
>> 4) The heat transfer is convective only (from cold air flowing around
>> the water container). No conduction or radiation.
>>
>> 5) There's no forced convection (i.e. no fans or forced flow into the ballast tank)
>>
>> 6) The free convection heat transfer is fairly efficient or the cold air
>> motion outside of the water container is substantial (i.e. Gr and Pr are large)
>>
>>
>>
>> If you do this, you end up with an equation that looks like this:
>>
>>
>>
>> -h * A * (T - To) = rho * V * (Cp * dT + hfs) / dt
>>
>>
>>
>> h = the convective heat transfer coefficient, which basically measures
>> how efficiently heat is being transferred. With our assumptions, we can
>> roughly approximate h = 1.52 * (T - To)^(1/3).
>>
>> A = the surface area of the water container
>>
>> T = the temperature of the water at time t, We'll use 32 °F here since
>> most of the heat transfer will be occuring while the water is undergoing the phase change
>>
>> To = the outside temperature (this needs to be below 32 °F)
>>
>> rho = the density of the water
>>
>> V = the volume of the water
>>
>> Cp = the specific heat of the water (assume around 4.2 kJ/ kg K)
>>
>> dT = the difference between the initial and final water temperatures
>>
>> dt = the time it takes to freeze
>>
>> hfs = the enthalpy of fusion (about 334 kJ/kg)
>>
>>
>>
>> Rearrange the equation and we set the energy required to freeze the
>> water (hA(T-To)) is equal to the energy required to cool it
>> (rhoVCpDT/dt) plus the energy required to turn it into a solid (rhoVhfs/dt).
>>
>> Suppose you have a typical water bottle as a simple example.
>>
>>
>>
>> Starting with h, if you begin at room temperature, h = 1.52 * (25-0)^(1/3) = 4.4 (W/m^2 K)
>>
>>
>>
>> Assume a cylindrical container meauring about 6" x 2.5". So PI * D * L = 0.03 (m^2)
>>
>>
>>
>> The outside air is at 0 °F (-18 °C) and the water starts at about room
>> temperature (20 °C). So T - To = -40 (°C)
>>
>>
>>
>> The volume is about 500 mL, the density is about 1000 kg/m3, so the mass is about 0.5 kg.
>>
>>
>>
>> The specific heat we said above was 4.2 (kJ/kg K) or 4200 (J/kg)
>>
>>
>>
>> The temperature change will be from room temperature to freezing, so 20 °C.
>>
>>
>>
>> The enthalpy of fusion from above is 334,000 J/kg.
>>
>>
>>
>> Plugging all this in and solving for dt gives a time of 31,667 s or
>> about 8 hr. 48 mins. For any volume of room temperature water going into
>> a freezing environment, the only thing that will change will be the
>> surface area (A), and the volume (V). The rest you can keep the same as
>> a basic approximation so you have:
>>
>>
>>
>> t = 1,900,000 V/A
>>
>>
>>
>> where V and A are in m^3 and m^2, respectively.
>>
>>
>>
>> The V/A for tail tanks and wing tanks vary only slightly. We should
>> probably adjust the heat transfer coefficient downward a bit from the
>> above example since the tanks in most gliders are insulated with the
>> composite/foam sandwich of the structure. This will make the time
>> longer. If it's warmer than 0 °F it will take longer still, so for
>> normal thermal soaring you would expect never to get to frozen solid.
>> Maybe on a really long wave flight you should worry.
>>
>>
>>
>> Lastly, as has been pointed out, depending on your venting, valving and
>> CG considerations, you may have localized water management issues from
>> small-scale freezing, but I wouldn't worry about a giant block of ice
>> exploding from my wing or tail.
>>
>>
>>
>> 9B
>
> Interesting calculation. I wonder why use such assumptions as
> "temperature of the surrounding atmosphere doesn't change", which it does
> as altitude changes and weather changes through a long flight. Also,
> "room temperature" is hardly close when filling tanks in winter or from
> well water..How does the result look if these assumptions are at their worst maximum?
>
> -Jim


--
9B

Jim

The assumption is the temperature of the atmosphere doesn't change due to
the heat transfer from your ballast water. I think that's a pretty safe
assumption given the relative heat capacities of the earth's atmosphere
versus 40 gallons of water. Otherwise ballasted sailplanes would be
responsible for global warming. ;-)

You are correct that over the course of a flight you go up and down in
altitude. You are also correct that the starting temperature for ballast
water is probably not room temperature. I picked 0 degrees for the OAT even
though the more typical temperature for 18,000' is closer to 20 degrees and
is considerably warmer at lower altitudes. I would say the temperature
differential assumption is actually pretty aggressive. I barely see
freezing temps on most flights well up into supplemental oxygen altitudes.
You also have to appreciate that the phase change to ice is the thing that
consumes the most energy, not getting from room temp to 55 degrees. The
simple sensitivity analysis I did would indicate that the actual time to
freeze your ballast tanks solid is much longer than 9 hours under any
realistic scenario.

About the time I made my original post I also put a gallon of water in my
zero degree freezer - I'll let you know how that goes...

9B

[Papa3[_2_]]

On Saturday, June 8, 2013 8:45:12 AM UTC-4, Andy Blackburn wrote:
> Jim > wrote:
>
> > On Friday, June 7, 2013 8:53:49 AM UTC-4, wrote:
>
> >> On Wednesday, June 5, 2013 8:41:20 AM UTC-7, Matt Herron Jr. wrote:
>
>
>
> >> What you're basically looking for is a solution to a reasonably
>
> >> straight-forward heat transfer problem. We can make a set of assumptions
>
> >> to make this a solvable problem.
>
> >>
>
> >>
>
> >>
>
> >> 1) The temperature of the water is basically spatially uniform.
>
> >>
>
> >> 2) The temperature of the surrounding atmosphere doesn't change.
>
> >>
>
> >> 3) The fluid properties (density and specific heat) are constant.
>
> >>
>
> >> 4) The heat transfer is convective only (from cold air flowing around
>
> >> the water container). No conduction or radiation.
>
> >>
>
> >> 5) There's no forced convection (i.e. no fans or forced flow into the ballast tank)
>
> >>
>
> >> 6) The free convection heat transfer is fairly efficient or the cold air
>
> >> motion outside of the water container is substantial (i.e. Gr and Pr are large)
>
> >>
>
> >>
>
> >>
>
> >> If you do this, you end up with an equation that looks like this:
>
> >>
>
> >>
>
> >>
>
> >> -h * A * (T - To) = rho * V * (Cp * dT + hfs) / dt
>
> >>
>
> >>
>
> >>
>
> >> h = the convective heat transfer coefficient, which basically measures
>
> >> how efficiently heat is being transferred. With our assumptions, we can
>
> >> roughly approximate h = 1.52 * (T - To)^(1/3).
>
> >>
>
> >> A = the surface area of the water container
>
> >>
>
> >> T = the temperature of the water at time t, We'll use 32 °F here since
>
> >> most of the heat transfer will be occuring while the water is undergoing the phase change
>
> >>
>
> >> To = the outside temperature (this needs to be below 32 °F)
>
> >>
>
> >> rho = the density of the water
>
> >>
>
> >> V = the volume of the water
>
> >>
>
> >> Cp = the specific heat of the water (assume around 4.2 kJ/ kg K)
>
> >>
>
> >> dT = the difference between the initial and final water temperatures
>
> >>
>
> >> dt = the time it takes to freeze
>
> >>
>
> >> hfs = the enthalpy of fusion (about 334 kJ/kg)
>
> >>
>
> >>
>
> >>
>
> >> Rearrange the equation and we set the energy required to freeze the
>
> >> water (hA(T-To)) is equal to the energy required to cool it
>
> >> (rhoVCpDT/dt) plus the energy required to turn it into a solid (rhoVhfs/dt).
>
> >>
>
> >> Suppose you have a typical water bottle as a simple example.
>
> >>
>
> >>
>
> >>
>
> >> Starting with h, if you begin at room temperature, h = 1.52 * (25-0)^(1/3) = 4.4 (W/m^2 K)
>
> >>
>
> >>
>
> >>
>
> >> Assume a cylindrical container meauring about 6" x 2.5". So PI * D * L = 0.03 (m^2)
>
> >>
>
> >>
>
> >>
>
> >> The outside air is at 0 °F (-18 °C) and the water starts at about room
>
> >> temperature (20 °C). So T - To = -40 (°C)
>
> >>
>
> >>
>
> >>
>
> >> The volume is about 500 mL, the density is about 1000 kg/m3, so the mass is about 0.5 kg.
>
> >>
>
> >>
>
> >>
>
> >> The specific heat we said above was 4.2 (kJ/kg K) or 4200 (J/kg)
>
> >>
>
> >>
>
> >>
>
> >> The temperature change will be from room temperature to freezing, so 20 °C.
>
> >>
>
> >>
>
> >>
>
> >> The enthalpy of fusion from above is 334,000 J/kg.
>
> >>
>
> >>
>
> >>
>
> >> Plugging all this in and solving for dt gives a time of 31,667 s or
>
> >> about 8 hr. 48 mins. For any volume of room temperature water going into
>
> >> a freezing environment, the only thing that will change will be the
>
> >> surface area (A), and the volume (V). The rest you can keep the same as
>
> >> a basic approximation so you have:
>
> >>
>
> >>
>
> >>
>
> >> t = 1,900,000 V/A
>
> >>
>
> >>
>
> >>
>
> >> where V and A are in m^3 and m^2, respectively.
>
> >>
>
> >>
>
> >>
>
> >> The V/A for tail tanks and wing tanks vary only slightly. We should
>
> >> probably adjust the heat transfer coefficient downward a bit from the
>
> >> above example since the tanks in most gliders are insulated with the
>
> >> composite/foam sandwich of the structure. This will make the time
>
> >> longer. If it's warmer than 0 °F it will take longer still, so for
>
> >> normal thermal soaring you would expect never to get to frozen solid.
>
> >> Maybe on a really long wave flight you should worry.
>
> >>
>
> >>
>
> >>
>
> >> Lastly, as has been pointed out, depending on your venting, valving and
>
> >> CG considerations, you may have localized water management issues from
>
> >> small-scale freezing, but I wouldn't worry about a giant block of ice
>
> >> exploding from my wing or tail.
>
> >>
>
> >>
>
> >>
>
> >> 9B
>
> >
>
> > Interesting calculation. I wonder why use such assumptions as
>
> > "temperature of the surrounding atmosphere doesn't change", which it does
>
> > as altitude changes and weather changes through a long flight. Also,
>
> > "room temperature" is hardly close when filling tanks in winter or from
>
> > well water..How does the result look if these assumptions are at their worst maximum?
>
> >
>
> > -Jim


I started to work on the equation the other night, but the Stanley Cup playoffs got me distracted :-) It involved dusting off my old textbooks, but I think Andy's work passes the sniff test.

Couple of points: Starting temp is obviously important. 2C vs 15C makes a difference. Out West, I'm sure most flights start with temps on the ground well up into the 20C range, so it's probably not a factor. Back East, we do a lot of ridge flights where the surface temps are probably less than 5C. If the water sat in a car-top container overnight or even in the wings, it's likely that the water started off around there. If it came out of a spigot, it's likely that it was closer to 10C.

Anecdotally: There were a lot of long ridge flights from Blairstown in the 1990s. Temps at altitude probably -5C and ground temps just over 0. Typical flights were 5-6 hours (any more, and it was the pilot freezing solid that was the issue). I don't recall anyone having any issues with bags or tanks freezing into solid blocks. I do remember a couple of cases where leaky LS valves lead to freezing on the flaps or tail. I also believe there were a couple of cases of asymmetrical dumping due to one wing valve freezing. The tail one was kinda scary, because I believe the rudder basically jammed.

So, my take is that there are significant risks, especially if the lower levels where you are flying are at or below freezing. But, the risks aren't so much the solid block of ice as problems with the valves and freezing from any small leaks.

P3

[Peter von Tresckow]

"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

[Craig R.]

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....

[jfitch]

On Saturday, June 8, 2013 8:04:15 PM UTC-7, Craig R. wrote:
> 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....

Having not studied thermodynamics you have saved yourself from a lifetime of boredom (even it if was only an hour a week). To a good approximation, the shape is accounted for in the surface to volume estimate, and the head space is not consequential to heat exchange.

[[email protected]]

On Saturday, June 8, 2013 8:23:00 PM UTC-7, jfitch wrote:
> On Saturday, June 8, 2013 8:04:15 PM UTC-7, Craig R. wrote:
>
> > 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....
>
>
>
> Having not studied thermodynamics you have saved yourself from a lifetime of boredom (even it if was only an hour a week). To a good approximation, the shape is accounted for in the surface to volume estimate, and the head space is not consequential to heat exchange.

I looked up the effect of various materials on heat transfer and it would appear that 1/4" of foam-composite sandwich roughly halves the heat transmission, extending the time to freeze by roughly double.

The starting temperature of the water doesn't matter that much in the end result (if the end result you are looking for is a solid block of ice). The enthalpy of fusion (turning 32-degree water into 32-degree ice) represents 75-90 percent of the heat transfer versus 10-25 percent to take the water from its starting temperature to 32 degrees.

Again, you would have to be on one of those 16-hour, 25,000 foot Sierra wave flights to worry about frozen-solid ballast tanks - even then I remain a bit skeptical that you'd have a problem. The main risk on a typical summer thermal flight in the 16-18,000' range is from leaking water freezing up on a valve or hinge that you care about. People who have experienced this seem to report pretty consistently that you can break free most of the time. I probably would avoid dumping ballast in freezing conditions if possible.

9B

[[email protected]]

On Saturday, June 8, 2013 8:50:02 PM UTC-7, wrote:
> On Saturday, June 8, 2013 8:23:00 PM UTC-7, jfitch wrote:
>
> > On Saturday, June 8, 2013 8:04:15 PM UTC-7, Craig R. wrote:
>
> >
>
> > > 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....
>
> >
>
> >
>
> >
>
> > Having not studied thermodynamics you have saved yourself from a lifetime of boredom (even it if was only an hour a week). To a good approximation, the shape is accounted for in the surface to volume estimate, and the head space is not consequential to heat exchange.
>
>
>
> I looked up the effect of various materials on heat transfer and it would appear that 1/4" of foam-composite sandwich roughly halves the heat transmission, extending the time to freeze by roughly double.
>
>
>
> The starting temperature of the water doesn't matter that much in the end result (if the end result you are looking for is a solid block of ice). The enthalpy of fusion (turning 32-degree water into 32-degree ice) represents 75-90 percent of the heat transfer versus 10-25 percent to take the water from its starting temperature to 32 degrees.
>
>
>
> Again, you would have to be on one of those 16-hour, 25,000 foot Sierra wave flights to worry about frozen-solid ballast tanks - even then I remain a bit skeptical that you'd have a problem. The main risk on a typical summer thermal flight in the 16-18,000' range is from leaking water freezing up on a valve or hinge that you care about. People who have experienced this seem to report pretty consistently that you can break free most of the time. I probably would avoid dumping ballast in freezing conditions if possible.
>
>
>
> 9B

Okay - I put a 2 liter bottle of fresh tap water in my 0-degree freezer with an electronic temperature probe in it. Started at 64 degrees F. Within 1:45 it was at 32 degrees F but totally liquid. After 2:30 it had a thin layer of ice around the inside maybe 1/32" thick that you could easily crack. At around 4:30 it had big chunks of ice in it and the bottle was looking a bit taught, but overall it was still pretty slushy. It's now 6:30 and there is still liquid water in the bottle, the temperature is still 32 degrees F but it's mostly ice. As it froze the freezer came up from 0 degrees to 2 degrees F presumably because of the heat transfer from the state change to solid ice.

I'd say the math works pretty well. If I can find a sleeve of foam core I'll try it again.

9B

[Mike the Strike]

How about testing the counter-intuitive experimental finding that warm water freezes quicker than cold (the suggestion is convection currents increase heat transfer).

Mike

[Mike the Strike]

On Sunday, June 9, 2013 6:11:35 PM UTC-7, Mike the Strike wrote:
> How about testing the counter-intuitive experimental finding that warm water freezes quicker than cold (the suggestion is convection currents increase heat transfer).
>
>
>
> Mike

Google "Mpemba effect"

[[email protected]]

On Sunday, June 9, 2013 6:14:19 PM UTC-7, Mike the Strike wrote:
> On Sunday, June 9, 2013 6:11:35 PM UTC-7, Mike the Strike wrote:
>
> > How about testing the counter-intuitive experimental finding that warm water freezes quicker than cold (the suggestion is convection currents increase heat transfer).
>
> > Mike
>
> Google "Mpemba effect"

I suspect it's BS. Most of the explanations are undercut by the fact that there is no such thing as thermal inertia. It doesn't matter how fast the initial cooling is, the warmer water still has to pass through the temperature of the cooler water, which it will do later and never catch up.

It's also almost impossible to test precisely because the point of being totally frozen is hard to detect.

[Tom Gardner[_2_]]

wrote:
> On Sunday, June 9, 2013 6:14:19 PM UTC-7, Mike the Strike wrote:
>> On Sunday, June 9, 2013 6:11:35 PM UTC-7, Mike the Strike wrote:
>>
>>> How about testing the counter-intuitive experimental finding that warm water freezes quicker than cold (the suggestion is convection currents increase heat transfer).
>>
>>> Mike
>>
>> Google "Mpemba effect"
>
> I suspect it's BS.

Consider a refrigerator in which a bowl is in contact with
the cooling coils, and the coils have a layer of frost.

Put bowls of hot and cold water onto the frosty coils.
Hot bowl melts the frost to produce a puddle of water,
but the cold bowl does not.

Water re-freezes so that the hot bowl is in much better
thermal contact with the cold coils, so heat is removed
faster and the hot water freezes sooner.

None of which is likely to be relevant in a glider.

[Mike the Strike]

No question that the Mpemba effect (if it exists) isn't relevant to the glider water ballast setup.

As the senior RAS physicist, I was just messing with 9B!

Mike

[[email protected]]

On Monday, June 10, 2013 3:05:24 AM UTC-7, Tom Gardner wrote:

> Consider a refrigerator in which a bowl is in contact with
> the cooling coils, and the coils have a layer of frost.
>
> Put bowls of hot and cold water onto the frosty coils.
> Hot bowl melts the frost to produce a puddle of water,
> but the cold bowl does not.
>
> Water re-freezes so that the hot bowl is in much better
> thermal contact with the cold coils, so heat is removed
> faster and the hot water freezes sooner.
>

Seems like an unlikely scenario. I've done it and the cold water melts the frost too because it takes a lot of energy to freeze water (cold or hot) which comes out of the frost. If the cold water was so cold that it was partially frozen, then maybe the frost wouldn't melt, but then it would be so far ahead of the warm water in terms of the enthalpy of fusion that the hot water would never catch up.

These thought experiments make a lot of assumptions that turn out not to be true - usually because the magnitude of the various effects at play are poorly understood by the people doing the thinking.

Quite right it's not applicable to the question from the OP.

BTW - in my empirical study, I was surprised how solid the ice became well prior to all the water being entirely frozen.

9B