How cold does it get in the belly of an airplane? 2

[zappedagain]

For instance, in the luggage compartment of a passenger plane this time of year? Does it get below 0C? Or is this question too open?

I just had a switching power supply fail when a demo unit got to a customer site. It was powered up soon after a long plane ride over the North Atlantic. The supply has an operational spec of 0-70C (storage -40 to +85). I'd expect it would be a bit out of spec if it started cold, but would the thermistors for the start up surge or something else get into problems at the cold temperature?

Z

 

[dpc]

I think it is supposed to be kept at least above freezing.

For a switcher, the last thing I would suspect would be cold storage temperature. There are so many other things that are more likely.

 

[melone]

Is it possible that the container with this supply in it was dropped?

 

[IRstuff]

Can't imagine that the compartment would be allowed to go near freezing, since that would mean that lots of things would freeze and break their containers.

TTFN

FAQ731-376

 

[IRstuff]

you can see:

http://www.nwa.com/travel/animals/csrestrictions.html#temperature

At least, certain parts of the luggage compartment are somewhat friendly to pets.

TTFN

FAQ731-376

 

[itsmoked]

All cargo holds are now pressurized with the same air in the passenger compartments as far as I know. Otherwise all the containers pop open and customers get annoyed. This likely means they don't get tooooo cold.

What your supply died from is likely this. If the supply was allowed to get 20~30 degrees colder than the location it ended up at then you got condensation. Doesn't matter what the storage temperature is allowed to be you will see in the spec non-condensing. This means that sure, you can have it anywhere in any temperature, but if you take it from cold to warm you have to let it sit up to several hours so it can reach the local ambient and evaporate any accumulated condensation.

You get a blown supply that by the time you open it to figure out what went wrong there is nothing visible. Your 'ice bullet' situation.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rmw]

I don't know why I believe this because I can't substantiate it, but I don't think all cargo space is maintained at cabin pressure. I think some is because some cargo can't endure conditions at altitude. Luggage space is for reasons already given, but for pure cargo, I don't necessarily think so. I don't know how they differentiate between cargo that needs to be protected and that that doesn't.

The reason is simple, air has weight and carrying it takes power and burns high dollar fuel. That is the reason that the cabin pressure (and corresponding luggage space pressure) is reduced to ~5000 ft. after takeoff and only repressurized right before landing (assuming that the landing is at an airport below 5000 ft. altitude-no ear popping at Denver).

If I am right about that, that makes the answer to the OP something like -40F or lower. You can research temperatures at altitude, but that is a temperature I remember seeing many times on transatlantic flights where they give various flight paramaters such as altitude, heading, lon., lat., and the like on monitors durng the flight.

I don't know why, but from time to time, I get luggage back that feels like it traveled in the -40F space and not the 'passenger air' space.

rmw

 

[FreddyNurk]

Regardless of all the other statements on whether or not the cargo bay is pressurised, surely you answered your own question with the specification you gave to start with.

I noted that you said operational temperature with 0 to 70 degrees, but unless the device was running in the storage hold, the storage range noted was -40 to 85 degrees (celcius). I do not believe that any cargo hold would get that cold, sure, depending on pressurisation and heating it would be cooler than the cabin, but its very unlikely to get 40 below.

The only way I could see this being related to temperature would be internal condensation after the unit has been exposed to those temperatures, and not warmed up and dried again afterwards.

Otherwise I'd be looking elsewhere.

 

[zappedagain]

Thanks for your feedback. I'll be getting the system back later this week so I can check it out.

Z

 

[zappedagain]

IT,

The funny thing is that my sales guy said it powered up properly when they first took it out of the box, but other parts of the system that are known to be temperature sensitive (won't start at <20C) weren't working. So they walked away for a while and when they came back and tried again they supply was dead. I expect if it was a condensation problem it would have clobbered it on the first power up. I hadn't tested the system on 230VAC/50Hz but the supply is rated for it so I wasn't too worried. Voltage surge on the mains?

Z

 

[itsmoked]

Left it alone!
Industrial sabotage with a pocket knife?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

Turning it on produced the heat necessary to cause the condensation that let the magic smoke out.

 

[dpc]

my sales guy said....

That should be a good clue right there.

 

[catserveng]

I used to travel quite a bit doing commissioning and startups of power generation equipment, had the same question come into my head because I was always eating batteries in my test equipment.

So for grins I left a recording temp meter with a probe attached in the logging mode on several trips in my tool case. On average the lowest temp was around 12-15C, the lowest I ever recorded was on British Airways from LA to London, measured -8C, most of the time it read in the area of 20C. Not very scientific, but it did satisfy a little of the curiosity I had.

 

[zappedagain]

Thanks cat!

Z

 

[jraef]

I for one do not believe that any of the cargo areas of a passenger jet would be left unpressurized and completely unheated. If they were, that would mean ALL adjacent walls would need to be insulated pressure bulkheads, and that would far outweigh the "weight of the air" if it were just pressurized like everything else.

Remember the ValuJet crash in the Florida everglades a few years back? The cause was determined to be not-quite-so-empty solid-ox canisters being carried in the cargo area and when they caught fire, the smoke filled the cabin and cockpit, disabling the crew. That means they shared airspace with the cargo area.

As to the power supply death, I too would suspect the condensation issue. I used to transport samples of large heat sinks with SCRs in them by checking them as cargo (security never liked seeing me carry those on board). Whenever I took possession of them after being unloaded, they were always wet.

Just because it powered up first without damage does not mean that wasn't the problem. It could easily have been that the initial damage was minor, but began a cascade of component failures that took a little longer to become catastrophic.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[zappedagain]

Thanks for the tips. I got the system back and replaced the power supply and the rest of the system is fine. The power supply is back at the manufacturer for failure analysis so I'll post a reply when I find out what happened.

Z

 

[itsmoked]

Back to the ice bullets.. They won't see anything so I bet they do a lot of speculation.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

Imagine how strong the floor would have to be if the cargo bay were unpressurized...

 

[LionelHutz]

The pressure bulkhead is just before the tail section of the plane. The cargo bays would be pressurized.

There were a few crashes of one plane caused by a poor repair to that bulkhead (I can't remember why the repair was bad). The bulkhead blew and the air escaping into the cargo hold pushed the floor down on the way out. The flight controls were in the floor.