[ARC5] An Interesting Failure Mode

[Bill Cromwell]

The temperature at 20,000 feet is far below zero. I don't think there 
were any pressurized (heated cabin) aircraft before the B-29. The 
mosquito was a plywood, twin engine aircraft. If the thin air (due to no 
pressurization) affected the fan then the fan also wouldn't be needed in 
the frigid air. No beer cooler required, too -evil grin-.

73,

Bill  KU8H

On 12/13/2016 02:36 PM, Richard Knoppow wrote:
>     Why would the cooling fan not be required?  The heat is still 
> being generated. The fan or blower is running faster because the 
> density of the air becomes less as altitude is increased so the load 
> on the blower becomes less. Its efficiency as a cooling devise would 
> also become less. Some sort of vibration isolation seems to be a 
> reasonable solution or a speed regulated fan or both.
>     This story fits in the catagory of opera singers being able to 
> shatter a wine glass. Who was it, Memorex that featured a glass 
> shattering.
> On 12/13/2016 5:55 AM, Bill Cromwell wrote:
>> Hi,
>>
>> I would be interested in that information, too. I would think at
>> altitude a cooling fan would not be needed. I would switch it off above
>> 10,000 feet. It could be done automatically or be part of the
>> operational checklist. So what did "they" do?
>>
>> Think how awful their problems would be if they had named the system
>> after accordion or banjo!
>>
>> 73,
>>
>> Bill  KU8H
>>
>>
>> On 12/12/2016 10:02 PM, J Mcvey via ARC5 wrote:
>>> so...what did they do to fix it?
>>> Change  the fan
>>> change the fan blade
>>> reduce the fan voltage
>>> install a baffle
>>> shield the tube?
>>> Scrap the whole system and design a new one?
>>>
>>>
>>> On Monday, December 12, 2016 8:14 PM, Jay Coward via ARC5
>>> <arc5 at mailman.qth.net> wrote:
>>>
>>>
>>> That's what happens when you name a system after a musical 
>>> instrument...
>>> Jay KE6PPF
>>> -----Original Message-----
>>> From: Robert Eleazer <releazer at earthlink.net>
>>> To: arc5 <arc5 at mailman.qth.net>
>>> Sent: Mon, Dec 12, 2016 3:09 pm
>>> Subject: [ARC5] An Interesting Failure Mode
>>>
>>> I was just reading about the use of the Oboe navigation system by the
>>> RAF in WWII.  They proved the system out in Wellington bombers and
>>> then switched to using Mosquito bombers, where they kept having
>>> failures, a tube would seem to explode.
>>> The problem turned out to be due to the higher altitude used by the
>>> Mosquito, 20,000 ft rather than the 10,000 ft of the Wellington
>>> flights.  At the higher altitude a cooling fan, which used a Hoover
>>> vacuum cleaner motor, would turn faster due to the thinner air.  The
>>> higher RPM would reach resonance with a certain tube in the Oboe
>>> equipment, which would shatter.
>>> Wayne
>>> WB5WSV
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-- 
bark less - wag more