[ARC5] Radios in XB-19?

[Tim]

Hi Smart Guys!  Question:  Why are DC-to-AC devices called "inverters" ??
Seems like an odd choice for a name...What am I missing?

Tim
N6CC

On Mon, Jan 11, 2016 at 5:47 AM, Michael Hanz <aaf-radio-1 at aafradio.org>
wrote:

> I think it more likely that Douglas and the Army had studied Navy
> practice, which included mounting an 800Hz alternator on one engine, and
> decided to try having both AC *and* DC available as a development
> platform.  The Navy was pretty much ahead on everything related to
> avionics, and by the late 1930s had recognized that new devices like radar,
> HF transmitters like the GO-9 and GP-7, and devices requiring small amounts
> of AC power, such as navigation equipment and the like, were going to need
> both kinds of power.  However, in their haste to implement a native AC and
> DC environment on their combat aircraft, the Navy missed the mark with
> 800Hz, because the higher frequency needed compensating capacitors
> installed that could be adjusted for a particular load to eliminate the
> effect of inductive reactance in the alternator.  As it turned out, 400Hz
> was a better compromise between eliminating that need and still reducing
> the size and weight of transformers in airborne equipment.  That's how we
> ended up with the current standard for aircraft.
>
> That being said, the Army was slow to follow the Navy's lead, preferring
> to keep the primary mode of power to DC, and distributing small DC to AC
> inverters to where they were needed in a point of presence approach.
> That's how they accommodated new pieces of equipment in all the heavies,
> including the B-29.  A DC bus was never far away throughout the airframe,
> and tapping into it was easier and weighed less than trying to run two
> separate busses throughout the plane during manufacture.  You can see a
> couple of these (by 1945) ubiquitous MG-149 alternators at the navigator's
> station in the Enola Gay - http://aafradio.org/NASM/Enola_cockpit_026a.jpg
> - though larger alternators were required by power hogs like the APQ-13
> radar.
>
> The Navy did the same thing (to an extent) with their 800-1 alternator (
> http://aafradio.org/docs/800-1.htm ), (again, fighting the inevitable
> evolution to 400Hz), but those appear to have been used for the same reason
> that the Army did - to serve unexpected pieces of equipment being
> retrofitted to aircraft after they came off the assembly lines.  It wasn't
> until after the war when technology settled down enough to think about
> providing both kinds of power throughout any given airframe.
>
> 73,
> Mike  KC4TOS
>
> On 1/10/2016 11:23 PM, Bart Lee wrote:
>
> ​I heard that 400 cycle power was implemented in the B-29 because
> otherwise the weight of the transformers would have been too much to fly
> well.  (Incidentally, my father was a B-29 Flight Engineer).  Maybe the
> XB-19 prototyped 400 cycle AC power.
>
> 73 de Bart, K6VK
>
> On Sun, Jan 10, 2016 at 4:44 PM, Jay Coward via ARC5 <arc5 at mailman.qth.net
> > wrote:
>
>> Well Jack and the Group,
>>  I've always wondered what radio equipment was in the Bolo.
>>  As far as AC in the XB-19 , it may have been the power distribution
>> system and the AC to DC was done locally at the equipment. Just guessing as
>> there is not much AC gear surfacing from that era.
>> Jay KE6PPF
>>
>>
>> -----Original Message-----
>> From: Jack Antonio <scr287 at att.net>
>> To: milsurplus <milsurplus at mailman.qth.net>; ARC-5 List <
>> arc5 at mailman.qth.net>
>> Sent: Sun, Jan 10, 2016 9:59 am
>> Subject: [ARC5] Radios in XB-19?
>>
>> Does anyone have any documentation on the radios installed
>> in the Douglas XB-19?
>>
>> Note, this not a typo, I am not referring to the B-18 Bolo.
>>
>> The XB-19 was the large experimental bomber that was used more
>> as a test bed for large aircraft systems, rather than a serious
>> contender for production.
>>
>> What drives the question, is that one of the features of the plane
>> was the use of an AC power system.
>>
>> So I'm wondering if the Army used AC powered radios in the plane.
>>
>
>
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