[ARC5] Radios in XB-19?

[Michael Hanz]

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 <mailto: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 <mailto:scr287 at att.net>>
>     To: milsurplus <milsurplus at mailman.qth.net
>     <mailto:milsurplus at mailman.qth.net>>; ARC-5 List
>     <arc5 at mailman.qth.net <mailto: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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