[ARC5] Radios in XB-19?

Mon Jan 11 15:46:11 EST 2016

You are inverting the DC back and forth?
Jay

-----Original Message-----
From: Tim <timsamm at gmail.com>
To: Michael Hanz <aaf-radio-1 at aafradio.org>
Cc: To: ARC-5 <arc5 at mailman.qth.net>; Military Surplus Mail List (milsurplus at mailman.qth.net) <milsurplus at mailman.qth.net>
Sent: Mon, Jan 11, 2016 10:57 am
Subject: Re: [ARC5] Radios in XB-19?

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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