[Milsurplus] 115 VAC 400 Hz tolerance, and the B-36

[Peter Gottlieb]

The 1600 Hz power comment is interesting.  As a teen I picked up on 
Canal St an aluminum power distribution panel which was marked "1600 CPS 
3 Phase" (or something to that effect) and had some very heavy wiring.  
All the breakers, those Heinemann bakelite toggle ones, were 3 phase and 
marked for 1600 Hz.  This is going back 4 decades but I remember the 
aluminum was heavy gauge, with plenty of lightening holes, and the 
design and wiring were of the probably late 50's style and not WWII 
era.  I really hadn't up to then, or since then, seen any mention of 
1600 Hz power and it's always been a point of mystery for me.  The panel 
had one input, a main breaker, and about a half dozen output breakers.  
I can't remember any more details.

Peter


On 1/15/2011 10:23 AM, Mike Hanz wrote:
> On 1/14/2011 8:48 AM, Ray Fantini wrote:
>> I would speculate that's why DC to AC inverters was used because until constant speed drives were developed there was no way to control AC frequency or phase of multiple generators in a large aircraft until the post war forties or the fifties, goes back to the B-36 again.
> I'm sure that was a factor, Ray.  The 28vdc bus in the B-29 and other
> combat aircraft was distributed all over the airframe, as were multiple
> junction boxes.  As the avionics evolved (as it did rapidly the last two
> years of the war) it was a simple thing to add another MG-149
> (http://aafradio.org/NASM/Enola_cockpit_026a.jpg ) or even larger
> inverter to the power infrastructure, close to the device requiring the
> power.  The Navy appears to have had a more forward thinking approach
> with their NEA-* ("Navy Electrical Alternator" perhaps?) series of
> engine driven alternators, which did have its own bus in some of the
> larger aircraft, but there was no attempt to worry about frequency
> control so much.  It appears that was a problem that was pushed off on
> the avionics designers, leading to a power frequency range spec of up to
> 1,600Hz! :-)   Their only mistake was to choose 800Hz as a standard
> frequency because of inductive load effects that needed lots of
> capacitors to correct.  The 400Hz standard was a better tradeoff in many
> aspects, which is why we still have it today, I suppose.  The Navy
> reluctantly began acquiring the MG-149 for their 400 Hz requirements
> toward the end of the war - there is a blurb about it in the Airborne
> Electrical Maintenance Notes document.  I will say that the Navy 800-1
> and USAAF MG-149 are not all that stable from a frequency standpoint, at
> least the ones I have here.  They do hop about in frequency a bit if you
> have varying loads....I notice the APA-10 panadapter baseline hunts up
> and down slightly with the centrifugal regulator corrections.
>
>
>> Trivia: the early versions of the B-36 used an ARC-8 (BC-348/ART-13) and later used AN/ARC-21. I am still looking for pictures, parts  or any information on the huge mysterious "drum" radio. Think the last time I brought this up the opinion was it was extinct.
> I still see AN/ARC-21 modules on ebay from time to time, even acquired a
> couple with some vague notion of potentially retrofitting my AN/ARC-65
> (bottom of http://aafradio.org/flightdeck/vhf.htm ) back to ARC-21
> condition, but haven't found all of them.  As KK5F mentioned, there are
> a couple of other list members who have them as well, one an original
> ARC-21, IIRC.  The ARC-65 case has a nomenclature plate inside that
> states that it is an ARC-21 part, reflective of the fact that most (but
> not all) of the ARC-65s were converted from an ARC-21 condition.  There
> are two different power supplies for either set - a weighty triple
> dynamotor assembly and a later 400Hz AC replacement.  The AC supply is
> an incredibly small box that is cleaner from a noise and maintenance
> standpoint, but relating back to the subject line, requires a 21 amp
> 115vac 400Hz power source in the transmit mode (37 amps while tuning!!)
> in addition to 20 amps of 28vdc, a daunting task even in this day and
> age.  The power connectors are unique enough to demand a *very* hefty
> price tag, even from Bill Perry which is where I found mine.  The latest
> control head for the ARC-65 has an AME (AM Equivalent) position to
> simulate AM transmission (carrier plus one sideband.)  I have the 400
> pound manuals for both the ARC-21 and ARC-65 and can provide details if
> you can tell me what in particular you are interested in.  There are a
> few snippets of interest in the link above (and the
> http://aafradio.org/flightdeck/arc-65.htm sublink) that may satisfy part
> of your curiosity, including a few photos of its components.
>
> 73,
> Mike   KC4TOS
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