[ARC5] [Milsurplus] Radios in XB-19?

Mon Jan 11 16:40:29 EST 2016

If you look just above the red fire extinguisher you will see the two grey MG inverters, primary and back up, in the bottom of the navigators cabinet.  These two inverters are the only source of 115v 400 cy AC that is used in the B-29 for bus power. Post war overhauled B-29’s used larger units. The small volt meter on the FE‘s panel gives the output and AC bus voltage of these inverters. Next to it is the DC volt meter that could be switched between all 6 engine driven generators and the APU. The ammeters for the generators are located above the flight engineers hatch.

Taigh

Taigh Ramey

Vintage Aircraft Inc.

7432 C.E.Dixon Street

Stockton, California 95206

(209) 982-0273

(209) 982-4832 Fax

 <http://www.twinbeech.com/> www.twinbeech.com

KEEP 'EM FLYING...FOR HISTORY!

From: antqradio at sbcglobal.net [mailto:antqradio at sbcglobal.net] 
Sent: Monday, January 11, 2016 12:21 PM
To: Ray Fantini <RAFANTINI at salisbury.edu>; Taigh Ramey <taigh at twinbeech.com>; 'Michael Hanz' <aaf-radio-1 at aafradio.org>
Cc: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] [ARC5] Radios in XB-19?

A look at the B-29 engineer's position shows an AC voltmeter.  I have no idea how extensive the AC distribution system was on the B-29 but it had at least one AC system.  Perhaps motor-generator since there is a light below that monitors inverters?

http://www.nmusafvirtualtour.com/media/035/B-29%20Pilot%20Station.html

AC meter is on right hand side of the console about half way down.  Further down are more circuit breakers and switches but harder for me to read the markings.

Also appears to be someone (or something) sitting in the bombardier's position.

Jim

  _____  

From: Ray Fantini <RAFANTINI at salisbury.edu <mailto:RAFANTINI at salisbury.edu> >
To: Taigh Ramey <taigh at twinbeech.com <mailto:taigh at twinbeech.com> >; 'Michael Hanz' <aaf-radio-1 at aafradio.org <mailto:aaf-radio-1 at aafradio.org> > 
Cc: "milsurplus at mailman.qth.net <mailto:milsurplus at mailman.qth.net> " <milsurplus at mailman.qth.net <mailto:milsurplus at mailman.qth.net> >
Sent: Monday, January 11, 2016 1:43 PM
Subject: Re: [Milsurplus] [ARC5] Radios in XB-19?

In the book” Magnesium Overcast” they claim that the B-36 was the first aircraft designed from the ground up to use the three phase 400 cycle AC distribution system being that resulted in a weight reduction of several thousand pounds compared to a DC system and the associated dynamotors for radio, radar and control systems. I will speculate that weight reduction and reliability had more to do with replacement of DC distribution on large aircraft and large transmitters in the design and construction of power supplies. Think the B-29 was a bit early for AC distribution.

Ray F

From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Taigh Ramey
Sent: Monday, January 11, 2016 1:16 PM
To: 'Michael Hanz'
Cc: 'To: ARC-5'; milsurplus at mailman.qth.net <mailto:milsurplus at mailman.qth.net> 
Subject: Re: [Milsurplus] [ARC5] Radios in XB-19?

>From my limited experience with WWII aircraft I believe that one of the primary needs for AC in the aircraft itself was for the engine and position instrumentation. It seems that smaller aircraft would use direct reading instrumentation for pressures etc. meaning you would have air, fuel and oil in a small line from the engine to the instrument in the cockpit. These lines would normally have fittings with small orifices to act as restrictions in case of a rupture in service for operational or combat reasons. This orifice would act as a restrictor to the flow to limit the amount flow thus causing an obvious hazard. 

It seems like the larger aircraft utilized selsyn systems or other electronic means for pressure reporting. I believe that this was also due to the effects of cold at altitude as well as for safety concerns and the longer runs needed in these aircraft. The length and temperature in which the fluid had to travel would create inaccurate readings especially over long runs due to the fluid viscosity at low temperatures, line loss etc. Moisture and condensation also caused problems in air transmission lines for instrumentation and imposed its own kind of errors.

Smaller aircraft seem to have mostly all direct reading instruments. Medium bombers and transports start to have pressure and flow transmitters of some kind. Larger bombers and transports will have more electrical pressure transmitters for instrumentation which is why I would bet that the B-19 would have had many. 

The B-17 and B-29 had the MG units (often one as a primary and one as a backup) and a small AC bus but it was mostly for instrumentation rather than radios. It seems like the radios used their own local AC in the form that we are familiar with. Radar also had their own power units.

Interestingly our museum’s late war production US Navy PV-2D harpoon has a lot of AC needs throughout the aircraft but they used all local AC. No AC bus at all. From the local Bendix dynamotors one each used for the flux gate compass and another one for the drift meter to the individual ones for all of the radios. There were two 800hz dynamotors, one primary and one as a backup (which we are still looking, hint hint!) for that were used for the IFF and radar. The Harpoon also had two engine driven 28.5 volt DC generators to power everything. 

In my WWII aviation experience I have not seen anything but DC engine driven generators. I have not seen any AC power created at the engine. Mostly they all used DC to AC conversion via motor generator sets or dynamotors of varying capacity. I believe this may have been because of the ability to accurately control frequency. I am certainly not an electronics expert in any way, in fact quite the opposite, but from what I have learned it was very hard to maintain frequency at the time with a reciprocating engine that would be operating at varying rpm. I have seen post war installations of AC engine driven power but they usually have a constant speed drive associated with them bolted onto the engine. These CSD’s were quite complex. 

I remember seeing the AC power generated on the Viet Nam era Beech QU-22 which was a military version of the A-36 Bonanza. The QU-22 had a large alternator that was belt driven off of a pulley on the crankshaft. The large bump on top of the cowling was for this alternator. They would vary the engine RPM to obtain the 400 cycles needed for the “prime mission equipment”. They used a finger resonance type of instrument on the pilots panel as a reference to get the frequency right on 400 cycles. I imagine that the CSD for the GTSIO-540 engine may have weighed about half of what the engine weighed thus the need for a simpler method to get the desired frequency. 

I have also seen in areas where it was critical to have accurate power, usually in gun sighting systems, where they would have a local carbon pile voltage regulator to further refine the incoming power presumably to produce a precise 28.5 volts as variations may make a large difference in the accuracy of the sighting system.

Taigh

Taigh Ramey

Vintage Aircraft Inc.

7432 C.E.Dixon Street

Stockton, California 95206

(209) 982-0273

(209) 982-4832 Fax

www.twinbeech.com <http://www.twinbeech.com/> 

KEEP 'EM FLYING...FOR HISTORY!

From: ARC5 [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Michael Hanz
Sent: Monday, January 11, 2016 5:47 AM
Cc: To: ARC-5 <arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net> >; milsurplus at mailman.qth.net <mailto:milsurplus at mailman.qth.net> 
Subject: Re: [ARC5] Radios in XB-19?

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