[Milsurplus] ARC-21 rebuttal

Mon Jul 30 21:27:29 EDT 2018

Second try, see PS below.

RolynnThe ARC-21 reliability issue was in the public eye 1953-54.  Reliability was approaching 100 hours or so but the BNS in this time period was much much lower.  Given enough time I am sure I can find my notes on BNS reliability but the below will have to do until then.  
Remember, I am reporting on the status of things about 10 years before your enlistment.  BTW, I was in USAF from '67 to '72 but I was a Ground Radio Tech, 30454 and spent all of my active duty time overseas.
"From the beginning, MA-6A tests demonstrated the incompatibility of the APS-64 radar with the experimental Motorola 10-inch radar scope. The radar presentation proved unsuitable for bombing and the reliability of the combined equipment was very low. This situation was especially critical since the APS-23 was going out of production in April 1955 and by that time only enough sets to support the B-47 or the B-52 program would be in existence—but not both. Accordingly, the Air Research and Development Command and the Air Materiel Command jointly decided late in 1954 to install the APS-23 in production B-52's until the APS-64 passed suitability tests. The B-47 remained committed to the tunable AFS-64. In this configuration, the K-4A emerged as the MA-7A bombing-navigation system.
The MA-7A was in production by November 1955 and development of the B-47 bombing and navigation system was essentially complete. Production continued through 1956, and in 1957 the B-47B and B-47E aircraft in the field were being retrofitted with the MA-7A. Bombing and navigation system development for the B-52, however, was far from complete. The MA-6A was still being considered for the Doppler radar and the astro-compass and beyond that the ASB-4 was on the books.65
Wright Air Development Center had delivered a B-47 with Doppler-augmented K-system to the Air Force Armament Center, in July 1955, for tests aimed principally at the MA-6A. The test installation also contained provisions for automatic crosshair-laying, semi-automatic fix taking, and dead reckoning navigation. The first flight at Eglin on 22 July 1955 revealed that the Doppler set caused "Wander" in the wind values calculated by the D-system, a condition which made the equipment completely unsatisfactory for bombing. General Precision Laboratories went to work on the APN-81, and Sperry on the computers already modified by International Business Machines, in an attempt to resolve the difficulties. By July 1956, the Doppler tie-in was at last working satisfactorily during test flights."
The above is excerpted from:DEVELOPMENT OF AIRBORNE ARMAMENT 1910 – 1961Historical Division, Office of Information, Aeronautical Systems DivisionAir Force Systems Command
Attached is the BNS flow chart for the K-MA-7A so that interested parties can see just how complicated the avionics was in the B-47, all of this was before solid state.  It's all tubes and relays!Regards,Jim
PS, I did not receive a copy of the original reply so I stripped the BNS flow chart and I am resending.  If anyone is interested in a copy, please reply off list. I wonder why people argue over the 10% of their differences and ignore the 90% they agree on?

      From: ROLYNN PRECHTL <k7dfw at clatskanie.com>
 To: Jim Whartenby <antqradio at sbcglobal.net>; "Milsurplus at mailman.qth.net" <Milsurplus at mailman.qth.net> 
 Sent: Monday, July 30, 2018 6:08 PM
 Subject: Re: [Milsurplus] ARC-21 rebuttal

 Just about every avionics system aboard the B-47 experienced the same problems in that they were designed on the cutting edge of an unproven technology developed at the end of WW2.  Never mentioned in these reliability criticisms of the ARC-21 is the B-47 Bombing and Navigation Computer.  It used over 300 vacuum tubes and an unknown number of relays in tying together various navigation systems and had a MTTF measured in single digit hours.

===============================================================================

I spent 1963 and 1964 as a MA-6A/MA-7A Bomb Nav Flightline Mechanic (32150E) at the 40th Bomb Wing, 40th AEMS, Forbes AFB.

This stated MTBF did not happen on my watch. The Bomb Nav system ran for many hours without malfunction. Some malfunctions reported in the 781 were coverups for operator error. There were malfunctions, but at a rate where my life on the flightline was a piece of cake. 

The CAU and SAU (where most of those tubes lived) were reliable.

This single digit MTBF idea is rubbish and the Wing wouldn't be able to pass an ORI if it were true. 

Curtis LeMay would never have allowed that MTBF to exist.

Rolynn
USAF 1962-1968
______________________________________________________________
Milsurplus mailing list
Home: http://mailman.qth.net/mailman/listinfo/milsurplus
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Milsurplus at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20180731/17a38b9d/attachment-0001.html>