[Milsurplus] ARC-21 rebuttal
Francesco Ledda
frledda at att.net
Mon Jul 30 19:11:42 EDT 2018
Jim, thank you for the valuable information.
Best, Frank K5URG
Sent from my iPad
> On Jul 30, 2018, at 16:20, Jim Whartenby <antqradio at sbcglobal.net> wrote:
>
> Mike said:
> The RCA AN/ARC-21 (and its AN/ARR-36 aux receiver) replacement for the AN/ARC-8 was late by years, fabulously over-budget, and initially of poor reliability to the point that the program was subject to several congressional hearings. Because of that, the AN/ARC-8 was guaranteed to have a long service life. AN/ARC-21 program delays also spawned USAF purchases of many much lower cost and trouble Collins 618S-1 (per Mike's correction) and 18S-4 and AN/ARC-59 (RT-380/AR, 18S-4A) sets for use in support and logistics aircraft rather than the very costly and scarce AN/ARC-21.
>
> Post-WWII the USN used the AN/ART-13 and AN/ARR-15 in a combo similar to the AN/ARC-8 called the AN/ARC-25. When its successor was being developed, the USN avoided much trouble, delay, and great cost by choosing the Collins AN/ARC-38 (and its AN/ARR-41 aux receiver). Congressional reports compared the USAF AN/ARC-21 programs rather unfavorably to these USN programs. IIRC, the USN's early 1950s per-system cost was about $7000, compared to the USAF's $21000.
> Mike
>
> The above is indeed based on a few facts, some of which were a bit hard to verify but the implications of the above do not hold up under examination. Kind of like the kid who farted in church. No matter what he did later in life, he was always remembered for that Sunday.
>
> There was no viable replacement for the ARC-21 in 1954, at least not for the aircraft for which it was designed, the B-47. The ARC-21 was installed in other support aircraft such as the KC-97, a modified B-29 used for aerial refueling. The ARC-21/65 also saw use in the B-36H&J and in the B-52B through G. Yes, there were initial teething problems with the development, testing and production of the very first fully synthesized and automatically tuned HF transceiver. No different then any other "first of" programs.
> 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. The B-47 aircraft itself had similar problems with underpowered jet engines, wings that failed with no warning and unexpected stress to the airframe, all of which was due to metal fatigue.
>
> Let's look at transceiver specifications:
> ARC-21 618S ARC-38
> Freq range: 2-24 mc 2-25 mc 2-25 mc
> Channels 44,000 144 32,250
> Ch. spacing 500 cycles NA 500 / 1000* cycles
> Freq. stability 0.0015% 0.007% 0.01%
> Altitude 50k feet 50k feet 50k feet
> Op. temp. -55C to +85C Unk Unk
> RF power >100 watts >90 watts* >90 watts*
> freq set direct input crystal code book
> Weight** 136 lbs 64 lbs 73 lbs.
> *Frequency dependent, high frequency spec shown
> **R/T + mount, approximately half of the ARC-21 mount is part of the R/T unit
>
> The 618S or ARC-38 operating at 50,000 feet seems a bit optimistic to me. Air pressure is down to about 11.5% that of sea level. How is the R/T unit cooled at this altitude? Neither the R/T unit nor the mounting rack have fans to move air. What about condensation of water on the modules as the aircraft climbs to operational altitude from hot and humid airfields?
>
> The parts of the B-47 airframe that did not carry "the bomb" or was pressurized for the aircrew was devoted to fuel storage. The wings of the B-47 were too thin to allow wing tanks, a problem avoided in the design of the B-52. The assigned space for the ARC-21 was in the rear section of the fuselage, behind the rear landing gear, just under the area where the vertical stabilizer transitions from the fuselage. The ARC-27 or ARC-34 UHF command radios were also mounted in this area. All equipments in this area were subject to vibration from flight and jet engine noise plus the bitter cold of high altitude flight.
>
> Even when mounted in other aircraft such as the B-36 or B-52, the ARC-21 or ARC-65 transceivers were mounted in the same unpressurized compartments so all R/T units were exposed to the same harsh environment. All of the installations I have seen for the 618S and ARC-38 transceivers show them mounted in crew compartments. One only assumes that close to normal air pressure allowed good ventilation and minimal water condensation inside the R/T unit.
>
> The ARC-8 was never considered for installation in any of the above aircraft. It was a WW2 design that was obsolete and long out of production. Sufficient components were in stock to meet replacement needs but not enough for the number of aircraft designed to fight in the Cold War. As per previous discussions on this list, few aircraft were ever upgraded with more modern avionics. One notable exception is the B-52 which has seen many avionics upgrades during it's long service life. The ARC-8 required a radio operator, the elimination of which was the reason for the development of the ARC-21.
>
> ARC-21 tidbits:
> > First use of mechanical filters (3 each) in a military radio, all designed and built by RCA
> > First radio to use a fully automatic antenna tuner, designed and developed by ERA, Remington Rand, Inc.
> > First radio transceiver able to operate at full transmit power up to 50,000 feet
> > Development contract date: 19 March 1948
> > 1st production contract: AF33(038)-18325, Date: 1952, Quantity: 3900, @ $15,372.77 ea.
> > First delivery to USAF, early February, 1953
> > 2nd production contract: AF33(600)-32331, Date: 1956, Quantity: 121, @ $13,231.24 ea.
> > 3rd production contract: AF33(600)-32926, Date: 1956, Quantity: 380, @ $12,039.95 ea.
> > 4th production contract: AF33(600)-33883, Date: 1956, Quantity: 551, @ $11,599.00 ea.
> > 5th production contract: AF33(600)-35867, Date: 1957. Quantity: 442, @ $11,288.82 ea
> > Total number of ARC-21's built as of 20 April 1961: 5,349
> > Total number of B-47 bombers built: 2,032 aircraft
>
> I have no idea of how many ARC-21s were converted to ARC-65s which were the USB only version of the ARC-21. At least two of the 10 modules were replaced outright when the ARC-21 was upgraded. I do not know what other modules were either modified or replaced. I will have to check the IRE article for more details. The reason for this upgrade was to recoup the investment made in the AM only transceiver. The latest document that I have for the ARC-65 is dated 1 Feb 1972 with Change 4 dated 21 January 1976. So this transceiver soldered on for quite a few years.
>
> As for the Navy avoiding much trouble by choosing the ARC-38, it should be noted that the Navy actually paid for the ARC-38 development. Backtracking a bit, the Navy let a contract to Collins Radio in 1947 for a long range airborne radio transceiver. It was designated as the ARC-26. After spending approximately $1,000,000 for development, the Navy canceled the contract in 1952 because it was too heavy and complex for Navy requirements. A new contract was let for the ARC-38 with a estimated cost of $5,800 per R/T unit. The ARC-38 was still undergoing tests by the Navy in 1954 and no production orders had been given to Collins Radio at this time. I do not know when the ARR-41 contract was let.
> Regards,
> Jim
>
> I wonder why people argue over the 10% of their differences and ignore the 90% they agree on?
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