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Thread: RAF Coastal Command Radar Altimeters

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    Default RAF Coastal Command Radar Altimeters

    Did Coastal Command aircraft use radar altimeters in WWII?

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    Hello,

    In a word, YES!

    AUS413792 Flight Lieutenant James Peter, Assistant Navigation Leader, 53 Squadron.

    'In March 1945, a need developed for meteorological flights to be made due west from Reykjavik towards the Greenland ice cap. 53 Squadron was called upon to provide a service. Meteorological flights involved slow climbs and descents along a straight track. A new wind had to be found for every change of altitude of 1,000 feet, so the navigator was kept very busy. We had to make regular descents to an altitude of 50 feet to check sea-level barometric pressure, so our radio altimeters were very welcome, and certainly an improvement on the method used by Halifaxes from Tiree, whereby the pilot was told to level out when the trailing aerial hit the sea.' (James Peter also made a north-bound trip from Reykjavik as a weather check for one of the RAF's early experimental trans-Polar flights.)

    See:
    Endurance:A History of RAAF Aircrew Participation in Liberator Operations of RAF Coastal Command 1941-1945.
    Jay,Alwyn.
    Maryborough:Banner Books,1996.
    p.188.

    Col.
    Last edited by COL BRUGGY; 19th October 2016 at 10:41.

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    518 (Met) Sqn in CC were using radalts in Halifaxes based at Tiree from mid-1943*. It meant that checking the MSL pressure (particularly at night!!) which had to be done at about 50ft ASL was a little less dangerous!!!!! Met Recce a/c landing back with salt spray dried on leading edges and windscreens was not a joke - it happened quite often!!!
    Now IIRC there were (at least!) two types of radalts. One was for use at medium/high altitudes, and the other for use at very low altitudes. Ian The Radar (if he's on the circuit) will, no doubt, be able to give us Chapter/Verse/Line on the matter!
    * "Even The Birds Were Walking", Kington/Rackliff, Tempus, 2000, ISBN 075242016X.
    HTH
    Peter Davies
    Last edited by Resmoroh; 19th October 2016 at 13:40. Reason: QSD
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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    It is probably worth noting that the radio-altimeter had to be used with extreme caution whilst flying over the sea, especially in rough conditions. Because the difference between wave tops and troughs could be as great as 50 or more feet, the height indicated by a radio-altimeter was subject to considerable variations, meaning there was a constant risk of flying into the sea, especially on dark nights.

    Conversely there was no guarantee the instrument provided a reliable return in even calm conditions. At 0200 GMT on 15 October 1945 Oxford PH480 (Radar Meteorological Flight) took off from Brawdy to obtain temperature readings whilst descending from 1500 feet over Cardigan Bay (some 30 miles west of Aberystwyth). The task required the readings at 100 ft intervals down to 200 ft. It was a moonless night and sea conditions were calm, but the radio-altimeter should have ensured a safe descent; instead the aircraft flew into the sea. Neither the wreckage nor crew were ever recovered. Crew - Flt/Lt D J Cotter (pilot), F/S A J Bidwell (navigator) and W/O E Moore (Met Air Observer).

    The cause of the accident was never determined.

    Sources: Cummings's The Price of Peace and conversations with Peter Rackliff who knew the crew and had made similar flights himself in the same aircraft.

    Brian

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    A must-read survey of the use of radio altimeters by the RAF (and particularly by Coast Command) in WW2, is Chapter 15 of "Signals, Volume III - Aircraft Radio" (pages 403 - 418), one of that large series of very useful (and quite readable) books known as the RAF Narratives. This particular volume was first published in 1956.

    In Britain, as early as January 1940, first trials were being undertaken with such an instrument, the carrier aircraft being none other than the Bristol 142, progenitor of the Blenheim family. However after a long series of trials of prototypes, many of which proved inconclusive or problematic, and requirements being issued for various types of radio altimeters to suit the specific needs of different RAF Commands, it seemed as though no really good designs were being produced, and many were considered to be no improvement on existing aneroid altimeters, despite huge efforts being put into research and development, and giving the projects the highest priority. Small numbers of production versions of the Type 2 Radio Altimeters were delivered to the Coastal Command Development Unit in June 1942 for fitment to CC Wellington aircraft "for installation and flight trials", but results of these trials were generally unsatisfactory, the history stating that "of the first eight models received by the CCDU, only four could be made serviceable because of faulty and incorrect wiring. All four were inaccurate below 200 feet", so all were sent to the RAE for modifications, then returned to the CCDU for flight trials of the altimeters which were concluded in August 1942, with the following comments. "Although on some particular flights performance of the altimeters was within acceptable tolerances, they were generally unreliable, largely owing to inferior mechanical design and workmanship. It was doubtful if any of the first 40 models would be satisfactory .... it was decided that, as work on them had progressed too far for further modifications, although known to be desirable, to be incorporated, the contract should be abandoned." Five modified models were delivered to the RAE in January 1943, and after inspection all were considered u/s with a total of 35 faults being discovered. Four of these were eventually rendered serviceable, and were sent to CCDU for installation in Wellingtons. However these trials only came to the gloomy conclusion that "there was but little promise of an efficient Radio Altimeter Type 2 being produced within a reasonable time. It was clear that even more development was required before main production could be restarted. Although trials of the apparently superior model Radio Transmission Equipment Limited version had not yet been completed, it was extremely doubtful whether the RAE would be able to recommend the design for further production, and, with the advent of (American) Type AYF, in July 1943 contracts for the manufacture of Radio Altimeters Type 2 were cancelled."

    The Type AYD (and its improved AYF version) was a newly developed American design which was by then already in mass production, and shipments of these began to arrive in the UK by April 1943, but development work on the British Type 4 altimeter was slowed to a low priority "as an insurance against failure of the American instrument." The American developments were closely followed by the British Air Commission in the USA, with RCA (Radio Corporation of America) being the primary firm involved in this work. First official production orders were place in November 1941, and in summer of 1942 the British Air Commission approached the Munitions Assignment Board for an allocation of AYD and AYF radio altimeters. The RAF were allocated a proportion of USA production, and by May 1943 nearly 350 AYD sets had been delivered to Fort Worth, Texas for installation in new Liberators destined for Coastal Command, plus 12 sets of equipment direct to the UK. To give an idea of the increasing rate of the AYF sets, the expected deliveries for April, May and June 1943 were 300, 400, and 500 respectively. The AYB set (and presume AYD and AYF were similar) provided satisfactory readings between 15 and 400 feet, its power consumption was low, and its weight, including cabling was only 26 pounds. These were the results of RAE tests in the UK in September 1942, and this was the sort of performance that the RAF was crying out for.

    Installation of first AYD sets to reach UK were made in Coastal Command Wellingtons from July 1943 onwards, "by five fitting parties from 26 Group. A start was made on the aircraft of 172, 407 and 612 Squadrons. By the end of March 1944 retrospective fittings in those squadrons, and Wellingtons of 179 and 304 Squadrons, Beaufighters of 144 and 254 Squadrons, and Halifaxes of 518 and 520 Squadrons had been completed, whilst the Liberators of 53, 59, 120, 224, 311 and 547 Squadrons had been equipped in the USA (that is, prior to delivery to RAF). Progress was being made with installations, on high priority, in Catalinas of 210 Squadron, Halifaxes of 58, 502 and 517 Squadrons, and Sunderlands of 10 RAAF, 228 and 461 Sqdns, and a programme of lower priority for 19 other squadrons, and for operational training units was planned. However the operations to be undertaken for the projected liberation of Europe necessitated the provision of radio altimeters in all aircraft of Coastal Command, and every endeavour was made to introduce aircraft production-line installation as rapidly as possible, and the number of installation parties was increased."

    "By November 1943, the RAE in Britain had completed flight tests of trial installations of AYD in sixteen types of aircraft (Wellingtons Mk. XI, XII, Beaufighter, Fulmar, Barracuda, Swordfish, Albacore, Firefly, Lancaster, Halifax, Catalina, Sunderland, Mosquito, Hampden, Liberator, Hudson). At first the RAE attempted to follow the installation methods recommended by RCA and the US Navy, particularly for positioning of aerials, but results were unsatisfactory until aerials were mounted under the tailplane, when performance was very satisfactory, error amounting to no more 5 per cent over the whole range. The great advantage of the tail installation lay in the fact that there was no possible source of spurious coupling between the aerials caused by the reflection from the airframe."
    David D
    Last edited by David Duxbury; 20th October 2016 at 00:41.

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    As noted in several responses the correct term was radio altimeters.

    Coastal command Met. Fortresses were fitted with radio altimeters for calculation of accurate sea-level pressure readings. The instrument was wired to two tee-shaped aerials located on the underside of the rear fuselage and featured an altitude limit switch with three coloured lights: red, green and amber. Red indicated the aircraft was below a pre-set altitude while amber indicated it was too high.

    Robert

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