Dakota III to Dakota IV conversion

[Franek Grabowski]

Dakota III and Dakota IV used different power units. In theory, it should not be that hard to convert Mk III into Mk IV but were there any such conversions made? Is there any case of such conversion being annotated in the papers, eg F.78s?
TIA
Franek

[David Duxbury]

So far as I know, the most important modifications made to C-47s/Dakota aircraft were immediately postwar, when aircraft with 2-speed engines (nominally all those called C-47Bs/Dakota IVs) were "defanged" to an extent and reverted to single-speed engines (without the high blower). This was intended to improve their mechanical reliability at the cost of losing their high altitude capability. I presume these mods were made at engine overhaul depots in whichever Command they were serving at the time, and some minor mods were probably required in the cockpit to delete any of the levers previously required to manipulate gear-changing controls. However some aircraft may have been left with the 2-speed engine if they were still required for flying "the hump", but whether any were still being used on these operations is quite unknown to me, and it is likely that C-47s were by this time superseded by later C-46s, C-54s, and C-87s. Surprisingly, C-47s were supplied to most Allied air forces from 1943 onwards, despite fact that vast majority of operators did not reqire this high-altitude capability. I know that in the RNZAF in the South Pacific during 1944, various engine problems with the 2-speed engines became endemic, and was usually blamed on "sludging" of the lubrication oil. The Directorate of Repair & Maintenance (RNZAF) put it this way:

(Monthly Report for January 1946): "During the month, conclusive evidence was obtained from engines dismantled at Ohakea, that inferior lubricating oil was responsible for excessive sludging. It was found that engines with the 2-speed blower units were affected to a greater extent, and C-47B aircraft were, therefore, grounded pending removal, stripping and cleaning of the engines and oil systems. This work is is now in progress at No. 1 Repair Depot, and the grounding of individual aircraft being automatically lifted when the above work had beeen completed. Further investigation into the origin of the inferior oil revealed that Island bases were the probably source of supply, and steps were taken to to ensure that RNZAF aircraft overseas were supplied with oil from New Zealand.

(Monthly Report for February 1946): "Over half of the C-47Bs grounded in January have been returned to service after having their engines removed, stripped and cleaned at Ohakea. Remainder of work is proceeding satisfactorilly."

(Monthly Report for March 1946): "Further investigation on C-47B sludging by DSIR (Department of Scientific & Industrial Research) culminated in a report which revealed that when the engines are inhibited and stored, the carbon is gradually loosened by the inhibitor. When the engines are replaced in service, the flushing and scouring action of the circulating oil washes the loose carbon off with the result that it circulates in the oil stream, and, if not filtered out, becomes deposited on, and blocks the pressure filters.

(Monthly Report for August 1946): "Pratt & Whitney R-1830-90D engines. Following the recent troubles experienced with blowers in the -90C engines, use was made of some modification kits to modify two -90C engines to -90D type engines. This mod converts the engine from a 2-speed blower to a a single-speed blower model. Two modified engines have now emerged from the RD (Repair Depot) and are no on issue to Whenuapai (the main operating base for all the in-service C-47Bs)./

[Franek Grabowski]

Many thanks, David!
I assume that C-47Bs were taken as a standard to ease logistics and operations. Post-war period certainly eased the requirements, so it was possible to operate the aircraft on a more rational basis. My question is that I have an aircraft that has a serial of C-47A/Mk III, but few years later it is listed as C-47B/Mk IV. Operational requirements in the area preferred high altitude capabilities, but I was not sure if it was any easy to convert C-47A to C-47B. Certainly not only hanging different engines. Overall I assume that it was not feasible so I suppose it is either an error in documents or some identity swap during a major overhaul.
Franek

[robstitt]

Hi Franek,

Some interesting info in the following, including power plant dimensions, which suggests that the engine swap would not have been a major undertaking.

https://www.thisdayinaviation.com/ta...c-47b-skytrain

Robert

[Graham Boak]

Presumably, had it been necessary to create a new engine installation for the 2-speed supercharger then the cowling would have been longer and the propeller in a different place relative to the fuselage. There seems to be no evidence for this.

[GSinclair]

RAAF intention end August 1946, All C-47 with R-1830-90B, -90C and -90D to be given new Lidcombe built -92 (C-47A model engines). The USAAF sytematically converted C-47B models to D models.

Long Beach finished C-47A production in June 1944, Oklahoma in July. The C-47 was always in short supply, so it is not surprising low priority operators like the RNZAF and RAAF received plenty of C-47B late in the war rather than C-47A early. As of end July 1944 the RAAF had received 55 C-47, a year later it was 122. In the end 124 C-47 of which 65 were B, RNZAF 58 Dakota, 1 C-47, 25 C-47A, 39 C-47B.

Production was 1,031 C-47, 5,253 C-47A, 3,365 C-47B.

What is the serial of the reported III to IV (A to B) conversion?

[Franek Grabowski]

Thanks guys. I agree that hanging C-90 engines on C-47A should not be a problem as I guess attaching points were just the same. The problem could have been with all the associated installations, making it not worth the effort.

What is the serial of the reported III to IV (A to B) conversion?

It was 42-108865 KG463 built as C-47A-10-DK. It later transpired as C-47B/Dakota IV, nonetheless I wonder if this was an effect of some mess up in the papers rather than conversion.

Aside, where there any C-47s delivered to the RAF in natural metal finish?
Franek

[Andy Marden]

There is nothing on KG463's AM78 to indicate any conversion.
When did the conversion take place?

[Franek Grabowski]

I have no idea, but she re-emerged on a civilian with a serial number from a block allocated to Dakota IVs. Hence my question. I would rather lean to some paper mess.