WesWorld

This improved version emerged in 1943 but I overlooked posting details.

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Technical Description

Four Brandenburgische Motorenbau 328G eighteen cylinder radial air-cooled engines rated at 2,800 hp for takeoff and 2,500 hp at 7,600 metres

Accommodation for a crew of six, comprising pilot, second pilot, flight engineer and wireless operator, plus two stewards. Passenger accommodation for sixty-four to ninety-four passengers depending upon layout.

Span 38.3 metres; Length 34.2 metres; Height 8.95 metres. Maximum gross take off weight 51,900 kg.

Maximum cruising speed 570 kph at 7,600 metres. Range with maximum fuel 8,300 kilometres; range with maximum payload 5,800 kilometres.

I'm a little confused on one point. When you say Maximum cruising speed, are you referring to the max (absolute or sustainable) speed of the aircraft, the speed at which it has the listed range figures, or something else?

Quoted from "snip"

I'm a little confused on one point. When you say Maximum cruising speed, are you referring to the max (absolute or sustainable) speed of the aircraft, the speed at which it has the listed range figures, or something else?

It is the speed at which the stated range figures are calculated.

What historical aircraft did you base this off of, if any? I am finding that 570kph figure to be a tad optimistic given some historical examples, mainly the DC-6, early Lockheed Constellations and the Boeing 377, which are the types that I have been able to locate that are most compatible to the Ju390B. All of those have cruise speeds noted as being ~500kph, somewhat less range, and less powerful engines all on a similar size and intended roll. A quick survey of British types does not yield any compatible designs of approximate physical dimension and intended roll, tho they do reinforce the trend. I will note that I have only used Wikipedia as a comparison tool at this point, so am more then happy to have better sources presented on ether side of this issue.

At this point in its development, the Ju390 might best be considered on its own development path, rather than a clone of a historical exemplar. Do you consider the speed excessive in its own right?

Based of the historical examples I have discovered, I feel that the combination of cruising speed and range is excessive for an aircraft of this approximate size. I am comfortable with ether figure taken by itself, but in combination I feel that it is pushing things a little to far. I have yet to find a WW-example that dislocates the OTL trends to such a degree that this design fits.

Considering both the Boeing 377 (an aircraft of far larger weight and engine power) and Wesworld's Bloch MB.972 Transatlantique (of somewhat smaller weight and slightly less engine power) some reconsideration might be appropriate. I would propose a reduction of the maximum cruise speed of the Ju390B to 530 kph. This should bring it into line with the Boeing product, which has a maximum cruise speed of 547 kph. The range figures cited are dependent more on fuel and payloads, as noted, rather than speed.

Quoted from "BruceDuncan"

Considering both the Boeing 377 (an aircraft of far larger weight and engine power) and Wesworld's Bloch MB.972 Transatlantique (of somewhat smaller weight and slightly less engine power) some reconsideration might be appropriate. I would propose a reduction of the maximum cruise speed of the Ju390B to 530 kph. This should bring it into line with the Boeing product, which has a maximum cruise speed of 547 kph. The range figures cited are dependent more on fuel and payloads, as noted, rather than speed.

I think that's a reasonable suggestion.

Given established WW and OTL figures, the revision seems very reasonable to me. Thank you for addressing my concerns.

Don't forget folks, there is the airliner thread I complied to help everyone keep track of WW airliners. (I need to update this again at some point, I tend to do minor nip and tucks, but there are a few types missing now I think)

For example, here are the Ju-390A stats:

Type: Junkers Ju390A
Classification: long-range airliner
Length: 32.5 m (106 ft 6 in)
Wingspan: 35.8 m (117 ft 4 in)
Height: 8.66 m (28 ft 4 in)
Wing area: 135.75 m² (1,453 ft²)
Maximum gross takeoff weight: 40550 kg (89,397 lb)
Powerplant: four 2,100hp Brandenburgische Motorenbau 328 18-cylradials
Maximum speed: 534 km/h (331 mph) 7600 m (24,934 ft)
Cruising Speed: 445 km/h (276 mph)
Range: 5500 km (3,417 miles) with 8800 kg (19,400 lb) payload
Passengers: 58 seated four abreast, 72 in high-density layout with facilities including toilets and galley in a pressurised cabin
Crew: four flight crew, two cabin crew
Cargo: baggage only
Operators: Lufthansa
Availability: In production.
Notes: now entering service with Lufthansa

Now, personally I feel the Ju-390B must be almost a new design with a new wing and much beefier structure to increase the payload and fuel load. I'm not sure an extra 2,400hp would have allowed a cruise speed far higher than the maximum speed of the Ju-390A, even Bruce proposed cruising speed is only 4km/h lower than the maximum of the Ju-390A, though an extra 2,400hp should help in that regard, but I'm guessing the maximum speed isn't going to be much higher. The other stats look ok to me.