Redesigning a heavy bomber wing

[wiking85]

Historically the He177 had serious problems with its engines and they waited until August 1943 to order a four nacelle version, which took until December 1943 to enter testing. If ordered on January 1st 1941 how long would it have taken to redesign and build a 4 nacelle He177 for testing? And then how much testing would be needed before they could put it into production?

https://en.wikipedia.org/wiki/Heinkel_He_177#Further_development-the_Heinkel_He_177B

Nearly four years after Heinkel had unsuccessfully requested that two of the prototype He 177 V-series airframes be built with four individual powerplants, the RLM's requirement that the He 177 perform diving attacks was finally rescinded by Göring himself in September 1942,[8] and with that, Heinkel's design work on the pair of "separately" four-engined versions of the He 177A, the A-8 and A-10, collectively renamed the He 177B in August 1943, was then able to progress.

By August 1943 much of the detail work for the He 177B series aircraft was well on its way to completion, and Erhard Milch eagerly approved the creation[34]

Because flight testing had shown the 177A-style single-tailed V101 prototype having increasingly serious stability problems with higher airspeeds, the second prototype, the V102, was both the first He 177B example to fly, on 20 December 1943, with the quartet of DB 603 engines, in combination with a brand-new empennage of twin tail configuration, fitted to it during the early autumn of 1943.

The first flights of the He 177B prototypes, starting with the He 177 V102 on 20 December 1943, occurred between late December 1943 and early January 1944 in the vicinity of the Vienna-Schwechat airfield, at the firm's Heinkel-Süd southern production facility. An additional prototype, the V104, whose purpose was to be the "finalized" production prototype for the He 177B-5, and also meant to be a twin tailed prototype like the earlier V102, was being completed there by order from the RLM, converted from an early production He 177 A-5.[35]

Its unclear if the redesign work was historically done before August 1943 and the order was just a formality to start construction and what the actual time it would have taken from scratch. Thoughts?

 

[tomo pauk]

The Avro Lancaster 1st flew some 18 months after the Manchester. I don't know how much time it took for the Avro's engineers to come out with the new wing, though. Guess that one year is plenty of time to have the 4-engined He 177 ready for testing, with reasonable resources available?

 

[Elmas]

The main problem is not the time needed to design the wing, the problem is the time needed to design and build the jigs to build the wings.

 

[nuuumannn]

Nearly four years after Heinkel had unsuccessfully requested that two of the prototype He 177 V-series airframes be built with four individual powerplants, the RLM's requirement that the He 177 perform diving attacks was finally rescinded by Göring himself in September 1942,[8] and with that, Heinkel's design work on the pair of "separately" four-engined versions of the He 177A, the A-8 and A-10, collectively renamed the He 177B in August 1943, was then able to progress.

I think this sentence might give a clue as to what the biggest hindrance might have been.

 

[drgondog]

The re-design effort to modify an existing wing from two to four engines is much more difficult than going from four to two engines.

The #2 and #3 engines are already optimized for placement with respect to propeller/fuselage interference and thrust line with one engine inoperable. Contemplating new fuel storage locations, looking at the new axes of thrust, the new weight conditions, new fuel requirements, new spar/old spar comparisons to support new engines and fuel, wing/fuselage attach, new rudder considerations for possible two engine/same side yaw control issues, new fuel line/fuel tank transfer, new inertial bending issues for inboard landing gear but extended weight/inertia of the new #1 and #4 engines, etc.

Easiest preliminary approach might be to consider a.) required 'new' thrust to 'new' drag at low speed to maintain enough lift and also yaw authority to control the new airplane, b.) review of the existing spar and torque box geometry with planned load and thrust at the 'new wing stations for the outboard engines, c.) look for available bays which could be modified for additional fuel, d.) try some load scenarios to look at the supporting structure of the wing and its ability to withstand the new additional weight, locations of weights out board in inner engines, look a G/N loading allowable in consideration of hard landings.. etc, etc.

Revisit take off/landing performance for the new mission GW in context of airfield minimum lengths and 50' clearance.

Revisit new Parasite Drag estimates as well as changes to aspect ratio and wing (if wing geometry changes are made) fo new Induced Drag estimation are required to re-examine optimal cruise speed and range performance.

Summary - it ain't trivial..

 

[stona]

It took just SIX WEEKS to convert a Manchester I air frame and wings to the Manchester III/Lancaster prototype (BT308 ) which flew on 9th January 1941.

It was a longer haul to a production Lancaster but this somewhat refutes the idea that it was a terribly difficult conversion from 2 to 4 engines. The first three Lancasters were delivered to No.44 Squadron on Xmas eve 1941. From conversion to 4 engines to delivery into service took just under ONE YEAR. It could be done, but not by the RLM/Luftwaffe.

Cheers

Steve

 

[drgondog]

All depends on the "As Is" and the "to Be" for that particular airframe. Strip dive bombing requirement from He 177 and the task of -re-design spar etc becomes much simpler.

 

[Zipper730]

If I recall the problem with the He-177 was the requirement for either glide-bombing or dive-bombing: This was largely due to Ernst Udet's obsession with dive-bombing, and the fact that the Germans supposedly didn't have a sufficiently capable bombsight when the plane was conceived (this, of course, would change due to the Dufresne spy ring).

It's interesting to point out that Ernst Heinkel stated the plane would never be capable of the requirements demanded of it, which honestly makes me wonder why they continued to demand diving capability

 

[Koopernic]

It took just SIX WEEKS to convert a Manchester I air frame and wings to the Manchester III/Lancaster prototype (BT308 ) which flew on 9th January 1941.

It was a longer haul to a production Lancaster but this somewhat refutes the idea that it was a terribly difficult conversion from 2 to 4 engines. The first three Lancasters were delivered to No.44 Squadron on Xmas eve 1941. From conversion to 4 engines to delivery into service took just under ONE YEAR. It could be done, but not by the RLM/Luftwaffe.

Cheers

Steve

As far as I know Roy Chadwick had worked for some 6 months on the 4 engine Manchester prior to the discussions that took place between him and Rolls Royce (with Hives, head of Rolls at the time over the likely delay of fixing the Vultures Bearing problems). I read 'working on' as meaning that he had the drawing office drafting the engineering drawings. Once there is a full set of completed drawings and parts lists production is easy,and a competent team of tradesman and sub contractors can work in parallel without stopping to wait on parts or to work things out. The engines were simply taken from the Merlin 'power eggs' that had been developed for the Beaufighter when there was a shortage of Hercules engines.

Ernst Heinkel had anticipated the engine issues and asked for permission to develop a 4 engine version as early as 1939. I suppose they could have used the Jumo 211 installation from the Ju 88 or the or He 111 or the DB601 installation from the He 111.

Ernst Heinkel complained that Luftwaffe and RLM officers continued to talk about dive bombing even after rescindment of the drive bombing requirement. Heinkel certainly made their own mistakes, such as the stress calculation mistakes in the wing.

Had the He 177 been in service in quantity it would have caused problems in the commerce war just as the U-boat threat was being reversed between late 1942 and mid 1943 and before the allies had developed sufficient carriers.

 

[yulzari]

So it could be six months to change the Warwick from 2 unobtainable engines to four production ones?

 

[Gixxerman]

The wing strength issue with the He177 is interesting, on the one hand it seems fairly known that the dive-bombing requirement eventually led to an ability during 'Steinbok' for the heavy bomber to climb to enough altitude so as to bomb in a shallow dive (with poor accuracy) but escape hostile airspace doing something close to 400mph making interception all but impossible (although there were losses nevertheless).

On the otherhand - and despite the required strengthening the dive-bombing requirement must have led to - there are numerous reports of the He177 wing having strength issues for a long time during it's development.
Were these all just diving problems or did the wing have a 'normal' strength issue regardless?
I haven't seen this answered much one way or the other.
Once the dive-bombing requirement was binned surely wing strength should not have been an issue?

Given Heinkel was pushing for a 177b/277 it is somewhat surprising they were incapable of mirroring the Manchester/Lancaster story (ironic as on the surface so much of their early story does).
I suppose this relates more to the 2 systems in charge the chaos the then German way seemed to excel at.

 

[Zipper730]

Ernst Heinkel complained that Luftwaffe and RLM officers continued to talk about dive bombing even after rescindment of the drive bombing requirement.

I was under the impression that very early on he told the RLM that the He-177 would never be capable of dive-bombing...

Heinkel certainly made their own mistakes, such as the stress calculation mistakes in the wing.

What loads were they to be stressed to?

 

[Koopernic]

So it could be six months to change the Warwick from 2 unobtainable engines to four production ones?

It sounds plausible to modify by redrawing the wing of an already flying bomber in 6 months. I imagine it could be done in much less time. As previously stated there would also be the need to produce production tooling

To be frank I'm not sure how much preliminary design work had been undertaken. It certainly had been thought about but how much detail drawing is not clear to me. I have a strong impression it was 6 months but can't recollect my sources.

 

[stona]

Ernst Heinkel had anticipated the engine issues and asked for permission to develop a 4 engine version as early as 1939.

Chadwick had also identified the need for four engines early. He did indeed have a handful of draughtsman working on a four engine bomber whilst the Manchester was still in production, but there was no guarantee that it would be adopted and it very nearly wasn't. Avro could easily have been forced into building the Halifax.

Given that both designers recognised the need for more engines why could the British deliver into service the first three of what would become arguably the war's best heavy bomber in Europe barely one year after the green light to build it, whereas the Germans never delivered a decent four engine bomber in any meaningful numbers to the Luftwaffe ? The answer lies in the decision making processes at the two ministries and perhaps equally importantly with the men making them.

Cheers

Steve