2-engined bombers: how big is too big?

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tomo pauk

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Apr 3, 2008
In the context of 1935-1945, piston engines of the time, propellers and superchargers on technology of the day. Ditto for aerodynamics, materials and structures.
I've put this in the what-if sub-forum in order to also discuss the might-have-beens.
 
well, you are going from 1000hp engines in 1935 (if you are lucky) to 2500hp engines in 1945 (or even 3000hp engines) so the allowable gross weight goes up considerably.
So do you want to use the higher power for speed or for load carrying. ala the Vickers Warwick or the Lockheed P2V-1
XP2V-1_NAN2-46.jpg

Prototype flew May of 1945. Granted it is maritime patrol and not really for contested air space over land.
In 1935 the "standard" was probably the Whitley for gross weight for a twin.
 
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Is the P4M a twin or four engine? The jets were for emergency, much the C-123K used jets. If the P4M is four engined, then so is the C-123K. In fact, the C-119 firebombers could be classed as trimotors. Just adding confusion, my best skill.
 
How about the Vickers-Armstrong Warwick? I have the Profile publication here.

Featuring the same geodetic construction, it was bigger than the Wellington. It reached service just as the four-engined heavies appeared. It spent the rest of the war doing air-sea rescue, transport, and reconnaissance. The British did not have suitable big engines available, and the Warwicks spent most of the war powered by Pratt & Whitney R2800s. The Bristol Centaruses became available right at the end of the war.

The Warwick is the only British aircraft I am aware of that used the R2800. I think it was the only aircraft powered by Centaruses that actually flew wartime missions.

Just for the record...

AircraftWingspanLengthWeight emptyPowerBomb load
Blenheim56' 4" 39' 9"8,100lb2X 840HP1,000lb
Wellington II86' 2"64' 7"20,258lb2X 965HP2,500lb
Ju-88A65' 10.5"47' 1.5"27,577lb*2X 1200HP4,410lb
B-25 Mitchell67' 6.7"52' 10.8"20,300lb2X 1700HP3,200lb
B-26 Marauder71'58' 3"24,000lb2X 1920HP3,000lb
Warwick B.Mk.I96' 8.5"72' 3"28,450lb2X 1850HP6,000lb
Mosquito B.IV54' 2"40' 9.5"21,794lb*2X 1280HP2,000lb
* Loaded weight

I pulled all of this from Profiles. Bomb loads vary quite a bit depending on the mission. Note how the Mitchell and the Marauder are smaller then the twin engined Vickers bombers, and substantially more powerful than the Wellington. These aircraft all flew very different missions.
 
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The Wellington gained both power and weight in later versions.
The P&W R-2800 was the 3rd engine installed in the Warwick and the 4th engine planned. The proposed Sabre installation not being done.
The R-2800 was defiantly 3rd choice with the Vulture engine (1st prototype) not making hoped for power and/or durability and Centaurus being very far from production status.

The JU-88 also made major changes between the A-1 and A-4 versions, a small increase in wing span and area, more power and a huge increase in weight.

The B-25 & B-26s both gained a lot of weight but kept the same engines (not going to argue about 80hp on a 2000hp engine) , B-26 got small increase in wingspan/area.

Part of the problem for the Warwick was the all up weight of 47,000lbs (?) (The British Bomber, Munson) .
An early B-26 could hold a 5 man crew, 400 US gallons, 2000lbs of bombs and assorted bits and pieces and weigh less that Warwick did at tare weight level while using the same basic engines. Granted the B-26 could hold 5-7,000lbs more but the Big Twins (Warwick and Manchester) were too heavily loaded.
 
Spec B.9/32 for a twin engined medium day bomber led to the prototype Wellington. During that process its empty weight rose from 6,300lb to 11,508lb by first flight in June 1936

Spec B1/35 was for a twin engined heavy bomber. Range 1,500 miles. Bomb load 2,000lb. Cruising speed 195+mph. The suggested engines were the Armstrong Siddeley Deerhound, Bristol Hercules or RR Merlin. That led to the RR Vulture powered Warwick being selected.

Then in 1936 the Wellington was redesigned before entering production and so gaining the look of a smaller Warwick. A Wellington I had an empty weight of 18,556lb and gross weight of 24,850lb.

The Warwick then found itself in competition for the RR Vulture engines as a result of the issue of Spec P.13/36 which led to the Manchester (which was initially for a twin engined medium bomber, the corresponding heavy bomber Spec being B.12/36 that led to the Stirling). By the time it flew in 1939 the empty weight was 27,032lb and a gross weight of 42,182lb (including a 7,500lb bomb load, 700 Imp Gal of fuel, 40 Imp Gal of oil, other operational equipment of 1,040lb and 5 crew). This was nearly double the figure in the Vickers tender 4 years previously.

The Spec that eventually led to the B-25 was issued in March 1938. The prototype NA-40 flew in early 1939. Empty weight 13,961lb gross 19,741lb. Range 1,200 miles with 2,100lb bomb load. Then completely redesigned as a larger aircraft with more range & greater payload with the B-26 being the competitor in the 1939 design competition.

Looking at the figures you can see just how quickly aircraft were developing in the 1930s.
 
Spec B.9/32 for a twin engined medium day bomber led to the prototype Wellington. During that process its empty weight rose from 6,300lb to 11,508lb by first flight in June 1936

Spec B1/35 was for a twin engined heavy bomber. Range 1,500 miles. Bomb load 2,000lb. Cruising speed 195+mph. The suggested engines were the Armstrong Siddeley Deerhound, Bristol Hercules or RR Merlin. That led to the RR Vulture powered Warwick being selected.

Then in 1936 the Wellington was redesigned before entering production and so gaining the look of a smaller Warwick. A Wellington I had an empty weight of 18,556lb and gross weight of 24,850lb.

The Warwick then found itself in competition for the RR Vulture engines as a result of the issue of Spec P.13/36 which led to the Manchester (which was initially for a twin engined medium bomber, the corresponding heavy bomber Spec being B.12/36 that led to the Stirling). By the time it flew in 1939 the empty weight was 27,032lb and a gross weight of 42,182lb (including a 7,500lb bomb load, 700 Imp Gal of fuel, 40 Imp Gal of oil, other operational equipment of 1,040lb and 5 crew). This was nearly double the figure in the Vickers tender 4 years previously.

The Spec that eventually led to the B-25 was issued in March 1938. The prototype NA-40 flew in early 1939. Empty weight 13,961lb gross 19,741lb. Range 1,200 miles with 2,100lb bomb load. Then completely redesigned as a larger aircraft with more range & greater payload with the B-26 being the competitor in the 1939 design competition.

Looking at the figures you can see just how quickly aircraft were developing in the 1930s.
The OP asked about how big a twin engined aircraft can be. We are therefore interested in things intended to be heavy bombers, which restricts us to the Avro Manchester, the Handley Page Halifax, the Vickers Warwick, and the Heinkel He177. All four of these aircraft were designed around big engines that were anticipated to produce 2000+ horsepower. A Lancaster sized aircraft would have good performance on a pair of Bristol Centauruses or Wright R3350s. These engines were not in any sort of functional production. The Manchester and Halifax were redesigned around four of the smaller Merlin and Hercules engines. The Warwicks were just never sent on bombing missions. The He177 became a drag on German resources.

The ability of two engines to power large aircraft is a function of how big and powerful those two engines are. Think of all the new, large airliners powered by giant turbo-fans.

The American medium bombers were built around big engines, but tactically, they were intended for different missions than the heavy bombers. Note their low service ceilings, somewhere in the low twenties. They weren't turbocharged.
 
The ability of two engines to power large aircraft is a function of how big and powerful those two engines are. Think of all the new, large airliners powered by giant turbo-fans.
To sort of reinforce this.
613px-P2V-2_NAS_Jacksonville_1952.jpg


Project started in 1943? but the Prototype didn't fly until 1945 with 2300hp engines. The P2V-2 in the picture showed up after 13 planes had been built and had 2800hp engines and later versions had even more power. Yes it is anti-sub or actually a 'maritime patrol bomber' in it's early history but it could hit 320mph, had 2-3 powered gun mounts depending on version and could carry around 8,000lb of ordnance. It is no B-29 but with two engines without turbo's that is pretty good.

as Mr Gibson as stated, a lot depends on the power of the engines you have available. You could make a big twin with lower power engines but you are going to need a big(huge?) wing and fly very slow.
In 1941 the US could have put a pair of R-2800s on this.
602px-XB-15_Bomber.jpg

and flown it with a huge load over a large distance, trouble was that a Whitley could out run it ;)
Finding a "happy medium" for a twin engine bomber was not easy.
 
The ability of two engines to power large aircraft is a function of how big and powerful those two engines are. Think of all the new, large airliners powered by giant turbo-fans.
Indeed, modern turbofans go up to pretty incredible sizes.

Sometimes people seem to think the B-52 is some uniquely gargantuan aircraft since it has frickin' 8 engines. Nope, by modern standards those engines are pretty small, something you'd find in a business jet. It was just what was available when the plane was designed. From a thrust perspective, the total thrust required by the B-52 could easily be met by two current day large turbofans.
 
Avro Anson -- 5375 lb according to Wikipedia. Can we include pre-war biplanes?
Was the Anson ever a bomber? As for biplanes, I'd accept anything that was still operational in squadron service post-Sept 1939, such as one of my faves, the Boulton Paul Overstrand, but it's heavier than my Potez.

IMG_2853.jpeg


I want to send the last squadron of Overstrands to RAF Base Obsolete (Malaya) in 1939 to serve alongside the Vickers Vildebeest.
 
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