Bomber engines: inline vs. radial

[gjs238]

The Lancaster used Merlins.
Would the US bombers such as the B-17, B-24 or others have been better off with inlines as well?
To turn it around, would the Lancaster have been better off with radials?

The question could be extended to 2 engine bombers as well.

 

[Shortround6]

They built about 300 Lancasters with radials, the B II version.

Halifaxes seemed to swap back and forth.

The Whitley started with radials and ended with Merlins.

The Wellington started with 9 cylinder radials, went to Merlins and then went to 14 cylinder radials.

With the drag of the large fuselages and multiple turrets the drag difference between inlines and radials on a four engine wasn't a great as on a single engine (or even a twin engine) fighter.

What mattered more was which engine would fit, what power it was giving at any given point in time and how many were available.

With it taking about 2 years from the start of construction on a factory and the delivery of large quantities of engines any major change in a program has to be approved quite a while in advance. The US made tremendous numbers of engines in WW II but flexibility was not part of the deal

For instance Ford built about 44,000 R-2800 engines by the end of 1944 and not a one was a mechanical two stage engine. Nash built just under 11,000 R-2800 engines in the same period and not a one was a single stage engine. Chevrolet built over 54,000 R-1830s, all single stage and was starting to phase in single stage R-2800s. and so on. The plants specialized in one engine type and configuration and seldom changed. It could have been done but the loss of production would have been months, Buick and Chevrolet were turning out 2400-3000 engines a month and Studebaker put out 2000+ engines (Cyclones) a month for at least 20 months in a row.

 

[Gixxerman]

Survivability is the thing here, I am always enormously impressed by tales of the radials ability to get shot up really badly yet still function 7 bring a crew home safely.
With no w/c system to fail destroy an engine I think I'd feel pretty comforted in relying on radials (the Lanc B2 had radials but relatively few were made).
Perhaps it is less of a consideration with the RAF flying at night.....although with all the German flak that was spraying chunks of metal around I'd be surprised.

 

[michaelmaltby]

B-17 with Allisons

 

[Shortround6]

The B-17 did have better performance but where were the Allisons to come from?

A Cyclone powered P-39 would be a really ugly plane

 

[tomo pauk]

IIRC Allison produced about the same number of the V-1710s in 1943 and 1944 - could that be read like there was ample resources to build more of V-1710s? Of course, with P-40 production to end in 1944, ditto for P-39 (P-63 not offering anyting better than top-line fighters of late 1943/start of 1944), no more Allison Mustangs from mid 1943, and the P-38 receiving the able competition/replacement in likes of Merlin Mustang P-47Ds, seem like that V-1710s are engines looking for airframes in 1944, even without production increase?

 

[beitou]

For instance Ford built about 44,000 R-2800 engines by the end of 1944 and not a one was a mechanical two stage engine. Nash built just under 11,000 R-2800 engines in the same period and not a one was a single stage engine. Chevrolet built over 54,000 R-1830s, all single stage and was starting to phase in single stage R-2800s. and so on. The plants specialized in one engine type and configuration and seldom changed. It could have been done but the loss of production would have been months, Buick and Chevrolet were turning out 2400-3000 engines a month and Studebaker put out 2000+ engines (Cyclones) a month for at least 20 months in a row.

It is when you see figures like those without even taking into account UK or Soviet production that you realise Germany lost the war on Dec 11 1941.

 

[wuzak]

With the drag of the large fuselages and multiple turrets the drag difference between inlines and radials on a four engine wasn't a great as on a single engine (or even a twin engine) fighter.

Was it?

The XB-39 was 14% faster (405mph vs 355mph) with 20% more power. Using the P=kV^3 approximation the XB-39 should have been only 6% faster. So some aerodynamics must be at play here? Note also that the XB-39 wasn't optomised for teh V-3420 - it was just made to fit the R-3350 firewall. The V-3420 was a little wider (1" IIRC) but substantially shallower.

The XB-38 also proved to be faster than the base aircraft - the B-17E. But not by as much - though the power was much the same between engines. Again the installation wasn't really optomised for the in-line.

 

[Shortround6]

Was it?

The XB-39 was 14% faster (405mph vs 355mph) with 20% more power. Using the P=kV^3 approximation the XB-39 should have been only 6% faster. So some aerodynamics must be at play here? Note also that the XB-39 wasn't optomised for teh V-3420 - it was just made to fit the R-3350 firewall. The V-3420 was a little wider (1" IIRC) but substantially shallower.

The XB-38 also proved to be faster than the base aircraft - the B-17E. But not by as much - though the power was much the same between engines. Again the installation wasn't really optomised for the in-line.

it was figured that the P-36 had 22% more drag (total, not just engine drag) than an early P-40. The in-lines could offer some improvement on the bombers, just not the big difference you see on early war fighters.

 

[model299]

The prototype was destroyed during the 9th test flight after developing an engine fire on the #3 engine. All further work was canceled, and the increase in speed was not deemed to be worth the added complexity and weight of the watercooling systems.

Sure does get points for looks in my book though! Some nice work on those cowlings.

 

[wuzak]

The prototype was destroyed during the 9th test flight after developing an engine fire on the #3 engine. All further work was canceled, and the increase in speed was not deemed to be worth the added complexity and weight of the watercooling systems.

I think, more to the point, the added speed wasn't considered sufficient enough to interrupt production to get the B-38 in production. Note the leading edge radiators between the engine nacelles. This modification probably made it less viable than if they used annualr radiators on a quick engine change module, as the Germans did.

The V-1710s were considered for the B-40 escort bomber gunship. The extra speed woul be handy to overcome the weight deficit that the YB-40 had over B-17s once the latter had dropped their bombs. In any case, the B-40 concept was soon dropped.

In the case of the XB-39, the nacelle was developed as a QEC by Fisher to replace the R-3350. They were tested on the Douglas XB-19, but with experimental turbos. For the XB-39 the turbos weren't fitted, altitude rated V-3420s were used instead. If the XB-39 used twin B-series turbos, as did the Wright R-3350 powered B-29s, performance may have been better. The reason for not adopting the B-39 was that it too would interrupt production. Not sure by how much, since the QEC was developed as a direct replacement for the R-3350 module. I would imagine that they could have been retrofitted, if need be, elsewhere.

Perhaps a more problematic issue is the priority level the Army gave the V-3420. Over its development life it was high priority, low priority, cancelled or prioritised for other programs. For instance, when Schweinfurt happened it suddenly dawned on the USAAF that they may actually need a long range escort - thus the P-75 program was born. And it took priority for V-3420s over the B-39 program, and since Fisher was developing the P-75 it delayed their work on the B-39 conversion.

Originally the B-15 was to be powered by V-1710s. It was thought in the early '30s that air cooled engines did not have the cooling capacity to deal with the boost levels required for high altitude flight, which were to be provided by turbocharging. But the V-1710s were not ready in time, and the XB-15 flew with R-1830s. Some say (like Wiki) that it was originally intended to use V-3420s, but these were not on the drawing board at the time. Dan Whitney's Vees for Victory states that the V-1710 was selected for both the XB-15 and Martin XB-16.

Also in the '30s it was felt that engines buried in the wings of aircraft would produce less drag than those in nacelles. Thus the Lycoming O-1230 and Continental O-1430 (later to become the IV-1430) horizontally opposed engines were developed to be buried in wings. A similar requirement led to the Wright R-2120 Tornado.

 

[davebender]

Not necessarily.

The B-17 and B-24 fell behind in range/payload because they had some of the least powerful engines by 1942. R2600 radial engines would probably improve performance just as much as Packard built Merlin engines.

 

[norab]

inline is a misnomer, that is an engine with the cylinders in a straight line, Merlins, Alisons et al, were vee block engines with the cylinders arranged in a V or inverted V like the Daimler-Benz's