Engines in UK heavies

[Tangopilot89]

Hi again, yet another question has come to me and I wish to pick some of your brains on it.

When browsing the forum, I came across a picture of a MkII Lancaster that had Bristol Hercules radial engines fitted. Plus I also recall Merlin engines being fitted to early HP Halifax bombers. Why all this engine swapping? Was it to see if both aircraft worked with both engine types in case production was slow on one of them? I did post this question with the Lancaster MkII picture but I'm not sure where it went, sorry.

Hope my questions are sensible,
Andy

 

[pbehn]

Hi again, yet another question has come to me and I wish to pick some of your brains on it.

When browsing the forum, I came across a picture of a MkII Lancaster that had Bristol Hercules radial engines fitted. Plus I also recall Merlin engines being fitted to early HP Halifax bombers. Why all this engine swapping? Was it to see if both aircraft worked with both engine types in case production was slow on one of them? I did post this question with the Lancaster MkII picture but I'm not sure where it went, sorry.

Hope my questions are sensible,
Andy

Neither the Halifax nor the Lancaster were scheduled to have Merlins, the Halifax was changed at the design stage while the Lancaster was a four engine version of the Manchester. This meant a huge increase in demand for Merlins just for new build engines it is about 56,000 units.. The Hercules engine was used in the Halifax to increase performance to bring it on par with the Lancaster and as another engine supplier on the Lancaster.

 

[GregP]

The USA did that, too, as a fallback. We built the XB-38, a B-17 with four Allison V-1710s. It outperformed the Wright-powered version in top speed but not service ceiling. The gain was not enough to justify the change. We also built the XB-39, a B-29 powered by four Allison V-3420s. It outperformed the Wright-powered version.

In both of these aircraft, there were teething trouble, as is normal. The XB-38 had an engine fire and the crew bailed out. The XB-39 flew very well without the turbos (the turbos were having issues at the time), and they were deemed an effective replacement, should they be necessary. In fact, they weren't necessary and the XB-39 was never produced.

The XB-32 was developed in case the XB-29 failed.

Not surprisingly, the British also planned ahead and tried many configurations in case of catastrophic damage to a factory subject to bombardment at times. I think all countries did some hedging and tried alternatives in case something became no longer available. Some even went so far as to make planes from non-strategic materials in case the strategic materials became in short supply.

Seems like prudence in these cases, and worth the development costs, had national survival been at stake (and it was).

 

[Tangopilot89]

Neither the Halifax nor the Lancaster were scheduled to have Merlins, the Halifax was changed at the design stage while the Lancaster was a four engine version of the Manchester. This meant a huge increase in demand for Merlins just for new build engines it is about 56,000 units.. The Hercules engine was used in the Halifax to increase performance to bring it on par with the Lancaster and as another engine supplier on the Lancaster.

So just to clarify: the Halifax was changed to Merlins at the design stage, but then the Hercules engine was used later on to keep performance on a par with the Lancaster, and in the Lancaster itself as an alternative engine supplier just in case demand for Merlins got too high?

My apologies, I'm not being deliberately awkward, I'm only trying to get my facts straight.

Thank you for your replies by the way

 

[wuzak]

The USA did that, too, as a fallback. We built the XB-38, a B-17 with four Allison V-1710s. It outperformed the Wright-powered version in top speed but not service ceiling. The gain was not enough to justify the change. We also built the XB-39, a B-29 powered by four Allison V-3420s. It outperformed the Wright-powered version.

In both of these aircraft, there were teething trouble, as is normal. The XB-38 had an engine fire and the crew bailed out. The XB-39 flew very well without the turbos (the turbos were having issues at the time), and they were deemed an effective replacement, should they be necessary. In fact, they weren't necessary and the XB-39 was never produced.

The XB-39 was delayed by the reallocation of resources to build the XP-75. By the time it flew, most of the B-29's engines issues had been sorted.

The turbochargers that were to be fitted to the XB-39 were experimental units with 2 stage compressors. But they weren't available for the XB-39 at the time of the first flight.

 

[pbehn]

So just to clarify: the Halifax was changed to Merlins at the design stage, but then the Hercules engine was used later on to keep performance on a par with the Lancaster, and in the Lancaster itself as an alternative engine supplier just in case demand for Merlins got too high?

My apologies, I'm not being deliberately awkward, I'm only trying to get my facts straight.

Thank you for your replies by the way

Many in fact most UK planes were designed around the RR Vulture and NapierSabre engines. The Vulture was used on the Manchester but didn't produce its projected output and so the Manchester became the four Merlin engine Lancaster. The Sabre was used on the Typhoon fighter but took an age to be made reliable and powerful. In the meantime the power output of the Merlin was increased by better fuels and superchargers.

The Halifax was bigger, heavier and had more drag than a Lancaster, to keep the bomber streams at best performance OVERALL the Halifax dropped the front turret and had the more powerful Hercules fitted.


It isn't possible to answer in a single short post, because.
The Merlin went from 1000 BHP to 2000BHP during the course of the war.
The Vulture was used on the Manchester but abandoned to concentrate on the Merlin as a necessity of war.
The Sabre was sort of sorted enough to keep the Typhoon in service but replaced by the Centaurus.
The Centaurus became the engine of the typhoons successor the Tempest and Sea Fury.
The Merlin powered almost every successful UK design and also a very successful USA design even though it was scheduled to be replaced in 1940/41.

The issues of engine power, supply and reliability ebbed and flowed throughout the war.

 

[Shortround6]

So just to clarify: the Halifax was changed to Merlins at the design stage, but then the Hercules engine was used later on to keep performance on a par with the Lancaster, and in the Lancaster itself as an alternative engine supplier just in case demand for Merlins got too high?

My apologies, I'm not being deliberately awkward, I'm only trying to get my facts straight.

Thank you for your replies by the way

Halifax went through two different versions of the Merlin, the Mark X and the MK XX with some strengthening and the "Hooker" supercharger, several hundred more HP. Early Hercules engines weren't that much better (be careful comparing take-off power vs power at altitude or max cruise power) while the later Hercules was around 250 or more horsepower ahead of the early ones.

There may have been some incompatibly with the air frames in regards to where the center of the propeller wound up in relation to the leading edge of the wing which made one powerplant a better fit aerodynamically than the other on a particular airplane.

 

[wuzak]

The Vulture was used on the Manchester but didn't produce its projected output and so the Manchester became the four Merlin engine Lancaster.

I believe the Vulture did reach its projected power output. However, it could not do so reliably.

It was the reliability problem that forced Rolls-Royce to de-rate the engine. Which also restricted development for extra power.

With the situation of the war and the need for Merlins, the Vulture program was first suspended (1940) and then cancelled (1941/42). So the Manchester would have to look for alternative engine - the Sabre and Centaurus were considered, but not ready.

It is quite possible that had development continued the Vulture could have operated at 2000hp reliably (it is known to have tested at 2500hp). But the question becomes, is it enough power for the airframe.

The Manchester had roughly the same power as the Martin B-26. But was much bigger and heavier. For the Manchester to work the two engines would have to produce 50% more power. ie 3000hp each. That wasn't going to happen any time soon - with the Vulture, Sabre or Centaurus.

 

[pbehn]

I believe the Vulture did reach its projected power output. However, it could not do so reliably.

It was the reliability problem that forced Rolls-Royce to de-rate the engine. Which also restricted development for extra power
.

That is exactly as I read it but I cant remember where. The de rating of the Vulture meant that in many situations the Manchester couldn't fly with one engine and it had no chance of doing that with a full bomb load.

 

[swampyankee]

Well, in the US:

Wildcats started with Pratt R-1830s, but the FM-2 variant used Wright R-1820s. The P-40 was, in many ways, a P-36 re-engined with an Allison V-1710, and also had a variant with the Merlin. The Mustang started with Allisons and ended up with Merlins.

Germany simultaneously produced radial and V-12 variants of the FW-190.

More recently, most commercial jet airliners are built with Rolls-Royce, GE, and Pratt& Whitney engines. The S-76 started with Allison 250s and switched to PWC engines (after the Allisons demonstrated a tendency to explode and destroy the tail rotor drive shaft) Boeing 707s were built with JT3s, JT3Ds, and Conways.

 

[Airframes]

The Lancaster B.II was fitted with Hercules engines mainly due to the need for RR and Packard Merlins elsewhere, should supply from the USA fall short or be disrupted. Once supplies of Merlins was firmly established, production of the Lancaster B.II ceased, with only some 350+ being built - haven't got the exact figure to hand at the moment.

 

[ChrisMcD]

The father of one of my girlfriends was one of the last Lancaster instructor pilots. He very much preferred the Hercules Lanc - but he was a deliberately awkward sod. I gather that he preferred that handling of what was already a very sweet aircraft to fly. By the way, I note that Winkle Brown also liked the Lanc II.

 

[Koopernic]

I believe the Vulture did reach its projected power output. However, it could not do so reliably.

It was the reliability problem that forced Rolls-Royce to de-rate the engine. Which also restricted development for extra power.

With the situation of the war and the need for Merlins, the Vulture program was first suspended (1940) and then cancelled (1941/42). So the Manchester would have to look for alternative engine - the Sabre and Centaurus were considered, but not ready.

It is quite possible that had development continued the Vulture could have operated at 2000hp reliably (it is known to have tested at 2500hp). But the question becomes, is it enough power for the airframe.

The Manchester had roughly the same power as the Martin B-26. But was much bigger and heavier. For the Manchester to work the two engines would have to produce 50% more power. ie 3000hp each. That wasn't going to happen any time soon - with the Vulture, Sabre or Centaurus.

The Manchester was over weight, like many aircraft. It wasn't like Rolls Royce to point the finger. The ability of aeronautical engineers and procurement specifiers to add weight exceeds that of aero engineers ability to add power.