Jump to content

Lancaster BII - why less performance?


Recommended Posts

Hi all, I am planning to build the new Airfix Lancaster BII, which looks like a bit of fun - and easier than my plan of many years ago which was to do an engine swap between an Airfix Halifax & Lancaster.

 

Looking into the MkII, a question occurs. The Hercules engines were more powerful than the Merlins generally used in Lancasters, and yet the MkII

 apparently had a lower ceiling. Not sure about speed or weight carrying capability, though I believe they were generally more lightly loaded, later on in service.

 

So - what went wrong? More power but poorer performance. Was that simply unlucky/poor design or what?  It's not inherently radial versus inline engines, since plenty other radials showed themselves to be every bit as good as inline engines - good airflow & cooling design means there need not be any extra drag penalty.  I'd be interested to find out if anyone has any information which might shed light on this.

 

I realise some the MkII's had bulged bomb bays and some had ventral turret, which would increase weight and drag, but not all had those fitted did they? In fact some had no dorsal turret I think. 

 

 

Puzzling.

 

John B

  • Like 1
Link to post
Share on other sites

Just guessing, but I would imagine the increased drag of the radial engines/cowlings was a factor, as well as the supercharger fitted to the Merlins was more than likely much more efficient than the supercharger fitted to the Hercules. I'm thinking @Graham Boak would be a good candidate for a more definitive answer.

Mike

Link to post
Share on other sites

I'll take the opportunity for a quick guess before more qualified people can answer: It is not just a matter of horsepower but of engine power at a specific altitude. Some engines produce their maximum power at low level, others (especially when equipped with a supercharger or a twin-stage supercharger) performed best at higher altitudes.

I guess the Hercules delivered optimum power at a relatively low altitude. Therefore the ceiling of a B.II might be lower than that of a Merlin-powered Lanc simply because the Merlin delivers more power at altitude. Of course, there were different versions of Merlins optimized for low, medium or high level.

  • Like 3
Link to post
Share on other sites

It's something that used to puzzle me, too, particularly as it was claimed that the later Halifaxes could look down on Lancasters below them in the bomber stream - certainly not possible when the Hali had Merlins.  As far as I can see Mike has it right, the Hercules did not have as good a supercharger.  Or, for whatever reason, just didn't have the same power above 20,000ft.  I did think that there might be a difference between the Hercules Mk.VI as used in the Lancaster and the Mk.XVI commonly seen on the Halifax, but a Halifax manual suggested little difference in the performance of the two engines.  One possibility might be that the Halifax cowling and nacelle was originally designed to fit the Vulture, so the Lancaster had a narrower nacelle - which means (perhaps) that the Hercules just didn't match well, and there was some base drag from this.  I'm not really sure about this, but I don't know the Lancaster installation well enough.  However the larger nacelle for the Vulture did mean that fitting the Hercules was less problem - once they had lowered the engine below the leading edge.  (One of those little aerodynamic touches that wasn't known at the time of the Halifax design but was for the Lancaster.)

 

It is possible that the crewman looking down on Lancasters was flying a Mk.VI with Hercules 100s, in which case then sure, but I suspect that all it showed was that the Halifax was no longer that inferior and there was always a mix of bombers at different heights.

  • Like 1
Link to post
Share on other sites

Some later B.III Halifaxes also had the rounded wingtips that may have created less drag on the tips and gave a bit more altitude. As I haven't re-read any of my Lancaster/Halifax books in a while, I may be way off.

 

 

 

Chris

Link to post
Share on other sites
1 hour ago, Graham Boak said:

One possibility might be that the Halifax cowling and nacelle was originally designed to fit the Vulture, so the Lancaster had a narrower nacelle - which means (perhaps) that the Hercules just didn't match well, and there was some base drag from this.  I'm not really sure about this, but I don't know the Lancaster installation well enough.  However the larger nacelle for the Vulture did mean that fitting the Hercules was less problem - once they had lowered the engine below the leading edge.

 

Nice try, but the Lancaster (inner) nacelles were also designed for the Vulture, thereby dictating the spacing between the Centre section ribs to a certain extent.

 

One comment made in Ian Allen’s “Lancaster at War 2” attests to the fact that a Lancaster II would climb just as well at cruise power with the cooling gills closed as it would at full chat with the gills open.  Some of the performance “issues” might have been due to their crews not knowing how to get the best performance out of them, but surely that should have been dealt with by the Handling Squadron at A&AEE when they wrote the Pilots Notes.

 

The extended wingtips of late Halifax IIIs, VIs and VIIs undoubtedly increased lift but also increased lift-induced drag.  They’d also have reduced roll rate but would marginally improve rate of turn at lower weights due to a slightly lower wing loading.  The Halifax III had benefitted from a significant weight and drag reduction programme that the Lancaster seemed to have avoided.

Link to post
Share on other sites

I've read a lot of similar literature to what you're all saying, but part of me also has a bit of humble opinion on this. From what I've read, part of the reason they originally used the Hercules was the shortage of Merlins. However they only made 300 or so and didn't put enough effort/time to work out the kinks before more Merlins were available. After that, they just didn't care to keep going. If it ain't broke, don't fix it!

  • Like 2
Link to post
Share on other sites

The main reasons I have for the difference between Lancaster I/III and II performance is engine weight, supercharging and fuel consumption.
Lancaster Mark I production, began October 1941, suspended from some time in April to some time in September 1943, apart from 5 in June, then resumed.
Mark II production August 1942 to March 1944, as people have noted, an insurance policy against shortages of Merlins.

Mark III production from December 1942.

 

Total Engine Weights, early Merlins 10,720 pounds, later 11,610 pounds, Hercules 12,335 pounds.

Fuel consumption, Merlin 22 or 24 weak mixture 7 pounds boost, 2,650 RPM, 260 gallons per hour, 2,300 RPM 225 g/hr, at plus 2 pounds boost 212 and 188 g/hr respectively. The Merlin 28 and 38 cut consumption, so 196 g/hr at +2, 2,650 RPM
Hercules weak mixture 2 pounds boost 2,400 RPM 236 g/hr, 220 at 2,200 RPM

 

Or to put it another way, weak mixtures the Merlin options range from -4 to +7 boost, 1,800 to 2,650 RPM, consumption from 96 to 260 gallons per hour.  The Hercules from -4 to +2, 1,800 to 2,400 RPM, 136 to 236 gallons per hour.

 

Rich mixture Merlins from +7 to +14 boost, 2,650 to 3,000 RPM, 320 to 500 g/hr, Hercules +6/2,400 RPM/478 g/hr or +8.25/2,800 RPM/640 g/hr.

 

The Merlin notes indicate outbound fuel consumption of slightly under 1.15 miles per gallon, 145 to 170 mph IAS, homeward from around 1.20 miles per gallon at 140 to 165 mph, down to 1.13 mpg at 185 mph IAS.  The Halifax III graphs just make 1.1 miles per gallon at up to 160 MPH IAS, the Halifax II and V homeward is 1.2 at 160 MPH IAS.

 

A comparison between the Halifax II and II in terms of fuel loads required, including a 200 gallon reserve, shows the III needed about 50 or more gallons extra fuel for the same distances, it was 65 gallons for 1,500 track miles, or pushing an extra 500 pounds.  The Lancaster I/III fuel load for 1,800 track miles was 2,095 gallons, the Halifax III 2,452.

 

Lancaster recommended Indicated Air Speeds, Merlin, Outbound for up to 15,000 feet 170 mph, 20,000 feet S gear 160 mph, return 160 mph, Hercules 165 mph, (Over 18,000 feet reduce as necessary to a minimum of 150 mph), return 160 mph.

 

Supercharging.  Hercules VI and XVI are reported as having maximum power altitudes of 4,500 and 12,000 feet, the Hercules 100 9,000 and 19,500 feet.  Merlin 22 6,000 and 12,250 feet, Merlin 24 2,000 and 9,500 feet.

 

The Halifax III and VII had the Hercules XVI, but the mark VI used the Hercules 100 with its much better supercharging.  The III was  in production August 1943 to April 1945, the VI July 1944 to November 1945, the VII May to September 1944 and January to March 1945 .  If you were in a mark VI you definitely had an altitude advantage.

 

I do note exactly fully believe the following performance figures, from the RAAF official history, but for comparison,

Lancaster I/II/X maximum speed 287 mph at 11,500 feet, service ceiling 24,500 feet, 1,660 miles with 14,000 pounds of bombs, mark II 275 mph at 14,000 feet, service ceiling 21,000 feet 1,000 miles with 14,000 pounds of bombs
Halifax III 282 mph at 13,500 feet, service ceiling 20,000 feet, 1,030 miles with 13,000 pounds of bombs, mark VI 312 mph at 22,000 feet, service ceiling 23,500 feet 1,260 miles with 14,000 pounds of bombs, so be in a VI and wave at the low flying Lancasters.

The Avro Lancaster by Harry Holmes notes the Lancaster I and III service ceiling was 23,000 feet, absolute ceiling 24,500 feet for example, it agrees about top speeds and says the range with 7,000 pounds of bombs was 2,530 miles, or 50 miles less than the RAAF figures.

  • Like 1
  • Thanks 1
Link to post
Share on other sites

Steve:  The main effect of increasing the span is to decrease the lift-induced drag, not increase.  There would be a small increase in zero-lift drag due to the skin friction of the increase in wing area, but this was considerably less than the reduction in the lift-induced drag.  Thus improving the take-off, max. altitude and range.  This would be counteracted to some extent at least by the increased maximum mass allowed because the wing was strengthened too. 

 

Re nacelle design, I was thinking more of nacelle cross-section.  Did this really not change from the Manchester?

 

The main weight and drag reductions from the awful Mk.II ser.1 had already been carried out by the time of the Mk.II series 1a with Merlin 22s, except the dropping of the nacelles - due on the Mk.II series 2, not not produced because of the success of the Mk.III.  It seems to me that the Mk.2 ser.1a must have been considerably superior to early versions anyway, but losses were still too high. How much this may have differed between sub-variants does not seem to have been assessed.

 

I don't recall reading the comment about climb rates on the Lancaster Mk.II - something smells there, doesn't it?  (and I don't mean overheating Merlins!)

 

JeffG: I think that there would still have been further investigations as to the shortfall had it been seen as a fixable problem giving performance gains = less losses.

 

Dogsbody:  the Mk.II didn't fit in with the Lancaster Groups because it would require special mission planning.  It fitted in better with a predominantly Halifax Group.  There was also the forthcoming problem of re-equipping the Canadians with Lancasters, so give them a few squadrons worth to play with and gain experience on the type, if not an ideal match.

 

Geoffrey: Good useful information but doesn't shine obvious `light on why the Halifax was so much better with Hercules, compared with the reverse for the Lancaster.  Merlin 24, 28 and 38 are irrelevant: the appropriate versions are the XX and 22.  The straightforward implication of this data is that the Mk.2 series 2 would have been superior to the Mk.III, but it seems otherwise.

 

Sorry if this seems a very bitty posting, but there have been a wide range of comments requiring responses.

  • Like 2
  • Thanks 1
Link to post
Share on other sites

Hello

Steve, induced drag would increase a bit with a larger wing area, however due to a better pressure distribution on rounded wingtips this would be more than offset by decreased wingtip vortices and consequently decreased induced drag.

Momentary I am away from my library, but IIRC Martin Middlebrook wrote in his book The Nurmberg raid about a brand new Halifax, which arrived to the unit just before the raid. Her crew found out she can cruise at 27.000 ft, and they flew the raid high above flak and night fighters in absolute safety. Needles to say, they were delighted. Cheers

Jur

  • Like 1
Link to post
Share on other sites

Lancaster II users,

3 Group, 115 Sqn from March 1943 to May 1944, 514 Sqn from September 1943 to July 1944.
5 Group, 61 Sqn January to March 1943
6 Group, 408 Sqn October 1943 to September 1944, 426 Sqn July 1943 to May 1944, 432 Sqn October 1943 to February 1944.

 

Climb speeds were about 5 mph faster for the Merlin versus the Hercules engined Lancasters, the Hercules version notes 155 mph IAS for maximum climb, 175 mph IAS for comfortable climb.  The Merlin Lancasters flew about 50 miles and burnt 110 gallons of fuel to climb to 10,000 feet, 130 miles and 255 gallons to 20,000 feet.

 

2 hours ago, Graham Boak said:

Geoffrey: Good useful information but doesn't shine obvious `light on why the Halifax was so much better with Hercules, compared with the reverse for the Lancaster.  Merlin 24, 28 and 38 are irrelevant: the appropriate versions are the XX and 22.  The straightforward implication of this data is that the Mk.2 series 2 would have been superior to the Mk.III, but it seems otherwise.

The topic was Lancaster II versus I/III, which is what I addressed, not Halifax II/V versus III/VII.

 

My understanding of I/II/V Halifax, version (sp = special), front guns, mid guns, rear guns (all 0.303, blank means none), engines (M = Merlin), fin type (Triangular or rectangular), The difference between the mark 2 and mark V was the undercarriage.  

Mark 1 series 1   /  2  /    /  4  /  M X  /  Tri
Mark 1 series 2   /  2  /    /  4  /  M X  /  Tri
Mark 1 series 3   /  2  /    /  4  /  M 20  /  Tri
Mark 2 series 1   /  2  /  2  /  4  /  M 20  /  Tri
Mark 5 series 1   /  2  /  2  /  4  /  M 20  /  Tri
Mark 2 series 1 (sp)   /    /    /  4  /  M 20  /  Tri
Mark 5 series 1 (sp)   /    /    /  4  /  M 20  /  Tri
Mark 2 series 1a   /  1  /  4  /  4  /  M 22  /  Tri/Rec
Mark 5 series 1a   /  1  /  4  /  4  /  M 22  /  Tri/Rec

 

So the series 1a had the same fuselages as the mark III with the specials having less weight and drag with the removal of the mid upper turret. The general conclusion is the upgrade in performance for the Hercules Halifax was a combination of the bigger wing and the engines.

 

The improvement in Halifax III performance brought it back up to Lancaster type altitudes, since firstly the lower flying Stirlings had to be withdrawn from raids on Germany, then the lower flying Halifaxes, they were the easier intercepts.  So Lancaster and Halifax loss rates became comparable again, that is what Bomber Command was measuring, later the Hercules 100 gave the Halifax VI a real performance boost at altitude.

  • Thanks 1
Link to post
Share on other sites

The difficult part of the question that arises is that if the Lancaster II has poorer performance with the Hercules that can be entirely blamed on the performance of the engine, then why did the Halifax do better?  To try to get an understanding it is necessary to find what is directly comparable to what isn't, and defining the difference between the multiple variants of the Halifax is important.  After doing this the problem remains, unless all the difference is allocated only to the position of the engines on the wing - which seems excessive.  It is unstated which variant of the Halifax Mk.II is responsible for the figures you quote, but clearly there were considerable differences to be found across the range.

 

If discussing why the Hercules Halifax is superior to the Merlin Halifax is irrelevant, then even by using your numbers why does the Lancaster with its superior aerodynamics not achieve better performance than a Halifax with the same engines?  Something is happening that is not related to the engine performance, presumably something to do with its installation?  Given that your figures for the Lancaster Mk.II will have come from official trials, ill-trained crew mishandling can be ignored.  It may have happened, but that's true of every type.

 

For future reference I would point out that in your list, the rectangular fins and later dorsal turret (BP Type A) were also seen on Mk.II/V ser.1(special) aircraft.  The reduction in drag of the Specials was due to the removal of the draggy Boulton Paul Type C turret from the nose and dorsal: the Specials had less drag than the earlier Mk.IIs but not the Mk.IIIs.  (Which is what I suspect you meant, but the brief comment was unclear.)  I suspect that the revised nose usually linked to the series 1a had less drag than the Tempsford nose on the Specials, which retained the clumsy bomb-aiming transparencies, but have not seen that described.

 

 

  • Thanks 1
Link to post
Share on other sites

All of the performance figures are for specific configurations, but unless you can obtain a full report you do not have all the details and are left with the published "typical" reports.  According to Harry Holmes the Lancaster I of January 1942 was tare weight 33,700 pounds, gross weight 60,000 pounds, take off power 5,120 HP, as of May 1944 tare weight 36,811 pounds, gross weight 65,000 pounds, take off power 6,440 HP, so you are left with which Lancaster I performance figures are being used in the references?  Add things like H2S, the paddle blade propellers, the reports 4 bladed propellers added 1,000 feet to the service ceiling of the Halifax, I think in the Coastal Command Weather Reconnaissance units and so on.

 

I did not say discussion of the changes to the Halifax were irrelevant.  The discussion I was joining was about Lancaster changes, if it is to be made into Halifax changes as well, plus comparisons, then please start with something other than a form of "it is not being addressed" as part of a "required response".

 

We know from things like the removal of armament that the Halifax II had performance issues as far as Bomber Command was concerned and these were solved by the mark III, in terms of loss rates when attacking targets in Germany.  The Lancastrian is to a first approximation an aerodynamic as possible Lancaster, but includes weight reductions like non self sealing fuel tanks, it gained 10% speed and range versus the standard Lancaster.  Using the Merlin 22 Lancaster figures versus the Halifax mark II shows how essentially with the same engines the Lancaster had 10% or so better performance, rather like the Hurricane I versus Spitfire I.  It also shows up in fuel loads for 1,500 track miles, Lancaster I/III 1,780 gallons, Halifax II 2,010

 

We can start with the airfoils in use https://m-selig.ae.illinois.edu/ads/aircraft.html
Aircraft, Wing Root Airfoil, Wing Tip Airfoil
Avro 683 Lancaster, NACA 23018, NACA 23012
Handley Page HP.56 Halifax, NACA 23021 ?, NACA 23007 ?
I note most sites go with this Halifax airfoil designation.  So the Halifax has a higher thickness to chord ratio at the root but much less near the tip.  The Lancaster's aspect ratio was 8, the Halifax II was 7.8, the III 8.5, a rather nice increase and so giving a reduction in induced drag and yes, it is paid for elsewhere.

 

http://www.wwiiaircraftperformance.org/Halifax/Halifax.html

mark II 1a maximum weight 60,000 pounds, at mean weight of 50,000 pounds, 253 mph, service ceiling 21,000 feet at max weight, cruising at 205 or 210 mph at 20,000 feet, time to 20,000 feet, maximum weight, 43.5 minutes, but the aircraft will not cruise at 20,000 feet until weight is reduced to about 56,000 pounds.
mark III maximum weight 65,000 pounds, at mean weight of 54,400 pounds, 282 mph, service ceiling 20,000 feet at max weight, cruising at 215 or 228 mph at 20,000 feet, time to 20,000 feet, maximum weight, 50 minutes
mark VI maximum weight 68,000 pounds, at mean weight of 56,200 pounds, 312 mph, service ceiling 20,000 feet at max weight, cruising at 218 or 260 mph at 20,000 feet, time to 20,000 feet, maximum weight, 50 minutes
mark VII maximum weight 65,000 pounds, at mean weight of 54,500 pounds, 282 mph, service ceiling 20,000 feet at max weight, cruising at 215 or 228 mph at 20,000 feet, time to 20,000 feet, maximum weight, 50 minutes

 

Ignoring the mark VI there is a good increase in top speed between the II and III and some increase in cruise speed and clearly some improvement in altitude performance, the aircraft gained new engines and 2% more wing area.  Halifax II range with maximum bomb load is 830 miles, with maximum fuel 1,660 miles with 5,250 pounds of bombs, the III is 1,150 miles, and maximum fuel 1,985 miles with 7,000 pounds of bombs, thanks to being able to carry an extra 104 gallons of fuel internally, this is a big performance increase.  The VI adds another 204 gallons.

 

http://www.wwiiaircraftperformance.org/Lancaster/Lancaster.html
mark I/III Merlin 24/224 maximum weight 68,000 pounds, at mean weight of 55,000 pounds, 287 mph, service ceiling 20,000 feet at max weight, cruising at 215 or 227 mph at 20,000 feet, time to 20,000 feet, maximum weight, 41.6 minutes
mark I/III Merlin 22/28/38 maximum weight 68,000 pounds, at mean weight of 55,000 pounds, 281 mph, service ceiling 20,000 feet at max weight, cruising at 216 or 227 mph at 20,000 feet, time to 20,000 feet, maximum weight, 41.6 minutes
mark II maximum weight 65,000 pounds, at mean weight of 53,500 pounds, 273 mph, service ceiling 21,000 feet at max weight, cruising at 210 or 222 mph at 20,000 feet, time to 20,000 feet, maximum weight, 45.5 minutes

 

So looking at these figures you do not see a big performance hit in terms of speeds and cruising.  Then comes range with bombs, the I and III range with maximum bombs is 1,660 miles, with maximum fuel 2,250 miles with 10,000 pounds of bombs, the II is 860 miles, and maximum fuel 2,070 miles with 6,000 pounds of bombs.

 

Halifax III 1,986 gallons enabled 1,985 miles with 7,000 pounds of bombs, the VI 2,190 gallons, 2,160 miles with 7,400 pounds of bombs, Lancaster I/III 2,150 gallons, 2,250 miles with 10,000 pounds, so again that performance advantage.  The interest is the Lancaster mark II with 2,150 gallons can do 2,070 miles with 6,000 pounds of bombs which is actually slightly worse in miles per gallon than the Hercules Halifaxes.

 

In summary in operational terms the Hercules engines mainly hurt the load carrying ability of the Lancaster, the upgrade done from Halifax II to III, the extra wing area, fuel tanks and new engines closed the performance gap with the Lancaster, including raising top speed and that cut loss rates.  The Halifax III range with bombs was about equivalent to the Lancaster II,   It does raise the interesting question of what would have happened if the Merlins had been retained in the Halifax III.  I note the ideas about how underslung engines were better and the Hercules thrust line was lower than the Merlin on the Halifax but have no idea how much this could affect performance but I note the wing changes did help.

 

Did all the Halifax II/V series 1 (sp) have a mid upper turret, or some?

 

What exactly is the time out when composing a reply? Thereby requiring a new log in to post an item?

  • Thanks 1
Link to post
Share on other sites

Wow, I didn't expect this. Most interesting discussion and much to think about, though a fair bit of thread  drift from the original question.

I like Graham’s early point about development being limited.  Blending different engines into a new airframe is not necessarily simple., so it seems much of the additional power of the Hercules engines  was being lost due to draggy installation, possibly plus some added weight.

 

I had forgotten to check the height bands at which the various superchargers operated –  thanks for that.

 

John B

Link to post
Share on other sites

Geoffrey: what I said was irrelevant was not the majority of your posting but what I understood to be the inclusion of Merlin variants that were normally not fitted to the Lancaster.   Which was incorrect, and I apologise.  However, I do agree entirely about the importance of being specific, in which case the Merlin XX/22s were the variant that would have been used for comparison at the time, the others coming later.  You do indeed refer to the 22 in your posting.   It was however a lucky Halifax that got the 22, Merrick does even include a photo one officially a series 1a but with Merlin XXs.

 

I would point out that the majority of the Halifax Mk.IIIs did not have the extended wing, and it was not available at the time the improved performance was noted.  It was always fitted to later variants.  The Mk.III was, bar the engine installation and a few details such as the additional permanent wing fuel tanks, the airframe of the Mk.II series 1a.  Including the refined nose - strictly the designation applied to those aircraft with Merlin 22s and the Morris block radiators - although the term was casually used to apply to the new nose whatever the engine installation.  I don't think I've seen a photo of a Mk.22-engined Halifax that didn't have the new nose.  It would be very interesting to know just what the improvement in performance actually was - Coastal Command was later to plea for  Merlin 22s to re-engine their aircraft but  I understand this to be more a matter of reliability: by this stage I suspect that the majority of Merlin XXs available would have been rebuilds of old production.

 

The value of the underslung engines was not just an idea but a discovery by the RAE just prewar and thereafter adopted as a design principle.  The particular problems of the Halifax installation has also been linked to flow affecting the fin and rudders, but this was (probably, if true) because of the particular details of the installation rather than just its principle.  (For it does not seem to have been a problem with the Whitley or Wellington.)   The idea of a "Mk.III with Merlin 22s" was built and flown as the Mk.II series 2, which only existed as a single prototype.  It would indeed be interesting to learn just what this machine's performance was, but it does not seem to have impressed, at least not as much as might be expected from the effect of the Hercules on the Lancaster.  Perhaps the Mk.III was considered "good enough" and a useful role for the Hercules being built in considerable numbers but beginning to lack suitable airframes.  Albemarles, Stirlings and Beaufighters being seen to be either totally or increasingly obsolete or at best obsolescent.

 

As for the fitting of dorsal turrets to the Specials.  Initially there was no dorsal turret, and the early aircraft were used on long range missions for the SOE.  However Bomber Command felt the lack, and the Type A turret was introduced, initially spare Defiant-type turrets that required a raised surround like that of the Lancaster, but later a dedicated variant that fitted lower.  The drag was considerably less than that of the Type C, and the armament doubled, so the penalty was clearly considered acceptable.   I'm unsure how many of the turretless examples were built, but suspect they would have been a minority of Mk.IIs and few of the later-arriving Mk.V.  Bombers, anyway.

 

I don't know of any time-out.  However, if you do lose a partially completed posting for whatever reason then you can go into the thread again, and when you hit Reply, your previous text will appear in the edit box and you can then continue as before.

 

 

 

  • Like 1
  • Thanks 1
Link to post
Share on other sites

John:  We don't actually know that it was a poor engine installation on the Lanc Mk.II, just that there appeared to be some hint of that.  It would be wrong to say this definitely.  One other factor might be the underfuselage turret installation creating more drag than assumed - although it looks like a fairly good installation to me.

Link to post
Share on other sites

As well as the engine differences, how about propeller types? If the Lancaster IIs had alternative engines due to a shortage of the usual type, is it possible that (a) an alternative and inferior propeller was also installed or (b) that a normal Lancaster prop was married to the Hercules with disappointing results? 

Link to post
Share on other sites

There has been a number of times this topic has come up with no clear answer.

 

I think realistically we need to break down the problem and I would suggest in the first instance focus on the Lancaster BI and BII and look at engine performance on these aircraft before confusing it with other issues or the Halifax performance anomaly. That can come later.  

 

I have yet to see performance curves for the Merlin XX or Hercules VI, that being brake horse power (BHP) plotted against altitude. I would be very interested to see when the superchargers were at their best (yes there are quoted numbers at a specific point, good to see the full curve) and how quickly performance dropped off around the sweet spot for the two speed superchargers comparing both engines. Hopefully someone within the BM community can share these. Certainly the Hercules was a performer at low to medium altitude. How was it optimised for high level work, if at all.  I have read of Bristol's issues with supercharger design. Let the numbers do the talking.  

 

If the Hercules maintains a higher BHP at high altitudes (greater than 20,000 feet) compared to the Merlin then we hunt for the next thing. Possibly engine management such as boost selection and fuel management. Am I correct that fuel mixture management was manual on the BII? If all this is OK then we can look into drag, thrust line and what ever. Or maybe just Harris's disdain for anything other than a Merlin engined Lancaster (I digress). 

 

If we find the significant contributor to the difference in performance of the Lancaster BI and BII was engine selection then we can approach the Halifax in all its own detail.

 

If we focus maybe we can settle this.

 

Ray 

 

 

 

 

 

   

 

 

  • Like 2
  • Thanks 1
Link to post
Share on other sites

Further to my earlier post, I have found this Hercules VI performance curve:

 

Hercules VI Performance Curve

 

Source: https://www.enginehistory.org/Turbochargers/Superchargers/BristolSuperchargers.shtml

 

Note that at 20,000 feet the Hercules VI bhp is given at just under 950. Up to 1000 feet you have those very high bhp numbers then dropping off with engagement of the supercharger speeds on the "M" Gear (and lowered to cruise boost) and then the "S" Gear. The superchargers take significant horsepower, but this more than compensates for the loss of horsepower associated with a normally aspirated engine as the aircraft gains altitude (not shown on this plot). 

 

The Hercules VI looks like a great engine for the time up to 16,000 feet. A great engine for getting heavy loads off the ground. If you go too high though performance suffers.

 

The comparison to the Merlin XX would be interesting, If around 18,000 feet the performance of the engines is comparable then any other factors such as engine fitment, drag and thrust line might really come into play.

 

Ray

  • Thanks 1
Link to post
Share on other sites

More info and sorry for the new posts each time as it comes together. I have now plotted the peak performance of the Merlin XX on supercharger "M" Gear and "S" Gear against the Hercules data. You can see that even though the Hercules was a "Hercules" down low, the Merlin XX was better set up for higher altitude work. In fact, even though it generated less BHP down low once it got high it started to outshine the Hercules. A full plot, if available, could show the cross-over point. I estimate some where around the 16,000 - 17,000 feet. 

 

Hercules VI Performance Curve with Merlin XX

 

I suspect for down low and with take-off the Lancaster would love the Hercules.  @Geoffrey Sinclair might be able to supply this data.  Up high the Merlin would be nice and if the following quote is true then the Hercules will struggle as fitted to Lancasters.

 

"Some of the Merlin Halifax's problems were caused by the way the engines were installed by Handley Page. Avro had designed the twin-Vulture installation for the Manchester, but when the Merlin Lancaster alternative was agreed in August 1940, Avro wisely accepted the advice of Rolls-Royce and installed the Merlins well forward and below the leading edge of the wing. The nacelles for the Merlins on the Halifax were shorter, and sited higher bringing the propellers very close to the leading edge of the wings. The high thrust line disturbed the airflow over the wing, causing loss of lift, whilst the proximity of the propellers to the wing's leading edge interfered with the efficiency of the propeller blades, causing heavy vibration, and reduction gear failures.

Plenty of Hercules would be available Stirling bomber production stopped, so Hercules VI, and later Hercules XVI engines were fitted on Halifax IIIs and VIs, installed with a lower thrust line in longer nacelles. The subsequent re-design of the Hercules supercharger and re-timing of the engine raised the ceiling, and maximum and cruising speeds of the later Halifax VIs significantly, and some crews found that they easily outclimbed Lancasters."

 

Source Wilfred Freemans biography, by Anthony Furse p.344 as quoted in https://ww2aircraft.net/forum/threads/avro-lancaster-vs-handley-page-halifax.17144/>

 

If anyone has this book maybe they could check the primary source that Furse has used.

 

The above, as also suggested by @Graham Boak and @John B (Sc)might also give some hint of why the performance was substantially improved with the Hercules Halifax particularly when fitted with the longer wings and having gone through some aerodynamic clean up. 

 

Ray

 

 

 

 

 

Link to post
Share on other sites

Thanks Ray  and Graham especially.

 

Graham, I agree that it's not fair simply to assume a poor or hasty installation or draggy nacelles etc. Just trying to find possible explanations. The ventral turret does look to have been fairly well designed, though presumably added weight. Prop type also may have affected things a great deal - thanks totd.  (I recall a machine we made a small modification to, trying to reduce prop damage on gravel surfaces by adding a very thin layer of helicopter style blade tape. The effect was startling - poor beast could hardly get off the ground! )

 

Ray - those graphs are fascinating, thank you. As ever there is more complexity in engines, especially high power pistons, than generally realised. I think you have brought out what is probably the major element in this.  Nacelle positioning too, with the prop effects on wing performance.

 

And of course, as an ex-sailplane pilot, 'there ain't no substitute for span'.  Longer wings mean less induced drag, better performance more easily.. 

 

(The comment made about preferences at the top of the RAF is apposite generally - evidence since shows that removing dorsal turrets and cleaning up airframes to allow greater speeds might well have reduced losses significantly, given the small speed margins wrt night fighters - and a ventral turret ought to have helped, given the mode of attack most preferred, especially when Schrage Musik came along. Hindsight suggests that people like Portal and Harris were given rather more leeway than they should have been. But then these were people under pressure, without the luxury of being able to sit back and assess as we can. Nor were they selected for those characteristics ! )

  • Like 1
Link to post
Share on other sites

Are you sure about the wing fitted to the mark III, since every reference I have seen says it had the bigger wing?  Including the performance report I used.  When was the wing introduced onto the production line?  So when it comes to the Halifax II and V specials, the mid upper/dorsal turret was not factory fitted at the start of production but was by the end, plus field modifications, possibly both ways?

 

Merlin 20 ceased production in May 1944, Merlin 22 in October (but after 227 were built in August, the next two monthly totals were 3 and 5)  The Merlin 24 and 25 were the ones in production.

 

Unfortunately the graph labels are not clear enough, but Merlin output versus altitude, http://www.wwiiaircraftperformance.org/merlin-lovesey.pdf

For Merlin XX 1,175 HP at 20,000 feet. https://www.456fis.org/SPITFIRE_ENGINES.htm

For Merlin XX 1,175 HP at 17,500 feet. https://en.wikipedia-on-ipfs.org/wiki/Rolls-Royce_Merlin.html

meantime the Halifax II performance chart decides it is 1,120 HP at 18,250 feet.  Overall it is holding its power output better than the Hercules VI/XVI.  It is clear the Hercules gave more power for take off and initial climb.

 

In late 1943 the Hercules XVI engines were becoming surplus due to the winding down of Stirling production and the move of the Beaufighter (and other types) to the XVII and XVIII marks etc..  Albemarles would continue their low level production rates through to May 1945, Wellington X production also kept going into 1945.  The Hercules VI effectively ended production in June 1943, the XVI began in September 1942, hit something like a pause button in November, (4 built December 1942 to February 1943) then resumed in March.

 

When I look at the performance charts the Halifax II struggled at altitude compared with other marks and Lancasters, while when it comes to cruising the Merlins and Hercules do not seem to have made a big difference at 20,000 feet, they did make a difference to range and bomb loads.  The altitude improvement in the Halifax III seems to be mainly wing or as others noted wing plus changes to the engine installation, the improved range due to more internal fuel.

  • Like 1
  • Thanks 1
Link to post
Share on other sites

I have read plenty of times about Bristol supercharger design being behind RR supercharger design. I have never been able to find out what the problem was though or whether it was a fundamental design flaw or Bristol just needed to tweak one aspect of the design.

 

Only thing that comes to my mind did the sleeve valves come into it did they prevent high boost.

Link to post
Share on other sites
1 hour ago, AltcarBoB said:

Only thing that comes to my mind did the sleeve valves come into it did they prevent high boost.

I think unlikely. I have not read anything that shows this was a limitation of sleeve valves as also evident in the ongoing performance development of the Hercules and then the Centaurus. Rolls Royce even went to sleeve valves with the Eagle although this did not go far with the advent of the turbojet. 

 

1 hour ago, AltcarBoB said:

I have read plenty of times about Bristol supercharger design being behind RR supercharger design. I have never been able to find out what the problem was though or whether it was a fundamental design flaw or Bristol just needed to tweak one aspect of the design.

I have read the the same but this may be unfair. Probably worthy of more up to date research. Possibly RR was the beneficiary of Stanley Hooker's involvement or the large impetus on fighter engine design to extract the most out of the Merlin/Griffon across a broad range range of flight conditions.  Was it Bristol management? The politics of supply? Different initial design requirements? A combination of all. There is no doubting the Hercules contribution and ability to do the job across a wide range of applications and usually not the glamour applications.  One thing for certain, if I was low over the North Sea in my Beaufighter I would be thankful for a couple of big Hercules to get me home.

 

Ray  

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...