Merlin 40 series performance curves??

[peril]

Anyone have a full curve for Merlin 45/46 engines, I need to confirm power under +16lb conditions at various alts below and above FTH.

I have found it hard to find good industry documented data on Merlins, harder than even Japanese planes, why is that? ;(

EG. most info I can find for the Merlin 45 is 1515hp @ 11000ft +16lb, I'd like to see the full picture if I can.

Thanks.

 

[HoHun]

Hi Peril,

>Anyone have a full curve for Merlin 45/46 engines, I need to confirm power under +16lb conditions at various alts below and above FTH.

I'm afraid I don't have one. In fact, I have found Merlin curves to be somewhat inconsistent in general, which is quite surprising considering that this is the engine Hooker et al. based their "Performance of the Super-Charged Aero-Engine" on.

For an analysis of the most common Spitfire types I did a while back, I relied on partially generic power curves to get a consistent picture. I cross-checked with Mike's WWII Aircraft Performance to make sure that the generic curves were reasonably close to measured data. I was happy enough with the results, but given the number of historic Spitfire variants, of course I didn't manage to cover them all

>EG. most info I can find for the Merlin 45 is 1515hp @ 11000ft +16lb, I'd like to see the full picture if I can.

This is a variant I didn't cover. In my notes I see that I had some data from the "Merlin Development" chart (coloured graphs) I'm sure you're familiar with, and I thought that possibly the "Merlin 45 (1942)" graph was for +16 lbs/sqin. This one was only indicated with 1370 HP at 11400 ft, though.

Regards,

Henning (HoHun)

 

[jerryw]

Hi Peril,

I'm afraid I don't have one. In fact, I have found Merlin curves to be somewhat inconsistent in general, which is quite surprising considering that this is the engine Hooker et al. based their "Performance of the Super-Charged Aero-Engine" on.

Regards,

Henning (HoHun)

In my copy of "Performance of a Supercharged Aero-Engine" the engine used throughout is a Merlin XX s/n C10225 (M.S. ratio 8.15:1, F.S. ratio 9.49:1)

 

[peril]

Yes, it seems no one has covered the most famous Spit Vs main engine, the Merlin 45.

It's a single stage SC based on the second stage of the Merlin XX I believe to save weight and size. You would have thought anything to do with a Spit V would have been well documented, it seems not unfortunately. (leaves a gap for a budding book writer).

Bugga.

If anyone finds this I think we could all use a look at it.

Thanks.

 

[HoHun]

Hi Jerryw,

>In my copy of "Performance of a Supercharged Aero-Engine" the engine used throughout is a Merlin XX s/n C10225 (M.S. ratio 8.15:1, F.S. ratio 9.49:1)

I actually didn't refer to any particular subvariantl in my comment - my point is if you have a consistent and universal method as developed by Hooker for the Merlin engine, one would expect you to come up with consistent results for all subvariants.

Regards,

Henning (HoHun)

 

[jerryw]

Below is a graph giving performance curves for some of the Merlin engines. This graph appears quite frequently in the literature, sometimes with bright colours to distinguish the various marks of engine.

 

[HoHun]

Hi Jerryw,

>There is one line for "1941 Merlin 46/47" and another for "1942 46/7" but I have never come across an explanation for this.

The Merlin 40-series engines had increasing boost limits during their life span.

Here is a time line we prepared over on another forum in an attempt to figure it all out:

29.04.1941 - Spitfire V X.4922: Merlin 45 @ 3000 rpm/+9 lbs all-out level, 2850 rpm/+9 lbs climb, increased to 3000 rpm above ca. 25000 ft
18.06.1941 - Spitfire VB W.3134: Merlin 45 @ 3000 rpm/+9 lbs all-out level, 2850 rpm/+9 lbs climb, increased to 3000 rpm above ca. 25000 ft
xx.01.1942 Merlin 45 type test +16lbs boost. (The Merlin 100 series. RR Heritage Trust).
03.01.1942 - Ministry of Aircraft Production mentions +12 lbs and +15 lbs boosts
08.03.1942 - Spitfire Vc AA.873: Merlin 45 @ 3000 rpm/+9 lbs all-out level, 2850 rpm/+9 lbs climb, increased to 3000 rpm above ca. 20000 ft
30.06.1942 - No. 129 sqn ORB, speed tests at +16lbs boost.
29.07.1942 - R.D.T.3. R.D.E.2. R.T.P.7 Increased Rating for Merlin Engines. Approval 3,000rpm +16lbs boost Merlin 45,46 and 47 engines, operational units of Fighter Command. Previously only applicable to Seafire aircraft and for special applications. 3 minutes duration.
xx.08.1942 - Air Ministry issues memorandum declaring conversion to +16 lbs is currently done
25.11.1942 - Spitfire VC AA.878: Merlin 45 @ 3000 rpm/+16 lbs climb and level
27.01.1943 - Spitfire VB W.3322: Merlin 45 @ 3000 rpm/+9 lbs all-out level, 2850 rpm/+9 lbs climb, increased to 3000 rpm above ca. 20000 ft, 3000 rpm/+12 lbs take-off
03.02.1943 - 1 Sqn (Spitfire V tropicalized and Aboukir filter) clipped wings and +18lbs boost. SB.45457 Performance improvements on Spitfire F Mark V. 
12.02.1943 - RAAF clears Merlin 46 and 47 for use of +12 lbs
25.05.1943 - Spitfire VB W.3228: cropped Merlin 50 @ 3000 rpm/+18 lbs climb and level

Regards,

Henning (HoHun)

 

[peril]

Thanks, I think I can see some conflicts here with data which is why I requested more info. The Merlin 45 data looks good 1515hp @ 11,000ft @ +16 but the 46/47 still looks Grey.

For the 46/47 I have 1414hp @ 14,000ft @ +16, which doesn't match the graph well. Info I have rates the 46/47 as a high alt engine, but from what I see above the Merlin 45 was better at higher alt than the 46.

Makes little sense based on the data I have seen.

 

[jerryw]

Makes little sense based on the data I have seen.

Peril, I've had a closer look at the graph I posted and I think you are right to say it doesn't all make sense!
The commonly quoted HP figures for the Merlin 45 come from the R-R Engine Lists which have been around for a while (relevant page, below)
I'm beginning to think that the HP figure arrowed is wrong. To get 1500 HP out of a Merlin about +18 lbs of boost was required (see lower graph). The Merlin 45 was only ever cleared for +16lbs.(as it says in the Table M.2).
I've changed the graphs originally posted to a version which is closer to the truth.

 

[peril]

Ah, yes that might make sense, ATM I also have an excess in climb at this 45 power curve (1515h) of ~250-300fpm over tested +16, +18 would explain a lot but it would be nice to have an official Merlin chart that confirmed this.

Rated alts Merlin 45 vs 46/47 is still a concern, I would like to see the higher alt engine achieve a bigger gap to the Merlin 45 curve. The SC ratios and size differed and the curve should differ in FTH and low end hp. The 46/47 curve should not achieve the same path as the Merlin 45 above FTH from my understanding.

It should over take it and sit above it at higher alts. What you have drawn below is a Merlin 45 with different boost levels.



Thanks.

 

[jerryw]

The SC ratios and size differed and the curve should differ in FTH and low end hp. The 46/47 curve should not achieve the same path as the Merlin 45 above FTH from my understanding.

It should over take it and sit above it at higher alts. What you have drawn below is a Merlin 45 with different boost levels.



Thanks.

It would really help if you would quote the sources of your info! You say "The SC ratios and size differed..." but, as far as the ratio is concerned, the R-R Lists give both the Merlin 45 and the Merlin 46/47 as 9.089:1!
Also, the curves and the engine data lists both do show a difference in FTH(Merlin 45 - 11,000 ft, Merlin 46 - 14,000 ft). The overall difference between a Merlin 45 and a Merlin 46 engine was not all that great.

 

[peril]

OK, when you change the SC properties your resultant FTH curve will move.

You are right in that only the size changed and ratio remained unchanged (my error from dealing with lots of engines lately). However this change from my understanding would logically be to improve the Merlin 46 curve 'above' the Merlin 45 FTH (to increase hp above 45 FTH). Given the target goals of the change an increased SC size would move the curve to higher alts at the cost of low alt 'max' hp.

You will note a similar downward movement of the M45 curve below the Merlin 45 from a smaller SC, at the cost of high alt hp. Of course this is based on my understanding of SC operations, but I'm sure that someone else will confirm/disprove my understandings.

Thanks.

 

[dairwin]

I have a 24 series engine, and refer to the below performance curve for expectations.

I don't have similar curves for the single speed engines you are discussing, but my understanding is that 45, 45M and 46 were horses for different courses; the 45M for low alt and the 46 for high alt. They all used a SC ratio of 9.089:1, but the SC diameter and type varied: 45 using 10.25", 45M 9.50", 46 10.85" (and true arc vanes).

The difference you are noting may also include the fact that lower diameter SC needs lower engine power to spin, giving higher sea level power, but lower altitude performance.

The SC diameter on the 24 series engine is the same as the 45 (10.25") but the two speed ratios of 8.1516:1 and 9.49:1 lap the single speed 45 engines of 9.089:1.

 

[peril]

Yes Dairwin, that is how I understand it as well. The larger SC would require more power and thus costs SL hp, but the bonus is a more hp at higher alts.

I have that 24 curve as well but it's not useful with this case.

 

[jerryw]

I quite agree with Peril. This Post by Dairwin is off the subject.
This Thread is about the Merlin 40 series engines, not the Merlin 20's.
This Post by Dairwin should be transferred to another Thread.

 

[jerryw]

Below is a copy of some power curves produced by Rolls-Royce during WW2 for some Marks of the Merlin engine, including the 40-series motors.
In my opinion, an error has been made in the labelling of the DARK GREEN part.
This reads: 1942
Merlin Mk 46/47.
It should read : 1941
Merlin Mk 45.

What do other people think??

 

[peril]

I just think they didn't draw it well, it actually looks correct if you extend the below FTH line over the Merlin 3 orange. With a constant 3000rpm this would be correct Merlin 45 or a 46/47 and shows the same engine curve with an increase in boost limits in 1942.

1942 looks like the +16 setting of ~11,000ft @ ~1400 hp @ 3000rpm

The 1941 look like +12 being ~14,000 ft @ ~1280hp @ 3000rpm


The presumption would be they are both same mark Merlins.

I think they are correct as drawn but perhaps boost level and mark unproven.

Need more data with defined boost and rpm.

 

[ThomasP]

I realize this thread is a very old one, but I ran across this Merlin 45 & 46 curve the other day and figured this is one of the threads where it should be posted. It is from one of the AP 1590 J & L series of operator's handbooks. It gives static BHP values - ie without RAM. Hopefully it will help clear up some of the erroneous HP values that pop up all the time in various secondary source charts and tables.

 

[Engineman]

Excellent post ThomasP.
Thanks for posting that graph. The graph does show how the 46 suffered the extra power loss below 11,000' compared to the 45 which had an 85bhp advantage at 9,000' and 70 bhp advantage at T/O. Of course, above 11,000' the graph shows an advantage to the 46 that builds to 50bhp @ 15,000', eroding to 30bhp by 30,000'.
If the 46 was "unpopular" as sometimes reported compared to the 45, I think that must reflect that unpopularity would be because the operating circumstances at that time made the lower altitude power advantage of the 45 more noticeable to pilots than the average 4% advantage of the 46 above 11,000'.
It is a funny thing though, as later the cropped supercharger Merlins, optimised for greater lower altitude power, were criticised as being "Clipped, Cropped and Clapped (out)".

Eng

 

[ThomasP]

The unpopularity might be due to the problems with detonation on the part of the Merlin 46. My spreadsheet indicates that detonation will be likely to occur if you exceed 2850 rpm and +9 lbs boost below ~20,000 ft when at climb speeds or less, and also below 10,000 ft at any speeds. There does not appear to be enough cooling from the normal temperate radiator.

The RAAF did tests and found the Merlin 46 equipped Spit Mk V unacceptable with the temperate radiator - due to detonation. They ended up installing tropical radiators and IIRC this brought the detonation problem down (under tropical conditions as encountered in the SWPA) to ~18,000 ft or less. Note that the tropical radiator was S.O.O. (Special Order Only).

The RAF and RR understood the problem before the Spitfire Mk VI (fitted with the Merlin 47 which was the Merlin 46 with a cabin supercharger added) entered service in Europe, but figured the detonation issue at lower altitudes was secondary to the 2,000 ft higher operational ceiling it was designed to provide the Spitfire. The RAF had enough Spitfires with the Merlin 45 that they only had to use the Merlin 46/47 equipped airframes when they wanted to. I do not know if the RAF used the Merlin 46/50A/56 to any extent in the ETO, but there were only 100x Spitfire Mk VI built.

The RAAF found the problem more problematic since a significant percentage (30-40%?) of the Spitfire Mk Vs they received had the Merlin 46 - sort of as hand-me-downs since the RAF did not want them - and did not really need the higher operational ceiling. Basically, the RAAF needed the low-medium-high altitude fighter, not the high-high(er) altitude fighter.

Incidentally, the FAA received some Merlin 46/50A/56 equipped Seafires, but as far as I know they were all fitted with the tropical radiators before arriving in the MTO. I have never run across any FAA reports covering the Merlin 46/50A/56 so do not know the extent of any problems.