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freakvollder
08-29-2010, 05:40 AM
A Question on the technical experts: What makes the Merlin engine so powerful?

The <span class="ev_code_RED">Merlin 66</span> for example is stated out with <span class="ev_code_red">1580hp</span> in the book <span class="ev_code_green">Schneider Trophy to Spitfire</span>, for 27 litres displacement this is not bad. I search for a good technical description. What strategy where followed by the British and American engineers to make the engine better?


best regards

K_Freddie
08-29-2010, 12:10 PM
I suppose like all developments, one improves things by adding/changing little extras..
More efficient components(less friction), turbocharger types, smoothing inlet/exhaust chambers, maybe changing stroke and bore dimensions... etc.

I don't think it was more powerful than other engine types, but it certainly seemed a lot more fuel efficient.
http://forums.ubi.com/groupee_common/emoticons/icon_cool.gif

JtD
08-29-2010, 12:36 PM
The main strategy for power improvements were increases in boost. Early Merlins had a boost as low as 6lb, latest model used up to 28lb. Now boost is roughly equivalent to power output. Since you have to add atmospheric pressure of about 14lb to the engine boost, this means a power increase of 42/20 or that the Merlin roughly doubled its power output over its lifespan. The engine saw a lot of minor modifications to allow this higher boost to be used. It also needed higher quality fuel.

Added to that, the engine saw loads of subversions and each subversion saw tons of other minor improvements. Noteworthy in regard to performance would be supercharger improvements, mostly aiming at higher efficiency.

But to go through all these modifications for all variants certainly is good for a couple of books.

Art-J
08-29-2010, 12:46 PM
Well, the most important factors in producing the power of piston engine are: displacement, revolutions per minute and break mean effective pressure. Merlin was not a big unit indeed, but it met two latter points well: the peak power was produced at unusually high 3000 RPM (compared to 2800 of DB-605 and eee... uhm... 2700? of Allison V-1710, I might be wrong here), plus from the 60- series onwards it had built in two stage, two-speed supercharger, which was pretty special for the engine of this size and class.

Add lots of details Freddie and JtD mentioned and you've got small but bada$$ machine.

Cheers - Art

MB_Avro_UK
08-29-2010, 12:56 PM
Technically speaking, the reason it was so powerful was that it was British.

No other data required. http://forums.ubi.com/images/smilies/halo.gif

Best Regards,
MB_Avro.

Bremspropeller
08-29-2010, 01:03 PM
Technically speaking, the reason it was so powerful was that it was British.

Exactly, so the Englanders could run away...

BillSwagger
08-29-2010, 01:09 PM
I don't see the merlin being that powerful or out of the range of contemporary engines.
I think what made a bigger difference was the supercharging and lighter weight of the airframe.
Getting higher manifold pressures out the same engine block was something that went on through out the war.
This requires adjustments in timing and better gas and better metals. Better headers with less moving parts can also help improve higher output performance or at least decrease engine wear.
The impellers also function as way to get more power and efficiency from the same engine block. This was something discovered while working out the quirks of the Packard Merlin.

These are areas that can be improved although still working off of the same displacement of the engine.

Rated power can also be misleading because other considerations to performance other than horsepower and manifold pressure is the reduction ratios/gearing and the propeller types. This area deals with transferring that engine power into the propeller where the propeller turns it into thrust. Of course having available power to do that at higher altitudes was essential.
This was also a big area in aircraft development during the 40s.



Bill

BillSwagger
08-29-2010, 01:17 PM
Originally posted by Art-J:
unusually high 3000 RPM (compared to 2800 of DB-605 and eee... uhm... 2700? of Allison V-1710, I might be wrong here),
Your not too far off.
I think most contemporary V engined fighters ran at about 3000 RPMs, including the Allison, however it saw a decline in RPMs after reaching full throttle height.


Bill

stalkervision
08-29-2010, 01:27 PM
"wizard power" http://forums.ubi.com/images/smilies/winky.gif

ElAurens
08-29-2010, 01:54 PM
When you compare BHP per Litre of displacement, the Merlin far outstrips the DB engines.

It's relatively smaller displacement means lighter crank and pistons/rods so it could rev higher. Also the Merlin used a higher compression ratio and could use more boost, as the Allies were able to supply ever increasing quantities of very high octane aviation fuel.

The Allison V-1710's weakness was it's lack of a good two speed/two stage supercharger. On the turbocharged P38 it could make very high power as well. And it is a more robust engine than the Merlin. Most racing Merlins today use Allison connecting rods as they are far stronger than the Rolls Royce rods are.

DuxCorvan
08-29-2010, 02:01 PM
Because it's got electrolytes. (http://www.youtube.com/watch?v=Ru6p5NLXxvY)

JtD
08-29-2010, 02:13 PM
Actually, the Merlin did not reach maximum power at 3000rpm. At least the models I've seen power charts for.

While 3000rpm are the rated rpm, the maximum power is reached at lower rpm at about 2850rpm. Higher rpm tend to give slightly lower outputs. You can find 2850 rpm for climb ratings for many Merlin variants for that very reason - maximum power. In level flight it went up to 3000rpm to give the prop a better advance ratio and thus higher efficiency. But actual shaft horsepower were lower than at 2850rpm.

IIrc, lower boost tended to give best power at even lower rpm. That's also meaning that the really high late war boosts might have given best power at more than 2850 rpm. Can't look it up at the moment,

JtD
08-29-2010, 02:17 PM
Originally posted by ElAurens:
...Also the Merlin used a higher compression ratio [then the DB]...

I don't think you're right, the Merlin used a lower compression ratio than both the DB 601 and the 605. (6.1-6.9-7.3, I think)

BillSwagger
08-29-2010, 03:09 PM
Originally posted by JtD:
The main strategy for power improvements were increases in boost. Early Merlins had a boost as low as 6lb, latest model used up to 28lb. Now boost is roughly equivalent to power output. Since you have to add atmospheric pressure of about 14lb to the engine boost, this means a power increase of 42/20 or that the Merlin roughly doubled its power output over its lifespan. The engine saw a lot of minor modifications to allow this higher boost to be used. It also needed higher quality fuel.


Do you know if changes in boost rating were also accompanied with hardware adjustments?

From some of my reading, a higher boost rating is obtained by using more throttle, however full throttle height remains the same. That would mean the aircraft performed better at lower altitudes but essentially would remain the same above FTH.
It seems natural to think that adjustments in the throttle arm would be required, but then that also suggests that adjustments in the intake hardware would need to be modified. Which leads to the story surrounding the improved impellers of the Packard Merlin, but i haven't read anything that makes that a direct connection to improved FTH and higher boost pressures. It would be my presumption.
I thought you might know more.

Bill

ROXunreal
08-29-2010, 03:25 PM
What makes Merlin so powerful is magic of course, duh.

Mike Dora
08-29-2010, 05:04 PM
The answer is Stanley ******.

http://en.wikipedia.org/wiki/Stanley_******

DrHerb
08-29-2010, 09:40 PM
http://www.enginehistory.org/rolls-royce.htm


One Second in the Life of a Racer
by Tom Fey

The Unlimiteds go flashing through the racecourse, engines howling, air shearing, heat waves streaming. Four hundred eighty miles an hour is 8 miles a minute, and the elite racers take about 70 seconds to cover the 9.1 mile Reno course. If you could take a souped P-51 racer flying the circuit at Reno, slow time down, and examine just one second, what would you find?

In that one second, the V-12 Rolls-Royce Merlin engine would have gone through 60 revolutions, with each of the 48 valves slamming open and closed 30 times. The twenty four spark plugs have fired 720 times. Each piston has traveled a total of 60 feet in linear distance at an average speed of 41 miles per hour, with the direction of movement reversing 180° after every 6 inches. Three hundred and sixty power pulses have been transmitted to the crankshaft, making 360 sonic booms as the exhaust gas is expelled from the cylinder with a velocity exceeding the speed of sound. The water pump impeller has spun 90 revolutions, sending 4 gallons of coolant surging through the engine and radiators. The oil pumps have forced 47 fluid ounces, roughly one-third gallon, of oil through the engine, oil cooler, and oil tank, scavenging heat and lubricating the flailing machinery. The supercharger rotor has completed 348 revolutions, its rim spinning at Mach 1, forcing 4.2 pounds or 55 ft³ of ambient air into the combustion chambers under 3 atmospheres of boost pressure. Around 9 fluid ounces of high octane aviation fuel, 7,843 BTUs of energy, has been injected into the carburetor along with 5.3 fluid ounces of methanol/water anti-detonant injection fluid. Perhaps 1/8 fluid ounce of engine oil has been either combusted or blown overboard via the crankcase breather tube. Over 1.65 million foot pounds of work have been done, the equivalent of lifting a station wagon to the top of the Statue of Liberty.

In that one second, the hard-running Merlin has turned the propeller through 25 complete revolutions, with each of the blade tips having arced through a distance of 884 feet at a rotational velocity of 0.8 Mach. Fifteen fluid ounces of spray bar water has been atomized and spread across the face of the radiator to accelerate the transfer of waste heat from the cooling system to the atmosphere.

In that one second, the aircraft itself has traveled 704 feet, close to 1/8 mile, or roughly 1.5% of a single lap. The pilot's heart has taken 1.5 beats, pumping 5.4 fluid ounces of blood through his body at a peak pressure of 4.7 inches of mercury over ambient pressure. Our pilot happened to inspire during our measured second, inhaling approximately 30 cubic inches (0.5 liter) of oxygen from the on-board system, and 2.4 million, yes million, new red blood cells have been formed in the pilot's bone marrow.

In just one second, an amazing sequence of events have taken place beneath those polished cowlings and visored helmets. It's the world's fastest motorsport. Don't blink!

JtD
08-29-2010, 11:46 PM
Originally posted by BillSwagger:

Do you know if changes in boost rating were also accompanied with hardware adjustments?

Typical changes when increasing boost were changes to the
- throttle (lever)
- engine mounting
- spark plugs
- engine timing
- propeller
- fuel supply

Not all of which were done every time boost was increased.

The increased boosts on the Merlin usually just meant higher power at low altitudes, below the full throttle altitude of the original boost setting, with unchanged high altitude performance.
The full throttle altitude of the new boost would of course be at a lower altitude than before at the lower boost.

Friendly_flyer
08-30-2010, 12:38 AM
From what I remember from trimming two-stroke moped engines in my teens, you can always squeeze more power out of an engine, but at the cost of reliability.

Moped engines are dumbed down to 2,5 hp in Norway, and since you did not need any license to drive, most of the lads experimented with boosting the engine, since being caught had very little consequences (no license to loose). Carburettors openings was filed, engine blocks sanded down to make higher pressure etc. These trimmed engines usually ran at higher RPM, but tended not to last too long.

Merlins was not particularly powerful (the P&W that powered the Thunderbolt produced far more power), but it was powerful for it's weight. What made the Merlin well suited was being able to keep putting out high amounts of power over time, from a very light engine. This is a question of engine reliability (a point where my friends the moped hobby mechanics fell woefully short) rather than of raw power.

The Rolls-Royce company had a lot of experience in making high reliability engines. What they did was to take the fledgling engine and run it at full boost until something broke. When that happened, that part was strengthened, and the process repeated. Parts that did not break could be thinned down until they did. Since the RR was a well established company with a lot of experience and economy at their disposal, they could do this very thoroughly, producing an engine that was reliable, despite light weight weight and high power output.

WTE_Galway
08-30-2010, 01:16 AM
Better quality rubber from British Borneo chaps http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

http://pics.towerhobbies.com/imagel/g/lgala0733.jpg

Insuber
08-30-2010, 03:03 AM
You will find some answers in this article, written in Nov 1945 by a Rolls-Royce engineer.

http://www.wwiiaircraftperform...g/merlin-lovesey.pdf (http://www.wwiiaircraftperformance.org/merlin-lovesey.pdf)

Cheers,
Insuber

jameson2010
08-30-2010, 05:35 AM
Thank you for posting this, a great read and very informative. Enjoyed it a lot. Cheers!

Friendly_flyer
08-30-2010, 06:49 AM
Interesting read! the answer to the question seem to be a basic engine design suited to development and a company putting sufficient money into their development department.

Kurfurst__
08-30-2010, 08:18 AM
Originally posted by Friendly_flyer:
Merlins was not particularly powerful (the P&W that powered the Thunderbolt produced far more power), but it was powerful for it's weight.

Depends compared to what.. certainly not compared to other inlines, for example the Allisons were lighter, and the French Hispanos were much lighter. Essentially the Merlin weighted and siyed the same as the DB or Jumo series, despite the latter's larger displacement, even the bare block of the engine, without 'non essential' the accessories like carburattor, supercharger, intercooler etc.

You have to look at the whole package - the cooling and oil systems and their piping are considerable bulk and drag, as is the coolant and lubricant, then goes the propellor. Radial engines for example may weight more than inline blocks, but you also have to factor in that there's no drag or extra weight from their coolant systems.

In the end, it is net, 'useful' thrust that defines the effiency of an engine.

Xiolablu3
08-31-2010, 01:26 PM
Originally posted by Kurfurst__:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Friendly_flyer:
Merlins was not particularly powerful (the P&W that powered the Thunderbolt produced far more power), but it was powerful for it's weight.

Depends compared to what.. certainly not compared to other inlines, for example the Allisons were lighter, and the French Hispanos were much lighter.. </div></BLOCKQUOTE>

Those daft Allies, they should have been using Alisons in the P51 and then they would have a much better plane...

Oh , hang on a minute.... http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif


But seriously,

The DB 605 had to use Mw50 to keep up with the late war Allied planes. How much weight did that system add?

JtD
08-31-2010, 01:57 PM
I'd say "it used" not "it had to use". The R-2800 in the P-47, F6F and F4U also used MW50 and that wasn't necessarily because "it had to" in order to keep up with Ki-43's and A6M's.

MW50 is a pretty effective and efficient way of allowing higher boost pressures and thus squeezing more hp out of the same engine. Add to that, it was available to the Germans, unlike high octane fuel.

Eventually, all major engines used in aircraft of WW2 were in many ways great engineering pieces. That's why they were used in huge numbers. I think it will be hard to find objective criteria where one ends up as clearly better than all others.

Xiolablu3
08-31-2010, 02:16 PM
Yeah, I think you missed my point,mate.

I maybe should have worded it differently, I will try again...

The Germans 'chose' to use MW50 in order to get get higher speeds from their aircraft. As Kurfurst was saying, you must add on all the gadgets etc which were used on the engine as well as just the engine. How much did the MW50 and piping of 1944/45 weigh?

BillSwagger
08-31-2010, 02:29 PM
water is about 8.35 lbs per gallon,
alcohol is about 6.55 lbs per gallon.

averages to about 7.45 lbs per gallon

If you knew how big the water tank was, that would probably be the bulk of the weight.

Xiolablu3
08-31-2010, 02:35 PM
Originally posted by BillSwagger:
water is about 8.35 lbs per gallon, a MW50 mixture is probably a little lighter than that.
If you knew how big the water tank was, that would probably be the bulk of the weight.

I have read that Rolls Royce and some other engine manufacturers didnt want to use MW50 because of the added weight, piping and complications. Cant recall the source however.

MB_Avro_UK
08-31-2010, 03:11 PM
Originally posted by Bremspropeller:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Technically speaking, the reason it was so powerful was that it was British.

Exactly, so the Englanders could run away... </div></BLOCKQUOTE>

Exactly...?? Explain please. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

Best Regards,
MB_Avro.

JtD
08-31-2010, 10:38 PM
Xio, I don't know how much it weighs. It's not that much, though. Like Bill said, the contents of the water tank would probably account for the bulk of the mass, and that you wouldn't count, just like you wouldn't count an extra fuel tank.

Skoshi Tiger
09-01-2010, 02:18 AM
Originally posted by MB_Avro_UK:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bremspropeller:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Technically speaking, the reason it was so powerful was that it was British.

Exactly, so the Englanders could run away... </div></BLOCKQUOTE>

Exactly...?? Explain please. http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

Best Regards,
MB_Avro. </div></BLOCKQUOTE>

It's quiet obvious isn't it? After giving Jerry a though drubbing, the last one back to base paid for the first round!

Stands to reason you needed powerful, efficient engines!

Cheers!

BillSwagger
09-01-2010, 03:22 AM
Originally posted by Xiolablu3:
I have read that Rolls Royce and some other engine manufacturers didnt want to use MW50 because of the added weight, piping and complications. Cant recall the source however.

Not every engine was well suited to a WEP water system at first. I think the bigger reason for not using it was because there may not have been room underneath the cowl, so to say. I don't know how cramped the spitfire engine compartment was, but i can assume that with a cooling system and oil system, and a MW system it would've been much more intricate. Even if you fit the pipping and extra gadgetry required, where do you fit a water tank? Even a relatively small five gallon bladder can take up considerable room. Keeping the design compact and small may have been a design goal.

It also seems more research with WEP water injection was done at the Pratt-Whitney plant. I'm not certain when water injection first started appearing on other types of engines, but it was first introduced to PWs line in 1943, and i have reason to think it would've been included on the Allison and Merlin when available. It may have also been that WEP was better understood as far as engineering it to a radial engine as oppose to a V engine.
The same article makes reference to the Germans use of water injection, in that their technique was more similar to actual fuel injection, as oppose to introducing the water prior to the inlet on the intake manifold.
The results were said to not be as successful for the Germans for this reason. At some point i think the technology must've become available for the Germans, and maybe someone could help back this up, but i think they had more success with N2O systems than with MW50. It may not have been a "had to use" type of choice for them, but it made a reputed difference at higher altitudes.



Bill

Kurfurst__
09-01-2010, 04:18 AM
Originally posted by Xiolablu3:
Those daft Allies, they should have been using Alisons in the P51 and then they would have a much better plane...

There was NOTHING wrong with the Allison. Simply the type of Allison used in the P-51 had a poor supercharger mounted on it... the one in the P-38 however...



The DB 605 had to use Mw50 to keep up with the late war Allied planes. How much weight did that system add?

The 115 light alloy tank weighted 32 kg, it was built in place of 32 kg of light alloy armor on the 109, so it was effectively a net 0 kg change. The MW-50 liquid was about 70 kg, and of course, consumed during use at some 2-3 kg per minute. Piping weight, negligible I guess, there were two or three light alloy pipes, how much could that weight, a pound maybe..? So on the 109 we speak of +70 kg (and plus 3-500 horsepower, a fairly good deal I would say) and on the 190D some +100 kg (and plus 2-300 or so HP again).

Now in comparison I also have the weight of the intercooling system on the Spitfire IX, with which a comparison can be made since both were used for the same purpose, charge cooling (in addition MW-50 provided considerable internal cooling to the engine in the combustion chamber). The aftercooler itself weighted some 32 kg, and there was a seperate intercooler radiator (42,5 kg) of the size of the oil cooler. Obviously some fluid was flowing through this system, I don't know how much but given the size of the radiator and the oil amount, 20 kg looks like a safe guess.

Essentially the system used on the Merlin adds the same weight as the MW-50, roughly, but there are three main differences:

Firstly, the intercooler radiator adds considerable drag, MW 50 doesnt. So with an intercooler some of the top speed that otherwise would be gained due to the power increase will be lost due to the drag increase.

Secondly, unlike MW-50 it can provide constant charge cooling without time constraints (although the two staged DB 605L would use MW50 for charge cooling at the 30 min military rating, too, enough for an hour of use), and this can be important for long range sorties for escort figthers. However this is only a must if you are using a relatively small displacement engine like the Merlin, which needs some supercharging even at lower speed cruising. For the Germans, with their larger displacement and as a result and in comparison modestly supercharged engines, this wasn't that much a problem, though they see it fitting to use intercoolers on their bomber engines.

Thirdly, MW-50 does provide internal cooling for the engine, not only just charge cooling. This may be important, since when evaporaing in the combustion chamber, and then going out on the exhaust, MW-50 essentially acts as eveporative cooling, and its very very effective at that. As a result the engine requires less cooling at max power, and thus less draggy radiators.

BTW the Packard-Merlin V-1650-9 pwered P-51H used MW-50 too, just the Allies called it ADI (anti detonant injection) or 'wet' boost. And, in any case, the DB 605D was certainly capable of producing up to 1,800 HP without MW-50, just on C-3.

Xiolablu3
09-01-2010, 05:54 AM
Originally posted by Kurfurst__:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Xiolablu3:
Those daft Allies, they should have been using Alisons in the P51 and then they would have a much better plane...

There was NOTHING wrong with the Allison. Simply the type of Allison used in the P-51 had a poor supercharger mounted on it... the one in the P-38 however...


. </div></BLOCKQUOTE>

It was only a joke, hence the winky. I know well the Turboccharger/Supercharger issue on the Alison. But as you have already said, you must add on the needed implenments for the engine to work as it was meant to, and the turbocharger supercharger issue on the Alison is there and cannot be ignored.

Thanks for the info on the Mw50

horseback
09-01-2010, 01:24 PM
It was my impression that the 'base' Allison weighed a bit more than the 'base' Merlin; The V-1710 designation refers to the cubic inches of displacement, considerably greater than the V-1650 Merlin's, so I would expect that the Merlin would be a bit lighter than the Allison before adding all the bells & whistles. The weight difference (as reflected in its performance above 4500m) in the later models was more likely due to the Merlin having a two-stage supercharger vs the Allison's single stage supercharger.

Engine installations vary greatly with aircraft type; the Corsair, Hellcat and P-47 all used the same 'base' R-2800, but the Corsair and Hellcat used a two-stage supercharger system while the P-47 used the GE turbosupercharger system (which was also used on the B-17, B-24 and the P-38, for example).

The Naval fighters enjoyed a fair performance advantage over the P-47 below about 6500m, but the bulkier turbosupercharger endowed the Jug with generally superior performance above that height; the weight and drag penalty was no longer as high because the turbosupercharger was more efficient than the high blower stages of the F4U or the F6F's superchargers.

I would suspect that the Merlin's supercharger system, as used in the Spitfire VII-XI/XVI and the Merlin Mustangs was quite a bit more efficient than in most contemporary fighters, given the amount of power still generated at higher altitudes.

More important, however, was how well the whole aircraft was designed and how well the Merlin stood up to not only the abuse of combat, but the extended flight times to the interior of the Axis held territories and back; a lot of warplanes of the time could hold sufficient fuel for that kind of trip, but very few had engines/systems that could do it reliably and perform successfully in the zone of combat at all altitudes.

cheers

horseback
horseback

JtD
09-01-2010, 04:04 PM
Originally posted by Kurfurst__:

Now in comparison I also have the weight of the intercooling system on the Spitfire IX, with which a comparison can be made since both were used for the same purpose, charge cooling...

Of course that comparison can be made, but then you can also compare apples to oranges.

What exactly did the DB605 two speed supercharger compress with MW50 off and on?
The Merlin's two stage charger compressed an air fuel mixture, where the evaporating fuel would cool the air whilst being compressed.

What was the charge intake temperature at 1.42 ata?

Art-J
09-03-2010, 01:43 PM
On a side-note, does anyone of you guys have a photo of Merlin 130- series engine? The one developed for DH Hornet, with "bells and whistles" repositioned to reduce the cross section area?

I wonder how this one looked like, but even The Almighty Google doesn't seem to come up wth the answer!

Cheers - Art