Napier Sabre - The Ultimate WWII Aircraft Engine - Part 1

while merlin engines may have propelled the majority of allied warplanes to victory a relatively under-appreciated engine the napier's saber in its following variants produced much more power at a lower overall weight than any other wartime engine produced in the era with a specific power exceeding that of any other engine that saw service throughout world war ii the sabre was the result of a fundamental shift in engine design philosophy more similar to a modern racing engine than other high performance in aero engines at the time the sabre utilized a relatively short stroke and high operating rpm to produce a staggering amount of power per cubic inch of displacement in fact at the time it was thought that a one horsepower per cubic inch metric was almost impossible to attain and the saber clearly shattered that number however despite performance that firmly placed its competitors behind it the sabre was treated as an outcast the british government and engine industry downplayed his achievements and rolls-royce the preeminent engine manufacturer at the time even attempted to politically force and appear to stop saber production after having failed to match its record-breaking performance this is the story of the napier saber engine an underappreciated gem that should be remembered as the wonder of engine design it truly was in the interwar period it became readily apparent that the next large conflict would heavily involve both fighter and bomber aircraft as military strategists such as guio duhet and billy mitchell began expounding the benefits of strategic bombing raids and the requisite supporting fighter aircraft engine manufacturers began rapidly developing what they hoped would be the next generational leap in engine power for the nepear company a relative newcomer to the aero engine race this was a perfect opportunity and so in an effort to design a hyper engine capable of beating the one horsepower per cubic inch limit they hired a man named frank halford who had a few radical design ideas that would prove potent namely alford theorized that an engine using relatively small cylinders running at an unusually high rpm with a short stroke would be smaller and lighter than more conventional engines yet produced the same output nepear agreed and they began work on developing a new series of engines alfred began with the rapier 1 in 1929 and later the dagger won in 1933 each of these used a vertical h configuration and featured 16 and 24 cylinders respectively the 529 cubic inch repair produced a 395 horsepower while the larger dagger produced 1 000 horsepower at 4 200 rpm unfortunately for an appear these engines received little commercial success despite their impressive performance for the time their creation did however cause rolls-royce to label them as a dangerous competitor causing them to begin lobbying the air ministry to keep their designs from being accepted and manufactured so with the cards stacked against them and wore on the horizon napier was forced to do something drastic during this time in 1935 halford joined the board of directors as technical director and doubled down on his design philosophy perhaps theorizing that an engine producing enough power would overcome any future political corruption the napier company might encounter he showed the initial 2 000 horsepower saber design to george purvis bulman the then deputy director of engine research and development for the british air ministry this was a risk as at the time no engine of the suggested size had made such power and even rolls-royce's designs had barely broken into four figures fortunately for both napier and the war effort bowman believed in halford and the saber project and arranged for an appear to receive the initial financial support to develop the engine development of the sabre began in earnest in 1936 and little time was taken developing the overall layout of the engine as halford knew from his previous designs how to make a lot of power in a small package the saber featured 24 total cylinders split into two tiers of 12 cylinders these tiers were arranged in a flat 12 orientation each connected to their own individual crankshaft the engine's design was essentially two engines mated together in a compact form but as you remember this is a lot of moving metal all these cylinders and helford's theory was that high rpm would be required to generate the power he desired and so while the sabre certainly had enough cylinder area to make 2 000 horsepower it needed something extra to make the speed and keep those cylinders fed in 1927 harry ricardo then the foremost engine designer at the time wrote a paper in which he theorized that the poppet valves that is these circular deals you see in cool engine cross-section images would suffer from a limit of 1 500 horsepower due to the limits of their volumetric efficiency pretty much these small oddly shaped openings for air to travel through would be better if they were bigger and more circular fortunately for an appear in the saber halford was aware of this proposed limit as he had previously worked for ricardo and in fact despite ricardo currently working for bristol engines his office at the time of the sabres early design phase was only 700 yards from halfords this arrangement was likely a huge advantage for halford as both his life experience with and proximity to ricardo likely inspired halfer to adopt ricardo's proposed solution to this problem the sleeve valve a sleeve valve design rather than the more traditional poppet valve would alleviate the issue of volumetric efficiency and thereby help alford achieve his high rpm dreams simply put the engine could breathe cleaner and faster with sleeve valves by offering a large unobstructed intake and exhaust port the sleeve valve created a more complete quick charging and scavenging cycle for the cylinder and also allowed a higher supercharger pressure to be used due to the ability of a sleeve valve design to delay detonation furthermore because the cylinder head is not required to host any poppet valves it can be tailored so that the spark plug is in the best possible location for efficiency these advantages also allow the saber to tolerate a higher mixture of lead in the fuel an important feature due to the fuel quality issues early in the war so with this winning combination of layout cylinder size operating speed and efficiency hofford suspected that the saber was capable of much more than his initial 2000 horsepower estimate however due to rolls-royce's suppression with the air ministry it would be over five years before halford was grudgingly allowed to conduct a type test at 2050 brake horsepower and 3700 rpm despite the sabre being capable of much more in fact throughout the saber's life it would be continually suppressed its reputation tarnished by differences between what halford knew it was capable of and what was allowed to be published due to the continual harassment by rolls-royce adding to this problem rolls royce were also made aware of all the development on the saber project allowing them to continue their slanderous campaign against napier but just when things were beginning to look ugly for napier and their saber engine in rolls lord beaver brook taking the role of minister for aircraft production in 1940 beaver brook wouldn't be swayed by those rr folks and commanded facilities to begin saber manufacture so just like that while the saber project would always be plagued by the influence of rolls royce it would at least be built and flown it might not receive the best air screws which were still being reserved for merlin's and might only be produced in limited numbers but it would seem battle and strike fear into the enemy like no other engine of the day so let's compare some data why was the saber the best engine of the war in this first chart i have the contemporary engines that you would find in a lot of the front line fighters we're comparing the allison 1710 to the merlin 61 to the db 605 am to the griffin 65 the saber 2 and the pratt whitney 2800 now the first thing that jumps out to me when i look at the chart is that the sabre is indeed in 1941 and 1942 making more horsepower than any of its contemporaries however it is quite a heavy engine which we will see will affect it greatly when we talk about its specific power and power to weight ratio later on but right now the saber is wearing weighing 2 360 pounds making it the heaviest engine by far in its class if we take a look at the cubic inches in weight relationship between some of these engines we do also notice something interesting that the allicin is able to displace 1700 cubic inches and only weigh 1400 pounds is quite an advantage when we talk about its eventual power to weight ratio which we're going to calculate so any time an engine can displace more than it weighs that's a that's a pretty big advantage and we can see pretty much every engine here is doing that except for maybe the merlin and the saber of course now for the life of me and my research i was not able to discover why some engines are able to enjoy this benefit of having a lot larger displacement compared to their weight while the saber is not i suspect it's because the saber has two crankshafts and the gears that are required to turn those two separate h-blocks into a single power unit but i can't confirm that conclusively before we take a look at the next chart we need to understand the way we're going to compare engines predominantly there's two ways to do it you can can take the total horsepower divided by the weight of the engine and get its power to weight ratio or you can take the total horsepower divide it divided by the displacement which gets you the specific power of the engine as we previously stated at this time engine manufacturers were really trying to get that one horsepower per one cubic inch of displacement mark that was the goal for efficiency for the engine but that metric of specific power doesn't really tell us the whole story especially when we consider what we previously discussed which is that some engines have a lot more displacement than they do weight so when we take power to weight into account and we start thinking about how this is going to actually fit into an aircraft while you may have a very efficient specific power your power to weight ratio may actually make your engine undesirable and that's exactly what we see here while the saber is obviously the most efficient engine in terms of displacement compared to every other engine in the category it is actually not the most desirable engine in terms of power to weight ratio we can see that the griffin the db605 and the merlin and the allison all make a better power to weight ratio and that's predominantly as we said because the saber is just a very heavy engine at this point based on its power rating it needs to be generating more power for all of the weight that it brings to the table and we will see when we compare this this data to the late war data and some of the revisions of the saber engine that they are able to accomplish just that one thing i wanted to bring up real quick just before we look at the late war data is why this 2200 horsepower number that the sabre arrives in 1940 with is quite impressive but as we said compared to its weight it's really not that impressive when we look at power to weight ratio so what's going on now in most of my research i wasn't able to find exactly pinpoint exactly what was going on but we can look at what was being revised in the subsequent revisions to the saber engine and it gives us some insight into probably what was happening i think that the sabre was not necessarily suffering from any fundamental design problems moreover it just really needed a redesign in getting boost to the engine it seems that the engineers were really struggling with designing a supercharger that could feed this engine and maximize the power that it was capable of we see some small revisions where they're doing some reinforcements to maybe allow more boost to come into the engine but they're very small changes there's nothing huge happening here what we do see is entries like new supercharger designed and then again advanced supercharger more boost added so we can see as time goes on as they begin boosting this engine higher and higher compared to its peers we can see that these numbers get quite large and this late war data that we're getting ready to look at we're not even pushing with these numbers the amount of boost that some of these other smaller engines are pushing so there may have been even more horsepower on the table for the saber and that's that's probably beyond my expertise to comment on but it is interesting to think about another thing that leads further queens to this idea that the predominant issue when the saber arrived on the scene was just the forced induction system was the reputation for the typhoons and other in another aircraft they were using the saber engines such as the tempest of having poor performance at high altitudes we could see that people were instructed to fly the typhoon down low it was predominantly used as a low fighter aircraft at first in the war because the nepear company had not yet resolved the force induction system the saber was a great platform but the induction system was not yet optimized also as a caveat before we move forward i also want to make sure that it's abundantly clear that i'm not calculating or using how these performance numbers are affected by altitude in these comparisons my main figure being utilized for this comparison about what makes a good engine is just the maximum amount of horsepower that can be generated and in terms of how that horsepower falls off with the increase in altitude that's going to be largely as we just said up to the forced induction system being used so that may greatly affect how these engines are perceived when they're implemented into aircraft because of whatever system is utilized alongside it may severely inhibit the potential of that engine but that is not going to be what we consider here just in terms of what the engine was capable of right so let's compare the late war data now for this data i went on the various sources that were talking about the specifications of these engines and i found the highest entry i could find for these engines while they were in service now with the exception of the allison engine which became a turbo compound engine which i believe disqualified it from this competition nothing generated more power than the sabre that i am aware of that actually entered production and was put into an aircraft there is some data towards the end of the war where they were capturing exhaust energy like a turbo and reading and feeding that back into the allison engine and driving the like the crankshaft with that and generating obscene like 3000 horsepower you know numbers out of a 1400 pound engine which i'm sure is possible but i think that technology that turbo compound business disqualifies it from our comparison so i've excluded that but i just wanted to just for clarity's sake reference that that did happen the allison did get quite insane later on but we do see that the saber does what it's it's designed to do because it has that high rp operating rpm which is an interesting thing we haven't really talked about in the video so far you know this engine's operating when it's at war emergency power at 4 000 rpm when we look at the merlin it's operating at 3000 rpm the griffin is 2700 rpm and that's about the range that you're gonna find all of these other engines in this high two to maybe low threes rpm regime whereas the saber is cranking around a thousand more rpm than any of these other engines it also has more cylinders than just about everything but the r2800 i believe and the the compression ratio is slightly higher but it's maybe just kind of negligible it's that most of these engines are running six to one whereas the sabre is running a seven to one but my best explanation for why we're seeing such a huge power increase compared to its peers here is we're really just unlocking this design when we add boost to it with this volumetric efficiency that we're being afforded by these sleeve valves this very nice opening of the ports and closing at a very rapid rate is giving us an exponential advantage when we're adding boost to the engine and i think that's my best guess as to why the performance is really outshining the more traditionally designed piers also i think an interesting point to bring up that really leads credence to this idea is that you can see rolls-royce begin to shift their design practices towards the piers method late in the war the griffin rather than being redesigned into an x-24 shape when they decided that they needed more power they start beginning to adopt essentially exactly the saber's design they start with the eagle 9 i believe it was and it is essentially a ripoff of the saber in my opinion it is an h24 pattern with the almost exact same specifications except for it's bigger and makes less power than the saber did i'm not sure on that one so let's look at our final chart we can see that now that we're comparing specific power and power to weight ratio at the end of the war after we've had some advancement time we're comparing these late war engines that the saber e122 is head and shoulders above its competition both in specific power and power to weight ratio because it was finally able to really unlock its full potential and generate that massive horsepower number that 2 300 pound figure is really less of a problem when you're generating 3 500 horsepower out of that package the math just works out right and as we said before it just makes sense based on the operating speed of this engine its higher compression ratio its ability to accept boost and predominantly its ability to delay detonation it has perfectly designed combustion chambers because the cylinder heads are not being crowded up by poppet valves and just a numerous other advantages that gave it this performance ability but i do want to make sure that i take a second to just mention that not everything was perfect and ideal for the saber when we looked through the history it had the same teething problems that most new other new engines had when they were first entered into production and service it had a very poor reliability record it was a very complex engine at the time you know imagine giving a bunch of forward mechanics that are used to working on the v type of engine essentially this completely different layout of a high-speed multi-unit power package with two h12 blocks it's just a completely different thing so naturally there's going to be some friction there but once they were able to finally get some of that stuff under control and really start cranking these boost numbers up we do really see why the sabre was the ultimate engine of the entire conflict really the proof is in the pudding when we look at the final numbers here specifically specific power of the saber e122 is 1.56 and a 1.48 power to weight ratio its closest competitor is the merlin 130 with a 1.23 specific power and a 1.23 power to weight ratio nothing comes close even the db 605 dc they are able to crank that power up to 1980 horsepower towards the end of the war and its specific power was never very good but it usually had a very good power to weight ratio its specific power was 0.9 and only a 1.18 power to ratio with that 1900 figure so it's just it's just a fact of 3 500 horsepower is a lot of horsepower so if you do have any sources that conflict with my sources or my data seems incorrect in any way shape or form don't hesitate to leave a comment subscribe and yeah let's talk about it because i i really did scrounge through pretty much everything i could find to find accurate information to make this video and i would very much like to know if my my research was wrong so feel free and as always thank you guys for watching [Music] you

Channel: Flight Dojo

Views: 688,707

Keywords: hawker typhoon, sleeve valve, wwii engine, napier sabre engine, wwii history, world war ii, typhoon

Id: Hk1-P5iksIc

Length: 20min 12sec (1212 seconds)

Published: Wed Apr 06 2022

Reddit Comments

[u/THEOnionTerror]

Those sleeve valve engines are absolutely fascinating, my favorite however is the Centaurus, built by Bristol coincidentally. Some theories today state that sleeve valves could still outperform the poppet valve designs due to the higher tolerances available in manufacturing which would lower the high oil consumption of these engines