How One Decision Ruined British Aircraft Engines

hey everybody it's chris from military aviation history and today i want to talk about a very popular subject i think in aviation circles especially with those focused on the second world war and that is to try to answer the question of why britain did not have a direct fuel injection engine in their lineup in the start of world war ii whereas germany did and in order to do that i have of course invited callum douglas who has been on the channel before uh he's of course the author of the great horse power race this is a fantastic book that i can thoroughly recommend and he's going to give you a really great breakdown of the issue at hand and explain exactly why britain did not have that direct fuel injection so i'm just going to hand it over to column at this point hi callum here author of the secret horsepower race which if you like world war ii aero engines is a pretty good place to start your reading thanks to chris for inviting me back to do another video with him so we're just going to talk about a contentious issue why didn't britain have fuel injection going into the second world war and it's really not that complicated we can have a look at this picture here which is a daimler benz if you have a look at the numbers along the bottom of the picture so number two is the high pressure fuel pump there's just a lot of little plungers that go up and down and squish a little amount of fuel through these steel pipes which are numbered 14 into the combustion chamber through the fuel injectors which are numbered 13 so that doesn't look that complicated does it so why didn't we have it so we should go over what a carburetor is as well to understand what we're trying to talk about so all the air going into the engine passes through a pipe and we need some way of getting the fuel to go into that and in a gravity carburetor which is what you have on an early spitfire you need to have what's called a float chamber so this is just a way of having fuel under gravity not under pressure with just a kind of set height for the top of where the fuel level is and there's a tiny little drilling which goes through into the middle of the pipe and to have the amount of fuel that we want to coming out of there we kind of need to make sure that this fuel level in the float chamber stays within quite a narrow range if it goes too high that'll cause a higher pressure on the jet and you'll get more too much fuel coming through which isn't good so we need to keep it at a pretty set level and this is done with a float valve which basically means the whole float chamber works like a toilet system that you have in your home and works exactly the same way which is if you get too much fuel in there the float rises and it stops the fuel coming in so in the same way that when your toilet system fills up it's stopped by filling up any further than it should by the float otherwise your house gets flooded and when the fuel is used up it opens and more fuel comes in and the jet is really just a very narrow drilling which is made of a certain size to get a certain amount of fuel flow and to get the fuel to actually come out because it's not pressurized to fuel here it's just sitting in there like a water in a bathtub so to get that to come out because the jet entry there is above the top of the fuel so it's not being forced through by the gravity you need to create a low pressure region and we do this with what clever people like to call a venturi it's just an or a choke um it's just a constriction in the air pipe and all this does is it means that if you know bernoulli's equation which i won't go through here if you increase the velocity of an airflow relative to velocity earlier on the pressure goes down and so that sucks the fuel out because the pressure above the fuel is atmospheric so that's basically how the fuel comes out in a carburetor so it's very very simple in principle however in an airplane there are some problems um four which is just a very brief list there are a lot more problems than this getting the carburetor to work in an aeroplane uh one is they get full of ice because it's really cold when you fly up a high altitude and when the fuel evaporates right in the middle of the choke it lowers the temperature um which is always classed as an advantage in engines because if you lower the temperature the density goes up and you make more power but it also means you get ice forming which is really serious problem uh so the second problem is um this is quite a sensitive piece of apparatus here with this kind of float that has to move up and down and keep the fuel at this level if you start doing aerobatics you can imagine what's going to happen to that so the whole fuel metering system goes haywire does not work very third problem is in warfare they decided after world war one that they were going to start to investigate safety fields the clues in the name it's basically a fuel that's halfway between diesel and petrol the idea is when bullets hit the fuel tank it doesn't all burst into flames this is a big advantage but it's really hard to get the stuff to burn a bit like diesel if you ever tried to light it so you need high pressure so you can't use safety fuels with a gravity carburetor the fourth problem is the fundamental mathematics of how this is all metered means that the density of the air coming through has an effect on the pressure and this changes as you climb but the density of the fuel does not so you've got these two interrelated things which do not vary in a linear fashion as you climb up to very high altitudes so to get this to work properly you need all sorts of widgets and little compensation valves and devices and stuff to make it really work so by the time you put one of these in an airplane it's a really complicated piece of kit which does not resemble a tube with a hole drilled through it anymore so you shouldn't imagine that fuel injection is this crazy complicated system and a carburetor is just nice and easy uh in an airplane it is not so that's what i see in a carburetor looks like it's really bad and if you can believe it in the usa about six percent of all civil aviation accidents which involved an engine failure are still caused by carburetor icing so it's a really serious problem and to this day not fully solved let's have a look at the timeline i'll just move my face so you can read it properly there we go so around the turn of last century industrial diesel engines use fuel injection because with diesel it's quite a non-volatile fuel so you have to or it doesn't work around about 1910 in an airplane uh the carburetor was a wick so that is literally a bucket of petrol with a rope dangled in one end and the other end dangled into the air inlet pipe to the engine so that's seriously basically what they were at that point so about 1924 the americans are the first people to really start to very seriously investigate fuel injection for aero engines and you can read more about that at the link in the bottom here so the germans followed not long afterwards in about 1927 they restarted the research after world war one and in 1928 as you can see in one of my other youtube videos the german air ministry decides to set down a specification document where all new aero engines would have to have fuel injection and by about 1935 this was achieved with the umo 210 g so in the uk we started researching to fuel injection very seriously in about 1932 at the ricardo company on the south coast and it all went a bit wrong and by about 1937 it was all cancelled in terms of the research done with government sponsored laboratories and 1940 the americans forged ahead with bendix and basically they had at that point perfected the pressure carburetor which solves a lot of the problems of a gravity carburetor that you have on a spitfire engine and to be honest it's not really a carburetor anymore it's kind of halfway between a fuel injection and normal carburetor so it's kind of a very primitive fuel injection system so why did britain fall behind i'll just move myself back over so here's some letters i'm going to show you i've highlighted stuff in yellow which is what i'd like you to kind of focus your eyes on through the video there's a lot more text so much that you can't read it in the duration of this video when you're listening to me so please come back and pause the video and read the letters in your own time so the first problem with icing the british thought they had that solved by adding in some alcohol to the fuel which it does although it doesn't always help the engine power so they thought they had that one kind of solved and they basically decided that they weren't going to bother with safety fuels and they were also going to stop experiments on multi-cylinder testing with fuel injection which is a really serious downer because a big part of the benefit of fuel injection is that the metering of fuel between all the cylinders in a multi-cylinder engine can be made much more even than you have with a carburetor so they didn't really discover the benefits because they stopped that test pretty serious failing 15 september 1933 we've got an re report here on the left that's royal aircraft establishment and they say there appears to be no grounds for dispensing with carburetor where normal fuels are concerned so normal fuels means not a safety fuel so they've basically pretty much given up bizarrely at ricardo we've got the blue graph here which is as we can see dated 14th of june 1932. and if you just concentrate on these two lines in the middle here these are basically engine power and the dotted line is with a carburetor and the solid line is with fuel injection so it's about 10 gain in power using fuel injection in this test and harry ricardo who owns the ricardo company the clue's in the name basically was britain's most respected engine development scientist so he knew fuel injection was a winner and yet our government labs at the time were giving the opposite conclusions pretty bizarre so george bulman this is his photograph here he was in charge of world war ii aero engine development at the ministry of aircraft production for most of world war ii and was pretty senior in the 1930s in the same role he had been speaking to the americans about fuel injection in 1934 and came back and basically said look the americans think this is really important why aren't we doing this and come back and read the letter pause pause the video later on but basically you can see that all the messages coming in to britain from their own test labs and from abroad were we need fuel injection but this was all ignored by a certain dr morley at the royal aircraft establishment who for reasons best known to himself doesn't like fuel injection and he submitted his final report into fuel injection which would have been his job for years before this and this is the actual page from the last page of his report further developments none contemplated so it's pretty amazing and i think this is actually nonsense really um so dr morley i think knew there was a benefit i just think he didn't want to countenance using a new technology i think he disliked carburetors and didn't like the idea of fuel injection and i think he pretty much doctored his reports to reflect that viewpoint and you can really see that he must have acted in this manner because you've also got reports from 1932 which totally disagree with the statement he made in his report saying that engines with large valve overlap which i'm going to explain about in a minute didn't have an advantage over the carburetor so if you just look at these middle two lines here so basically this axis here the y axis is basically the engine power so fuel injection with valve overlap we've got about 10 15 advantage in power um the only reason it stops here is because the fuel pump didn't have enough capacity to to keep the power going up and if you look at carburetor without valve overlap the fuel injection system is even better i mean you're talking 20 percent power improvement um so the americans thought it was an improvement and the british labs thought it was an improvement and dr morley basically said he didn't agree and this is nonsense so what's high valve overlap and why did that produce even more power in the last graph than the engine without the valve overlap so the valve overlap is how much duration both the inlet the blue and the exhaust the red valves here are open at the same time so when the crankshaft turns round it does two revs to do one cycle of the valves opening and closing and the white line here is how much the in the exhaust valve sorry is off the seat so this is the db601e and the red line is the inlet valve and the blue line here is the fuel injection plunger how much that's moving up and down so the valve overlap is from here to here this is an extraordinary amount of valve overlap it's huge it's five times more than you might normally be used to and this means if you look at the little picture down the bottom here both the valves are off their seats a little bit and this means that the air coming into the engine passes right through the combustion chamber and out the exhaust ports again and this cools the valves down which are very problematic at the time to keep the valves cool you can't run very high supercharge boost if the valves overheat because you get detonation the exhaust valves are the worst for this the other thing it does when you've got air passing right the way through it removes all the spent gases that you've got in this little combustion chamber volume at the top because when the piston comes up and down it obviously can't go right to the top because it bangs into the cylinder head so you've always got this little volume at the top which the piston doesn't quite manage to expel so having the valve overlap you get nice clean fresh air ready for the next cycle in here and it works really really well to improve the power you can't do with the carburetor for obvious reasons because if you have both the valves open at the same time too much all the fuel flies out the exhaust pipe and it goes on fire in the exhaust pipe you get terrible fuel economy and it overheats everything you can't do it so how do you do the direct injection well you just put the fuel in after the valves are closed so the yellow region here is when the fuel is actually going into the chamber so these little diagrams here this is the six jets that come out of the fuel injector and db601e engine so the fuel only comes out in this yellow region after the valves closed here so by choosing when the fuel goes in you can do this with a fuel injected engine you can't with a carbureted engine germany also thought the same thing so 16 july 1934 fuel injection results in an increase in performance of 10 to 17 percent with the same fuel consumption that's a bmw test 17th of april 7th of april 1937 after dr morley had submitted his incorrect report that there wasn't an advantage the royal aircraft establishment decided they would just send his report out to industry and that's the end of the matter they just sent his report out to industry so what do you think all the people at rolls royce and bristol and napier read dr molly's report and what did it say there's no advantage so that basically completely stopped serious british research into fuel injection before world war ii and it's all the fault of dr morley at the royal aircraft establishment who as far as i can tell just doesn't like fuel injection he's a stick in the mud and you could say well did he just get unlucky with the tests he did it's possible i'm not saying he consciously decided to spoil britain's war effort but i do think he was a stick in the mud and just there may have been a subconscious bias there and he just didn't want to countenance the idea that fuel injection was the way to go i think we've all been in situations where we've done something similar to that phase 2 1939 now it gets a bit sticky because britain starts to realize we have made a mistake so this is the first german aircraft to crash and british soil and world war ii it crashed in the llama muir hills uh near edinburgh so it's about two hours drive from me and this is a quote from rolls-royce test engineer jeffrey bone so he did an audio interview um i think after he retired in which case in which he recorded this and you can read it on your own but he's basically saying yeah we started testing these engines and we saw that basically the rolls-royce engineers weren't quite as clever as they thought they were after they started looking at this stuff so about the same time they started to also realize there's a problem with the su carburetor and a spitfire so june 1939 tests of merlin su carburetta and unbelievably at this point and finally riding down the carburetor is sensitive to tilting i don't know why it took them so long to figure this out it really doesn't take a genius to work out that that's going to be the case but this is the date the report was done so i can't say any more than that again unbelievably at the bottom here further developments none contemplated i can't explain that um i think it's just crazy i have no other explanation um i think they just didn't really have a solution to it and that's because a lot of these problems are just such a fundamental problem with what kind of carburetor the su was you pretty much can't do anything about it so i think that's why it says no proposed further developments i think they just didn't know what to do and so if you have a look at the graph on the right here that's a tilting test so that's the aircraft doing this and the y-axis is the ideal amount of fuel you want to come through so 100 is 100 so that's what you want and you can see as you tilt obviously the amount of fuel actually going through completely deviates from that so it just doesn't work very well the tests with the captured yumo engines from the llama mural heinkel continued and june 1940 the royal aircraft establishment starts to release their own official report these engines operate with mixture strengths considerably weaker than those demanded by carburetor engines and show exceptionally high fuel economy when it's remembered that the engine is controlled by the pilot with only a throttle lever i.e the pilot doesn't have rich and lean settings to do on the dashboard and all this kind of stuff the attainment of such consumption is remarkable these advantages are sufficiently important to justify a complete investigation so amazingly years after deciding there was nothing more to learn from fuel injection they've now got a hold of a german fuel injection system and the cat's out of the bag because they can't fudge it anymore it's now out of the hands of dr morley and everyone's realized we've got to do something about this and beatrice schilling was doing something about it everyone knows her from the miss shillings orifice story which is a little washer installed in the fuel supply to the float chamber it's just a kind of temporary fix it just means the engine doesn't completely stall it's not a final solution but actually her main work wasn't making this little restrictor she actually spent the first few years designing a completely new carburetor called the rae carburetor which is basically a pressure carburetor like the americans were designing that's what she spent most of her time on not designing this little widget and so this is her report it's in the references to the biography of her if you can get hold of it sadly out of print 24th june 1940 progress statement number four cutting out of merlin engines under high acceleration this is really when they're getting into okay in combat we've got a serious problem now the germans were just sticking their nose down to escape and the british planes you stick the nose down to follow them and the engine goes you can see that even in um air shows where you've got pretty good pilots flying if you look quite often at the spitfire when it's doing near the top of a loop you can hear it so that's that's what's happening and the reason i wanted to show you this is i'm not going to go through all of this now but just look at this this this is her list of problems as to what's causing the cutting out so everyone thinks she solved it by putting this little restrictor in that got us through the worst of it it stopped it stopping but this is certainly there's five severe fundamental problems with the merlin carburetor so i just wanted to show you that it's not one little problem it's a fundamental problem with the entire notion of a carburetor and basically if we have a look at later tests the fuel consumption from the german engines was again shown by the rae to be exceptionally good and the local fuel consumption is of considerable interest so what do you do when you decide you do need to have direct injection well it's not really that complicated in principle so what we've got is a little bellows here and that's connected to the boost pipe of the engine and that's just a little bellow so when the pressure is low it expands and when the pressure is high it contracts and that just moves this little shaft back and forwards along the passage shown by the red arrow that is just connected to a little lever with a pin through it and that twists the fuel injection plunger that moves up and down once for each fuel injection cycle there's a little cam underneath it that just does that and you see there's a little spiral groove on the side of this plunger so how to get different amount of fuel for the same amount of plunge you twist it and that little spiral groove has got a little drilling in the side that lets feel out let's escape out and by altering the twist it alters the point in time where that little groove meets the exhaust port for the fuel so that's how you get a different amount of fuel through so you meter the fuel to get the right amount in the engine there's a few more widgets you need to do it perfectly but fundamentally that's all it is and a lot of people say oh i've compared the fuel consumption for this allied engine i looked at this german one it doesn't look that much different there's no point doing that there's too many differences between the engines what you need to do is compare the fuel consumption between the same german engine with a carburetor and the same german engine with fuel injection that's the only reliable comparator so the early daimler-benz engine here with a carburetor right in the middle of the v pressure carburetors actually and that consumed 240 grams of fuel per ps hour so ps basically a horsepower and with fuel injection 205 and so if one imagines we're making a thousand horsepower in something like a messerschmitt or a spitfire that difference in fuel consumption gives you 15 minutes more flight at a thousand horsepower just by having direct fuel injection not even increasing the size of the fuel tank at all so that's a really significant advantage i don't know how many reports you've read from the battle of britain of pilots ditching on the beach because they didn't quite make it home well imagine you've got 15 minutes more flight at full power that's what you could have had with direct fuel injection and eventually the clock went full circle and beatriz shillings work on the ra pressure carburetor was used by the hobson company to make a direct injection system for the bristol centaurus and bristol report on this shows all these advantages for having it which professor dr morley at the rae had earlier denied the existence of and it's all now proven once they actually tried it and so that's the direct fuel-injected bristol centaurus which is post-war and so that's the slightly sad story of why britain didn't have fuel injection in world war ii and while we eventually realized we should have and went full circle and our best engines after world war ii um in many cases had direct fuel injection like this centaurus so this is britain's biggest mistake in engine development in world war ii so i hope i've explained a little bit more about how that happened and you can read a lot more about it in my book so just thanks very much to chris for inviting me on and i'll see you all later so i hope that you enjoyed that and i want to thank of course colin douglas for this excellent presentation he has given us and if you are interested in the subject first of all let us know what you thought about this video in the comment section below but then also check out the description because i'm of course going to be linking column douglas's book the great no the secret horse power race but it was also a great horsepower race i might add and uh yeah you will also find after helpful links in the description below as per usual also don't forget you can support my channel and this sort of content via patreon or channel membership so if that is something that you would like to do do check out those options as well and as always i wish all of you a great day and see you in the sky

Channel: Military Aviation History

Views: 308,378

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Id: DOSe4lmy8S4

Length: 27min 22sec (1642 seconds)

Published: Thu Nov 11 2021