greetings this is Craig it's time to discuss turbo charging in World War two airplanes and include comparisons to the advanced multistage supercharger configurations in use by the US Navy during the war turbo charging more correctly called turbo super charging was a large factor in the u.s. airpower doctrine before the war and a key factor in the design of many significant airplanes including the b-17 b-24 p-47 and p38 before we dive into the details we need to cover some history in the 1920s designers of military aircraft engine started to focus on super charging super charging by definition forces extra air into the engine allowing it to maintain peak rated power levels or close to them up to high altitudes as high as twenty thousand feet or even higher this broad definition includes exhaust driven turbo superchargers but for the purpose of this video and to match common modern terminology I'll often refer to exhaust driven turbo superchargers as turbos or turbochargers and mechanically driven units as superchargers it quickly became very obvious to aircraft and engine designers in every country building airplanes that supercharging in one form or another was the way forward in 1920 NACA released a report on super charging this 1920 report was largely a mathematical exercise which focused on figuring out the increases in an aircraft service ceiling that could be reasonably expected from super charging the report concluded that an increase in service ceiling from 25,000 feet up to 37,000 feet could be expected a gain of 50 percent which was huge this particular report is often cited in other reports hence my decision to reference it here by 1920 there was just no question that super charging was the way forward for aircraft engine power but there were many types of supercharger compressors and drive systems and at first it wasn't clear which type would be the best but early on the centrifugal compressor one out in aircraft applications and in u.s. built performance car of the 1920s and 30s the ideal drive system was still in question with some favoring mechanical Drive and some favoring and exhaust driven compressor aka a turbocharger let's take a look at an actor report from 1924 this particular report is NACA report 321 it's actually a translated German report as there was a lot of crossing over of information from Germany to the United States at the time this report shows several forms of supercharging in use during the early 1920s although it does not offer a specific comparison of them the first example is that of a routes supercharger while they don't work well in airplanes route superchargers can be highly effective in cars the routes unit uses mechanically driven intermeshing loads as seen near the bottom of this image to move air into the engine here's an image of a routes installed on a Mercedes racing engine once again it's mounted 90 degrees to the engines crankshaft and driven with bevel gears instead of being 90 degrees off in the horizontal plane as it would be in a BF 109 it's 90 degrees off in the vertical with very few exceptions centrifugal routes airplane or car the Germans love to drive superchargers at a 90 degree angle to the crank during this era I have never found a complete explanation for this the Ruud supercharger just doesn't work well in airplanes and no world war ii aircraft was equipped with this type of supercharger the next type is the Zoeller like the roots it has its advantages in automobiles but really never went anywhere in the aviation world like the roots these were mechanically driven but used internal vanes to move the air and is often called a vane type supercharger next we have an idea that keeps coming back over and over remember this report was published in Germany in December of 1923 it sort of reminds me of Lucien the football every 20 years or so someone tries to run a supercharger driven by an electric motor and every time after a lot of hype it fails to make an interpreter today this idea is back now they're calling it an electric turbocharger which is really a misnomer since a turbocharger by definition is driven by a turbine it's an electric supercharger a period maybe this time it will work automotive electrical systems are getting better and so are batteries I'm keeping an eye on it but I'm not holding my breath in any case it certainly never worked in an airplane so let's move on next we have a centrifugal compressor driven by an exhaust turbine this is a turbocharger a Frenchman named Auguste Rateau was the first to fit such a device into an airplane this particular setup is highly advanced with two exhaust valves per cylinder one exhaust valve is ported to the turbine the other bypasses the turbine the valve timing for the valves are independent in an effort to maximize turbo performance while minimizing exhaust back pressure into the cylinder this exhaust valve system was eventually abandoned in favour of a conventional system running all of the exhaust through the turbine another solution is to drive the centrifugal compressor mechanically in this particular report this isn't discussed probably because of its German origins allow me to explain in the early days of aviation racing cars were just as fast or sometimes faster than airplanes thus there was a lot of overlap in regards to engine technology in the United States the Indianapolis Motor Speedway which opened in 1909 was the pinnacle of motor racing and had an influence on engine designs at Indy cars could maintain very high speeds without much need to slow down thus they could operate their racing engines within a narrow range of rpm much like an airplane in these conditions a centrifugal supercharger could dominate for this reason and some others US automakers like Duesenberg cord and Auburn exclusively used this a typical type this particular picture was taken before the start of the 1924 Indy 500 race which was won by a Duesenberg meanwhile in Europe racing was quite different they ran long endurance races on real roads the involved a lot of variation in speed thus power was needed through a wide range of RPM at the time the best way to do that was with a root supercharger thus Mercedes Fiat Bentley Alfa Romeo and the other European manufacturers went with the roots type so far we have several types of superchargers in contention for use in military airplanes so naturally at some point NACA had to do a comparison of these to find the best way forward and they did just that this brings us up to NACA report number 384 which was released January 1st of 1932 this is probably the most important macro report with regards to world war ii airplanes at least u.s. airplanes I believe that this report more than any other shaped the course of aircraft development in the US and led directly to the development of the b-17 b-24 p38 p-47 and most of the naval fighters and indirectly the Merlin powered p-51 so let's dive into it this report starts off by giving you the conclusion so let's begin there now I'm not gonna read all of this word for word but I'll put up the section of the report that covers what I'm saying of course if you want to pause and read their exact words for yourself please do so by 20,000 feet the difference between the most efficient type of supercharging and the least efficient is only about 6% remember there including turbos in their definition of supercharging however above 20,000 feet the turbosupercharger equipped engine develops considerably more power than any other type that's quote considerably more power unquote they go on to mention that the roots type was the least efficient and resulted in the least power NACA already knew that as they had previously done extensive testing of this type but I think they just included it in this test for completeness with the benefit of 20/20 hindsight of course we know that this is shaping up to be a battle between the gear driven centrifugal supercharger and the turbocharger while the roots-type does have some serious advantages over the other types they just don't apply to aircraft and it's the same with aka the vain type for these reasons we'll be focusing on the gear centrifugal and turbo compared with the turbo the geared centrifugal z' method of control which was throttling was unsatisfactory from the standpoint of net engine power I discussed this at great length in my f4f Wildcat video the short version is that in order to prevent / boost at low altitudes the throttle has to be partially closed at full power superchargers hate being throttled all of this means that the turbo has a significant advantage above 20,000 feet and an advantage at lower altitudes when the geared type is throttled this graph shows a theoretical 100 horsepower engine with various types of superchargers and with a series of units sized specifically for each altitude in other words it's the best case scenario for each type and at each altitude we can see that a conventional unsupervised and as soon as it gains altitude at 12,000 feet it's down to about 62 horsepower at 20,000 only 44 horsepower and up to 40,000 feet it's down to only 17 horsepower now let's look at the chart of the 20,000 foot mark we can see that the geared centrifugal has about 97 horsepower and the turbo still has 100 horsepower now let's remember this is assuming in both cases that a compressor is used sized specifically for 20,000 feet above that altitude even under perfect conditions the geared centrifugal starts to fall behind eventually falling behind about 15% at 40,000 feet now you'll notice that the chart includes a line on the far right for what I'll call a magic supercharger this is a supercharger that generates enough boost to maintain 29.92 inches of mercury all the way up to 40,000 feet without drawing any power in other words it creates free boost which in the real world doesn't happen however it shows the power consumption of the various drive systems for example at 30,000 feet this magic supercharger actually adds power and we get about a hundred thirteen horsepower where did this extra 13 horsepower come from on our 100 horsepower engine well in this case it came from reduced exhaust back pressure because the chart assumes ambient pressure at the exhaust outlet which is much lower than the manifold pressure of 29.92 inches the higher the plane goes the greater this advantage as is seen on the line compared to the geared centrifugal we're comparing the gear terrifico with turbo I should say since both have similar Drive power requirements the power numbers are actually pretty close of course they both run the same compressor so the difference is in the two drive systems geared versus exhaust driven now contrary to popular belief the power to spin a turbo is not free but it is efficient to quote NACA regarding a turbocharger quote the net engine power is the total engine power supercharged less the reduction in power due to increased exhaust back pressure unquote back pressure costs power and the turbo causes it when using a geared centrifugal power is quote the total power developed less the power required to drive the supercharger unquote on the chart we can see that at 30,000 feet the drive power requirement the boost needed to maintain 29.92 inches that's 14.7 PSI or a thousand thirteen millibar roughly it's about gonna be about 10 psi of boost in this case and the drive power requirement will be about 13 horsepower for the turbo and about 20 horsepower for the gear centrifugal that difference of seven horsepower may not seem like much but we need to remember that this engine only has 100 horsepower so it's the percentages that matter here on a 1500 horsepower engine that's gonna be about a hundred and five horsepower so it's really starting to mean something more importantly the turbocharger doesn't cause throttling losses which the supercharger does at any point below its critical altitude this hugely favors the turbo let's look at these throttling losses next this chart shows the net engine power of a 100 horsepower supercharged engine with six different sizes of gear centrifugal superchargers each optimized for maximum power at a specific critical altitude below this altitude power suffers due to the throttling losses above it suffers due to the superchargers and ability to maintain manifold pressure supercharger a is the low altitude supercharger it makes its maximum power at 5,000 feet so not much throttling is required at sea level thus it's throttling losses are only about five horsepower at sea level however it suffers greatly at higher altitudes at 20,000 feet it can only provide enough manifold pressure 457 horsepower now let's look at the other extreme a supercharger F this supercharger is optimized for 30,000 feet at sea level it's in a world of pain at 29.92 inches of manifold pressure it's working against such strong throttling losses that it can only produce 68 horsepower that's a 32 percent loss in power as I've said before superchargers hate being throttled they have to do a lot of extra work to compress the air at the supercharger Inlet because the air pressure there is so far below ambient in other words it has to compress more to reach a given manifold pressure value now up at 30,000 feet the throttling losses are zero and the engine is putting out ninety five horsepower all the other examples are somewhere in the middle so you can see that a geared single speed single stage centrifugal is going to require some serious compromises we're going to come back to this chart in a moment and explain how it relates to u.s. naval fighters this next chart shows the routes geared centrifugal and turbo all set up with single stages and geared for a 20,000 foot critical altitude the routes seems to do well here but that's only because this chart deals with relatively low boost levels only what's needed to maintain sea level pressure again the routes isn't really relevant to this discussion at this point the geared centrifugal is at a huge disadvantage against the turbo below 20,000 feet here at sea level it's behind 80 horsepower to 100 now this lack of concern over throttling losses for the turbo meaning if you're using a turbo you're really not calf throttling losses that means that the designers could use the turbo and use one optimize for much higher altitude because they didn't have to worry about sacrificing the power down low which is what they eventually did but we'll get to that so far things look pretty bad for the gears centrifugal its power suffers greatly from throttling down low and it can't quite compete with the turbo up high so why did the US Navy seem to marry itself to the geared centrifugal for its planes well there are two main reasons the first is simply packaging and NACA pointed out that the geared centrifugal is compact and light and it lends itself very well to installation and aircraft with air-cooled radial engines since the US Navy was hell-bent on avoiding the use of liquid cooled engines anyway with the exception of airships the geared sand terrifical x' would be easy to package into their planes second the report points out that they would not be likely to be used unless either they were improved or set up in multiple stages and that's exactly what happened both of those things happen prior to World War two thus with multiple stages of geared superchargers and with big radial engines with plenty of room in the fuselage right behind them the geared centrifugal z' were made to work really well not as well as a turbo but pretty close now let's finish up Mack a380 for by reviewing the conclusions below 20,000 feet there's little difference between the turbocharger and a gear driven centrifugal but above 20,000 feet the turbo is superior about two years after that report in 1934 the US Army Air Corps proposed a bomber to replace the aging v10 shown here the specs called for it to be able to fly at 10,000 feet for 10 hours and have a top speed of 200 miles per hour but they also stated that they would prefer if it had a top speed of 250 miles per hour and a range of 2,000 miles keep in mind in 1934 there were still a lot of biplane fighters flying around many of them couldn't do much over 200 miles-per-hour one of our newest fighters the Boeing peashooter could get up to about 230 miles per hour so asking for a 250 mile per hour bomber with 2,000 mile range was asking quite a bit Boeing responded with a proposal for a large four-engine bomber although turbo superchargers were not in the original prototypes there was plenty of room in the big plane to fit them and the first production of the plane the b-17 B had them when these planes started showing up in 1939 the plane had a range of 3,000 miles and a maximum speed of 292 miles per hour at 25,000 feet this performance helped reinforce the bomber doctrine that was dominating the air core at the time even the latest fighter the Curtis Hawk could not catch a b-17 at high altitude of course at low altitude it could the hawk had a top speed of 313 miles an hour but that was down at 8,500 feet u.s. bomber doctrine at this point was focused and focused pretty heavily on high altitude precision bombing it was thought largely because of its turbochargers the b-17s would be almost impossible to intercept and if intercepted by enemy fighters they could be repelled by the firepower of the bomber formation of course that's not exactly how it went but if you look at this from the standpoint of someone in 1939 you can see the logic here it's very difficult to package turbos into a fighter it's easy into a bomber and here was the b-17 able to fly at 25,000 feet it was faster than any US fighter currently in service at that altitude and faster than most known potential enemy fighters with the benefit of hindsight we know that the BF 109 was among the very few fighters that were faster at 25,000 feet and that u.s. fighters would soon be catching up but in 1939 things were looking pretty good for the bomber General Electric the company that made the turbochargers for the b-17 stated in a 1943 training video in regards to turbocharged bombers quote almost without exception these planes have returned safely from their missions unquote that was true early in the war before we started on in Germany in the video they later point out in the cases when we did lose bombers they were usually operating below 25,000 feet which was also true at the time US air power doctrine focused heavily on the four-engine bomber with large numbers of b-17s being built the slightly more advanced b-24 was built in even greater numbers and was also equipped with turbo superchargers as a side note the b-24s pilots manual seems to assume the pilots are just prone to being idiots nearly every picture in it has some sort of caption admonishing bad techniques I don't see that very often in other publications of the time it's pretty unique to the b-24s manual I don't think it means anything it's just an interesting observation fitting turbos and all the related piping into a four-engine bomber was relatively easy fitting it into a fighter was another matter entirely the latest proposals coming from the Army Air Corps had some pretty high performance requirements and it was felt by at least some designers that the best option to achieve their goals would be to build a fighter equipped with the turbosupercharger remember the Curtiss p36 Hawk from earlier notice it has an air-cooled radial engine well we need to back up and take a detour fluid moment here did you ever notice that all of the liquid cooled V type engines used in world war ii were developed at about the same time the u.s. allison v 1710 was developed in 1929 first ran in 1930 the Germans began development of an inverted liquid cooled v12 in 1930 test ran and in 1931 this engine was to be the basis for the famous DB 601 which first ran in 1935 over in Britain the rolls-royce Merlin first ran in 1933 and the Spanish hispano-suiza 12y first ran in 1932 you may not have heard of this engine but it was used in French fighters more importantly was the basis for the Russian kill mah VK 105 which powered over a dozen types of Soviet warplane so it was very we used during the war all throughout aviation history until the advent of the jet there was this see-sawing ballad going back and forth between air-cooled radials and liquid-cooled v types and in the 1920s generally speaking the big radials were favored so what was it that caused this sudden development of all of these engines with the exceptions of the US Navy and the Japanese most countries suddenly focused development on planes that were going to have liquid cooled v types the tide shifted against the air-cooled radio it might surprise you to learn that this switch was not caused by some new engine technology or manufacturing techniques it was the advent in 1926 of ethylene glycol this new coolant allowed for smaller cooling systems thus less cooling system drag and that was enough to give the liquid cooled engines just enough performance advantage so that they had an edge on the radials although it would later switch back that's another story this takes us back to the Curtiss p36 Hawk it was designed before the allison v12 was really ready for primetime the hawk first flew in 1935 in 1937 curtis made one of the first attempts to build a turbocharged fighter and here it is this is the p37 it is essentially a p36 with an allison v12 and the entire turbo system located between the engine and the cockpit you can see how far back they had to move the cockpit the plane had too many technical issues to resolve so they removed the turbo kept the liquid cooled engine move the cockpit forward again and developed it into the p40 and so ended the Curtiss Wright corporation's attempts to build a turbocharged fighter let me ask you a question what u.s. built plane was primarily flown by the leading ally days of the war well it was this man alexander pokryshkin and the soviet pilots scored 47 of his 65 kills in the p39 Airacobra the p39 represents bell aircrafts attempts to bill the turbocharged fighter this time instead of moving the cockpit back they decided to move the engine back instead way back as in behind the cockpit the idea was that would leave more room behind the engine and allow for a streamlined nose with heavy nose mounted weaponry and a forward cockpit the problem was that it didn't leave a lot of the room and they were cooling problems that were never resolved this is actually quite a long story about all this but the short version is that they gave up and like the Curtiss p-40 they just made do with an allison v12 and it's built in single stage single speed low boost supercharger thus like the p40 the p39 was useless at medium and high altitudes about this time the aircraft for the US Navy were getting multi stage multi speed superchargers Allison was sort of put in an awkward position here they knew that the US Navy was not going to purchase a carrier base plane with a liquid-cooled engine yet the Army Air Corps clearly wanted a turbocharged fighter so initially they didn't bother developing a multi-stage or multi speed supercharger for use in Fighters they relied on others to build the turbochargers and the airplanes this hurt allison greatly when the p-51 came around and it's the main reason they had to use the merlin let's move on if there is one way to be sure to have enough room for your turbocharger it's to simply build a really big airplane that's exactly the method used by the Republic Aircraft Company for their P 43 Lancer this worked the airplane had acceptable but not great high altitude performance however it was really obsolete about the time it entered production so it was only produced for about one year the importance of this plane is primarily that it led to the p-47 thunderbolt which we'll get to following along the idea of making the plane really big well we can make it even bigger by using two engines Lockheed introduced the p38 with twin Allison's each packin a turbo and the boom behind the engine in principle this was a great idea in execution had some issues the p38 was incredibly complex more importantly and a lot of people don't know this this was Lockheed's very first attempt at building a combat airplane and they really domain head first on this they did a remarkable job and it was the first fighter to exceed 400 miles per hour and level flight however the early versions had a lot of issues mostly related to operations in sub-freezing temperatures that made the plane a bit impractical at high altitudes especially high altitude over Europe thus defeating the whole idea of using turbochargers in the first place the plane had tremendous success in the Pacific and eventually it's issues were resolved but by then the decision had already been made to replace them in Europe with p-51s thus the p38 was never really able to show what its turbos could do when up high the whole p38 story is so complex that it will need its own video so let's move on now before we get to the non-us airplanes that were turbocharged we need to talk about the p-47 Thunderbolt building on the lessons from the p43 lancer republic went with a big fuselage and put the turbo and intercooler in the back ran ducting all over the place and boosted manifold pressure like there was no tomorrow even early versions could boost enough to maintain full manifold pressure up to 27,000 feet when deliveries started in late 1942 the p-47 with its top speed of about 430 miles per hour was the fastest combat airplane in the skies at least at high altitudes further development resulted in combat versions with top speeds over 470 miles per hour and test versions that could exceed 500 miles per hour those of courses were never operational as with the p38 this plane needs about a 1 hour video to really explore the design now both Germany and Japan used turbochargers and experimented with them at least to some extent I don't know of a single German turbocharged combat aircraft from World War two however the Germans were familiar with turbo charging and they built many types of aircraft within those many subtypes and variations of the subtypes so there may have been a small number of turbocharged fighters or bombers at some point in the war but I haven't found any solid evidence of this just some vague references they did however absolutely build a turbocharged reconnaissance airplane it was a diesel powered version of the ju 86 none of these still exist a diesel powered version that is here's a picture of the uomo 207 which powered the airplane now the Japanese were at least somewhat interested in turbo charging they built an a6 m30 with the turbocharger for testing it never flew its engine configuration is shown here then they built an airplane which you could almost call a Japanese p-47 it was the ki 87 or ki 87 it had performance much like an early p-47 Thunderbolt probably had a lot of potential but they only built a single example because it first flew in April of 1945 just too late to get that into production for the war we need to look at what the US Navy was doing so we can have a comparison between their multistage superchargers and turbo charging of course there is never a perfect apples to apples comparison but I think I have two planes that are pretty close here both the f4u-1 Corsair and the p-47 be thunderbolt used the are 2800 engine and both developed 2,000 horsepower let's take a look at the supercharger configuration used in the f4u dash 1 Corsair the system uses dual superchargers with high and low speeds on the second stage it's almost exactly like the setup explained in my f4f Wildcat video just a lot bigger and badder so in effect even though not literally the Corsair has three superchargers note in this picture the far side intercooler is not shown it does have to again watch my Wildcat part one video if you want a more complete explanation of how this is laid out because it's essentially identical now let's go back to one of the previous NACA charts and graph the horse powers of the Corsair on this chart of course this chart for a 100 horsepower engine but that's okay we can use it in terms of percentage unfortunately the data out there for the Corsair - one is a bit incomplete the peak power numbers for each stage and related critical altitudes those are straight out of the World War 2 era flight manual so there is accurate as you can get however chance Voth didn't give much more data than that so I had to borrow the throttling curves for the losses there and the power drop-off with altitude from grummons data for the f6f hellcat that data was much more complete the this version of the Hellcat uses an engine that's almost identical to of course they're both are are 28 hundreds with 2,000 horsepower at the same manifold pressure settings the main difference being one has an updraft the other has a downdraft carburetor and there's some packaging differences for the inner core's my point here is that this may be off by 50 horsepower or so at certain points but the peak numbers are dead accurate so we'll use the Corsairs military power rating of 2,000 horsepower since it works really well on a percentage scale the Corsair - ones big are 2800 engine can put out as much as 2250 at war emergency power at military power the Corsairs main stage blower which is always engaged and shown here by the Green Line can maintain its full 2,000 horsepower to 2500 feet this stage is heavily biased for low-level activity notice in this case it will maintain that 2,000 horsepower all the way down to sea level because the designers allowed it to run with slightly more manifold pressure below 2500 feet at military power to offset the throttling losses above 2500 feet the Corsair will lose manifold pressure and power will start to drop off but at about 5,500 feet depending on the atmospheric conditions that day the pilot can in big engage the auxilary supercharger often called the ox blower into low speed this will enable the engine to regain manifold pressure and as the aircraft climbs the throttling losses will be reduced in this configuration the engine will have 1,800 power when this stage reaches its critical altitude of 18,500 from there the high speed on the Ox blower can be engaged and this will enable the plane to keep its manifold pressure up to about 23,000 feet at which point the engine will have sixteen hundred and fifty horsepower from there power will increase correction power will decrease pretty significantly as the aircraft climbs notice the area where the lines intersect that's sort of a gray area where it's a bit of a toss-up as to whether it's better to run the main blower and accept the decreasing manifold pressure or to engage the low speed on the Ox blower and take the throttling losses the official answer was to switch to the higher stage when full throttle manifold pressure decreased below a specific value note that the lines are not exactly parallel to those predicted by NACA there are several reasons for that but it's mainly because superchargers improved over that 10-year period in regards to throttling losses power above the critical altitudes doesn't quite keep up with the predicted numbers due to the installation in the actual airplane when you actually put something in a real airplane it's going to behave a little bit differently than it did on the test bench so the Navy solution was big radial engines and two stages of supercharging with two speeds on the auxilary stage blower and the Army Air course by and large was to go with the turbocharger let's take this opportunity to compare the coarse errors excellent supercharging system with that of the land-based p-47 be thunderbolt the p-47 be uses the are 2800 with a single speed single stage main blower just like the Corsair but instead of a second stage two-speed supercharger the thunderbolt uses turbo now before I post the Thunderbolts power I have to make something clear these are not war emergency power numbers for either airplane we're not trying to compare airplanes here just the differences as they relate to the turbocharger the Corsairs numbers are for military power the Thunderbolts are for emergency maximum these two ratings are the same thing they both have almost manifold pressure values 52 inches for the Thunderbolt 53 for the Corsair and both have the same 5-minute limitation the only different name because of different manufacturers and one is US Navy the other is US Army Air Corps or Army Air Force depending on what year we're talking about as you'll see while both have 2,000 horsepower ratings the two systems yield very different results so here it is the thunderbolt is shown via the grey line and it maintains its full 2,000 horsepower from sea level all the way up to 27 thousand feet where it will have a 600 horsepower advantage over the Corsair from there power drops off but it's still very strong I think this chart shows the power advantage of the turbosupercharger it's not just about the power at altitude although that is a big factor it's about the ability to vary the speed of the supercharger independently of the crankshaft in order to maintain power throughout a large altitude range of course it's not all sunshine and rainbows for the turbo this comes at a tremendous penalty and packaging requirements which is why the Thunderbolt fuselage is so fat and the Corsairs is so skinny plus the Corsair had some extra extra packaging trips to help keep it sleek which are described in my video on Corsair design features on the p-47 side its drag isn't as high as you might think in fact its overall drag is about equal to the Corsair you see at this time most designers were using NACA wings however a few years earlier when Republic aircraft was still severe ski aircraft Alexander severe ski himself decided he was going to design his own wing he came up with the svorski s3 airfoil which it turns out was really good and yet another test done later so the wing was competing against later designs but this wing had the lowest drag of all the conventional wing designs that were tested although not lower than the newest low drag types for NACA but those weren't available at the time they were designing seven at the power settings we've been using at 25,000 feet the Corsair has a speed of 390 miles per hour just over 400 miles per hour according to some reports versus 424 the Thunderbolt just for the record the performance numbers of early Corsairs the f4u - ones are all over the place reports vary by about 20 miles per hour at altitudes some of those are referencing a very cleaned up Corsair that had some special low drag modifications you have to kind of watch that but in any case we're talking about operational combat variants here at 30,000 feet the Corsair can only manage about 365 miles per hour it's still really good though but the 420 the Thunderbolt can go 426 miles per hour at 30,000 feet so it high altitude the Thunderbolt is faster a lot faster now at lower altitudes because horsepower is very close and drag is fairly close with a slight advantage going to the Corsair it's much closer at 52 inches of manifold pressure both airplanes run about 350 miles per hour at sea level with a slight edge going to the Corsair overall the two planes are pretty even in speed until about 20,000 feet now it's time to summarize all of this after NACA released report 384 in 1932 in January of 32 the designers of aircraft which would be used by the US Army the US Army Air Corps began focusing heavily on turbocharging because the idea of a fast high-flying four-engine bomber fit neatly into their doctrine and it was relatively easy to turbocharge big airplanes subsequent provoked proposals for fighters required them to have enough performance to be able to climb high enough and go fast enough to intercept potential turbocharged enemy bombers although none ever existed many companies tried to build a turbocharged fighter but it was very challenging and the only complete success was the Republic p-47 Thunderbolt although the p-38s early issues were eventually solved but it was too late to take advantages of its abilities at high altitude now the Navy took heed of nagging eighty-four and naval aircraft were designed with modern multi stage multi speed gear driven centrifugal x' for the advantage in simplicity and packaging it also kept costs much lower in comparing the Corsair in p-47 it appears that NACA called everything about right in 1932 the Corsairs up proved its performance up to twenty thousand feet is on par with the much more expensive p-47 and higher in some ways but at high altitudes in 1943 the p-47 Thunderbolt was king now turbochargers don't go much farther in terms of military aviation the advent of the jet put the brakes on a lot of piston engine development some of it was pretty exciting too but the b-29s had turbos and it could operate say they could operate at 30,000 feet and in 1945 were proving very difficult to intercept and shoot down after the war Republic built the turbocharged rainbow an airliner capable of a maximum speed of 470 miles per hour with a 400 mile per hour cruise speed at 40,000 feet and a 4,000 mile range that target was called for for for 400 miles an hour at 40,000 feet for 4,000 miles there was also a reconnaissance version for the military but the tremendous expense of this airplane killed it off it was almost four times the price of the TC six which could fly almost as far although at much lower speeds typically about 300 miles per hour and carry quite a bit more thus only two rainbows were built before the project was cancelled and in my view cancellation of the rainbow really marked the end of turbochargers in military aviation or for that matter high powered aviation piston engines period I plan to make a full video about the p-47 I might even do that next it's one of my favorite planes because of its technology and its ability to get you home I'll leave you at this picture and a poem by Lieutenant EC Buckley a thunderbolt pilot have a great day and I hope to see you here for my next video you
