Lockheed P-38 Lightning Design Info

greetings this is greg the lockheed p-38 lightning was one of the best and most versatile airplanes in world war ii i think most aircraft enthusiasts know that it was a successful fighter especially in the pacific and the mediterranean theaters i think fewer people know that the reconnaissance versions of the planes were very successful in their role a statement on the lockheed martin website says that the recon variants quote obtained 90 percent of the aerial film captured over europe unquote there were many other variants of the p-38 as well for example a night fighter version that had a two-man cockpit was radar-equipped and had some other changes to help keep it hidden in the darkness as with most fighters the p-38 could and did drop bombs it could carry a 4 000 pound bomb load and one source has its maximum bomb load at 5200 pounds there was also a specific bomber variant that had a glass nose a two-man crew and the norden bombsight system another version of that bomber variant used a ground scanning radar system to enable it to bomb through overcast layers even a torpedo bomber version was considered at least considered this picture shows the plane carrying dummy torpedoes for testing and the weight and balance data for the plane does include torpedo payloads but as far as i know it never actually operated as a torpedo bomber there was even an air ambulance configuration which could carry two patients in external transport pods i'll cover all of these variants and the degrees to which they were used and the successes and failures in follow-up videos but in short the p-38 could perform and perform well every type of mission that could be expected of a world war ii fighter now some might say well big deal in that era there were a lot of twin-engine airplanes that performed multiple roles that's true but the difference is that during that era most twin engine fighters proved incapable of fighting enemy single-engine fighters and thus were relegated to these alternative roles like night fighting and ground attack that was not the case with the p-38 lightning it was competitive with enemy single-engine fighters throughout the war and was employed in other roles due to the plane's versatility in regards to a twin-engine plane that really couldn't compete with single-engine fighters in air-to-air combat the most classic example i can come up with is the messerschmitt bf-110 i'm bringing up the 110 here specifically because it's one of the two planes that were constantly being compared to the p-38 in documentation from that period both planes have powerful liquid-cooled v12s they're both obviously twin engines they both have twin tails as you can see in this identification slide they actually look quite similar from the front the other plane that was often compared with the p-38 was the british mosquito i don't need to go into too much detail on this right now i did talk about it a little bit in my mosquito video but i'll be covering this comparison a lot more as this series continues if you haven't watched my mosquito video yet you may want to after this one let's get into the topic at hand the p38 lightning itself i want to cover the plane's main design features in other words this video is going to be a fairly basic overview at least by this channel standards the p-38 was lockheed's answer to a us army air corps proposal made in 1937 that called for a high altitude interceptor they used that word interceptor capable of reaching 360 miles per hour and capable of climbing to 20 000 feet from sea level in six minutes now this was a very tall order in 1937 lockheed wanted not only to design a plane to reach these relatively lofty goals they wanted to exceed them by building the first fighter plane to be capable of reaching 400 miles per hour in level flight at the time design work started there were no aircraft engines powerful enough to enable a single engine fighter plane not a race plane but a fighter plane to reach that speed thus lockheed had to use twin engines to comply with both the air corps proposal and their own goals the project was a huge undertaking for lockheed not only because of the extreme for the time requirements but more significantly much more significantly and i think a lot of people overlook this but because lockheed had never built a fighter plane before in fact they had never built any true combat airplane they had built planes for the civilian market some of which like the vegas shown here were purchased by the military but they were not combat airplanes the vegas were fast lockheed had some pretty good knowledge about how to make airplanes fast in fact the vegas were about equal in speed to contemporary fighters from the mid to late 1920s the vega also had tremendous range and altitude capability so lockheed had a good handle on performance in terms of speed and altitude they also understood multi-engine aircraft and they had built the excellent model 10 electra in 1935. it would do about 195 miles an hour so jumping from sub 200 mile per hour civilian airplanes to a 400 mile per hour fighter was a tall order and as you might expect there were some bumps in the road which we'll be talking about but first let's cover the basic design of the p38 the most striking feature has to be the twin boom layout so let's start there why build a twin boom fighter it certainly wasn't the norm it wasn't the only option though that they considered these are sketches from kelly johnson one of the 38's primary designers the sketches show that multiple configurations were considered before we get into them i want to say that there had been other twin boom airplanes before the lightning in world war one caproni built bombers with twin booms in the late 1930s folker had the g1 which was a decent airplane hughes had the d2 some say that the p-38 design was stolen from hughes i don't think that's likely i think it's more likely both design teams simply reached the same conclusions when looking at the data requirements and available engines of the time of course after the war we had a lot of twin boom airplanes both fighters like britain's excellent de havilland vampire seen here and cargo planes like this c-119 of course both of these use twin booms for very different reasons than the p-38 so let's get back to those sketches from kelly johnson to get an idea about why lockheed chose this design i'll go through these pretty quickly this one is what i'll call a conventional twin-engine airplane with engines mounted on the wings like this b-26 marauder this is the layout that has been used by the vast majority of twin-engine propeller driven airplanes from world war ii up until today normally if you're going to design a twin engine prop driven airplane this is going to be your go-to configuration now these two are interesting they have twin engines mounted in the fuselage with some sort of mechanism set up to drive propellers that are out on the wings one example has rear mounted pusher props now as far as i know no production airplane has ever flown with either of these configurations and even without the complexity of those prop drive mechanisms i don't think these designs would have worked out for reasons which will become apparent this one is a twin fuselage design which should not be confused with a twin boom design it's not the same thing the twin fuselage layout was famously used on the p82 i have to say i find this ideas a little bit disturbing i feel that if i flew such a craft every time i looked out to one side i would feel like i'm flying too close to another airplane personal feelings aside no question that this worked the p82 performed pretty well so that leaves us with this one the push pull design using twin booms there have been planes like this and they can perform pretty well but the downside is that once you put two engines in the fuselage and then whatever else you need armament seats or whatever there's not a lot of room left for example the cessna 337 has the push-pull layout and twin booms it's a wonderful airplane i have flown one it has plenty of performance great flying quality some real advantages over a conventional twin however it's very short on baggage space for a six-seated airplane in my view it's that lack of space in the fuselage that really kills off well these three contenders right at the start why because of the turbocharger turbocharging systems took up a lot of space in the 1930s and 40s and these three configurations just don't have any place to put all the needed components now why bother with turbochargers well because lockheed was going to need to use some form of secondary supercharging or second stage supercharging on the p-38 in order to get the desired performance and that really had to be a turbocharger for several reasons the chosen engines were allison v-1710s they have a gear-driven centrifugal supercharger built into them but it's just a single stage and not capable of delivering power at high altitude which the 38 was going to need the p-38 was going to need to have power throughout a wide range of altitudes second stage was going to be needed to do that and allison didn't have a second stage mechanical supercharger for their v12 at this time in fairness to allison neither did rolls-royce daimler or any of the other aircraft v12s in production in 1937. allison hadn't bothered with a second stage mechanical supercharger because the army air corps was going all in on turbochargers i have a whole video explaining the history and reasons for that the technical reasons but the short version is that naca had determined and published in this report that a turbo which was called a turbo supercharger at the time to mesh with modern parlance i will frequently just call it a turbo or turbo charger in any case the turbo supercharger had significant advantages over a mechanically driven supercharger the army air corps really latched on to the information in that report and wanted turbos for the second stage on high altitude airplanes as evidenced by the fact that nearly every high altitude u.s army air corps plane in development around this time and up until u.s entry into world war ii was turbocharger equipped including the b-17 flying fortress b-24 liberator the p-43 which was a predecessor to the p-47 the p-47 thunderbolt and the p-39 era cobra although the era cobra was not produced with its turbo and thus it turned into a low altitude airplane and of course the p-38 which has turbochargers this means lockheed had to use the turbos for three main reasons first they needed a second stage to get the performance they wanted throughout that altitude range also the army air corps wanted turbos and lastly there was literally no other choice for the allison v12 the need for turbos eliminates these three designs because you simply can't fit the turbo systems in there i'm not sure why the twin fuselage design was eliminated but i think it was due to weapon placement concerns i'm basing that on the fact that lockheed mentions the p38s weapon configuration a lot in period publications they were very proud of the centerline mounted weapons the twin fuselage design would not have allowed that much firepower to be placed right in front of the pilot so what about what i'm calling the conventional layout well it certainly proved itself in nearly every role in world war ii in typical fighter versus fighter combat it usually didn't work out that well but in just about everything else this design excelled so why not the conventional configuration well i think that answer is going to be self-evident as we go over the plane's design so let's take a look at this cutaway diagram to get a good idea of how everything's laid out in this airplane let's look at those twin booms at the front we have a curtis electric constant speed propeller right behind that we have an allison v1710 liquid cooled v12 and on the left boom and we're talking about production airplanes right now the prototypes are a little different but on the left boom the prop rotates counterclockwise as seen from the rear on the right boom it's clockwise which would be the normal rotation for an allison and most u.s fighters during the war i'll get into propeller rotation later there's actually a lot to talk about with that the booms are quite large people underestimate how large these things are each one is about the width of the fuselage on a typical v12 powered fighter look at just about any other late 1930s fighter and you'll see that the point of maximum width on the fuselage is usually where the exhaust stacks are the exhaust stacks on a v12 are the limiting factor in regards to minimizing width the p38s exhaust stacks are enclosed in the booms so each boom is about the width of a typical fighter that's powered by an allison v12 like the p40 pictured here under the engine we have two oil coolers which are fed from air scoops at the front now this is a later p38 because i don't have a cutaway diagram of an early version at least not a good one a key difference is the intercooler configuration a later p38 much like this airplane much like a p47 thunderbolt takes in air from below the engine in a scoop that's divided into three sections the two outboard sections direct air to oil coolers and the center section delivers air to the intercoolers now the early 38s are quite a bit different they have wing mounted intercoolers which is why they only have the two scoops the twin scoops under the engines and those of course are for the oil coolers now just aft of the engine we have the oil tank for the dry sump system it lubricates the engine and that's about even with the wings leading edge near the trailing edge of the wing the boom contains the turbocharger aka turbo supercharger aka turbo of course it still has a mechanically driven supercharger at the back of the engine but we can't see that in this diagram in between the oil tank and the turbo so in between the leading edge and the trailing edge of the wing and the boom there is a lot going on not only do we have the wing structure there but this area also houses the main gear retraction mechanism exhaust piping to the turbo charge air piping from the turbo coolant lines oil lines and more this is a very busy area aft of the turbo we have a space for the main landing gear wheel when retracted aft of that an oxygen bottle two cooling system radiators and another oxygen bottle just after that is the battery on the other side the other boom is pretty much the same there are some differences um i already mentioned engines and props rotate in opposite directions in a normal us production variant also the left boom has the battery the right boom doesn't have a battery in that same area of the boom it has a little cargo compartment you can't put put much in it but it's there oh and the right side wheel well holds a hand crank for starting there are other minor variations as well you might be starting to see the reason for the twin boom design in order to get all that stuff into the boom and minimize the cross section by not putting much stuff side by side the booms have to be really long so long in fact that minimal extension is needed to interconnect them with a tail in this magazine we have an article written in 1944 by hal hubbard the vice president and chief engineer at lockheed during this time kelly johnson was working for hal hubbard under hal hubbard i should say during the p38s development so i think this is a pretty good source i'll be using a lot of screenshots of this article but i'll post it in its entirety in the patreon section it's pretty interesting not just the article but the magazine it's shocking how many ads were in world war ii era aviation magazines just as a point of interest most of the pages are mostly ads we'll be focusing on the article by hal hubbard the first page of which is on the right side here each page in the article itself is free of ads or i suppose you could say that the entire article could be considered an ad for lockheed let's see what hal hubbard has to say about the 38's design i'm paraphrasing here but he points out that the two engines were needed to reach the performance goals there just wasn't a single engine powerful enough to do the job in 1937. the armament was packaged in front of the pilot in the fuselage this was where the designers thought it would be most effective every time i read something from lockheed about the 38 they almost always mention the weapons configuration in fact it's mentioned at least three times in this article alone regarding the twin booms and again i'm paraphrasing but he says that once everything needed was put into the booms turbos landing gear and so on that they were so long that extending them a bit more to carry the tail just made sense he also points out that there isn't really a specific advantage to a twin boom design so again it was all about packaging let's go back to our cutaway drawing and finish going over the airplane the main portion of the wing is not anything exotic it's a naca 2 3 let me say it again 2 3 0 1 6 profile which was used on various other airplanes the same profile was used on the douglas dc-4 aka c-54 it seems to me that lockheed was trying to go well beyond the requirements of the 1937 proposal from the army air corps not only by getting it up to 400 miles per hour which of course was much faster than the specified 360 mile per hour speed in the proposal but i think lockheed also wanted it to have enough maneuverability to combat enemy fighters hence the wing choice the p-38's wing gives it a relatively low stall speed for an aircraft with such a high wing loading and that's a key factor in determining turn performance to make the wing even more effective the designers gave it fouler flaps fowler flaps extend in a way that increases the wing area and adds a lot of lift relative to the amount of drag they cause especially at intermediate settings most fighters of the day like this p40 had split flaps which didn't add much lift but did cause a lot of drag and that was actually the point they added enough drag so you could point the nose down and descend to the runway without increasing air speed that's bullet point two here from the faa split or even plane flaps just don't add a lot of lift foulers on the other hand do add a lot of lift let's take a look at some comparison numbers of stall speeds flaps up and flaps down to see how effective the p-38s flaps were all the p-38 pilot manuals for all the variants show the same numbers at 15 000 pounds which is about where we would be for air-to-air combat the stall speed indicated flaps up power off 94 miles per hour with flaps down power off at 69 miles per hour those speeds are of course indicated air speeds meaning what's red right off the cockpit airspeed indicator of course those numbers are pretty meaningless for comparison to other airplanes until they are corrected to calibrated numbers the p38s manual doesn't have calibrated numbers that go low enough for us to figure this out plus there were two different pitot tube locations on these planes which further compounds the issue thankfully the army air force material center did some testing on a 38 at 14 800 pounds close enough and got us exactly the information we need they found that the calibrated stall speeds were 112 miles per hour with the gear and flaps up and 88 miles per hour with them down with the flaps down and gear up it's 86 miles per hour calibrated i really wish i had that data for all world war ii fighters but we just don't a lot of times i have to sort of take an educated guess anyhow power on stall speeds in the p-38 are dramatically lower as power than the power off stall speeds due to the accelerated slipstream over the wing and flaps as you can see even with only 25 inches of manifold pressure and that's not much the flaps down stall speed drops another 13 miles per hour that's huge and i'm going to talk about this factor later in greater detail when we get into maneuverability let's see how the stall speeds compare to the spitfire mark 5 with its split flaps the p47 which has slotted flaps and i'll also add in the de havilland mosquito and p-51 both of which have conventional plane flaps not many world war ii fighters have a lower stall speed than the spitfire mark v its numbers are 73 miles per hour and 64 miles per hour as can be seen here the manual does have numbers for calibration but they only go down to 100 miles an hour i'm gonna have to interpolate off the chart here and that's not ideal but it's the best i can do i figure we need to add about 6 miles an hour to those numbers so we get 79 and 70 miles per hour using the same methods for the p47 we get 115 and 100 for the mosquito we get 105 and let's call it 95. for this variant of the mosquito i cannot find any airspeed correction data so either it didn't need it because its airspeed indicator was dead on all the time which is incredibly unlikely or maybe i just can't find it so i'll have to take the mosquitoes indicated numbers and consider them as calibrated um also note that the mosquito's weight is a bit higher than it would be if it was going to be set up as a fighter airplane but that's okay i'm not trying to compare aircraft performance just yet when i do i'll even out the weights and hopefully i'll have some better calibrated stall speed data for the mosquito right now we just want to see the effects of the p-38s wing design and the fowler flaps so here are the numbers notice the p-38 has the highest wing loading here yet even with flaps up its stall speed is slightly lower than the p47s that's the benefit of the p38's naca wing of course that wing has its downsides too which we'll cover later take a look at the flaps down numbers the fowlers make a big difference much more so than the split flaps on the spitfire or the plane flaps on the p51 the thunderbolt slotted flaps are about in the middle better still the fowler flaps can be put halfway down into the maneuver position this gave a lot of extra lift with little drag that's kind of the point of fowler flaps most p-38s including all g models and later versions had this maneuver position on the flap handle all the pilot had to do was put the flap handle there and the flaps went to that position on earlier p38s the position was still selectable meaning you could still position the fouler flaps to be optimal for maneuvering but it required an extra step because there wasn't a designated maneuver position on the handle on these earlier planes the pilot had to put the flap handle to down observe the flat movement and then when they reached the point you wanted which was about halfway put the handle back into the closed position so what i'm saying here is that all p38s effectively have maneuver flaps it's just a question of whether um it's a specifically labeled point on the flap handle and how easy they are to select the takeaway should be the p-38s wing was not super special it wasn't a low drag wing or a really high speed wing um it was sort of a jack of all trades wing and with the maneuvering flaps out the p-38 could really turn it could actually out-turn a lot of single-engine fighters due to its low stall speed back to our cutaway drawing let's talk about aerodynamic drag for a moment i'm just going to talk about the total drag in this video i'm not going to break it down into various types not for now the p-38 has quite a lot of total drag not just because it's big but because the design work happened to start in 1937 and a lot was learned in the next few years lessons the 38 was just a little bit too early to benefit from for example take a look at those exposed turbos on top of the booms maca discovered just how much drag exposed turbos would cause and it was considerable they came up with a fairing to enclose turbos while still allowing for enough cooling exhaust flow etc now that fairing was used on the p-47 thunderbolt in short there was a lot of data from naca coming out about reducing drag and that benefited the p47 and the p51 but the p38 was just a little too early to take advantage of it on the subject of drag if we look at the plane closely you'll see all kinds of little air scoops on the booms zooming in we can see a scoop on the side of each engine nacelle this one cools the exhaust manifold and there are a total of four of these on the airplane exhaust manifolds on a turbocharged engine get hot and the p-38 cowlings don't have a lot of room in them so these cooling scoops were needed notice these little tiny scoops again there are four of them on the airplane these cool the spark plugs which get hot due to their proximity to the exhaust manifolds these scoops connect to little tubes called blast tubes they blast ram air onto things that they need to keep cool there are quite a few of them on the plane and they also cool the magnetos and tack generators on the tops of the booms forward of the turbos we have more scoops these are also connected to blast tubes and these cool components of the turbos then we have this big scoop under the trailing edge of the wing this provides ram air into the turbo in other words this is the scoop that provides air that's needed for the engine to run it's not for cooling interestingly the p-38 has two sources of inlet air for the turbochargers this ram air scoop is the normal source but in most versions of the plane the pilot can select filtered air to come from the wheel well this will cost a little bit of power but it will protect the engine by only letting in filtered air this is great if operating off of a dirt runway certain p38s have this selection slaved to the landing gear position in other words gear down you get filtered air and with the gear up you get ram air for more performance a lot of fighters of the period required additional components to get a decent amount of air filtration for operating in rough conditions these usually rob some of the airplane's performance but that's not the case with the p-38 it gets the best of both worlds in that regard and it's built right into the airplane so that was pretty forward thinking of lockheed aft on the booms we have the radiators for engine cooling and we have four of them back there and they're big all of these scoops the exposed turbo plus the wing design and the overall size of the p-38 as well as some other things we'll talk about later mean it has quite a bit of total drag at some point i'll get into the p-38s drag in more detail but for now just know that while it looks very sleek it really isn't at least not by us fighter plane standards as evidence of this consider that a p-38d which is an early model with 1150 horsepower per side that airplane at 5 000 feet we'll have a maximum true airspeed running flat out 322 miles per hour now that's not bad but comparing it to other 2 000 horsepower fighters it's not that great and that's because of all the drag for example the early p47b thunderbolt will go about 20 miles per hour faster a little more a little less depending on propeller type and that's with 300 less horsepower and we don't normally think of the thunderbolt as a plane with low drag although actually the thunderbolt is pretty slick for how large it is but the p38 is not a low drag airplane that's my point none of this means that lockheed wasn't trying to minimize drag they were external surfaces were flush they were butt jointed it was the first u.s fighter to be built this way it also utilized flush riveting in some sections it's just that the size the frontal area and all of those cooling scoops as well as some other things added a lot of drag now i want to talk briefly about the cockpit section in some period manuals they call this the gondola sometimes the fuselage i think i'll go with gondola and try to use that just for the sake of continuity the gondola houses from front to back the main armament cockpit radio equipment and at the very back hydraulic reservoir speaking of hydraulics like most u.s fighter planes the p-38 had a hydraulic system this is in addition to the hydraulics that operated the brakes that's a separate system and that was pretty standard on warplanes by this point but we're talking about the main hydraulic system and that operates the flaps landing gear radiator coolant shutters and more some airplanes it does cannon charging some airplanes it does aileron boosters there's a engine driven hydraulic pump powering this system on each engine thankfully if it only had a hydraulic pump on one engine then if you lost that engine right after takeoff it would be a disaster as you wouldn't be able to retract the gear thus you might not be able to continue your climb i'll get into that more when we discuss multi-engine flying as it relates to world war ii airplanes up front there's a lot of firepower four 50 caliber machine guns and normally a 20 millimeter cannon there were some other configurations but that's the standard setup now there's room for a lot of ammunition up there up to 500 rounds per gun for the 50 cals and 150 rounds for the cannon among major us front line fighters the p-38 was the only one to have a 20-millimeter cannon from very early in the war and that's because the early u.s 20-millimeter cannons were prone to jamming however the 38 configuration made it easy to clear the jams from the cockpit so they kept the cannon in there and went with the hydraulic charging mechanism speaking of jams the machine guns in the early planes would jam due to feeding problems at high g loads they fixed that by staggering the guns which is why in many p-38s you see the gun there the barrels are uneven in terms of the distance that they stick out of the nose that's because they're staggered for off so they can have straight belts going in to feed the guns the twin boom design also allows pretty easy installation of tricycle landing gear and that was uncommon on world war ii fighters this was a big plus on a high-powered twin-engine airplane we're getting near the end of the video here i do realize i've left a lot uncovered however keep in mind this is just part of a series i have a lot more i want to talk about in regards to this airplane the next p-38 episode is going to cover the controversies that surrounded the plane i'll get into the plane's technical problems some of which were quite serious and i'll explain how they were solved at least solved in most cases that should also dovetail into the reasons the plane was so successful as a fighter in the pacific but less so over fortress europe i want to thank all my subscribers especially my patreon supporters who got early access to this video i've added all p38 manuals that i have to the patreon section and i've put good resolution images of the hal hubbard article with pictures and so forth in that patreon section as well and for the higher tier patreons i'll just put the whole magazine in there for non-patreons i don't want you to be left out so i'll post the rest of the article on now so just the text format so you can pause the various pages and read it for yourself if desired that's all i have for this moment i hope everyone has a good day i look forward to reading your comments and keep an eye on this channel for the next episode thank you and goodbye you

Channel: Greg's Airplanes and Automobiles

Views: 230,380

Rating: 4.9470229 out of 5

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Id: UneGXm6edV4

Length: 41min 33sec (2493 seconds)

Published: Wed Jun 23 2021

Reddit Comments

[u/I_That_Wanders]

Unfortunately, it was a difficult beastie to fly. To convert it from cruise to combat mode required a few minutes of work. In the Pacific and Med, where there's vast amounts of nothing but open water and you can see the enemy from a few hundred miles off, this wasn't an issue. In continental Europe, with its mountains and hidden air fields, it was.

[u/beneaththeradar]

maybe? but keep in mind the Germans had already produced two contemporary twin engine, twin boom aircraft (FW 189, BV 138) by the time the P-38 entered production, and Sikorsky and Caproni had been experimenting with designs that incorporated both in the interwar period.

*BV138 was actually 3 engines, twin boom. now THAT is pretty weird.

[u/Madeline_Basset]

If it's Greg's Airplanes and Automobiles then it's certainly worth a watch