It would be great if you'd like to post some of those photos. They would have a very historical interest and value. If you feel that might be too off topic for this thread you could always start a new thread.
Not a problem to post. I have to find the drive they are stored on, got them digitizied earlier this year.
The Ground Crew chapter will likely be a little ways away...I am thinking sometime in the first half of 1944.
In the meantime, after taking a much needed break for the past few days, I have started to work on the next chapter which will have some details around the development of the P-38J and some information on the next block of improvements coming for the P-38H. If it fits with the narrative (i.e. I can segue it nicely) I may also include an update on how the production lines at Bell and Vultee are coming along.
In the meantime, after taking a much needed break for the past few days, I have started to work on the next chapter which will have some details around the development of the P-38J and some information on the next block of improvements coming for the P-38H. If it fits with the narrative (i.e. I can segue it nicely) I may also include an update on how the production lines at Bell and Vultee are coming along.
One can't help but think that the best way to improve these ATL P-38Hs is to make them into P-38Js. All in good time I suppose. And I'd would sure like to know how well things are coming along in New York and Tennessee.
The changes are going to end up being pretty extensive and some of them not easily accomplished (such as introduction of Water Injection with the new engines and propellers, etc.). There are other little tweaks and changes that I have not even mentioned yet but which will be included in the J when it finally hits production--again, some of them not easily upgraded in the field. There is one pretty important upgrade being introduced in the H-18, and two others in the H-20 (Dec '43/Jan '44), another in the H-25 (winter '44), and the final H will be the H-30 which will include most of the J upgrades that are possible in the H without major re-engineering. Late Spring/early Summer '44 should see the combat introduction of the J if all goes well.
I've just recently caught up to the last combat installment and the post-mortem. An observation and a question:
Heidinger did not know that neat trick of gunning one engine and nerfing the other and turning hard; you made a big deal of someone inventing it on the fly over the Med. I'd have thought every time someone did something new like that it would get written up and distributed to all active squadrons but apparently not, or not every time anyway; this was someone he knew and flew with on That Thursday demonstrating it but Heidinger still didn't know how it was done.
Having survived and gotten back, and being transferred back to the States to train a whole batch of new pilots, he asks how it is done and now he knows, verbally anyway. Being told and doing it are not the same thing. But soon enough he'll be home stateside with a bunch of rookies to train, and he'll have a chance to try it out for himself under semi-controlled conditions. (Will he? Is it such a desperately dangerous stunt, risking breaking something, ruining an engine or two, or just spinning out of control that either he will have the good sense not to mess with with it, or try it and die?) If he can do it himself a couple times, it becomes something he can have his trainees learn in their final flights. Even if he doesn't dare try it out, or does but decides he'd better not have any green pilots trying it just for fun, he can still at least tell them what he was told and explain when and why they'd want to try it if they had to in a final verbal lesson on the ground.
Assuming he doesn't kill himself trying it out, now a whole batch of new pilots are going to Europe or the Pacific having at least heard of it. Maybe he can write it up and have it put in the manual.
One way or another, a lot of Allied pilots are going to learn the trick. (Would it work on Mosquitos too? Or any two engine fighter such as Beaufighters or the Black Widow? Maybe even a Comet?)
This is one reason American and other Allied forces ended the war with high proficiency pilots while the Axis, worst with the Japanese but hitting the Germans too, ended with a lower level of pilot proficiency than they started. The Americans and with American help, Commonwealth, Free French and others (don't know about the Soviets doing this though) could afford to rotate their best pilots out of combat for a year or so and have them train larger numbers of new pilots with the latest tricks from the front. The Japanese especially had built up a corps with flying skills second to none, but a combination of desperation and a more warlike culture prevented them from risking losing any proficiency on the front for the sake of training, and so as their aces and competent wingmen were gunned down one by one, the corps just lost these skills, and the trainees were being trained by less and less knowledgable trainers, and would not have time in combat to learn what they should have been taught generally. Worse of course was that as the Axis powers spiraled down on the fronts and lost access to vital resources such as good avgas and reliable spare parts, the services could ill afford to give them a decent amount of flying time in training, having to reserve what little they had for actual combat. Even if the Germans had started with a plan for rotation and training, they could not afford to do it as the Eastern Front collapsed and their logistics began to crumble.
So it is a damn good thing Heidinger gets rotated stateside, not just for him but for the war being won with fewer Yankee losses and more scores against the Axis. The front line squadrons take a hit from removal of him, and soon enough the other aces, but they are alive to not only train hundreds more to take their place in time, but to later return to the fronts with superior airplanes in a superior tactical situation they will appreciate and take advantage of.
The question---
Heidinger goes through the wringer he does, makes the kills he manages to anyway, saves a B-17 crew entirely, and husbands his way with a damaged engine all the way back past Lille and over the Channel, only to find his damned landing gear don't want to drop!
He has a couple tricks still up his sleeve--he even has the experience of landing a -38 gear up but he doesn't want to risk it, I suppose because he'd wreck his third plane for sure and probably it is risky as hell. Fortunately he figures out how to shake them down but he's bleeding fuel and glide energy doing it.
I wonder, would it be hard to design retractable gear in general so that the machinery mainly works to bring them up, cranking them in against a fixed spring mechanism that once compressed, is guaranteed to snap them right down and lock them down upon release of a couple retainers, and make those fail-safe so there is always a way, even if it involves blowing a part of the gear mechanism off the plane, to make them go down and lock that way? Any mechanism can be damaged under fire, and I suppose if it worked the way I am thinking, sometimes one would come loose in midair and give a pilot cruising along at 450 mph a very nasty surprise, and of course the drag from it dooms a plane so stricken to come down immediately regardless of how well its engine works and its gas supply is adequate. Of course an undamaged plane ought to be able to retract the gear again. And if the retainer mechanism is designed right it should be very rugged and hard to bollix up, so such accidents would be rare--more rare than situations where the things will not come down due to combat damage I would hope.
Gear are not designed that way though, this I know. How well has the option of trying this, pump the things up but have them fail-safe pop down for sure, been explored? Has it been tried and rejected, or do gear go on being cranked down as well as up because that is the way they did it first and kept on doing by tradition alone?
The question is prompted in part by the fact that the Space Shuttle's gear always dropped under gravity, and there was no way to crank them back up again in flight. Apparently the drop never went partway so they were down but not locked down either. This suggests to me making them drop with a simple foolproof method ought to be feasible.
Heidinger did not know that neat trick of gunning one engine and nerfing the other and turning hard; you made a big deal of someone inventing it on the fly over the Med. I'd have thought every time someone did something new like that it would get written up and distributed to all active squadrons but apparently not, or not every time anyway; this was someone he knew and flew with on That Thursday demonstrating it but Heidinger still didn't know how it was done.
Having survived and gotten back, and being transferred back to the States to train a whole batch of new pilots, he asks how it is done and now he knows, verbally anyway. Being told and doing it are not the same thing. But soon enough he'll be home stateside with a bunch of rookies to train, and he'll have a chance to try it out for himself under semi-controlled conditions. (Will he? Is it such a desperately dangerous stunt, risking breaking something, ruining an engine or two, or just spinning out of control that either he will have the good sense not to mess with with it, or try it and die?) If he can do it himself a couple times, it becomes something he can have his trainees learn in their final flights. Even if he doesn't dare try it out, or does but decides he'd better not have any green pilots trying it just for fun, he can still at least tell them what he was told and explain when and why they'd want to try it if they had to in a final verbal lesson on the ground.
Assuming he doesn't kill himself trying it out, now a whole batch of new pilots are going to Europe or the Pacific having at least heard of it. Maybe he can write it up and have it put in the manual.
One way or another, a lot of Allied pilots are going to learn the trick. (Would it work on Mosquitos too? Or any two engine fighter such as Beaufighters or the Black Widow? Maybe even a Comet?)
This is one reason American and other Allied forces ended the war with high proficiency pilots while the Axis, worst with the Japanese but hitting the Germans too, ended with a lower level of pilot proficiency than they started. The Americans and with American help, Commonwealth, Free French and others (don't know about the Soviets doing this though) could afford to rotate their best pilots out of combat for a year or so and have them train larger numbers of new pilots with the latest tricks from the front. The Japanese especially had built up a corps with flying skills second to none, but a combination of desperation and a more warlike culture prevented them from risking losing any proficiency on the front for the sake of training, and so as their aces and competent wingmen were gunned down one by one, the corps just lost these skills, and the trainees were being trained by less and less knowledgable trainers, and would not have time in combat to learn what they should have been taught generally. Worse of course was that as the Axis powers spiraled down on the fronts and lost access to vital resources such as good avgas and reliable spare parts, the services could ill afford to give them a decent amount of flying time in training, having to reserve what little they had for actual combat. Even if the Germans had started with a plan for rotation and training, they could not afford to do it as the Eastern Front collapsed and their logistics began to crumble.
So it is a damn good thing Heidinger gets rotated stateside, not just for him but for the war being won with fewer Yankee losses and more scores against the Axis. The front line squadrons take a hit from removal of him, and soon enough the other aces, but they are alive to not only train hundreds more to take their place in time, but to later return to the fronts with superior airplanes in a superior tactical situation they will appreciate and take advantage of.
The question---
Heidinger goes through the wringer he does, makes the kills he manages to anyway, saves a B-17 crew entirely, and husbands his way with a damaged engine all the way back past Lille and over the Channel, only to find his damned landing gear don't want to drop!
He has a couple tricks still up his sleeve--he even has the experience of landing a -38 gear up but he doesn't want to risk it, I suppose because he'd wreck his third plane for sure and probably it is risky as hell. Fortunately he figures out how to shake them down but he's bleeding fuel and glide energy doing it.
I wonder, would it be hard to design retractable gear in general so that the machinery mainly works to bring them up, cranking them in against a fixed spring mechanism that once compressed, is guaranteed to snap them right down and lock them down upon release of a couple retainers, and make those fail-safe so there is always a way, even if it involves blowing a part of the gear mechanism off the plane, to make them go down and lock that way? Any mechanism can be damaged under fire, and I suppose if it worked the way I am thinking, sometimes one would come loose in midair and give a pilot cruising along at 450 mph a very nasty surprise, and of course the drag from it dooms a plane so stricken to come down immediately regardless of how well its engine works and its gas supply is adequate. Of course an undamaged plane ought to be able to retract the gear again. And if the retainer mechanism is designed right it should be very rugged and hard to bollix up, so such accidents would be rare--more rare than situations where the things will not come down due to combat damage I would hope.
Gear are not designed that way though, this I know. How well has the option of trying this, pump the things up but have them fail-safe pop down for sure, been explored? Has it been tried and rejected, or do gear go on being cranked down as well as up because that is the way they did it first and kept on doing by tradition alone?
The question is prompted in part by the fact that the Space Shuttle's gear always dropped under gravity, and there was no way to crank them back up again in flight. Apparently the drop never went partway so they were down but not locked down either. This suggests to me making them drop with a simple foolproof method ought to be feasible.
The USAAF worked a little different than the modern Air Force. During WWII Groups, and even Squadrons, had a fair amount of autonomy in practice. This is why different Groups would have different Standard Operating Procedures, use different tactics, and had more or less success than others. In fact, the P-38 is a fairly good example of OTL differing practice and illustrates fairly well how certain practices were not disseminated throughout the Fighter force--such as engine leaning techniques used by some groups in the PTO but never shared with the forces in Europe or the Med (in fact, it may have been limited to SWPA groups only...I am not even sure if the CBI ever adopted Lindbergh's lean settings).
In this case, it would be pretty normal for a difficult, desperate, and dangerous maneuver such as that used by Hilgert to be shared operationally for a time and only within a single Squadron or Group. The risk involved with the Lockheed Stomp (ATL "MacKay Turn") would probably cause the Army brass to have a fit and issue a restriction against its use in training or normal operations--much like removing the throttle stops. Sure, the throttles can be set up to produce more than WER of 60"Hg...but doing so will drastically increase the risk of destroying the engine.
For Heidinger, he may practice the maneuver a little. Most likely, he would start just by performing rolls and turns with a slight difference in throttle between the two engines and as he becomes more confident in the timing and handling will slowly increase this difference. I could see "Thrust Assisted Rolls" or "Throttle Assisted Turns" (i.e. a lesser, more controlled version of the maneuver) becoming part of an advanced P-38 curriculum but I do not see the full MacKay Turn being advocated by anything more than word-of-mouth. After a few accidents, I would imagine Group and Squadron commanders, followed by HQ from a Numbered Air Force (e.g. 8th AF HQ) issues prohibitions against the full maneuver. OTL late war standard P-38 training included some single engine time to familiarize the pilots with how the bird handles in such conditions and this would be an expansion on that.
In most cases, no. It worked as it did in the P-38 because it had a) counter-rotating propellers, and b) those propellers rotated opposite of what they did in other twin-engine A/C with counter-rotating props. In many twin-engine A/C the propellers spin the same direction which produces a tendency for the A/C to roll against the propellers due to torque. So, if the propellers rotate counter-clockwise when viewed from the front the A/C will want to clockwise--or vise versa. Killing one engine does not fundamentally change the torque effect beyond reducing it. In other 2-Engine A/C the propellers spin the opposite direction from each other to mitigate this torque, but they spin inward (toward the fuselage) at the top the arc. This means that if an engine quits the torque of the good engine counter-acts the weight and drag of the dead side, basically causing the A/C to rotate the dead side up thereby stabilizing the plane and making it easier to maintain level flight with a canned engine. The P-38, however, had propellers which rotated outward (away from the fuselage/central nacelle/gondola) at the top of the arc. This meant that if an engine failed, the torque from the good engine would cause the airplane to tend to rotate into the dead engine, exasperating the effects of weight and drag on that side. This unique (or nearly unique) feature of the P-38 is what made it so dangerous to loose an engine near the ground--the sudden torque and drag could cause the A/C to simply flip over into the dead side and if near the ground that was almost always catastrophic for obvious reasons. But, it is also what made the Lockheed Stomp possible. By leveraging that strong rolling and turning tendency into a dead engine the A/C could perform the high-G snap roll and reversal.
I hope that clarifies it?
Maybe. Honestly, though, the P-38 gear system was pretty good. It had the primary hydraulic system, a hand pump to act as a back up in case hydraulic pressure was lost, and the emergency gravity release. The only way I think it could be any better would be to allow a cross-suction from the primary hydraulic system and the gear/brake hydraulic system so that if fluid is lost from one the fluid from the other could be used. Now that I think about it, that may have actually already been in place...I will have to look over the hydraulic system diagram again.
The system you describe is almost what the P-38 used as its final fail safe. Pushing the hydraulic hand pump selector all the way down through the emergency wire released pins which connected the gear to the hydraulic actuators and allowed the gear to freely fall down with gravity to their fully down position where spring-pins would lock them in place. The yawing of the airplane wasn't actually to get the gear to drop but instead to bounce them around the gear doors so they hit the doors with enough force to unlock them and drop open.
Ch.24 - What Comes Next? (Nov 1943)
Another short technical update. The big changes are yet to come but they take a while.
I would like to give a big Thank You to @tomo pauk for his help with the engine chart and give a shout out to @phx1138 and everyone over at the A Better Allison V-1710 thread for providing some additional inspiration.
==========================================
24 November 1943
Wright Field
Dayton, Ohio, USA
Lt. Col. Ben Kelsey looked at the latest information on the new engine proposed by Allison for use in the next P-38. The XP-38J had been tested with a hodge-podge assembled from a combination of an Allison E21R and Allison -75/-77 (F15R/L) engines but the engine itself needed considerable refinement and re-engineering to unify the design into a single power plant and get it production ready. The new engine, funded by the US Army Air Forces as -117/-119 and now carrying the official internal Allison designation of F29R/F29L, looked quite promising and if it can actually deliver the projected performance could put the P-38J in an entirely new class of fighter.
The report Kelsey was reviewing had been forwarded his way from the Engineering Branch and was the initial results from Allison’s bench testing of the engine. In addition to the test results, the report including an outline of the general design aspects of the F29 engine and described the changes in the unit tested.
There were several major changes which set the new engine apart from those previously used on the Lightning. Internally, the most significant of these changes was a new crank with 12 counterweights rather than the six previously used. This new crank was only slightly heavier than the old crank but because of the better distribution of the rotational weight it reduced vibrations and allowed the engine to increase its best speed from 3000 RPM to 3200 RPM and the absolute red line from 3150 RPM to 3350 RPM for a slight gain in peak output.
The biggest change was in the introduction of Water/Methanol Injection to the engine, as tested in XP-38J several months earlier. With the new engine properly calibrated and built up for Water Injection the power output on the bench was considerably greater than estimated from the previous performance tests. While there was some concern about the added weight of the water to the already heavy P-38 Kelsey had been assured that Lockheed was working on a solution to ensure it did have too large an impact on maneuverability and climb.
The engine report included the results of several tests using slightly different configurations. During the first series of tests the engine had the same Bendix-Stromberg PD-12K7 Carburetor as the -89/-91 engines of the P-38H which was discovered to have insufficient air-flow to accommodate the higher RPM and Manifold Pressures attainable with the new engine. This was replaced with a PT-13E9 carburetor having three 4 3/16” barrels instead of the two 3 15/16” barrels of the PD-12K7. The larger carburetor showed a significant improvement in total output on the bench and, with Water Injection, allowed the engine to surpass 2300 Brake Horsepower in the second series of tests.
For the final series of tests the -117 continued to use the PT-13E9 carb but also featured revised cylinder heads and an altered intake manifold to improve the consistency of the fuel-air mixture and ensure even distribution to all cylinders. The details of the changes were less important to Kelsey than the results and those were particularly impressive, showing a tested peak output at 3200 RPM and 38”Hg. Manifold Pressure with Water Injection of 1111 Brake Horsepower while operating on Grade 100/130 fuel and a calculated maximum at 76”Hg. M.P. with W.I. of 2314 B.H.P.
Kelsey looked at the Engine Power Chart enclosed with the report and was impressed by the overall improvement in maximum performance it showed even while largely maintaining parity with the -89/-91 engines currently in use under normal operating conditions.
Before Lockheed would be able to fit and test the engine in an actual airplane, however, they will need a suitable propeller. His contacts at Lockheed had indicated that they were working with both Hamilton-Standard and Curtiss Electric on possible solutions to the thrust limitations on the airplane. Both had already submitted their hub and blade design proposals but no testable models had yet been delivered. The Curtiss blades best replicated the thrust lines of the extant P-38s while the H-S blades were estimated to have a slight edge over the Curtiss ones in overall performance but would require a larger shift in trim or Center of Gravity on the airplanes to accommodate the outward movement of thrust and heavier installation. The hubs were designed to the same specifications and size to fit to the new 2.36:1 gear box but where Curtiss Electric used an expanded and improved version of their electric pitch control Hamilton-Standard used their Hydromatic system dependent on engine oil hydraulics. Both systems had advantages over the other but neither would fundamentally change propeller performance.
One late entry was a proposal from the young Aeroproducts Propeller Company which had worked with Bell on their P-39 and again was working with them on the P-63 prior to its cancellation as well as developing a propeller for use with the newest P-51. Building off their previous experience they were proposing a four-blade high-activity propeller based around their novel Unimatic constant speed system. This system had a fully independent hydraulic system within the hub which gave it the benefits of both the Curtiss Electric system and the Hydromatic. The added weight of the hydraulic system and the fourth propeller blade were largely offset by Aeroproducts’s use of hollow steel propeller blades instead of solid aluminum as used by the other companies, making the entire rotational weight less than that of a similarly laid out H-S Hydromatic. It would also have the added advantage of using a smaller over-all propeller diameter—11’10”, only two inches greater in radius than the current P-38 propeller—which when paired with the same 2.36:1 reduction ratio would reduce propeller tip speed and improve its efficiency at the top of the engine range.
Before Kelsey, Lockheed, and the Air Force could decide which propeller would be best they will have to wait for functioning models to test with the engine and airplane. To help with that, Kelsey had authorized Lockheed to build several YP-38J pre-production aircraft, modified from the first few Fiscal Year 1943 block aircraft. Allison was already working with Lockheed to get the new engines installed and they were finalizing the Water/Methanol tank installation location. Once complete, these aircraft were to be fitted with the competing propellers and sent to the Air Force proving grounds in Elgin, Florida for direct comparison testing in early winter.
One possibility being bandied about was to select two propeller systems (either Hydromatic and Electric three-blade or Unimatic and Electric four-blade) and have all Lightnings produced in Burbank use one and those from Wheatfield use the other. This would distribute the production so that a catastrophe in either propeller manufacturer’s facility would not prevent continued production of the airplane while also keeping both work forces busy without over-burdening either one. The best modularity would be achieved with a mix of Unimatic and Electric as that would allow replacement of the entire propeller assembly in the field without modification to the airplane or engine oil system.
Kelsey wanted to a light a fire under the engineers but knew the work would take time and that he would have to be patient. To hold him over, Lockheed had sent one of the first P-38H-18-LOs—#42-103982, fresh off the line—to Wright Field for Performance Acceptance Testing. It was largely the same as the Block-15 airplane but with a new automatic shutter on the intercooler inlet. The shutter was driven by a small electric actuator anchored below the intercooler core which slides the shutter down and rearward to open it and pushes it up and forward to partially close it. Under normal operation it should be fully open but when the Carburetor Air Temperature drops below the normal operating limit of 15.6° C the motor engages to shutter to progressive close it and reduce the inlet size to limit the amount of air flowing into the intercooler.
Lockheed also reported that they sent an upgrade kit including the system to their pilot, Tony LeVier, who was still spending time with the P-38 Groups in England so that he can oversee its testing in operational conditions. If successful, Kelsey was already planning to place an order for a few hundred of the kits (which includes the entire nacelle “chin” sub-assembly) to send over to the 8th Air Force to retrofit their P-38H’s currently in service. The sub-assembly includes the outer panels with a redesigned intake shape, the new inlet door and electric actuator, the intake duct, intercooler core, exit duct, as well as the charge air Inlet manifold and cooled air Exit collector. The entire assembly can be replaced in only a few minutes by the ground crew but it also requires adding a new switch to the Carburetor Air Temperature gauge line to engage the shutter at low C.A.T. Since the inlet shutter only activates at low C.A.T. and the exit shutter at high C.A.T., Lockheed built the system to run off the same circuit as the exit shutters which obviated the need for crews to add a new circuit breaker in the cockpit and run the associated wiring through the wing.
In addition to the Block-18 Lightning, Wright Field had also recently accepted delivery of #43-10911, the nineteenth P-38 to come off the Bell production line. In total Bell had completed 36 Lightnings to date and they were on pace to get production up to 100 per month by February. They had not yet received any of the B-33 turbos from G.E. or the new chin sub-assemblies AiResearch so they were still building their aircraft to Block-10 specification, making their current aircraft designated P-38H-10-BE.
A similar situation was occurring down in Nashville where Vultee was working on completing their first few TP-38H-10-VNs. They were all being fitted out to Block-10 standards due to lack of B-33 turbo-superchargers but since they were intended for training and familiarization and not for combat there was little pressing need to get them upgraded or get the Vultee lines up to current Lockheed standards. In fact, a proposal had recently come across Kelsey’s desk to use the nacelles, booms, outer wings, and empennage assemblies from older F and G Model P-38s still stateside to mate with the Vultee center-section for a quick and easy way to get more two seaters. These could be re-engined as possible or as needed but for the most part they will be sufficient for training purposes. In any event they will be superior to the RP-322s and RP-38Es still being used.
The latest news from the 8th Air Force was that the P-38 was serving well as a long rang escort in the 78th and 55th Fighter Groups. The 20th Fighter Group was still awaiting their full allotment of aircraft and equipment but their pilots were getting experience by filling in with the other Groups where needed. The biggest requests were for larger Drop Tanks and simply more P-38s. Kelsey was working with the Chief of the Fighter Branch to plan out several more P-38 groups, at least one of which, the 479th, was slated to join the 8th AF no later than May 1944. The group was still being organized on paper and Kelsey expected it should be staffed by the end of the year with pilot and aircraft assignments to follow.
There were still a few recurrent issues being reported by the active groups, however. The chief concern was engine reliability almost entirely related to cold temperatures. Kelsey hoped that the new intercooler inlet duct would help alleviate some of the problems but there were other problems that would still need to be addressed such as reports of battery failures and freezing Turbo Regulators. In total the incidence of engine failures was roughly the same as that experienced by the P-47s but since the P-38 had two engines there were twice as many to fail causing a marked decrease in the total sortie rate for the P-38 Groups verses the P-47 groups.
Another concern being expressed was related to the ever increasing altitudes at which the Lightnings were operating. Apart from the engine problems it was causing it was also impacting the pilots themselves. The Group reports have been showing a slight but steady increase in the number pilots temporarily grounded after suffering varying levels of anoxia and even a few cases of the Bends.
Recent evaluation of a captured German Messerschmitt Bf.109G-5, a type now being used by several groups in Western Europe, revealed that they installed a rudimentary pressurization system in the airplane to help their pilots deal with the altitude and both the RAF and USAAF were now looking into similar modifications in several of their existing aircraft to provide some help as well. Kelsey was pressing even harder than others because he knew that the well pressurized B-29 would soon be entering combat and it would need a Very Long Range Escort that could operate with it for long duration at high altitude.
Both Republic and North American were busy developing updated versions of their flagship fighters, the P-47 and P-51 respectively, for this purpose. The increasing success of the P-38 as a high-altitude escort over the past few months, however, had made Kelsey start to re-think Republic’s involvement. He felt the Lightning was proving to be a superior escort than the Thuderbolt and would require fewer modifications to achieve the long-range requirements of the B-29. All it needed was a reduction in its fuel requirements—something that was promised with the P-38J—and the possibility of partial cabin pressurization.
Maybe it was time for a visit to Lockheed.
I would like to give a big Thank You to @tomo pauk for his help with the engine chart and give a shout out to @phx1138 and everyone over at the A Better Allison V-1710 thread for providing some additional inspiration.
==========================================
24 November 1943
Wright Field
Dayton, Ohio, USA
Lt. Col. Ben Kelsey looked at the latest information on the new engine proposed by Allison for use in the next P-38. The XP-38J had been tested with a hodge-podge assembled from a combination of an Allison E21R and Allison -75/-77 (F15R/L) engines but the engine itself needed considerable refinement and re-engineering to unify the design into a single power plant and get it production ready. The new engine, funded by the US Army Air Forces as -117/-119 and now carrying the official internal Allison designation of F29R/F29L, looked quite promising and if it can actually deliver the projected performance could put the P-38J in an entirely new class of fighter.
The report Kelsey was reviewing had been forwarded his way from the Engineering Branch and was the initial results from Allison’s bench testing of the engine. In addition to the test results, the report including an outline of the general design aspects of the F29 engine and described the changes in the unit tested.
There were several major changes which set the new engine apart from those previously used on the Lightning. Internally, the most significant of these changes was a new crank with 12 counterweights rather than the six previously used. This new crank was only slightly heavier than the old crank but because of the better distribution of the rotational weight it reduced vibrations and allowed the engine to increase its best speed from 3000 RPM to 3200 RPM and the absolute red line from 3150 RPM to 3350 RPM for a slight gain in peak output.
The biggest change was in the introduction of Water/Methanol Injection to the engine, as tested in XP-38J several months earlier. With the new engine properly calibrated and built up for Water Injection the power output on the bench was considerably greater than estimated from the previous performance tests. While there was some concern about the added weight of the water to the already heavy P-38 Kelsey had been assured that Lockheed was working on a solution to ensure it did have too large an impact on maneuverability and climb.
The engine report included the results of several tests using slightly different configurations. During the first series of tests the engine had the same Bendix-Stromberg PD-12K7 Carburetor as the -89/-91 engines of the P-38H which was discovered to have insufficient air-flow to accommodate the higher RPM and Manifold Pressures attainable with the new engine. This was replaced with a PT-13E9 carburetor having three 4 3/16” barrels instead of the two 3 15/16” barrels of the PD-12K7. The larger carburetor showed a significant improvement in total output on the bench and, with Water Injection, allowed the engine to surpass 2300 Brake Horsepower in the second series of tests.
For the final series of tests the -117 continued to use the PT-13E9 carb but also featured revised cylinder heads and an altered intake manifold to improve the consistency of the fuel-air mixture and ensure even distribution to all cylinders. The details of the changes were less important to Kelsey than the results and those were particularly impressive, showing a tested peak output at 3200 RPM and 38”Hg. Manifold Pressure with Water Injection of 1111 Brake Horsepower while operating on Grade 100/130 fuel and a calculated maximum at 76”Hg. M.P. with W.I. of 2314 B.H.P.
Kelsey looked at the Engine Power Chart enclosed with the report and was impressed by the overall improvement in maximum performance it showed even while largely maintaining parity with the -89/-91 engines currently in use under normal operating conditions.
Before Lockheed would be able to fit and test the engine in an actual airplane, however, they will need a suitable propeller. His contacts at Lockheed had indicated that they were working with both Hamilton-Standard and Curtiss Electric on possible solutions to the thrust limitations on the airplane. Both had already submitted their hub and blade design proposals but no testable models had yet been delivered. The Curtiss blades best replicated the thrust lines of the extant P-38s while the H-S blades were estimated to have a slight edge over the Curtiss ones in overall performance but would require a larger shift in trim or Center of Gravity on the airplanes to accommodate the outward movement of thrust and heavier installation. The hubs were designed to the same specifications and size to fit to the new 2.36:1 gear box but where Curtiss Electric used an expanded and improved version of their electric pitch control Hamilton-Standard used their Hydromatic system dependent on engine oil hydraulics. Both systems had advantages over the other but neither would fundamentally change propeller performance.
One late entry was a proposal from the young Aeroproducts Propeller Company which had worked with Bell on their P-39 and again was working with them on the P-63 prior to its cancellation as well as developing a propeller for use with the newest P-51. Building off their previous experience they were proposing a four-blade high-activity propeller based around their novel Unimatic constant speed system. This system had a fully independent hydraulic system within the hub which gave it the benefits of both the Curtiss Electric system and the Hydromatic. The added weight of the hydraulic system and the fourth propeller blade were largely offset by Aeroproducts’s use of hollow steel propeller blades instead of solid aluminum as used by the other companies, making the entire rotational weight less than that of a similarly laid out H-S Hydromatic. It would also have the added advantage of using a smaller over-all propeller diameter—11’10”, only two inches greater in radius than the current P-38 propeller—which when paired with the same 2.36:1 reduction ratio would reduce propeller tip speed and improve its efficiency at the top of the engine range.
Before Kelsey, Lockheed, and the Air Force could decide which propeller would be best they will have to wait for functioning models to test with the engine and airplane. To help with that, Kelsey had authorized Lockheed to build several YP-38J pre-production aircraft, modified from the first few Fiscal Year 1943 block aircraft. Allison was already working with Lockheed to get the new engines installed and they were finalizing the Water/Methanol tank installation location. Once complete, these aircraft were to be fitted with the competing propellers and sent to the Air Force proving grounds in Elgin, Florida for direct comparison testing in early winter.
One possibility being bandied about was to select two propeller systems (either Hydromatic and Electric three-blade or Unimatic and Electric four-blade) and have all Lightnings produced in Burbank use one and those from Wheatfield use the other. This would distribute the production so that a catastrophe in either propeller manufacturer’s facility would not prevent continued production of the airplane while also keeping both work forces busy without over-burdening either one. The best modularity would be achieved with a mix of Unimatic and Electric as that would allow replacement of the entire propeller assembly in the field without modification to the airplane or engine oil system.
Kelsey wanted to a light a fire under the engineers but knew the work would take time and that he would have to be patient. To hold him over, Lockheed had sent one of the first P-38H-18-LOs—#42-103982, fresh off the line—to Wright Field for Performance Acceptance Testing. It was largely the same as the Block-15 airplane but with a new automatic shutter on the intercooler inlet. The shutter was driven by a small electric actuator anchored below the intercooler core which slides the shutter down and rearward to open it and pushes it up and forward to partially close it. Under normal operation it should be fully open but when the Carburetor Air Temperature drops below the normal operating limit of 15.6° C the motor engages to shutter to progressive close it and reduce the inlet size to limit the amount of air flowing into the intercooler.
Lockheed also reported that they sent an upgrade kit including the system to their pilot, Tony LeVier, who was still spending time with the P-38 Groups in England so that he can oversee its testing in operational conditions. If successful, Kelsey was already planning to place an order for a few hundred of the kits (which includes the entire nacelle “chin” sub-assembly) to send over to the 8th Air Force to retrofit their P-38H’s currently in service. The sub-assembly includes the outer panels with a redesigned intake shape, the new inlet door and electric actuator, the intake duct, intercooler core, exit duct, as well as the charge air Inlet manifold and cooled air Exit collector. The entire assembly can be replaced in only a few minutes by the ground crew but it also requires adding a new switch to the Carburetor Air Temperature gauge line to engage the shutter at low C.A.T. Since the inlet shutter only activates at low C.A.T. and the exit shutter at high C.A.T., Lockheed built the system to run off the same circuit as the exit shutters which obviated the need for crews to add a new circuit breaker in the cockpit and run the associated wiring through the wing.
In addition to the Block-18 Lightning, Wright Field had also recently accepted delivery of #43-10911, the nineteenth P-38 to come off the Bell production line. In total Bell had completed 36 Lightnings to date and they were on pace to get production up to 100 per month by February. They had not yet received any of the B-33 turbos from G.E. or the new chin sub-assemblies AiResearch so they were still building their aircraft to Block-10 specification, making their current aircraft designated P-38H-10-BE.
A similar situation was occurring down in Nashville where Vultee was working on completing their first few TP-38H-10-VNs. They were all being fitted out to Block-10 standards due to lack of B-33 turbo-superchargers but since they were intended for training and familiarization and not for combat there was little pressing need to get them upgraded or get the Vultee lines up to current Lockheed standards. In fact, a proposal had recently come across Kelsey’s desk to use the nacelles, booms, outer wings, and empennage assemblies from older F and G Model P-38s still stateside to mate with the Vultee center-section for a quick and easy way to get more two seaters. These could be re-engined as possible or as needed but for the most part they will be sufficient for training purposes. In any event they will be superior to the RP-322s and RP-38Es still being used.
The latest news from the 8th Air Force was that the P-38 was serving well as a long rang escort in the 78th and 55th Fighter Groups. The 20th Fighter Group was still awaiting their full allotment of aircraft and equipment but their pilots were getting experience by filling in with the other Groups where needed. The biggest requests were for larger Drop Tanks and simply more P-38s. Kelsey was working with the Chief of the Fighter Branch to plan out several more P-38 groups, at least one of which, the 479th, was slated to join the 8th AF no later than May 1944. The group was still being organized on paper and Kelsey expected it should be staffed by the end of the year with pilot and aircraft assignments to follow.
There were still a few recurrent issues being reported by the active groups, however. The chief concern was engine reliability almost entirely related to cold temperatures. Kelsey hoped that the new intercooler inlet duct would help alleviate some of the problems but there were other problems that would still need to be addressed such as reports of battery failures and freezing Turbo Regulators. In total the incidence of engine failures was roughly the same as that experienced by the P-47s but since the P-38 had two engines there were twice as many to fail causing a marked decrease in the total sortie rate for the P-38 Groups verses the P-47 groups.
Another concern being expressed was related to the ever increasing altitudes at which the Lightnings were operating. Apart from the engine problems it was causing it was also impacting the pilots themselves. The Group reports have been showing a slight but steady increase in the number pilots temporarily grounded after suffering varying levels of anoxia and even a few cases of the Bends.
Recent evaluation of a captured German Messerschmitt Bf.109G-5, a type now being used by several groups in Western Europe, revealed that they installed a rudimentary pressurization system in the airplane to help their pilots deal with the altitude and both the RAF and USAAF were now looking into similar modifications in several of their existing aircraft to provide some help as well. Kelsey was pressing even harder than others because he knew that the well pressurized B-29 would soon be entering combat and it would need a Very Long Range Escort that could operate with it for long duration at high altitude.
Both Republic and North American were busy developing updated versions of their flagship fighters, the P-47 and P-51 respectively, for this purpose. The increasing success of the P-38 as a high-altitude escort over the past few months, however, had made Kelsey start to re-think Republic’s involvement. He felt the Lightning was proving to be a superior escort than the Thuderbolt and would require fewer modifications to achieve the long-range requirements of the B-29. All it needed was a reduction in its fuel requirements—something that was promised with the P-38J—and the possibility of partial cabin pressurization.
Maybe it was time for a visit to Lockheed.
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I'm not aware that the Bf-109 G6 trop captured by the Americans displayed even rudimentary pressurization, nor did the RAF G-6 captured at Manston. They both featured the tell-tale fresh air inlet. The G-5, built in far less quantity, did feature pressurization, but also evaded capture and testing at this time.
You are correct. I got my 109 models mixed up. I changed the text to read G-5. As for one not being captured OTL...well, with all the improved P-38's running amok maybe they forced a G-5 down over England. Butterflies and all
OK, hive-mind...
Any ideas on where to trim some fat off the P-38? With all of the equipment that has been added and those still in the pipeline we are getting pretty heavy. The WI system alone will add around 600 lbs when all is said and done. I am already looking at a light weight canopy (one-piece) but what else can be removed? Maybe the armor around the turbos since they are now more reliable? Smaller landing gear?
What else do you have?
Any ideas on where to trim some fat off the P-38? With all of the equipment that has been added and those still in the pipeline we are getting pretty heavy. The WI system alone will add around 600 lbs when all is said and done. I am already looking at a light weight canopy (one-piece) but what else can be removed? Maybe the armor around the turbos since they are now more reliable? Smaller landing gear?
What else do you have?
In general, did any major front line fighter model, or bomber or attack plane for that matter, trim off any "fat" over the course of the war, unless it was a clear win-win thing as with the improved canopies?
I would guess the trend was always, more more more, and performance maintained and improved by more and more powerful engines. This might also mean more gas being guzzled except insofar as more engine power came from efficiency improvements alone--which there is some room for, but I would guess that a comprehensive study showed that pilots accepted heavier and moderately curtailed range and loiter if it meant they could have all the mod cons and MOAR DAKKA!
Maybe they'd accept some trimming of armor weight in general as a challenge to fly better and harder. Pilots think It Won't Happen To ME, I have The Right Stuff--especially if I'm not weighed down with all this sissy armor. I imagine American pilots did appreciate they were highly valued enough to merit protection and preferred their plane to be tough too, but this is in comparison to Axis, especially Japanese, planes--they'd admit that despite being hotshot enough to dodge the bullets still they weren't crazy. But if something has to go, I bet pilots say "armor!"
But what they really want is all the armor and more, all the guns and more, all the speed and climb and acceleration and more, and oh yes I need a good heater and these automatic shutter controls are the bees knees and I want a radar, damn it! Give me more horsepower!
Americans have access to naturally high octane petroleum from Long Beach California and the logistics tail to distribute it, and will cheerfully burn all that av gas. They can afford bigger, stronger engines and that's what they want.
So any cases anyone knows of the Army Air Force or the Navy BuAer going "whoa!" on the weight and making hard calls like this, and the result being accepted in the field without the pilots getting their mechanics to add on all the saved weight and more in field mods would be very very instructive. More engine power is coming--but in this moment of weight bottleneck, what OTL precedent is there for these hard calls being made and working well?
I'm afraid that realistic gains will be small. Akin to the Mustang - in order to subtract several hundreds of pounds from P-51B/C/D/K, a whole new aircraft 'family' was developed, the 'Lightweight Mustangs' - F, G and H.
That you're reading & enjoying it:
That you can use it to make this thread better makes my day. (x25 or so... ) (Trying not to gloat. ) Thx for the ID on the 3bbl. (One hopes the P-39 & P-40 guys TTL are paying attention... I know postwar hot rodders will be thankful.)Another fine update. And a tech-heavy one, which (I should confess) is my favorite kind.
That made me think of something I'd neglected before (& a post on the V1710 thread will follow
): has anybody considered valvetrain changes for faster opening & more valve lift? Or cam changes for more duration at max lift? (I have a hunch the changes would be small, but...)And this is something I don't think I'd have considered in connection with an engine change. Thx for educating me.
This would be the first hollow-bladed prop in service? Or just on the P-38?
If my math's right, the fourth blade means swept area equal to a 3-bladed prop about 21" greater diameter. I'm guessing it means a big improvement in applying horsepower to deliver thrust.
Am I understanding correctly the potential logistics headache of the proposal would be overcome by making the airplane suitable to operate with either?
Which leaves me a bit amazed just how good the crews were & just how sophisticated the repairs they could do were.
I understood the block numbers differed by factory; wouldn't it be -1-BE? Even tho built to Block 10 standard?
Are these replacing OTL single-seaters, or are they TTL original? That is, would the 479th OTL have been a single-seater outfit?
Thinking of that, was there any consideration given to converting the 99th FG from A-36s to P-38s? (I can just see the AAF brass saying, "Those n-'s will never be able to fly a twin-engine fighter!" & Davis proving 'em wrong.
)IIRC, there were issues with fires thanks to backfiring through the turbos. Has that arisen, or been solved?
That sounds like a death knell for the P-47N...
You should...that one was all you.Trying not to gloat.
Normally it wouldn't be too big of an issue but when you're still using a propeller originally designed for use with a 1000-1100 hp engine and now you're looking at going over 2300...well, a new propeller is more than appropriate and completely needed to capture the power.
I am not sure about this. I doubt it. Aeroproducts Propeller Company (AeroProp) had already been making Unimatics for other aircraft in service and afaik they were all hollow blade.
I haven't ran the numbers yet. It is something I intend to do when they are actually testing the A/C. The swept area may be equal but there are losses due to a smaller disc area (even though it has a larger area ratio) and the natural losses of added blades (which according to a NACA paper I read only amounts to about 2% when going from a 2-blade to a 4-blade).
That is exactly what the intent is. If they use the Unimatic and Electric then each propeller unit is a fully replaceable assembly and even if an airplane was originally fitted with one it can be switched out to the other in the field without any additional equipment required (such as alterations to the engine oil system as would be required with the Hydromatic).
I always thought that too. For some reason my notes have it written down this way (maybe it was just a way for me remember?). I will go back and check, if I need to correct it I will.
OTL the 479th was a P-38 Group. Now that I think on it though, I believe it was active in coast defense stateside in '43 before being sent to England. I may have to re-write that part of the chapter.
I haven't covered it in detail yet, but it is certainly possible some of the engine and turbo failures a result of this issue.
Yes...but it may open up the door for the P-47 CAS version we discussed a couple months ago...
I guessed, & it feels pretty good--but you listened, & took the trouble to figure out how they'd do it, so I shouldn't get swelled-headed over it.You should...that one was all you.
Okay, I was misunderstanding you, thinking this was more a case of needing to change with every upgrade; you're meaning, going from 1100 to (say) 1600 would need it, & from 1600 to 2000+, correct?
IDK either, & I have a sense hollow blades were reasonably common already, so a first on the P-38. Which isn't trivial anyhow.
I'd be very interested in seeing comparative performance of 3- & 4-bladed props of the same diameter for drag & delivered thrust. IDK how they measured it, but AIUI, the 4-blade "uses" more of the available hp, & I'd be curious to know how it works--& how big the difference is. So, if you're looking at a "new prop" update...
Right again. I'm having a good day.
That may be the first actual mistake I've caught.
I'm not going to beef.
Awaiting with interest in both cases.
And FYI, after looking at the cam specs you provided, I'd have to guess the potential power gains wouldn't be more than about 25hp, & that's probably generous.
Well, yes...and no. The P-38 kept the same propeller, OTL, from the E to the L. It isn't so much about the HP improvement of the plane but about the design limits of the prop. Even with a 2000 hp engine the prop would still work but you would be missing out on a lot of potential because of the pitch and aerofoil limits of it.
This paper is the one I have referenced.
Regarding production block identifiers, I am still unclear on this and cannot seem to find a deffinative answer. In looking at assigned A/C Serial Numbers, though, it seems OTL Vultee P-38s started with P-38L-5-VN, I have not any reference to a P-38L-1-VN. Maybe the block numbers are universal, rather than factory specific?