WI: NACA Modified P-38

[pdf27]

Even more mystifying, when the Germans had figured it out in 1935, before the L.22 was even conceived. AIUI how this problem worked, it wouldn't even have needed wing sweep as such: that is, the spar could still attach perpendicular. It just needed leading edge sweep. Or have I missed something?

Essentially the wing sweep adds in loads of new and really nasty characteristics, particularly around stalling. These took a long time to fix, and even now the pilot's notes will say something like "if you get into a spin, eject immediately". Given that the aircraft of the time could only reach the Mach numbers required to benefit from this in a near-vertical dive and you can get 80% of the benefits from going to a very thin wing (as per the Spitfire, albeit for different reasons) then the average service pilot would not benefit from swept wings. It's worth noting that the the X-1 went through the sound barrier without much trouble, but the DH.108 was a deathtrap.

There's a little bit of it in the video below - it's worth noting that all the swept-wing spinning is done in a Hawker Hunter, which is almost unique for a swept wing aircraft in that it's actually cleared for intentional spinning. My understanding is that the ETPS is unique in teaching spinning a swept-wing aircraft, simply because they have a Hunter. Other aircraft can be spun if they have a recovery chute, but that isn't an option for a service aircraft.

 

[Draconis]

First, I want to thank the General for his links & quoted material. It's been very interesting reading. 😎

Even more mystifying, when the Germans had figured it out in 1935, before the L.22 was even conceived. AIUI how this problem worked, it wouldn't even have needed wing sweep as such: that is, the spar could still attach perpendicular. It just needed leading edge sweep. Or have I missed something?

Two things puzzle me (& both probably reflect my lack of understanding ).

First, when hitting control freezing due to compressibility, why not just pull the throttle back (60% power?): speed reduces, flow over wings slows, tail unfreezes. I recognize, doing this in combat was not a desirable approach...but it would've saved engineering test pilots & allowed them to report what the aircraft was doing, & so get to an answer sooner.

Second, was it impossible, when faced with an inability to pull out, to push through & outside loop? Was the tail so blanked that was impossible? (That's my guess.) Was it too heavy a strain on the aircraft? (That seems possible.)

When the un-DRF equipped P-38 was stuck in compressibility tuck you had no pitch (elevator) control to speak of. So pushing through into an outside loop wasn't a feasible maneuver. But it was still possible to recover from the dive. Test pilots like Tony LeVier were able to do this and he passed the technique onto P-38 pilots in the UK when he did his P-38 demonstration tour. I wish I could find some description online of what the method was. Here's what I think is what they did.

Pull the two throttles back all the way to idle so as to eliminate the engines thrust. You can't do much with the control yoke. You might not even be able to hold unto it if it's slamming forward and back as the elevator is slammed by the shock waves coming off the wing. But you can gently walk the rudders. Yawing and skidding will slow the plane down. I would think you'd not want to boot on too much rudder to avoid over straining the already stressed tail section. This technique combined with having descended to the the thicker air at lower altitude would slow the P-38 below its critical Mach airspeed there by returning pitch control to the pilot. Allowing a normal pull out.

I would guess that the thicker air at low altitude would slow a DRF-less, completely throttled back P-38 down enough that a pull out would be possible before crashing even if the pilot didn't attempt to slow the plane down by any other method. Throttling back in a problem filled dive would be second nature to any pilot. And the denser air could do the rest. But, that is if the shock waves haven't already tore the tail off and/or the pilot hadn't also broke off the tail by hauling back on the yoke with everything he had. Knowledge is everything.

If the pilot had been trained on how best to cope with compressibility he'd know how to recover without destroying the airplane. The DRFs introduced enough improvement that extraordinary efforts were no longer required to pull out. The plane would pull out on its own if you let it. Or else you'd have to hold it in the dive and simply throttle back while in the dive if the buffeting gets too severe.

 

[McPherson]

When the un-DFR equipped P-38 was stuck in compressibility tuck you had no pitch (elevator) control to speak of. So pushing through into an outside loop wasn't a feasible maneuver. But it was still possible to recover from the dive. Test pilots like Tony LeVier were able to do this and he passed the technique onto P-38 pilots in the UK when he did his P-38 demonstration tour. I wish I could find some description online of what the method was. Here's what I think is what they did.

Pull the two throttles back all the way to idle so as to eliminate the engines thrust. You can't do much with the control yoke. You might not even be able to hold unto it if it's slamming forward and back as the elevator is slammed by the shock waves coming off the wing. But you can gently walk the rudders. Yawing and skidding will slow the plane down. I would think you'd not want to boot on too much rudder to avoid over straining the already stressed tail section. This technique combined with having descended to the the thicker air at lower altitude would slow the P-38 below its critical Mach airspeed there by returning pitch control to the pilot. Allowing a normal pull out.

I would guess that the thicker air at low altitude would slow a DFR-less, completely throttled back P-38 down enough that a pull out would be possible before crashing even if the pilot didn't attempt to slow the plane down by any other method. Throttling back in a problem filled dive would be second nature to any pilot. And the denser air could do the rest. But, that is if the shock waves haven't already tore the tail off and/or the pilot hadn't also broke off the tail by hauling back on the yoke with everything he had. Knowledge is everything.

If the pilot had been trained on how best to cope with compressibility he'd know how to recover without destroying the airplane. The DRFs introduced enough improvement that extraordinary efforts were no longer required to pull out. The plane would pull out on its own if you let it. Or else you'd have to hold it in the dive and simply throttle back while in the dive if the buffeting gets too severe.

Provided you had enough altitude and "some" aileron control to flatten the angle of attack on the main wing as you finally pull out of the "controlled dive' you created.

 

[EverKing]

But, that is if the shock waves haven't already tore the tail off and/or the pilot hadn't also broke off the tail by hauling back on the yoke with everything he had. Knowledge is everything.

This is what happened to Ralph Virden on the OTL dive test of 4 November 1941. During his attempt to recover from a Compressibility Dive / Mach Tuck using experimental spring loaded elevator servo tabs the strain was too much for the tail and the entire empennage separated at 3500 AGL costing him his life and YP-38 689.

I would agree that pulling the throttles to just above Idle/Cut-Off with props fully forward (to increase drag) would be a natural way to help avoid additional acceleration during the dive and I would suspect was part of the procedure. Luckily it was the center section with reached crit Mach and stalled, rather than the outer-wings, so aileron control was usually maintained throughout the dive. I am uncertain if skidding/slipping the rudder was part of the process and given a big-twin's tendency to enter flat-spins I would be hesitant to touch the rudder at all through an uncontrolled dive with the tailplane nulled. AIUI, the recovery technique LaVier demonstrated pretty much involved patience as the A/C reached thicker air down low followed by a gentle recovery initiated with the elevator trim control and followed by a 3-4G pull out once full elevator authority was established. Riding the dive down had to require nerves of steel.

 

[phx1138]

When the un-DFR equipped P-38 was stuck in compressibility tuck you had no pitch (elevator) control to speak of. So pushing through into an outside loop wasn't a feasible maneuver. But it was still possible to recover from the dive. Test pilots like Tony LeVier were able to do this and he passed the technique onto P-38 pilots in the UK when he did his P-38 demonstration tour. I wish I could find some description online of what the method was. Here's what I think is what they did.

Pull the two throttles back all the way to idle so as to eliminate the engines thrust. You can't do much with the control yoke. You might not even be able to hold unto it if it's slamming forward and back as the elevator is slammed by the shock waves coming off the wing. But you can gently walk the rudders. Yawing and skidding will slow the plane down. I would think you'd not want to boot on too much rudder to avoid over straining the already stressed tail section. This technique combined with having descended to the the thicker air at lower altitude would slow the P-38 below its critical Mach airspeed there by returning pitch control to the pilot. Allowing a normal pull out.

I would guess that the thicker air at low altitude would slow a DFR-less, completely throttled back P-38 down enough that a pull out would be possible before crashing even if the pilot didn't attempt to slow the plane down by any other method. Throttling back in a problem filled dive would be second nature to any pilot. And the denser air could do the rest. But, that is if the shock waves haven't already tore the tail off and/or the pilot hadn't also broke off the tail by hauling back on the yoke with everything he had. Knowledge is everything.

If the pilot had been trained on how best to cope with compressibility he'd know how to recover without destroying the airplane. The DRFs introduced enough improvement that extraordinary efforts were no longer required to pull out. The plane would pull out on its own if you let it. Or else you'd have to hold it in the dive and simply throttle back while in the dive if the buffeting gets too severe.

That sounds very like what I had in mind. ISTR it being said just waiting to get to lower altitude would save the aircraft, because denser air moved the critical Mach number enough. You've also confirmed my suspicions the elevators were blanked, so thx for that.

Essentially the wing sweep adds in loads of new and really nasty characteristics, particularly around stalling. These took a long time to fix, and even now the pilot's notes will say something like "if you get into a spin, eject immediately". Given that the aircraft of the time could only reach the Mach numbers required to benefit from this in a near-vertical dive and you can get 80% of the benefits from going to a very thin wing (as per the Spitfire, albeit for different reasons) then the average service pilot would not benefit from swept wings. It's worth noting that the the X-1 went through the sound barrier without much trouble, but the DH.108 was a deathtrap.

I'd call a straight thin-section wing on a service fighter a bad call. It seems to need better understanding of a problem already badly comprehended by Lockheed, & seems to beg for trouble: AIUI, the razor wing of the X-1 & F-104, while excellent for high-Mach ops, was deficient in low-speed lift, which, in a piston aircraft, is something like 75% of the envelope. (Compared to the F-104, anyhow.)

It's also answered fairly well by German swept-wing (-edge) research.

 

[Draconis]

The NACA modifications described in this ATL didn't only help to alleviate the P-38s compressibility problem. Another problem that the P-38 pilots endured was almost nonexistent cockpit heating and very poor ventilation. Pilots had to endure extreme heat when flying low altitude missions in hot climes. And worst of all they had to face extreme, almost unendurable cold while flying long missions at high altitude. As exemplified by the multi hour bomber escort missions flown in the Stratosphere over Europe where the outside air temperature would reach minus 50 degrees and the inside temperature being not much better.

As the P-38 didn't have a huge avgas fired heat maker situated directly in front of the cockpit getting adequate cockpit heat was a little more complicated then with the single engined fighters. OTL Lockheed didn't do a very good job at this. The heating system they did design was inadequate. In EverKings ATL NACA modified P-38 the mounting of the oil coolers and glycol radiators in the extended leading edge of the centre wing sections put a good source of heat adjacent to the cockpit greatly simplifying the engineering needed to supply adequate heating.

But what could Lockheed have feasibly done to improve the heating and ventilation in the unNACA not improved P-38s of our time line? One possibility would've been to redesign a more efficient way of piping heat and fresh air into the cockpit. A redesign that could also function as a cool air supply fed from a location that would not be ingesting gun exhaust. Along with this thumbnail diagram I'm supplying a link to the same image that can be enlarged to provide a closer look at what I'm describing to hopefully clarify my concept.

https://conceptbunny.com/wp-content/uploads/2017/10/Lockheed_P-38_Lightning.gif

On this P-38 diagram the leading edge of the right wing centre section is exposed. The length of this straight section from cockpit wall to engine nacelle is only about 6 feet. As can be seen it carries a wiring harness between the cockpit and the engines. I'm going to make the assumption here that the left side is identical. I think it would be a good location to fit ducting for heating and ventilation. The exit louver or port for this ducting would emerge on the inside just above the pilot's knees.

One consideration. Is there enough room in the space between the wiring harness and the leading edge to install ducting of a sufficient diameter? About 3 inches I think? It's not easy to say for sure but looking closely at the expanded diagram it looks like it isn't. There is also the matter of the path the wiring harness takes after exiting the wing.

If there isn't room to fit ducting into the wiring harness channel then why not use the channel itself as a duct? The only apparent entrances to the structure are where the wiring harness pass through at the engine nacelles and cockpit. The wiring is not branching off into the wing anywhere. So sealing the length of the wiring harness channel to prevent air leakage shouldn't be a difficult job. Only at the harness entry points will a rubber gasket be required. Similar gaskets will be needed to seal the exit and entry of the air feed piping and exit piping for the air.

As mentioned the air exit would be mounted on the inside of the cockpit slightly aft of the instrument panel and above the knees. It would be a port with a slatted louver for directing the air where desired. I don't think the louver would be wider then about 4 inches so it shouldn't be too difficult to find a place to fit.

The more complex issue is how and where to design and place the air intake. Referring again to the expanded cutaway drawing I think the best location is slightly above the lower edge of the inside topmost engine panel. Ahead of the bulkhead and behind and just above the exhaust manifold cooling intake. There looks like there is room to fit the piping in between the cylinder head cover and the exhaust pipe.

On the panel in the proposed location would be mounted a small closable rectangular intake scoop. About 3 inches wide and no more then one inch high when open. Visualize a small flap door hinged at the rear with side flashing. It would lift at its front facing side into the airstream to open when the pilot selected for heat or ventilation. Being located directly in the prop wash close to the propellor a small inlet of just 3 inches wide by 1 inch high should scoop a sufficient amount of air at sufficient pressure to feed through the short run to the cockpit. The cockpit is also being supplied from both the left and right side after all.

A straight run to the cockpit if it's ventilation that is required. For heating the air feed from the scoop will be Y'd off from the scoop piping to a small heat exchanger mounted on the nearby exhaust pipe that is running several inches below the ventilation piping. The forced air from the extended scoop would be directed by a flap valve at the Y section to either a straight through run to the leading edge wiring harness channel and then into the cockpit or directed instead through the exhaust mounted heat exchanger and from there piped back into the wiring harness channel and into the cockpit through the same exit louver. The pilot would select for heat or cool after opening the air scoop on the engine nacelle.

This suggested solution solves both the heating and ventilation problem using the same equipment. It puts the air intakes faraway from ingesting gun exhaust and close to a powerful heat source. The pilot has the options to choose between using either one vent or both vents for either heating or cooling. Or no vents at all depending on conditions.

Would it work? I couldn't say for sure without being able to look over an actual P-38 with an engineer or two I could ask questions of. But going by the diagrams I don't see any obvious show stoppers. Would this installation provide adequate heat? Better then what they actually used? I'm not certain but it's hard to see how it could be any worse then what they had.

 

[phx1138]

https://conceptbunny.com/wp-content/uploads/2017/10/Lockheed_P-38_Lightning.gif

That diagram deserves a thank you.

On this P-38 diagram the leading edge of the right wing centre section is exposed. The length of this straight section from cockpit wall to engine nacelle is only about 6 feet. As can be seen it carries a wiring harness between the cockpit and the engines. I'm going to make the assumption here that the left side is identical. I think it would be a good location to fit ducting for heating and ventilation. The exit louver or port for this ducting would emerge on the inside just above the pilot's knees.

One consideration. Is there enough room in the space between the wiring harness and the leading edge to install ducting of a sufficient diameter? About 3 inches I think? It's not easy to say for sure but looking closely at the expanded diagram it looks like it isn't. There is also the matter of the path the wiring harness takes after exiting the wing.

Two things crossed my mind.

First, your proposal of making the wiring run in a hot air duct seems like a good one, having it do double duty. I have a cautious question about how hot the air flowing is, & how fast, with possible risk to wire separation & shorting, but I imagine the heat isn't extreme & fastening could (would) be made sufficiently secure: just be careful.

Second, it appears to me there's space aft the main inboard tank. Couldn't that be used to run wiring, as well as fit another fuel tank? Or ducting & a tank?

The route of the ducting seems to depend on where the heat is being tapped from, & how hot the source is.

A third thing may be an issue: does the joint between the duct & the source invite exterior icing, or interior pressure changes (as flow volume changes) due to the temperature differential, or internal icing (due to flow speed changes), between a cold duct & a hot source?

I may be over-complicating this... I wouldn't want to see it rejected because of my kibitzing.

 

[Draconis]

That diagram deserves a thank you.


Two things crossed my mind.

First, your proposal of making the wiring run in a hot air duct seems like a good one, having it do double duty. I have a cautious question about how hot the air flowing is, & how fast, with possible risk to wire separation & shorting, but I imagine the heat isn't extreme & fastening could (would) be made sufficiently secure: just be careful.

Second, it appears to me there's space aft the main inboard tank. Couldn't that be used to run wiring, as well as fit another fuel tank? Or ducting & a tank?

The route of the ducting seems to depend on where the heat is being tapped from, & how hot the source is.

A third thing may be an issue: does the joint between the duct & the source invite exterior icing, or interior pressure changes (as flow volume changes) due to the temperature differential, or internal icing (due to flow speed changes), between a cold duct & a hot source?

I may be over-complicating this... I wouldn't want to see it rejected because of my kibitzing.

Taking a very close look at the exposed leading edge in the expanded P-38 cutaway diagram it appears that the wiring harness is securely tied down by straps every foot or so. They're not going to move around. I wouldn't think an, at most 30 or 40 degree Celsius airflow over the wiring would bother the insulation. Those planes cooked sitting in the hot tropical Sun and who knows what temperatures were reached inside the airframe. I don't know about if the 1940s fibre based wire insulation degraded easily when the planes sat cooking in the Sun. If they didn't then I wouldn't think the much less hotter cockpit heating air would bother it.

The wing structure you're referring to in the centre section behind the secondary spar tapers down to a thin edge. That structure already contains the P-38's flaps and the activating mechanism for extending them. I don't think there is room for anything else there. The lower part of the section moves down and outward on rails. Fowler flaps.

In your 3rd observation, considering the P-38 cockpit wasn't pressurized I wouldn't think the pilot would notice any pressure changes when the air intake scoop would be opened or closed. Not anything close to the pressure changes that would be felt when there are changes, especially rapid changes in altitude.

Regarding icing forming on and clogging the air scoop intake. If it happens not a big deal in itself. If the outside air is warm enough for icing to occur losing the cockpit heat wouldn't be the worse thing. In any event heavy icing conditions are something a pilot is supposed to avoid because of the much worst dangerous problems they create. Clogging the turbocharger air intake. Altering the shape of the wing air foil. Icing will also add a lot of extra lot of weight to the plane.

Or were you thinking of some kind of venturi effect chilling the air in the ducting? Not sure how that would apply here. And in any event even if heat is not selected the ducting from the air scoop to the wing is mounted inside the front engine nacelle close to the exhaust manifold and exhaust pipes. A pretty warm place.

 

[phx1138]

Taking a very close look at the exposed leading edge in the expanded P-38 cutaway diagram it appears that the wiring harness is securely tied down by straps every foot or so. They're not going to move around. I wouldn't think an, at most 30 or 40 degree Celsius airflow over the wiring would bother the insulation. Those planes cooked sitting in the hot tropical Sun and who knows what temperatures were reached inside the airframe. I don't know about if the 1940s fibre based wire insulation degraded easily when the planes sat cooking in the Sun. If they didn't then I wouldn't think the much less hotter cockpit heating air would bother it.

Probably not, except, how how is (frex) the top of a V1710? It's pretty damn hot...

The wing structure you're referring to in the centre section behind the secondary spar tapers down to a thin edge. That structure already contains the P-38's flaps and the activating mechanism for extending them. I don't think there is room for anything else there. The lower part of the section moves down and outward on rails. Fowler flaps.

I'd forgotten about the actuators... I was looking further outboard for that becoming a Thing.

In your 3rd observation, considering the P-38 cockpit wasn't pressurized I wouldn't think the pilot would notice any pressure changes when the air intake scoop would be opened or closed. Not anything close to the pressure changes that would be felt when there are changes, especially rapid changes in altitude.

Regarding icing forming on and clogging the air scoop intake. If it happens not a big deal in itself. If the outside air is warm enough for icing to occur losing the cockpit heat wouldn't be the worse thing. In any event heavy icing conditions are something a pilot is supposed to avoid because of the much worst dangerous problems they create. Clogging the turbocharger air intake. Altering the shape of the wing air foil. Icing will also add a lot of extra lot of weight to the plane.

Or were you thinking of some kind of venturi effect chilling the air in the ducting? Not sure how that would apply here. And in any event even if heat is not selected the ducting from the air scoop to the wing is mounted inside the front engine nacelle close to the exhaust manifold and exhaust pipes. A pretty warm place.

I don't mean cockpit, I mean in the ducting: hot air changing speed & volume from the "tap" to the duct causing problems. So yeah, some influence from venturi effect. It's the distance between the engine (warm to hot) to cockpit (less so) that concerns me, especially if the duct is running in the leading edge, exposed to (comparatively) much colder air. Probably I'm overestimating the problem(s).

 

[McPherson]

A third thing may be an issue: does the joint between the duct & the source invite exterior icing, or interior pressure changes (as flow volume changes) due to the temperature differential, or internal icing (due to flow speed changes), between a cold duct & a hot source?

It very well could, which is why I am dubious about an HVAC conduit in this area. I want it inside the fuel tank cavity. It would still have to be insulated.

 

[Draconis]

It very well could, which is why I am dubious about a HVAC conduit in this area. I want it inside the fuel tank cavity. It would still have to be insulated.

No HVAC here. Nothing higher then 24 volt DC in the P-38. Like most planes of its era. The wiring harness channel is uninsulated but it's only 6 feet in length. Being uninsulated wouldn't matter for ventilation only. But for heating sure, especially at extreme low temperatures. There has to be enough and hot enough air being pushed through the channel so it's still warm when it exits into the cockpit. This is a function of air flow amount, how effective the heat exchanger is, the fact it's only a 6 foot run and also there is two heaters sending warm air to the cockpit. The fine design details are beyond my scope.

 

[phx1138]

It very well could, which is why I am dubious about an HVAC conduit in this area. I want it inside the fuel tank cavity. It would still have to be insulated.

I'd be disinclined, because that's going to cut into fuel, & even slightly, I'd sooner not, if possible. Turning over the root leading edge to this doesn't look like a major engineering project, with no impact on fuel; running the duct through the tank well seems also to want new tank design, & that's still more tooling changes, & more production delay, on a project already fairly well behind where it could be.

Insulation might be the key to preventing my complaints becoming actual headaches.

 

[Draconis]

I'd be disinclined, because that's going to cut into fuel, & even slightly, I'd sooner not, if possible. Turning over the root leading edge to this doesn't look like a major engineering project, with no impact on fuel; running the duct through the tank well seems also to want new tank design, & that's still more tooling changes, & more production delay, on a project already fairly well behind where it could be.

Insulation might be the key to preventing my complaints becoming actual headaches.

Yes, the whole direction of my proposed redesign is trying to take the OTL P-38 problems and solve them in the simplest and easiest way possible so as to not impact production. Adopting the NACA recommendations would be better. But I like pursuing this thought experiment of how to improve the OTL design in the less disruptive way as possible.

The thing about insulation is in that leading edge space where the wiring harness runs is there might not be enough room for a sufficient amount. No room for isolated ducting of sufficient diameter likely also means no room for insulation. So the solution is to push enough hot air through that it's still warm when it enters the cockpit.

 

[McPherson]

I'd be disinclined, because that's going to cut into fuel, & even slightly, I'd sooner not, if possible. Turning over the root leading edge to this doesn't look like a major engineering project, with no impact on fuel; running the duct through the tank well seems also to want new tank design, & that's still more tooling changes, & more production delay, on a project already fairly well behind where it could be.

Insulation might be the key to preventing my complaints becoming actual headaches.

Give the pilot electrically heated overalls and wire an outlet service cockpit forward for that into the electrical bus. All inside the pilot pod. Warm him up like bomber crew members that way. He can also be ground trained to withstand cold and hot temperatures in what is called a sauna and a freezer. Solve it in the human being?

 

[Draconis]

Give the pilot electrically heated overalls and wire an outlet service cockpit forward for that into the electrical bus. All inside the pilot pod. Warm him up like bomber crew members that way. He can also be ground trained to withstand cold and hot temperatures in what is called a sauna and a freezer. Solve it in the human being?

That is what they did in OTL. They developed an electrically heated "bunny suit" for the pilots. That solved the hypothermia problem. It didn't solve the frost forming on the inside of the windshield and canopy problem. A truly dangerous problem that one. Or the cold soaked and stiff switches and levers. My thinking is why not take the available heat from the two engines and solve all the heating problems and also the when in hot weather the over heated cockpit ventilation problem too. With a minimum of redesign work. Save the electricity for the gun heaters.

 

[McPherson]

A truly dangerous problem that one.

Is there enough electric reserve in the gun heaters to wire the glass in the canopy windscreen and install an electric de-icer co-opted off that circuit? As for cockpit greenhouse effect, the silly plane is doing several hundred knots. How about ram-feed ventilation?

 

[Draconis]

Is there enough electric reserve in the gun heaters to wire the glass in the canopy windscreen and install an electric de-icer co-opted off that circuit? As for cockpit greenhouse effect, the silly plane is doing several hundred knots. How about ram-feed ventilation?

I'm not sure how you'd wire in windshield defrosters in bullet proof glass without weakening it. Ram air ventilation is what I'm suggesting here. With the air intakes on the engine nacelles to avoid gun exhaust being ducted into the cockpit. This also puts the air intakes location close to the heat source for the cockpit heating.

 

[phx1138]

The thing about insulation is in that leading edge space where the wiring harness runs is there might not be enough room for a sufficient amount. No room for isolated ducting of sufficient diameter likely also means no room for insulation. So the solution is to push enough hot air through that it's still warm when it enters the cockpit.

I'm looking at it from the other side. The top of those V1710s is always going to be damned hot ("I don't know what that is in degrees I understand"...), so "hot enough" shouldn't be a problem. I was thinking about insulating just enough to prevent interior icing due to the delta-t from inside to outside (at any point).

Putting in a simple electric blower fan would keep the air flowing fast enough to keep the canopy warm, & venting at the canopy base will distribute it as you want. Put the fan on a thermostat, & fit the ducting with a "dump" to outside.

If you want to vent the air out when it's too hot (in summer), OTOH, I'd look seriously at a boundary layer scoop (what rodders today call an NACA scoop {& what all too many mis-identify as a "NASA scoop" }), like NASCAR uses: it'll suck air out nicely, & create zero (or near-zero) drag. In fact, venting hot air out might just allow you to manipulate the airflow around the pod & reduce drag a fraction. (That could work all year round.)

 

[EverKing]

An interesting proposition--running a heating duct through the center section leading edge. There may just be enough room but I can't confirm that. I have a full P-38 construction manual and while it gives detailed build instructions for the outer wing (remember the screw count holding the OW leading edge on?) all it gives us the for the center section construction is the following paragraph [stress added]:

[SECTION IV. Part 1, pp b.] CENTER SECTION.--The center section , the forward booms, and the fuselage are jig-mated, riveted, and bolted together. A main beam and front and rear shear beams are main structural members of the center section, and to them are attached the ribs, skin, and intermediate structure. Space is provided for four self-sealing fuel tanks. The center section supports the fuselage, engine nacelle, boom attachments, and two flaps. The surface control cables and trim tab cables are carried outboard from the fuselage inside the main beam. A tube in each forward fuel tank compartment provides passage for the power plant control cables. The leading edge of the center section is detachable at the front shear beam, providing access to plumbing lines and conduit.

Paragraph c. goes into the Outer Wing Assembly immediately after this.

I cannot find any good information about that space before the front shear beam anywhere but there are indications of some of what is being run through there including the Push/Pull control cable for the cockpit heating duct butterfly valve:

and hydraulics for the Main Gear and coolant system:

...and fuel lines (to the main fuel valves and cross suction valve):

What I was really hoping to find was a view of the internal structure of that removable leading edge assembly. I suspect the internal ribs are constructed similarly to those of the outer wing with a main "D" shaped support at the front, albeit with small openings in it for weight savings.

Still, even if we only consider the few systems shown above (and there are others, but I didn't want to completely spam the post) I am doubtful there was enough space in the existing P-38 wing to accommodate another heater duct from the engine nacelle directly to the cockpit there. Of course, there may always be the option of moving all of this (or at least the fuel and hydraulic lines) the main spar where the existing heat duct is and then putting the heat duct forward but that may open maintenance/access issues to these critical supply lines--which is why I am pretty sure they are up front to begin with.

Just wanted to pipe in with my $0.02.

 

[vl100butch]

Just wondering since we've been in technical debates for what seems like forever, is there going to be any more combat action?