WI: NACA Modified P-38

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]:



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:
View attachment 628007

and hydraulics for the Main Gear and coolant system:

View attachment 628009

...and fuel lines (to the main fuel valves and cross suction valve):
View attachment 628010

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.
Good stuff. Now I am even more unhappy about piping through that run.
 
Just wondering since we've been in technical debates for what seems like forever, is there going to be any more combat action?
Yes, I am still planning on picking up the TL again. Unfortunately, real life has been keeping me absolutely swamped lately. Major projects at work, re-organization of our CAP squadron, home renovation and preparation to move in the next few months...not to mention Kids' activities and so on.

So, yes, it will happen but I can't say when exactly. I do thank you, and everyone, for your abundant patience with me!
 
Yes, I am still planning on picking up the TL again. Unfortunately, real life has been keeping me absolutely swamped lately. Major projects at work, re-organization of our CAP squadron, home renovation and preparation to move in the next few months...not to mention Kids' activities and so on.

So, yes, it will happen but I can't say when exactly. I do thank you, and everyone, for your abundant patience with me!
That's all good. Real life takes precedence.
 
I didn't recognize that there were fuel lines running behind the centre section leading edge. It seems like a vulnerable spot to me. The P-38 can be flown without hydraulics and any wiring harness damage that might be inflicted by hits on the leading edge. But the pressurized fuel lines are also exposed to any bit of shrapnel or bullets. Of course an alert pilot would shut off the fuel flow through there if possible if there is a battle damage fire.

It would appear there is even less room behind that leading edge then I had originally thought.

Another good reason Lockheed should have implemented the NACA recommendations. The fuel lines would have been buried behind radiators and the added airframe structure.

Or, if we still have to work with the OTL P-38 then remove the existing inadequate blast tube fed heating lines. Use the space within the main spar where the old heating line ran and run the fuel lines through there. Is there enough space within the main spar structure to accommodate the fuel lines? I'm not sure looking at these diagrams. It would certainly be a far more protected area then directly behind the leading edge. Would this become a maintenance problem? If what's being used is unbroken 6 foot or so lengths of tubing connected at either end I don't see any likely maintenance issues. In that short run within the main spar structure that won't be much flexure.

In the centre section leading edge channel the hydraulic lines and wiring harness can remain. Add in the control cables for the new design air scoop and heat/cool valve and there is still room to push a sufficient amount of heated air through the leading edge channel. I hope. :)
 
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Or, if we still have to work with the OTL P-38 then remove the existing inadequate blast tube fed heading lines. Use the space within the main spar where the old heating line ran and run the fuel lines through there. Is there enough space within the main spar structure to accommodate the fuel lines? I'm not sure looking at these diagrams. It would certainly be a far more protected area then directly behind the leading edge. Would this become a maintenance problem? If what's being used is unbroken 6 foot or so lengths of tubing connected at either end I don't see any likely maintenance issues. In that short run within the main spar structure that won't be much flexure.
This is what I was wondering in my post with,
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.
Maintenance access is my main concern. You may be right about having just a straight 6' section of solid tubing for all the fuel lines if we run them through the main spar but I wonder how you would inspect them? That's the advantage of having them where Lockheed placed them: first, they really aren't much more vulnerable than anywhere else unless, second if there is minor damage or wear on them it can be spotted by ground crew before it becomes a problem. Running the fuel lines through the main spar box sounds like a good, safe, place, but only in comparison on the odd and random event of debris or shrapnel hitting the lines in the LE. Now that I think about it, if they do fail--or worse if there is a fire in the line--in the main spar it could be far worse than if they were to fail in the LE. Once that spar is compromised you're done for...at least you'll have a little time if there if fire or other damage to the center section LE.
 
I got a much better look at the centre section leading edge in this video. Going by that cutaway drawing I posted earlier I had thought it was mainly a wiring harness that runs behind the leading edge. In fact it's mainly hydraulic lines. And the previously discussed fuel line. It looks quite packed in there. I'm still not completely sure it would be impossible to use that space to run hot air and cool vent air through. But it doesn't look promising.

The beautiful Glacier Girl.

From about 1:00 to 1:30 you can get a good close up look at that area. But watch the whole video. It's pretty nice.
 
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Good stuff, @Draconis !

I really should just get in contact with the owners of my "local" (about an hour and half away) P-38 and see if I can't get an inside look during their next annual or other maintenance window. I am friends with some of the owner's extended family and I am pretty sure I can point them to this thread and get any access I'll want.
 
Good stuff, @Draconis !

I really should just get in contact with the owners of my "local" (about an hour and half away) P-38 and see if I can't get an inside look during their next annual or other maintenance window. I am friends with some of the owner's extended family and I am pretty sure I can point them to this thread and get any access I'll want.
That sounds like a fun Summer time day trip when, hopefully, the pandemic is winding down. Please take a few pictures or videos if you do go. BTW, can you tell us which P-38 is owned by family friends?
 
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Since it doesn't look like my proposed heating and ventilation redesign for the OTL P-38 would've have been a practical approach let's take another look at would Lockheed actually did in OTL. Taking a close look at figure # 371 that EverKing has posted at post # 2679 it can be seen that, at least for the P-38L, Lockheed did run heating tubes to the necessary spots in the cockpit to warm the pilot and to defrost the front and rear windshields. So why was it still inadequate? There was not enough warm air being pushed through into the cockpit even though the tubing was there.

I would think that was the result of either/or the too narrow width of the feed lines running from the blast tubes to the cockpit and the inadequate heating of the outside air flowing into the OTL blast tube/ heat exchanger. The solution I think would be to design a higher capacity blast tube/heat exchanger that can handle and heat a larger volume of air flow taken in by a slightly larger air intake. If the width of the passage way through the main spar will not permit the use of wider diameter piping for the larger volume of heated air then put in a second pipe parallel to the first with both connected together at the blast tube and cockpit. That doubles the heated air flow.

This approach uses the OTL existing locations with a minimum of modifications. I think the OTL placement of the heating tubing in the cockpit would have been sufficient if enough hot air could have been pushed through them. A pilot with warm feet is a happy pilot. :)

There is still the problem of the lack of cockpit ventilation when flying in hot conditions. Placing a closable intake vent on the lower side of the nose just above the nose gear door should be low enough to be below the gun exhaust stream. If the intake vent is located near the aft end of the nose gear bay it would only require about a 4 or 5 feet of length of ducting to run to an exit port on or nearby the instrument panel. The idea is to have the ventilation blowing in on the pilot's face and upper body. If we are using 2 inch ducting then running the tubing inside the nose gear bay shouldn't (hopefully) have been too difficult.

These proposed solutions for the OTL P-38s' cockpit heating and ventilation problems seem modest and practical to me. Providing there aren't some solid engineering stumbling blocks that I'm not aware of. But this also fits in with the OTL pattern of other problems with the P-38 that needed relatively simple fixes that were never done. For example improving the canopy design or, though perhaps a little more complex, the fitting of paddle bladed propellors. But nobody wanted to risk interrupting the production lines.
 
That sounds like a fun Summer time day trip when, hopefully, the pandemic is winding down. Please take a few pictures or videos if you do go. BTW, can you tell us which P-38 is owned by family friends?
Fagen Fighters F-5G-6-LO (Ser# 422-8235, AF# 44-27231) currently flying as a P-38L-5-LO wearing the markings of Robin Olds's "Scat III" of the 479th FG. Ron Fagen's niece and us use to send our kids to the same daycare and we became friends during that time. They have quite the collection down in Granite Falls, MN and they put on a nice airshow every couple years (if you recall I went to one a few years back and shared a few of the many pictures from that day).
 
I know everyone is anxiously awaiting a narrative update with the next chapter (still going to happen, I promise!) but I have been having fun with XFOIL playing around with the airfoils I selected for the ATL XP-81. My instincts have served me well here and it looks like I picked just about the perfect wings for the planned mission of high-speed very long range escort. Low drag, high speed 6-series wings with a medium-high aspect ratio and adequate wing area, all with enough internal volume for about 600 USG of fuel (and plenty of room to spare for expansion in the tanks and enough space for all the other equipment that needs to be in the wings.

One exciting part I was just playing was modeling high sub-sonic flow at 30,000 feet. The wings only contribute a Cd of 0.005 +/- 0.0002 for all cruise speeds (including both frictional and parasitic drag) at altitude. I haven't figured out the total Cd for the airplane and will more than likely just guestimate it but this is a good start. The Center Wing section (ignoring the intersection of the booms and fuselage) looks like it can hit about Mach 0.85 before separation with a shock wave starting to form just above that and the outer wings can get to about Mach 0.90, without accounting for tip vortices. The tail is nice and smooth, too, starting to separate at just below Mach 0.9.

I have also been playing around with take off speeds. It looks the full wing design can lift about 18000 lbs a smidge over 110mph (less than 0.5 degree of rotation needed). I don't have software that can properly model fowler flaps but considering the increase of wing area and lift provided a 5-10 mph decrease should be expected at T/O Flaps.
 
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