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Sockmonkey

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Maybe too much power to stay reliable? Look up the Rolls Royce Crecy, IIRC basically a two-stroke Merlin with the goal of making a 5,000hp Spitfire. The test engines didn’t last particularly long.
According to the articles, it was mostly the sleeve valves that screwed it up.
 

cblink.007

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It’s a neat thought to have and while I’m not smart enough to intuitively know the nuts and bolts of how heat transfer works I like to look to history for clues on this sort of thing. I figure when it comes to aviation all the easy stuff was figured out by 1945 or so.

What if your copper tunnel was turned inside out and was instead a copper skin on the airplane that radiated off all of the engine heat to the passing air? Turns out it’s been done already, and successfully, on the old Schneider Cup racers. Many of them used almost their entire wing surfaces as radiators and sometimes the fuselage and float surfaces too. It led to some pretty fast airplanes, in fact the fastest going for a while.

Then along comes a fighter like the P-51 (and a bunch of others but the P-51 makes the best example) where it has a traditional radiator buried in the fuselage but with a bit of a twist: a small intake led to a duct that widened up to a pretty large radiator which heated the air before squeezing it out through a tapering exit duct. By adding heat to the air it made a sort of rudimentary ramjet and was said to have actually produced thrust. I don’t think it was much thrust but in the case of the Mustang it’s at least enough to overcome the drag of the duct and radiator, and maybe a bit more.

I don’t know if there’s much to be had beyond that.
This Mike Arnold video discusses cooling (and interference) drag quite a bit in an E-AB application...

 

pictsidhe

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According to the articles, it was mostly the sleeve valves that screwed it up.
The twin cylinder test engines ran great. The V12s broke the everything. Oil starvation from the end fed crank and squirter design was strongly suspected, but not checked. Rolls Royce Heritage has an interesting book on the Crecy. RRH are currently closed due to some sort of zombie virus problem over there
 

Jay Kempf

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My understanding is that the P-38 used a GE type B turbosupercharger system. That system fed intake air first into the turbocharger (located in the boom, with the shaft vertical), then through the LE intercooler, through the carburetor, then into the engine shaft driven supercharger.

Deuelly, please comment.


BJC
Yeah, it kills me how many of these boosted systems were carbureted. (how the heck do you spell carbureted?)

Guess I was misled all these years reading and researching the P38 by the inclusion of Super in the Charger description. Always understood it to be shaft driven off the back of the engine. A very unique and interesting power installation regardless.
 

Jay Kempf

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With parts at 50+ years old and not built to today's standards I would hardly expect to be able to keep one running at all.
 

BJC

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No Leading Edge intercooler
OK. I can't see a heat exchanger in your posting.

Here is an excerpt of a description of the P-38,


Design Analysis No 8
The Lockheed P-38

By Hall L Hibbard
Vice-President and Chief Engineer, Lockheed Aircraft Corp.​

...

Current P-38s are equipped with turbosupercharged 12 cylinder liquid-cooled V-1710 Allisons with a military and takeoff rating of 1,520 hp to 27,000 ft at 3,000 rpm.
...

Carburetors are Bendix-Stromberg PD-12K7, and differ from the conventional vented float chamber type in that the fuel system is closed from fuel pump to discharge nozzle. Fuel is delivered to the carburetor by the engine driven fuel pump at a pressure of 16 to 18 psi. Fuel delivered to the carburetor is metered in accordance with the mass air flow through the throat as registered by the venturi tube and automatic mixture control unit. Metered fuel then passes through the discharge tube to the discharge nozzle where it is sprayed into the air stream entering the internal supercharger.
...

Outer wing panels consist of main beam, rear shear beam, and upper and lower stressed skin, forming a box beam, and hydro-pressed sheet 24ST ribs spaced at 12-in centers. Outer skin and corrugated stiffener are 24ST Alclad. The leading edge has no ribs and is made up of formed inner skin and shallow chordwise corrugations of 24ST. These are built up of upper and lower halves, joined at the leading edge with piano hinge fittings, and are removable. In earlier models the inter-coolers were housed in the leading edge of the wing, which now carries fuel cells.
BJC
 

Deuelly

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My understanding is that the P-38 used a GE type B turbosupercharger system. That system fed intake air first into the turbocharger (located in the boom, with the shaft vertical), then through the LE intercooler, through the carburetor, then into the engine shaft driven supercharger.

Deuelly, please comment.


BJC
The early P-38s had intercooler in the wings as seen in the attached picture.
Screenshot_20200724-103634_Gallery.jpg
On the later P-38s they put fuel in the wings and moved the coolers. Our P-38 is a later "L" model. In these installations the cooler is in the engine cowling. The red arrow below points to its approximate location. Also the air intake for the cooler was located centrally between two oil intakes as seen below.
Screenshot_20200724-103804_Gallery.jpg
Screenshot_20200724-103835_Gallery.jpg
The turbo air intake was located on the side of the boom.
Screenshot_20200724-103728_Gallery.jpg
In the upper boom the exhaust and hot side of the turbo can be seen.
Screenshot_20200724-103746_Gallery.jpg
Our turbos are still operational and require very little maintenance. We fly quite often and try to have it at Oshkosh as much as possible.

Brandon
 
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Aesquire

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The Early P-38s used the Leading Edge D-tube in front of the spar as an intercooler. It worked ok but not great on the polished aluminum prototypes. Once camo paint on the outside, and Zinc Chromate on the inside was added, the coatings greatly reduced the heat transfer. Plus the design had very limited area to volume of hot air to be cooled. So they went to a whole new boom & cooling design.

Also the original Allison PRSU that was pretty & pointy and made the P-38 & P-40 early versions so streamlined looking had reliability problems so they went to the offset Spur gear design that moved the prop shaft "up" off center from the engine. Requiring redesign of the nose of the nacelle (P-38) and fuselage (P-40) to fit the new engines.

XP-38.jpg

here you see the newer design, and note the side mounted radiator pods have a boundary layer scupper.


In the ORIGINAL usage an Intercooler was between the 2 stages of supercharging, if the air is cooled between the final or only stage of supercharging, it's an Aftercooler. Over the years people just used the term intercooler for all charge coolers. Which is incorrect, so pedantics argue all the time... ;)

Ironically, the new system didn't have good control over cooling for the oil and the induction air, and at high altitudes in the European Theater ( where it's colder than Southern California ) they had oil congeal, leading to oil starvation and engine failure, and the cold air would condense the fuel out of the mixture, which would puddle in the intake manifold, giving uneven mixtures, and explosions in the intake, also causing engine failure. In the Pacific, the generally lower altitudes and warmer temperatures the problem was much less.

That they never fixed the problem was typical in WW2 where there was pressure, even orders/demands that the production not be slowed to solve problems in a lot of machines. A LOT.
 
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Deuelly

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That they never fixed the problem was typical in WW2 where there was pressure, even orders/demands that the production not be slowed to solve problems in a lot of machines. A LOT.
They must have fixed it at some point. The late model P-38s don't seem to have any problems with temperature in the oil or induction air. It must have been one short production order with the problems.

I know that even on a cold Minnesota winter day the the automatic cooler doors keep everything right in the green, and will send temps through the roof if you close them.
 

BJC

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In the ORIGINAL usage an Intercooler was between the 2 stages of supercharging, if the air is cooled between the final or only stage of supercharging, it's an Aftercooler.
Since the P-38 cools the engine intake air between two stages of compression, I’m fully satisfied with Hall Hibbard’s usage of the term “inter-coolers”.


BJC
 

Bill-Higdon

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OK. I can't see a heat exchanger in your posting.

Here is an excerpt of a description of the P-38,




BJC
Correct there were convential heat exchangers in the leading edge of the early P-38's but they didn't use the leading edge itself as a heat exchanger. The German Heinkel HE-100 used the wing skin as a heat exchanger, one of the reasons it lost the competition to the BF-109 IMHO
 
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Sockmonkey

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The twin cylinder test engines ran great. The V12s broke the everything. Oil starvation from the end fed crank and squirter design was strongly suspected, but not checked.
Seems like it would be great to use on an inline liquid-cooled four-cylinder.
The bit about using junk heads was interesting. Some new designs try and adjust the stroke and cylinder pressure with a variable crank connection. Adjustable junk heads seems like a much more practical way to do that. It kind of smells like someone fixating on a lesser, but proprietary design to squeeze more money out of the project.

That they never fixed the problem was typical in WW2 where there was pressure, even orders/demands that the production not be slowed to solve problems in a lot of machines. A LOT.
I remember one horror story where an artillery piece had the wrong diameter barrel and they went so far as to forbid changing it because they wouldn't admit they screwed up.
 

Erik Snyman

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The Early P-38s used the Leading Edge D-tube in front of the spar as an intercooler. It worked ok but not great on the polished aluminum prototypes. Once camo paint on the outside, and Zinc Chromate on the inside was added, the coatings greatly reduced the heat transfer. Plus the design had very limited area to volume of hot air to be cooled. So they went to a whole new boom & cooling design.

Also the original Allison PRSU that was pretty & pointy and made the P-38 & P-40 early versions so streamlined looking had reliability problems so they went to the offset Spur gear design that moved the prop shaft "up" off center from the engine. Requiring redesign of the nose of the nacelle (P-38) and fuselage (P-40) to fit the new engines.

View attachment 99486

here you see the newer design, and note the side mounted radiator pods have a boundary layer scupper.


In the ORIGINAL usage an Intercooler was between the 2 stages of supercharging, if the air is cooled between the final or only stage of supercharging, it's an Aftercooler. Over the years people just used the term intercooler for all charge coolers. Which is incorrect, so pedantics argue all the time... ;)

Ironically, the new system didn't have good control over cooling for the oil and the induction air, and at high altitudes in the European Theater ( where it's colder than Southern California ) they had oil congeal, leading to oil starvation and engine failure, and the cold air would condense the fuel out of the mixture, which would puddle in the intake manifold, giving uneven mixtures, and explosions in the intake, also causing engine failure. In the Pacific, the generally lower altitudes and warmer temperatures the problem was much less.

That they never fixed the problem was typical in WW2 where there was pressure, even orders/demands that the production not be slowed to solve problems in a lot of machines. A LOT.
She sure is pretty.....
Erik in Oz.
 
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