1941: the best case for 350+ mph CV fighters?

[Shortround6]

The FM-2 didn't have an intercooler and the frontal area/diameter of the respective engines was not governing factor in the frontal area of the fuselage and even on the Hawk 75 where it was, the cowlings minimised the difference.

 

[pinsog]

Above 12,000 feet the turbocharged Wildcat would gain 200 hp over the original. Would a 20% increase in power not overcome the drag of an intercooler? At 25,000 feet is a 43% increase in power

 

[pinsog]

Question: If the increased diameter of the 1820 is not a factor on a Wildcat, then why would an intercooler be a factor if its less share footage than the increased diameter? (48 inch diameter plus intercooler vs 55 inch diameter)

I'm not arguing as much as trying to get my head around this

 

[Shortround6]

You are going to get better performance than the original engine, the question is it enough to get you to 350mph?

Here is a picture of a B-24 intercooler from another thread.

It is the silver finned box visible through the engine mount.

A general rule of thumb was that a 2nd stage supercharger and intercooler cost around 30mph below 15,000ft.

It depends on how tidy you can make the installation. In the above photo the duct above the brass oil cooler is the carburetor inlet. Note size difference (required air flow?) between it and the intercooler.

Another photo showing a B=24 intercooler.

Yes you could split the intercooler into two units for packaging but you are going to need pretty close to that volume of intercooler and those size ducts to handle the airflow.
Note size in relation to the R-1830 engine.

There was one very untidied mock up of a turbo and intercooler on a P-39 that cost 40mph at low altitude. Not the original.

You may get 340-350mph at 25,000ft, are you willing to give up even 20mph at lower altitudes to get it?

 

[pinsog]

Is a bomber intercooler larger than a fighter intercooler since it has to work at lower speeds? (Im picturing the difference between a heavy 4WD truck pulling a trailer and a sports car with the same engine

Where was that gigantic intercooler mounted on a P43?

 

[Shortround6]

It was mounted in the rear of the plane. A lot of the drag has to do with the air flowing through the ducts and the intercooler "core" and not necessarily the increase in frontal area.

The idea of the truck vs Sports car only works so far. the intercooler is only cooling the incoming air, not the engine, incoming air gets too hot and the mixture detonates in the engine, wrecking it. A
And most fighters had a best climb speed of under 200mph IAS so they aren't climbing at a speed (horizontal speed) that much faster than the bombers.

 

[Kevin J]

View attachment 538477
Referring to drag on the hypothetical F4F-3 with a turbocharger.
This is about the only thing I could find to make a comparison. The FM2 went from a 48 inch diameter P&W 1830 to a 55 inch diameter Wright 1820, one would think that would be a huge increase in drag, BUT, look at the 1200 hp normal rating for the FM2 on the graph.
Top speed at normal rating of 1200 hp (same as the turbocharged F4F-3 would have) went from 278 to 292 at SL, from 295 to 308 at 5500 feet. About a 15 mph increase with a 55 inch diameter engine instead of a 48 inch diameter engine.
If you continue the 1200 hp speed on the graph in a straight line all the way up to 25,000 feet, like it had a turbocharger instead of the single stage Wright, the top speed would hit 350 at 20,000 feet just like the calculations showed, and would, I assume continue to gain speed up to 25,000 feet where the turbocharger was rated.

The other question I would have, which could only be known by actual testing is which would be better, a lighter weight but larger diameter turbocharged Wright 1820 for better climb. Or a heavier but smaller diameter P&W 1830 that would probably be faster and have better over the nose visibility.

That extra increase in top speed of between 10 mph at SL up for over 20 mph at altitude and the substantial increase in climb rate would sure be nice when tackling a Zero, giving the pilots a decent platform for boom and zoom early in the war until the Hellcat arrived

Surely you're looking for low altitude performance only to combat incoming Jap attack aircraft maybe even Kamikaze. The turbo is unnecessary.

 

[pinsog]

"a general rule of thumb was that a 2nd stage supercharger and intercooler cost 30 mph below 15,000 feet"

I very much appreciate your knowledge on these subjects and have learned a lot from you over the years, but you understand that I have a hard time believing that unbolting the turbocharger and removing the intercooler from a P47 Thundebolt, P38 Lightning or P43 Lancer without reducing the size of the airframe could increase top speed by 30 mph below 15,000 feet. That is why Im having trouble seeing an F4F-3 lose much speed by adding a turbocharger since the aircraft doesn't have to get bigger to fit it, its all internal.

Do you see my confusion?

 

[XBe02Drvr]

This is about the only thing I could find to make a comparison. The FM2 went from a 48 inch diameter P&W 1830 to a 55 inch diameter Wright 1820, one would think that would be a huge increase in drag, BUT, look at the 1200 hp normal rating for the FM2 on the graph.

What a mere comparison of engine diameters fails to address is internal cooling drag. The ducting that forces the airflow to hug the cylinder fins on the single row 1820 is relatively simple and straightforward. The double row 1830, OTOH, faces the tricky proposition of keeping the rear cylinders cool, making the airflow path twisty and torturous, and generating extra drag. Pratt and the airframe builders got better at this as time went on, but never approached the low drag simplicity of Wright's 1820.
My engines instructor at mech school had been an 8th AF mechanic, first on Mustangs, then on the heavies. As part of a troubleshooting crew, his group helped out B17 and B24 squadrons dealing with particularly thorny maintenance issues. He said that under the cowling, a B24's engine installation was a plumber's nightmare, with induction, intercooler, exhaust, and cooling air ducting going every which way. It's the drag you don't see that gets you.
Cheers,
Wes

 

[pinsog]

What a mere comparison of engine diameters fails to address is internal cooling drag. The ducting that forces the airflow to hug the cylinder fins on the single row 1820 is relatively simple and straightforward. The double row 1830, OTOH, faces the tricky proposition of keeping the rear cylinders cool, making the airflow path twisty and torturous, and generating extra drag. Pratt and the airframe builders got better at this as time went on, but never approached the low drag simplicity of Wright's 1820.
My engines instructor at mech school had been an 8th AF mechanic, first on Mustangs, then on the heavies. As part of a troubleshooting crew, his group helped out B17 and B24 squadrons dealing with particularly thorny maintenance issues. He said that under the cowling, a B24's engine installation was a plumber's nightmare, with induction, intercooler, exhaust, and cooling air ducting going every which way. It's the drag you don't see that gets you.
Cheers,
Wes

It does make the single row 1820 setup on the B17 make sense

 

[pinsog]

Maybe others can learn from my questions and all your detailed explanations. Not just arguing to argue. A lot of this makes sense but not all of it

 

[Shortround6]

"a general rule of thumb was that a 2nd stage supercharger and intercooler cost 30 mph below 15,000 feet"

I very much appreciate your knowledge on these subjects and have learned a lot from you over the years, but you understand that I have a hard time believing that unbolting the turbocharger and removing the intercooler from a P47 Thundebolt, P38 Lightning or P43 Lancer without reducing the size of the airframe could increase top speed by 30 mph below 15,000 feet. That is why Im having trouble seeing an F4F-3 lose much speed by adding a turbocharger since the aircraft doesn't have to get bigger to fit it, its all internal.

Do you see my confusion?

You are part right, once you have sized the airplane to hold all that stuff, just taking it out won't magically get you 30mph.
But as X XBe02Drvr has said, there is a lot of internal drag associated with the installation.
How much rearranging of the internals of an F4F-3/4 you are going to have to do is also subject to question or interpretation.
On the F4F-3/4 the intercoolers were in front of the wheel wells and exhausted into them. The wheel wells and retracting mechanism take up a fair amount of the fuselage behind the engine. There is a 117 gallon fuel tank under the pilots seat but it is narrow enough to allow the pilot to look down past it and out through a small window (or 2?) on each side. How useful this was I have no idea. there was a 27 gallon or larger reserve tank behind the cockpit but low in the fuselage. radio equipment took up some of the space in the rear of the plane

The P-43 is supposed to have carried it's fuel in the wing/s in integral tanks (which leaked) I have no idea if they were one foot apart or several feet apart were the exhaust pipe ran along the belly of the plane.

Photo of P-35 refueling.

Not saying you can't run the exhaust pipe underneath the fuel tank/s in the Wildcat but it may require smaller tanks or another tank added someplace else?

Just about every American turbo (P-47 excepted) was mounted a number of feet from the engine and with an exposed exhaust pipe. Speculating it was to reduce the temperature of the exhaust gases before they reached the turbo. Routing the exhaust pipe past/through the landing gear and fuel tanks may not be insurmountable but harder than on the P-43. Getting cooling air for rear mounted intercooler and getting the air back to the engine may require a lot of stuff to be relocated.

Take a look at a cutaway of the wildcat. there really wasn't a lot of empty space in in the fuselage.

P-43 had both the fuel and the landing gear in the wings.

 

[pinsog]

Surely you're looking for low altitude performance only to combat incoming Jap attack aircraft maybe even Kamikaze. The turbo is unnecessary.

I missed your post. I agree that attacks in carriers weren't 'high altitude' as such, but divenombers might approach above 12,000 feet with Zero's above that. The turbocharger would give 200 more hp at 12,200 feet than the F4F-3 had in real life, 1200 hp vs 1000. (100 hp extra SL-5500, 150 hp extra from 5500-12,200, 200 hp extra from 12,200-19,000, 340 hp extra at 25,000) Also vastly increase climb rate at all altitudes.

The real question is at what level does extra hp overcome drag? How much extra drag would there be? Etc

I tend to lean toward 100 extra hp at SL would overcome extra drag and top speed would at least remain the same. One or 2 very knowledgeable people are at least questioning that idea if not completely disagreeing. I hope my questions can help them explain to all of us what their theories are so we can all benefit

 

[Kevin J]

I missed your post. I agree that attacks in carriers weren't 'high altitude' as such, but divenombers might approach above 12,000 feet with Zero's above that. The turbocharger would give 200 more hp at 12,200 feet than the F4F-3 had in real life, 1200 hp vs 1000. (100 hp extra SL-5500, 150 hp extra from 5500-12,200, 200 hp extra from 12,200-19,000, 340 hp extra at 25,000) Also vastly increase climb rate at all altitudes.

The real question is at what level does extra hp overcome drag? How much extra drag would there be? Etc

I tend to lean toward 100 extra hp at SL would overcome extra drag and top speed would at least remain the same. One or 2 very knowledgeable people are at least questioning that idea if not completely disagreeing. I hope my questions can help them explain to all of us what their theories are so we can all benefit

Compare the single stage XP-41 (323 mph) and turbo Lancer (356 mph) the single stage F4F-3A (312 mph), the two stage F4F-3 (331mph). The Vultee Vanguard with a single stage engine did 340 mph at 20000 feet, 358 with the two stage engine of which very few were available in 1941. By Pearl Harbour only one carrier had Wildcats. As I see it, the best you'll get out of a turbo Wildcat at altitude is 343 mph which is 12 mph more than the F4F-3 at an altitude that is not required and with added complexity.

 

[pinsog]

Compare the single stage XP-41 (323 mph) and turbo Lancer (356 mph) the single stage F4F-3A (312 mph), the two stage F4F-3 (331mph). The Vultee Vanguard with a single stage engine did 340 mph at 20000 feet, 358 with the two stage engine of which very few were available in 1941. By Pearl Harbour only one carrier had Wildcats. As I see it, the best you'll get out of a turbo Wildcat at altitude is 343 mph which is 12 mph more than the F4F-3 at an altitude that is not required and with added complexity.

I brought up the P66 Vanguard once and they pointed out it was a much smaller aircraft than the Wildcat or the P36.

The XP-41 vs P43 Lancer is a great example, The F4F-3A vs F4F-3 is another great example.

I'm showing turbocharged Wildcat at more like 350+ at 19,000 feet. 10 mph faster down low (all depending on increased drag). I guess whether 20 mph extra is worth it depends on if your 10 mph faster or 10 mph slower than the pursuing Zero. You'll also gain quite a bit of climb over the whole range.

You gain some complexity with the turbo, but you gain complexity with a Hellcat and Corsair as well. A bit of complexity along with 20 mph extra might keep you from getting killed

 

[pinsog]

Does anyone have any data on the XP-41? That might be a good way to compare single stage vs turbocharged engines at SL-10,000 feet in the same airframe.

 

[pinsog]

Shortround and Xbe02Drvr, I'll be back later to pick your brains. Going to be busy most of the day.

Shortround, I agree with your 'shifting stuff around to fit turbo inside F4F-3'. I said back on page 6 or 7 that this would have needed to be done probably on the prototype, although I feel pretty sure it would fit, if done at the beginning.

Please think about this, would a P47 gain any speed at SL if turbo and intercooler were removed and air intake for turbo and intercooler were removed?

 

[Reluctant Poster]

I thought it was the exhaust pipe driving the turbine and I also agree that they were trying to cool it as much as possible and the exposed pipe was probably as easy/cheap/power free way of doing it as they could come up with.[/QUO


The exposed pipe may have been cheap and easy but it can't have been very effective. The surface area is too small to have an appreciable cooling effect. Look at a your car radiator and calculate the surface area of all those fins. In addition it must have had a disastrous effect on the aerodynamics. The P-47 installation is much better aerodynamically it wasn't just moved inside for aesthetics. The typical American practice of hanging the turbocharger in breeze was not a good idea. It may not have been too critical for bombers cruising at 160 mph but for fighters it would affect performance.
The other thing to note is that turbulent flow is what you want for heat transfer but not what you want for drag. I've always been surprised that the leading edge intercooler of the P-38 worked at all.

 

[Shortround6]

Compare the single stage XP-41 (323 mph) and turbo Lancer (356 mph) the single stage F4F-3A (312 mph), the two stage F4F-3 (331mph). The Vultee Vanguard with a single stage engine did 340 mph at 20000 feet, 358 with the two stage engine of which very few were available in 1941. By Pearl Harbour only one carrier had Wildcats. As I see it, the best you'll get out of a turbo Wildcat at altitude is 343 mph which is 12 mph more than the F4F-3 at an altitude that is not required and with added complexity.

We seem to have a lot of confusion here between singe stage engines, two stage engines and turbo engines.
This is not helped at all by some sources that should know better confusing the different engines.

The XP-41 is listed by the "National Museum of the Air Force" as using a turbo supercharger. However they also say the engine was a R-1830-19 which P & W lists as a mechanical two stage engine. So which is it?

I would also note that the -19 engine was rated at 1200hp for take-off but for 1050hp at 4,000ft, 1050hp at 11,000ft and 1050hp at 17,500ft all at 2550rpm.
The -19 engine was also supposed to have flown in a Hawk 75.

Seversky had two prototypes at the 1939 fighter trials. One with a turbo (the AP-4, later P-43) and one with the two stage mechanical engine (AP-2, later XP-41).
Please note that this 2 stage R-1830 may have differed considerably from later 2 stage engines. A written description and photographs of the outside of the Curtiss plane (and P & W patent drawings?) show (or indicate) the auxiliary stage laying horizontal in bottom of the fuselage behind the engine unlike the later 2 stage engines where the aux stage is vertical and in the same housing as the primary supercharger. None of this is conclusive without better evidence.
There are plenty of photos floating around with the wrong captions.

The Vultee Vanguard never got a two stage engine. All of them seem to have gotten 2 speed single stage engines.

 

[Shortround6]

Does anyone have any data on the XP-41? That might be a good way to compare single stage vs turbocharged engines at SL-10,000 feet in the same airframe.

Unfortunately any data may be in archives, a lot of what is published seems to have been "extracted" from charts/graphs. I tend to doubt very highly that a variety of planes ALL hit their max speed at 15,000ft for example even though that makes a good basis for comparison. Some may have been a bit faster just under 15,000ft and some a bit faster just over 15,000.

A lot of charts showed speeds in 5,000ft increments of altitudes.
Also as noted the XP-41 may have used a two stage mechanical engine but a very early one and perhaps not comparable to the ones used in the F4F.