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

[Shortround6]

Now turbocharged cars are ubiquitous.

Difference is that the engine driven supercharger on some of those aircraft engines was delivering 7-9lbs of boost several thousand feet above sea level. They could deliver more boost than the fuel would support without knocking or detonating.

So in those days turbocharging was only/primarily used to get sea level performance at altitude?

That was the Army's goal. Please remember that the US Army had been working with turbo-chargers since the late 20s. Fuel may have been 70-77 octane. The early engines had no engine driven supercharger. AS fuel got better and the engine makers added or improved the superchargers on their engines (on some 1920s radials they were actual called mixing fans to improve the distribution of fuel and increase atomization rather than really increase boost). The US went to 100 octane fuel before anybody else but due to an insistence not to use aromatic compounds it was pretty much 100/100 fuel and not 100/130. This limited the amount of boost that could be used (still better than 87 octane) even running rich.

The Early P-38s used 6.44 supercharger gears instead of the 8.80 gears to get more take-off power and used the turbo to get altitude performance even in the teens that they would have lost compared to the "altitude rated" engines with their 8.80 gears. The P-38F switched to 7.48 gears and the P-38H went to 8.10 gears. But by that time the P-40s and P-39s were using 9.60 gears. This is one reason the "military power" of the P-38 engines was always higher than the non-turbo engines of the same time period. They were using the turbo to make for the lower pressure of the engine powered supercharger. By spinning the supercharger slower it took less power leaving more power available to drive the propeller.
The radial engines were rarely geared (supercharger wise) for even medium altitude performance. The R-1830 and R-1820 during 1939-1942 could only hold 1200hp to around 3-5000ft.
By changing gears you could get more power in the low teens but on a single speed engine that meant giving up 100hp or more for take-off/low altitude to prevent detonation.
The turbo R-1830, R-1820, R-2800 engines all used the lowest the supercharger gear the company offered in order to get the best take-off/base line performance.

10/130 fuel changed things.

Of course geared supercharger were already used to enhance sea level performance, when did things change and turbochargers get unleashed at low level?

The turbos got "unleashed" once;
A) better materials were used in the basic engines.
B) 100/130 fuel became wide spread (for the US this meant sometime in 1942, plans for "hot rod" aircraft have to take into account that the fuel development was faster than either engine development or airframes).
C.) WEP ratings were approved (trading increased maintenance and shorter engine life for increase performance)
D) Water injection was introduced to allow even higher boosts than 100/130 fuel would allow on the air cooled engines.
E) 1944, the introduction of 100/150 fuel along with water injection on the P-47s.

trying to used turbo on an R-1830 in 1940-41 to bump up the pressure at low altitude fails at least 3 of those conditions. Perhaps they could have OKed a higher power setting and gotten less engine life. but the increase would not have been as large with the poorer fuel and the maintenance and blown engines would have been higher. Water injection might have seen a quicker service introduction (jimmy Doolittle was fooling around with it in the early 30s) but I don't know how far the experiments were from service introduction.

 

[Conslaw]

Difference is that the engine driven supercharger on some of those aircraft engines was delivering 7-9lbs of boost several thousand feet above sea level. They could deliver more boost than the fuel would support without knocking or detonating.



That was the Army's goal. Please remember that the US Army had been working with turbo-chargers since the late 20s. Fuel may have been 70-77 octane. The early engines had no engine driven supercharger. AS fuel got better and the engine makers added or improved the superchargers on their engines (on some 1920s radials they were actual called mixing fans to improve the distribution of fuel and increase atomization rather than really increase boost). The US went to 100 octane fuel before anybody else but due to an insistence not to use aromatic compounds it was pretty much 100/100 fuel and not 100/130. This limited the amount of boost that could be used (still better than 87 octane) even running rich.

The Early P-38s used 6.44 supercharger gears instead of the 8.80 gears to get more take-off power and used the turbo to get altitude performance even in the teens that they would have lost compared to the "altitude rated" engines with their 8.80 gears. The P-38F switched to 7.48 gears and the P-38H went to 8.10 gears. But by that time the P-40s and P-39s were using 9.60 gears. This is one reason the "military power" of the P-38 engines was always higher than the non-turbo engines of the same time period. They were using the turbo to make for the lower pressure of the engine powered supercharger. By spinning the supercharger slower it took less power leaving more power available to drive the propeller.
The radial engines were rarely geared (supercharger wise) for even medium altitude performance. The R-1830 and R-1820 during 1939-1942 could only hold 1200hp to around 3-5000ft.
By changing gears you could get more power in the low teens but on a single speed engine that meant giving up 100hp or more for take-off/low altitude to prevent detonation.
The turbo R-1830, R-1820, R-2800 engines all used the lowest the supercharger gear the company offered in order to get the best take-off/base line performance.

10/130 fuel changed things.



The turbos got "unleashed" once;
A) better materials were used in the basic engines.
B) 100/130 fuel became wide spread (for the US this meant sometime in 1942, plans for "hot rod" aircraft have to take into account that the fuel development was faster than either engine development or airframes).
C.) WEP ratings were approved (trading increased maintenance and shorter engine life for increase performance)
D) Water injection was introduced to allow even higher boosts than 100/130 fuel would allow on the air cooled engines.
E) 1944, the introduction of 100/150 fuel along with water injection on the P-47s.

trying to used turbo on an R-1830 in 1940-41 to bump up the pressure at low altitude fails at least 3 of those conditions. Perhaps they could have OKed a higher power setting and gotten less engine life. but the increase would not have been as large with the poorer fuel and the maintenance and blown engines would have been higher. Water injection might have seen a quicker service introduction (jimmy Doolittle was fooling around with it in the early 30s) but I don't know how far the experiments were from service introduction.

Jimmy Doolittle's work for Shell Oil - as a champion for 100-octane fuel, probably did more for the allied war effort than the raid on Tokyo.

 

[Csch605]

The USN had considered the P-36 for potential naval service, but not the P-40.

On the otherhand, they did consider and evaluate a P-39 (XFL-1).

The XFL-1 was a response to the USN's 1938 request for a replacement for the current aircraft in service - it may be of interest that of the companies that responded (Bell, Brewster, Curtiss, Grumman, Vought) only three contracts were awarded: Bell (XFL-1), Grumman (XF5F) and Vought (XF4U). All three prototypes first flew in 1940 and all three were over the 350 mph mark.

View attachment 365172

Without the 37 mm this thing does not scare me one bit. Looks like a scared puppy. Although she is really clean and quick looking.

 

[pinsog]

I'm not sure about diameter of the piping, however, there was the XF4F-5, with R-1820 + turbo. Seems like the B-17Bs were delivered with similar powerplant from second half of 1939 on - 1200 HP up to 25000 ft. No problems encountered when flying to Brazil and back (in several 'hops', of course).
Might be an interesting read: link

Tomo pauk, quick question, where was the turbo installed on the XF4F-5?

 

[GrauGeist]

Two F4F-3s were held back as the XF4F-5 and each one was tested with a supercharged engine.

BuNo 1846 was fitted with a turbo-supercharged R-1820-54 engine and BuNo 1847 was fitted with a two-stage supercharged XR-1820-48 engine.

 

[pinsog]

Two F4F-3s were held back as the XF4F-5 and each one was tested with a supercharged engine.

BuNo 1846 was fitted with a turbo-supercharged R-1820-54 engine and BuNo 1847 was fitted with a two-stage supercharged XR-1820-48 engine.

Do you have any idea where they put the turbocharger on #1846?

 

[ThomasP]

Hey Shortround6 & pinsog,

re: Military rating for the R-1830 2-stage at altitude

There is a NACA test report on the R-1830-86 2-stage as used in the F4F floating around somewhere on the internet (my apologies for not being able to provide a link but I ran across it several years ago, before I ever planned to post on this site). I believe the test was titled "Calibration of the P&W R-1830-86 engine" or something very close to that.

In the report it talks about the changes incorporated to increase the power (to 1100 BHP) at altitude (from memory somewhere around 18K ft) using UK 100/130 equivalent fuel (i.e. having a high aromatic content). The date of the test was early-1943, before(?) widespread availability of the US equivalent fuel grade using alkylates. Again, if my memory is correct, the engine tested was modified with a new carburetor and fitted with 'C' type cylinders (i.e. a modified design with increased cooling area similar to the type used on the 'C' series R-2800 and R-2600 engines). There did not seem to be any problem obtaining the power, at least under test conditions, and NACA recommended adoption of a 1100 BHP at altitude Military rating.


re: 2-stage BHP vs turbo BHP

Although this only an educated guess on my part, I suspect that the difference in BHP between the mid-war R-1830 installations on the B-24 with turbo (1200 BHP) and the F4F-3 &-4 (1100 BHP) indicates that the difference in BHP absorbed by the installations at altitude was about 100 BHP??


re: cooling problems on the R-1830-76 and -86

My understanding relative to the F4F fitted with the R-1830-76 & -86 2-stage engine was that the primary problem was cooling under sustained high power settings. The Normal power ratings (as I am sure you are already aware) were 1100/1050/1000 BHP from SL to 19,500 ft. The reason for the very poor climb rates of the F4F-3 & -4 in service was that the early engines (without the 'C' type cylinders) could only sustain about 930 BHP for more than a few minutes under climb conditions due to overheating. This is why we see the reduction in the Grumman F4F-3 Detail Specification estimate/guarantee climb rate from 3300-3070 ft/min to 1890 ft/min in service, and the F4F-4 Detail Specification having an estimate/guarantee of only 1690 ft/min.

 

[Shortround6]

In the report it talks about the changes incorporated to increase the power (to 1100 BHP) at altitude (from memory somewhere around 18K ft) using UK 100/130 equivalent fuel (i.e. having a high aromatic content). The date of the test was early-1943, before(?) widespread availability of the US equivalent fuel grade using alkylates.

By early 1943 the US and Britain were on their 3rd joint specification for 100/130 fuel. The first called for much increased (over US standards) use of aromatic compounds and up to 3cc of lead (per US gallon), the 2nd allowed for up to 4.6cc of lead per gallon and little or no change in aromatics from the first specification. The 3rd held at 4.6 cc of lead but allowed different aromatics to be used. It was this 3rd specification that caused trouble with the engines in the P-38s. BY 1943 which may have been when the report was written(?) (but actual testing down months earlier?) US fuel was equivalent to British fuel, individual refineries fuel could differ but ALL aviation fuel was being made to the same specifications.

the engine tested was modified with a new carburetor and fitted with 'C' type cylinders (i.e. a modified design with increased cooling area similar to the type used on the 'C' series R-2800 and R-2600 engines).

There were some R-1830 engines built near the end of war that were rated at 1350hp for take off. I don't know about the carburetors but the cooling fin arrangement was changed. Quite possibly to something similar to the R-2800 C series. These engines seem to show up mostly on P4Y-2s (or C-87s) as single stage two speed engines. There were also allowed to run at 2800rpm instead of 2700rpm which doesn't make power comparison any easier. A few may have showed up in B-24Ns with turbos.

The R-2600 (and late R-1820s) got better cooling fins but they used a different method of construction, the fins were sheet metal and pressed into place in grooves in the cylinder barrel.
P&W was using forged/machined fins on the cylinder barrel. The late R-1830s got their fins on a muff or jacket that was slid over the cylinder wall, as did R-2800s (THE "C" got more/larger fins).

 

[tomo pauk]

Tomo pauk, quick question, where was the turbo installed on the XF4F-5?

By the look at pic found at the 'America's hundred thousend' book pg. 472, my best guess is that it was installed just behind the engine.

...
re: 2-stage BHP vs turbo BHP

Although this only an educated guess on my part, I suspect that the difference in BHP between the mid-war R-1830 installations on the B-24 with turbo (1200 BHP) and the F4F-3 &-4 (1100 BHP) indicates that the difference in BHP absorbed by the installations at altitude was about 100 BHP??

Difference at 25000 ft was probably more than 300 HP, where the turboed R-1830 was still rated for 1200 HP military power.

re: cooling problems on the R-1830-76 and -86

My understanding relative to the F4F fitted with the R-1830-76 & -86 2-stage engine was that the primary problem was cooling under sustained high power settings. The Normal power ratings (as I am sure you are already aware) were 1100/1050/1000 BHP from SL to 19,500 ft. The reason for the very poor climb rates of the F4F-3 & -4 in service was that the early engines (without the 'C' type cylinders) could only sustain about 930 BHP for more than a few minutes under climb conditions due to overheating. This is why we see the reduction in the Grumman F4F-3 Detail Specification estimate/guarantee climb rate from 3300-3070 ft/min to 1890 ft/min in service, and the F4F-4 Detail Specification having an estimate/guarantee of only 1690 ft/min.

I'd say that problem with F4F trying to climb was that it was too much of an airplane for the R-1830 to haul around, especially the fully navalized F4F-4 with 6 heavy MGs and full protection for pilot and fuel. Such a big and heavy aircraft needed perhaps 50% more power to climb well and fly fast.

 

[pinsog]

By the look at pic found at the 'America's hundred thousend' book pg. 472, my best guess is that it was installed just behind the engine.



Difference at 25000 ft was probably more than 300 HP, where the turboed R-1830 was still rated for 1200 HP military power.




I'd say that problem with F4F trying to climb was that it was too much of an airplane for the R-1830 to haul around, especially the fully navalized F4F-4 with 6 heavy MGs and full protection for pilot and fuel. Such a big and heavy aircraft needed perhaps 50% more power to climb well and fly fast.

I have that book. Thank you. Found it.

If the turbocharger will survive the heat of the exhaust that powers it while being that close, then adding a turbocharger would have been very simple and could have been done anytime very easily with virtually no modification. Just a bit of sheet metal work from the firewall forward along with new mounts etc.

 

[ThomasP]

Hey guys,

I found the NACA document I mentioned above. The full title is "Calibration of Pratt & Whitney R-1830-86 Engine" and the link is:

"https://apps.dtic.mil/dtic/tr/fulltext/u2/a800376.pdf"


Hey Shortround6,

The dates of the test were from 6 March 1942 to 21 April 1942. My understanding is that that was about the time that the US started testing the ~final blend(s?) of 100/130 grade fuel similar to the UK ~final 100 octane blend(s?), but I do not for sure.

The report identifies the fuel type as having 20% aromatic content, and compares the results (in a very general way in one paragraph) to those using AN-VV-F-781-4. I find the wording "with regular Specification AN-VV-F-781-4 and approximately 16 percent aromatic 100 octane fuels" (page 4 paragraph 5) confusing. I can not tell if this refers to 2 or more different fuel specifications (i.e. AN-VV-F-781-4 AND 16% aromatic fuels) or if AN-VV-F-781-4 has 16% aromatic content?? Also I do not know for sure which of the different specifications fits a 20% aromatic content, if any, although I remember reading that the one of the standard UK 100 octane blends (100/130 grade) used this content. If you have any idea I would appreciate the info.

Unfortunately the report does not specify the exact mods to the cylinders to aid cooling (i.e. muffs, fins, heads, cylinder sleeves, etc.).