Why didn't the P&W 1830 get WEP?

[Shortround6]

You could very well be correct. But just looking at the figures P & W didn't get much more out of the supercharger even on the later engines. the 1350hp R-1830 was only good to 2000ft. using the same gear ratio. The R-2000 engine was good for the 1450hp to 1000ft at 2700rpm and some engines were rated at 1450hp at 2800ft at 2800rpm. Extra rpm got better altitude or typo?

 

[tomo pauk]

IIRC the proper term for the curved impeller vanes was 'parabollic vanes', and can be recognised on this picture; please note that this is a C series V-1710 - ie. early version. The carb is connected to the impeller by just an elbow, nothing messes the airflow between the carb and impeller.
The R-1830-64 (= late model) with straigth impeller vanes (cutaway) - a nod for the V-1710. The carb is above the accesory case, and there is a shaft and it's shroud going through the airflow - another nod for the V-1710.

 

[GregP]

Hi Tomo,

I am aware of the ariframes that used the engine, but after the Wildcat, we didn't build an R-1830 fighter. The U. S. A. didn't fly the P-36 during the war much, we didn't buy the P-43, and we didn't fly any Australian airplanes much. I was thinking of mass-produced fighters designed or a new variant after we got into the war. The only one that comes to mind is the FM-1 / FM-2, and we made relatively few of them. If I recall, we made about 5,928 out of some 100,000 fighter manufactured during the war.

However, you are certainly correct that we DID make R-1830-powered fighters. But I think we put a LOT more R-1830s into B-24s.

 

[swampyankee]

I think the R-1830 could have made considerably more power as it had a greater piston area than did the Curtiss-Wright R-1820, and at 2700 rpm, was running a lower piston speed than did the CW engine at 2200.

Without knowing more about what was going on, I can't be definitive, but I suspect that the reason was that the customers -- dominantly, the US government -- didn't see a need for a more powerful variant. Pushing things to the same level as the R-1820, which was a contemporary engine of very similar technological level, it's not extreme to think that the R-1830 could have been pushed to 1700 (with the same ratio of horsepower to cylinder surface area) to 1900 hp (with the same ratio of horsepower to piston area). I suspect that, during the war, the government -- the guys who were writing the checks -- felt that P&WA needed to spend much more effort on development of the R-2800 and, towards the end of the war, the R-4360.

As an aside, pushing both parameters to the same level as the R-2800, the R-1830 could have been pushed to nearly 2000 shp.

 

[wuzak]

I think the R-1830 could have made considerably more power as it had a greater piston area than did the Curtiss-Wright R-1820, and at 2700 rpm, was running a lower piston speed than did the CW engine at 2200.

Without knowing more about what was going on, I can't be definitive, but I suspect that the reason was that the customers -- dominantly, the US government -- didn't see a need for a more powerful variant. Pushing things to the same level as the R-1820, which was a contemporary engine of very similar technological level, it's not extreme to think that the R-1830 could have been pushed to 1700 (with the same ratio of horsepower to cylinder surface area) to 1900 hp (with the same ratio of horsepower to piston area). I suspect that, during the war, the government -- the guys who were writing the checks -- felt that P&WA needed to spend much more effort on development of the R-2800 and, towards the end of the war, the R-4360.

As an aside, pushing both parameters to the same level as the R-2800, the R-1830 could have been pushed to nearly 2000 shp.

You are assuming the R-2800 at 2800hp? Only a few very late war models achieved that.

You are also assuming that the required cooling could be achieved on the R-1830.

 

[swampyankee]

You are assuming the R-2800 at 2800hp? Only a few very late war models achieved that.

You are also assuming that the required cooling could be achieved on the R-1830.

Yes, to both questions. I also realize that the late-war R-2800 had very little commonality with the early war engines. I certainly think those values could have been reached with development -- these were extrapolated using power/area values for the R-1820 and the R-2800 -- but I think that the development was simply not done, as the engine was too small for a modern front-line fighter. I also suspect that the R-1830 was not much less labor-intensive to build than was the R-2800, and more expensive to build than the R-1820, so for second-line aircraft, like the FM-2, the Wright engine would be preferred. The R-2800 was probably one of the one or two most advanced piston engines built by anybody during the war.

As an aside, the two areas I used were total piston area, which is simple geometry, and the equivalent "wall area," which is stroke times bore times pi.

 

[Shortround6]

Please look at cruising powers or max continuous powers rather than WEP power of late model R-2800 engines. The R-2800 was NEVER rated at more than 2800hp in service. Granted that is prop shaft power and not power in the cylinders which is the actual cooling problem. Also please note that the R-2800 "C" which was the engine that made 2800hp (a record for air cooled radial engines as far as power per unit of displacement ) was a totally new engine that shared only the bore and stroke with the "B" series engines (which could make around 2500hp in similar conditions).
The "C" series engine used aluminium cylinder barrels with steel liners instead of single piece steel cylinders. Cylinder heads were forged instead of cast with deeper, closer spaced fins. New pistons on new connecting rods on a new crankshaft running in a new crankcase.
And they ONLY got those power levels by using a turbocharger. The turbo, being powered by the exhaust gases, freed up several hundred (if not 300 or more) horsepower to go to the prop instead of driving the second stage or high gear of a 2 speed supercharger.

To make an R-1830 that made much over 1300hp you would have to do the same thing, Throw out everything and build a new engine using all new parts and new manufacturing techniques. And in the end what have you got?
The R-2800 B engine used in an early P-47 was good for about 1625hp max continuous. The max cruise using lean mixture was 1200hp. The "C" series engines with their better cooling (difference in fins/baffles) could improve on those somewhat
Post war Commercial C15 engine was good for:
2100hp take-off dry and 2400hp take-off wet using 13lb boost at 2800rpm.
1700hp at 16,000ft at 2800rpm in high gear (a lot of power to drive supercharger and losses due to higher intake temperature)
1700hp normal at 7300ft in low gear at 2600rpm
1500hp normal at 17,500ft at 2600rpm.
1150hp max cruise at 13,000ft at 2250rpm.

Now please note that normal was really max continuous and required rich mixture. These would be the power levels used by airliners or bombers for climb once the landing gear was retracted. Then throttled back to max lean cruise or lower for flight.

Now to understand why the 1830 went nowhere lets use the above power levels adjusted to an engine of 1830 cubic inches and using the same power per cubic inch.
1570hp for take-off wet.
1375hp for take off dry. (Hmmmm. 1350hp take-off R-1830s were built)
1375hp at up to 3000ft in low gear. military (the 1350HP engines could hold it to 3900ft)
1110hp at 16000ft in high gear. (late R-1830 could make 1100hp at 13,500ft) military (older engines could make 1050hp at 13,100ft)
1110hp at 7300ft normal (late R-1830 could make 1100hp at 8200ft) low gear
720hp cruise (lean) at 13,000ft. (standard R-1830 was good for 700hp at 12,500ft).

Problem with a hot rodded R-1830 is that is does very little for transports and bombers and in fact might cut into payload by being heavier. The 1350hp take-off R-1830 with single stage two speed supercharger was about 30lbs lighter than an R-1830 with two stage supercharger and and about 70lbs heavier than a 1200hp R-1830.
The 1350hp R-1830s used forged heads and the same aluminium barrel/steel liner as the "C" series R-2800. a few other things may have trickled down as well.
Without thrashing the engine (running at higher RPM) the hot rodded R-1830 doesn't offer much over the standard version. A reason P & W went with the R-2000 and tried for the R-2180?

How much work would be needed to design an R-1830 running at higher rpm to equalize the piston speeds (and how much more would it weigh?)

 

[wuzak]

How much work would be needed to design an R-1830 running at higher rpm to equalize the piston speeds (and how much more would it weigh?)

The R-1830 would need to rev to 3055rpm to have the same piston speed as the R-2800 at 2800rpm.

 

[Shortround6]

An R-1830 running at 3055rpm would have about 18.6% more stress on the crank and reciprocating parts as an R-1830 running at 2800rpm (the 1350hp version) or about 27.6% more stress than an R-1830 running at 2700rpm.
The stress going up with square of the speed is a real problem with high rpm aircraft engines. It is also a real problem in that it changes and adds to the vibration problems.
It could have done, but would it have been worth the effort?
P & W went to the R-2180 to get more power than the R-2000 rather than try for more RPM. R-2180 used parts from the R-4360 so it was cheaper but since the R-4360 used pretty much R-2800 cylinders there were a lot of common 'basic' items that might have been finished off different in final stages.
R-2180 ran at 2800rpm and weighed 1900lbs for a 14 cylinder engine.
A high rpm R-1830 might use few, if any parts (aside from nuts and bolts) common to the older R-1830s.

 

[swampyankee]

The premise was an increased rating for short-term use in combat aircraft, not a long-term rating for commercial aircraft.

Uprating the R-1830 to the same output as the Wright R-1820 is likely to have been fairly straight-forward, but, during WW2, the R-1830 was primarily being used on transports and bombers, which may have needed more takeoff power, but would not have benefited from a WEP rating; this means that the two wartime customers (or at least totally dominant customers) for the R-1830 would not fund any development to get a much higher rating, especially as P&WA's engineers were fully committed on other projects.

 

[Piper106]

I think that the Navy would have welcomed a 1500 or 1550 HP water injection version of the R-1830 for the PB4Y to help with overload take-offs at the beginning of long patrol missions. That could have been done by turning up the boost at 2800 rpm. The hard work for the P&W engineers would have been strengthening the engine to hang together, plus going to a forged cylinder head with machine cut fins (just like the C series R-2800s) to dissipate the extra heat. .

 

[Shortround6]

I think you are both over estimating the amount of safety margin in the R-1830 or the amount of "room" between the service ratings and possible failure.
Quite possibly P& W could have "Uprated" the R-1830 like Wright did with the R-1820. Just build a new engine keeping the old bore and stroke. The "H" series engines were the ones rated at 1300 and up. the "G-200" were the ones that stopped at 1200hp for take-off.
The G-200s were good for 2500rpm take-off and military (at low level) and weighed about 1320lbs with a two speed supercharger.
The 737C9HD1 was good for 1425hp take-off at 2700rpm and went 1360lbs
The 955C9HE1 was good for 1525hp (wet) take-off at 2800rpm and went 1420lbs. It was a post war engine and didn't show up until 1947. There was a version that could make 1525hp dry but needed 115/145 fuel.
On the FM-2 Wildcats the early ones used a a version that was good for 1300hp (the R-1820-56) at 2600rpm but later ones got the R-1820-56A with a new crankshaft that allowed 2700rpm and 1350hp.
I have said it before, the H series engines got a new crankcase, new cylinders, new cylinder heads, new pistons, new connecting rods and new everything else. You cannot put H series cylinders on a G-200 crankcase as they use a different number of bolts to hold the cylinder to the crankcase.

radial engines really hate overspeeding. with 7 or 9 sets of pistons and connecting rods acting on one crank throw things can get real nasty real fast. The R-1820 had two roller bearings. The R-1830 had 3 roller bearings to start. Some may have gotten plain bearings, the R-2000 used plain bearings. A V-12 has 7 main bearings, one between each pair of cylinders.
Just about every large radial that increased rpm by even 100rpm required a different model or series with sometimes very major alterations/modifications.
The 1350hp very late war R-1830s did use cylinder construction like the R-2800. The two speed engines were used in navy P4Y-2 Privateers.

In order to get a major increase in WEP you need excess supercharger capacity. The R-1830 didn't have a lot of excess capacity.
It was running at 48in or 9lbs of boost just to get 1200hp at 2700rpm. An Allison with 8.8 supercharger gears was getting 1150hp take off at 44.5in of boost. the Allison had all kinds of excess supercharger capacity at low altitude.

I would note that the R-2800 made 2000hp using 52in maniflod pressure but it could only hold 52in to 1500ft (yes 1500 ft ) using the engine mounted single stage supercharger. In other words just fiddling the boost control was going to get you very little. The P-47 could get major increases in WER power by closing the by-pass valve on the turbo charger and using the turbo to deliver pressurized air to the carb. This solved the "lack" of supercharger capacity very handily (although at the cost of the turbo, intercoolers and ducting.)
The two stage engines never reached the power level of the P-47 because they needed hundreds of horsepower to drive the extra stage.
For example a P-47 could make about 2300hp or bit over using 56in of maniflod pressure at the standard 2700rpm.(it depends on altitude) while an F4U-1 could make only 2135hp at similar altitudes (10-15,000ft) using low gear on the auxiliary supercharger to get 59in pressure. About 200 less horsepower using 5% more manifold pressure.
You run into the cooling problem, the F4U was making more power in the cylinders. it just need around 300hp of that power to drive the supercharger. But the F4U is going to need as much or more cooling than the P-47.

For hot rod R-1830s you need not only a stronger engine with better cooling, you need a much larger, more complicated supercharge system