don4331
Senior Airman
Retract the tail wheel for a few mph?
Can we make a faster better performing Wildcat in 1942?
- Thread starter Wild_Bill_Kelso
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Wild_Bill_Kelso
Senior Master Sergeant
- 3,231
- Mar 18, 2022
Four guns and 300 rounds each could maybe allow for a bit more fuel and / or improve climb rate a fair amount and speed a little.
I still say you can take 6" off of each wing and that will help some too.
The best mileage may come from some improvement to the supercharger so you are getting closer to full power at higher altitudes.
I still say you can take 6" off of each wing and that will help some too.
The best mileage may come from some improvement to the supercharger so you are getting closer to full power at higher altitudes.
Shortround6
Major General
Cutting the ammo to 300 rounds would improve climb a bit (around 150lbs) but no real change in speed. If you put in bigger fuel tanks the improved climb goes away and really, 160lbs is only 25 gallons US.
6in of wingspan clip may be the same as washing and polishing the wing.
Seriously. They cut 2 ft off each side of the Spitfire and only gained about 5mph at low altitude. Lost a few mph at high altitude, cross over point was around 20,000ft ?
There was something going on with the Supercharger and/or cooling in the F4F-4. P&W never gave it a "Military rating" and in some manuals they didn't allow the 2700rpm limit for the engine for anything except take-off. Flight limits are 2550rpm and lower pressure than used for take-off. I wonder if they could not keep the engine cool when running the Aux supercharger? In high gear the engine was using perhaps 150hp to drive the Aux supercharger and the intercooler/s may not have removed all the heat.
A better supercharger might have helped a bit. But the US was a bit behind the curve in actual supercharger design. P&W got there but it took a while (1944?)
ThomasP
Senior Master Sergeant
There was some design study done on the F4F with an improved 2-stage SC for the R-1830. I do not think it went very far as they realized that they would have to increase the length of the forward fuselage to accommodate the new SC unit and have to increase the length of the aft fuselage as well. There were other detail changes as well (like a retracting tail wheel and covered main gear doors), and the sum of the changes along with the delays in production caused them to feel that it was not worth it as most of the fuselage components would be a new design. The wing was pretty much the same as for the F4F-4.
I am going from memory but IIRC the length was increased by ~3 ft (~1 ft forward and ~2 ft aft), with a weight increase of ~350 lbs total for the performance mods. Speed increase at altitude was expected to be ~20 mph vs the standard F4F-4. The improved SC was supposed to allow 1100 BHP (vs 1000 BHP) at altitude. I do not think the article mentioned any of the other performance differences in the R-1830 with the new SC.
I am going from memory but IIRC the length was increased by ~3 ft (~1 ft forward and ~2 ft aft), with a weight increase of ~350 lbs total for the performance mods. Speed increase at altitude was expected to be ~20 mph vs the standard F4F-4. The improved SC was supposed to allow 1100 BHP (vs 1000 BHP) at altitude. I do not think the article mentioned any of the other performance differences in the R-1830 with the new SC.
ThomasP
Senior Master Sergeant
The WWII era R-2180 was not test run until 1945, so maybe too late for this thread?
That would be the 2180E, installed in Europe on an airliner type.
Pre-war type was 2180A, sold with DC-4E in Japan in 1939, plus powering two military prototypes.
ThomasP
Senior Master Sergeant
Huh . . . that's a new one to me.
Shortround6
Major General
The Performance may not have been as good as some people are hoping. It may have done what was claimed, but what was claimed was not what was needed.
Hard to tell as they stopped development early. However the proposed 2 stage supercharged engine went about 200lbs more than engine in the Wildcat.
To kind of point out the problems in supercharger and cooling this engine offered 1150hp at 17,500ft. The Merlin XX offered 1120hp at 18,500ft using a single stage supercharger and no intercooler.
The 2 stage supercharger seems to have weighed about 150lbs. which is about what the turbo would weigh but the turbo needs more volume and plumbing/ducts.
Now maybe you could get the engine up to about 1550hp T-O in late 1942 to match the power per cylinder of the R-2800 but this thing is about the size of an R-2800 with 2 cylinder missing from each row.
Hard to tell as they stopped development early. However the proposed 2 stage supercharged engine went about 200lbs more than engine in the Wildcat.
To kind of point out the problems in supercharger and cooling this engine offered 1150hp at 17,500ft. The Merlin XX offered 1120hp at 18,500ft using a single stage supercharger and no intercooler.
The 2 stage supercharger seems to have weighed about 150lbs. which is about what the turbo would weigh but the turbo needs more volume and plumbing/ducts.
Now maybe you could get the engine up to about 1550hp T-O in late 1942 to match the power per cylinder of the R-2800 but this thing is about the size of an R-2800 with 2 cylinder missing from each row.
SIze does not bother me at all, F4F was to much of an aircraft for the engines it had anyway.
ThomasP
Senior Master Sergeant
Leaving aside the weight difference, the R-2180 early variant was Ø54" and the R-1830 was Ø48" - giving a frontal cross-section of 2290 in2 vs 1810 in2 respectively, or ~26% more area. The increase in drag would negate a significant amount of the increase in BHP. How much additional drag I cannot really estimate as too much depends on the installation. An example of this type of increase in drag, however, is the Grumman XF5F-1. When deciding whether to use the Ø54" R-1820 single-stage or Ø44.2" R-1535 2-stage (2290 in2 vs 1530 in2 respectively), they calculated that the increase in power of the R-1820 (900 BHP) with ~50% more frontal area than the R-1535 (750 BHP) would result in only about 7 mph increase in Vmax - the increase in drag due to the larger diameter installations used up somewhere around 100 BHP per engine.
- Thread starter
- #32
Wild_Bill_Kelso
Senior Master Sergeant
- 3,231
- Mar 18, 2022
This sounds like almost exactly what I was looking for
- Thread starter
- #33
Wild_Bill_Kelso
Senior Master Sergeant
- 3,231
- Mar 18, 2022
Well you can kind of get the best of both worlds out of this. I think 150 lbs would help with climb, and if you burn the outer wing tanks first (or after the fuselage tank maybe) then you'll have the lighter wings again. 25 gallons may be worth the effort.
6in of wingspan clip may be the same as washing and polishing the wing.
Sure... which they rarely did in wartime. Do both if you can, but if you lose the 1' wingspan (6" from both wings) you may get that extra 5 mph, and some other benefits...
They also almost doubled the roll rate with the clipped wing Spitfires. I believe acceleration improved as well.
I think a lot of people believed in the turbo as the leap frog of all the supercharger details, but seeing as they already had a two stage s/c working pretty early, there was room to do more with that.
A switch from R-1535 to the R-1820 drove the frontal area of the nacelle up on the F5F.
On a F4F, fuselage is already too wide, even the R-1820 installed didn't spoiled the lines of the fighter. Frontal area of the fuselage remained the same.
ThomasP
Senior Master Sergeant
True (maybe?).
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don4331
Senior Airman
How poor was the supercharger in R-1830? How much air gets past the landing gear on way out of intercooler? (Corsair with leading edge oil coolers/ducting to intercooler/intercooler exhaust ducting seems a lot more efficient.)
Supercharger in RR Kestrel V was only operating at 37% efficiency (producing 1.5 psi boost), I've read that the compressor in GE turbo was in same range. Elllor and Rubbra's improving efficiency to 65%, then Hooker's follow on to 75% keeps a lot of heat out of the engine.
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- #37
Wild_Bill_Kelso
Senior Master Sergeant
- 3,231
- Mar 18, 2022
This is what I mean. There was room to improve efficiencies, probably. I'm not sure though maybe the internal space in the F4F was just too cramped.
The problem with this is the F4F didn't have enough space to mount a decent intercooler installation* with the R-1830. There's just no way to shove a R-2180 and a turbo in one.
*The intercoolers discharged directly into the front of the wheel wells.
Shortround6
Major General
Few comments on superchargers.
As in it takes 65hp to get the desired airflow and pressure but it takes 100hp to drive the compressor you have compressor operating at 65% efficiency. The problem is where does the other 35hp go? Only 2% or less goes into friction/drag in the supercharger gears. The rest is converted to heat in the intake mixture.
A 75% efficient supercharger would take about 87hp to get the same airflow/pressure (65hp required to do the work) as the less efficient supercharger leaving the engine with 13 more HP going to the crankshaft and a lot power turning into heat, just over 1/3 less. Now this is the extra heat over and above what is going to happen from a strict mathematical formula for the heat of compression.
This does not tell us anything about the airflow or pressure ratio of the supercharger, except that trying to get high boost from a poor supercharger is going to take a lot of power and very hot hot air.
The supercharger on the Kestrel V gave 1.5lbs boost at 14,000 but could give 6lbs at sea level or higher, 6lbs seems to be detonation limit the British were not going to exceed using their 87 octane fuel. The Kestrel V at altitude would run at 2900rpm and used an 8.8 gear ratio on the supercharger, however I have no information (others may have a lot of information) on the impeller size, number of blades, size/shape on the inlet and diffuser vanes/housing.
At any rate Kestrel V at 14,000ft was compressing the air about 1.88 times the standard atmospheric pressure (17.57 in hg/8.63lb/sq/in)
The Kestrel XV at 14,500ft running at 3000rpm and using a 9.4 supercharger gear could give 6lbs and was compressing the air about 2.45 times.
The Merlin III supercharger at 16,250ft had a pressure ratio of about 2.62 (no RAM as are the others). In the late 30s this was as good as it got.
The engine in the F4F-4 was limited to 7.66lbs of boost at 19,000ft.
The F4F may have been limited by it's cooling fins but basically the two stage R-1830 with intercooler roughly equaled the Merlin X/XII single stage supercharger.
One simple chart says that an equal amount of cooling air to intake air to get a 40 degree drop in charge temp, you need 1.5 to 1 ratio to get just over 50 degree drop and a 2 to 1 ratio gets you just over a 60 degree drop.
The R-2800 used higher supercharger pressures but these were intercooled so we don't know what the pressures and temps were between the stages, We do know that the R-2800s were moving a lot more air through the intake system.
You may very well be right about 37% but that seems awfully low. Efficiency of the supercharger is measured by the power it take to compress the air the desired amount by the power it takes to drive the compressor.
As in it takes 65hp to get the desired airflow and pressure but it takes 100hp to drive the compressor you have compressor operating at 65% efficiency. The problem is where does the other 35hp go? Only 2% or less goes into friction/drag in the supercharger gears. The rest is converted to heat in the intake mixture.
A 75% efficient supercharger would take about 87hp to get the same airflow/pressure (65hp required to do the work) as the less efficient supercharger leaving the engine with 13 more HP going to the crankshaft and a lot power turning into heat, just over 1/3 less. Now this is the extra heat over and above what is going to happen from a strict mathematical formula for the heat of compression.
This does not tell us anything about the airflow or pressure ratio of the supercharger, except that trying to get high boost from a poor supercharger is going to take a lot of power and very hot hot air.
The supercharger on the Kestrel V gave 1.5lbs boost at 14,000 but could give 6lbs at sea level or higher, 6lbs seems to be detonation limit the British were not going to exceed using their 87 octane fuel. The Kestrel V at altitude would run at 2900rpm and used an 8.8 gear ratio on the supercharger, however I have no information (others may have a lot of information) on the impeller size, number of blades, size/shape on the inlet and diffuser vanes/housing.
At any rate Kestrel V at 14,000ft was compressing the air about 1.88 times the standard atmospheric pressure (17.57 in hg/8.63lb/sq/in)
The Kestrel XV at 14,500ft running at 3000rpm and using a 9.4 supercharger gear could give 6lbs and was compressing the air about 2.45 times.
The Merlin III supercharger at 16,250ft had a pressure ratio of about 2.62 (no RAM as are the others). In the late 30s this was as good as it got.
The engine in the F4F-4 was limited to 7.66lbs of boost at 19,000ft.
The F4F may have been limited by it's cooling fins but basically the two stage R-1830 with intercooler roughly equaled the Merlin X/XII single stage supercharger.
Intercooler design is another ballgame. The needed airflow is highly dependent on the amount of cooling desired.
One simple chart says that an equal amount of cooling air to intake air to get a 40 degree drop in charge temp, you need 1.5 to 1 ratio to get just over 50 degree drop and a 2 to 1 ratio gets you just over a 60 degree drop.
The R-2800 used higher supercharger pressures but these were intercooled so we don't know what the pressures and temps were between the stages, We do know that the R-2800s were moving a lot more air through the intake system.
