F4F-4 Pratt & Whitney R-1830-86 Supercharging?

[Greg Springer]

Hello Everyone,

 

I am wondering exactly how the system worked. There is an air intake for the downdraft carburetor and two intakes for the intercoolers’ “cold side” air. Ducts from the upper ends of the intercoolers appear to enter the intake manifold below the carburetor. The ducts to the lower ends of the intercoolers appear to emerge from the bottom of the supercharger casing. Since the purpose of the intercoolers is to cool down the compressed air from the blower, am I correct in assuming that the air exits at the bottom of the casing, passes upwards through the intercoolers and enters the intake manifold? Where does the air come from that is being compressed by the supercharger? Is it from ducts branching off from the carburetor intake?

 

Cheers!

 

Greg

[Slartibartfast]

Carb intake -> carb -> compressor -> intercooler(s) -> intake manifold.

[t.valdez]

Wouldn't the carb inlet air come from the intercooler? I thought the idea of the intercooler was to reduce the temperature and thus the density of the air that came from the impeller of the supercharger, which deters detonation and increases effciency. The job of the carburettor is to add fuel to the air and then to the intake manifold. I was thinking that it is not a good idea to add to compress carburetted air to the compressor because this might result in premature burning, and expansion of fuel, which has a high vapor pressure.

And, when added to water-methanol injection, also used to lower the temperature of the intercooled air results in a very complex system to provide power at altitude or as needed.

[Slartibartfast]

No, the compressor is after the carb because it helps homogenize the air-fuel mixture. Yeah, not what we do with automobiles but aircraft mfrs didn't have to deal with exhaust emissions, evaporative emission or throttle response (at least to the degree car owners demand).

[Greg Springer]

Hi guys,

 

I got this reply from Pat Donahue over on HyperScale:

 

"Greg, you are pretty much right. Induction air enters the aux. blower section through 2 oblong ports at the top of the aux. blower section. The air was compressed and then it went through the intercoolers and then to the carb. The fuel was added and then the mixture went to the main stage blower which distributed the mixture to the cylinders. I would ASSUME that there was some type of shuttle valve in the cowl carb. intake that would direct air either directly to the carb. if one was operating in main stage blower or diverted the induction air to the aux. stage blower if that was being used. I'll see if I can find an induction diagram. Yes, both blowers were mechanically driven. It was a 2-speed 2-stage supercharging system, the world's first in production. When the aux. stage blower was not in use it was left in neutral as in takeoff or landing and at low altitude so as not to over-boost the engine. ie the engine was running only on the main stage blower, no extra supercharging or innercooling from the aux. section blower."

 

This seems to be like the system on the R-2800 as well.

 

Greg

[Slartibartfast]

I'd like to see that diagram. It would be a nightmare to make that system work. At least for auto carbs, it's either suck-through (carb -> compressor) or blow-through (compressor -> carb), not both. Reference pressure for the float chamber is the biggest hurdle as a blow-through system has to be sealed so there's no pressure loss. A flapper valve to switch to ambient air has to accomodate an ambient pressure signal for the float chamber AND maintain a seal when pressurized.

[Greg Springer]

Hello Bruce,

 

In my online search I found a description of the carb. It was a Stromberg single-throat downdraft "pressure type". Would that indicate it was downstream from the auxiliary supercharger? BTW how can you be in La Porte and Houston at the same time? Something you learned from the Guide? 8^)>

 

Cheers!

 

Greg

[Slartibartfast]

Hello Bruce,

 

In my online search I found a description of the carb. It was a Stromberg single-throat downdraft "pressure type". Would that indicate it was downstream from the auxiliary supercharger?

Don't know, will have to see if my few engine references go into carburetor details.

 

BTW how can you be in La Porte and Houston at the same time? Something you learned from the Guide? 8^)>

 

Cheers!

 

Greg

42, baby!