Supercharger Education Requested

[II/JG17_HerrMurf]

So, I have a basic understanding of turbo superchargers. More air in = more power out.

 

I know they come in simple turbo’s which run off of exhaust gasses and true superchargers which are gear driven. There are single stage, multi stage, single and multiple gear types, waste gates, power takeoffs, and various gadgets to make them stronger and or more efficient. I need a bit of an education regarding their use in WWII and how they are modeled in BOS.

 

Which aircraft have them? What type is used on each model? Are they modeled correctly in the game? Where should the engines for each type be the strongest? How are they controlled – manual, fully automatic or something in between? Are they always on or are they triggered by RPM, pressure or something else?

 

For this discussion please keep it to the aircraft which are in the sim. The only exceptions would be other aircraft present, but not yet modeled, in the Stalingrad area of operations. Late war discussions and other theaters are not welcome in this thread, please.

 

Thanks,

 

HerrMurf

[FlatSpinMan]

Just checking: have you read Chuck's guides?

I guess you have an are looking for more detailed info.

[39bn_pavig]

I don't know a great deal but this is what I know. The superchargers in BoS (and ww2 aircraft in general) weren't designed so much for more power as for more efficient fuel burning. At high altitudes as the air becomes thinner the supercharger would be engaged to compress more air into the cylinders and allow the fuel to continue to burn despite the thinner atmostphere. Most BoS craft only have two supercharger "gears" and the second should be engaged around the 1700-2000m altitude mark, though this differs for each plane. 

 

A second performance boost system - engine boost - is available in many planes. This corresponds to modern fuel injection, and can provide more power. As fuel burns slower at higher altitudes however engine boost should only be used closer to the ground. Because of this, engine boost and higher supercharger levels are mutually exclusive. I believe the russian aircraft have an auto safety engaged which turns off boost if the supercharger is engaged, or turns down supercharger if boost is engaged.

 

The superchargers can increase manifold pressure I believe, and work from a gear fed pressure pump. This requires some time to rebalance when changed, so you shouldn't switch on and off the supercharger in rapid succession or you may induce engine wear.

[JtD]

Basically all aircraft engines of WW2 had superchargers, all aircraft in game have them. Most of these chargers were gear driven, all in game are gear driven, basically two speed/gear systems everywhere. Superchargers are always on, since they are linked directly to engine rpm - besides being possibly able to select a gear, you do automatically change them if you change engine rpm.

 

They are generally modelled correctly in game, though who knows what's in the code, and some have one or the other issue. The engines are strongest at the full throttle altitude of the first charger gear. Where this is exactly at, and how to use them, please look it up in the already mentioned aircraft guides.

 

The most unique supercharging system of the aircraft modelled is with the DB60X on the Bf109, where the two solid metal gears for two different supercharger ratios and therefore altitudes were replaced with essentially a single hydraulic clutch, which changed the ratio by continuously adjusting the oil level inside the clutch depending on the outside pressure, once above 2000m. Below that, filling is constant at it behaves very much like a fixed gear.

 

True turbochargers (exhaust driven) were the exception, while thermodynamically superior, they are a bit more demanding. The P-47 and P-38 were the only two (numerous) front line fighters to use turbochargers, so you won't find them at Stalingrad. I'm also not aware of any other aircraft types with turbochargers, that were used in significant numbers at Stalingrad.

[II/JG17_HerrMurf]

Are there power curves associated? Where do they change gears and how is it accomplished? Do they change on atmospheric pressure or some other criteria?

[4H_V-man]

Actually none of the superchargers in BoS are two-speed. They are single-stage superchargers. At low atlitude you have no boost, at different altitudes depending on the aircraft you then engage the supercharger. Later model Spitfires, as well as Corsairs and Hellcats had two-speed superchargers though in Il-2 it was mis-labeled as stages one, two, and three. P-38s and P-47s had turbochargers, referred to at the time as turbo-superchargers.

[Matt]

Actually, they are all two-speed, single-stage superchargers in BoS except for the Il-2, which uses a single-speed supercharger.

 

And the supercharger is engaged all the time, there's no way to "engage" it yourself.

Edited September 16, 2014 by Matt

[Descolada]

Are there power curves associated? Where do they change gears and how is it accomplished? Do they change on atmospheric pressure or some other criteria?

Depends on the supercharger. Depending on where you want power you can design it to produce maximum power at pretty much any altitude you'd like. The yak 1 for example has the 1st speed be superior up until 2000-2500m, at which point you switch. That speed then makes the most power a little bit below 4000m or so. High altitude performance was not really a concern for the russians given how they employed their airforce, and the later designs really reflect this with their absurd low altitude performance in comparison to the higher altitude performance. Thats another reason why they didn't mind the p39s limitations so much, a lack of performance above 14k ft or so wasn't a big deal when they were focused on providing CAS and escorts to sturmoviks well below 10k ft.

[II/JG17_HerrMurf]

What do the speed and stage correspond to? What is the difference - from each other and also speed to speed or stage to stage?

[JtD]

A two speed supercharger is one supercharger going at two different speeds. You change speeds by changing the gearing at which the supercharger is run, same thing you do with your cars gearbox.

A two stage supercharger are two superchargers in a row in the induction system. You can sometimes engage and disengage a stage, and/or change the speed at which one of them is running.

Speeds and stages can be combined, the mentioned F4U had a two stage three speed supercharger, with one of the superchargers running with a fixed gear ratio and the other having three settings - neutral (off), low and high.

 

Thanks Matt for correcting me on the Il-2, it had actually slipped my mind. Single stage, single speed.

Edited September 16, 2014 by JtD

[II/JG17_HerrMurf]

Thanks,

 

This thread did exactly what it was intended to. I am much better informed than yesterday.

 

Thanks again guys.