P47 Boost lever and turbo management incorrect?

[MadkiteMadkite]

 

So according to things as I understand the turbo at low and medium altitude does not respond correctly to the boost lever.

 

Currently if you have the throttle wide open andnthe boost off so you don't have the full pressure. Almost all the boost lever movmet does nothing. Only the last little but makes it come on. And then it's speed is regulated to the pressure requested by the throttle. 

 

Where it should I think rev up from the begging of moving the lever up as far as I understand. The engine won't overpressure as it will regulate its pressure. But driving the turbo faster than needed will cost power. Like running second supercharger stage when not needed. 

 

Currently you only get full pressure by advancing the boost lever to full. So its like its regulates. Which at low alt I wouldn't think you would need to. 

 

Maybe I have it wrong but it just seems odd. Doesn't seem as it should. 

 

Perhaps the devs want to look in to it. 

[MadkiteMadkite]

Anyone have any thoughts on this?

 

Will do some more testing on it when I get time. 

[DD_Arthur]

3 hours ago, MadkiteMadkite said:

Anyone have any thoughts on this?

 

What do you mean by “low and medium altitude”?

 

On the P47 I don’t think the supercharger provides extra power below seven thousand feet and I don’t think the turbo does anything below twelve thousand feet?

[MadkiteMadkite]

4 hours ago, DD_Arthur said:

 

What do you mean by “low and medium altitude”?

 

On the P47 I don’t think the supercharger provides extra power below seven thousand feet and I don’t think the turbo does anything below twelve thousand feet?

Above 1200 feet you have to start to use the tubo to get 52" boost. Lower if its running higher even on the ground. The supercharger only has one speed and only just provides adequate pressure at sea level. 

 

As soon as you climb the tubo makes up the difference till about 22000 feet where depending on what pressure your running it starts to run out of boost. 

 

As far as I understand in the P47 manual. As soon as you start to increase the boost lever at any altitude. The tubo rpm will begin to rise. You can waist power diving it at too high an rpm for the required boost at lower to medium altitude. As the more you use the tubo the more back pressure in the exhaust system. So you lose power using more boost lever input than necessary. 

 

Currently, the rpm does not rise at all at least at low atitude until the boost lever is nearly set to max.

 

So the issue is how the tubo responds to boost lever input. 

 

7000 feet is the minimum atitude before you allowed to link the throttle and boost leaver in the manual if I remember correctly. 

[Knarley-Bob]

I was thinking, that the 'boost' was the water injection. I have the super charger linked with the throttle. Don't know if this is right or not. If not, how does one use it?

KB

[MadkiteMadkite]

The water injection is actally worked by the switch on top of the throttle handel. 

When used it allows you to have a higher manifold pressure before the engine suffers from detonation. 

 

The boost lever contoles how much exhaust is either directed straight out to the air in directed to the turbocharger. 

 

So as you gain altitude. You have to use the boost lever to direct more and more exhaust to the tubo spinning it faster and faster to keep the manifold pressure.

 

If you direct more exhaust than needed to the tubo, you lose HP because of the back pressure on the exhaust. Up to 300hp. So it's not insignificant. 

 

At the moment the boost lever doesn't seem to do what it should in the correct way. 

 

You should get some rpm on the tubo even on the deck if you start to advance the boost lever. You get nothing for nearly all its movement at the moment. 

 

Edited December 16, 2021 by MadkiteMadkite

[MadkiteMadkite]

So I did some further testing.

 

At high altitude the boost leaver seems to work the tubo as expected. 

 

At low atitude it just has a huge dead zone which I am sure it shouldn't. So only the last 10% of movmet does anything. 

 

Also when testing for running the tubo more than necessary for power loss, there was none. Which is incorrect. 

 

The only downside to running the tubo more than needed is the inlet air temperature increases so you have to open the cooling vents for the intercooler more, so slows you down more from drag. 

 

Currently here is little to no penalty from just leaving the tubo at 100% all the time. 

 

Which is not how the P47 works. 

[Badger1_1]

has this been fixed yet?

[LukeFF]

If you guys can put together a concise report of what you think is wrong (please, no YouTube videos ?), then I'll let the QA guys know about it.

[Charon]

The basic mechanics of the throttle and boost levers are correct as modeled in game. There are things I can nitpick (lack of pulsation at altitude, effect of turbo overspeed, the timers, that you can run high power and auto-lean safely; I've also heard it claimed the critical altitude, before the turbo comes on, is slightly too low). But the response to the throttle and boost levers themselves is basically correct; it even correctly models some very nitpicky things like how the turbo RPM increases when at high altitude the throttle is slammed shut with the boost open.

 

Greg makes several mistakes in this video, and I've got a long post over on Reddit disecting these myths.

On 12/12/2021 at 9:08 PM, MadkiteMadkite said:

Currently if you have the throttle wide open andnthe boost off so you don't have the full pressure. Almost all the boost lever movmet does nothing. Only the last little but makes it come on. And then it's speed is regulated to the pressure requested by the throttle. 

This is correct because the boost lever, not the throttle, that controls the regulator's target manifold pressure. (Technically it controls target exhaust backpressure, which can be related to manifold pressure under some simplifying assumptions, but as a pilot you can just think "target manifold pressure" and 95% of the time this is correct).

 

At low altitude with the throttle open and the boost fully retarded the regulator will see plenty of backpressure, so has no reason to spin up the turbo. Under these conditions the P-47 basically flies as if it has no manifold pressure governor, since the throttle lever is directly linked to the carburetor throttle. You'll see this as you climb or descend with the boost lever closed.

 

At low altitude and full throttle the boost lever only produces an effect once it's advanced to a power setting that can't be obtained with full throttle -- indeed, this is the whole point of turbosupercharging your plane: you get a high-powered supercharger for high altitude without paying the cost to drive it at low altitude.

 

  

  

On 12/16/2021 at 2:34 PM, MadkiteMadkite said:

Also when testing for running the tubo more than necessary for power loss, there was none. Which is incorrect. 

 

...

 

Currently here is little to no penalty from just leaving the tubo at 100% all the time.

 

In my testing, full boost and throttling back to 34.4" costs 17mph relative to full throttle and boost pulled back.

 

Full test procedure:

 

Quote

 

P-47D-28 at 20,000ft, standard atmosphere, Oil Neutral, Intercooler Neutral, Cowl Flaps closed, Auto-Rich, Trim Neutral, 2280 RPM, full fuel, no mods, 34.4" MP. These are straight out of the Jan 1945 pilots manual, page 50, column III*. I ran three trials**:

Full Throttle, Boost as needed: 223mph indicated.

Interconnected: 221mph

Full boost and throttled back: 206mph (a 15mph penalty!)

 

*: By the book, this should have been Auto-Lean, but I'm a dummy.

**: And then repeated it to check, because the difference was so stark.

 

 

Edited September 30, 2023 by Charon

[ZachariasX]

42 minutes ago, Charon said:

Full boost and throttled back: 206mph (a 15mph penalty!)

That would be some ~20% power loss or 400 hp. This is quiet in line with the supercharger inefficiences plus increased CAT.

 

Good work there...