reported Rev indicator,color green and blu

[oreste]

I wanted to ask about the colors used in the two instruments: rev counter and manifold pressure indicator.There are two zones in both instruments: blue zone and green zone, they should indicate what is recommended for cruising and for normal power So while cruising we have a lower pressure in the blue band between 30 and 35 but in the rev counter instrument I find the highest revs in the blue band, it is not correct in my opinion. In my opinion, in the rev counter you have inverted the colors while in the pressure gauge they are right.I have always seen advice for cruising: low pressure and low rpm while when you want to give power you use high pressure and high rpm, at least beyond 2300.If we give power with a lower number of revolutions we ruin the engine or at least we overheat it.

[oreste]

Here is an example of how the colors blue and green were used in the original manual of the P 51 D and K.

[-0303-]

Wondered about that too. Blue and green colors flipped on RPM gauge?

Notice "cruising" and "operating" captions (from DCS manual).

 

Wish the 1947 manual above was readable. Think it says

Blue: "Desired operating range for lean mixture and / or desired cruising range"

Green: "Desired operating range"

 

Edited December 30, 2020 by -0303-

[Diesel_Thunder]

The colors are not flipped on the RPM gauge, that is the intended colors.

 

Increasing the RPM has the effect of reducing the cylinder combustion pressures, which in turn reduces engine stress and cylinder temperatures. Especially at lean cruise settings, which was desirable for long range missions.

 

Decreasing RPM at the same settings raises the cylinder pressures and more importantly the temperature. This reduces your detonation margins, making it a lot easier to damage the engine if the pilot wasn't careful with his power settings.

 

I recall reading some figures that the difference in fuel consumption at cruise power was around 20 gallons per hour between the rich and lean setting on most single engine R-2800 powered aircraft. Lot of science and engineering goes into these amazing engines.

 

EDIT: I was incorrect with this post, see below.

Edited January 19, 2021 by Diesel_Thunder

[grafspee]

Lean mixture not only reducing fuel consumption by just changing AFR, but also higher AFR will provide more power at the same MP/RPM settings.

So you burn less at the same time you fly faster at lean mixture, so you can reduce MP to fly as fast as at rich mixture or you can just cruise faster.

DCS p-51 and spitfire have this lean rich mixture in automatic mode, so both will automatically use lean mixture settings when MP will be at desired level.

Edited January 9, 2021 by grafspee

[Diesel_Thunder]

After putting in some good time and research on this, I do believe the P-47's tachometer colors are indeed reversed. The span of the arcs are correct, and at the correct RPM ranges, just the colors are reversed.

 

The excerpt that @oreste posted above from the real P-51 D/K manual, the real manual that @grafspee posted in another thread that covers the P-47 25 - 35 models, and the real manual that I found for the P-47 N all agree with this assessment.

 

The blue arcs were painted on both the MP gauge and tachometer for the pilot as a quick reference for setting the mixture to AUTO LEAN for long range missions. Both gauge needles had to be in the blue arc in order to use auto lean. There are quite a few tables published in the manuals with RPM, MP, fuel flow, mixture setting, and true air speeds that can confirm this.

 

I've attached a screenshot of of what it should look like:

Edited January 19, 2021 by Diesel_Thunder

[grafspee]

P-47N this pane has so good stuff like automatic oil/intercooler doors.

And of course 72" with water  at 2800rpm

 

Edited January 19, 2021 by grafspee