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The dotted black line is for 13.75 tons, the solid black is same power for 11.5 tons. The added red line is for the effect of inter-cooling.
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Maybe, the instructions are not clear.
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Hence engine power stays roughly the same,
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Increasing charge density will increase power at the same manifold pressure, above or below FTH.
This is also why aircraft experience increased performance in low density altitude conditions.
The intercooler on the Jumo 211 series functioned under exactly the same principle. Increase the charge density and you will increase power under all conditions.
It is a very simple concept.
Lower temperature means more air molecules in a given volume are required to create a given pressure.
It takes more oxygen to maintain the same boost pressure at a lower charge temperature.
Oxygen is off course what the engine needs to support combustion, more oxygen molecules means more power.
That is why
if you look at an actual aircraft power chart for a turbo or supercharged engine, it will tell you to
correct power for air temperature at the intake for the same manifold pressure.
The formula on the chart is
HP * SQRT (Temperature ratio)
BTW,
It is actually the density ratio but the chart I posted from the Lycoming O-360 series Operating Manual already corrects for pressure altitude.
If you were not running your power through a chart such as that, then power equals:
HP * SQRT (Density Ratio)
Density ratio is your Temperature ratio divided by Pressure ratio.
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reduction of temperature means an equivalent reduction in manifold pressure
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I see you edited your post!
The supercharger can produce a give pressure at a given density altitude above FTH. If we increase the charge density with our intercooler, then our power will increase above the same engine without the intercooler at the same manifold pressure and rpm.
It varies according to the standard formulation. It does not matter to the power production if we increase density at any point in the intake before the charge enters the combustion chamber, the effect on power is the same.
So, getting back to the thread and this sidetrack's relevance.
While we disagree on the shape of the curve, JtD and I are in agreement that the red line curve warrants an explanation.
It appears to be added after the fact and the data upon which it is placed on the chart should be made transparent.