Ju-88 a1 Jumo 211B BETA 1.08.18956

[Crumpp]

Why would an intercooler increase speed above full throttle altitude?

It looks like a line added to the chart.

The principle is correct. The inter-cooler was designed to increase charge density.

IIRC, the general rule of thumb is for every 10 degrees of temperature drop there is a 1.8% increase in power.

The extended kg with a total weight 11500

However, I think the increase has more to do with the weight. If I am reading the post correctly, the extended line is some 2250Kg lighter.

[JtD]

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.

Inter-cooling does increase charge density if air supply is unlimited, so for altitudes below full throttle altitude power and speed increase are there (6% in case of the Jumo 211F/J), however, above full throttle altitude air supply is somewhat limited. Very much like ram effects on the inlet side increase manifold pressure, inter-cooling reduces manifold pressure. The effect above full throttle altitude should be somewhat less than below.

In the meantime I've looked up range tables for the Ju 88 where speeds with inter-cooling are only higher below FTH, supporting my point of view. So I'm withdrawing the question, the red line is wrong. Back on topic, good to see a bomber getting some attention.

[CaptainDoggles]

Originally Posted by JtD

In the meantime I've looked up range tables for the Ju 88 where speeds with inter-cooling are only higher below FTH, supporting my point of view. So I'm withdrawing the question, red line is wrong. Back on topic, good to see a bomber getting some attention.

Did your sources have a graph similar to the one posted in this thread?

I'd be willing to bet that this "red line" is just an intercooler performance line that doesn't drop off fast enough above FTH. Someone just copied the curve from the highest black line.

[Crumpp]

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.

Maybe, the instructions are not clear.

Hence engine power stays roughly the same,

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.

reduction of temperature means an equivalent reduction in manifold pressure

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.

[Jam656es]

I was pushing my engines to see what the various limits were when I had a single damaged item