Folks,
I'm looking for some help from any of our resident aeronautical engineers as I don't seem to understand how the db601 power curve is happening.
My problem starts with the following chart.
Notice I have extended blue lines to simulate the output power as if the fluid coupling was removed by extending the upper one and dragging it down to FTH power.
By looking at the blue lines, my logic tells me that the fluid coupling slip bellow 2100 meters, is saving the engine around 125 sPS
Ok assuming all the above is correct, let's start with some math...
I'm using the following formula to calculate the power consumed by the supercharger:
Gamma / (Gamma - 1) * Q * P0 / Efficiency * (( (P2/P1)^ ((Gamma - 1) / Gamma)) - 1)
Where:
Gamma = 1.41
Q = Engine displacement in M^3 * RPM /60 /2 (33.9 Liters displacement in this case)
Efficiency = Guesstimaged at 0.7
With this formula I calculated the following values power consumption values:
Altitude |
Power sPS |
Power Watts |
Temperature Kelvin |
Pressure Pascals |
Compression Ratio
to get to 1.3 ATA |
0 |
40.3 |
29640.74 |
288.16 |
101300 |
1.28 |
2100 |
65.56 |
48226 |
274.52 |
78514 |
1.65 |
4500 |
81.26 |
59770.18 |
258.87 |
57751 |
2.25 |
So, if at FTH I need 59770.18 Watts to compress 2.25 times and at 2100 I need 48226.00, that means that the fluid coupling would be limiting to 80.68% the power transmitted.
The same math but done in compression ratio would be 73.33%
Going back to the chart, if the difference between the fluid coupling at full transfer and at reduced transfer is around 125 sPS, that would mean that I would need the supercharger to consume around 678 sPS at FTH.
Where does this number come from?
If we said that we need 73.33% of the compression at fluid coupling end, that means that the 125 sPS shown on the chart correspond to the difference of 26.67% (I know these numbers are not exact as I'm not inverting the formula above but should be good enough to illustrate my point)
So, according to the chart I would need the supercharger to consume 680 sPS at FTH but my math tells me is only using 81.26.
This is where I scream HELP! What am I doing so wrong????
db601 edited.png
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