Engine Performance Tuning Tutorial

[Ivan]

Finished with the bedtime reading to my son a bit earlier than I thought I would....

So far, the calculations for values to plug into the AIR File have been pretty obvious.
Volume of a single cylinder was simple geometry and metric conversion.
(I got 177.93246 Cubic Inches per cylinder from the bore and stroke values listed.)

RPM is obviously as listed.
Critical altitude of somewhere around 20,000 - 23,000 feet will do. (I don't think this number makes any difference at all.)
The Throttle settings for German Aircraft were listed in ATA (Atmospheres Absolute) and THAT conversion may not be obvious.
Attached is a spreadsheet to help with that calculation.
To use, just plug in your values in the Left Column and see what the results are in the other columns.
I wrote up this spreadsheet to help with conversions almost 3 years ago.
If anyone finds an error, please let me know.
Also let me know if you know what the Russians used for Throttle settings.

Initial values are for ambient pressure, so don't change them; They make a good reference and starting point.

The values I got were the following:
1.80 ATA = 52.315 inches Mercury
2.02 ATA = 58.709 inches Mercury

- Ivan.

P.S. If anyone wants to comment but doesn't want to do it as a post here, please contact me at Ivan1GFP@yahoo.com or in a PM.

[Ivan]

For those that are curious, I figure that the numbers might have a bit more validity if the engine is tested in an AIR file that is very similar to what a complete FW 190D-9 version would look like. Having weights and basic aerodynamic numbers correct will make a service ceiling test more repeatable in the finished AIR file.

Here are the planned modifications to the stock P-51D:

Wing Area
Wing Span
Chord
Wing Efficiency

Zero Fuel Weight

Fuel Tank Volumes and Locations

Cockpit Viewpoint <---- Has no effect but makes testing not look as strange.

DP File <---- Affects Flying Weight.

CL Graph will not be changed ---- YET. Up to the stall, it looks fairly reasonable.

Coefficient of Drag ---- Will be changed after first correct reading of Sea Level Engine power.

Hope this makes sense.
- Ivan.

[Ivan]

For the purposes of working on Engine Tuning, it helps to get a fairly good estimate of the aircraft's weight.
Attached is an updated Damage Profile that should reflect the weight of the munitions carried by the FW 190D.
The source for the round counts is a Focke Wulf manual.
The source for the weights of a round and one link of the disintegrating belt is from a Schiffer Book about Kurt Tank, Focke Wulf's Designer and Test Pilot.

The Focke Wulf manual specifies that the cowl guns have no convergence. The wing root guns are set to converge at 600 meters.

Damage values are the ones I worked out based as a compromise between CFS Stock values and 1% values. The differences are mostly due to my belief that a cannon shell that relies on explosives for effect have no significant additional damage due to extra velocity.
The choice of using 3 x 250 Kg bombs is because although the FW 190 could carry a much larger bomb, a single 250 Kg bomb can also mimic the load of a 300 liter drop tank.

- Ivan.

[Ivan]

Attached is a copy of the stock P51D Flight model with just the basic data changed to match the FW 190D-9.
The engine has not been modified.

Here are the basic changes and how they were calculated:
Record 301
Modified to match the visual model I am using.

Descriptions
Modified to describe the purpose of the AIR File.

Record 1204
Wing Area: 196.98 square feet becomes 197 in the AIR file
Wing Span: 10.51 meters according to the factory specifications.
Wing Efficiency: Changed to 5250 which is a fairly average value.

Fuel Tanks (according to Kurt Tank flight test contain 569 liters).
Center 1: 232 liters = 61.3 Gallons (Same as stock FW 190A)
Center 2: 337 liters = 89.0 Gallons (Doesn't match with any numbers I have seen)

Zero Fuel Weight
Calculated from 4293 Kg (9464.5 pounds) loaded "Clean".
- 800 rounds 13 mm ammunition (150 pounds)
- 500 rounds 20 mm ammunition (219 pounds)
- 232 liters fuel (367.73 pounds)
- 337 liters fuel (535.24 pounds)
------------------
8192 pounds
The weight of MW50 is specified as 125 Kg for 115 liters in a tank behind the cockpit.
Perhaps we should deduct half of that for an average load condition in combat?
If so, that would make the Zero Fuel weight 8054 pounds.
Either value still seems a touch heavy to me, but it is close enough as an estimate for engine testing.

For what it's worth, this weight is almost two TONS heavier than the Zero Fuel weight of the stock P-51D which is why I believe the P-51D has totally unreasonable values.

- Ivan.

[Ivan]

I finally got around to installing the JuMo 213A in the FW 190D basic AIR File and took it for a test flight. Attached is the updated AIR file.

Here is what was changed: (All unstated data has been specified in prior posts.)

Record 500 - Reciprocating Engine Specifications
Propeller Pitch Max
Propeller Pitch Min
Propeller Diameter

Record 505 - CFS Reciprocating Engine
Displacement per Cylinder
Compression Ratio
Cylinder Count <---- Unchanged from 12
Maximum RPM
Maximum Horsepower <---- Changed to 1600. I believe this only affects sound effects.
Negative G Effects <---- Becomes "None". This is a fuel injected engine.
Engine Type <---- Remains "Water Cooled".
Supercharger <---- Remains "Yes".
Max Manifold Pressure <---- 1.8 ATA equivalent in Inches of Mercury.
Supercharger Boost Gain <---- THIS WILL NEED TUNED LATER!!!! Unchanged for Now.
Critical Altitude <---- 6600 Meter equivalent in feet.
WEP Type <---- Becomes MW.
WEP Manifold Pressure Increase <---- Becomes difference between 1.80 ATA and 2.02 ATA.
No Mixture Control <---- Copied from Stock FW 190A: "KommandoGerat" controlled everything.
No Panel Magneto Switch <---- Copied from Stock FW 190A.

Record 508 - Engine Torque versus RPM
Maximum RPM changed from 3000 to 3250.

Record 509 - Engine Per Cylinder Friction Loss
Maximum RPM changed from 3000 to 3250

Record 510 - Propeller Parameters
Propeller Diameter
Propeller Pitch Max
Propeller Pitch Min
Reduction Gear Ratio <---- Changed to 1/(0.417).

Record 511 - Propeller Efficiency
Copied from Stock Me 109G using AirEd.

Record 512 - Propeller Power Coefficient
Copied from Stock Me 109G using AirEd.

Attached for explanation of parameters is a copy of the FDE Control File I use.

[Ivan]

The First Flight Test was either very good or very bad depending on your point of view:

Without changes to anything other than what was specified in prior posts, the engine power at an altitude of 500 feet was almost exactly what we would want. The maximum speed was also pretty much exactly what we were trying for.

The Sea Level (Take-Off) Power is somewhere between 1726 HP and 1776 HP depending on which source you believe. Kurt Tank's Flight test of a standard D-9 showed 586 kph (360 mph) at 300 meters altitude.

See Attached Screenshot of performance values from my version of Jerry Beckwith's excellent test panel. One thing to note from this screenshot is that the propeller pitch is a couple degrees higher than I would have wanted. I expect a bit of overspeeding at higher altitudes with less dense air.

[Ivan]

Values that match exactly what you are looking for are good if the goal is something to be used in a project. For a tutorial, this is bad because there isn't an opportunity to demonstrate how to adjust parameters to get what you want.

For the purposes of this tutorial, we will pretend that we are not trying to reproduce the mid-production Jumo 213A. Early versions of this engine typically produce about 100 HP to 150 HP LESS than advertised, so we will attempt to detune this fine running 1740 HP engine down to around 1620 HP without changing the manifold pressure limits. Depending on how quickly I get bored, we may also try to simulate a "Blueprinted" engine of 1800 HP or so.

At this point, some folks probably have figured out what is coming next. Adjusting the engine power is actually quite easy:

To INCREASE Engine Power,
Increase Torque in Record 508 -OR-
Decrease Friction in Record 509
(or some combination of the two)

To DECREASE Engine Power,
Decrease Torque in Record 508 -OR-
Increase Friction in Record 509.

Note that the effects are not the same.
Although the engine output at Sea Level (and up to critical altitude) will be the same with either method, the engine power will fall off faster if Torque and Friction are both higher for the same power output.

Next comes a lot of Modify and Test cycles....
(Lather, Rinse, Repeat....)