Engine Performance Tuning Tutorial

[Ivan]

Specifications for the JuMo 213A-1 are the following:

Cylinders: 12
Bore: 150 mm
Stroke: 165 mm
Compression: 6.5
Reduction: 0.417 <---- This was hard to find. I found it in Janes Fighting Aircraft of WW II.
Maximum RPM: 3250
Propeller Diameter: 3.300 meters

Performance (varies a bit depending on the source)
1750 PS (1726 HP) or
1755 PS or
1776 HP at Take-Off (3250 RPM)
Throttle setting should be 1.8 ATA

WEP at sea level produces 2050 HP to 2240 HP depending on the source you believe
Throttle setting should be 2.02 ATA

Critical altitude is around 6500 meters altitude.
Aircraft critical altitude (presumably with ram-effect) is around 7000 meters.

Power at altitude varies all over the place depending on your source but appears to be at least 1600 HP at 18,000 feet.

If anyone has more reliable information, please respond along a listing of the source.

Thanks.
- Ivan.

[Ivan]

My understanding of the Propeller Power Coefficient is that it is a number representing the power absorbing ability of the propeller. It represents how hard the propeller is to spin. In the case of a constant speed or variable pitch propeller as typically found in a WW2 fighter, it is a representation of how hard the propeller is to spin at each pitch setting as plotted against its advance ratio.

This is the means by which the game selects the correct pitch setting to use based on engine power and how fast the aeroplane is moving. Strictly speaking, it isn't necessary to get this right to get the proper engine power but it does influence how the power is used.

The Power Coefficient will vary depending on air density, but I chose to use an altitude of 500 feet to gather my data.

Since I don't know how to generate my own graphs, I will copy the closest match from one of the stock aircraft. The values for the stock aircraft are shown in the attached spreadsheet.

[Ivan]

Note that the specifications for the JuMo 213A did not include the propeller pitch settings.
I could not find that data so will be using the values for the stock FW 190A which seem fairly reasonable:
(23-65 Degrees). In any case, although the attached spreadsheet lists them, they are grayed out because they are not actually used.

Although the prior post doesn't show it, the power output of the engines of the FW 190A-8 and FW 190D-9 were very similar at low altitudes. The better engine power at altitude, slightly better streamlining and lighter weight is what I believe made the difference.

Note that the Power Coefficient from the spreadsheet attached is 0.24. This is a measurement of how hard the engine with its reduction gearing can turn a propeller. Note that this calculation completely ignores the number of blades and the profile (activity factor) of the blades.

None of the stock aircraft go quite that high. The two closest are the Me 109G (0.1721) and the FW 190A (0.1684). I will probably start with Records 511 and 512 from the Me 109G and do a final test with the FW 190A. Perhaps it is a good idea to start with the FW 190A propeller because of its similarity to the one on the FW 190D.

Although the choice influences flight performance to some extent, it does not affect engine power.

The AIR File records may be copied from one file to another using AirEd.

Next comes the first "Flight Test"..... (which will not be tonight).

Good Night.
- Ivan.

[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.

[No Dice]

Thank you Ivan for this thread, although some is above my Intel level, it is very interesting to follow.

Thumbs up dude,

Dave

[Ivan]

Thanks, No Dice.

I had thought this thread would be much easier than this.
I thought I would be done after posting the next installment about tuning supercharger settings, but there is still:
Testing with AIR files
Idle speed
Propeller animation which I will probably take back to the thread I started a couple months ago.

The reference data is also quite a lot more difficult to find than I first thought it would be.

- Ivan.

[Ivan]

Here are a couple more Engine Power Graphs.
Please observe that the forms are quite similar.
The number of peaks corresponds to the number of speeds in the supercharger.

The Merlin graph is fairly self explanatory but the Jumo 213A graph might need some translation:
Sonder-Notleistung ==> Special Emergency Power (WEP)
Start und Notleistung ==> Take-Off and Emergency Power
Steig und Kampfleistung ==> Climb and Combat Power
Mehrleistung durch GM1 ==> Increased Power via Nitrous Oxide Injection
Reiseleistung ==> Cruise Power
Krafftstoff verbrauch ==> Fuel Consumption

The bottom of the graph shows exhaust thrust.

Note that 1 PS is slightly less than 1 HP but for our level of precision you can pretend they are the same.
(1750 PS = 1726 HP)

....

[Ivan]

Attached is an annotated graph of Jumo 213A Engine Power.
The Blue shows the specific power curve we are trying to approximate.
The Red Dots show the three points at which we will be trying to best match the power curve.

They represent:
1. Power at Sea Level.
2. Power at Critical Altitude where Aircraft's maximum level speed is achieved (6600 Meters).
3. Power at Service Ceiling (11400 Meters).

We have already seen how easily the Engine Power can be adjusted at Sea Level.
We have demonstrated how Engine Power at high altitude (Service Ceiling) can be adjusted to some extent.

....

[Ivan]

The maximum speed for the FW 190D was achieved at 6600 meters or 21650 feet.
On the graph in the last post, engine output looks to be 1440 PS.
The conversion factor is 1.01387 so this is equivalent to 1420 HP.

In the AIR file, the variable to adjust for tuning critical altitude can be found here
Record 505: Supercharge Boost Gain.

Since we started with the stock P51D, it is still 5.36.
A quick flight test gives the following results:
00500 feet ==> 52.3 inch MP 1722 HP
17500 feet ==> 52.3 inch MP 2020 HP
20000 feet ==> 52.3 inch MP 2071 HP
22500 feet ==> 52.3 inch MP 2123 HP
25000 feet ==> 52.3 inch MP 2177 HP
27500 feet ==> 52.0 inch MP 2219 HP

Only the two rows in BOLD are really relevant.
In fact, a single test at 21650 feet would have told us quickly that we needed to adjust.

Changing the Supercharger Boost Gain to
2.68 ==> 1163 HP which is obviously way too low.
3.30 ==> 1549 HP which is closer
3.20 ==> 1487 HP
3.10 ==> 1424 HP which is pretty close.
(There is no point in getting any closer at this stage.)

A quick speed run at this altitude gives us 421 mph which is way too low.....