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Jet Engine Performance

vololiberista said:
If it works it works!! Now take your a/c to Kuwait load real weather and see how much your engines exceed limitations. N2 N1 and EGT. This way you can build in pilot mishandling and perhaps even shut down the engines.
Click to expand...

Isn't there a lot of unrest there these days? :laughing:

Actually that would be cool to build in some of those things. Learning about all of this makes me want to look at the other areas in the air file.
 
The best way to build in engine failures is with some XML gauges. They can even be hidden. By default, FS plane engines don't fail.
-Pv-
 
Paul,

How are you with 1506/1507? I tried to follow Roy's example however I cant seem to make it work.

Now what I have been after all along on my JT-15D is for the N1 and N2 readings to be the same or very close to the RW aircraft. That I have done with 1503, 1504, and 1502.

The other goal Id like to accomplish here is to get the power settings to match up with my performance charts.

For example: (From the Constant Mach .73 Cruise Chart)

31,000
ISA 0
N1 94.2
TAS 427
PPH 1325 (all engines)

Right now I am tweaking 1506, the mach number ratios.

To hold 427 TAS and Mach .73 I am at an N1 of 88.7

My thoughts are to dial down the mach ratios in the mach column in 1506 until I get it.

I'd rather just leave 1507 alone, unless that is the one better adjusted.
 
How can 31,000 ft be zero ISA? It should be -47C (-53F.)
You'll never get the engines tuned at zero and 31K ft.

Here's how to calibrate FSX for engine testing:
In the Weather tab, select the Clear theme.
Do not use real world weather and disable "changes over time"
No Winds. You can add clouds for interest if you like, but NO Turbulence.
I keep it clear and do my tests taking off toward ocean to increase frame rates
and reduce per restore loading time.

Now select User Defined, Customize and Advanced.
In the Temp tab,
Ground level = 15C (59F)
These two set a stagnant Troposphere:
Create a 35,100 foot level and set it to -56.5C = (-70F)
Create a 65,617 foot level and set it to -56.5C (-70F)
End of stagnation, beginning of 1 degree lapse rate:
Create a 80K ft level and set it to -52C = -62F

Make all the dew points 1 or more degrees colder than the temperature.

Now with a working (default) 737, climb to a normal test altitude you will use a lot, or several of them on your way up.
These all need to be made in one continuous flight.
At each altitude, create a saved flight and name them appropriately noting altitude, temperature and speed.

In the future, you can restore these flights, and change to the plane you want to test.
If you want to avoid changing planes every test restore, you'll need to create a take off and climb profile save set for your
test plane.

Note: If you do not do it this way and try to create saved flights from a condition where the plane did NOT
ORIGINATE on the ground, FSX will destroy the weather you created every 60 miles and return the calibrated
temperatures to the default FSX clear which sets and caps ISA at 35,000 ft and -56.5C. Only flights were the weather conditions
were created on the ground will remain intact as set in the UI. For planes which never exceed 35K ft, just setting the Clear theme is enough.

An alternative is the use Active Sky Next in manual global mode to do this, but the upper altitudes above 50K ft are a bit buggy in the ASN UI.

-Pv-
 
Roy's table 1503 is based on actual n2 at sea level at 15 degrees celsius. Get those figures right and then follow his computations for all the other altitudes in 1503 which are cn2. Then again following his computations map those numbers to 1504. These plus engine limitations are based at sea level and ISA. If you have got the sea level ISA numbers correct then the engines should perform correctly at altitude in the sense of N1 N2 and their limitations. Temperature is another matter. As is fuel flow. Again EGT must be correct at sea level ISA. for this you will probably have to adjust EGT in the air file. Also you'll need fuel flow tables. How many kilos are burned per minute during taxi for example. What is the expected fuel burn at a specific altitude, oat, weight and airspeed. Adjust your fuel flow scalar in the a/c cfg.
As said above for engine failure you will need to write up some xml gauges to test failure conditions.
This is a little list of all the engine parameters I have set up.

<!-- Engine Fire Scenarios --> for each of 4 engines.
<!--P7 corrected Values --> instead of EPR P7 is the back end part of the EPR ratio
<!--Hot Start Bypass Flow --> Measures EGT and valve settings so that engines don't exceed the prescribed value. Also important for airframe de-icing.
<!--Engine Cooling Air --> Warning if temperature excessive plus calculation made to determine duct temperature ie. mixing of airflows for de-icing.
<!--EGT Ambient Cooling --> When waiting at a stand after a flight the engines cool down naturally. You should not restart until a specific value reached
<!-- Engine Vibration --> This generates a value according to elapsed time and n2 values. If exceeded engine shuts down.
<!-- Engine Limitations Exceeded --> will stop the engines after a time limit above the specified limitation.
 
LOL! I should have explained, my bad.

MOST RW aircraft performance charts are set up so they read ISA -10, ISA, ISA +10, so it is implied what ISA is for any given altitude. So yes in the case you gave then it would be -57C -47C or -37C.

Already had saved flights. 30k 33k 35k as that is how my performance charts are set up.

"Now with a working (default) 737, climb to a normal test altitude you will use a lot, or several of them on your way up.
These all need to be made in one continuous flight.
At each altitude, create a saved flight and name them appropriately noting altitude, temperature and speed."

I did this too. Just did not know about the FS Trashing wx back to default. Thanks.

I appreciate the other testing pointers! Thanks.

I am working on FS9.

I have AS Evo will check on that. All I am doing is getting or trying to get 1506/07 in the ball park. Which they are now. +/- 1.0% N1 and +/- 5 knots on airspeed.

My question was 1506 or 1507 which is better to adjust? One or the other or both if you know.

Thanks.
 
vololiberista said:
Roy's table 1503 is based on actual n2 at sea level at 15 degrees celsius. Get those figures right and then follow his computations for all the other altitudes in 1503 which are cn2. Then again following his computations map those numbers to 1504. These plus engine limitations are based at sea level and ISA. If you have got the sea level ISA numbers correct then the engines should perform correctly at altitude in the sense of N1 N2 and their limitations. Temperature is another matter. As is fuel flow. Again EGT must be correct at sea level ISA. for this you will probably have to adjust EGT in the air file. Also you'll need fuel flow tables. How many kilos are burned per minute during taxi for example. What is the expected fuel burn at a specific altitude, oat, weight and airspeed. Adjust your fuel flow scalar in the a/c cfg.
As said above for engine failure you will need to write up some xml gauges to test failure conditions.
This is a little list of all the engine parameters I have set up.

<!-- Engine Fire Scenarios --> for each of 4 engines.
<!--P7 corrected Values --> instead of EPR P7 is the back end part of the EPR ratio
<!--Hot Start Bypass Flow --> Measures EGT and valve settings so that engines don't exceed the prescribed value. Also important for airframe de-icing.
<!--Engine Cooling Air --> Warning if temperature excessive plus calculation made to determine duct temperature ie. mixing of airflows for de-icing.
<!--EGT Ambient Cooling --> When waiting at a stand after a flight the engines cool down naturally. You should not restart until a specific value reached
<!-- Engine Vibration --> This generates a value according to elapsed time and n2 values. If exceeded engine shuts down.
<!-- Engine Limitations Exceeded --> will stop the engines after a time limit above the specified limitation.
Click to expand...

Yep. As stated earlier, I have all that and have corrected as such. The Pratt Whit JT-15 uses ITT and my tab data charts show FF however in PPH. I am very close and not sure whether to adjust the aircraft.cfg under fuel flow scalar, which works, or in the air file.

Q. What is your method for FF adjustments?
Q. What is your method for adjusting EGT/EPR in the air file. I am curious. Thanks!
 
Adjust the fuel flow scalar in the cfg file-fuel_flow_gain= 1 if your 1505 is now correct. EGT and EPR can be adjusted in the air file. You should find engine parameters that indicate what they should be at idle thrust and so tweak the numbers in the air file to generate the required values.
 
Ok... I think there's one aspect of this discussion that's probably really misleading... he's not setting up actual engine performance, he's setting up EEC controlled performance. The engines can actually perform higher than what he's creating.
 
vololiberista said:
Adjust the fuel flow scalar in the cfg file-fuel_flow_gain= 1 if your 1505 is now correct. EGT and EPR can be adjusted in the air file. You should find engine parameters that indicate what they should be at idle thrust and so tweak the numbers in the air file to generate the required values.
Click to expand...

Yes, there is PLENTY of data out there on the Pratt. Whit. JT-15D on slam tests, engine limits etc, to be able to adjust these records to make them accurate.

Your procedure is what I thought would be the procedure. I actually have RW recorded data from the last trips I just flew on the job. For instance:

CRUISE @ FL 400

N1(1) 97.4 N2(2) 97.4 (These are controlled by when you select FAN synchrophaser which is in turn controlled by the HMU and EEC. Not simulated on this engine but maybe I can with some edits.
ITT(1) 540 ITT(2) 560
N2(1) 87.5 N2(2) 87.5
PPH(1) 500 PPH(2) 500

TAS 413
SAT -59
TAT -36
RAT -36
ISA 0
KECP - KAUS 1/16/2015

Using Roy's Engine Performance paper again, I have been able to get N1 and N2 to work out well. Some tweaks yet to do. But almost there. So 1502 1503 and 1504 are done. I even get N1 to go to 104 and N2 stays at 96 during slam tests and full throttle tests at SL those are the limitations and that is very close to what we get with TO PWR on our takeoff runs. This was very informative learn how to get it to work right.
 
Last edited:
WarpD said:
Ok... I think there's one aspect of this discussion that's probably really misleading... he's not setting up actual engine performance, he's setting up EEC controlled performance. The engines can actually perform higher than what he's creating.
Click to expand...

Nope. The engines that shipped with this model were shipped with the ECS system ON. As they should be as that is normal operation. So whether the ECS system was on off or non existent, the original engines were still off in both power settings and N1 to N2 ratios. No big deal, they just need to be adjusted so they are somewhat accurate.
 
WarpD said:
Ok... I think there's one aspect of this discussion that's probably really misleading... he's not setting up actual engine performance, he's setting up EEC controlled performance. The engines can actually perform higher than what he's creating.
Click to expand...

There are charts for ECS off operations however continued operation with ECS off is not recommended by Beech or Pratt. I had to ferry a Falcon 10 once with our EECs out on one engine and let me tell ya it was a handful. So one does not operate wth EECs off normally.

However for whatever reason you find yourself needing the little bit extra performance you might get with an ECS off takeoff, you may want to rework your flight planning and simply takeoff with less fuel and make a fuel stop. Usually guys in the hotter regions consider this, and usually only for takeoffs.

For instance:

A RAT 10 and 5000 foot MSL strip ECS on N1 setting is 96.8
A RAT 10 and 5000 foot MSL strip ECS off N1 setting is 97.4

So you can see EECs do not make that much of a difference performance wise on or off. BUT! engine control without the EECs is challenging to say the least not to exceed engine limits.
 
Right... I'm just making certain the thread's "clear" that you're technically derating the engines to perform as if the EEC was in control. Not arguing what's right/wrong... don't even see that. :)
 
Hmm. I think that is a good way of putting it! Interestingly enough, they did build an EFC "test" into the Beechjet (Small little black buttons to the top of the start buttons). The EFC test works like the real world drop in N2 that we see when we run the first flight of the day checks and tests. Very cool how they did that. Haven't figured that out. What else is interesting is how the engine behaves with the EFCs off, when selected off. So really in my opinion I think they set up the engines to run like they have EEC control, BUT, the numbers in the records are simply off. So the hope here is to put RW Flight data with Roy's system to get the engines to perform more accurate. :teacher:
 
You should try a take-off from Kuwait with real weather. Especially in the Summer months. Because of the heat your n1 n2 numbers will max out immediately! For example the RR Conway 550 n2 at 105% is limited for only 20 seconds before the engine has to be shut down. So a full throttle take-off from there was a no no! Having to shut down four engines shortly after take-off makes for an interesting flight. (if they weren't shut down they would be severely damaged) You "will" also get a hot start!
 
You should try a take-off from Kuwait with real weather. Especially in the Summer months. Because of the heat your n1 n2 numbers will max out immediately! For example the RR Conway 550 n2 at 105% is limited for only 20 seconds before the engine has to be shut down. So a full throttle take-off from there was a no no! Having to shut down four engines shortly after take-off makes for an interesting flight. (if they weren't shut down they would be severely damaged) You "will" also get a hot start!
Click to expand...

You raise an interesting point. AKAIK there are no direct temperature effects on turbine performance in the simulator. In general the sim assumes a standard atmosphere, at least up to the tropopause. The main input is Inverse Air Pressure which I think just comes from altitude.

I have never tried messing with the atmospherics so I just have no idea but would be interested in what others have experienced in the sim.

I am pretty aware of the effects of high temperature from my days flying the F-4M which had Spey turbofans. Flight refueling at 30,000 ft in a tropical atmosphere was tough. We would take on 17500 lbs of fuel which took about 12 minutes of close formation and as the aircraft weight increased so did the power required. Towards the end we sometimes were sliding back with full MIL power and had to select min reheat on one engine. The squadron I was on flew non-stop from UK to Singapore in about 14 hours. A long trip, sitting on an ejection seat.
Roy
 
WOW! Thanks for sharing that Roy! I had no idea. Not to stray off topic too much, but I was able to ride along on a KC mission out of Grand Forks ND. This was WELL before 911. We refueled the Happy Hooligan squadron from Fargo ND, an absolute awesome experience. I had never thought about having to add power let alone reheat. Fascinating!
 
Roy Holmes said:
You raise an interesting point. AKAIK there are no direct temperature effects on turbine performance in the simulator. In general the sim assumes a standard atmosphere, at least up to the tropopause. The main input is Inverse Air Pressure which I think just comes from altitude.

I have never tried messing with the atmospherics so I just have no idea but would be interested in what others have experienced in the sim.

I am pretty aware of the effects of high temperature from my days flying the F-4M which had Spey turbofans. Flight refueling at 30,000 ft in a tropical atmosphere was tough. We would take on 17500 lbs of fuel which took about 12 minutes of close formation and as the aircraft weight increased so did the power required. Towards the end we sometimes were sliding back with full MIL power and had to select min reheat on one engine. The squadron I was on flew non-stop from UK to Singapore in about 14 hours. A long trip, sitting on an ejection seat.
Roy
Click to expand...

Hi Roy,
As far as performance goes as you say it's difficult to judge but certainly EGT goes thorugh the roof and both n1 and n2 are significantly higher at a hot airfield. So that must have a knock on effect in the sim I would assume. Kuwait in the Summer goes up to 54 celsius so it's a good place in the sim to stress the engine with real weather. The one I have noticed is that normally EGT will show ambient temp and then start up to (in my case) 540c on an ISA day and significantly higher on a very hot day. The quirk is that on a hot day engine cooling is no different to a cold day.
With the 10 of course I'm trying to correctly model its hot and high performance. Thrust seems to be unaffected if I set the same take-off n2 at a hot or "normal" field.

I did get the engines to shut down with the hot start bypass isolated in Kuwait. The EGT soared past 650c!!! Thank goodness it's only a sim as I would have been responsible for costly damage!
 
Hi Roy,

Question do you use a weather program like Active Sky? I found a difference in performance using it. Valid parameters, data, analysis I don't have but we could definitely get.
 
Volo,

I have my 1505 worked out to the best I can tell. Slam tests are good and rather accurate. Spool tests are accurate too.

Q. What do the numbers on your fuel (left column) represent? Is that liters per? Gallons? Pounds? Ratio? Thanks.

Q. What did you do to work out your 1506 if I may ask.

Q. Also what did you do to work out 1507?
 
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