FO Power Setting and Torque Limits...

[ESzczesniak 128]

As at least some of you are aware, the coding for FS2Crew has the FO simply advancing throttles to full open. This is not a knock against FS2Crew, as it's the only reasonable way to code it. However, at some higher elevations and higher OAT's, this can exceed maximum EGT. It sure would be nice if the FO could set the engines without blowing EGT though so that you can concentrate on steering down the runway.My thought was that if we could set a hard torque limit on the engines, then even if the FO advanced the throttles fully, the torque limit would stop the application of power before exceeding EGT's. Unfortunately airlines pay thousands of dollars for charts to determine similar torque and reduced torque limts, and as such don't tend to share them with PC flight simulators.However, my thought was this may be crudely simplified down to one or two variables. Seeing as I only have MS Excel, multivariate analysis isn't an option and I tried looking at this with density altitude as the variable. It would make sense that the less air mass moving over the engine, the worse cooling it will have. There is a logic to ambient air temperature being it's own seperate variable (in addition to it's factor in density altitude), but as I mentioned, I can't do a two variable regression with the software I have.So I set out to 5 different airports, recorded the altitude, altimeter, OAT and dew point. Then set the condition levers to flight and advanced the throttles just to the point before the TTL light illuminated and recorded the torque (this was a static test, but EGT did not appear to drop if the aircraft was accelerating down the runway within the simulator--it should drop slightly in real life though). The airports at the time I was at them were spaced between 3,500 and 9,500' density altitude (summer temps right now). I plotted them out and from the small n I have, it appears a solid linear relationship exists that might allow us to set these torque limits. I will continue to try and add to n for a more reliable data set.However, at the moment I have the formula of Max Torque = -0.0017 x Density Altitude + 103.12. The R^2 value is 0.9959--very strong. Perhaps try it a bit and see how it works for you. The idea is that you would set the torque limiter to the value you get from this equation (maybe 0.2 to 0.5 less just as a safety margin). Then, as the FO applied "full throttle", it would stop once reaching this set torque limit thereby preventing EGT's above maximum allowed EGT. Additionally, should anyone want to help me add to the data, just repeat the procedure and send me the altitude, OAT, altimeter and torque value by PM and I can add it to what I have. Additionally, this formula would suggest that if your departure density altitude is less than approximately 1,800' then you can use 100% torque without any worries of exceeding EGT. We'll see how all this holds up as I try to add more data to this.It should be noted that this is an attempt to determine the maximum torque allowed by intrinsic engine parameters (i.e. maximum EGT). What makes this different than those thousand dollar airline charts is this makes no comments based on runway length, aircraft weight and obstacle clearance. This is just ot keep you from frying your engines by asking for too much torque.Granted, it's a bit of a crude and complicated work around. However, trying to finess the throttles to max power while steering down the runway can be a bit tricky and it would be nice to be able to have the FO "set power" without worrying about EGT's. Of course, there will be one additional calculation for each flight, but at least this can be done during the quiet preflight period and not the busy and hectic time of the takeoff roll.

[byork 2,258]

Thanks for sharing that!

[JHepburn 0]

As at least some of you are aware, the coding for FS2Crew has the FO simply advancing throttles to full open. This is not a knock against FS2Crew, as it's the only reasonable way to code it. However, at some higher elevations and higher OAT's, this can exceed maximum EGT. It sure would be nice if the FO could set the engines without blowing EGT though so that you can concentrate on steering down the runway.My thought was that if we could set a hard torque limit on the engines, then even if the FO advanced the throttles fully, the torque limit would stop the application of power before exceeding EGT's. Unfortunately airlines pay thousands of dollars for charts to determine similar torque and reduced torque limts, and as such don't tend to share them with PC flight simulators.However, my thought was this may be crudely simplified down to one or two variables. Seeing as I only have MS Excel, multivariate analysis isn't an option and I tried looking at this with density altitude as the variable. It would make sense that the less air mass moving over the engine, the worse cooling it will have. There is a logic to ambient air temperature being it's own seperate variable (in addition to it's factor in density altitude), but as I mentioned, I can't do a two variable regression with the software I have.So I set out to 5 different airports, recorded the altitude, altimeter, OAT and dew point. Then set the condition levers to flight and advanced the throttles just to the point before the TTL light illuminated and recorded the torque (this was a static test, but EGT did not appear to drop if the aircraft was accelerating down the runway within the simulator--it should drop slightly in real life though). The airports at the time I was at them were spaced between 3,500 and 9,500' density altitude (summer temps right now). I plotted them out and from the small n I have, it appears a solid linear relationship exists that might allow us to set these torque limits. I will continue to try and add to n for a more reliable data set.However, at the moment I have the formula of Max Torque = -0.0017 x Density Altitude + 103.12. The R^2 value is 0.9959--very strong. Perhaps try it a bit and see how it works for you. The idea is that you would set the torque limiter to the value you get from this equation (maybe 0.2 to 0.5 less just as a safety margin). Then, as the FO applied "full throttle", it would stop once reaching this set torque limit thereby preventing EGT's above maximum allowed EGT. Additionally, should anyone want to help me add to the data, just repeat the procedure and send me the altitude, OAT, altimeter and torque value by PM and I can add it to what I have. Additionally, this formula would suggest that if your departure density altitude is less than approximately 1,800' then you can use 100% torque without any worries of exceeding EGT. We'll see how all this holds up as I try to add more data to this.It should be noted that this is an attempt to determine the maximum torque allowed by intrinsic engine parameters (i.e. maximum EGT). What makes this different than those thousand dollar airline charts is this makes no comments based on runway length, aircraft weight and obstacle clearance. This is just ot keep you from frying your engines by asking for too much torque.Granted, it's a bit of a crude and complicated work around. However, trying to finess the throttles to max power while steering down the runway can be a bit tricky and it would be nice to be able to have the FO "set power" without worrying about EGT's. Of course, there will be one additional calculation for each flight, but at least this can be done during the quiet preflight period and not the busy and hectic time of the takeoff roll.

Check my math, please. What's your calculated density altitude and torque at 5,540ft (KDEN pressure altitude-- I think...meaning actual height ASL) and 26C? Once I feel good about my ability to calculate pressure altitude, then I will help with this. Also, when we're done, we should try and get the white hash mark EGT calculated as well...so that we can figure reduced thrust takeoffs :)Thanks!

[stefltt 11]

Here is how I calculate Pressure altitude. The rule is that the pressure decreases 1HPa per 28ft when altitude increases.Let's take an example :Airport is KDENAltitude of the airport : 5540ft ASLQNH today is 1023HPa, so it is 10 HPa more than 1013HPa (standard). 10 HPa equal 280ft.so the pressure altitude today for this QNH is : 5540ft - 280ft = 5260ftit is better to do a drawing to understand but here in this forum I cannot draw when posting a message ! So I will try to explain.Place 1023HPa at the bottom of your page and draw an horizontal line.Place 1013HPa somewhere up on the page and draw an horizontal line.the difference between the two lines is 280ft.Place KDEN airport above 1013 line and draw an horizontal line.The difference between KDEN line and 1023HPa line is 5540ft.The difference between KDEN Line and 1013 HPa line is the pressure altitude.KDEN 5540Ft ASL ---------------------------------------------------------------------------------------------------"Altitude" 280ft ASL 1013 HPa -------------------------------------------------------------------------------------------------------Sea Level 0ft 1023HPa ---------------------------------------------------------------------------------------------------------

[Guest BlueRidgeDx]

Guys,I posted this over in the PMDG Turboprop forum, and I'm reposting here for your review:There has been a lot of discussion regarding Takeoff Torque settings since the release of FS2Crew. A few folks have taken the initiative, and are actively looking for ways to approximate the performance data. There are some good ideas floating around, and I just wanted to add my take on the issue.I first attempted to adapt the real data for use in the simulator, but unfortunately, the amount of data that I have is too small of a sample to be able to extrapolate with any kind of accuracy. Second, the real data didn't really match the simulator in most cases, which I chalk up to the fact that the FSX turboprop model is totally boned.So instead, I spent the evening flight testing the J-41 in FSX and recording the simulator data. I tabulated that data, and the result is a simple spreadsheet that covers the entire operational temperature range, and from Sea Level up to 6000ft (Pressure Altitude). I'd be willing to do the work to get the data valid out to 8000ft if there is demand for it, but we'll see how that goes.I tested the data at about half a dozen airports using current weather and had very good results. Please test it out and verify that the data works throughout the range of conditions, and provide any feedback so I can tweak as necessary...Note: I found that the most accurate method is to use the closest altitude and temperature from the chart. For example, if the field elevation is 5150, and the temp is 11C, it's best to use to use the value that corresponds to 5000' and 10C. In the real world, you would typically go to the next highest value in order to find the most conservative limit, e.g. 5500' and 13C. That method is not preferable using this data.

[trisager 2]

I posted this over in the PMDG Turboprop forum, and I'm reposting here for your review:

Thanks for this!

[ESzczesniak 128]

Hello guys,Unfortunately, it turns out that I am mistaken regarding the way the torque setting works. Its sole purpose it to provide a visual display (hash mark on the torque gauge) of you're desired torque. It does not in fact limit the torque in anyway. What this means is that this has no real use for helping us with the FS2Crew FO setting the power.However, as a general project to give us ideas on torque vs. EGT limits, it still has uses and I'd be happy to try and coordinate projects to increase our data and give us an idea where to set the torque for either max torque or for the white line torque. For those asking, my formula for density altitude is:Denisty Altitude = Current Altitude + Absolute Value(1000*(29.92-current altimeter) + 120*Absolute Value(Current Temp - Standard OAT at Given Altitude)The ideal temperature at a given altitude can be looked up in charts, or found with the formula:Stanard OAT = -0.002*Altitude +14.986I fly in the USA, so I have the odd mix of units aviaiton uses here--altimeter in inches and OAT in degrees C.Anyway, this is still useful information, but not nearly as valuable as when I thought we could use it to limit the FO power setting.EDIT: I also had an error in my spreadsheet originally. The formula I have currently is:Max Torque = -0.0014 x Density Altitude + 99.422, R^2>0.99It seems to accurately predict within +/- 1% so far on my testing.