PT6A implementation notes.
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Unfortunately this really comes down to writing a wholly external engine simulation - ie: the Majestic Dash - Which I don't think is fair on Nick to accomplish all on his own.
I really wish I could have taken some Asobo people for a run/flight in a PT6 powered airplane before they made 2020. They have some very backwards ideas of how a free-turbine TP is modeled. For developers like Nick - it really hamstrings them unfortunately.
About those charts in the AMM in the 76 & 77 chapters. They are there as a baseline to establish trends and performance on the ground and as a maintenance tool to confirm the propeller & FCU rigging relationship is correct. They are not a tool to determine airworthiness or establish engine performance numbers.
For those with access to the actual Pratt manual, you'll see that the only performance factor in determining airworthiness of an engine, is if it can make static take off power of the day, without exceeding limitations.
The test conditions for the ground are much different than what the aircraft sees in the air. Hence why we have many charts and tables in the AFM.
Being a "flight" simulator, I'd expect Nick to focus his fine-tuning based on those figures in the AFM. Rather than the AMM stuff.
Patrick
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@Black-Square Thanks for the reply! I really meant my post as a question to the community and not an attempt at attention or duplicating information. I realized I hadn't actually validated if it was just me and I didn't want to spool you up about a one off if it was just me — see what I did there, I'll see myself out thanks. I have run into the same scenario with the xplane turboprop model and its attempt at a prop governor. So I have a question for you. Do you have the blade geometry for the D-L104DSZ-0 blades? I posted what I have below
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Unfortunately this really comes down to writing a wholly external engine simulation - ie: the Majestic Dash - Which I don't think is fair on Nick to accomplish all on his own.
I really wish I could have taken some Asobo people for a run/flight in a PT6 powered airplane before they made 2020. They have some very backwards ideas of how a free-turbine TP is modeled. For developers like Nick - it really hamstrings them unfortunately.
About those charts in the AMM in the 76 & 77 chapters. They are there as a baseline to establish trends and performance on the ground and as a maintenance tool to confirm the propeller & FCU rigging relationship is correct. They are not a tool to determine airworthiness or establish engine performance numbers.
For those with access to the actual Pratt manual, you'll see that the only performance factor in determining airworthiness of an engine, is if it can make static take off power of the day, without exceeding limitations.
The test conditions for the ground are much different than what the aircraft sees in the air. Hence why we have many charts and tables in the AFM.
Being a "flight" simulator, I'd expect Nick to focus his fine-tuning based on those figures in the AFM. Rather than the AMM stuff.
Patrick
@plhought said in PT6A implementation notes.:
I really wish I could have taken some Asobo people for a run/flight in a PT6 powered airplane before they made 2020. They have some very backwards ideas of how a free-turbine TP is modeled. For developers like Nick - it really hamstrings them unfortunately.
About those charts in the AMM in the 76 & 77 chapters. They are there as a baseline to establish trends and performance on the ground and as a maintenance tool to confirm the propeller & FCU rigging relationship is correct. They are not a tool to determine airworthiness or establish engine performance numbers.
True but now as a pilot how do you evaluate whether or not the aircraft is making the correct power? That requires the engines to be rigged correctly. So does it hamper the simulation, a couple of the points do. Working from a first principals approach to the engine, right now we are completely breaking conservation of energy on the ground before we even get into the air. I know and understand I am a highly detail oriented person.
There's nothing like flying a BE200 and getting temp limited on the climb. It is interesting to see how the assumptions in both sims hamper tuning. For instance in xplane, you used to have to use maximum thermodynamic power not rated to get the proper critical altitude behavior.
Ultimately my goal with bringing these issues to light is to get a better, higher fidelity simulation. And Nick has the data. I'm building more that may be helpful for the prop model right now. It's in Nick's hands, I'm interested to see what ultimately happens and offer constructive feedback .
Crash
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As I stated before. The only measure of airworthiness, and what I pilot sees - is the static take-off power charts in the AFM. Nothing more.
The AMM charts are not part of any 24hr or operational check for flight crews. Nor are they to be used to determine the performance margins of said engines. They are simply a set baseline for maintenance. For example, in my career we will use them to gauge any changes after a fuel nozzle change. By comparing to the last numbers (if recorded) at the previous nozzle change vs. numbers post change. That way - we can enter that into our airborne trend monitoring, and not get alerted that an ITT trend decrease is not an instrumentation issue.
I'm not sure what you mean by "conservation of energy". I'm confused what you are stating here.
In simple terms - once again - the AMM charts are not used in the real world to gauge an engines health. We use recorded trend monitoring recorded during flight, never on the ground.
I've seen engines that run 40+ degrees cooler than the ground performance charts for a given torque, vs. engines that run 20+ degrees hotter for the same given torque and conditions. Some new, some old.
But they make power of the day without exceeding limitations. Once again, that is the only airworthiness performance limitation. If an engine temps out or NGs out at altitude - that's inconsequential. If they make Take Off power - that's all that matters.
So once again, you can't use the AMM charts as an absolute reference of engine performance. They are a maintenance tool only. In fact, the engine manual even breaks this down further, as we have trim resistors, compressor classes, adjustments marked on the data-plate etc. All to "spoof" and adjust the instrumentation so that the engines don't exceed their torque or power limitations (ie: engine and airframe is only rated for 750hp. We technically can't have it producing more than that - even if it's got a very good compressor or turbine that is capable of producing it).
@ProfCrash said in PT6A implementation notes.:
True but now as a pilot how do you evaluate whether or not the aircraft is making the correct power?
In simple - that's what an engineer's/mechanic's signature is for. The pilot is not a determining authority of the airworthiness of an aircraft.
The cruise performance charts in the AFM are a much better resource for modelling. As for the intricacies of PT6 beta handling - unfortunately that is not something that can be broken down into tables and charts. No matter how one may try. Woodward? Bendix? Z-gap? No z-gap? Etc etc.
Patrick
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@plhought said in PT6A implementation notes.:
As I stated before. The only measure of airworthiness, and what I pilot sees - is the static take-off power charts in the AFM. Nothing more.
The AMM charts are not part of any 24hr or operational check for flight crews. Nor are they to be used to determine the performance margins of said engines. They are simply a set baseline for maintenance. For example, in my career we will use them to gauge any changes after a fuel nozzle change. By comparing to the last numbers (if recorded) at the previous nozzle change vs. numbers post change. That way - we can enter that into our airborne trend monitoring, and not get alerted that an ITT trend decrease is not an instrumentation issue.
The use of the AMM acts as a starting point to evaluate current engine state vs expected. If there is a deviation it is worth noting and investigating. That is what I did here.
I'm not sure what you mean by "conservation of energy". I'm confused what you are stating here.
This is from a first principals approach to physics. F=M x A, if you are applying a force to a mass it will accelerate in some direction. Acceleration is a change in velocity with respect to time. Kinetic energy is the 0.5*mv^2, or in the case of rotating bodies, KE_r = 0.5 * MOI * (V_r)^2 its the same thing just in a rotating frame. And a change in kinetic energy for a body not due to changing in mass then has to be due to a change in velocity, which is an acceleration and those can only occur due to a change in force
And the conservation of energy is Initial energy = final energy. The thermodynamics are defined by the brayton cycle (https://www.grc.nasa.gov/www/k-12/airplane/brayton.html). So if the Np changes speed then there is a net decrease in the energy but the Np is getting the same amount of energy from the turbine so we can do the same thing to NP -> Ke_Np_turb = Ke_prop + Ke_air. and the Ke_air can be further expanded to Ke_air = Ke_air_drag + Ke_air_thrust.(Ke_prop_initial + Ke_air_drag_initial + Ke_air_thrust_initial) = (Ke_prop_final + Ke_air_drag_final + Ke_air_thrust_final)so lets run some numbers. I have a prop and it is spinning with 1000J of kinetic energy, then the prop is pushing on the air and that is initially taking 50J of energy to spin the air around the prop (spiraling slipstream drag) because the prop is streamlined, the air pushed past the prop is accelerated and the change in velocity of the air results in the air having a kinetic energy of 3950J. The total energy of the prop system is 5000J. That means what ever the new state of the prop, the energy total MUST be the same. So now the prop is feathered, well in the feathered state now the drag energy is 4500J, the prop is feathered which means no forward thrust, so Ke_air_thrust_final = 0 which means now the prop ke has to reduce down to a speed equivalent to 500J of energy.
1000 J + 50 J + 3950 J = 500 J + 4500 J + 0 J.
so the prop had a net change of -500J of kinetic energy Ke = MOI x (V_r)^2, so if the MOI didnt change then the only thing that could happen is the prop slowed down. Now, here is the other bit. Ke_air_drag + Ke_air_thrust are measurable, that is the torque on the Np shaft. The hot air flows over the Np turbine and tries to spin it, and because of Newton's third law (action-reaction) the prop pushing on the air to transfer the energy results in the air pushing back opposite to the direction of rotation that is torque in the system. That is measured by the movement of the first stage ring gear in the helical gear moving a pilot valve to admit pressurized oil into the gallery where the transducer is before passing through a calibrated orifice back to the oil sump.The starship currently changes blade angle without registering a torque. that means there is an inconsistency in the amount of energy in the system. try it yourself but sitting at min alpha (FLT idle) and feather the props) and think back in the context of whether that makes sense with the conservation of energy
In simple terms - once again - the AMM charts are not used in the real world to gauge an engines health. We use recorded trend monitoring recorded during flight, never on the ground.
I've seen engines that run 40+ degrees cooler than the ground performance charts for a given torque, vs. engines that run 20+ degrees hotter for the same given torque and conditions. Some new, some old.
But they make power of the day without exceeding limitations. Once again, that is the only airworthiness performance limitation. If an engine temps out or NGs out at altitude - that's inconsequential. If they make Take Off power - that's all that matters.
So once again, you can't use the AMM charts as an absolute reference of engine performance. They are a maintenance tool only. In fact, the engine manual even breaks this down further, as we have trim resistors, compressor classes, adjustments marked on the data-plate etc. All to "spoof" and adjust the instrumentation so that the engines don't exceed their torque or power limitations (ie: engine and airframe is only rated for 750hp. We technically can't have it producing more than that - even if it's got a very good compressor or turbine that is capable of producing it).
@ProfCrash said in PT6A implementation notes.:
True but now as a pilot how do you evaluate whether or not the aircraft is making the correct power?
In simple - that's what an engineer's/mechanic's signature is for. The pilot is not a determining authority of the airworthiness of an aircraft.
I looked at the gauges, and if the engine was rigged properly to not exceed engine limits as you point out, then I should generate the thrust required per my Torque, ITT, Np, Ng. If any one of those are indicating something spurious, I am grounding the aircraft as not airworthy with a maintenance item because either the instruments are faulty or the engine is, and both are required to be functional and be airworthy. And I have the authority to do so as Pilot in Command of a civil aircraft as outlined in 14CFR91.7.
§ 91.7 Civil aircraft airworthiness.
(a)No person may operate a civil aircraft unless it is in an airworthy condition.(b) The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur.
Never in my aviation career was I told that because a sign off said something was airworthy that I had to take it.
Edit: Did you mean Pilots dont have the authority to dictate an engine tune? then yes. A pilot does not have the authority to make specific maintenance actions. Fly it by the numbers but if the numbers don't match within the allowable tolerances, then time to stop the process and start asking questions. Airworthiness is a joint venture between mechanics and pilots. But the final determination lies with the PIC.
The cruise performance charts in the AFM are a much better resource for modelling. As for the intricacies of PT6 beta handling - unfortunately that is not something that can be broken down into tables and charts. No matter how one may try. Woodward? Bendix? Z-gap? No z-gap? Etc etc.
Patrick
It already has happened, libturbine is a specific engine thermodynamic model used to do the thing you are talking about. See the Hotstart Challenger 650 and its full implementation of the hydro-mechanical FCU. its being used to update their TBM 900 as we speak. The Xplane stock turboprop model has correct and fully functioning Alpha and Beta modes. So can it be done, yes. Can it be done in MSFS, maybe not as well.
Crash
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I won't lie, I appreciate your impassioned response, but a lot of it is beyond the remit of this forum.
I've only been working on and living with these machines for 20 years, but okay. I guess if I can't quote CFRs, and allow pilots to use maintenance tables to ground an airplane prior to every flight, I guess I don't know what I'm doing. Guess that note at the beginning of chapter 77 means nothing.
Find me any numerical limitation in the AMM Chapt 77 Engine Operating Chart for ITT, Ng or Wf, and I'll hand in my license.
Anyways, I'm getting testy. Good luck with the modelling. It's always good people are passionate about this hobby I suppose. Will be cool to see a proper PT6 simulation one day.
Cheers,
Patrick
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I won't lie, I appreciate your impassioned response, but a lot of it is beyond the remit of this forum.
I've only been working on and living with these machines for 20 years, but okay. I guess if I can't quote CFRs, and allow pilots to use maintenance tables to ground an airplane prior to every flight, I guess I don't know what I'm doing. Guess that note at the beginning of chapter 77 means nothing.
Find me any numerical limitation in the AMM Chapt 77 Engine Operating Chart for ITT, Ng or Wf, and I'll hand in my license.
Anyways, I'm getting testy. Good luck with the modelling. It's always good people are passionate about this hobby I suppose. Will be cool to see a proper PT6 simulation one day.
Cheers,
Patrick
@plhought said in PT6A implementation notes.:
I won't lie, I appreciate your impassioned response, but a lot of it is beyond the remit of this forum.
I've only been working on and living with these machines for 20 years, but okay. I guess if I can't quote CFRs, and allow pilots to use maintenance tables to ground an airplane prior to every flight, I guess I don't know what I'm doing.
Cheers,
Patrick
I'm not sure I understand what you mean but that seems a bit reductive. I wouldn't presume to tell a maintenance professional how to tune an engine but I can evaluate an engine for airworthiness on during the course of operations and note discrepancies like, "Engine 1 Torque appears to not make rated torque at take off Ng" or "Right prop appeared to not feather during feather check" or "Engine 1 REV UNLOCK illuminated during taxi". I won't tell a Maintenance professional what adjustments need to be made, because it isn't my signature on the log. But that determination of a discrepancy means the aircraft is no longer airworthy. And on the flight log I certify the airworthiness of the aircraft, or lack there of by a discrepancy. It's a joint venture between both sides of Ops.
The statements made about engine conservation of energy are well within scope of the forum specifically because of my first post and the basis for the engine tune. It really sounds like there's a miscommunication somewhere here but I'm not sure what. It's a pretend airplane at the end of the day we both like.
I noticed something about the engine and asked for clarification based on the documents from the aircraft. The statements made about the aircraft were about the very high fidelity of systems (engines included). I was trying to clarify if the discrepancy between the model I noted were isolated to me or otherwise. I tried to address your questions as completely as possible with the completeness I would appreciate from anyone else. I flew for over 15 years and now teach physics. sharing knowledge is what I do.
In complete levity of your chapter 77 limitation, challenge accepted
. If you want more from 76 lmk 
All the best
CrashEdit: you updated your post while I was comping this one @plhought. Regarding the note from C77 on the engine parameters chart
I was using the graph as a reference to compare, nothing more nothing less, and if you note, the exception of N1, everything is very close. A delta FF like that seen would be totally fine imo, its a 4.6% variance and so long as other params are good,
The ground performance worksheet though would be more of a concern to me worth investigating if I was evaluating an engine, would you come to the same conclusion? The "sole criteria" aspect seems to be referring to doing something like the ground performance worksheet. Would you use that as the basis for airworthiness?
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@plhought said in PT6A implementation notes.:
I won't lie, I appreciate your impassioned response, but a lot of it is beyond the remit of this forum.
I've only been working on and living with these machines for 20 years, but okay. I guess if I can't quote CFRs, and allow pilots to use maintenance tables to ground an airplane prior to every flight, I guess I don't know what I'm doing.
Cheers,
Patrick
I'm not sure I understand what you mean but that seems a bit reductive. I wouldn't presume to tell a maintenance professional how to tune an engine but I can evaluate an engine for airworthiness on during the course of operations and note discrepancies like, "Engine 1 Torque appears to not make rated torque at take off Ng" or "Right prop appeared to not feather during feather check" or "Engine 1 REV UNLOCK illuminated during taxi". I won't tell a Maintenance professional what adjustments need to be made, because it isn't my signature on the log. But that determination of a discrepancy means the aircraft is no longer airworthy. And on the flight log I certify the airworthiness of the aircraft, or lack there of by a discrepancy. It's a joint venture between both sides of Ops.
The statements made about engine conservation of energy are well within scope of the forum specifically because of my first post and the basis for the engine tune. It really sounds like there's a miscommunication somewhere here but I'm not sure what. It's a pretend airplane at the end of the day we both like.
I noticed something about the engine and asked for clarification based on the documents from the aircraft. The statements made about the aircraft were about the very high fidelity of systems (engines included). I was trying to clarify if the discrepancy between the model I noted were isolated to me or otherwise. I tried to address your questions as completely as possible with the completeness I would appreciate from anyone else. I flew for over 15 years and now teach physics. sharing knowledge is what I do.
In complete levity of your chapter 77 limitation, challenge accepted
. If you want more from 76 lmk
All the best
CrashEdit: you updated your post while I was comping this one @plhought. Regarding the note from C77 on the engine parameters chart
I was using the graph as a reference to compare, nothing more nothing less, and if you note, the exception of N1, everything is very close. A delta FF like that seen would be totally fine imo, its a 4.6% variance and so long as other params are good,The ground performance worksheet though would be more of a concern to me worth investigating if I was evaluating an engine, would you come to the same conclusion? The "sole criteria" aspect seems to be referring to doing something like the ground performance worksheet. Would you use that as the basis for airworthiness?
No, I would not use the Ground Performance procedure as determining the airworthiness of an engine. Just like it states in the amm notes.
Having worked on and managed on-condition PT6 fleets where we have some hot sections with 9000+ hours between overhauls - we would be grounding aircraft every day and putting a lot of pilots out of a job if we did.
Once again, the only real determining operational method of checking the airworthiness of an engine, as per the Pratt manual, is if it can make it's take-off power without exceeding the absolute engine limitations. Those charts are in the AFM.
Beyond that, we look at borescopes, oil analysis, filter patch checks, and trend monitoring taken at cruise. Instrumentation checks every couple hundred of hours usually catches any variations in those systems as well.
There is no means available to the pilots for snagging something in your scenario of not making a specific Tq for a given Ng. Changes in temperature, density, anti-ice on or off, variations of the engine itself would make such a determination totally unreliable.
And your picture of torque calibration is not an operational limitation with the engine running - it's when we have a dead-weight tester plumbed into the torque transducer and are inspecting the Tq indication system. It's disconnected from the engine during this procedure.
I'm pleased your eager to share your knowledge and such, good luck with your endeavours.
Patrick
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I'm really enjoying blasting around the sky in the Starship.
So I noted a couple interesting things with the engine model in MSFS 2024
- at -4% throttle the engine runs away in reverse.
- Torque indications are 0% ground fine or reverse beta. This can't be (see note 6)
- when moving EDIT: power levers from FLT IDLE to GND FINE the fuel scheduling and N1 change, which they should not as this only actuates blade angle. The thermodynamic output of the engine is constant therefore if blade angle changes so should rpm as the sum of all the forces change on the prop
- Feathered prop lever state is not respected when moving from FLT IDLE to ground fine. Edit: Props will unfeather and move to beta state.
- Prop load vs torque values. If you are at any nominal torque value and actuate the props, the torque doesn't change. This isn't possible since the torque reading comes directly from the first stage ring gear moving aft on on the helical splines in the engine casing resulting in more or less oil to the torque sensor which compares this metered oil to the sump pressure via a calibrated orifice. So if the prop forces change so must the torque. Torque values seem to be internal computations disconnected from sim data.
- Low Pitch Prop test switch does not change blade pitch above FLT IDLE, and rpm indication is being adjusted in the gauge only. See 76-00-00 P12 Step 2(c). Actuation of the Low pitch prop should affect blade angle regardless of power lever position. Actuating this switch in sim and advancing power results in 0 rpm change which is impossible because the thermodynamic power is increasing with a fixed pitch prop.
In AMM 61-21-00 Page 7 is the procedure for the AFX system. it appears the system isn't properly implemented as the system fails operational tests steps (h)-(i).
In AMM 76-00-00 Page 16, The ground performance worksheet lists several values to evaluate the current engine tune.
Parameter: Target / Actual
Start N1: 53-55 / 66.5
Gnd Fine N1: 65.5-66.5 / 72.8
Max Rev N1: 83-85 / 74.7
FLT IDLE Torque (Target is Per 76-00-00 P16 & P12 Step o.): Can not be determined (see note Edit: 6)
GND Idle Torque (Target is Per 76-00-00 P18 & P13 Step p.): 9% / 24%In AMM 77-00-00 Page 1, The procedure is outlined for periodic engine performance checks. the charts are on page 2, the procedure is on pages 1 & 3.
New engines.
Pressure: 29.92" Temperature: 15C
Torque: 80%
Parameter: Target: Actual L / Actual R
ITT: 740: 752/747
N1: 97.5: 100.0/100.1
FF: 650: 678/682Has anyone else seen this engine behavior or is something funky happening with my sim? Is this a result of the legacy prop model being used?
Thanks,
PrfCrashSources: https://www.bobscherer.com/Pages/Starship%20Resources.htm
@ProfCrash said in PT6A implementation notes.:
Low Pitch Prop test switch does not change blade pitch above FLT IDLE, and rpm indication is being adjusted in the gauge only. See 76-00-00 P12 Step 2(c). Actuation of the Low pitch prop should affect blade angle regardless of power lever position. Actuating this switch in sim and advancing power results in 0 rpm change which is impossible because the thermodynamic power is increasing with a fixed pitch prop.
To help illustrate what Dr. Crash is mentioning here - here's a quick vid of a low-pitch test on a 1900D. You'll see the Tq increase he's talking about as a result of the blade angle getting coarser.
Patrick
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@ProfCrash said in PT6A implementation notes.:
Low Pitch Prop test switch does not change blade pitch above FLT IDLE, and rpm indication is being adjusted in the gauge only. See 76-00-00 P12 Step 2(c). Actuation of the Low pitch prop should affect blade angle regardless of power lever position. Actuating this switch in sim and advancing power results in 0 rpm change which is impossible because the thermodynamic power is increasing with a fixed pitch prop.
To help illustrate what Dr. Crash is mentioning here - here's a quick vid of a low-pitch test on a 1900D. You'll see the Tq increase he's talking about as a result of the blade angle getting coarser.
Patrick