A10C engine model

[bkthunder]

Equal ITT does not determine equal thrust (see the real engine records). Thrust for high-bypass ratio engines is more a function of Nf. ITT, in general, it's a matter of efficiency of compressor, fan, turbines.

 

So, playing with efficiency figures adjusting the model or dealing with manufacturing tolerances and wear in the real engine you can see different ITT with the same thrust.

 

I mentioned above that ITT limiter adjustment is a mean to obtain necessary predicted fan speed, i.e. specified thrust.

 

Yo-Yo, thanks for answering. I don't want to push you but you didn't say how much thrust does the engine in DCS-A10C produce.

 

I understand what you say about ITT being a limiting factor to control N1/N2 rpm. I will add a quote from a related discussion (from a crew chief):

 

ITT is limited by limiting maximum fuel flow in order to prevent compressor discharge temperature from becoming excessive during operation at high thrust/low altitude/low temperature.

 

So as it seems, fuel flow also has a play in this.

Anyone is interested in checking the fuel flow parameters in DCS as opposed to RL? Does it make sense?

 

In the A-10 specifically, setting a specific ITT is the preferred method for setting thrust and obtaining matched climb performance between aircraft. In other words, when flying something like an Instrument Trail Departure (ITD), a flight of four A-10s must fly through Instrument Meteorological Conditions (IMC). With no radar, and no ability to maintain visual separation, the standard procedure is for all flight members to set 800 ITT and adjust pitch to maintain 200 KIAS. Each aircraft strives to maintain 1,000 feet of vertical separation from the preceding aircraft. ITT is then adjust in 25 degree increments in order to maintain spacing.

 

Using ITT in the manner described above makes it a control instrument, thus correct indications are important. Especially when ITT values correlate to a known amount of thrust and thus aircraft performance. N1 (Fan RPM) is generally a better direct indicator of thrust, but nonetheless, standard practice in the A-10 is to use ITT for climb and Fuel Flow for cruise. Fan RPM is only really checked once during the takeoff roll.

This seems to contradict what you said, because a given ITT = a guaranteed amount of thrust, hence why it is used as a primary indication by real A-10s

Edited August 5, 2016 by bkthunder

[David OC]

This seems to contradict what you said, because a given ITT = a guaranteed amount of thrust, hence why it is used as a primary indication by real A-10s

 

A10 Flight could use the ITT setting when close together, the way I see it if you sent your

2nd element up to a much different height then you would or could run into trouble going off the ITT and stay together.

 

Engine delivers full-rated power at altitude by having the margin to increase rpm and ITT

So the engine is trying to keep a throttle/trust setting using a governor.

 

So there could be a difference in ITT if one part of the flight is flying in different air temperature or in less dense air.

 

Few quick resources

http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node85.html

Thesis: Performance Analysis of J85 Turbojet Engine PDF

[Yo-Yo]

 

This seems to contradict what you said, because a given ITT = a guaranteed amount of thrust, hence why it is used as a primary indication by real A-10s

 

So, you would say that the recorded engines has different thrust at TO? Or they have equal thrust due to equal Nf or played with different ITT for it?

[mvsgas]

This seems to contradict what you said, because a given ITT = a guaranteed amount of thrust, hence why it is used as a primary indication by real A-10s

 

It seems the manual contradict each other as well. 1A-10A-1-1 Figure A2-16 page A2-31

[ATTACH]145888[/ATTACH]

 

So which is the direct indication of thrust fan RPM or ITT?

 

Another example, 1A-10C-1. page 1-6 change 10

Bypass air produces over 85% of engine thrust. Therefore, engine fan speed is the best indication of thrust.

and

Thrust will increase as fan speed increases.

 

Edit

The more I thinking about this, the more I think is a matter of misunderstanding the manuals. Fan speed show the power output of the engine. But as a pilot you can not control fan speed directly. The parameter most directly affected by throttle position is ITT. So Fan speed is thrust while, ITT is throttle position. So ITT being lower in DCS does not indicate less power, just indicated we need to find the ITT number in DCS to set the throttle.

Edited August 6, 2016 by mvsgas

[David OC]

The main reason to test an engine in a test cell is basically to prove that the engine is capable of providing the minimum required certified engine thrust.

 

When an engine is repaired, inspected or overhauled in the engine shop, it requires an extensive series of tests to ensure that the engine is fit for reinstallation again.

 

I would like to know if there is a difference to the military specification on minimum required certified engine thrust?

 

This was taken from the link below

https://blog.klm.com/how-do-we-test-jet-engines

 

In 2006, the A-10 Propulsion Upgrade Program entered the system design and demonstration phase. This program upgrades the A-10's current TF34-100A engines to provide approximately 30% more thrust.

http://www.globalsecurity.org/military/systems/aircraft/systems/tf34.htm

 

Now this 30% more thrust would be a newer version right?

So you can download the data sheet here www.geaviation.com

 

Thrust range: 9,065-9,275 lbs is this the 30% more engine tho?

Notice the range here so 9065 is OK on the engine test.

 

This is quite a small range above I would like to know what the range is on ww2 engines if they were even tested.

 

EDIT: What is the range difference too for the older TF34-100A engines?

Edited August 6, 2016 by David OC

[mvsgas]

I'm not an engine guy, but AFAIK, in the military test cells, they do not check for thrust output. The engine manufacturer do. So when engine in the USAF or others go to test cell after a major repair or simply schedule maintenance, they check for temp being in a range at certain throttle setting. Like I said before, don't know much about the A-10 but in the F-16 for example, they check for Fan/core RPM at certain % range, temp, oil pressure, etc. at a Power Lever Angle (PLA)

So at 60 degrees PLA, Core RPM should not exceed "this", oil pressure should be "X" to "Y", etc.

[bkthunder]

So, you would say that the recorded engines has different thrust at TO? Or they have equal thrust due to equal Nf or played with different ITT for it?

 

I don't know, as others have stated these points seem to contradict themselves.

What I quoted is coming from a crew chief. Not an engine designer or engineer, but nonetheless, someone who spent more time around a real A-10C than most other people, so his point deserves some attention IMO.

 

The fact that ITT is used as the main engine gauge in the A-10, in RL procedures, also points to it being a pivotal number.

 

Did you notice I asked you a few times, how much thrust does the TF-34 in DCS produce (sea level, standard day)?

[David OC]

From the DCS Manual

At maximum thrust, each engine produces 8,900 pounds of standard thrust at sea level on a standard day.

 

ED would perhaps have a set of engine test cell data on the engine I'm guessing, so they may have data points

across the trust profile and know if it's all within the limits of said data.

 

developed thrust, Fuel consumption, oil consumption, rotor speeds, pressures and temperatures.

 

It may not be the absolute best performing suite 3 TF34-GE-101 engine or data? are we talking 165 pounds? on the suite 3, unless

you have more sets of cell data on a new suite 3 engine? To compare to the one's we have, I don't see how or why you would try and change

all the data points on the engine we have.

 

What exactly would Yo-Yo change all the engine parameters to, just it Guess? This would take a longtime.

Yo-Yo is just as much into perfectionism like most of you, so I'm thinking he will not just be guessing it

to perhaps get it in a range to a suite 3 engine. What is the minimum trust range on a suite 3 TF34-GE-101?

[Raistlen007]

Regarding the AoA stall issue, here is a HUD video of an A-10 taking on F-16s. You'l notice the stall warnings go off multiple times during the video, including during extreme banks, climbs, and dives, and not once did the A-10 spiral out of control like it does in DCS.

 

[ame]

[/ame]

[David OC]

We are taking about the engines here, this video has no relative information. The DCS A10C fly's great like your video to, with minimum fuel and no ordnance.

 

Edit: The video you posted was posted in 2012, so the engines here may well be up to 30% better trust then what we have in the suite 3 TF34.

Edited August 7, 2016 by David OC

[Raistlen007]

If I should open a separate thread for the AOA, I will, but I tried doing that maneuver myself with min fuel and no ordianance, and I can't do it. The airplane stalls coming up from the dive and doesn't let you complete the maneuver. I challenge you to replicate the maneuver yourself. Just try it.

 

Edit: After many tries I've managed to get pretty close, but during a climb turn the DCS flight model seems to bleed a lot more airpseed than the real life counterpart in the video does. The engine thrust issue might not just be engine modeling. Could be aerodynamics or drag modeling issues, which is why I feel the AoA issue and the engine issue might be related.

Edited August 7, 2016 by Raistlen007

[mvsgas]

If I should open a separate thread for the AOA, I will, but I tried doing that maneuver myself with min fuel and no ordianance, and I can't do it. The airplane stalls coming up from the dive and doesn't let you complete the maneuver. I challenge you to replicate the maneuver yourself. Just try it.

 

Edit: After many tries I've managed to get pretty close, but during a climb turn the DCS flight model seems to bleed a lot more airpseed than the real life counterpart in the video does. The engine thrust issue might not just be engine modeling. Could be aerodynamics or drag modeling issues, which is why I feel the AoA issue and the engine issue might be related.

Would love to replicate it, could you tell me, in the video, how many units of angle the pilot use, 15, 20? What was the aircraft configuration? Aircraft weight? Ambient conditions?

 

 

We are taking about the engines here, this video has no relative information. The DCS A10C fly's great like your video to, with minimum fuel and no ordnance.

I agree

 

 

I think I'm done, I do not see the A-10C engines under performing as original post mention.

[Raistlen007]

Would love to replicate it, could you tell me, in the video, how many units of angle the pilot use, 15, 20? What was the aircraft configuration? Aircraft weight? Ambient conditions?.

 

Even without knowing the exact conditions, if we create in the simulator ideal or plausible conditions we can deduce whether or not it is possible for the airplane in the sim to preform close to the real thing, or if not then we know there is a real gap.

 

Don't take my word for it. Don't listen to how I feel about it. Jump in and just try it yourself. See if you feel like you can comfortably and reliably replicate that maneuver without stalling and spiraling out.

 

If you feel like you can and the sim is accurate enough to your taste, and you feel I'm wrong, that's a valuable data point.

 

Edit: You can clearly see the heading, altitude, airspeed, and attitude in the climbs and dives. It isn't hard to time the turn and deduce a precise rate of turn.

[SCU]

Disclaimer, I have no real knowledge of jets, never piloted one, maybe never will, let alone military jets. But, :megalol:, I do my research and analyze (basicly only just notice stuff, basic human skill) the vids and tapes. So you can choose to believe what I say or not, that's your choice, just don't exclude my findings as wrong unless there is evidence to the opposite.

 

 

 

A few FYI's about this video. Did you know that all the chirps and distorted sounds you hear from the start through the video are not just some tape distortions but actually the AN/ALR 69 RWR's F-16 specific tone, one of many for each known radar type, which are not modeled in DCS (just a unified tone for any moving contact on the RWR screen). If the modelling of this sort of breaches classified information or some other restriction then I understand why it wasn't modelled. Otherwise I see no reason.

 

Also this A-10 did almost exactly a solid 12 seconds of chopped stall warning tone, it is literally impossible to do this with whatever precision anyone has in DCS without having a wing dip and losing control over the jet, and just so you know there is no precision required for this since doing more pull at critical AoA shouldn't be having the loss of control effect we have in DCS as evident in this video at 0:37 mark where the pilot pulls even more inside of the chopped tone and is also a fact from the actual A-10C (& A) flight manual that has been mentioned before in this thread if you care enough to look for it.

 

The DCS A10C fly's great like your video to, with minimum fuel and no ordnance.

 

Edit: The video you posted was posted in 2012, so the engines here may well be up to 30% better trust then what we have in the suite 3 TF34.

 

You don't know how much fuel the A-10 in the video has and whether it has ordinance or not. It could be about 6.5K lbs of fuel like the other jet says on the comms at the start of the video "*something* Two Three 6.5, 5 Gs". If that's his wingman then that could be an indication of how much fuel the A-10 in the vid had because wingmen mostly have close enough fuel load to each other. I could be wrong though. The best way to get through this is to test it at the top best ideal conditions, minimal weight & no ordinance like Raistlen said.

 

This video is well before 2012. It's actually an A-10A model evident by the absent G-meter indicator at the top left of the HUD and different weapons information in the bottom left, probably the video is sometime in the 90's to early 2000s

 

I only want this simulator be what it's meant to be. As realistic as possible. Not 100%, which is impossible even for Air Force sims, but also not 20 (I'm not saying that it is, it's much higher :), just trying to make a point), I paid money expecting that, this is how it was advertised and this is what I and everyone who paid good earned money should get.

 

If I sound deeply critical or picky... or both, I really truly didn't mean it and am sincerely sorry if that's the case, this is just my way of making a point :smilewink:.

Edited August 8, 2016 by SCU

[David OC]

You don't know how much fuel the A-10 in the video has and whether it has ordinance or not.

 

I only want this simulator be what it's meant to be. As realistic as possible. Not 100%, which is impossible even for Air Force sims, but also not 20 (I'm not saying that it is, it's much higher , just trying to make a point), I paid money expecting that, this is how it was advertised and this is what I and everyone who paid good earned money should get.

 

If I sound deeply critical or picky... or both, I really truly didn't mean it and am sincerely sorry if that's the case, this is just my way of making a point .

 

That was my point no one knows the plane setup by watching a video.

 

I don't think you should even reference 20? A good reference would be 96%. It's very hard to get to 98%. Like I said Yo-Yo is not going to play with this by guessing the parameters with a dart, to get it perhaps in range of a better TF34 performing, this would take a very long time to do.

[SCU]

That was my point no one knows the plane setup by watching a video.

 

The DCS A10C fly's great like your video to, with minimum fuel and no ordnance.

 

The second quote suggests, for me at least, that you think that the A-10 in the video had minimum fuel and no ordnance. That's why I replied saying that that's something you and us don't know.. unless of course the comms thing I mentioned was true then at least we know a fuel count.

 

 

I don't think you should even reference 20? A good reference would be 96%.

 

Which is why I mentioned inside parenthesis that I was not saying it was 20% actual game realism. I think now in hindsight that 20 was too extreme, but I was just saying it as an example. I agree that the A-10C in DCS is in the 95% to 98% realism range, but it's the little things that can make your simulation experience a lot more immersive, for some people it can be a make it or break it thing.

[Yo-Yo]

Looking at the discussion "what is the thrust in the DCS - 8900 or 9065 lb" I wopuld like to mention that 9065/8900 = 1.019, i.e. the discussed difference is less than 2%, so, for example the difference in max speed for these two numbers is less than 1%....

 

Then, I'd like to say that in RL the thrust of real engines as well as other parameters never meet the specified parameters that are something like AVERAGE.

 

Real parameters make a dispersion cloud like at the first two pictires. As they are form Russian high school textbook for "an engine" (the real type is not specifed for some reasons) I will explain the abbreviations:

n_ВД - Ng

n_НД - Nf

Tt* = ITT, K

P = thrust in kN

Cуд - Ce kg/(kN*h)

 

The graphs represent the test result of 100 produced engine.

Edited August 8, 2016 by Yo-Yo

[Yo-Yo]

And these are the figures for TF 34 -2 and -100. The last is a kind of official GE data. As far as you can see -2 is very close to -100 even in numbers.

The third picture, I think, explains the difference between ACTUAL ITT value and THE LIMIT AREA somebody likes to refer to.

Edited August 8, 2016 by Yo-Yo

[David OC]

Thanks for the data Yo-Yo much appreciated:thumbup: how's is the F18 FM coming along:P

[bkthunder]

And these are the figures for TF 34 -2 and -100. The last is a kind of official GE data. As far as you can see -2 is very close to -100 even in numbers.

The third picture, I think, explains the difference between ACTUAL ITT value and THE LIMIT AREA somebody likes to refer to.

 

Thanks for some details!

In the second picture (PLA vs T5), are the two lines referring to the 2 different engines (ytf-34 and tf-34)?

 

Just as a side note, I was asking how much thrust we have in DCS because it could be different from what is written in the manual, which is what the Real A-10 has. So basically in dcs we have exactly the same thrust figures as in those tables?

 

EDIT:

I paste here a comment made on another forum, by one of the that were posting here (former simulator/ ground instructor).

I think this sheds quite some light on the whole thing, because he says that ose numbers are for an UNINSTALLED engine.

 

Read on

With thrust levers at MAX the engine delivers maximum thrust...period. There is no FADEC, and no de-rate involved.

 

Use of MAX thrust is not time limited in the A-10. If the engines had such a limitation, it would be reflected in the flight manual, which it is not.

 

The -100A ITT limit is 865, as proscribed by the flight manual, and as placarded in the aircraft.

 

The -100A ITT limit of 865 is an increase of 35 degrees from the -100 engine. These 35 degrees are available to increase the trim margin. Meaning, ITT between 830 and 865 would be observed on engines which required increased ITT trim to produce PTFS (i.e. rated thrust). In other words, not a brand spankin' new engine.

 

The data provided by Snoopy in the engine overhaul TO is for an uninstalled engine on a test stand. For installed engines, thrust is lower (8,900 pounds vs. 9,065 pounds) due to inlet restriction, and ITT is higher due to higher bleed extraction used for pressurization and air conditioning. The factory data sheet numbers are not obtainable with an installed engine.

 

Multiple passages in the flight manual refer to expected ITT values in excess of those achievable in DCS.

 

Multiple passages in multiple documents direct a power reduction after takeoff to a climb ITT of 800...the implication is that MAX thrust produces ITT in excess of 800.

 

Actual TEMS data from real live A-10 sorties show that ITT easily exceeds 800.

 

I don't understand the difficulty in acknowledging the above facts.

 

As for my opinion, I'd personally like to see engines with varied parameters. No two engines are the same, and although they should all operate within limits, within those limits there should be some variation. There are some engines in the A-10 fleet which require trimming near the 865 limit. Some only need 820. None require less than 800. I'd like to see the engines modeled such that real-world procedures are applicable when operating the airplane in DCS. That means, I'd like to be able to reduce power to 800 ITT after takeoff.

 

Like Forrest Gump said: that's all I got to say about that.

 

Edited August 10, 2016 by bkthunder
Added details

[David OC]

bkthunder,

 

That was a message to me on said forum, where is my reference on this subject? It's all good it's not needed:thumbup:

Edited August 11, 2016 by David OC

[NineLine]

 

EDIT:

I paste here a comment made on another forum, by one of the that were posting here (former simulator/ ground instructor).

I think this sheds quite some light on the whole thing, because he says that ose numbers are for an UNINSTALLED engine.

 

Read on

 

Are we sure the numbers on a freshly installed engine dont differ from an engine that has a bunch of flight hours on it? A lot of variables seemingly being guessed at. We would need to see all those variables to really get the full picture, and then at the end of the day, how much difference does it really make.

 

Testing I did I saw numbers near 820 (+ or -).

 

The bottomline of the discussion comes to this as well, ED can model stuff based only on what they have information on. Someone saying they have more info, but cant legally share it doesnt help ED at all, I hope that makes sense. Yo-Yo cant just take a number someone says something can reach and magically make it happen, the FMs dont work like that. And again, how much of an issue is this really, if any?

 

Its been an interesting discussion though, and gave me an excuse to hop back in the A-10 some.

[KansasCS]

Looking at the discussion "what is the thrust in the DCS - 8900 or 9065 lb" I wopuld like to mention that 9065/8900 = 1.019, i.e. the discussed difference is less than 2%, so, for example the difference in max speed for these two numbers is less than 1%....

 

Then, I'd like to say that in RL the thrust of real engines as well as other parameters never meet the specified parameters that are something like AVERAGE.

 

Real parameters make a dispersion cloud like at the first two pictires. As they are form Russian high school textbook for "an engine" (the real type is not specifed for some reasons) I will explain the abbreviations:

n_ВД - Ng

n_НД - Nf

Tt* = ITT, K

P = thrust in kN

Cуд - Ce kg/(kN*h)

 

The graphs represent the test result of 100 produced engine.

 

Philosophical question here:

Is it possible and/or was it ever considered by ED to simulate performance variations?

[KansasCS]

 

The bottomline of the discussion comes to this as well, ED can model stuff based only on what they have information on.

Certainly the information given should be enough to warrant further investigation? Or is a 1-2% margin not enough to justify rewriting FM code?

 

General honest questions: Is it up to the community to provide for every last little temperature figure, graph or chart in order to raise concern? Shouldn't substantial pointing in a direction be enough? At which point does ED say: Our data says otherwise but this guy seems to raise some issues with enough evidence to make it worth looking into, because heck, there is a very slight chance we might be wrong?

 

I guess with the volume of raised concerns and 'bug' reports, the bar is set pretty high, understandably, but still.

 

About the data used for modelling the engine?

Was that used from a test stand or extrapolated to match engines mounted on the airframe? Seems like there is a slight performance difference between mounted and dismounted engines.

[NineLine]

I dunno. I still dont know if there really is an issue. If we have something modeled by documents ED had, then its really not an issue.

 

We have to remember that there are a number of systems on the A-10 that are not modeled, or not modeled to real world specs. Part of that is based on what they were allowed to do when they entered the agreement for the military side of the contract, some has to do with just not having the documentation to model everything.

 

ED themselves stated the A-10C wasnt modeled 100%, so if there really was an issue that performance was off by 1% to 2%, I cant see them making a change to try and get there. That said, I know how passionate this stuff is to people like Yo-Yo, and if he was given the documentation (and I mean full documentation needed for FM programming, probably stuff already stated couldnt be handed out due to legal reasons) I could see him taking a crack at it. But without that info, I doubt he would want to take a shot in the dark, and I dont think we would either when it could mess something else up.

 

This is all personal opinion of course, and what I believe. But I cant imagine ED getting too carried away with this with all the FMs in progress right now (Spitfire, Hornet, MiG, etc..). Now if someone can get Yo-Yo the docs he needs, who knows. Right now I would have to say its not going much farther than this discussion.

 

I urge people to continue to discuss though, and actively look for anything that might be useful to help ED out. As I said, its been interesting and informative with only a few bumps in the road. I learn a lot from these discussions, hope others do to.