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problem with getting the right RPM value for some aircrafts!


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Dear Pete,

I do face a problem here and I thought maybe you are able to show me the right direction.

My problem is getting the right RPM value for some aircrafts.

I am talking about the following Offsets: 0898 and 08C8

I use the standard Cessna (172) which comes with FS9 and I use the values provided by FSUIPC (3.6) in order to calculate the RPM (H898*H8C8/65536) I do get the right RPM value.

If I use my favorite MAAM DC-3 aircraft and I do the same calculation I do get a value which is much lower. The same happens if you use the standard Baron 58 which comes with FS9.

So far the problem.

Now my question:

With the FSUIPC SDK comes a program called "FSLOOK". If I start FSLook and have a look at the values provided by this program I found the following:

There is a variable called "Engine_N1_RPM". If I use the standard 172 Cessna from FS9 the "Engine_N1_RPM" value is equal to 0898 provided by FSUIPC or FSInterrogate2std.

If I have a look at the same values but using now my Gooney Bird it starts to get interesting:

FSLook is giving me a different value for "Engine_N1_RPM" then FSInterrogate2std or FSUIPC. Using the FSLook value for the calculation (Engine_N1_RPM*H8C8/65536) is giving me the correct RPM value.

Now my problem:

I have no idea where this value "Engine_N1_RPM" is coming from. The help function from FSLook says "FS2000 Token Varialbe Display" and so I assume the problem is coming from the airplane itsself since it is supposed to compatible to FS2002 and not a FS9 only model. But somehow FSLook is able to provide the right value.

My question to you now:

Is it possible to get the value provided from "FSLook" through FSUIPC as well?

Thank you for your support in advance and thank you for all the hard work to the simmer community.

Best Regards

Nobbi

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Is it possible to get the value provided from "FSLook" through FSUIPC as well?

Odd that the values are different. Possibly it comes from a mismatch of aircraft to FS version. Have you checked the RPM values available at offsets 2400, 2500, 2600, 2700?

Regards,

Pete

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Pete,

only your support is worth it the money for FSUIPC and WideFS already! This does impress! Thank you!

Well, I have checked offset 2400 and I get the same readings like 0898*08C8/65536 which means a "wrong" value for my DC-3 and a right value for the C-172.

The interesting thing is that FSLook is getting the right thing. I know, the program is 6 years old already (regarding to the help dialog).

You wrote that there is maybe a mismatch between the aircraft and the FS version. What do you mean by this?

Thank and best regards

Nobbi

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Well, I have checked offset 2400 and I get the same readings like 0898*08C8/65536 which means a "wrong" value for my DC-3 and a right value for the C-172.

That's very very strange.

Is there any relationship? Maybe the scaling value is wrong for some reason. Can you quote some comparative figures for me?

The interesting thing is that FSLook is getting the right thing. I know, the program is 6 years old already (regarding to the help dialog).

I seem to recall that it somehow reads the Gauge values. Not sure how, I'd need to burrow into the code. Are you writing something to run inside FS, or is this an external program? If inside FS you could try reading the Gauge token variables. I *thought* that they came from the same place as those 2400 etc offsets, which is why I'm puzzled.

You wrote that there is maybe a mismatch between the aircraft and the FS version. What do you mean by this?

Well, not really sure, but maybe it works on one version of FS and not another -- it is possibly making some assumptions somewhere which turned out to be incompatible.

Let me see a two columns of comparative figures, please, see if there's a relationship I can figure.

Regards,

Pete

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Hi again Nobbi,

I just noticed this:

... The same happens if you use the standard Baron 58 which comes with FS9.

... so, as I obviously have this aircraft I thought I'd take a quick look.

With the default Baron, if I set the thottles to give a steady reading of 1500 RPM on the FS panel, I get the following through FSLook and FSUIPC:

FSUIPC:

0898 = 9128 (decimal)

08C8 = 10800

So RPM = (9128 x 10800) / 65536 = 1504. Correct!

FSLook gives 9130 or so -- i.e. the same value as 0898.

So, I'm afraid I cannot agree with you regarding the Baron. How are you arriving at your conclusions?

Regards,

Pete

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Pete,

ups. Sorry about the Baron. Please have a look at the stock DC-3 which comes with FS9. There you will see the problem. I have no idea why I wrote Baron 58. Sorry!

Well, here are the numbers (I produced them with the FS9 stock DC-3):

RPM shown by the Gauge: ~1100 (idle)

Value by FSinterrogate2std (0898): 3707

Value by FSLook (Engine_N1_RPM): 6590.88

Calculated RPM using 0898: 610,894

Calculated RPM using Engine_N1_RPM: 1086,143

RPM shown by the Gauge: ~2700 (full throttle)

Value by FSinterrogate2std (0898): 8995

Value by FSLook (Engine_N1_RPM): 15992.2

Calculated RPM using 0898: 1482,330

Calculated RPM using Engine_N1_RPM: 2635,433

I hope this helps. Sorry again about the Baron58. But as I said, those values are coming from the stock DC-3.

Actually I am not writing any application at all. But I am using those instruments from Simkits ans when I face problems with the RPM Gauges I started to have a look at it. Thats how I approached you.

Since those Simkits guys do use the offsets 0898 and 08C8 they are provided me the wrong values for my DC-3 but the right values for people who are using a C-172 or a Baron 58 ( :oops: ).

I hope those values do help you to chase the problem.

thanks

Nobbi

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ups. Sorry about the Baron. Please have a look at the stock DC-3 which comes with FS9. There you will see the problem. ...

Well, here are the numbers (I produced them with the FS9 stock DC-3):

Okay, let's compare yours with mine:

RPM shown by the Gauge: ~1100 (idle)

-- Okay I get an idle of 1050, approx. definitely below 1100

Value by FSinterrogate2std (0898): 3707

-- I get 3634, close enough.

Value by FSLook (Engine_N1_RPM): 6590.88

-- Yes, I get 6461.

Calculated RPM using 0898: 610,894

-- How do you arrive at that? 0898 is 3634, 08C8, the scaler is 10800, and 3634 x 10800 / 65536 gives 599 (using my figures -- but yours cannot be 1,000 times bigger!). Offset 2400, which is the RPM directly from SIM1.DLL gives 599 too.

Calculated RPM using Engine_N1_RPM: 1086,143.

-- Yes, similar here.

Interesting. The value direct from the Simulator is something like 1/1.8 of the value shown on the gauge and given by the gauge interface, and that ratio seems consistent. There must be something else in the Aircraft CFG or AIR file which scales it, other than the scaler. I'll take a quick look

Pete

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There must be something else in the Aircraft CFG or AIR file which scales it, other than the scaler. I'll take a quick look

I bet this is the culprit:

gear_reduction_ratio= 1.778 //Propeller gear reduction ratio

For the Cessna and Baron that value is 1.0.

I'm not sure I can find that internally in order to apply it -- odd that no one else has ever been bothered by it these last 34 months of FS2004!

Regards,

Pete

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I'm not sure I can find that internally in order to apply it -- odd that no one else has ever been bothered by it these last 34 months of FS2004!

Okay, found it! Knowing the exact value to look for and having two aircraft with specific known values made it quite easy after all.

I am now scaling the value in 0898 (etc) by the gear reduction ratio. (I can't do this for the value in 2400 (etc) because that offset is actually mapped directly into the variable inside SIM1.DLL itself.

Please try the attached FSUIPC, version 3.618. [DELETED - see 3.619, later in thread]

Regards,

Pete

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Pete,

you are the hero (at least for engine #1!)!!!!

I downloaded and used version 3.618 now and for Engine1 (0898) everything looks just perfect.

How ever, offset 0930 shows me complete different values now:

Full Throttle:

#0898: 15658

#0930: -32628

Idle:

#0898: 6580

#0930: 4696

Those datas I got from FSinterrogate and FSUIPC 3.168 while FSLook do show me always the same numbers which are comparible with offset #0898 now. I know where the negative value is coming from, but the numbers itself do look very different to me. The aircraft I used was again the Bar...err DC-3...

Again, thanks for your great support!

/

Nobbi

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How ever, offset 0930 shows me complete different values now:

Yes, sorry. Not only N1 -- many Engine 2,3,4 values would have been wrong. In my hurry to get a fix to you (in joy on finding the answer so easy) I made a mess with the structure containing the data and misaligned all of the Engine 2-4 data! Ugh!.

Try 3.619 attached, instead, please.

Note that, at present, I have assumed that the same (Engine 1) gear ratio applies to all engines. If you know of any aircraft which has different gearing for different engines please let me know, as I will have to make the code rather more sophisticated then ...

Regards,

Pete

FSUIPC3619.zip

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Pete,

well, now you made it! Thanks a lot.

The values for Engine # 1 (0898) and Engine # 2 (0930) do work just fine.

In case I should find some other problems I will let you know. Well, since the DC-3 does have only 2 Engines I am not able to test the values for Engine # 3 and #4 but I will keep my eyes open.

Again (and I am sorry if I repeat myself here over and over again and I am sorry in case you are getting sick of reading this over and over again :roll: ): THANKS A LOT for this kind of support which is just assume!

Best Regards

Nobbi

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  • 2 years later...

Well I still can't get prop RPM value using both methods.

Airplane: FS9 default King Air 350

Gauge prop RPM ~1700

Method 1, as stated in doc:

0898 x 08C8 / 65536 = 36215 x 54144 / 65536 = ~29919

Method 2, 0898 / gear reduction from CFG file:

36215 / 17.6 = ~2057

Am I doing something wrong?

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Well I still can't get prop RPM value using both methods.

You are attaching this message to one almost 3 years old! What happened in between? Lots of things have changed since then!

Please state version number of FSUIPC, and if not the very latest (see Updates Announcement), try that first. Also, state version of FS as well, please. FSUIPC3 works with anything since FS98 except FSX/ESP and CFS3.

Pete

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I've just found this post searching net for solutions but still had some problems.

Now I figured it out it should be 0898 x 08C8 / 65536 / gear_reduction_ratio.

I could swear I tried only 0898 / gear_reduction_ratio and I got right value but I had to be wrong.

So formula is clear now but do I still need to read CFG file for gear_reduction_ratio? Isn't there any direct access to prop RPM value through FSUIPC?

I use latest version of it ofcourse.

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Now I figured it out it should be 0898 x 08C8 / 65536 / gear_reduction_ratio.

Seems odd. I'm sure there are plenty of apps using FSUIPC and getting the correct RPM for their instrumentation without having to use such means. Perhaps it is limited to just that one aircraft?

So formula is clear now but do I still need to read CFG file for gear_reduction_ratio? Isn't there any direct access to prop RPM value through FSUIPC?

I use latest version of it ofcourse.

What is "the latest version", then? PLEASE give version numbers! They are not so hard to find, after all. Why the reluctance? Folks have said "latest version" and they meant the latest they've seen -- once that was a year old one! Do you really mean you've gone to the Updates announcement as I asked and downloaded the one from yesterday?

And which version of FS? FSX, ESP, FS9, FS2002, FS2000 or what?

I can check things for you, but you need to answer my questions, please!

Pete

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Sorry Pete. I will try to be more precise.

It's FSUIPC 3.85 for FS2004 downloaded one week ago.

The only place in doc I found is:

0898

Engine 1 Jet N1 as 0 – 16384 (100%), or Prop RPM (derive RPM by multiplying this value by the RPM Scaler (see 08C8) and dividing by 65536).

And I discovered for every prop plane it must be 0898 * 08C8 / 65536 / gear_reduction_ratio which could be sometimes just 1.0 as for C172.

I could read the CFG file but how should I know the exact path of such file?

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It's FSUIPC 3.85 for FS2004 downloaded one week ago.

Okay. It might be worth trying the latest version, 3.871, from the Updates, as I suggested. There's been quite a lot of work done since last November. However, I suspect that area is mainly one I attended to in the FSX version, FSUIPC4.

Are you testing this in FS2004, or an earlier version of FS? It may make a difference!

The only place in doc I found is:

0898 Engine 1 Jet N1 as 0 – 16384 (100%), or Prop RPM (derive RPM by multiplying this value by the RPM Scaler (see 08C8) and dividing by 65536).

Right -- that's always been how it worked, since FS98 at least. But in my latest copy of the Offsets list,

Have you checked 0896 at all? Oh, no, don't worry. I see it gives the same as 0898.

And I discovered for every prop plane it must be 0898 * 08C8 / 65536 / gear_reduction_ratio which could be sometimes just 1.0 as for C172.

I think that is what misled those who told me about these values, since FS98 days. Checking in the FSUIPC4 Offsets, I see this fact was already discovered for FSX, because the RPM Scaler offset includes this comment (in red):

(On turboprops this will give the shaft RPM, since there is currently no Gear Reduction Ratio available to fix values on such aircraft. I will fix this when I can)

I also remember putting the request in to the FS team for the Ratio to be provided, via SimConnect. I didn't realise the same problem applied to FS9 and before too -- I will have to add the same comment to the documentation.

I could read the CFG file but how should I know the exact path of such file?

Oh, that's easy enough. You read the AIR file pathname. The CFG file is in the same folder, so just strip of the filename part and append 'aircraft.cfg'.

Hmmm. I wonder where the panel gauges get the value from -- or probably they don't need the real value, just the percentage of maximum, which is what the values provided really are? The graphics would be designed with the scaling in mind ...

Regards

Pete

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I also remember putting the request in to the FS team for the Ratio to be provided, via SimConnect.

But actually SimConnect gives direct access to prop RPM value.

Anyway, back to FS2004...

I updated FSUIPC to ver. 3.871

I found the formula I provided before:

0898 * 08C8 / 65536 / gear_reduction_ratio

is true for some planes only. It's ok for King Air 350, C172, Beechcraft B58 but it's not for DC3 or Cessna Grand Caravan.

DC3 has 1.778 gear reduction ratio in aircraft.cfg file but I obtain true prop RPM from 0898 * 08C8 / 65536 / 1.0 (not 1.778)

and Cessna GC gives completly wrong results...

So I'm stuck again. I have no idea how to get this value :(

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But actually SimConnect gives direct access to prop RPM value.

Ah, yesoffsets 2400, 2500, 2600, 2700 provide this for Engines 1-4. But actually it is "PROP RPM:x" or "GENERAL ENG RPM:x" depending on which one is actually changing -- it varies by aircraft type. I think the reduction ratio is needed for those which don't update the "PROP RPM", only the "GENERAL ENG RPM" value.

Anyway, back to FS2004... I'm stuck again. I have no idea how to get this value :(

i think it is the same problem in FSX, for some aircraft. But I wouldn't swear to it, and maybe it got changed in SP1 or SP2 in any case.

If you find out how to get it, let me know and i'll see what i can do for it in FSUIPC. I did think of trying to hack into the RPM gauges to see how they got it, but then it occurred to me that they probably just work with the percentage of max figure -- they don't need the actual, that is just a dial inscription.

Or do they?

Sorry, all the stuff relating to the innards of aircraft systems is a mystery to me. I just exposed what i found or that folks found before me (a lot was carried forward from pre-FSUIPC days, from FSW95 and FS98).

Let me know if you find anything concrete and useful. Thanks,

Pete

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  • 9 years later...

Hi there,

I know, it's an old topic but I'm putting it here not to spoil the forum with yet another similar topic. Please feel free to relocate it as appropriate.

Anyway, I'm trying to get the values for Prop RPM percentage (%) and Torque pressure (psi) for Aerosoft Twin Otter DHC-6-300 and to display them on the screen via a LUA script. The script works OK but I'm not sure if the offsets I'm working with are correct - the values match with the aircraft's gauge indicators only if divided with certain 'guesstimated' scalars , as shown below (e.g., 386.45 and 327.66).

So, is there any elegant solution to get correct values for the above parameters?

PS: FSX Acceleration with FSUIPC v4.972a

    propRPM1 = round (ipc.readDBL(0x2400) / 386.45)
    propRPM2 = round (ipc.readDBL(0x2500) / 386.45)
    torque1 = round (ipc.readUD(0x08F4) / 327.66)
    torque2 = round (ipc.readUD(0x098C) / 327.66)

Thanks!

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The offsets you are using for Prop RPM are exactly that -- the Prop RPM as supplied by Simconnect with no interference by FSUIPC. It is NOT a "percent". Note that for a turboprop it's probably the shaft RPM -- see the comment about gear reduction ratio in my published offset list.

However, the Torque offsets you are using ARE percents, using 16384 as 100%, and the SimConnect variable they are from says they are "Turb Eng Max Torque Percent"s. And I would have thought the way to get a % value using normal 0-100 range is to divide by 163.84 not 327.66  (dividing by 327.68 would give exactly half the actual % value provided). 

There are Engine Torque offsets in ft-lbs. Not sure where you "torque pressure" from in psi or anything else. what is "torque pressure"? Surely torque is always a force, not a pressure?

Pete

 

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