PDA

View Full Version : RW pilots: Seeking RW CHT information to calibrate CHT model



teson1
August 28th, 2012, 14:29
Dear RW pilots.

I'm looking for information on engine CHT you observe during flight phases with your real-world planes (start_up, T/O, climb and cruise) to confirm accuracy/realism and tweak a model of CHT for piston engine aircraft I've coded.

-> I've compiled a questionnaire (see below) and would appreciate if you could enter your flight practices and CHT observed.
I'd appreciate if you could have a look and enter any information that you may have available (even if partial).
Just reply with quote and enter the information in the questionnaire, or send by PM to me.
Thanks !!!

The model is based on NACA Technical Note 1092 (1946)
"Flight investigation of the cooling characteristics of a two row radial engine installation I - Cooling corellation".
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930081717_1993081717.pdf

The module calculates the Cylinder Head Temperature CHT of a piston engine aircraft as a function of operating parameters:
- Power
- Mixture
- Cowl flap position
- Supercharger
- Airspeed
- Air temperature
High power operations like take-off and climb require care not to overheat the engine.

I believe this model is more realistic than the FS model of CHT.
However, as I have zero experience with RW aircraft I'm not sure whether it applies to all piston engine aircraft, and to what extent, or any at all, and whether the way I have configured planes is realistic in any way.
Thus I would appreciate if you could provide information on CHT you observe in the different flight phases with your planes.

If you would like to try out the CHT model and compare to behavior of your real plane you can download the beta of RealEngine v1.4 including the CHT module at the following place:
http://www.mediafire.com/file/6b2nbw9o6i4wv0p/RealEngine_v14_Beta1_120826.zip

(Installation instructions and suggestions on how to configure, as well as configuration files for a few airplanes are included).
I've come up with a relatively simple 4-step process to configure for an aircraft, but I'm not sure how realistic the outcome is.
Displaying the CHT value generated requires editing of CHT .xml gauges, or replacing these in the panel.cfg by supplied gauges, but this step is not very difficult I believe, and instructions are included with the readme.

Your support on real CHT in flight (as well as issues or suggestions for improvement) is highly appreciated!

Thanks!

Gunter

___________________________________________

Questionnaire:

1. Aircraft
Aircraft manufacturer/model):
Engine manufacturer/model/HP:
Comments regarding your airplane that may be of value with respect to CHT:

2. Run-up
What idle RPM are you using?
What temperatures does CHT reach during idle?

3. Take-Off
What engine settings do you use for T/O (MP/RPM or other)?
What mixture do you set for T/O (Mixture lever fully advanced?)?
Cowl flaps position (if available)?
What temperature does CHT reach during take-off run?
How fast does CHT rise during take-off run?
What is CHT limitation/redline for your engine during T/O?

4. Climb
What engine settings dou you use for climb (MP/RPM or power or other)?
What mixture do you set for climb?
Cowl flaps position (if available)?
What IAS do you climb at?
What temperature does CHT reach during climb?

5. Cruise
What engine settings dou you use for cruise (MP/RPM or power or other)?
What mixture do you set for cruise?
What IAS do you cruise at?
Please indicate typical cruise altitude.
What temperature does CHT reach during cruise?
What is CHT limitation/redline for your engine during cruise/continuous operation?
How fast does CHT settle to a new value after changing cruise parameters (MP/RPM/power)?

6. Any special observations regarding behavior of CHT in your plane?

Notes:
I am aware that there are many different practices possible depending on flight requirements. Any information you may have is highly appreciated.
Ideally please indicate temperatures and operating parameters ect for a low-level take-off and roughly ICAO atmospheric conditions, but any information you may have are willing to share will be helpful.

Thanks !!

fliger747
August 29th, 2012, 02:24
What you are doing could be quite useful. However the cht responses of gen av engines bear about zero relation to twin row radials such as the R2800. They especially depended on rich mixtures at high power settings for flow through cooling at high power settings. The piston equipment i Fly seldom has CHT issues, especially the cub which does not need cowl flaps, to the IO540 stuff, which do have cowl flaps of a sort, but not much adjustment is required.

In even gen av aircraft of moderate power and speed range, the biggest effects will be power setting, cooling air flow and mixture. CHT can be used to set mixture in cruise, though not ideal. Generally FSX and it's kin relate CHT to RPM. This might work for the primitive small Cessna models the sim started out with, but is misguided effort with const speed props. In developing the Uvier DC2 we had issues with overheating at low power settings but with props set to high RPM on final, which is clearly wrong.

I think the basic principals for large radials apply, but with quicker response and lower temp variations than the big radials.

Good luck! T

fsxar177
August 29th, 2012, 14:25
Will be interesting to see what kind of results come in. Thanks Gunter!

Joseph

teson1
August 29th, 2012, 18:24
Thanks for the feeback!

Yes, i had wondered whether and how heat exchange and cooling of these high-powered radial engines differ from lower power engines/engines of different type and installation.
Without real-world experience, and unable to find information on actual CHT temperatures of GA engines to compare to, I had no way to find this out. Thus my questions/questionnaire. :)

In fact other NACA studies of radial engines using a similar methodology have resulted in other exponents in the heat exchange correlation equations already, so not even for similar engines the model is exact (and the model describes the studied engine only adequately).

I don't expect the model to hit CHT behavior for every plane spot-on.
What I'm shooting for is that the model results in CHT for a large range of airplanes that are more close to reality than the FS model.

As you say FS CHT model essentially factors in RPM, airspeed, cowl flap position and air temperature. FS CHT model does not depend at all on engine power or mixture! *1

In principle the NACA model can be modified to result in smaller temperature variations by tweaking one or two internal coefficients or relations I believe.
So while it's unrealistic to expect exact CHT values for any and all aircraft and flight conditions from the NACA model, the model may be tweaked to fit real performance if needed. It might be possible if needed to come up with slightly modified models for different aircraft type, e.g. GA with fixed pitch propeller (*2)/GA with variable speed propeller, high-powered radial engines ect, that may result in CHT behavior more close to reality than what FS provides.

I'd like to find out whether the NACA model is better suited than FS, and how to configure/tweak it for most realistic performance with a wide array of planes.
But for this I need some RW data to compare with.
(It may be that it's no improvement over FS model, and in that case I've no problem to drop it. It's been an interesting and stimulating trip to learn about engines in any way.)

So, to all pilots, I would highly appreciate any information on CHT you observe in your planes !
Please maybe consider to note down CHT values/flight parameters during your next flight. :)

Thanks!

Gunter

*1 Of course the error by FS of basing CHT on RPM, and not power, results in the effect that with all other significant parameters the same (air speed, CF, air temp) the same RPM yields the same CHT, whatever the engine power/MP.
For a given RPM and an aircraft with a variable pitch propeller this means that in cruise reducing power (=same RPM, but lower MP) results in higher (!) CHT due to the lower resulting airspeed.
This seems to be no principal issue for aircraft with fixed pitch propellers, as engine power is directly related to RPM in most flight conditions for these (here only the effect of mixture is not considered at all).

*2 It may be that for fixed pitch aircraft the FS CHT model is very good, so it may be that it does not make sense to use an alternative model for these. Would also depend on comparing FS CHT values with what is observed in real life.






What you are doing could be quite useful. However the cht responses of gen av engines bear about zero relation to twin row radials such as the R2800. They especially depended on rich mixtures at high power settings for flow through cooling at high power settings. The piston equipment i Fly seldom has CHT issues, especially the cub which does not need cowl flaps, to the IO540 stuff, which do have cowl flaps of a sort, but not much adjustment is required.

In even gen av aircraft of moderate power and speed range, the biggest effects will be power setting, cooling air flow and mixture. CHT can be used to set mixture in cruise, though not ideal. Generally FSX and it's kin relate CHT to RPM. This might work for the primitive small Cessna models the sim started out with, but is misguided effort with const speed props. In developing the Uvier DC2 we had issues with overheating at low power settings but with props set to high RPM on final, which is clearly wrong.

I think the basic principals for large radials apply, but with quicker response and lower temp variations than the big radials.

Good luck! T

fliger747
August 31st, 2012, 07:21
For the Uvier project, the DC2 had only manual mixture control, so we wanted to be able to have mixture effect CHT. As the DC2 had no cowl flaps, we were able to use invisible cowl flaps to try to cause a change in CHT. However the fixation on RPM in the sim still caused serious issues at high rpm low mp low air speed situations such as approach. The sim would produce very high unrealistic CHT in this case, which was bad as we had an engine damage model tied in that would kick in.

Trying to remember what the cub or 180 runs for CHT, something fairly cool like 140 C?. Almost never an issue in Alaska, except if too cool. Many years ago I flew turbocharged twins, which were more temperamental ( pun). The big issue with engines running higher temps is shock cooling with too quick a power reduction. Another issue can be too fast a power application before the engine is warm, as the pistons expand more quickly than the cylinders, which can cause serious issues!

Cheers. T

teson1
September 1st, 2012, 09:54
I've been eyeing with the DC-2 already. I think i'll have to finally get it . :)

One question: Are the advanced engine effects also included with the FS2004 model, or only with the FSX one?

Thanks.

Gunter

RyanJames170
September 1st, 2012, 10:15
http://eaavideo.org/video.aspx?v=994808107001 about CHT and EGT

http://eaavideo.org/video.aspx?v=994986557001 about leaning and effects on performance

should answer ur questions i would think.

as for cooling it is based more on airflow over the engine, why one opens the cowel flaps on the ground and closes them in flight for cruse.
there might be some info in the over haul video as well.

fliger747
September 1st, 2012, 10:17
Hard to believe but the DC2 FSX project was almost like starting from scratch. Ask Rob Cappers! I did get to see Uvier in the hangar while it was undergoing one of it's periodic restorations and since it was in some disassembly, didn't get to fly in her. The FSX one is much more advanced! Having the real plane and reference to her pilots was a big help in all phases.

T

RyanJames170
September 1st, 2012, 10:17
http://eaavideo.org/video.aspx?v=994808107001 about CHT and EGT

http://eaavideo.org/video.aspx?v=994986557001 about leaning and effects on performance

should answer ur questions i would think.

as for cooling it is based more on airflow over the engine, why one opens the cowel flaps on the ground and closes them in flight for cruse.
there might be some info in the over haul video as well.

edit:

http://www.youtube.com/watch?v=Ts_irHU35yc&feature=plcp over haul video

teson1
September 2nd, 2012, 15:21
Ryan,
these are great webinars.
Thanks for posting!

Pilots, still hoping for some numbers to check the model against ;)
Thanks.

RyanJames170
September 2nd, 2012, 21:06
Ryan,
these are great webinars.
Thanks for posting!

Pilots, still hoping for some numbers to check the model against ;)
Thanks.

im me with your email addy and i will send u all my POH's and engine manuals i have along with a few service bultines as well. it might help

teson1
September 4th, 2012, 11:47
Ha! I've got quite some, but one can never have too many. ;) PM sent.