Verify climb rates

[hbeni]

I'm not sure the maximum climb rates still match the POH 5-18ff.

Standard atmosphere is: 15 °C /101 3 HPa = 29,92 inHg

[hbeni]

Settings:
Start in Limnos; no wind, standards Atmosphere
Plane configured as per POH 5-19; complex engine operations disabled

What I got is not very reliable i think, because hand flown and VS wobbling alot (but still wobbling around at "too much" I think).

POH 5-19	Max perfomance climb
ALT	IAS	FPM
600	82	1328
1200	81	1077
4000	81	1131
6200	79	1003
8230	77	955
10000	76	600

Is there any good way to measure this in a precise manner?

@Octal450 Josh, maybe do you have a simple autopilot at hand, that I can plug in and that keeps the plane level and at a desired speed (which I can provide by a table)?
@Octal450 Edit: The speed needs to be controlled by pitch...

[hbeni]

Hm, @HHS81 , could this be related to #517 ?

[Octal450]

Hi,
My new generic autopilot can do that. It is in next and 2020.3.19. Select wing leveler then Heading control on, and then select then speed by pitch radio button and Velocity control on.

Note that it will make adjustments "softly". So if you change power or such you'll need to allow a moment for it to compensate.

You have to comment out the dedicated autopilot and its dialog to access it (or manually add it)

Aircraft/Generic/generic-autopilot.xml (the helper file is NOT required)
FGDATA/gui/dialogs/autopilot.xml

Kind Regards,
Josh

[hbeni]

Thanks Josh, will try this!

what is basicly wrong? Too much lift generated?
(I‘m not sure it is a great idea if i start messing with the FDM!)

[wlbragg]

(I‘m not sure it is a great idea if i start messing with the FDM!)

It'll be fine! :)

[HHS81]

what is basicly wrong? Too much lift generated? (I‘m not sure it is a great idea if i start messing with the FDM!)

Indeed!
It might be that other things like changes in JSBSim, Atmosphere model etc. might be the reason. The fdm had been tuned from the beginning to match the POH, and when the fdm had been untouched since then, there might be other reasons.

[HHS81]

I think I found the issue: When I tuned the engine settings (not the fdm!) I used following METAR to simulate standard atmosphere:
00000kt 19SM 15/05 1013 NOSIG

FlightGear offers now a international standard atmosphere setting:
00000kt 19SM 15/M99 1013 NOSIG

So my simulated ISA has humidity, which influence the engine and prop power.
I checked both ISA, and with my wrong ISA I got POH matching climb rates, and with the correct ISA I got a much higher, unrealistic climb rates as observed by Beni.

So it will need to tune the MP-alt-volumetric-efficiency-curve inside the propulsion.xml with the correct ISA-settings to match POH-Values

Good thing: the fdm itself (lift, drag etc...) won`t need any changes for this issue!

[hbeni]

Thanks for investigating and pointing me to the correct location for tuning, @HHS81 :)

Meanwhile I (temporarily) added the generic autopilot and renamed our gui file, so F11 can access the original dialog (thanks @josh, works like a charm 🥳 ). The wing leveler from the start on helps, and levelling out at the sear at about 80 knots and then activating pitch speed control and slowly shoving in the throttle makes the plane climb and for me easy to read non-bouncing values :)

This is what I got now however i have a question how to read altitude:
The POH says "pressure alt", so do i need to take the absolute real Altitude (from /position/altitude-ft, or from altimeter calibrated to 29.92? The value seems to differ here (altimeter is showing about 700ft less).
The values below show the raw value from /position/altitude-ft.

[hbeni]

ok. Found out that my weather was messed up and you need to reaply when choosing it from the launcher.
Now the altimeter is showing correctly :)

[hbeni]

POH 5-19 Max perfomance climb

ALT	IAS	FPM	difference
500	79.6	1222	+297 / +132%
2000	78.4	1018	+183 / +121%
4000	78.5	1007	+257 / +134%
6000	77.8	933	+273 / +141%
8000	76	763	+198 / +135%
10000	74.2	638	+168 / +135%
12000	73.3	530	+155 / +141%
14000	71.9	325	+40 / +114%

[hbeni]

So the values seem off for roughly one third.

What is the correct approach to correct this?
Just add a modifier *(2/3) to the calculations?

I'm a bit lost here, because the table is also mapped against manifold pressure, and essentially i did just check one of the power curves

[hbeni]

Just add a modifier *(2/3) to the calculations?

Just tried, that messes with the fuel flow and this is then all over the place.
I get 26.5inHG MP (full throttle), fuel flow 14.1 (full rich) a climb rate of 1285 fpm at2000ft...
With *1.3 i get weird fuel flow too and also very off numbers.

[hbeni]

Playing with a simple modifier against systems/engine/MP-alt-bsfc-lbs_hphr-curve works better, playing with that a little:

Modifier: *1.3.

POH 5-19 Max perfomance climb
(releaned to the fuel flow placard)

ALT	IAS	FPM
500	?	was hard to measure but below 1000
2000	80	850
4000	78	770
6000	77	728
8000	76	559
10000	76	520
12000	74	350
14000	71	160

So this somehow sort of worked.
What I don't understand: The POH says on 4-25 (Enroute climb):

The mixture should be set to 15 GPH or full rich (whichever is less) until
reaching the altitude at which full throttle is reached, after which no
further adjustment of the mixture control is needed.

With the max perforance climb you are on full throttle - are we expected to initially set the mixture and then leave t there for the climb, assuming fuel flow will decrease automatically in the proper relation? (it does this somewhat closely, however i had to relean for about 1gal/h for the altitude steps)

[hbeni]

So confusing - you adjust something, then something else is not working anymore (the airspeeds I tested at 14.000ft where off now)

Heiko - please help :)

[Octal450]

@hbeni Glad you like it :)

Best of luck on solve your issue. @ me if you need anything. :)

Kind Regards,
Josh

[hbeni]

@Octal450 I think we need @HHS81 to hep tuning this. I ave no Idea how this all really works and just adjusting numbers blindfolded.

Is there a way to easily mass test those settings, besides of actually running flightgear and climbing manually?

[hbeni]

https://wiki.flightgear.org/JSBSim_Engines
maybe we just need to tune the rated engine settings?

[HHS81]

https://wiki.flightgear.org/JSBSim_Engines maybe we just need to tune the rated engine settings?

No

Please have a bit patience, I'm busy.

[hbeni]

I think the T variant is more off, just seen with a short test flight at Keflavik at initial climbut at Vy (weather preset "warm sector"):